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Night Sky Photography - An Equatorial Mount: My lucky day!  Rate Topic 
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Posted by Robert: Wed Mar 6th, 2019 19:03 1st Post
One of the inconveniences of dark sky photography is the Earth keeps moving, nothing new I know but still a nuisance when trying to take a still picture of a particular part of the sky.  I mentioned this to a friend because I was considering utilising an old mixer worm drive gearbox to create my own rotating mount with which to track the stars.

My friend called after a few days and asked if I was interested in a motor which moved 15º every hour, the penny didn't drop but I'm always interested in anything mechanical so I agreed.  Cutting long story short, I now have my own somewhat old, equatorial mount.  The price? 50 used paving bricks.  At first the mount wouldn't work, the motor drive lead was broken and the control unit wouldn't power up.  I figured out the pinouts for the six core cable myself, little or no info on-line.  The mount is a Vixen Optics Photo Guider, apparently good for a 15 Lb payload, provided it's counterbalanced.  What I didn't realise at first was the motor is a stepper motor, I was expecting a synchronised DC motor regulated by a timer circuit.   These devices sell for between £500 and £10,000, depending on size and power.

Eventually I discovered the reason why the controller wouldn't work, somebody had reversed the polarity of the voltage regulator inside the controller. o.O

I now have it running beside me as I type.  I started it at 10:00pm last night, I am interested what it will say at 10:00pm tonight, it has clock calibrations on the head which you use to help with tracking.  It has a polar scope which has to be aligned with Polaris with an offset because as well as spinning, we are drifting in space compared with Polaris.

I need to create a red LED illuminator to illuminate the polar scope, the calibration markings are clearly visible in daylight but not in the dark.  I am considering a fibre optic bonded with a small red LED in shrink sleeving, with a small button cell battery and switch, it's only needed when setting up the tripod at the beginning or after making adjustments to the setup.

I am hoping it will handle my 300mm f/2.8 lens on the D800.  As soon as I get a clear sky I will try it out.

This was the battery pack:



This is the mount, with the Nikkor 300mm f/2.8 and D800 mounted.



I am investigating various forms of power supply, the controller will handle from about 6Volts to 30Volts but the higher the voltage the more heat it dissipates, so I am working on a maximum of 12 nominal.  I do have ideas for using EN-EL4 D3 batteries which are nominal 10.8Volt, 2600mAh or perhaps some racing pack batteries.

It's been a very interesting few days.

I need to make a new 'wedge' mount to adjust the elevation, the one which was fitted wasn't fit for purpose, too small and seized up.  I intend to craft one from solid aluminium bar, with a fine tune adjustment for Polaris alignment. I also need to create a counterbalance bar so I can slide a weight into the correct position to counter the weight of the camera and lens.



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Posted by chrisbet: Wed Mar 6th, 2019 19:36 2nd Post
That's my sort of challenge - well done.

I love rescuing equipment - my wife hates me cos I keep repairing the washing machine instead of buying a new one!

I fitted an MGA with a red top racing battery - made up a special cage to mount it in the engine bay ( they usually live in inaccessable cages by the rear axle! I was very impressed with its power for such a small battery - you could hold it in one hand easily!



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Posted by jk: Wed Mar 6th, 2019 20:04 3rd Post
Nice mount.
The motor will drive well off the powerpack that you made for use for your Nichai UV light.  Double utility. :-)  :applause:

You can use an LED off that powerpack as well but you will need a dropper circuit to reduce to 3v for the LED.  You might be able to use a direct feed off an additional Lion battery (3.7v) but that seems huge overkill for that.  
There are some nice torches on ebay.

https://www.ebay.co.uk/itm/Rechargeable-USB-Mini-Ultra-Bright-LED-Torch-With-Beam-Focusing-Flashlight-UK/153232085887?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

I got one of these recently.  Great little torch.  Needs one of the Lion batteries that we use for D3 replacement battery.



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Posted by Robert: Wed Mar 6th, 2019 20:28 4th Post
Have now set it up in back bedroom, abandoned the 24Hr test because I had moved it several times and even switched it off, so hardly a valid test.  I have the D800 clicking away every 15 minutes taking a photo of a clock, the mount is zero'd in on the hub of the second hand.  I intend to leave it running for 24Hrs to see how it performs with weight on the arms, I have a crude counterbalance to offset the camera and lens (Nikkor 105mm f/2.5) intentionally not perfectly balanced to see what happens.

The UV power pack uses 18650 cells, the output for the LED is current regulated.  I could modify it to provide a full current output via an XLR socket or similar.  I need to keep weight down because I intend to use this kit on mountain tops.  The camera, lens and tripod with the mount will be heavy enough without adding heavy lead acid batteries.  I don't expect sessions longer than a couple of hours, the current draw for the motor is 300mA so well less then 1Ah for two hours use (I think!).

