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Re: (meteorobs) 1X "binoculars"? Thanks Mike,and another/question
Mike,
Thanks for the great optical info. I had a feeling that there was an
optical reality that prevented my idea from being a viable one.
As to image intensifiers, has anyone tried these for meteor observation.
Do they work with a wide angle view of the sky satisfactorily ? If so,
any recommendations for a supplier/brand/model?
Also, assuming they work for observing meteors, can they be used to
submit useful data to meteorobs/NAMS/IMO ? (This last question is
essential as to whether I would seriously consider using an intensifier.)
Thanks for any help out there,
Dustin Brown
Mike Linnolt wrote:
> Dustin,
>
> Your idea for a 1x "telescope" that just amplifies your LM, is not
> theoretically possible, regardless of the size of the objective you
> plan to use. Here is why. Magnification (M) is the ratio of your
> objective focal length (F) over your eyepiece focal length (f). so,
> M=F/f.
> >From geometrical optics, you can see that the exit pupil (p) (which
> is the area at the output end of your eyepiece, in which all the
> objective's light is concentrated) is related to the eyepiece focal
> length (f) just as the objective diameter (D) is related to the
> objective focal length (F). So, p/f=D/F. Rearranging the equality, we
> get D/p=F/f. But F/f is just M, so we get D/p=M.
> So, basically, the magnification also equals the ratio of your
> objective diameter to your exit pupil. For 1x magnification, the
> objective diameter must equal the exit pupil (D/p=1). Now, since
> your eye has a typical maximum dark-adapted pupil diameter of
> 7mm, it means that the scope exit pupil should not exceed 7mm.
> Any wider exit pupil from the scope "wastes light", because your
> eye is unable to accept a wider input. So, that means your
> objective diameter cannot exceed 7mm, either, for 1x
> magnification, if you dont want to waste any light. For example, if
> you use a 10" (254mm) objective (LM~14.2), at 1x, the exit pupil
> would also be a whopping 10". Your 7mm eye pupil would only
> intercept 7mm^2/254mm^2 = .00076 = .076% of the light from the
> objective. You are losing (100%-.076%) 99.924% of the 10"
> objective light, which is equivalent to about 7.7 magnitudes, so the
> LM~14.2 drops back to normal naked eye LM~6.5.
>
> So, in summary, you cannot gather more light than the maximum
> size of your eye pupil allows in, using any passive optical system
> with 1x magnification.
> If you want to see fainter LM, get an image intensifier, etc.
>
> Thats the story,
> Mike.
>
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