Why does older CoolPix-995 work with scopes, and DSLRs will not?

Perhaps this should be posted in a "Digiscoping" news group, but I
don't believe there is any such.

Anyway, for several years I've been using my CoolPix-995 successfully
with a Swarovski AT-80-HD spotting scope, and would like to upgrade
the camera to something with more resolution and a larger sensor.
Specifically, a good DSLR with an Image Stabilized lens.

Unfortunately, I keep hearing both (1) DSLRs are not suited for
Digiscoping and (2) if you insist, you must remove the camera's lens
and shoot without it, using a special adapter and a T-Mount. But it's
almost impossible to find an explanation as to why these two
statements are correct.

Can anyone give a good technically sound and logical explanation as to
why the CoolPix series and others like it CAN be coupled up close to
the scope's eyepiece, and the DSLR types cannot without the above
modification and loss of use of its lenses? It is these Image
Stabilized lenses that make a workable arrangement using them so
desirable for this application.

Thanks for any explanation (preferably based on factual knowledge, not
opinion).

Olin McDaniel

The eyepiece of the spotting scope is designed for something
about eye-sized, and I could bang on about entrace and exit
pupil sizes, but instead...

Look at the diameter of the front of your Coolpix's lens.

Look at the diameter of the frony of the dSLR lens tou want
to use.

Compare and contrast. Which is more like the size of the eye
that it's about to replace behind the scope?


--
John Bean

"John Bean" wrote in message
...
The eyepiece of the spotting scope is designed for something
about eye-sized, and I could bang on about entrace and exit
pupil sizes, but instead...

Look at the diameter of the front of your Coolpix's lens.

Look at the diameter of the frony of the dSLR lens tou want
to use.

Compare and contrast. Which is more like the size of the eye
that it's about to replace behind the scope?

Good explanation.

Not to worry, though, the DSLR / T-mount solution is also very good, and
will probably give superior results. Since the eyepiece and camera lens are
absent, there will be fewer pieces of glass in the optical path.
--
Mike Russell - www.curvemeister.com

On Sun, 10 Jun 2007 21:06:59 GMT, "Mike Russell"
-MOVE wrote:

"John Bean" wrote in message
.. .
The eyepiece of the spotting scope is designed for something
about eye-sized, and I could bang on about entrace and exit
pupil sizes, but instead...

Look at the diameter of the front of your Coolpix's lens.

Look at the diameter of the frony of the dSLR lens tou want
to use.

Compare and contrast. Which is more like the size of the eye
that it's about to replace behind the scope?

Good explanation.

Not to worry, though, the DSLR / T-mount solution is also very good, and
will probably give superior results. Since the eyepiece and camera lens are
absent, there will be fewer pieces of glass in the optical path.
--
Mike Russell - www.curvemeister.com


OK John, so the diameters are the cause of the incompatibility.

But, Mike, if I've got to use the T-Mount and maybe the Swarovski's
adapter - my real question is why don't they add a correction lens in
that adapter tube? Why throw away the magnification the lenses, such
as the Swarovski's eyepiece provides? These give 20X to 60x
magnification, all within the eyepiece itself. (You did say "since
the eyepiece and camera lens are absent". Check what you said.) My
further question is - do these adapters really work without both such
lenses? I thought they only required removal of the camera lens, and
fitted onto the eyepiece which was left in place.

Now, what I really suspect, but cannot confirm it since it's tough to
get in touch with them directly, even via a web site, perhaps
Swarovski may actually include such a corrective lens in their ~$280
and $460 adapters. Can anyone on here tell me if that's true or not?
That's essentially what my original post was all about.

Now, back to you John. There are items being sold to make such a
combo compatitible. The problem is - they fail to explain how they
are solving the diameter difference problem, and how removing one or
both lenses manages this. That's precisely what I'm looking for an
understanding of.

And perhaps I shouldn't expect the 3000mm focal length (35mm
equivalent) I get with the CP-995 and the 20X eyepiece on the scope,
but that's what I'd like to match. Simply that!!! What are the
other options? $8000 lens plus $300 2X tele-extender? That gives me
about half what I get now, but now I'm working at only 3 MP
resolution. I want the best of both worlds, 8 to 10 MP resolution
plus the 3000mm equivalent focal length. Don't we all? An adapter
designed for DSLR cameras (like the 30D) and a good lens is the
desired goal. Let's pursue this as if price was not the major
obstacle. Can it be done? Or is it just not worth it?

