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    Default Using an 80mm refractor telescope with 400mm focal length for wide field...



    ...astrophotography.... ? I want to do some astrophotography...either prime focus with a skywatcher 80mm ed APO with a 500mm focal length or possibly a piggy back with my camera on a motorized mount and scope. My question is for the prime focus scenario...since telescope magnification is a product of the focal length of the lens arrangement and the eye piece, if I was using my DLSR in place of the eye piece, would this 500mm telescope produce an image magnification similar to that of just using my Canon 400mm f5.6L lens? This is not a "cheap lens." It uses ultra low dispersion glass and is in the $1,200 class of lenses. Mounting this lens on a Canon 20d would produce an effective focal length of 640mm with f5.6.

    SO in simple terms, my question is with a camera attached to the telescope instead of the eye piece, do you get any sort of high power magnification?

    I don't have either rig yet but if I can get a similar picture with my current lens then I will put more emphasis on the quailty of tracking mount and use a less expensive achromatic scope for visual gazing and alignment on targets.

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    Hi Nola, and welcome to the forum!

    Rather than type reams which is going to confuse me quite as likely as confuse you, have a read of this. The author refers to film SLR photography but the principles are the same for DSLR

    Astronomy For Beginners...Astrophotography...The Prime-focus Method

    In simple terms no you don't get extra high power mag in Prime focus, but you do collect a lot of light.

    Incidentally, the SWED80 has a FL of 600mm so is at f/7.5.

    What I should point out is that if you want to pursue AP (astro photography) the telescope mount that you use is the key factor, and will usually cost more than the telescope itself. You need to be able to keep the rig rock solid whilst tracking for long periods.

    In the case of an ED80 I wouldn't go under an HEQ5 mount or an EQ6 preferred, (whereas for visual only, an EQ3 mount will carry the same scope OK) and that will cost you more like 2 to 3 times the price of the scope. Nevertheless you can get away with a lot less if you are satisfied with short exposures on the bright objects like the moon, and Saturn and Jupiter

    HTH

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    Just to add what is purely an opinion to the above, I am inclined to suggest what you have already mentioned, and that is to go for a good solid mount and a cheaper achro, then Piggy Back the camera. If it all works out and this is what you want to continue with, later you can add a better scope for prime focus work, and provided that you start with the right mount, you will still use the achro as a guide with the camera in prime focus.

 

 

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