RMS extension tube - sourcing

cvhmanchester · Post by **cvhmanchester** » Fri Feb 22, 2019 4:09 pm

I am using a Canon 20 mm 3.5 macro lens (which has an RMS thread) on a Canon bellows. But the bellows bulk makes lighting difficult.

Does anyone know where I can get a tube, say 30-50 mm long, with RMS threads, male and female either end? ebay etc throws up very short Chinese versions.

Thank you

ray_parkhurst · Post by **ray_parkhurst** » Fri Feb 22, 2019 4:55 pm

Maybe try one of the cone-shaped RMS adapters? They are not RMS both ends, but it's easy to adapt the M42 end to the bellows.

edited to add: if you do go that way, you may need to flock the inside. I've had contrast problems with some of the cone adapters.

Chris S. · Post by **Chris S.** » Fri Feb 22, 2019 5:26 pm

I like Ray's idea about using a cone-shaped adapter with a bellows--and echo his point about flocking it.

Also, you can assemble an RMS extension tube of nearly any length you wish by combining Thorlabs SM1 (one-inch diameter) tubes with Thorlabs Optical Component Thread Adapters.

A similar line of tubes and adapters is available from Edmund Optics, but the cost will probably be higher. Both companies make excellent products, with Edmund being a bit more posh. Newport and others may also have parts to assemble what you need. This said, I would mainly look at Thorlabs.

These assemblies should also be flocked.

--Chris S.

Macro_Cosmos · Post by **Macro_Cosmos** » Sat Feb 23, 2019 1:36 am

Wemacro offers M42 tubes which are already flocked.
https://www.wemacro.com/?product_cat=ex ... ro&paged=3

I have a set, they are far better than those cheap ebay ones.

ChrisR · Post by **ChrisR** » Sat Feb 23, 2019 3:34 am

I'd wouldn't use the cones for a 20mm lens which you have to get close to the camera, they're too long (as well as shiny!). Straight to M42 is how I go.

Rms tubes do come up, but they're shiny and hard to flock as they're so small.

ray_parkhurst · Post by **ray_parkhurst** » Sat Feb 23, 2019 8:14 am

ChrisR wrote:I'd wouldn't use the cones for a 20mm lens which you have to get close to the camera, they're too long (as well as shiny!).

The cones are ~52mm long, so if 50mm is the absolute max, I agree, but they are pretty convenient having both extension and adapting in one shot. You'll need to flock most anything you put on there.

JKT · Post by **JKT** » Sat Feb 23, 2019 2:49 pm

I should hope that flat T2->RMS adapters are still available.

I chose that as the availability of T2 (42x0.75) extensions in different lengths seemed to be quite good as opposed to M42 (42x1). With that combination you don't waste much length.

ChrisR · Post by **ChrisR** » Sat Feb 23, 2019 7:55 pm

T2 tubes aren't too easy to find

ray_parkhurst · Post by **ray_parkhurst** » Sat Feb 23, 2019 8:04 pm

ChrisR wrote:T2 tubes aren't too easy to find

Yeah, M42x1 are much easier for extensions, adapters, helicoids, etc.

Chris S. · Post by **Chris S.** » Sat Feb 23, 2019 11:56 pm

ChrisR wrote:T2 tubes aren't too easy to find

Would Edmund Optics T-Mount Extension Tubes, with their M42 x 0.75 threads, substitute for T2 tubes? If I recall correctly, the main difference between the T-mount and the T2 mount is the latter's rotatability, which would not be needed for every application.

--Chris S.

Len Willan · Post by **Len Willan** » Sun Feb 24, 2019 12:37 am

Canon made a series of M39 Flocked extension tubes that were used with a Leitz mount, they could be suitable
Check it out here
Using Wemacro 46C Clamps to hold Infinite Tube Lens
http://www.photomacrography.net/forum/v ... highlight=

JKT · Post by **JKT** » Sun Feb 24, 2019 3:55 am

ChrisR wrote:T2 tubes aren't too easy to find

Chris S. wrote:Would Edmund Optics T-Mount Extension Tubes, with their M42 x 0.75 threads, substitute for T2 tubes?

I was using T2 just to describe the thread, which is same M42x0.75 between T and T2.

The ones you linked to will naturally work, but there are cheaper ones as well: Ebay search gives just a few hits, but the set of 5, 10, 15 and 20 mm tubes ... or a few of them will work in many cases and the price is right.

On the other hand, sometime ago I couldn't find such sets for M42 - only few isolated ones. Thus I ended up with T2.

After I had the tubes fixed, I got the Raynox, step-up 42->43 and step down 49->42. Male and female reversing rings for T2 are also on their way, so that should take care of that. All I need is to order Mitutoyo...

ChrisR · Post by **ChrisR** » Sun Feb 24, 2019 5:17 am

I see there is now a 5-10-15-10m "T" threaded cheap set, I hadn't seen that. Ebay item 183195679508 seems to be all you'd need. The same seller does a 45mm tube.

The Canon 20mm f/3.5 needs short extension for its relatively limited useful magnification range. From 4 or 5x, better options are available, and below that, the working distance is rather short even though it performs very well.

The most suitable thing I have for that, which I have praised before, came from William at Wemacro, though I don't see it on his site now. That was a male M42 tube with a female M42 tube, each with an extended thread, and a locknut. Effectively it's a short rigid helicoid for about 20 - 40mm.
I (probably like many of us) have a few M42 tubes which go down to very short lengths, which are very cheap and fine for up to say 25mm.
A flat M42 adapter on the RMS thread doesn't significantly restrict the light getting to the subject, if at all.

I have a few T2 threaded bits and pieces, but generally I regard it as a nuisance!