I could do with a right angle viewfinder for the polar scope. I'm told the Nikon DR-3 (about £25 on eBay? a little more for DR-4 ) works with this setup and is easy enough to fit. A modified Nikon DK-22 can provide the threads for the adapter that the DR-3 screws into.



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Posted by Robert: Wed Mar 6th, 2019 20:52 5th Post
Thanks Chris and JK for commenting.  Nothing I love more than making something work, or creating something from nothing.

I just spent the last week making a block cutting saw for cutting paving blocks. It works perfectly and has reduced the probability of my cutting off my toes!  I also get better cuts.

I visited a friend the other day and he is resurrecting a 1935 Triumph 250 motorbike, he is fitting a 500cc JAP speedway racing engine into it, making a wonderful job.  When it\'s finished he will have something really special.  He intends to speed hillclimb it.

Not outstanding iPhone images in mixed lighting...



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Posted by jk: Wed Mar 6th, 2019 22:03 6th Post
Robert wrote:

The UV power pack uses 18650 cells, the output for the LED is current regulated.  I could modify it to provide a full current output via an XLR socket or similar.  I need to keep weight down because I intend to use this kit on mountain tops.  The camera, lens and tripod with the mount will be heavy enough without adding heavy lead acid batteries.  I don't expect sessions longer than a couple of hours, the current draw for the motor is 300mA so well less then 1Ah for two hours use (I think!).
I thought you were using 18650 batteries.  Four of those in series will power the motor.

There are Seagull magnifying right angled eyepieces that also work on D3.  I have one in Spain.   Great for macro work.
https://www.ebay.co.uk/itm/Seagull-1-2X-Right-Angle-View-Finder/323719897956?hash=item4b5f35a364:g:81AAAOSwo8NceVDr



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Posted by Robert: Wed Mar 6th, 2019 22:36 7th Post
jk wrote:
I thought you were using 18650 batteries.  Four of those in series will power the motor.

There are Seagull magnifying right angled eyepieces that also work on D3.  I have one in Spain.   Great for macro work.
https://www.ebay.co.uk/itm/Seagull-1-2X-Right-Angle-View-Finder/323719897956?hash=item4b5f35a364:g:81AAAOSwo8NceVDr
Have just looked, it consists of two pairs of 18650 batteries, the way I have configured it it's entirely possible to add another socket for the Equatorial mount, which can be switched from the current limited UV LED outlet to a separate outlet which could be unrestricted.

I will check out the link you have given me.  I could do with one for close up work with the D800 anyway.  It can be hard to get one's head in the position needed when the camera is on a stand.  Not a great fan of live view if I can avoid it.



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Posted by Robert: Fri Mar 8th, 2019 23:03 8th Post
Well, the mount is up and running.

I ran the first test revolving with a clock for 24 Hrs, it was within half a second in time, accurate on rotation over 24 hrs.

I took it out after the test finished at midnight Thursday, night I got up there about ten to one, set the Vixen mount up and tried to zero it on Polaris.  Initially the lenses of the finder scope misted up and internally as well. Eventually I started to get somewhere when it all went dim.  I couldn't understand it the stars were so dim, I thought the finder scope was defective, I looked up at the sky and realised a herd of clouds had wandered in and obscured the stars so I went and had a sandwich and a coffee in the hope it would clear. I was almost ready to pull sticks and head home for bed when suddenly the clouds melted and I was back to a lovely clear sky.  The gear had cooled nicely and after a break, everything kind of fell into place.

I made a few trial exposures, set the Vixen mount motor running and left the D800 clicking away with the 70-300 VR lens, AF and VR turned off of course. I went with 25second exposures, f/5.6 and ISO3,200, intervalometer set to take an exposure every 40 seconds.  I should have left it at 30 seconds but it was OK.

The 25 second exposures produced an almost round star with very little elongation, I haven't got my head around the slightly erratic movements but it's WAY better than anything I have seen before.  Room for improvement of gear and technique but that's to be expected.  I never handled an equatorial mount before, I need to get used to setting it up to align with Polaris.

I will post some images tomorrow, too tired right now.  Quite amazing, really pleased, it's better than I hoped with a  ton of scope to improve.



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Posted by jk: Sat Mar 9th, 2019 08:04 9th Post
Sounds like you have found a treasure.
Look forward to seeing some of your images when you get up and running.  I never like the streaky stars effect that comes with long exposures made without an equatorial mount.  
At least I now know a man who can work one of these things.  Will be interested to follow the story and learn more.



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Posted by jk: Sat Mar 9th, 2019 08:09 10th Post
I am interested in your exposure time.  From some of my reading it seems that they recommend 20-25sec maximum to eliminate movement abberations.  I guess that drives you towards a 2 frames per minute rate.  

