Less expensive alternative to 400mm camera telephoto

I've used these little scopes before and they provide excellent
resolution and contrast,
owing to the fact they use only one achromat instead of multiple
elements.
This thread was from dpreview.com and is not my post.

http://forums.dpreview.com/forums/re...6713601&page=1

RichA wrote:

I've used these little scopes before and they provide excellent
resolution and contrast, [...]

Poor close focus, zero autofocus, no aperture control, and no image
stabilization. What more can we ask for?!

Nitwit. Rich, even you must be able to think this through: if it were
possible to obtain EF 500/4 (or similar) results at 1/20 the price,
don't you think people would already be doing it on a wide scale?

Just because you can't cope with a "manual" lens doesn't mean everyone
is so crippled.
As for it not being taken advantage of by others, lets just chalk it up
to narrow thinking from people like yourself. You probably think
telephoto has to be white to function
well. A more refined version of this kind of lens (apochromatic) will
make
mince-meat of all camera lenses except for the most expensive apos from
Canon, Nikon.

BTW; There is a rudamentary stop down mechanism available for these
lenses that allows
them to be stopped down to about f10.
Close focus is probably limited to around 5ft. How much closer do you
want with a 400mm
telephoto??? A rack and pinion focuser on a long lens affords much
greater focus range
than internal focusing in a camera lens.
But it's a cheap solution so anyone who is remotely curious can try it
for themselves.

RichA wrote:

Just because you can't cope with a "manual" lens doesn't mean everyone
is so crippled.

So sayeth the armchair photo-dingbat. Go ahead and try to use a
telescope as a lens on a terrestrial camera. Unless one is a complete
****head (hey, you!), one rapidly learns the value of one's time.

As for it not being taken advantage of by others, lets just chalk it up
to narrow thinking from people like yourself.

Did you know that the Orion ST80 has a _plastic_ tube?

I bet you didn't.

HA HA HA HA HA HA HA.

You probably think telephoto has to be white to function well.

You appear to have forgotten the ST80 is itself white.

A more refined version of this kind of lens (apochromatic) will make
mince-meat of all camera lenses except for the most expensive apos from
Canon, Nikon.

Yes. A "more refined version". Perhaps you refer to the various
Takahashi, TeleVue and Williams' offerings? Go ahead and tell us how
much they cost. Hint: even the Orion 80ED is beginning to hit $500,
and still no AF, aperture control, and the rest of it.

BTW; There is a rudamentary stop down mechanism available for these
lenses that allows
them to be stopped down to about f10.
Close focus is probably limited to around 5ft. How much closer do you
want with a 400mm
telephoto??? A rack and pinion focuser on a long lens affords much
greater focus range
than internal focusing in a camera lens.

Yes, this must be why the fellow you quoted at dpreview's forums needed
an extender tube to hit 20 feet. Don't you even read the articles you
reference?

But it's a cheap solution so anyone who is remotely curious can try it
for themselves.

.... and discover why everyone else wants a has a telephoto lens that
fits the camera. Why waste a good $200+ for nothing?

On 17 Jan 2006 16:19:36 -0800, "
wrote:

RichA wrote:

Just because you can't cope with a "manual" lens doesn't mean everyone
is so crippled.

So sayeth the armchair photo-dingbat. Go ahead and try to use a
telescope as a lens on a terrestrial camera. Unless one is a complete
****head (hey, you!), one rapidly learns the value of one's time.

As for it not being taken advantage of by others, lets just chalk it up
to narrow thinking from people like yourself.

Did you know that the Orion ST80 has a _plastic_ tube?

I bet you didn't.

HA HA HA HA HA HA HA.

You probably think telephoto has to be white to function well.

You appear to have forgotten the ST80 is itself white.

A more refined version of this kind of lens (apochromatic) will make
mince-meat of all camera lenses except for the most expensive apos from
Canon, Nikon.

Yes. A "more refined version". Perhaps you refer to the various
Takahashi, TeleVue and Williams' offerings? Go ahead and tell us how
much they cost. Hint: even the Orion 80ED is beginning to hit $500,
and still no AF, aperture control, and the rest of it.

The Orion is a bargain at $500.00.
The Tak Sky 90 is about $1900.00. You get what you pay for,
but with the Taks you are paying for mechanical excellence (no
plastic) and optical accuracy.
But for prime focus, you'd be hard pressed to tell the difference
between the cheap Orion achro and the apos, except for some
minor colour error. If you use an eyepiece to do projection
(higher focal length) photography, that is where the apo will
come into it's own. Consider a camera lens with a 25x-50x
tele-converter on it. How would it perform? One guess.
Those scopes are asked to do this when they image planets.

