T-mount questions

I have some questions about using a T-mount to put a micro-four-thirds
camera on a telescope.

1) Is the way it is supposed to work that the telescope has one half
of the T-mount that is custom to the telescope, and the camera has
the other half that is custom to the camera, and any telescope and
any camera can meet in the middle?

2) Does the galileoscope kit come with a T-mount? I can find no
mention of a T-mount in their FAQ, but they do have pictures
than people have taken through the scope.

3) On Amazon, I find three very different looking T-mount adapters
that claim to work with micro-four-thirds:

http://www.amazon.com/Fotodiox-Adapt...pr_product_top

http://www.amazon.com/Opteka-T-Mount.../dp/B0036YWB40

http://www.amazon.com/Bower-T-m4-T2-...m_cr_pr_sims_t

These are very definately not the same length. People seem to like the
first and hate the second, BUT--I am thinking of buying one of Opteka's
ridiculously long focal length telefoto lenses, and I suspect that I
may need their T-mount instead of someone else's. Are all T-mounts
supposed to be interchangable or not?

--
Please reply to: | No nation is drunken where wine is cheap.
pciszek at panix dot com | --Thomas Jefferson

On 06/07/2012 04:35, Paul Ciszek wrote:
I have some questions about using a T-mount to put a micro-four-thirds
camera on a telescope.

1) Is the way it is supposed to work that the telescope has one half
of the T-mount that is custom to the telescope, and the camera has
the other half that is custom to the camera, and any telescope and
any camera can meet in the middle?

Pretty much. It is harder for T2-mount camera lenses since they have
much less back focus. A telescope can usually be adjusted to work with
any suitable camera adapter.

2) Does the galileoscope kit come with a T-mount? I can find no
mention of a T-mount in their FAQ, but they do have pictures
than people have taken through the scope.

3) On Amazon, I find three very different looking T-mount adapters
that claim to work with micro-four-thirds:

http://www.amazon.com/Fotodiox-Adapt...pr_product_top

http://www.amazon.com/Opteka-T-Mount.../dp/B0036YWB40

http://www.amazon.com/Bower-T-m4-T2-...m_cr_pr_sims_t

These are very definately not the same length. People seem to like the
first and hate the second, BUT--I am thinking of buying one of Opteka's
ridiculously long focal length telefoto lenses, and I suspect that I
may need their T-mount instead of someone else's. Are all T-mounts
supposed to be interchangable or not?

They are supposed to be. If they were not you could not buy a T2-mount
lens and then use it on different makes of camera. The ones made for use
with telescopes might not be usable with ordinary T-mount camera lenses
though if the drift length is too long they will not allow the lens to
reach focus at infinity (where the stars are).

--
Regards,
Martin Brown

On Jul 5, 11:35*pm, (Paul Ciszek) wrote:
I have some questions about using a T-mount to put a micro-four-thirds
camera on a telescope.

1) Is the way it is supposed to work that the telescope has one half
* *of the T-mount that is custom to the telescope, and the camera has
* *the other half that is custom to the camera, and any telescope and
* *any camera can meet in the middle?

2) Does the galileoscope kit come with a T-mount? *I can find no
* *mention of a T-mount in their FAQ, but they do have pictures
* *than people have taken through the scope.

3) On Amazon, I find three very different looking T-mount adapters
* *that claim to work with micro-four-thirds:

http://www.amazon.com/Fotodiox-Adapt...c-AG-AF100/dp/...

http://www.amazon.com/Opteka-T-Mount...Olympus/dp/B00...

http://www.amazon.com/Bower-T-m4-T2-...dp/B0010C3VAI/...

These are very definately not the same length. *People seem to like the
first and hate the second, BUT--I am thinking of buying one of Opteka's
ridiculously long focal length telefoto lenses, and I suspect that I
may need their T-mount instead of someone else's. *Are all T-mounts
supposed to be interchangable or not?


Just avoid the Opteka refractive lenses, unless you like working with
long, LONG focal ratios. Stick to the mirror lenses, then you have at
least a hope of getting something decent from it. Honestly, though,
go to Orion Telescopes and look at their Maksutov mirror-lens tube
assemblies and avoid the Opteka stuff.

On 07/07/2012 02:31, RichA wrote:
On Jul 5, 11:35 pm, (Paul Ciszek) wrote:
I have some questions about using a T-mount to put a micro-four-thirds
camera on a telescope.

1) Is the way it is supposed to work that the telescope has one half
of the T-mount that is custom to the telescope, and the camera has
the other half that is custom to the camera, and any telescope and
any camera can meet in the middle?