Limitations are (I guess):
How fast can the camera process in between frames?
How much does the camera heat up working continuously?
How long does your battery last?



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Posted by Robert: Sat Mar 9th, 2019 08:45 11th Post
It's a massive challenge, I know a little about the stars but really getting into it with a proper mount, albeit old, I reckon it's about 1985 ish.  It must have been very advanced in it's day because it uses stepper motors, even now there are manufactures who are still using DC synchronous motors nearly 35 years on.

Think 'star drift' is a factor, I couldn't lock on to Polaris because I couldn't see it clearly enough so I used the Ursa Minor group instead right next to Polaris, which is also etched into the polar finder. in the 35 years since the mount was etched I believe the stars have drifted.  I also need to do tests to check the alignment of the scope.  Given the polarity of the motor had been swapped I don't take anything at face value.

There seems to be a regular deviation in the mount which I need to understand, it may be caused by hard grease on the worm wheel having solidified and causing a regular change in resistance.  I am hoping it will be 1/144 of a day interval because thats the worm gear ratio, it might also be the meshing of the 40 tooth drive wheels between the motor and the worm shaft. For a delicate mechanism it's a pretty crude drive, with an open pair of gears and one imprecise bolt to secure the motor in position, you can't turn the motor shaft because it's geared back by 1/120th down-gearing, unless somebody has in the past and bent something in the  motor drive.  Anything is possible, it might even have been dropped.

Given the use of stepper motors, I could make my own driver controller, I have all the bits with an Arduino programmable controller right here.  Will post pix later.



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Posted by jk: Sat Mar 9th, 2019 09:34 12th Post
Try NightSky Pro on iphone. It is excellent.



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Posted by Robert: Sat Mar 9th, 2019 16:14 13th Post
I do use Night Sky, not pro, yet...  It was that app which helped me locate Polaris in the end.

Here are some images from my first attempt with the Vixen Polar mount.

The first is a 100% crop (that is one sensor pixel to one screen pixel, these are all screenshots from Lightroom, hosted on Flicker) this is with the polar mount doing it's thing, nor perfectly set up but pretty near.



The second is a similar crop after I had switched off the Vixen tracking motor.



Now for the trails, bear in mind each exposure starts at 40 second intervals, 25 seconds of exposure, 15 seconds gap.

34 'Star Trail Stacked' exposures using the Vixen Polar mount.  The squiggles are due to uneven tracking, why it's uneven I don't yet know.  Like I said above, it may be due to the motor gear's alignment with the main worm gear shaft, or it may be due to stiff grease causing hard spots in the rotation.



This is 38 'Star Trail Stacked' exposures, including the ones with the motor switched off, you can clearly see the exposure length and gap in the final four exposures, the mount is really doing it's stuff, almost perfect.



Finally a 100% crop of the previous image.



I have a lot of testing to do to check out the veracity of the polar scope and the uneven tracking.



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Posted by jk: Sat Mar 9th, 2019 20:03 14th Post
Have you seen this article?
https://themcdonalds.net/richard/wp/setting-up-an-equatorial-mount/



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Posted by Robert: Sat Mar 9th, 2019 22:21 15th Post
No, will have a look in the morning, thanks.



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Posted by Robert: Mon Mar 11th, 2019 23:51 16th Post
I have looked at the link JK, thanks it's a good, a well explained set of articles, which don't assume the reader is accustomed to the jargon of astronomy, it never fails to puzzle me why, in writings aimed at explaining complicated processes to total novices, the writer often uses incomprehensible terminology which is only meaningful to an expert.

I have unravelled the mystery of the wiggly lines. The motor output is 1/10th of a revolution per minute, 10 minutes per rev.  The repeat time of the wiggly lines is 10 minutes.  I am putting the uneven tracking down to the motor to worm shaft gears being too closely meshed and the gears not perfectly concentric.  I have adjusted the meshing and tomorrow I am expecting to do a trial run in daylight to test the tracking and to adjust the polar scope, which is well out of adjustment.  Somebody has been fiddling because it's so far out, it couldn't have been used properly as it was.  I went to the local brickworks and asked to borrow their chimney, the manager was somewhat suspicious but said OK so long as they get it back tomorrow!

:lol:

(At this point the Splash screen kicked in, I simply back swiped on my track pad and OK'd sending the form again nothing lost, brilliant, thanks Chris, that's long overdue.)

Said chimney...


It's handy having the lightning conductor because it gives me a pin point accurate reference in the image.  I am hoping when I have adjusted the polar scope, the rotated image will have all the images centred at that point, in fact this afternoon I used the nearest corner of the chimney as the target..



