Something aside from high priced camera telephotos

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728

Companies that make/sell them a
Orion telescopes
William Optics
Celestron
Meade
Takahashi (not cheap)
Astro-Physics (American, not cheap)
TeleVue (American, not cheap)
TMB (American, not cheap)
Stellarvue
Synta
Sky Instruments
Astro Tech

On Sun, 05 Aug 2007 19:02:07 -0700, RichA wrote:

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728


Has anyone actually compared the optical performance?

You can get an Orion 80mm APO scope (which is a 600mm f/7.5 lens) for
about $600. It is a doublet with one ED element, so it is probably a
very good achromat not an actual apochromat. It is not very fast, it
has no auto-focus, and you can only use it wide open. The achromat is
probably tuned for visual use.

Or you can spend at least 10x that amount and get for example a Nikon
600mm f/4, with a wider aperture, an aperture that you can change, and
auto-focus. It is probably at least as heavy and awkward as the
telescope.

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

Bob S

Bob S wrote:

http://forums.dpreview.com/forums/re...ssage=24145728


The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

The sample full size crops on that link look awfully darn good. On an
Oly DSLR, that 840mm is a 1680mm field of view, he must be using one
hell of a sturdy tripod! I wonder if that covers the frame on an APS
sensor DSLR?

--
Paul Furman Photography
http://edgehill.net
Bay Natives Nursery
http://www.baynatives.com

On Aug 12, 11:44 am, Paul Furman wrote:
Bob S wrote:
http://forums.dpreview.com/forums/re...ssage=24145728

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

The sample full size crops on that link look awfully darn good. On an
Oly DSLR, that 840mm is a 1680mm field of view, he must be using one
hell of a sturdy tripod! I wonder if that covers the frame on an APS
sensor DSLR?


Yes, they are still making most apos to cover 35mm film. Some require
an addtional field flattening lens for such wide coverage, but then
they still produce better edge definition than most camera lenses that
suffer from other aberrations.
True apochromatism is always an argument in itself, but the 2 and 3
element ED and fluorite lenses in these things will control any colour
error under most situations. If it says apo, it will suffice for
photography. If it says, achromatic, you might see some colour, but
it depends on focal ratio and front lens size, shorter focal ratios
and larger front lenses producing more colour error.

Bob S wrote:
On Sun, 05 Aug 2007 19:02:07 -0700, RichA wrote:

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728


Has anyone actually compared the optical performance?

You can get an Orion 80mm APO scope (which is a 600mm f/7.5 lens) for
about $600. It is a doublet with one ED element, so it is probably a
very good achromat not an actual apochromat. It is not very fast, it
has no auto-focus, and you can only use it wide open. The achromat is
probably tuned for visual use.

Or you can spend at least 10x that amount and get for example a Nikon
600mm f/4, with a wider aperture, an aperture that you can change, and
auto-focus. It is probably at least as heavy and awkward as the
telescope.

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

Bob S

In general, the performance is quite good. In the digital_astro
yahoo group (not usenet), this has been an ongoing topic.
But a couple of notes: the telescopes are optimized for
infinity focus, and degrade closer. Camera lenses are optimized
to work over a larger distance range. So if, for example,
you want to photograph birds close up, performance may
not be as good as a camera lens.

Note too, your comparison was biased: the aperture of the
80mm lens is 80 mm. Your 10x higher price 600 f/4 lens
has a 150 mm aperture. Perhaps compare to a 400 mm f/5.6
lens and a 1.4x TC (560mm f/7.8), which can be had for
under $1000.

Some of the conclusions regarding lenses versus telescopes
is that (for astronomy, with stars being one of the toughest
optical tests one can do) no lens is perfect. The telescope
versus camera lens trades one small problem for another, and
the better optical designs cost more in both telescopes
and camera lenses. But both can be very good.

Roger

Roger N. Clark (change username to rnclark) wrote:
Bob S wrote:
On Sun, 05 Aug 2007 19:02:07 -0700, RichA wrote:

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728


Has anyone actually compared the optical performance?

You can get an Orion 80mm APO scope (which is a 600mm f/7.5 lens) for
about $600. It is a doublet with one ED element, so it is probably a
very good achromat not an actual apochromat. It is not very fast, it
has no auto-focus, and you can only use it wide open. The achromat is
probably tuned for visual use.

Or you can spend at least 10x that amount and get for example a Nikon
600mm f/4, with a wider aperture, an aperture that you can change, and
auto-focus. It is probably at least as heavy and awkward as the
telescope.

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

Bob S

In general, the performance is quite good. In the digital_astro
yahoo group (not usenet), this has been an ongoing topic.
But a couple of notes: the telescopes are optimized for
infinity focus, and degrade closer. Camera lenses are optimized
to work over a larger distance range. So if, for example,
you want to photograph birds close up, performance may
not be as good as a camera lens.

Note too, your comparison was biased: the aperture of the
80mm lens is 80 mm. Your 10x higher price 600 f/4 lens
has a 150 mm aperture. Perhaps compare to a 400 mm f/5.6
lens and a 1.4x TC (560mm f/7.8), which can be had for
under $1000.

