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Helicoid question
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PostPosted: Thu Apr 23, 2015 2:53 am    Post subject: Helicoid question Reply with quote
I'm hoping that someone can give me a overview of how Helicoid's are normally used? I'm looking for two things. I want something to give me canon 5d more mirror clearance, and something to allow me to get infinity with m/l39 adapters. Would a
pentax M42 Helicoid Allow me some flexibility for more lenses? And perhaps even allow me to get infinity with a m39 lens? Where would I start in locating a correct pentax M42 Helicoid?

I was thinking eos to m42 adapter, and then pentax M42 Helicoid, and lens or m42 pentax M42 Helicoid and m39 adapter and m39 lens.


Thanks for educating a nub.. :0)

Last edited by vroger on Thu Apr 23, 2015 9:10 pm; edited 1 time in total


PostPosted: Thu Apr 23, 2015 5:02 am    Post subject: Reply with quote
Flange to film or sensor for M39 lenses is 28.8mm.
Canon EF is 44mm.

So You have to press M39 lenses 15,2mm INTO Your EOs. I don't see any space for helicoid and M42 adaptere, do You?

http://en.wikipedia.org/wiki/Flange_focal_distance

Thomas


PostPosted: Thu Apr 23, 2015 5:22 am    Post subject: Reply with quote
Short answer:

Shave the mirror of your 5D to get little more clearance.

Use m/l39 on your EOS-M to get infinity.


PostPosted: Thu Apr 23, 2015 11:19 am    Post subject: Reply with quote
duckrider wrote:
Flange to film or sensor for M39 lenses is 28.8mm.
Canon EF is 44mm.

So You have to press M39 lenses 15,2mm INTO Your EOs. I don't see any space for helicoid and M42 adaptere, do You?

http://en.wikipedia.org/wiki/Flange_focal_distance

Thomas


EF-M is 18mm flange focal distance. So infinity focus should be pssible with that but not the 5D.

vroger, Helicoids are simply adjustable extension tubes, allowingthe distance between lens & camera body to be adjusted within a range. The further away the lens is the closer it focuses, ( how much depends on the lens - longer focal length lenses have to move farther to reduce focus). Flange focal distance is the distance behind the mounting flange that the lens reaches infinity focus, nothing in the universe is beyond infinity so having the sensor closer than that will put everything OOF.

Stacking a number of adapters will increase the distance from the lens to the sensor, and could easily make infinity focus imposible - in some cases it may even make the farthest point of focus within the lens so You'll never focus on any subject. Ideally you want the total distance across the mounts of your adapter stack with the helicoid reduced to be equal to (or slightly shorter than) the difference between lens flange focal distance & camera flange distance. Thats 10.8mm for m39 on the EF-M (rather short for all you want to fit) and as Tom says minus 15.2mm for the standard EF. If the total is longer than this infinity focus will not be possible (without added lenses) but closer subjects might still be practical.


PostPosted: Thu Apr 23, 2015 12:53 pm    Post subject: Reply with quote
DConvert wrote:
duckrider wrote:
Flange to film or sensor for M39 lenses is 28.8mm.
Canon EF is 44mm.

So You have to press M39 lenses 15,2mm INTO Your EOs. I don't see any space for helicoid and M42 adaptere, do You?

http://en.wikipedia.org/wiki/Flange_focal_distance

Thomas


EF-M is 18mm flange focal distance. So infinity focus should be pssible with that but not the 5D.

vroger, Helicoids are simply adjustable extension tubes, allowingthe distance between lens & camera body to be adjusted within a range. The further away the lens is the closer it focuses, ( how much depends on the lens - longer focal length lenses have to move farther to reduce focus). Flange focal distance is the distance behind the mounting flange that the lens reaches infinity focus, nothing in the universe is beyond infinity so having the sensor closer than that will put everything OOF.

Stacking a number of adapters will increase the distance from the lens to the sensor, and could easily make infinity focus imposible - in some cases it may even make the farthest point of focus within the lens so You'll never focus on any subject. Ideally you want the total distance across the mounts of your adapter stack with the helicoid reduced to be equal to (or slightly shorter than) the difference between lens flange focal distance & camera flange distance. Thats 10.8mm for m39 on the EF-M (rather short for all you want to fit) and as Tom says minus 15.2mm for the standard EF. If the total is longer than this infinity focus will not be possible (without added lenses) but closer subjects might still be practical.


Thanks for the explanation of Helicoids. If it's just a adjustable tube that makes sense. Thinking my only option would be a teleconverter that has more clearance for some M42 lenses.


PostPosted: Thu Apr 23, 2015 8:54 pm    Post subject: Reply with quote
No way on earth to use LTM39 lenses on a Canon DSLR and get infinity.

Someone could make a lensed adaptor. To my knowlege there isnt one and if there were it wouldn't be terribly good quality.
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