6*30 finder scope

[happy-kat]

I've plans for this orion 6*30 finder scope that came with an ST80 and have unscrewed the end which you look through and revealed this thread. The opening is a bit larger than a C mount thread and overall the same size as a 1.25 T mount so it wont accept a thread of that size. I'm looking to join to this and offer a male C mount thread to couple to the device I want to attach.

Any ideas on the thread size on the finder scope please?

The outside diameter is 32.61mm and the opening is 28.47mm

Edited August 28, 2022 by happy-kat

[Mandy D]

Measure the thread pitch, then add that to the minor diameter and you will have both pitch and diameter of the thread.

So, if ten turns of the thread measure 10 mm with your ruler, the pitch is obviously 1 mm, add this to the 28.47 and you get about 29.5 mm. Allow a bit for slop and it is likely to be an M30 x 1 mm thread. Of course, the thread size will not be specified by the manufacturer as this is not a "user" thread, so it could be anything they like including M29.5 x 1 or 1-5/32" by some crazy pitch.

[happy-kat]

Thank you. Having had a think the easiest solution like like doing something like this.

A cap to slip over the end of the finder and a C mount thread on the top. Now to find a C mount thread already designed to give a head start.

[Mandy D]

13 hours ago, happy-kat said:

Thank you. Having had a think the easiest solution like like doing something like this.

A cap to slip over the end of the finder and a C mount thread on the top. Now to find a C mount thread already designed to give a head start.

Yes, good idea. Easy to deal with as you can get a c-mount adapter easily. Just cut it down to suit and make it a tight fit in your cap, probably glue it into place. Here is a link to one:

https://www.rothervalleyoptics.co.uk/rother-valley-optics-c-mount-125-adaptor.html

Or, better yet, it looks like they make the exact part you are looking for:

https://www.rothervalleyoptics.co.uk/skywatcher-finderscope-to-c-adaptor.html

Edited August 24, 2022 by Mandy D

[happy-kat]

Thank you.

The finder I have is 30mm and I already have a C-mount to T mount and the tube is the same size as the 30mm so wont fit over or in the finder though I could get a 2" sized one and pack it out with bluetac to fill the gap.

[happy-kat]

Having removed the end you look through and holding a camera I was unable to reach infinity focus as I was running out of in focus travel.

This is what you see after taking the end off which you look through, that bit also appeared to have some sort of barlow element in it plus the cross hairs.

What's revealed.

The top piece is a ring that holds a prism in place. I used my finger nail in a groove to unscrew it.

These two pieces can then be carefully shaken out, you can see the thread the ring screwed in to.

Having fashioned a bog roll tube using rubber bands and tape I could experiment with the camera to work out where the camera needed to be for infinity focus. The bog roll tube cut out light ingress to the camera.

Using tape I could mark where the tube was to start and how far I needed to pull the finder from the tube to reach infinity focus, 17mm.

OTA 118mm

Extra needed 17mm

Theoretical depth of neximage 5 17.5

152.5mm - 22mm depth of front lens = 130.5/30 = f4.35

Next onwards to design and get printed a c-mount with extended adaptor to couple the camera to the tube.