Trouble focusing and lack of detail

[04Stefan07]

Last night I thought I would give Mars a crack to image (I know it can be difficult to get a really good photo of it).

Now I know SCT focusers are horrible and are very fiddly especially with the mirror shift and that it can be tricky to obtain detail on Mars depending on the atmospheric conditions. For some reason I felt like I couldn't get Mars into focus last night and there was hardly any detail on it at all.

What I used:
- Celestron C8-A
- ZWO ASI224MC
- Dew shield and dew band (50 - 80% warm)

I have added an image of what the capture video looked like and two images after being stacked with AutoStakker.

Also I popped my QHY5L-II in to see what would happen as well and I got the exact same results so there must be something up with the scope itself. To also test I took a few shots of the Moon which looked to have come out fine. It's only Mars, Jupiter and Saturn I am having trouble with. (Saturn looked alright but I think it can be better).

I have seem some great shots taken of Mars with this OTA so I know it's possible to get something decent. The only issues I can think of which is collimation (was done by a professional when I got the scope serviced so that should be fine) and possible cool down time of the glass.

Can anyone suggest any other possible issues or any test I can perform to find the issue?

Thanks!

[Merlin66]

Cooling down and general seeing conditions????

[04Stefan07]

I am hoping it's seeing conditions.

[casstony]

Don't draw conclusions from one night, especially if there wasn't another scope set up to compare with. Jetstream was a problem last night and I couldn't see any better on Mars.

[04Stefan07]

Yep, I need someone else who images with the same telescope as me to see what results they got.

Also I wouldn’t mind seeing results from other types of telescopes from Melbourne last night too.

[Paul Haese]

Every time an OTA comes off and goes back onto a mount it needs to be checked for collimation. SCT's hold collimation well but you need to check it regularly for high res imaging. Also you should check collimation with the camera in the scope. It might need a slight tweak to give really sharp views. Collimating an SCT is very simple and takes a few minutes on an out of focus star.

Seeing will also be a problem as well as optics being at ambient or near to it. You have to pick your nights and the scope should be thoroughly cooled. You'll know if the optics are not cooled as the diffraction rings will have a v in them.

[04Stefan07]

Hey Paul.

What would I need to collimate the SCT? Any good guides out there as well?

[Paul Haese]

Stefan,

you'll find a few guides here on collimation of an SCT I am sure.

You will only need a set of allen keys to adjust the corrector screws at the front (not the one in the centre) and a reasonably bright star. Defocus until you can see a couple of diffraction rings and then adjust one screw at a time, by loosening one a little and then tightening another. If you go the wrong direction reverse the procedure. You only need to loosened a quarter of a turn each time.

If you are not sure, get someone from your local area who can collimate an SCT to show you how it is done. Once you learn you will never look back. This is just part of service of equipment you own.

[Nikolas]

Stefan it's definte;y seeing conditions, weather has been appalling in Melbourne with crappy transmission and unsteady skies

[04Stefan07]

Thanks mate.

I’ll keep a set on me. When seeing conditions are better and still having issues I will give it a go!

[04Stefan07]

I certainly hope so, it’s so frustrating!

[barx1963]

Stefan
There was an excellent article a while back in S&T (both US and Aust editions) on collimating an SCT with a star test. I am scanning it now and will send you a copy.
I did mine and was dead easy. I made it a bit easier by replacing the standard screws with Bob's knobs as mentioned in the article. I know Sirius Optics in QLD stock them.
My 8" Edge is the only scope I have been able to collimate entirely with a star test and no other tools.Took about 10 minutes.

Cheers

Malcolm

[glend]

For SCT/Edge focusing, especially for imaging with a barlow, you can not beat using a Duncan Mask. They are easy to make at home and give you a precision that a star test alone is difficult to achieve.

http://alpha-lyrae.co.uk/2013/12/31/schmitt-cassegrain-collimation-made-easy-using-a-duncan-mask/

[04Stefan07]

Thanks mate, received it!

Will have a read :)

[04Stefan07]

Another little project to have a look at :P

[ChrisV]

I'll be interested to see how you go Stefan - is it seeing or collimation.

My Mars images look similar - some night worse than others. I'm using a 1000mm focal length newt with a 2x barlow. I've collimated my scope with an orion cheshire collimator and a laser collimator (which I've also collimated). Then I've tweeked it with an out of focus star when the scope has cooled. So I'm sure it seeing, rather than collimation - or I'm not getting good focus ..

[netwolf]

I find this helps me with my c8. Mars is challenging with dust storms making focus difficult. I also use Firecaptire focus and Sharpcap has some nice focusing routines. Best to focus on nearby star or even the Moon first. Else bump up gain and exposure till its bright and focus until you have a tight height round circle then back of ur gain and exposure.

[04Stefan07]

Going to have another crack at it soon.

Have left my scope outside so far for about an hour to match the outside temp.

Fingers crossed!

[StuTodd]

+1 for the Duncan mask suggestion from Glen.

Cost $0 and 10 minutes to make and it gave excellent collimation. As ever, you'll need to have the scope cooled down to outside temp.

[OICURMT]

Pages 6-8...

http://www.astrogeeks.com/Bliss/OccultVideo/SCTCoolingFreestar8n.pdf


OIC!