Olin McDaniel

"Olin K. McDaniel" wrote in message
...
On Sun, 10 Jun 2007 21:06:59 GMT, "Mike Russell"
-MOVE wrote:

"John Bean" wrote in message
. ..
The eyepiece of the spotting scope is designed for something
about eye-sized, and I could bang on about entrace and exit
pupil sizes, but instead...

Look at the diameter of the front of your Coolpix's lens.

Look at the diameter of the frony of the dSLR lens tou want
to use.

Compare and contrast. Which is more like the size of the eye
that it's about to replace behind the scope?

Good explanation.

Not to worry, though, the DSLR / T-mount solution is also very good, and
will probably give superior results. Since the eyepiece and camera lens
are
absent, there will be fewer pieces of glass in the optical path.
--
Mike Russell - www.curvemeister.com


OK John, so the diameters are the cause of the incompatibility.

But, Mike, if I've got to use the T-Mount and maybe the Swarovski's
adapter - my real question is why don't they add a correction lens in
that adapter tube? Why throw away the magnification the lenses, such
as the Swarovski's eyepiece provides? These give 20X to 60x
magnification, all within the eyepiece itself. (You did say "since
the eyepiece and camera lens are absent". Check what you said.) My
further question is - do these adapters really work without both such
lenses? I thought they only required removal of the camera lens, and
fitted onto the eyepiece which was left in place.

Now, what I really suspect, but cannot confirm it since it's tough to
get in touch with them directly, even via a web site, perhaps
Swarovski may actually include such a corrective lens in their ~$280
and $460 adapters. Can anyone on here tell me if that's true or not?
That's essentially what my original post was all about.

Now, back to you John. There are items being sold to make such a
combo compatitible. The problem is - they fail to explain how they
are solving the diameter difference problem, and how removing one or
both lenses manages this. That's precisely what I'm looking for an
understanding of.

And perhaps I shouldn't expect the 3000mm focal length (35mm
equivalent) I get with the CP-995 and the 20X eyepiece on the scope,
but that's what I'd like to match. Simply that!!! What are the
other options? $8000 lens plus $300 2X tele-extender? That gives me
about half what I get now, but now I'm working at only 3 MP
resolution. I want the best of both worlds, 8 to 10 MP resolution
plus the 3000mm equivalent focal length. Don't we all? An adapter
designed for DSLR cameras (like the 30D) and a good lens is the
desired goal. Let's pursue this as if price was not the major
obstacle. Can it be done? Or is it just not worth it?

Olin McDaniel


For someone who uses telescopes, I would have thought you would know a
little more about Optics.

The Eyepiece lenses do not produce a "real" Image, It cannot be brought to
focus outside the Telescope.

The P & S Camera lens will be able to bring this virtual Image to focus at
the sensor.

A DSLR with a lens attached would be able to do that also, but the
difference in size between the front element glass and the Scope VF glass
would make this almost unworkable.

Removing the scope VF and the DSLR lens will allow the Scope to bring its
image to focus on the Sensor, and the adaptors just ensure that extraneous
light is kept out, keep the Camera steady on the scope, and the adjusters
allow the scope to focus.

You are trying to re-invent the wheel. The magnification is determined by
the front element of the scope. That is why they need to build such
enormous scopes for professional astronomy.

Roy G

In article , roy.gibson1
@REMOVE.tesco.net says...
You are trying to re-invent the wheel. The magnification is determined by
the front element of the scope. That is why they need to build such
enormous scopes for professional astronomy.


The large aperture is to capture light from faint objects..
Magnification is secondary.

T.
--
Do Binary Tripods have 11 legs ?

"Tony Gartshore" wrote in message
...
In article , roy.gibson1
@REMOVE.tesco.net says...
You are trying to re-invent the wheel. The magnification is determined
by
the front element of the scope. That is why they need to build such
enormous scopes for professional astronomy.

