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12-04-2018, 09:48 AM   #1
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Questions about T mounts / T adapters

I have a Celestron Omni XLT 120 Refractor telescope and would like to use my K200D with it. The problem is i'm finding mounts that look like there threaded to the camera and the K200D lens are bayonet mount . I was looking at the Celestron universal 1.25" T-adapter #93625 and a vello T-mount lens adapter, assuming that the one fits onto the other. Could use some help with this.


12-04-2018, 10:07 AM - 1 Like   #2
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Not having a telescope for astrophotography but having looked into it some I found that it seems like it is a world of adapters on top of adapters. Basically see if you can get to M42 (42mm x 1mm thread pitch) and then go from there to modern camera mount. Some times you will find that it is easier to get to T-mount (42mm x 0.75mm thread pitch) which is another one that is easy to get to a modern camera mount with yet another adapter.

If you don't get a better response I suggest asking over in the astrophotography group as a number of them are shooting through telescopes.
12-04-2018, 10:14 AM   #3
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QuoteOriginally posted by MossyRocks Quote
Not having a telescope for astrophotography but having looked into it some I found that it seems like it is a world of adapters on top of adapters. Basically see if you can get to M42 (42mm x 1mm thread pitch) and then go from there to modern camera mount. Some times you will find that it is easier to get to T-mount (42mm x 0.75mm thread pitch) which is another one that is easy to get to a modern camera mount with yet another adapter.

If you don't get a better response I suggest asking over in the astrophotography group as a number of them are shooting through telescopes.
Thanks for the help I'll check the astrophotography group
12-04-2018, 10:44 AM - 1 Like   #4
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The t mount telescope adapter allows a t mount adapter to connect to your telescope. T mount adapters for many different mounts exist.

Both of these together mount the camera to the scope:

T-Mount Telescope Eyepiece Adapter | Edmund Optics

FotodioX Lens Mount Adapter for T-Mount T/T-2 Screw Mount T2-PK

12-04-2018, 10:57 AM - 1 Like   #5
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Using a tube of appropriate diameter for a telescope, that also had a male T-thread at the opposite end became the standard way to mount a camera on a telescope a very, very long time ago, probably when the T-mount system was first introduced. Suppliers devoted to telescopes for astronomy are one of the more reliable sources for camera T-mounts, but photo suppliers such as B&H also offer T-mounts as they also sell astronomical telescopes.
12-04-2018, 11:10 AM   #6
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Basically there are the two parts as you indicated. The camera adapter in your case would be a K adapter which has the K mount on one side and a female T thread on the other. The second part is the telescope adapter which has a male T thread on one side and the tube which goes in your eyepiece holder (1.25 or 2 inch slide fit) on the opposite side. The ones you mentioned should work.

Having the first part lets you use any accessory which has the male T thread. That includes other adapters and some lenses. The downside to a T adapter is there are no mechanical or electrical connections to the camera so everything is manual (aperture settings, etc.) if you use the adapter with a lens. Of course with your telescope, the aperture is fixed so there is no need for coupling to the camera. You have aperture priority operation and select exposure using the shutter speed.

Last edited by Bob 256; 12-04-2018 at 11:16 AM.
12-04-2018, 01:57 PM - 1 Like   #7
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Yeah, the thing that gets people confused is they think there's some universal T-mount adapter for their telescope.

Actually, in most cases, you need two things to get your camera onto your telescope. The first is an adapter tube supplied by the telescope manufacturer (usually called a "camera adapter"). That usually threads on in place of the eyepiece mount (on some spotting scope types, it actually mounts over the eyepiece). Sometimes the adapter tube comes in the box with the telescope. Sometimes it's an extra-cost accessory. Either way, that's what you need, and it will be made specific for your brand and model of telescope (they vary in thread size, length, etc).


That adapter should have 42x0.75mm threads on the back of it - that's where you thread on your T-mount (which you usually purchase through photography retail suppliers). In your case you need a T-mount - K mount adapter.

Nearly all T-mounts are made in two parts: the inner part is threaded 42x0.75mm for your gadget. The outer part is your camera mount (K, in this case). Little screws attach the two rings together. Loosening them allows you to get your camera properly upright on your gadget (telescope in this case).
12-04-2018, 03:28 PM - 1 Like   #8
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Note T mount looks similar to m42 but has different thread pitch.

