Chris49

Hi Nigella, This is my best effort from March 2017 - not an APOD 😉: EOS7D not modded, mounted on tracking A-VX, 70-300 at 280mm at f/8, best 12 out of 16 - 4min subs at ISO1600. One dark and one bias, stacked in DSS. I found stopping down the lens made a huge difference to the star roundness. Chris

With longer than 90 sec subs, the stars start to become sausages. This is I believe the result of flexure between the main and the guide scope. I have now improved the guide scope rigidity by putting it in rings on top of the main scope, but I haven't had a chance to try this yet - part of the back garden was underwater this morning. 🙁 Your NGC891 is stunning - thanks for showing me what can be done. Chris

I see what you are getting at, but I come back to the HFR values that I get for the stars in the subs with Sequence Generator Pro - these range from 3.5 to 6. When I watch videos of people using SGP, they get values as low as 1.2 so my stars are large at that stage. I suspect they then get bigger still with my attempts at processing, probably because I have stretched them too much. Your comments are certainly making me think!! Thanks Chris

I did watch your video last night and it looks very useful. I'm such a novice with processing that I will need to follow it through step-by-step with an example of my own to understand it. I have CS6 - yours may be a different version but I guess that won't matter. Your star reduction certainly shows an improvement on my picture. Thanks Chris

You are right, they are not. So I was just lucky they came out roughly round! Back to improving the guiding! Thanks Chris

You are right of course, but I think it is a case of "small steps" to make progress without getting discouraged. I am a bit wary of the OAG because people say they are hard to use. I hope to get there eventually! Thanks for the advice. Chris

I'm not too far off then. Thanks for posting your image. Chris

The guide scope is the standard Celestron 50mm finder #51611 and holder that comes with the EdgeHD8 - not very satisfactory as it is not rigid. Guide cam is SX Ultrastar. I have since moved it to rings mounted on a Vixen dovetail on top of the main tube. This is much more rigid and is symmetrical for balance so that should help. Mount is iOptron GEM45 - just getting used to it, but I am impressed so far, way better than my A-VX which had so much Dec backlash that it never came back! Thanks for the encouragement! Chris

There I was thinking 10 minutes processing was a bit excessive - I was hoping my subs were going to be nearly perfect straight out of the camera 😀. Chris

That sounds a really clever technique. There's a lot to this astro stuff when you get into it! Thanks Chris

I don't think it does reject UV, hence my worry that UV might be out of focus and lead to blobby stars. I thought that was more a problem with refractors than reflectors though, although there is the corrector plate I suppose. I do have an LP filter to try, but although Clear Outside says I have Bortle 4, I find that hard to believe! I will search for PS star reduction as you suggest. Thanks Chris

Thank you Carole. I will be more careful next time. So far I have had very little idea what I am trying to do and even less about how to do it! It's all part of the learning curve. Chris

Thanks Vlaiv, that's very helpful. I guess I have been unrealistic up to now. I will work towards what you suggest. Chris

Stacked in DSS, stretched a bit in Photoshop - I may well have clipped off the brighter stars. Chris

A lot to think about here. Clearly I will try to find a place to put the filter and concentrate on improving the guiding. Also maybe I should include the #94242 0.7x reducer - I was trying without because it is the tiny galaxies that I'm really after. Thank you for your advice. Chris