Skywatcher 9x50 finder and T-adapter: back focus

[JimFR]

I’ve just acquired the above (birthday prezzie!).

It’s a nice finder, and a definite boost from the 7x30 bundled with the scope!

However, I’m struggling to get anywhere near focus with my Pentax K50 on the end of it... anyone know why? There’s no focus mechanism to speak of, other than the objective lens’ mounting thread...

[tooth_dr]

12 minutes ago, JimFR said:

I’ve just acquired the above (birthday prezzie!).

It’s a nice finder, and a definite boost from the 7x30 bundled with the scope!

However, I’m struggling to get anywhere near focus with my Pentax K50 on the end of it... anyone know why? There’s no focus mechanism to speak of, other than the objective lens’ mounting thread...

Are you trying to image through the finderscope or use it for guiding?  The focus on a 9 x 50 finderscope is done by rotating the objective lens, and locking into place using the thin black threaded part that sits below the body of the objective lens.  I use a camera with a 12.5mm back focus on my 9 x 50 finderscope and when it's is threaded up fully, via an adapter, it sits flush with the end of the finderscope tube.  So my sensor sits 12.5mm from the edge of the metal.   I suspect the sensor/flange distance on the Pentax is about 46mm so you will need to move the camera closer to the objective lens or thread the object lens further down the tube.  I dont think you will have 33mm to spare (pretty sure it wont work).  Even if it does work, it wont be very nice quality.  Sorry!

Edited October 29, 2020 by tooth_dr

[JimFR]

The idea was to use with a webcam or boardcam or similar, but had the dslr to hand to “try it out”. I suspect you’re right, that deep sensor location could be the issue!

I’ll be adding a T2 to 1.25” push fit adapter which should be ok.

Edited October 29, 2020 by JimFR

[tooth_dr]

9 minutes ago, JimFR said:

The idea was to use with a webcam or boardcam or similar, but had the dslr to hand to “try it out”. I suspect you’re right, that deep sensor location could be the issue!

I’ll be adding a T2 to 1.25” push fit adapter which should be ok.

Can you post a photo! I’m not sure how you plan on connecting everything?

[JimFR]

On 29/10/2020 at 12:48, tooth_dr said:

Can you post a photo! I’m not sure how you plan on connecting everything?

Not yet, I don’t have all the bits, but the webcam will slot into the 1.25”-T2,

which will screw onto the T2-tube adaptor,

which will screw into the finder scope tube.

I’ll post a picture when I’ve got it set up, with results!