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Posted by jk: Tue Mar 12th, 2019 07:57 17th Post
Well I think I am following your train of thought but I will need to read the article on the set up.
If anyone has the patience and perseverence to work it out then it is you.
Hope the testing today proves successful.



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Posted by Robert: Tue Mar 12th, 2019 09:56 18th Post



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Posted by jk: Tue Mar 12th, 2019 10:50 19th Post
So your reference (polar) point is the nearest (front) corner of the chimney.
So everthing should revolve around that reference point?  
So all the reference points in all the pictures should overlap in a single place?

Or am I missing something?



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Posted by Robert: Tue Mar 12th, 2019 16:14 20th Post
jk wrote:
So your reference (polar) point is the nearest (front) corner of the chimney.
So everthing should revolve around that reference point?  
So all the reference points in all the pictures should overlap in a single place?

Or am I missing something?
Yes, the reference point was the corner of the chimney, I have just adjusted the polar scope and loaded the images into Lightroom, it was extremely difficult in the wind, I may have wasted my time today.
Will see in a few minutes I have 193 images to sift through, I know many of them are scrap because the AF went awol perhaps because the camera was being buffeted by wind.



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Posted by Robert: Tue Mar 12th, 2019 23:01 21st Post
Well I have had a session today but the wind was really strong (and is getting stronger)  It was buffeting the camera and the mount.  I aligned the polar scope as best I could, not perfect but much better.  I am still not certain which marks I should be calibrating it to.  The adjustment was with a  1.3mm hex key, very fiddly, fortunately the grub screws which do the adjustment were not seized.

I took four series of images, one set like the chimney ones of a church spire about 5 miles away. The horizontal alignment was reasonable, the vertical alignment was rubbish but I think the mount moved down on the tripod while I was rotating the camera by hand, causing the error.

Then I took some at 40 second intervals just stationary to act as a control test.  Then I took 34 more with the motor drive in forward direction, then about the same in reverse.  I hadn't fitted a counterbalance, the D800 with the 70-300 lens is quite heavy so I wanted to see if the weight affected the accuracy of tracking. The motor was raising the camera in forward mode and lowering it in reverse mode.

All three sets of images produced a similar sized cluster of results, given the gale which was blowing at the time I was quite pleased.  There did not appear to be any significant difference between the motor raising the camera or lowering it.  The unpowered exposures of which  there were only 18 showed a very similar cluster with no pattern or apparent regular repetition patterns like the star trail exposures did.

I am running out of energy so I will post the images tomorrow.

On a side note the Splash screen has popped up twice while I have been typing this, I just swiped it away and carried on, the text was exactly as it had been before the Splash screen popped up.

I am also designing a better wedge mount for the EQ mount.  It's extremely difficult to align the polar scope exactly without a screw adjustment.  I was going to try and use a worm and wormwheel but I have decided it's too coarse an adjustment, it needs something very fine.

Something like this...
.



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Posted by jk: Wed Mar 13th, 2019 00:04 22nd Post
How many planar directions do you need for adjustment of the polar sighting scope?


Whilst it is so windy you have a really tricky situation.  Is there anyway that you can setup inside pointing out of a window?



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Posted by Robert: Wed Mar 13th, 2019 08:02 23rd Post
jk wrote:
How many planar directions do you need for adjustment of the polar sighting scope?
Not quite sure what you mean, there are three adjustment screws in the 'scope, that in itself makes it a bit tricky to adjust, four would have been better, making the adjustment in two planes.  The accuracy has to be very close.  A star is tiny, I have to eliminate all tracking errors which enlarge or elongate the star, that is incredibly challenging.

The object of the accuracy of tracking is to allow long 'bulb' exposures of perhaps 30 minutes, currently 30 seconds is probably the limit for a reasonably sharp image.  It's one of those exponential things where to double the accuracy you have to expend ten times the effort.  Eventually you get to the Hubble stage.

If I could get stable five minute exposures I would probably be happy, I think that would bring the likes of the Orion nebula within my range of targets.  I don't want to get into astronomy as such, would just like to be able to do a bit more than just star trails and Milky Way.  I haven't even tried the fisheye on the mount yet.  Up until now I have relied on star stacking software, I think combining the EQ mount with multiple short (30 second) exposures will be my optimum route.

Ah, I think I know what you mean now...

The wedge mount in the image above provides elevation on a horizontal axis and rotation on a vertical axis, it only requires those two planes of adjustment to align with Polaris.  The adjustment has to be very fine. Impossible with a conventional video head or even worse a ball head.  A large geared head would not be stable enough.


