Re: [APML] OT: 240 Galaxies in 3 square degrees of Virgo

[Éder Iván <eder@prof.hu>]

Hi Jerry,

Check your collimation please!

BTW, beatiful image! Do anybody know what is the limiting magnitude of the 
image?

Ivan


At 08:35 2005. 04. 19.t Conve, you wrote:

>>I wondered about it because I'm about to start using a DSLR, and they are 
>>more sensitive to star distortions than film.  I'm also using an AP 
>>refractor (180f9) and don't know if I will need to use a flat field lens 
>>as well.
>
>
>Hi Don,
>
>If you want the stars to be points in the corners of the frame, you will 
>almost certainly have to use a field flattner. I definitely have to at 
>f/8. And I could see the astigmatism on film very easily.
>
>This is not a defect in the lens, it comes from the focal plane not being 
>flat. It is curved, and you will see astigmatism in the corners if you 
>don't use the field flattner.
>
>Jerry
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