Basic DSLR / Scope question

[cv01jw]

Morning All

As a newcomer to astronomy and astrophotography I have been looking at inexpensive ways of getting into imaging to see if I like it, without spending too much money.

A long time ago I bought a used Canon 400D and it came with, amongst other things, an adapter which I could not figure out.  I dug it out last night and to my surprise it is a telescope mount adapter :).  I have charged up the camera and it works, so I appear to have a basic astrophotography setup ready to try.   One thing I am having trouble figuring out is the magnification I will obtain when using the camera – I know this is not really important but I am interested.  I understand the geometry behind working out magnifications, but I cannot think how to work out the focal length the camera is using in place of an eyepiece, other than somehow trying to measure it?  Am I missing something?

Thanks in advance.

 

James

[mikeyj1]

look for 'astronomy tools' under the resources tab above, that will help you calculate the field of view.  it's not directly the magnification but rather the 'image scale' that you will see as the combination of the focal length and the sensor size of the camera. 

cheers

Mike

[billyharris72]

Hi James:

It's a good question with an odd answer. The truth is it doesn't really make sense to think in terms of magnification when dealing with AP, since it very much depends on what scale you view the image at too. Normally we deal instead with field of view and pixel scale (how many arc seconds a single pixel covers). That gives you a number that works a bit like magnification, but it can't be directly compared (I think).

Pixel scale is given by

camera pixel size (microns) / telescope focal length (mm) *206.3 (arc seconds)

And you can work out field of view by just treating the sensor as one big pixel.

Stole this from http://astronomy.tools/calculators/ccd

An excellent website from our beloved sponsor.

Billy.

[DAVE AMENDALL]

 I always imagined a focal plane SLR to be similar to a 20mm eyepiece as a non tec response. I think somebody told me this back in the film usage days.....Dave

[michael8554]

14 hours ago, cv01jw said:

I cannot think how to work out the focal length the camera is using in place of an eyepiece

You have taken the kit lens off your 400D and attached it to another longer focal length lens - your telescope.

So the focal length is whatever focal length your telescope is.

Michael

[cv01jw]

Thanks for the responses.

I have looked up the specs for my camera and used the calculator to find I have a resolution of 2.94" / pixel.  Is this good?

[ollypenrice]

I'm another who would forget the term magnification from the outset. It is meaningless, perhaps even more so in the case of digital imaging than film imaging (since if you image with smaller pixels you'll get a bigger image on your PC screen.)

Many planetarium software packages allow you to model a given focal length of lens/scope for a given size of chip on a map of the sky. This will give you an idea of what to expect.

Olly