But the reason these designs perform so well is that they are
relatively "pure" optical systems. They don't cram 6 or more elements
into one tube like camera lenses do. Some zooms have 17 elements,
up to 30 individual surfaces, that's why they are so bad when it comes
to being compared to primes or any other decent lenses.
A cemented 80mm achromat simply does not lose light or
contrast because it only has 2 multicoated lens surfaces. It's as
pure an optical system as they get.

BTW; There is a rudamentary stop down mechanism available for these
lenses that allows
them to be stopped down to about f10.
Close focus is probably limited to around 5ft. How much closer do you
want with a 400mm
telephoto??? A rack and pinion focuser on a long lens affords much
greater focus range
than internal focusing in a camera lens.

Yes, this must be why the fellow you quoted at dpreview's forums needed
an extender tube to hit 20 feet. Don't you even read the articles you
reference?

Then Orion has changed the focus tube draw length. Sky Instruments
(who are the importer of these) had them and the minium focus distance
was considerably shorter.

But it's a cheap solution so anyone who is remotely curious can try it
for themselves.

... and discover why everyone else wants a has a telephoto lens that
fits the camera. Why waste a good $200+ for nothing?

Robots need not apply.
-Rich

Rich dfs wrote:
But the reason these designs perform so well is that they are
relatively "pure" optical systems. They don't cram 6 or more elements
into one tube like camera lenses do. Some zooms have 17 elements,
up to 30 individual surfaces, that's why they are so bad when it comes
to being compared to primes or any other decent lenses.
A cemented 80mm achromat simply does not lose light or
contrast because it only has 2 multicoated lens surfaces. It's as
pure an optical system as they get.

By that logic a single convex lens must have the best quality possible.

--
Ray Fischer

On 18 Jan 2006 02:24:10 GMT, (Ray Fischer) wrote:

Rich dfs wrote:
But the reason these designs perform so well is that they are
relatively "pure" optical systems. They don't cram 6 or more elements
into one tube like camera lenses do. Some zooms have 17 elements,
up to 30 individual surfaces, that's why they are so bad when it comes
to being compared to primes or any other decent lenses.
A cemented 80mm achromat simply does not lose light or
contrast because it only has 2 multicoated lens surfaces. It's as
pure an optical system as they get.

By that logic a single convex lens must have the best quality possible.

In fact, for monochromatic light, it can be. Which is why some solar
telescopes have used it. But not for polychromatic light, obviously.
But if you are a DSLR user, an inexpensive telescope with a few
eyepieces and a projection adapter can be a very flexible way to
obtain different long focal lengths to experiment with.
-Rich

Rich wrote:

But the reason these designs perform so well is that they are
relatively "pure" optical systems. They don't cram 6 or more elements
into one tube like camera lenses do. Some zooms have 17 elements,
up to 30 individual surfaces, that's why they are so bad when it comes
to being compared to primes or any other decent lenses.

Canon's 70-200 f/2.8 IS L compares badly to primes and 'any other decent
lenses'? Your religion there *is* my belly laugh.

Oh, did I mention that it has 23 lenses in 18 elements?

-Wolfgang

On Thu, 19 Jan 2006 12:54:38 +0100, Wolfgang Weisselberg
wrote:

Rich wrote:

But the reason these designs perform so well is that they are
relatively "pure" optical systems. They don't cram 6 or more elements
into one tube like camera lenses do. Some zooms have 17 elements,
up to 30 individual surfaces, that's why they are so bad when it comes
to being compared to primes or any other decent lenses.

Canon's 70-200 f/2.8 IS L compares badly to primes and 'any other decent
lenses'? Your religion there *is* my belly laugh.

Oh, did I mention that it has 23 lenses in 18 elements?

-Wolfgang

It's not really a telephoto, is it? 200mm has such a low manification
(about 4x) that the extra elements don't matter as much as they would
if it was a 400mm or longer telephoto. The higher the native
magnification of the lens, the better it has to be. 18 elements = 36
surfaces. Reflection scatter and loss at each surface means you lose
50% of the light from the image. The rest is lost or suffused over
the surface of the image, resulting in lower contrast, resolution and
colour saturation. You cannot avoid this.
-Rich