Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_30_second_exp_2_winners.thumb.jpg.b5430b40547c40d344fd4493776ab99f.jpg

blinky

Cant get a decent flat image from my lightbox

Recommended Posts

My setup is a ZWO ASI1600 mono with the ZWO filters and a ZS73 scope. I made a light box with some CCFL tunes in a box with translucent plastic to diffuse the light. To my eye it all looks nice and even, I also put a couple of layers of white pillowcase over the scope as well to further diffuse it. The problem I have is shown below in one of the sample flat images, I always seem to get a donut in the centre of the screen, no matter what filter I use. Any ideas, workarounds?

20191202_202832.jpg

20191202_202838.jpg

Share this post


Link to post
Share on other sites

Just set the filter to clear and still have the same issue - I don't think its the camera as I don't see this problem in subs just flats.  Its also not related to short exposures as even with the Ha filter and 3 min subs to get a decent signal I still see it.

Share this post


Link to post
Share on other sites

This was taken without the flat box at all, just the pillowcase and aiming it upwards st the illuminated roof

20191202_204439.jpg

15753195355433799643587632461911.jpg

Share this post


Link to post
Share on other sites

Ice on objective or sensor?

Variable thickness of the cloth?

I don't know - just chucking these ideas up in the air.

I hope you find the answer - that would drive me nuts!

 

Share this post


Link to post
Share on other sites

Doubt it was ice, never know of course but I don't think it was, never had it before when imaging so cant see how I would have ice when taking flats, tried without the cloth and its the same.

Share this post


Link to post
Share on other sites

what if you put a half a dozen sheets of plain paper on the end of the scope and point it skywards in daylight.

Share this post


Link to post
Share on other sites

Not tried, working 9-5 and its dark when I get home but from memory that works fine

Share this post


Link to post
Share on other sites

Does the FITs header tell you the gain and offset Craig? If so compare these with your lights.

I know you were using SGPs flats wizard, have you tried shooting a flat as a light? Just thinking the flats wizard might be not shooting at the same gain and offset, or somehow seeing something else up.

Share this post


Link to post
Share on other sites

That thought occurred to me - I think the wizard is using the default I set to use for focus which is 300 gain and I wonder if reducing it will resolve the issue.  Will try that

Share this post


Link to post
Share on other sites

I have a similar setup at the moment - ASI1600 + filter wheel + ZS71. I imaged on Sunday night and took flats on Monday morning around 10am (still about freezing). My flats looked just like yours with a big dark circle in the middle. However my issue was condensation - either on the ASI1600 window or the rear of the Ha filter. I got a hairdryer to warm up the filter wheel/top of the camera, set the camera to expose for 1s continuously and watched the dark area disappear! Got perfect flats after I let it all stabilise for a few minutes.

What was the temperature when you were taking your flats?

John

Share this post


Link to post
Share on other sites

-20 - the camera was up and running for around 20mins, I did think that but could not see anything and why would I not see that when imaging?  Its a possibility though, especially as you had the same issue.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.