Bright circle - question to experts

[IanP]

This is a single shot (75sec) of M45 - Orion 80ED + Canon 60Da
The picture is slightly overstretched to demonstrate the problem ..
What may cause this bright circle?
Let's assume it's light pollution, shouldn't it be uniform across the whole picture?
Thnx,
IanP

[Peter.M]

Are you connecting the camera to the scope with a 1.25 inch t ring adaptor or something? What you are seeing is called vignetting and it is caused by the camera not being fully illuminated by the telescope. It is quite bad in that image which is why I ask if you have a restricting adaptor in the light path

[IanP]

That's right. So, the 1.25" is to small? Do you think 2" should work?

[pluto]

Yeah you need a 2", I had the same problem with the 1.25" adaptor I got with my SW ED80, I bought this one: http://www.bintel.com.au/Astrophotography/Adapters/Bintel-Camera-Adapter-2-/35/productview.aspx
When I bought it in-store at Bintel a couple of weeks ago I thought it was only $29...?

[IanP]

Thanks Hugh,
The current price is $39+p&h but I think it's worth trying ..
:thumbsup:

[Nico13]

Here you go Ian have a look at this,
This is a shot with ED80 and a 2" adapter and slr with APS C size chip same as yours would be.

Cheers

http://www.iceinspace.com.au/forum/attachment_browse.php?a=126841

Forgot to mention I also have a field flattener on the camera adaptor

[LewisM]

There's a guy in America on eBay that makes a one-piece adaptor and 2" tube - no inner T-ring, no grub screws - just one solid piece (no wiggle). He makes Canon, Nikon, Pentax and Olympus. Fully illuminates my full size sensor on the 5D MkII I use. Cost total was $35 US with postage.Have a look on eBay and see - I'd have to wade through all the wife's million purchases to find him again :)

[IanP]

Yeah, the picture look perfect!!!
Thnx for confirmation .. Just orderd the 2" adapter from Bintel ..

[IanP]

Although I've already orderd the 2" adaptor from Bintel I'd like to have a look (and possibly get it too) at this one-piece adaptor from US ..
Thnx
#Ian

[Astro_Bot]

Was it this one?

http://www.telescopeadapters.com/homepage.htm#TRUE2

[IanP]

Thnx, looks like it ..
In the meantime I found on ebay the same thing for US$55+$7p&h=AUD62 ..
:thumbsup: