| Joined: | Mon Apr 2nd, 2012 |
| Location: | South Lakeland, UK |
| Posts: | 4066 |
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Sorry, I clean forgot to take picture of setup, will try tomorrow. I took the D3300 out specially to make some pix for posting but I was so focused on adjusting the mount that I clean forgot to take pix of it.
I spent all last night outside with the mount, determined to overcome my lack of understanding of the adjustments and practice setting it up. Part of the problem has been that the Polar scope reticule wasn't adjusted properly. It's impossible to set the altitude and azimuth if the Polar scope itself isn't set right in the first place. I had been trying and no matter how hard I tried, I got nowhere. Going back to basics today I spent time adjusting the reticule in daylight, I now have it set up very close to an optimum setting. It isn't easy because it requires adjustment in two axis with three screws, possible but for very fine adjustments it's not easy, the Allen key is 0.9mm (tiny), I have fitted the Allen key into a small screwdriver handle to make it possible to hold with my arthritic fingers. Four adjustment screws would have been much easier.
I still need to fully understand the time element since it can cause an error from zero to twice the distance between the celestial North pole and Polaris. As Polaris appears to describe a circle around the celestial North pole, one has to know *where* around that circle Polaris actually needs to be, because that is what determines where the centre of the circle is, it needs to be exactly centred on celestial North, an incorrect time causes an eccentric rotation, it would be exactly right once in 24 hrs. Difficult to describe, this adjustment is achieved by rotating the Polar scope to the correct angle, like setting a clock, which is correctly determined from periodic tables, by the date and time of day, a bit like tide tables, in fact probably uses the same base calcs. It can also be determined from the position of Ursa Major but in reality using Ursa Major is only a very rough guide.
The more I use the EQ mount the more I realise how exacting the settings need to be. Even with modern and very expensive EQ mounts they are only as good as the alignment and support allows. For really accurate alignment massive foundations and an incredibly solid structure are needed. A tripod mounted setup is way too flimsy and then add the distortions caused by air movements.
With the practice I have had, I can now get the mount roughly aligned in a few minutes. For most purposes that's probably good enough to reduce star-trailing to acceptable levels but for what I want I think I will also adopt another technique, rather than making very long exposures, which risk showing star-trail elongation of the image, I will take many relatively short exposures using the EQ mount to maximise the exposures and minimise the elongation. Because drift is likely over long sessions, using image alignment software will align the images exactly.
My eventual hope is to be able to make pictures of planets, star clusters and nebula, I might eventually get a modest telescope if I find one at the right price.
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Robert.