Magnification/eyepiece size for digiscoping (1 Viewer)

I am curious as to what eyepiece size/magnification is popular for digiscoping. I am attempting to determine if using a lower power (24-30 mm) eyepiece would improve the light levels delivered to my digital camera. Common sense would dictate that the larger exit pupil provided by a lower powered eyepiece should give a brighter image. With this thought in mind what size eyepiece (relatively speaking for your setup) do you feel delivers the best combination of magnification and a bright image? I see folks often reference the Nikon 82 mm model with the 30x eyepiece for digiscoping but also see many folks opting for 24-34 mm eyepieces in combinations with a variety of other scopes which should yield lower magnifications (16x-20x). I realize this is going to vary somewhat because of objective diameter.

Any thoughts on this issue would be appreciated.

Gday Frank,
I am at present using an 80mm scope, with a 20-60X zoom, I have managed to been able to use 40-60x and 20x between 20 and 40 is a no go zone, I have a 24X eyepiece which is no good for my setup. I deffinately get brighter images at 20X. Using it in my small garden the 20X works well, nearly filling the screen at it's nearest focusing distance, on a dove. I have found that I do have to make compensations on exposure, don't really have any specific numbers as that depends on curcumstances at the time. DOF is the biggest problem I find,or should I say lack of it. Ernie

Ernie,

Thank you for the response. At 20x with the 80 mm scope you are getting a 4 mm exit pupil out of the eyepiece. Based on what you are saying the larger exit pupil gives you a brighter, and theoretically, more detailed image because of the increased amount of light entering the camera lens, right? Doing something similar with my 65 mm scope would then entail me utilizing a 16.25x eyepiece (24 mm). Would a lower magnfication eyepiece (30-34 mm) give me an even brighter and more detailed image or would I reach the point of diminishing returns because of the aperture size of my camera lens?

between 20 and 40 is a no go zone, I have a 24X eyepiece which is no good for my setup.

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Why do you say this? Is it because of an eye relief or field of view issue and vignetting or something else entirely?

Hi Frank, I would say your right in your assumptions. The reason for the no go zone between 20 and 40x is very severe vignetting. I am not going to suggest that the quality of images deminishes at the larger magnifications, because I have some nice images taken from 25-50meters at 60x, the main difference is, the exposure times are shorter, hence more chance of out of focus shots. Ernie

Hi Frank - I'll say this, at least your keen to learn!

I mainly use my 20x eyepiece on my 66.5mm scope. - and get NO vignetting at all, even at maximum wide angle.

I occaisionally use my 32x eyepiece and at maximum wide angle 'often' get no vignetting. With even a titchy amount of zoom all vignetting disapears.
(I say often, because under certain rare lighting circumstances I do get a slight touch of vignetting with the 32x. Haven't bothered figuring out why yet!!)

Brightness is no problem with either.

BUT this is important: Some people say you always need to get the camera lens as close to the eyepiece as possible, - This is WRONG. It may be true for some setups. But on 2 of my setups, I get far less vignetting if I move the camera back to about 10mm from the eyepiece. I feel this also has other optical advantages too.

I use a Fuji F10 and it works very well digiscoping (especially up to ISO400.)
Light levels are no problem, even on overcast days. - but overcast days do not give good definition.

I was looking through the very best optics available last weekend - swarovski, zeiss, lieca, etc. and some of these gave me 'blackouts' when I looked through the eyepieces to closely. I guess this is also whats happeneing with some cameras.

Hi Frank - I'll say this, at least your keen to learn!

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Thank you. Without asking these questions I am never going to get my digiscoping setup to where I want it. I think all of this is relevant and yet never see many of these questions answered on the various digiscoping websites I have visiting...and I have hit many at this point.

I am wondering if there is a "magic number" in relation to objective diameter, exit pupil and magnification. Is it possible that you "need" a 4 mm exit pupil on the scope's eyepiece in order for the camera lens to get enough light for a great picture? Might that just apply to the 65 mm and under scopes? Would it be possible that the 80 mm scopes can get away with a smaller exit pupil because the objective lens tends to give more detail and contrast because of size alone? Which is brighter with binoculars a 10x40 or an 8x32? Which yields better resolution? Both have 4 mm exit pupils but the larger objective on the 10x40 should yield a brighter image with better resolution. I would be willing to bet that much the same could be said for spotting scopes.

I use a Fuji F10 and it works very well digiscoping (especially up to ISO400.)
Light levels are no problem, even on overcast days. - but overcast days do not give good definition.

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Does the Fuji F10 have aperture priority mode? If so then that might explain the difference between your setup and mine. My aperture is determine by the camera. I cannot manually change it. I can change the shutter speed and ISO setting though.

I was looking through the very best optics available last weekend - swarovski, zeiss, lieca, etc. and some of these gave me 'blackouts' when I looked through the eyepieces to closely. I guess this is also whats happeneing with some cameras.

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I am guessing the blackouts are because the scopes have extremely long levels of eye relief and that would back up your assertion that putting the camera too close to the eyepiece lens would be counterproductive. I would be willing to bet that the reason folks suggest doing this though is to reduce the chance of stray light entering into the eyepiece/camera lens connection.

Thank you again for the help. Every little bit counts.

Hi Frank - sorry only just read the F10 aperture priority mode question, and no it doesn't have one. The camera chooses the shutter speed and aperture. I use a high ISO to try and get it to choose a fast speed.

Thanks. I see I am not alone in going that route then. I have been posting over in the Pentax spotting scope forum on this subject matter as well. I have some new pics I am going to post on the image quality help thread and on the Knight Owl EWA thread in the Pentax forum. Comments would be appreciated.

I have taken to stopping down a bit - to f/8 or even f/11 - on the theory that even if I'm a bit out with my focus, the added depth of field will compensate. On the whole, it seems to be working, but you need excellent light.

With the 100-400 Canon (I guess the Sigma is similar) it helps a lot to zoom out to 100mm, get the bird in frame, then zoom back in to 400. Alas, I mostly have the big 500 prime mounted, usually with the 1.4 TC, and that is not a good lens for flight shots: no zoom, shallower depth of field, and it's very heavy and clumsy. But by the time you swap lenses, of course, the bird is gone.