FF dslr's - yay or nay?

[sejanus]

Hey guys

I notice than pretty much everyone is using dslr's with what I call small chips - i.e. not full frame 35mm sensors like in the Canon 5D or 1Ds series or Nikon D3 series.

Do the full frame dslr's show lots of vignetting/field curvature when plugged into something like a 80ED or 120ED refractor?

hope this makes sense!

[renormalised]

Field curvature will be minimised by a field flattener. If you can get one specific for your scope, great, but a "generic" flattener will do.

Vignetting can be combated by getting a large enough focuser so that the light path to the ff CCD isn't hampered by anything internally. You'll need at least a 2" focuser or larger for a 35mm CCD chip. Same goes for the flatteners and anything else you connect up in the imaging train. Anything can cause vignetting, but flatteners can be a source of the problem. Sometimes, it's unavoidable, so you have to live with it and just adjust your piccies accordingly.

[sejanus]

thanks, very helpful

[j.w.white]

I shoot with the Nikon D700 and love the wide field on my EdgeHD 800. It's kind of cheating in that the field flattener is already build in, but it is sharp out to the edges of the chip. Vignetting is not that big of an issue and is easily controlled by processing with image flats. My biggest gripe with the D700 (aside from the diminished red sensitivity - no one yet mods these) is the weight. I'm getting a much lighter camera (will be modded!) to use on my Meade 5000 APO so the crayford focuser will not be constantly pulling out.

[sejanus]

I'm using 1 series Canon's, which are about the heaviest dslr's out there! I think no matter what I get I'll need to get a better focuser.

[Terry B]

It depends on the scope. My VC200L was made originally to illuminate a 35mm full frame camera. The small refractors that are popular as imaging scopes don't seem to have as big a light cone so there will be some light loss in the corners. As long as there is some illumination to the corners it should be fixable with flats.

[bmitchell82]

if your asking if going and purchasing a FF dslr for astro use, i wouldn't bother get a dedicated astro CCD about the same price and 10x as good!

If you already have a FF dslr, well meh flats and cropping will clean them up but its all down to telescope design.

[sejanus]

Yeah I already have ff dslr's hence the question.

The astro ccd's look very trick - maybe one day :) But I think I'd try and reach the limit of the dslr's first - there are some fantastic results from them around here & on the web.

The cameras are 21mp so even if I need to crop them a bit to help vignetting wise I'd imagine there'd still be quite a few pixels left over!

[bmitchell82]

learn how to take flats.
and just chuck it on and see what happens.! figure out the details later.!

[Octane]

I found when imaging with my 5D Mark II that flats have to be absolutely critical.

If the flats are not well-illuminated, then, the stacking algorithms make a meal of your data. The one I use, anyway.

H