Whilst it is so windy you have a really tricky situation.  Is there anyway that you can setup inside pointing out of a window?
I have considered that, I need my target at least a Kilometre away.  I don't have a window which provides a suitable target.  I am happy enough, I have shown that the adjustment had yielded improvement.  I will just wait until the gales subside.  Maybe next week?  There are no clear skies in the current 14 day forecast but I have decided I need to accustom myself to the complexities of the EQ mount in daylight before attempting it in the dark again.  It's one thing finding Polaris by eyesight, quite another with a telescope which inverts and reverses the image.



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Posted by jk: Wed Mar 13th, 2019 08:12 24th Post
Robert said.... "The wedge mount in the image above provides elevation on a horizontal axis and rotation on a vertical axis, it only requires those two planes of adjustment to align with Polaris.  The adjustment has to be very fine. Impossible with a conventional video head or even worse a ball head.  A large geared head would not be stable enough."

OK so two.
I need to think about this more now I understand more but still a complete novice. ;-)



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Posted by Robert: Wed Mar 13th, 2019 09:50 25th Post
Here are the results of my tests yesterday:

Firstly a general full D800 frame view of the target at 300mm, distance to spire approx 5 miles.  I have added two spots to each image to help track the movement more easily.  On some images the spots are a bit of a guess, but not very far out of position.



and a 100% crop:



This is the StarStacker grouping of the control cluster, camera stationary, well wobbling a bit, but not being moved by the motor! 18 exposures, again 100% crop.



This is the StarStacker cluster of the ascending set, 34 exposures with the camera being raised by the motor without a counterbalance, ideally all the dots should be in exactly the same place.



This is the StarStacker cluster of the descending set, 31 exposures with the camera being lowered by the motor without a counterbalance, it doesn't seem to show any signs of running more quickly than the ascending set.



These images are stacked with the frame fixed but revealing each layered image and the differences between the images is visible. Bear in mind a 50mph wind was blowing at the time, the camera was being buffeted badly .

Quite obviously the test needs repeating without the gales, but at least I now know I can adjust the polar scope and it's better than it was.  There is no longer a tracking error pattern.



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Posted by jk: Wed Mar 13th, 2019 10:52 26th Post
Like all these technical things there is a learning curve and the last bits are part of 80/20 rule.
Last image looks pretty good considering the conditions.

I think that you need to prove that it is not atmospherics and wind effects that are detracting.



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Posted by jk: Wed Mar 13th, 2019 23:28 27th Post
Dont know if this helps your design thoughts.
http://www.baselabtools.com/Fine-Adjustment-Screws_c_86.html

If you use a two point screw adjustment it gives greater precision.

I also remember that some of the finest guage valve adjustments work using semi-precious/precious stones in the valve.

I am trying to spark design ideas but I may be generating noise!  Tell me to shut up if I am causing confusion.



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Posted by Robert: Thu Mar 14th, 2019 00:34 28th Post
They are stunning!  Wow, 240 tpi!  Didn't realise they existed.

JK, all input is welcome, it's the wilder ideas that sometimes crack the nut. :devil:  Nature produces the occasional freak, that's how evolution works, occasionally the freak fits a niche, then it's no longer a freak, it thrives.

I am even considering using a EPSU (Electronic Power Steering Unit) to act as a servo motor to amplify the output from the relatively low power output from the Vixen motor, I just checked out the price of the current Vixen super model it's about £2500 and weighs 7 Kg, my mount with wedge weighs about half that.

It's probably a step further than I need but I thought of it on my way back from Lancaster on Sunday night.  The EPSU takes the input torque and amplifies it if needed, otherwise it remains passive. I  don't think it will affect the speed of rotation and the torque assistance is fairly easily adjustable.  After all, we are only talking about a quarter of a turn for a six hour session.

I am also thinking of ways of making rock solid mount.  Tripod isn't  really solid enough for this sort of thing.  Most serious astronomers have a pillar, a heavy tube buried in the ground or attached to a very large block of  concrete like a pile.  That's the only way to get a really stable place to lock the camera (or telescope) down.  I may be taking my drill with me next time I venture into the hills!

On a different aspect I really have to consider where I am going.  I don't want to become an astronomer, I do have an interest in astronomy but I feel once you have looked at one star you won't see much difference with the next!  I would however like to be able to make nicer Milky Way images, combined with nice landscapes, or even rock formations such as the stacked boulders in your recent images.  I would also like to photograph the gas clouds like the Orion nebula and some of the other more visible nebula. Possibly Saturn? The Moon? But photography has to remain at the centre of these activities.  I'm a bit like a butterfly, constantly flitting from one subject to another, but that's what I enjoy, fresh challenges.



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Posted by Robert: Thu Mar 14th, 2019 16:16 29th Post
In my  quest for some cloudless skies I did a Google search, I came up with a site called 'Clear Outside'.

https://clearoutside.com/

It's very good, they have arranged for a full clear night on Sunday/Monday from midnight.

