52mm Tubes, and other adapters.

ChrisR · Post by **ChrisR** » Tue Mar 07, 2017 7:22 am

While in communication with an ebay supplier about an adapter or two, I suggested that sets of 52mm tubes would be useful.

I'm fairly well served by a stack of the things, but I'm aware they aren't particularly easy to obtain.
What lengths would members would find useful?

Standard ring sets come typically
7 + 14 + 28 = 49mm or
13 + 21 + 31 = 65mm.

My preference would be 5 + 11 + 25 + 55 or so.

Any other adapters? Raynox reversing kits would be an obvious possibility.
You're welcome to use a pm if you don't want to go public.

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 9:04 am

The standard series is terribly limited by the fact that each size is an integer multiple of the smallest size. This makes it impossible to fill gaps closely by buying multiple sets of rings. Best would be a set of numbers with no common factors, including some low prime numbers like 3 and 5. Then we could get really close to any desired size by buying multiple sets (good for the vendor!)

rjlittlefield · Post by **rjlittlefield** » Tue Mar 07, 2017 11:05 am

From my standpoint, a good proposal would include specific numbers and a comprehensive illustration of why it's a good proposal.

I'm used to sets with the standard 1:2:4 ratio, such as 7 + 14 + 28.

I know that with those:
a) I can get within plus or minus half a short tube of any length I want, and
b) by adding a single helicoid with range of a least one short tube, I can get exactly any length I want.

This is simple and motivates me to buy multiple sets.

But 5 + 11 + 25 + 55 is new to me. I don't understand its advantages, so as a potential buyer I'm not attracted to it.

Potential sellers will have the same concern, I imagine.

--Rik

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 11:52 am

Lengths that share no common divisors give you better coverage of different extension lengths. We'd also want to avoid lengths that are the exact sums of some of the other lengths. The standard 7, 14, 28 series violates both these conditions. One could use numbers that approximate the 1:2:4 ratio.

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 12:17 pm

Maybe 5, 9, 29 if limited to three. With multiple sets you could then cover 5, 9, 10, 14, 15, 18, 19, 20, 23, 25, 27, 28, 29, 30, 33, 34, 35, 36, 38, 39, 40, etc. Coverage would be virtually complete from this point onward.

Compare that to the standard set's coverage over the same interval: 7, 14, 21, 28, 35. And the coverage doesn't get any denser as we go past 40mm.

I don't see any disadvantage to making them in non-integer ratios. You can still use a focusing helicoid if you want (if you can find a sturdy one with 52mm diameter).

ChrisR · Post by **ChrisR** » Tue Mar 07, 2017 1:58 pm

Do you want small increments, or larger increments the longer the assembly gets?
If you start with a geometric progression such as 1:2:4:8, you can add them to make an arithmetic one -
1:2:3:4:5...
I would mostly want larger increments as the assembly gets longer, which is quite hard to achieve.
If you allow multiple sets, and want ultimate flexibility, then start with the shortest practical, probably 5mm, then you need 6, 7, 8...

Cheap simple and good are unfamiliar bedfellows but the Long Screw wouldn't be too bad. It also allows rotation setting, if you aren't too fussy about length. The skinny ring locks it. I don't see why the threads shouldn't be say 15mm long. On 2 inch" pipe threads they're 3-4 inches, but they're 11 tpi, not 0.75mm.

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 2:44 pm

Again, it would be better not to make them integer multiples of each other, no matter what the final goal. There is no advantage to reducing the number of lengths you can achieve. Your 1:2:4:8 is just the standard set, plus one more. It leaves many lengths unobtainable unless the smallest tube is very thin. Even then, you get more choices from tubes that are not integer multiples of each other; see above.

lothman · Post by **lothman** » Tue Mar 07, 2017 3:03 pm

beside a tube length smaller 30mm why not using a bellows?

ChrisR · Post by **ChrisR** » Tue Mar 07, 2017 3:13 pm

Lou :Yes, that's why my preferred set in post 1 wasn't 1:2;4..

If you only have one set of tubes then you do get arithmetically equal increments with 1:2:4...

if you want to be using more than one set, you're still best off with 1:2:4....
Plus another set with different, smaller increments.

So if you actually had

40, 80, 160

you could make evenly spaced 40 lengths up to the largest 280.

If you now allow another set, you want 20, 10 and 5. Then you get steps every 5, all the way from 5 to 315.

The Ah But comes with the skinniest ring. In our practical case, that's probably 5mm. So you start wanting 6mm, 7mm, etc to fill in the gaps.

If you only allow one set,
or you only allow two or more identical sets, then the optimum is maybe some other range of numbers.
It depends then whether you want a geometric or arithmetic progression.

The 52mm Nikon K rings had a skinny M/F baoyonet ring then bayonet adapters and plain 52mm tubes:

lens + K1 + body == 5.8mm extension
lens + K3 + K2 + body == 10.8mm extension
lens + K3 + K2 + K1 + body == 16.6mm extension
lens + K3 + K4 + K2 + body == 20.8mm extension
lens + K3 + K4 + K2 + K1 + body == 26.6mm extension
lens + K3 + K5 + K2 + body == 30.8mm extension
lens + K3 + K5 + K2 + K1 + body == 36.6mm extension
lens + K3 + K4 + K5 + K2 + body == 40.8mm extension
lens + K3 + K4 + K5 + K2 + K1 + body == 46.6mm extension

they can be hard to find, outside of the US, and you still don't get much 52mm tube.

ChrisR · Post by **ChrisR** » Tue Mar 07, 2017 3:17 pm

Lothar - 52mm bellows? Often bellows + adapters is just too ungainly, or the diameter of the bayonet is too small.

naturepics43 · Post by **naturepics43** » Tue Mar 07, 2017 3:17 pm

This e-Bay seller has 12 - 24 - 36 lengths in 52mm dia. plus lots of lens reversing rings http://www.ebay.com/sch/Lens-Adapters-M ... tals&rt=nc

ChrisR · Post by **ChrisR** » Tue Mar 07, 2017 3:26 pm

I see 12 and 24, no 36?

naturepics43 · Post by **naturepics43** » Tue Mar 07, 2017 3:37 pm

Try this link You have to look in the description for the length. http://www.ebay.com/itm/371761276862?_t ... EBIDX%3AIT

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 3:57 pm

Chris, it is never better to make regular series. Never 5, 10, 15. You'll always have more choices with non-integer multiples.

Edit: And if you allow a second series, the last thing you should do is make them integer multiples of the first series, as in your suggestion of 40, 80, 160. You are unnecessarily enforcing a 5mm gap between sizes. There's no benefit to that, only a downside.

Lou Jost · Post by **Lou Jost** » Tue Mar 07, 2017 4:10 pm

This subject interests me because I like to make dedicated rigid tubes for my infinity-focused Raynox or other short-mount tube lenses. But this was an excercise in frustration. The darned tube makers all do that crazy integer-multiple strategy (and different manufacturers even use the same lengths!%^5%%%) making it impossible to achieve close-to- infinity focus without buying a (not very stable) focusing helicoid for each one.