Extension Length Calculator

I'm no need anything from $400 anyway )). I can get FoV from several mm to several meters with one microscope lens and one helicoid. Just wondering of using extension rings for $400 setup.
35-90mm can cover any size coin from the table above. Even less expensive 25-55mm helicoid with two constant rings 7 and 14 mm can do it.

Ray, Better to see something once than to hear about it... ))

https://www.coincommunity.com/forum...213_moon.jpg

Yes. It's $6.34 more. But you paid also for 3 rings to complete short helicoid.

@ngs428, I'm sorry that with my suggestion your calculator will be useless. ))

Yes. Without your post I would not pay attention to this side probably.

If you're eliminating parts, then couldn't you use a M39 to M42 focusing helicoid and get rid of the M42-M39 adapter? Here's one on ebay (from China) listed at $34.94 w/S&H.

Wouldn't you then just need:
- camera to M42 adapter
- M42-M39 35-90mm Focusing Helicoid
- Nikon 75mm El-Nikkor lens

ngs428,

Not so much for you, as you already have a system setup, but for others who might be contemplating this system.

In looking at the various posts about this system, it seems that many potential users thought it complex and didn't understand how it all fit together. Getting it down to just 3 parts (a converter to convert their camera to a M42 screw mount, a helicoid to provide focusing and a lens) IMHO is much simpler to understand and would help those who didn't understand the complexity of how the original system was put together.

There is another reason I recommended the 17-31 adapter originally. With the shorter adapter, I thought it would be feasible to use a 50mm lens instead of the 75mm while still framing up to Dollars. This would allow use of the very inexpensive Nikon 50/4, which has a much worse reputation than it deserves. But ultimately folks like the 75/4 much better, so it never really came up that the 50/4 was an option.