Step down adapter

[woldsman]

I’m using this attachment to attach a filter wheel to (I think) an M42 thread. It’s about 0.4 to 0.5mm too wide. Is there a thinner option? Something 1.5mm wide would work though, ideally, I’d like to screw an adapter into the M42 thread adding nothing to back distance.

Confess to being confused about threads. I already have an an M48 to M42 adapter screwed in with zero addition to back distance. The diameter of the filter wheel thread is about 37.25mm.

Photos attached to illustrate what I have.

Thanks & clear skies!

[vlaiv]

I think it would be better if you describe whole train and required spacing.

Shaving 0.5mm of something that is already very thin is going to be tall order. Most adapters don't list thickness of such feature so you can't be sure in advance if it will help or not.

It is probably better idea to look at the whole thing and see if you can save some length in different place - even if it is greater than 0.5mm - it is easier to add extension or shim then it is to reduce length.

[woldsman]

1 hour ago, vlaiv said:

I think it would be better if you describe whole train and required spacing.

Shaving 0.5mm of something that is already very thin is going to be tall order. Most adapters don't list thickness of such feature so you can't be sure in advance if it will help or not.

It is probably better idea to look at the whole thing and see if you can save some length in different place - even if it is greater than 0.5mm - it is easier to add extension or shim then it is to reduce length.

Thanks! Image train is: Samyang 135mm lens, canon zwo bayonet adapter with the front removed & a M48 M42 step down screwed in (15.5mm), manual filter wheel (20.87mm), zwo asi183 minin camera (sensor 6.5mm back). This gives me 42.87mm and I need 44.3mm. Am left with 1.43mm and the adapter as shown is 1.97mm. With a different lens adapter, I made back distance but suffered from tilt so am back to the bayonet. I am very close to achieving focus with the 1.97mm adapter - a case of so near yet so far. 
 

A zwo electronic filter would I think screw right in but that’s an expensive option. Don’t know of thinner manual filters for 1.25” filters.

[vlaiv]

37 minutes ago, woldsman said:

Thanks! Image train is: Samyang 135mm lens, canon zwo bayonet adapter with the front removed & a M48 M42 step down screwed in (15.5mm), manual filter wheel (20.87mm), zwo asi183 minin camera (sensor 6.5mm back). This gives me 42.87mm and I need 44.3mm. Am left with 1.43mm and the adapter as shown is 1.97mm. With a different lens adapter, I made back distance but suffered from tilt so am back to the bayonet. I am very close to achieving focus with the 1.97mm adapter - a case of so near yet so far. 
 

A zwo electronic filter would I think screw right in but that’s an expensive option. Don’t know of thinner manual filters for 1.25” filters.

Still not sure where the problem is?

If I understand correctly, you have following:

Canon EOS - to M48 and M48 to T2 that is total of 15.5, right? How much path is each component?

Then you have Filter wheel that is 20.87mm thick with T2 thread on each end right?

Finally you have ASI183 with 2" removed which leaves T2 thread that goes into filter wheel - and that makes 6.5mm only to sensor (from camera front to sensor).

Why would you want to use above adapter when everything fits properly one to another (above adapter seems to be some sort of male M48 to male T2 thread or similar)?

Instead of using it - you can simply add 3x0.5 spacers somewhere in your train. Maybe use 0.5mm one in front of filter wheel and 1mm between filter wheel and camera?

https://www.firstlightoptics.com/adapters/baader-t2-delrin-spacer-ring-set.html

Or is that adapter needed for "first leg" of the train - Canon EOS + M48 to T2 and you need to shorten the optical path?

[Elp]

An image of your image train might help. I'm also a little confused on how it's setup, I have both the removable filter drawer Eos adaptor and the plainer one where you can screw a filter inside it, the only room I have after either of those Eos adaptors is the 11mm female to female camera spacer ring and my 183. Any shortfall I use a 0.3 or 0.5mm aluminium spacer ring on the end of the camera nose.

[woldsman]

Thanks for these responses  - am working away from home this week. Will update with an image of the imaging train.

[woldsman]

An update (thanks again for replies). Back distance of 44mm obtained with a TS Optics CCD to EOS adapter to M48 male  (10mm) & M48 to M42 short version adapter (3.5mm) plus some shims.

Edited March 26, 2023 by woldsman