Some of the conclusions regarding lenses versus telescopes
is that (for astronomy, with stars being one of the toughest
optical tests one can do) no lens is perfect. The telescope
versus camera lens trades one small problem for another, and
the better optical designs cost more in both telescopes
and camera lenses. But both can be very good.

Roger

Here are some images with an ED80, including complete (uncropped)
images). Note the coma in the corners.
http://www.pascarellas.com/galaxies.aspx

Roger

On Aug 12, 2:04 pm, "Roger N. Clark (change username to rnclark)"
wrote:
Bob S wrote:
On Sun, 05 Aug 2007 19:02:07 -0700, RichA wrote:

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728

Has anyone actually compared the optical performance?

You can get an Orion 80mm APO scope (which is a 600mm f/7.5 lens) for
about $600. It is a doublet with one ED element, so it is probably a
very good achromat not an actual apochromat. It is not very fast, it
has no auto-focus, and you can only use it wide open. The achromat is
probably tuned for visual use.

Or you can spend at least 10x that amount and get for example a Nikon
600mm f/4, with a wider aperture, an aperture that you can change, and
auto-focus. It is probably at least as heavy and awkward as the
telescope.

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

Bob S

In general, the performance is quite good. In the digital_astro
yahoo group (not usenet), this has been an ongoing topic.
But a couple of notes: the telescopes are optimized for
infinity focus, and degrade closer. Camera lenses are optimized
to work over a larger distance range. So if, for example,
you want to photograph birds close up, performance may
not be as good as a camera lens.

May not be. But SA present due to using the lens at less than
infinity is no worse (and likely less so) than using most camera
lenses wide open with all the aberrations they possess.

Note too, your comparison was biased: the aperture of the
80mm lens is 80 mm. Your 10x higher price 600 f/4 lens
has a 150 mm aperture. Perhaps compare to a 400 mm f/5.6
lens and a 1.4x TC (560mm f/7.8), which can be had for
under $1000.

True. But no lens/TC combo will match an apo telescope in
definition. Having 10-14 elements in the light path is just no
prescription for providing sharp, high contrast images, no matter how
good the coatings are. It's akin to taking 2 or 3 element
apochromatic telescope and screwing 10 UV filters on the end of it.
If it's avoidable, people will hopefully avoid it.
Anyway, telescopes that cost a fair bit but can be used as relatively
fast telephotos a
TeleVue NP101 a 500mm f5 flat field design.
Takahashi's 106FSQ, 500mm f5 flat field design.
Pentax's 100mm f4 photo-visual scope with helical focusing, like a
fair sized camera lens.
All are corrected for field curvature and will likely give any lens a
run for it's money if the best resolution and contrast are the goal.
But then an AF 400mm Canon will likely produce more usable shots, far
more easily.


Some of the conclusions regarding lenses versus telescopes
is that (for astronomy, with stars being one of the toughest
optical tests one can do) no lens is perfect. The telescope
versus camera lens trades one small problem for another, and
the better optical designs cost more in both telescopes
and camera lenses. But both can be very good.

Roger

Yes, a top flight 400mm f4 apo with a 100mm aperture is about $3000,
as much or more than Japanese camera lenses of that focal length and
speed. It would be interesting to compare them.

On Aug 12, 9:28 pm, "Roger N. Clark (change username to rnclark)"
wrote:
Roger N. Clark (change username to rnclark) wrote:



Bob S wrote:
On Sun, 05 Aug 2007 19:02:07 -0700, RichA wrote:

Check out this thread. These apo telescopes which have diffraction-
limited optics are an interesting alternative to traditional camera
telephotos. Though they don't have the speed (most are between f5 and
f8) they can be used wide open, since they do not have the optical
aberrations camera lenses do and therefore don't need to be stopped
down. With their relatively large front apertures (range from about
60mm to over 150mm) they provide a reasonable f-ratio and long focal
lengths. They aren't for sports or action, but for certain things
like some wildlife, etc, they can work very well and their image
quality is impeccable.

http://forums.dpreview.com/forums/re...ssage=24145728

Has anyone actually compared the optical performance?

You can get an Orion 80mm APO scope (which is a 600mm f/7.5 lens) for
about $600. It is a doublet with one ED element, so it is probably a
very good achromat not an actual apochromat. It is not very fast, it
has no auto-focus, and you can only use it wide open. The achromat is
probably tuned for visual use.

Or you can spend at least 10x that amount and get for example a Nikon
600mm f/4, with a wider aperture, an aperture that you can change, and
auto-focus. It is probably at least as heavy and awkward as the
telescope.

The telescope might be tempting for someone with a limited budget who
did not need to shoot fast action.

But what about the performance?

Bob S

In general, the performance is quite good. In the digital_astro
yahoo group (not usenet), this has been an ongoing topic.
But a couple of notes: the telescopes are optimized for
infinity focus, and degrade closer. Camera lenses are optimized
to work over a larger distance range. So if, for example,
you want to photograph birds close up, performance may
not be as good as a camera lens.

