stargazermanc

So this evening I managed to set up and the collimation was indeed out so I spent some considerable time making alterations at different focus and as you can see from the pictures, the collimation is as good as I can get it with a camera versus a high powered eyepiece. I checked several times going out of focus and back in so pretty confident that it is now sorted. Unfortunately the clouds rolled in so I didn’t have time to take any proper test stacks but from the test shot I did get, it does look like a tilt issue which could be my next headache.

None, it is being done using a camera as I said in a previous reply. In terms of the tilt, I don't think this is the camera side as I use it regularly on my redcat and zs73 with zero tilt. It could be my mirror which has been suggested on another forum.

So you think the second image is the more accurate back focus distance? I am going to check the collimation. Once I have sorted that and got as close as I can on the backfocus then I can start looking at the tilt.

Thanks for the tip.

Hi the focus is handled by the eaf and asiair pro. I am going to check the collimation again on the next clear night

No. I'm using my camera and defocus inwards and outwards to ensure its good in both directions. Which backfocus would you say is the closest?

So last night I managed to do some testing before the clouds rolled in. I managed to take 10 x 60sec exposure of Capella at 3 different back focus lengths (105 mm, 109.5 mm & 126 mm) based on the spacers I had available, each time I refocused using the ZWO EAF. Each image is the stacked output and stretched. There is definitely something not right, I am going to recheck my collimation but what do people think?

No other focuser is compatible with ASIAIR. Yes I have an eaf attached to each of my scopes as it's easier and not a quick job to change between scopes, especially when using an SCT and a refractor.

After reading everyone's advice, I have decided to abandon taking a test stack without the reducer as I don't think I have a mirror issue and I think my collimation is good, I think my issue is the back focus distance which in my case is not the 105mm as stated in multiple sources but probably longer... I need to take some new test images as I have messed about with that many combinations now that I have forgotten where I got up to. So on the next clear night, I will setup with 105mm back focus, take a test stack of Capella, review and take it from there.

Surely he must be mistaken in the backfocus being 82mm!

If you could measure your back focus then I would really appreciate it as it is possible that there isn't anything wrong with my mirror or reducer, its just the 105mm back focus is incorrect. I think my collimation is spot on so the poor star shapes are down to the back focus. My version is also the xlt version, with the antares 6.3 reducer, asi2600mc pro. I am not planning to use a filter wheel / drawer as I will be only shooting galaxies in RGB.

Thanks but I was looking for real world examples.....

I hope someone may be able to give me the correct figure. I have been trying to image using my C8 with fr and asi2600mc pro. I appear to have really bad coma at 105mm backfocus. I have checked collimation and that appears to be fine so someone has suggested there might be a problem with the mirror but to narrow done the issue, he has suggested that I remove the focal reducer from the equation and take a stacked image of capella at the native fl. I will do this on the next clear night but does anyone know what back focus distance I need when not using a focal reducer on this scope?

I have no way to add as the all the adapters are fixed in length.

Does anyone have any thoughts on how to fix this? Everywhere I read it says 105mm back spacing which I have achieved using the following: Celestron T Adapter (50mm) + 16.5mm Spacer + 21mm Spacer + ASI2600mc (17.5mm) I thought it might be collimation so last night I again used Deneb to check and whilst it isnt perfect it was the best I could get it.