The large aperture is to capture light from faint objects..
Magnification is secondary.

The aperture size determines resolution as well as light intensity.
Magnification is an analog equivalent of digital zoom. It does not increase
the amount of information available, but it is important because it does
affect the number of pixels you can put on a given object.

The upshot is that the coolpix 995 is a favorite among digiscopers for a
reason - it captures a lot of detail using a conventional eyepiece. A
T-mount will theoretically make better use of the telescope objective
optics, but may, as the OP points out, not have enough magnification to use
the entire width of the sensor.

BTW - I recall that a Russian experimenter removed the optics of the cp995,
and imaged directly on to the sensor without an eyepiece, basically
recreating the T-mount concept, only with a tiny sensor. The person who did
this was able to capture a good image of the Orion nebula, even with just a
moderately long lens. I don't have a link, unfortunately, but can look
around some more if you are interested.
--
Mike Russell - www.curvemeister.com

Roy G wrote:

The Eyepiece lenses do not produce a "real" Image, It cannot be brought to
focus outside the Telescope.


Wrong! Completely wrong, unless you are using a Galilean telescope that
uses a negative lens for an eyepiece, and there haven't been many of
those around in the last 400 years (I believe some really cheap
binoculars still use this design). Of course an eyepiece can project a
real image. I've projected the image of the sun onto a screen many
times. The objective lens or primary mirror forms a real image in front
of the eyepiece, and the eyepiece then can form a second, real image of
that image somewhere beyond. Just think of the eyepiece as a simple,
positive lens, with the telescope primary image on one side and the real
image formed by that simple lens on the other side, outside the
telescope. Though what this has to to with the subject at hand is
another question. There is absolutely no reason a DSLR camera cannot be
used in the same way as a small P&S, with the lens remaining in place.
The problem isn't with the diamter of the lens, but its long focal
length and the subsequent magnification you will get. As others have
said, you could be much better off removing the lens (and maybe the
telescope eyepiece if it is a long focal-length telescope) from the camera.

Sorry to jump on this, but I've been reading a lot of questionable
statements in this thread, some clearly wrong. This was going too far
for me, especially after saying someone should know better.

Joe

In article 466db935@darkstar, Joseph Miller
writes
Roy G wrote:

The Eyepiece lenses do not produce a "real" Image, It cannot be
brought to focus outside the Telescope.


Wrong! Completely wrong, unless you are using a Galilean telescope that
uses a negative lens for an eyepiece, and there haven't been many of
those around in the last 400 years (I believe some really cheap
binoculars still use this design).

Actually he isn't wrong at all, just describing the situation of the
telescope in use as set up for normal viewing. When correctly focussed,
the telescope and eyepiece produce parallel rays, (even on a Galilean
telescope) with the image focussed at infinity. This allows you to look
through the eyepiece and see an image with your eye relaxed, just as you
normally would when viewing a distant object, where the rays entering
your eye from that object are parallel, to be converged onto your retina
by the lens in your eye.

Of course an eyepiece can project a real image. I've projected the
image of the sun onto a screen many times.

Yes, you can but you will notice that the distance to your "screen" is
significantly greater than the distance between the camera mount and the
sensor. Also, if you then look through the telescope the eyepiece will
require adjustment to bring the image into focus for direct view (or at
least it will if you have normal or corrected vision). All you are
doing to focus on a screen is changing the separation of the primary
lens or mirror and the eyepiece so that the rays coming out of the
eyepiece converge to a point at a finite distance rather than infinity
as parallel rays do.

You can do exactly the same thing with a Galilean telescope too!

Any telescope can produce convergent, divergent or parallel rays
depending on the instrument focus.

Sorry to jump on this, but I've been reading a lot of questionable
statements in this thread, some clearly wrong. This was going too far
for me, especially after saying someone should know better.

Pot, meet kettle - you are both black, so you can be buddies. ;-)
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

In article , M-M
writes

You CAN use a DSLR and an eyepiece on a spotting scope. However
everything has to be manual.

Not at all, you should be able to use aperture priority auto exposure
mode without any problem. Obviously you can't use any other auto mode
because the scope only has one aperture and no aperture control link
with the camera.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)