I have also downloaded the app for my iPhone, so I can check it while I am out.

Will see what we actually get on Monday... Am hoping for a good night.



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Posted by jk: Sat Mar 16th, 2019 12:21 30th Post
Bon chance.
Clear but cold!



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Posted by Robert: Sat Mar 16th, 2019 14:12 31st Post
It seems to be moving slightly but there seems to be a window of about six hours of almost clear skies.



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Posted by jk: Sat Mar 16th, 2019 21:39 32nd Post
Lots of flooding up North take care!



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Posted by Robert: Sat Mar 16th, 2019 22:19 33rd Post
Thanks JK, Just been looking at the news, they have called off the three peaks race due to flooding.

I will be at about 350 Metres (about 1,150 feet), but I do have to pass through Broughton Mills, a tiny hamlet with a very tight bridge, a square bend off this tiny narrow hump back bridge, then it goes down to beck level.  If I am going to have a problem it will be there, although there is a splash well up in the hills where the road becomes a river for 50 yards.  Onto the road through one field gate and back off the road through another field gate. I have seen it a foot deep through there.

It will all be gone by tomorrow night. Seathwaite has the highest rainfall in an inhabited area in UK over 24 Hrs and is about a mile from where I go for my night sky photography.

Seathwaite Farm, Cumbria, November 19 2009 – 314mm*
Martinstown, Dorset, July 18 1955 – 279.4mm
Bruton (Sexey’s School), Somerset, June 28 1917 – 242.8mm
Upwey (Friar Waddon), Dorset, July 18 1955 – 241.3mm
Cannington, Somerset, August 16 1924 – 238.8mm
Loch Sloy Main Adit, Strathclyde, January 17 1974 – 238.4mm
Long Barrow, Devon, August 15 1952 – 228.6mm
Upwey (Higher Well), Dorset, July 18 1955 – 228.6mm
Bruton (King’s School), Somerset, June 28 1917 – 215.4mm
Timberscombe, Somerset, June 28 1917 – 213.1mm
Rhondda (Lluest Wen Reservoir), Glamorgan, November 11 1929 – 211.1mm
Upwey (Elwell), Dorset, July 18 1955 – 211.1mm
Kinlochquoich, Highland, October 11 1916 – 208.3mm
Camelford, Cornwall, July 8 1957 – 203.2mm
Bruton (Pitcombe Vicarage), Somerset, June 28 1917 -200.7mm
Wynford House, Dorset, July 18 1955 – 200.7mm
Otterham, near Boscastle, August 16 2004 – 200.4mm
* Figure recorded by the Environment Agency

There are many recorded high amounts of rainfall in the West Country.



____________________
Robert.

 


Posted by Robert: Mon Mar 18th, 2019 17:01 34th Post
Well the six hour window collapsed into two much shorter sessions.  Nothing exciting materialised except I became slightly better at setting up!

I have yet to analyse the images but the last set with my 16mm fisheye seems pretty reasonable.  The main thrust if my efforts were to assess the improved alignment of the polar scope, I think it's much better but key to this will be a new solid and adjustable base mount to fit on the tripod and to mount the polar rotary tracker in very accurate alignment with the celestial North Pole.

I have reached the drawings stage, I need to design the details of the adjustments and somehow devise some method of locking the adjustment robustly but without imposing great stress on the mount which will cause it to move out of alignment, the adjustment is extremely fine, accuracy needs to be in the region of 5 arc seconds or better, that means you can barely touch it because even a very heavy tripod will flex that much easily.

It really needs bolting down, to something very solid.  I do have ideas.



____________________
Robert.

 


Posted by chrisbet: Mon Mar 18th, 2019 17:27 35th Post
Just an off the wall thought - if you need something that remains perfectly in alignment with the earth's axis, would some sort of gimbal work?



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Posted by jk: Mon Mar 18th, 2019 17:52 36th Post
Robert, it is now illegal to use child labour so no sending the boys up mountains with predrilled slabs!
  :lol::lol:



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Posted by Robert: Mon Mar 18th, 2019 20:10 37th Post
LOL, what  about a generator and rock drill?

A helicopter would come in handy...



____________________
Robert.

 


Posted by Robert: Mon Mar 18th, 2019 20:23 38th Post
chrisbet wrote:
Just an off the wall thought - if you need something that remains perfectly in alignment with the earth's axis, would some sort of gimbal work? It's getting the alignment which has to be pretty exact with basic and robust design.  Something like a Wimberly might be OK for the articulation but it has to be rock solid, Wimberlys are not rock solid.

