Understanding finderscopes.

[LukeSkywatcher]

Hi all.

Just thought i'd fire of a quick question regarding finderscopes seen as i just got one in the post today courtesy of Robhal.

The finderscope is a Celestron 8x20. Really nice little finder. Crisp clear image through it and it even has nice crosshairs in it to pinpoint objects.

So my question is regarding the specs of it.

I know it is 8X. Thats fine i understand that part. Its the 20 that i am wondering about. Surely that cant be 20mm...............can it. Its smaller then the lens on my 15mm EP.

Thanks.

[Moonshane]

hi Luke

finders are usually specified like binoculars with the 8x (as you say) meaning the magnification and the 20 representing the aperture/objective. therefore I'd expect the aperture of the fat end of the finder (the lens rather than the shade etc) to be equal to approx 20mm.

I find an optical finder and a red dot finder work superbly together. good luck with your latest purchase - I see you've been splashing out lately

[Cornelius Varley]

The 20mm refers to the diameter of the objective lens at the front of the finder.

Peter

[LukeSkywatcher]

hi Luke

finders are usually specified like binoculars with the 8x (as you say) meaning the magnification and the 20 representing the aperture/objective. therefore I'd expect the aperture of the fat end of the finder (the lens rather than the shade etc) to be equal to approx 20mm.

I find an optical finder and a red dot finder work superbly together. good luck with your latest purchase - I see you've been splashing out lately

I paid exactly NOTHING for the finderscope. Another SGL member was giving stuff away for free and i took it off of him. I have also gotten a filter wallet and a copy of "Practical Astronomy" from him.

[LukeSkywatcher]

The 20mm refers to the diameter of the objective lens at the front of the finder.

Peter

Ahhhhhhhhhh ok. Now that makes more sense. I just compared the "front" end of the finder to a 15mm EP i have and it is slightly bigger.

Thanks for clearing that up for me. I was comparing the other end (the end you observe through).

I STILL cant fathom out how the 20mm objective on the finder is just under half of the diameter of a pair of 10X50 bins. Maybe it is..............and i just aint seeing it.

*Self edit*

I just compared the finder scope objective to a pair of 10X50 bins and it actually is just under half the size.