Problem fitting finder to binos

[WinchesterAstro]

I am trying to attach a finderscope to my Opticron Oregon 20 x 80 binoculars. Following the instructions here...

 

https://stargazerslounge.com/topic/318029-how-would-you-attach-a-red-dot-finder-scope-to-binoculars/

 

... I have now attached a short rail, so that it looks like this:

 

 

But when I tried with a cheap finder from an old telescope but the rail was too wide.

 

The Baader website says that the Sky Surfer III fits onto this type of rail (a 'Picatinny/Weaver' rail) here https://www.baader-planetarium.com/en/baader-sky-surfer-iii-red-dot-finder.html Can anyone confirm this?

 

Alternatively, there are adapters that will turn my picatinny/weaver rail into a dovetail of 11mm:

 

https://www.amazon.co.uk/ToopMount-Tactical-Alloy-Weaver-Picatinny-Accessories/dp/B087Z7TVMW/ref=sr_1_38?crid=K0H6YZ2X4A4F&dchild=1&keywords=dovetail+to+picatinny+rail+adapter&qid=1634902378&qsid=262-0831571-8964842&sprefix=dovetail+%2Caps%2C381&sr=8-38&sres=B08CBSSBRS%2CB07QSFPPLF%2CB06X18BT41%2CB08GKK41QJ%2CB08GKM6WQJ%2CB08FFS7B57%2CB07M9GGNL2%2CB08CZ3VFTY%2CB0778VTKLS%2CB07MLR92XM%2CB08QF219NH%2CB08GL69H6J%2CB01D2HT8B4%2CB08GKKH4D7%2CB0922XQNFN%2CB08GKN8JS7%2CB08FR36H33%2CB085RBPSMY%2CB08GKP9J9W%2CB071ZG8SP5

ToopMount Tactical Scope Riser Base Mount 20mm to 11 mm Scope Rail Mount Base Aluminum Alloy Weaver Picatinny to Dovetail Adapter Hunting Accessories : Amazon.co.uk: Sports & Outdoors Shop ToopMount Tactical Scope Riser Base Mount 20mm to 11 mm Scope Rail Mount Base Aluminum Alloy Weaver Picatinny to Dovetail Adapter Hunting Accessories. Free delivery and returns on all eligible orders. www.amazon.co.uk

 

But here too I don't know whether this would be the right size for a finder.

 

In short, does anyone have measurements for precisely what width different finders need? I assume there's some leeway...

[BinocularSky]

4 hours ago, WinchesterAstro said:

In short, does anyone have measurements for precisely what width different finders need? I assume there's some leeway...

Not a lot of leeway on the very common RDFs (branded Orion EZ Finder II, Celestron Starpointer, etc.), because the clamp has also to grip a dovetail on the RDF itself, and it is only properly non-wobbly when the sides of the clamp are parallel. The dovetail on the mounting stem is 14mm wide at the top, tapering to approx 10mm (difficult to measure precisely) with a depth of approx 3mm.

HTH

[Kimboman]

What about this type from Celestron  it on my 15x70 pro bios

[Sky-searcher]

Used the same rifle clamp with a few layers of insulation tape to increase the diameter of the bar on my 20x80’s.