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Starlord19

Planetary imaging through a diagonal?

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Hello. I have a 127 Mak and an ASI120MC and have been enjoying my first forays into planetary imaging with pleasing results. I just pop the camera into the diagonal in place of the ep and it seems to work fine. Twice now I have been advised not to use the diagonal but to put the camera directly into the visual back. However nobody has told me how or why this would improve my results, which seem to be fine anyway. Can somebody please explain this to a beginner? 

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Diagonal is just not necessary for imaging, but it adds another optical surface - one which causes loss of light (how ever small percent that might be) and introduces additional aberrations (how ever small they might be) since no surface is 100% flat.

That is the reason you were given that recommendation - diagonal is not necessary and it lowers the quality of recording to a certain degree. It is up to you to decide on trade off - is it somehow more convenient for you to use diagonal (for example you don't own adequate extender) or are you after the maximum quality of image given the equipment.

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Do what works for you but have as few bits of glass between the camera and the light coming out the scope. More glass = more light lost.

Peter

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As Chris has said, removal of the diagonal will require more back focus (outward) travel of the focuser. This usually means buying a T extension tube....

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Getting rid of the diagonal , means a smaller image , because of a shorter f/l.

Trade off really. U can always use extension tubes , which is what I have done.  

 

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Thanks everyone. So it is basically a case of the less glass then the less light lost, makes perfect sense. I will give it a try without the diagonal and see what the results are like. However I can get focus with the diagonal and I can swap and change between the ep and camera easily so unless there is a noticeable improvement I'll probably just carry on as I am!

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On 2/6/2016 at 13:22, Grotemobile said:

Getting rid of the diagonal , means a smaller image , because of a shorter f/l.

Trade off really. U can always use extension tubes , which is what I have done.  

 

There is an interesting old thread on here about this. 

Olly

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