I don't do this myself nor do I have an E-series camera but I do have
related experience and some comments below.
khen lim wrote:
> Hi guys
>
> I have no doubts there're plenty of people here who have and are using their
> E-series with spotting scopes. I'm new to this area but someone pointed me
> in the direction of Meade Kestrel. I've checked and realise there are two
> models. One is an 80mm with 20-60X mag and the other is 60mm with a 15-45X.
> My questions posed to you are as follows:
>
> 1. Do you use same tech principles for binos to read specs for spotting
> scopes?
Yes, spotting scopes, binos, astro scopes all operate the same way.
Exit pupil diameter is an important measure for brightness in
binoculars. Computed by objective diameter divided by magnification.
The specs for both of the scopes you mentioned note that the exit pupil
diameter ranges from 4 to 1.3 mm which means that the relative
brightness of the 80mm scope is the same at 20X or 60X as the 60mm scope
is at 15X or 45X. 3mm is a typical human pupil diameter in daylight.
7mm is typical maximum diameter of the dark adapted eye. 7x50
binoculars are referred to as "night glasses" since the exit pupil is
50/7 = 7.1mm diamter or the maximum that will fit through the dark
adapted eye and yield maximum brightness. At minimum magnification
these scopes will have a 4mm exit pupil which will yield a fairly bright
image in weaker morning and late afternoon light which is important to
birders since that's when the birds are active.
> 2. Any personal experiences in terms of using E-500 with spotting scopes
> that you can share?
Sorry, none
> 3. Reliability issues?
> 4. Optical issues?
You will likely have to use what is called "afocal projection". The
scope is focused as for the eye which produces an image that, from the
camera's perspective, is at infinity. The camera lens is focused at
infinity and put behind the eyepiece and very close to it. Minor
focusing adjustments may be required since your eye may not be perfect.
Afocal projection produces very high magnification. Effective focal
length is equal to scope magnification x lens focal length. The 80mm
scope at minimum magnification of 20X and using a 25mm lens gives you an
effective focal length of 500mm. The effective aperture would be 500/80
= f/6.25. Running it up to 60X with a 25mm would give you 1500mm at
f/18.75.
Direct projection (eyepiece projecting an image directly into the camera
without camera lens) is also possible if the scope's eyepiece has the
required range of movement to focus the image directly on the sensor.
Effective focal length is more difficult to compute here since you need
the projection magnification value and the focal length of the scope
which you don't have.
> 5. Anything else is welcome
You biggest problem (and it's a *big* one) is rigidly mounting the
camera in optical alignment with the eyepiece (which is at an angle to
the body of the scope) *and* then controlling the whole terribly
unbalanced gizmo... not to mention seeing and focusing manually at f/6.5
(on the bright end) to f/19 on the dim end.
If you want a spotting scope these look they might be good ones. But if
you want to take pictures through a scope I'd suggest a different
solution that is equally usable for spotting and picture taking. The
better solution has to start with mounting, balance and vibration
control. I'm sure Richard can fill you in about his Takahashi but it
needn't be as expensive at that wonderful piece of glass.
Good luck,
Chuck Norcutt
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