DSLR directly to 42(43?)mm focus extender? Or how to achieve prime focus?

[Loopnova]

I've been looking into attaching a Canon DSLR to a 150/750 scope. I know there are problems with achieving focus because the usual adapter that accepts 1.25" eyepieces puts the camera too far away from the focal point. It occured to me what if I were to cut out the middle man entirely and just attach the camera directly to the extending part of the focuser? Mine is threaded so I can unscrew the 1.25" adapter (see picture for the result of this). Surely there is a small t-ring that will attach to my camera and then allow me to screw it into the 42 or 43mm threaded opening of the extender?

Edited March 11, 2020 by Loopnova

[alacant]

Hi

This and -if it really is female m42- this will do it and bring the dslr sensor closer. 

If not, the next step is to bring the two mirrors closer.

HTH

 

[Loopnova]

Thank you for the link, that's precisely what I was imagining! Seems like a pretty uncommon solution and I'm beginning to realise why - even if it works, the downside is that the focuser will be obstructing some light inside the tube right? Maybe before I buy anything I will get the scope focused on a distant target and hold the camera as close as I can get to the focus extender to see what sort of result I can get.

I'm willing to move the mirror but I wonder how this will affect my viewing ability with normal eyepieces? Is it possible to move both mirrors to preserve the 750mm focal length?

Edited March 12, 2020 by Loopnova

[alacant]

Unless you're only intending doing video of the moon and planets, you're also going to need a coma corrector or other method to correct the field. There are no 42mm fit correctors AFAIK. 

The items to which I link are economical and are always useful to have around or buy a t to 1 1/4 adaptor and simply either cut the tube or use longer primary mirror bolts.

HTH.

Edited March 12, 2020 by alacant

[Nicola Hannah Butterfield]

I hope this is appropriate, I imaged this with 10x 60's subs at prime focus with  a SW. 200P on an NEQ6 mount. it is cropped a little to avoid the worst of the coma, this was my first attempt at at this type of photography on the new mount which I got 6/4/2020 and yes I know there are other issues.

SW200P prime focus T2 to EOS mount direct on focuser, Canon 6D, ISO 200

Edited March 14, 2020 by Nicola Hannah Butterfield

[Kevin Francis]

Here's another method to achieve prime focus.  Video included.  Author will also support your installation.

[Kev M]

On 12/03/2020 at 14:50, Loopnova said:

I'm willing to move the mirror but I wonder how this will affect my viewing ability with normal eyepieces? Is it possible to move both mirrors to preserve the 750mm focal length?

You only need to move the main mirror.

The focal length will remain the same.

To achieve focus with eyepieces you may need to fit an extension tube, extremely easy just screws in and very cheap.