2) Does the galileoscope kit come with a T-mount? I can find no
mention of a T-mount in their FAQ, but they do have pictures
than people have taken through the scope.

3) On Amazon, I find three very different looking T-mount adapters
that claim to work with micro-four-thirds:

http://www.amazon.com/Fotodiox-Adapt...c-AG-AF100/dp/...

http://www.amazon.com/Opteka-T-Mount...Olympus/dp/B00...

http://www.amazon.com/Bower-T-m4-T2-...dp/B0010C3VAI/...

These are very definately not the same length. People seem to like the
first and hate the second, BUT--I am thinking of buying one of Opteka's
ridiculously long focal length telefoto lenses, and I suspect that I
may need their T-mount instead of someone else's. Are all T-mounts
supposed to be interchangable or not?


Just avoid the Opteka refractive lenses, unless you like working with
long, LONG focal ratios. Stick to the mirror lenses, then you have at
least a hope of getting something decent from it. Honestly, though,
go to Orion Telescopes and look at their Maksutov mirror-lens tube
assemblies and avoid the Opteka stuff.

Never heard of Opteka before but they seem to be some kind of cheap jack
lens maker. Mirror lenses tend to be around f10 and have donut bokeh so
I doubt that their refractive lenses are much slower. I would expect
cheap lenses to have rather poor chromatic aberration which would be an
annoyance for astronomy. The Russian made MTO 1000mm f10 is not a bad
example of a Mak lens (or at least some are good).

The OP would be well advised to scour the second hand pages for non
autofocus high quality long focal length lenses for this purpose. He can
after all use with anything with a T2 mount on it. Manual focus 300mm f4
and 500mm f4 lenses are out there to be had at a discount.

--
Regards,
Martin Brown

In article ,
RichA wrote:

Just avoid the Opteka refractive lenses, unless you like working with
long, LONG focal ratios. Stick to the mirror lenses, then you have at
least a hope of getting something decent from it. Honestly, though,
go to Orion Telescopes and look at their Maksutov mirror-lens tube
assemblies and avoid the Opteka stuff.

OK, this telescope claims better image quality that the others on
the page:
http://www.telescope.com/Orion-Apex-...yword=maksutov

And it comes with its own "eyepiece adapter with T-threads" so I don't
have to worry about finding the right one on *that* end. However, I am
still faced with the problem that T-mount adapters for the micro-four-
thirds camera come in a variety of lengths, ranging from a shallow ring
to a tube longer than it is wide. How do I determine which is the right
one for this telescope? The descriptions of the various adapters are
no help, because the different shapes are made by different manufacturers,
and none of them say "This won't work for..." But the difference has
to be important, as the different adapters are going to be placing the
focal plane of the camera at different distances from the optics.

--
Please reply to: | "We establish no religion in this country, we
pciszek at panix dot com | command no worship, we mandate no belief, nor
Autoreply is disabled | will we ever. Church and state are, and must
| remain, separate." --Ronald Reagan, 10/26/1984

On 2012-07-06, Paul Ciszek wrote:

2) Does the galileoscope kit come with a T-mount? I can find no
mention of a T-mount in their FAQ, but they do have pictures
than people have taken through the scope.


This Galileoscope kit
http://www.astronomy2009.org/globalprojects/cornerstones/galileoscope/
doesn't come with a camera adapter. A "universal" 1-1/4" to t-thread
adapter will fit.

Bud

(Paul Ciszek) wrote in
:

I have some questions about using a T-mount to put a micro-four-thirds
camera on a telescope.

1) Is the way it is supposed to work that the telescope has one half
of the T-mount that is custom to the telescope, and the camera has
the other half that is custom to the camera, and any telescope and
any camera can meet in the middle?

2) Does the galileoscope kit come with a T-mount? I can find no
mention of a T-mount in their FAQ, but they do have pictures
than people have taken through the scope.

3) On Amazon, I find three very different looking T-mount adapters
that claim to work with micro-four-thirds:

http://www.amazon.com/Fotodiox-Adapt...AG-AF100/dp/B0
03EAVUO8/ref=cm_cr_pr_product_top

http://www.amazon.com/Opteka-T-Mount...ympus/dp/B0036
YWB40

http://www.amazon.com/Bower-T-m4-T2-.../B0010C3VAI/re
f=cm_cr_pr_sims_t

These are very definately not the same length. People seem to like
the first and hate the second, BUT--I am thinking of buying one of
Opteka's ridiculously long focal length telefoto lenses, and I suspect
that I may need their T-mount instead of someone else's. Are all
T-mounts supposed to be interchangable or not?


http://www.flickr.com/photos/eliasjordan/3764624097/

On 07/07/2012 16:43, Paul Ciszek wrote:
In article ,
RichA wrote:

Just avoid the Opteka refractive lenses, unless you like working with
long, LONG focal ratios. Stick to the mirror lenses, then you have at
least a hope of getting something decent from it. Honestly, though,
go to Orion Telescopes and look at their Maksutov mirror-lens tube
assemblies and avoid the Opteka stuff.