The head I have is supposed to have a 5 Kg payload, but the payload is supposed to be balanced so the motor doesn't slow down uphill or speed up downhill.  Speed has to be consistent 1 revolution per 24 Hrs.  The 300mm lens and D800 weigh about 2.5 Kg so it needs about a 1.5 to 2Kg counterbalance, less then the camera/lens, because it can be hung out on an arm so you get the right leverage without adding too much to the payload.

The design is coming together, I am tempted to make a wood mock up to avoid making a metal one which has a snag.

Just about to process last nights images, this will be interesting...



____________________
Robert.

 


Posted by jk: Mon Mar 18th, 2019 20:52 39th Post
Looking forward to see those images.  I am sure it will be a big improvement.   Problem is that further improvement will be a lot of work for just inch-pebbles.  
Per ardua ad astra!



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Posted by Robert: Mon Mar 18th, 2019 23:19 40th Post
Here you are JK...

Please bear in mind these are not intended to have artistic merit, they are simply the results of experiments and an attempt to learn how to set up an Equatorial mount for photography.  I am learning and making gross mistakes.

These images were made with a Vixen EQ-polar mount and a D800 with 70-300 lens and 16mm f/2.8 fisheye lens.  They were 25 second exposures taken at 26 second intervals - one second gap.  The black spot right of centre must be a spec of dust on the sensor.

The first image was made without the Vixen mount motor running, about 40 exposures.  The bright star to the left near the centre, is Polaris.  You can see how far it is from the celestial polar centre.



This was taken after the initial 40 exposures, I switched the motor on but the setup must have been very wrong.  I think I rotated the polar locating scope the wrong way, I was trying to get Ursa minor aligned but somehow I missed!



This is the two above images in one.



Finally back to Stickle, only a short session with the fisheye. 74 images stacked.  Notice I am much nearer the correct polar centre.  Again, 25 second exposures at f/4.0 for some reason only ISO200, I must have forgotten to re set it for astro, I usually run at ISO 1600.

I need to sit down and set up some dedicated menus for astro photography.



____________________
Robert.

 


Posted by jk: Tue Mar 19th, 2019 10:01 41st Post
I can see some improvement.
Yes in first shot the centering is off but it is not horrific.

Second and third images have some slight curvature in the light lines which (to me the unknowledgeable) looks like something is offset. I dont know what but it is at least consistent.

This may be a long ride but it will be fun watching the progress.



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Posted by Robert: Tue Mar 19th, 2019 10:44 42nd Post
The biggest issue at the moment is the 'wedge' the adjustment of elevation to equal the latitude, for long time exposures >30 seconds, it needs to be within a couple of arc seconds 5 at most and alignment with true celestial North within a similar margin.  Magnetic North is simply misleading.

I am working on the design of the adjustment assembly, currently trying to find a short length (100mm?) of 8mm fine thread (1mm pitch) stainless rod.  Those adjusters you pointed me to were amazing but way too accurate! For now anyway!  I can find high tensile steel fine pitched rod and I may go with that but unless I keep it greased, it will corrode because of the condensation and damp air, due to being used outside at night.

At the moment I am using a Manfrotto 701 HDV head but the clamp locking is not positive enough and  the adjustment is a nightmare.  It has to be fine screw adjustment to stand a chance.  If I can get to the point where the rigidity of the tripod is my limiting factor I will be satisfied.  Currently fine adjustment of elevation and heading is the limiting factor, there isn't any!!!

I have considered the Manfrotto geared head but the SKU 400 which is about the only one rigid enough is £834.95.

https://www.manfrotto.co.uk/studio-geared-head

The other gears heads are gangly and wouldn't afford the rigidity needed, if indeed the SKU 400 would due to it's height, the head needs to be simple, very solid and squat.



____________________
Robert.

 


Posted by Robert: Sun Mar 31st, 2019 08:31 43rd Post
My engineering is progressing slowly, I have mostly finished the upper parts, I have made the altitude adjustment, I have created a clamp arrangement for the altitude movement.

This is turning the bore for the Polar alignment scope in the support arm in my lathe, the small green casting is the original, inadequate support arm/wedge mount.



The altitude adjustment is from about 43º to 60º, I live at about 54º so I have plenty of adjustment available.



The next part is making the base adjustment, which is a slightly clever way of adjusting and clamping the base down using a dovetail post.  I have never seen this idea before so I have no idea how well it will work.  Time will tell.  All I need then will be a clear night, free of clouds.  Currently an hour at midnight on Thursday is forecast.



____________________
Robert.

 


Posted by chrisbet: Sun Mar 31st, 2019 08:41 44th Post
Certainly looks robust, but how do you get your eye to the polar scope?



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Posted by Robert: Sun Mar 31st, 2019 09:08 45th Post
Ah, very good point!