12-05-2018, 04:59 AM - 1 Like   #9
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I bought a celestron C90 spotting scope in the 1980's and when I got it it came with a Tmount adaptor. The shop I bought it at, sold different camera mount attachments, so I got Pentax and Nikon just in case.

I don't know if the Adaptors were made by celestron or third party, but t mount was still quite popular when I bought the scope.

The only issue that needs to be addressed, which became apparent with the release of the K10 is that the anodized coating in the Tmount needs to be removed to short all the contacts. Some functions don't work otherwise. It does not matter for the aperture because there is not one on a mirror lense, but I think the camera still wants to see something connected
12-05-2018, 07:09 AM   #10
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Thanks for all the good information. I have come across the following that looks like a good idea just more money than I'm thinking of paying. At 80.00 US I don't know.
Pentax K SLR / DSLR 2" UltraWide True-2 Prime Focus Adapter

Model: T2PXKU
Condition: New product
Fits Pentax K SLR/DSLR. Our True-2™ UltraWide Adapter is a true 2" prime focus adapter that takes you directly from the bayonet mount to a 2" barrel with as few wasted photons as possible, adding as much as 10mm additional clear aperture over legacy adapters!

12-05-2018, 11:01 AM - 1 Like   #11
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In astro-photo, the standard way to connect camera equipment is the T thread (M42x0.75, male thread on the lens side, 55mm flange distance to focus plane; as mentioned, do not confuse with M42 mount, which has a thread pitch of 1mm and a shorter flange distance).


So, the normal way to go is an adapter from 2" (I think the Omni XLT has a 2" focuser) or from 1.25" to T thread, and a second from T thread to Pentax K. Each should be around $20. This is by far the most flexible solution, and I see almost no reason to buy a direct adapter (skipping the T thread). The only exceptions I see are if you have very limited backfocus - which is not the case with refractors, or to avoid vigneting - which is not the case with APS-C format of the K200D, plus you need some field corrector as well for large sensors. With refractors you usually have the opposite problem - too much backfocus, because they are designed to work with a diagonal mirror between the telescope and the eyepiece.

BTW, some telescopes already offer a male T thread somewhere (on the outside of the 1.25" barrel or on the 2" to 1.25" adapter).
12-05-2018, 12:01 PM   #12
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QuoteOriginally posted by rlupsa Quote
In astro-photo, the standard way to connect camera equipment is the T thread (M42x0.75, male thread on the lens side, 55mm flange distance to focus plane; as mentioned, do not confuse with M42 mount, which has a thread pitch of 1mm and a shorter flange distance).


So, the normal way to go is an adapter from 2" (I think the Omni XLT has a 2" focuser) or from 1.25" to T thread, and a second from T thread to Pentax K. Each should be around $20. This is by far the most flexible solution, and I see almost no reason to buy a direct adapter (skipping the T thread). The only exceptions I see are if you have very limited backfocus - which is not the case with refractors, or to avoid vigneting - which is not the case with APS-C format of the K200D, plus you need some field corrector as well for large sensors. With refractors you usually have the opposite problem - too much backfocus, because they are designed to work with a diagonal mirror between the telescope and the eyepiece.

BTW, some telescopes already offer a male T thread somewhere (on the outside of the 1.25" barrel or on the 2" to 1.25" adapter).
When would you want to use the eyepiece attachment option rather than directly connecting to the focuser?
12-05-2018, 01:04 PM   #13
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QuoteOriginally posted by UncleVanya Quote
When would you want to use the eyepiece attachment option rather than directly connecting to the focuser?
I suppose the question is about eyepiece projection. Short answer: to change the effective focal length of the telescope.


The eyepiece takes the image created by the telescope objective (the 1000mm f/8.33 in the case of Omni 120 XLT) and projects it on the camera sensor. That projection can enlarge or reduce the image (depending on the FL of the eyepiece and the distances from the eyepiece to the telescope focal plane and to the camera sensor).

For bright objects (Moon, planets), 1000mm is ok, even a bit short for planets. For deep space objects (galaxies, nebulas) it is quite long, unless you have a very good motorized mount, you do a very good polar alignment, and, preferably, you have auto-guiding.

Using eyepiece projection is quite hard to do the mechanical arrangement. Quite few eyepieces have a thread on the side away from the telescope, and you can find an adapter to T thread. And then T thread extension tubes for tuning the distance to the camera, in order to tune the magnification (to the telescope side, the focuser has typically a large travel). Also, you may get vignetting. There is a bit of calculations to be done to figure out the setup.
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