what is the magnification of a telescope without any eyepiece

Started 7 months ago | Questions thread
OP Metastro Forum Member • Posts: 56
Re: That's slightly complicated...

Jon555 wrote:

If you just attach a camera then it's the same as a lens, so a 600mm focal length telescope is the same as a 600mm camera lens for what you see. As to resolution that depends on the camera sensor size, MP count and Telescope quality.

With Barlows it depends where you put them. My 2x Barlow becomes 3.5x if I move it about in the chain of stuff between the Telescope and the Camera. So for my colour Moon photo I went:

Scope-Barlow-Diagonal-2" Extension Tube-T2 wide adaptor-T2 to EOS adaptor-Camera

(I needed the diagonal and extension tube to get enough back-focus.)

Which gave about 2200mm equivalent, and the light was spread out so much (f/6.6 Telescope) I needed ISO1600 and stacked the images to get a good result. Placed after the diagonal the Barlow would be about 2x.

For a sanity test the Moon is about 0.516 of a degree across (varies somewhat as its orbit isn't circular). So for example in my image it was about 53.5% of the image width, so giving a horizontal FoV of about 0.96 degrees and so a equivalent focal length (as was an FF camera) of around 2200mm.

Oh and remember you'll need to flip stuff shot in a Telescope to give a right-way-up look (or if you forget people will just assume you're in Australia/similar).

You can just use the focal length/50 for approximate magnification, but as you are unlikely to use the image uncropped it's a bit meaningless.

Thanks Jon555,

I was getting too caught up in the theoretical mathematics behind it I think. In my beginners case I am thinking purely about the scope, a barlow and straight to camera. So I can see now that, as you say, it's just the fl scope length, multiplied by the barlow strength.

As I do more research and have read everyones answers, I can also see that magnification is only a small aspect of this. It's difficult to calculate what is 'optimal' when using a camera as the camera sensor itself introduces many variables. So from what I can see there is no 1 size fits all. Its about:

Seeing conditions

the scope and any attachnments

the camera sensor

the subject

(and more I have yet to learn)

I understand now that you simply have to do the maths on a per subject basis - which is fine, my original question has definitely been answered!

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