It's not easy at any time looking up at 54º, the standard solution is to use something like a DR-3 or DR-5 right angle eyepiece.

https://www.keh.com/shop/nikon-manual-focus-dr3-rt-angle-view-attach-fe-fm-ser-240550.html

I am going to try a novel approach, I have a little Go-Pro Session cube camera which can stream video via wi-fi to an iDevice or my MBP laptop.  Placing it on the eyepiece of the Polar scope it gives a nice clean image. Given it's a one off setting at the beginning of the session it should speed things up for getting the Polar alignment quickly and easily rather than kneeling in a muddy or rocky field.

I am also coming to the idea that I  don't actually need a tall tripod.  A dwarf stand of some sort, a stubby tripod or something similar and leave the camera at ground level or on a large rock.  The assembled mount weighs about 7.5Kg, add camera, lens and counterbalance it weighs close to 10Kg.  A small solid mount at ground level would get the job done.



____________________
Robert.

 


Posted by jk: Sun Mar 31st, 2019 12:48 46th Post
Looks like you have been using some large hunks of aluminium.
Nice work.

The GoPro will make for less back-breaking or neck-aching and squinting down the sighting telescope.

Agree with you that a shorter tripod is better than a taller one.

Look forward to seeing how you get on.



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Posted by Robert: Sun Mar 31st, 2019 23:15 47th Post
OK, brief test this evening, really good sky tonight despite not going far.

The new wedge mount is excellent, needs finishing properly and details refining but it works a treat.  It's very solid and the adjustments work really well, way better than before, need much more practice but I took two series of exposures with and without the motor running.  I am currently processing the images as I type,  I took some without the motor running then I started the motor and all the stars stopped moving, but... they are giggling about.  I am not yet sure what's causing that, it may be the gear train again or it might be mirror slap shaking the camera arm.  The D800 mirror does seem to generate a fair old whack, at that magnification it must have some effect on sharpness.  I need to look into locking the mirror up.

I seem to have managed to find the celestial North.  I still haven't a clue how I did it, I wasn't sure which star was Polaris, which has been my problem before but I am gaining some understanding.  Polaris describes a circle around the celestial North axis, the trick is knowing at what point around that circle Polaris should be.  It relates to a 24 Hr clock, as you might expect...  This evening I wasn't able to see Ursa Minor, which would have clinched it.

I tried the Go-Pro Session but the images of stars in the dark were not bright enough.  It's fine in daylight but not in the dark.  I still need to make a small red LED lamp for the Polar Scope.  Will post some images in the morning.



____________________
Robert.

 


Posted by chrisbet: Mon Apr 1st, 2019 07:56 48th Post
Rather than the Go Pro, how about making a slide to take the phone on front camera?



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Posted by Robert: Mon Apr 1st, 2019 09:32 49th Post
Not quite clear on what you mean...  Given my experience last night I am leaning towards a DR-3 right angle eyepiece.  The added complexity of electronic devices is unwelcome.  Time is a major factor and faffing about with these electronic things is very time consuming and frustrating when they don't always respond as expected.  Unless I can get a simple, cheap dedicated mono camera with low light capability, I think I will try a right angle eyepiece, they are simple and clear.  That will  get the job done without adding complexity.  I need to speak with my buddy, he has right angle eyepieces, I could maybe try one first.

OK, I have pix.

This was the viewpoint, on Kirkby Moor, overlooking the Duddon Estuary.  D800 with Nikkor 16mm fisheye lens. Note the depth of focus Chris!!! lol

The three glowing patches in the sky to the right Sellafield, Whitehaven and Workington.



This is the first set, I think they are of the Northern stars of Orion's belt, bottom right, I had intended to centre on the belt but the camera must have moved, camera on the EQ mount but motor not running.  Ten 15sec exposures taken at 30 second intervals f/5.6.  D800 with 70-300 VR Lens (VR and AF turned off)



This was the best single exposure of the set of 34 at 100%, round stars, no trailing.



This was the worst single exposure of the set at 100%, no trailing but atmospheric disturbance has resulted in a poor image.



This is a stacked image of the best nine exposures



This is a stacked image of all 34 exposures, very little trailing but a disturbed and less than crisp image.



All in all I am delighted.  The effort of creating the heavy duty mount has been worthwhile, the adjustments work well and the alignment is accurate enough.  Good Polar wedge mounts  are very expensive, nowhere near as robust as mine which has cost zilch.  I am unlikely to want to use it far from the car so the weight isn't really an issue.  The weight contributes a great deal to the rock solid foundation it provides.  Viewing through the Polar scope isn't as easy now but it's still entirely possible.  Have to tidy the workshop now then I can turn my attention to a bit of refining.



____________________
Robert.

 


Posted by chrisbet: Mon Apr 1st, 2019 21:07 50th Post
I applaud your efforts :cheersduo:



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