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| Night Sky Photography - Page 3 | |
| An Equatorial Mount: My lucky day! | Rate Topic |
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| Posted: Tue Mar 12th, 2019 18:01 |
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21st Post |
Robert
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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 coa**e an adjustment, it needs something very fine. Something like this... 
____________________ Robert. |
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| Posted: Tue Mar 12th, 2019 19:04 |
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22nd Post |
jk
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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?
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 13th, 2019 03:02 |
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23rd Post |
Robert
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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.
____________________ Robert. |
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| Posted: Wed Mar 13th, 2019 03:12 |
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24th Post |
jk
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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. 
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 13th, 2019 04:50 |
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25th Post |
Robert
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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.
____________________ Robert. |
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| Posted: Wed Mar 13th, 2019 05:52 |
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26th Post |
jk
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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.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 13th, 2019 18:28 |
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27th Post |
jk
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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.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 13th, 2019 19:34 |
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28th Post |
Robert
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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.  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.
____________________ Robert. |
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| Posted: Thu Mar 14th, 2019 11:16 |
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29th Post |
Robert
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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.
____________________ Robert. |
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| Posted: Sat Mar 16th, 2019 07:21 |
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30th Post |
jk
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Bon chance. Clear but cold!
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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