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| Night Sky Photography - Page 5 | |
| An Equatorial Mount: My lucky day! | Rate Topic |
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| Posted: Tue Mar 19th, 2019 05:01 |
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41st Post |
jk
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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.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Tue Mar 19th, 2019 05:44 |
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42nd Post |
Robert
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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. |
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| Posted: Sun Mar 31st, 2019 03:31 |
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43rd Post |
Robert
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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. |
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| Posted: Sun Mar 31st, 2019 03:41 |
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44th Post |
chrisbet
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Certainly looks robust, but how do you get your eye to the polar scope?
____________________ If it is broken it was probably me .... |
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| Posted: Sun Mar 31st, 2019 04:08 |
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45th Post |
Robert
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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. |
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| Posted: Sun Mar 31st, 2019 07:48 |
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46th Post |
jk
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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.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Sun Mar 31st, 2019 18:15 |
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47th Post |
Robert
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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. |
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| Posted: Mon Apr 1st, 2019 02:56 |
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48th Post |
chrisbet
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Rather than the Go Pro, how about making a slide to take the phone on front camera?
____________________ If it is broken it was probably me .... |
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| Posted: Mon Apr 1st, 2019 04:32 |
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49th Post |
Robert
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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. |
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| Posted: Mon Apr 1st, 2019 16:07 |
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50th Post |
chrisbet
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I applaud your efforts 
____________________ If it is broken it was probably me .... |
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