OK, this telescope claims better image quality that the others on
the page:
http://www.telescope.com/Orion-Apex-...yword=maksutov

And it comes with its own "eyepiece adapter with T-threads" so I don't
have to worry about finding the right one on *that* end. However, I am
still faced with the problem that T-mount adapters for the micro-four-
thirds camera come in a variety of lengths, ranging from a shallow ring
to a tube longer than it is wide. How do I determine which is the right
one for this telescope? The descriptions of the various adapters are
no help, because the different shapes are made by different manufacturers,
and none of them say "This won't work for..." But the difference has
to be important, as the different adapters are going to be placing the
focal plane of the camera at different distances from the optics.

Generally telescopes have sufficient back focus that you don't actually
have to worry about it. Pick one that is mid length and cross your
fingers. When matched with photographic lenses you absolutely have to
use the right T adaptor both for the fixing (every manufacturer has
their own quirky design of latch or older screw thread) and for the
drift length to the focal plane. Mostly for telescopes they will all
work but with lenses you need to choose matched parts.

To give you an idea with my SCT by combining a 2x converter or a 0.63x
converted with various lengths of extension tube I can obtain
magnifications that range from x3.4 to x0.55 and still focus at infinity.

If you are worried about focusing at infinity choose the shortest of the
T adapters but I suspect the right one for a micro 4/3rds with a
nominally standard 35mm T-mount lens will be one such that the distance
to the focal plane is made equal to what it is on a 35mm camera.

That is a 4/3rds T adapter tube will be longer than the one for a full
size 35mm camera (which mostly tend to look like fat rings).

--
Regards,
Martin Brown

On Jul 7, 11:43*am, (Paul Ciszek) wrote:
In article ,

RichA wrote:

Just avoid the Opteka refractive lenses, unless you like working with
long, LONG focal ratios. *Stick to the mirror lenses, then you have at
least a hope of getting something decent from it. *Honestly, though,
go to Orion Telescopes and look at their Maksutov mirror-lens tube
assemblies and avoid the Opteka stuff.

OK, this telescope claims better image quality that the others on
the page:http://www.telescope.com/Orion-Apex-...egrain-Telesco...

And it comes with its own "eyepiece adapter with T-threads" so I don't
have to worry about finding the right one on *that* end. *However, I am
still faced with the problem that T-mount adapters for the micro-four-
thirds camera come in a variety of lengths, ranging from a shallow ring
to a tube longer than it is wide. *How do I determine which is the right
one for this telescope?

The _T-ring_ that attaches to a camera's lens mount provides threads
that work with a generic _T-adapter_ that is usually either 1.25 or
2 inch OD to match a telescope's focuser. For SCTs and Maks there
are usually adapters specific to make and model at the "telescope" end
but that still have a T-thread that fits any T-ring at the camera
end.

The descriptions of the various adapters are
no help, because the different shapes are made by different manufacturers,
and none of them say "This won't work for..."

If the blurb says "works for," it might be safe to assume that the
adapter "won't work for" anything else. Or maybe it will.

But the difference has
to be important, as the different adapters are going to be placing the
focal plane of the camera at different distances from the optics.

Making up for the "different distances" is done by focusing the camera
just as you would for any lens.

On 2012-07-10, wrote:
On Jul 7, 11:43*am, (Paul Ciszek) wrote:

But the difference has
to be important, as the different adapters are going to be placing the
focal plane of the camera at different distances from the optics.

Making up for the "different distances" is done by focusing the camera
just as you would for any lens.


The photographic t-mount to camera adapter puts the front face of the
adapter 55 mm from the focal plane of the camera. A simple 1-1/4"
to t-mount adapter for the telescope adds a few millimeters to that.
Most small refractors have enough back focus to work with that. Most
newtonian reflectors do not. Schmidt-cassegrainian telescopes have more
than enough back focus, and the manufacturers supply camera adapters that
are designed to work with their telescopes. "Back focus" is the distance
from the end of the telescope to the focal plane of the telescope. To get
your camera in focus the focal plane of the telescope has to coincide
with the focal plane of the camera. If the camera focuses too far out
you can easily add an extension. If the camera focuses too close in and
you run out of back focus you have to modify the telescope by shortening
the tube on a refractor or moving the primary mirror on a newtonian.

Bud