Note too, your comparison was biased: the aperture of the
80mm lens is 80 mm. Your 10x higher price 600 f/4 lens
has a 150 mm aperture. Perhaps compare to a 400 mm f/5.6
lens and a 1.4x TC (560mm f/7.8), which can be had for
under $1000.

Some of the conclusions regarding lenses versus telescopes
is that (for astronomy, with stars being one of the toughest
optical tests one can do) no lens is perfect. The telescope
versus camera lens trades one small problem for another, and
the better optical designs cost more in both telescopes
and camera lenses. But both can be very good.

Roger

Here are some images with an ED80, including complete (uncropped)
images). Note the coma in the corners.http://www.pascarellas.com/galaxies.aspx

Roger

Yes, but they support (at least) a 35mm field and can be corrected
with a field flattener/coma corrector. The highest end photo-visual
apos will support medium format 6x7cm image planes with a flat,
undistorted field. The Orion ED80mm scope only costs about $500. Go
to one that costs what a top flight camera lens costs and you
eliminate the field curvature and you get higher contrast images which
will also likely be sharper. Even at less than infinity, the
aberrations the apo may have will be lower and less image degrading
than a wide open camera lens. But then these things will not
replace an I.S. AF faster f-ratio telephoto.

RichA wrote:
On Aug 12, 2:04 pm, "Roger N. Clark (change username to rnclark)"
wrote:
In general, the performance is quite good. In the digital_astro
yahoo group (not usenet), this has been an ongoing topic.
But a couple of notes: the telescopes are optimized for
infinity focus, and degrade closer. Camera lenses are optimized
to work over a larger distance range. So if, for example,
you want to photograph birds close up, performance may
not be as good as a camera lens.

May not be. But SA present due to using the lens at less than
infinity is no worse (and likely less so) than using most camera
lenses wide open with all the aberrations they possess.

Do you have any real evidence for this statement?
I disagree. In a typical optical design, multiple elements
are needed to control aberrations to cover the focus
range.

Note too, your comparison was biased: the aperture of the
80mm lens is 80 mm. Your 10x higher price 600 f/4 lens
has a 150 mm aperture. Perhaps compare to a 400 mm f/5.6
lens and a 1.4x TC (560mm f/7.8), which can be had for
under $1000.

True. But no lens/TC combo will match an apo telescope in
definition. Having 10-14 elements in the light path is just no
prescription for providing sharp, high contrast images, no matter how
good the coatings are. It's akin to taking 2 or 3 element
apochromatic telescope and screwing 10 UV filters on the end of it.
If it's avoidable, people will hopefully avoid it.

Again where is the evidence? Here is an example to the contrary:
http://www.clarkvision.com/astro/vei...0.JZ3F4242.jpg
(2.7 megabytes)
The image is with a Canon 500 mm f/4 L IS and Kenko pro 300 1.4x TC.
The stars are very sharp over most of the field and limited
by the blur filter of the camera, not the lens. Note the fainter
stars look square (due to the pixel grid). If the lens blurred more,
the stars would be round.

An APO will show color fringing due to chromatic aberration. Remember,
and APO (3 element lens) corrects color only at 3 wavelengths
(at infinity focus).

Anyway, telescopes that cost a fair bit but can be used as relatively
fast telephotos a
TeleVue NP101 a 500mm f5 flat field design.
Takahashi's 106FSQ, 500mm f5 flat field design.
Pentax's 100mm f4 photo-visual scope with helical focusing, like a
fair sized camera lens.
All are corrected for field curvature and will likely give any lens a
run for it's money if the best resolution and contrast are the goal.

I agree at infinity focus.

But then an AF 400mm Canon will likely produce more usable shots, far
more easily.

Right.

Some of the conclusions regarding lenses versus telescopes
is that (for astronomy, with stars being one of the toughest
optical tests one can do) no lens is perfect. The telescope
versus camera lens trades one small problem for another, and
the better optical designs cost more in both telescopes
and camera lenses. But both can be very good.

Roger

Yes, a top flight 400mm f4 apo with a 100mm aperture is about $3000,
as much or more than Japanese camera lenses of that focal length and
speed. It would be interesting to compare them.

They will do quite well at infinity, but will generally degrade
faster than camera lenses when focusing closer.

Roger

RichA wrote:
Yes, but they support (at least) a 35mm field and can be corrected
with a field flattener/coma corrector. The highest end photo-visual
apos will support medium format 6x7cm image planes with a flat,
undistorted field.

At infinify focus.

The Orion ED80mm scope only costs about $500. Go
to one that costs what a top flight camera lens costs and you
eliminate the field curvature and you get higher contrast images which
will also likely be sharper.

Proof? See my other post this morning.

Even at less than infinity, the
aberrations the apo may have will be lower and less image degrading
than a wide open camera lens.

Proof? Again, an APO only corrects color at 3 wavelengths,
and only at infinity focus. Research what happens at
closer focus. There is a reason camera manufacturers
design multiple elements into camera lenses.

Roger