JimH123 Loc: Morgan Hill, CA

Here is an example using a small scope with a 2" focuser and a full frame camera, but using a 42mm T-Adapter. Notice that there is just a tiny bit of vignetting in the corners. With astro imaging, this can be improved with light frames.

The 2nd image is with the T-adapter and connection to the scope.

The 3rd image is with a 48mm T-Adapter and notice that the vignetting is gone.

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nikonshooter Loc: Spartanburg, South Carolina

Go to this site and enter your info - you will know exactly what your FOV will be

https://astronomy.tools/calculators/field_of_view/

JimH123 Loc: Morgan Hill, CA

Ed, this is a useful site. But the OP has another obstacle. He is wanting to capture a full frame image through a 1.25" socket. The utility leaves that out and assumes no light path restrictions, of which he has a severe one..

SonnyE Loc: Communist California, USA

I was impressed that my modest telescope and even the Infinity camera was listed.
Orion ED80T CF, Atik Infinity Camera. Seems to be pretty accurate based on my experience.
I wound up with this: (Yep, pretty mediocre.)

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mikedent Loc: Florida

Great advice, thank you!

JimH123 Loc: Morgan Hill, CA

You didn't mention what camera you were using other than it was Canon and a crop sensor. If you are using a Canon DSLR with EF-mount, then the flange distance is 44mm.

If this is the case, switching to a mirrorless camera would give you a much shorter flange distance and get the camera closer to the scope so that possibly, the barlow lens might not be needed which would give you a much wider FOV, even with a mirrorless crop sensor camera.

Which mirrorless camera to use is another question. I will use Sony as an example since that is what I already have. You could explore if there is an option like this for Canon mirrorless.

There are many Sony mirrorless cameras that could be used. They all use the same E-Mount. And the flange distance is only 18mm. This is already 26mm closer than a Canon DSLR camera.

Then you need an appropriate T-adapter. Assuming that you stay with a crop sensor body, you wouldn't need a 48mm wide T-Adapter and can get by with a 42mm wide T-Adapter. I assume you are using a 42mm to 1.25" nosepiece adapter so that it can be plugged directly into the telescope eyepiece socket.

T-Adapters for mirrorless cameras come in two different length. The normal E-Mount T-Adapter is long enough so that when you attach it to the camera, it ends at the same distance from the sensor as a much thinner T-adapter on a DSLR would end. THIS IS NOT THE ONE TO USE. This is used when you need a field flattener and it is required to have this field flattener be 55mm from the sensor.

What you would need is a thinner T-Adapter. This one is 42mm wide and 10mm thick:

https://www.telescopeadapters.com/t-minus-short-format-for-mirrorless-interchangeable-lens-mil/57-t-minus-ring-for-sony-e-mount-nexa7a9qxvg-series.html

Or if you prefer to switch to a 48mm wide T-Adapter, this would work:

https://www.telescopeadapters.com/wide-48mm-format-t-rings/55-wide-48mm-t-ring-for-sony-e-mount-nexa7a9qxvg-series.html

Of course this would require a 48mm to 1.25" nose piece adapter to plug into the scope.

Ot even better, a 48mm to 2" nose piece adapter such as: (provided you can use a 2" focuser on your scope)

https://www.amazon.com/Astromania-M48X0-75-Adapter-Telescope-Eyepiece/dp/B01G53EE98/ref=pd_lutyp_crty_cxhsh_2_2/146-8930085-4425930?_encoding=UTF8&pd_rd_i=B01G53EE98&pd_rd_r=ab904f8c-ecb7-40c5-84fd-80d9947805ed&pd_rd_w=mD8Vw&pd_rd_wg=ukr6J&pf_rd_p=7be52ccc-ac4f-4c23-8fa3-4436102d5169&pf_rd_r=DKAR6RWFHXQHHV16CM5D&psc=1&refRID=DKAR6RWFHXQHHV16CM5D


Summary:

Using a mirrorless camera with the thinner, 10mm, T-Adapter, you can get the sensor 26mm closer than using a DSLR.

Now it is fairly easy to find out if 26mm closer is enough to achieve infinity focus, provided you can find a friend who has a mirrorless camera. All you need to do is to set the scope for its farthest focus and to place a mirrorless camera without a lens above the eyepiece socket (without the barlow) and to then move it away maintaining it to be inline with the eyepiece socket. If you can watch the LCD display and find a spot that comes into focus, then you will know that it will work.

I don't know if 26mm closer is enough. But it might?

mikedent Loc: Florida

Thanks for this comprehensive option! I have Canon T2i body, so pretty basic. I'll work with that for a while and see if it's worth it to me to change formats, maybe after another GAS attack?

SonnyE Loc: Communist California, USA

Oh Man, GAS attacks get me into so much trouble!
I'm holding back on a major bubble to get a new mount.
It is getting painful! But the unrelenting storms we are getting helps.
Oh, there goes my clicker finger again, twitching.

Do you think changing the focuser would be wise?
I should think if you intend to fly deeper into this black hole of Astrophotography, you might want to consider putting those funds toward a different telescope.
Or a 2" focuser that just happens to be attached to a different telescope.

(See how fast I can spend your money?)

Albuqshutterbug Loc: Albuquerque NM

I know I am late to the party but this is how I shoot with my Canon T2i and my Celestron 6” newton.
The first picture is my focuser showing it fully assembled. I unscrew the 1.25 adapter leaving the primary focus tube that is threaded on the outside rim to do what I wanted to do. This is the stock focuser by the way. I then use my t adapter without it’s snout threading it on snugly. The cameras can then mount up like attaching to a lens. I have no issues focusing with either my T2i or my 5D mark ii. I can also thread the 1.25 lens mount back in after detaching the camera to locate targets at lower mag with an eyepiece. If you have the stock Celestron focuser this should get you rockin.
The last picture was shot with this combo and is a long exposure that worked out really well for me.
Good luck,
Jim

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JimH123 Loc: Morgan Hill, CA

Yep. That is the way to do it. Looks like you are using the 48mm T-ring.

mikedent Loc: Florida

Nice setup!

SonnyE Loc: Communist California, USA

You T-ring looks like my T-ring, Jim.

JimH123 Loc: Morgan Hill, CA

Measure the opening. Some are 42mm and some are 48mm. I prefer the wider opening. But my filter wheel uses 42mm, so I have to use adapters, or use the 42mm T-Ring.