Iris for mounting barrel lenses?

[John Kasaian]

G'morning!

I have a lensboard with a heavy iris thats supposed to hold barrel lenses. This sounds really cool, but I've neve been able to get a lens to mount looking "straight." The iris looks to be in excellent condition and none of the substantial leaves are bent or distorted. Is there a trick to using these things? Where on the barrel should I "clamp" the iris? Thanks!

[CP Goerz]

I clamp the lens barrel at the point where the threads for the flange are, it has a bit more grip and security than the smooth sided barrel. If the lens is particularly heavy or a long tele type design I would have a board made for regular use.

CP Goerz

PS: As a wee side...I found that if you use an 'iris' for shuttered lenses the image will be a bit blurred due top the shutter twisting during the exposure from its own vibration etc.

[Jim Galli]

John, I was able to reduce a 42cm Xenar to near Zero value with one of those contraptions. Of course CP would say it was near zero Value in the first place.

[Jason Greenberg Motamedi]

I found that the only way of using these is to clamp the lens onto the iris by using a flange or retaining ring.

[george jiri loun]

Make a simple collar with a groove which you put on the lens. Or to make things simpler - put two collars on the lens and fasten the iris in between.

[John Kasaian]

Thanks guys! The iris isn't really much use since I put a 450 Nikkor on it's own lensboard, however I thought it would be cool to experiment with different barrel lenses on the 'big screen' but so far I haven't been able to secure them very well. Unfortunately most of the retaining rings for my barrel lenses have apparently gone to retaining ring twilight zone long before I got ahold of them. I'm thinking of seeing what the local plumbing supply has in the way of rubber or plastic gaskets that might lend themselves to a temporary 'crush fit' then I'll try your suggestions.

[wfwhitaker]

John,

I have several of these devices which for lack of a better name I have christened with the very unappealing name "lens chuck". (At least it's less of a mouthful than "universal lens mounting ring"! ...and it basically works like the chuck on a drill.) The best place to clamp the lens is the relief at the base of the thread where the smooth part of the barrel begins. That gives the iris blades a secure place to rest. If the blades land in the thread, the lens will probably be cocked slightly as you pointed out. Make sure the threads are fully through the iris and the base of the barrel is flush against the blades.

Within their limits these things are very useful if you have a number of barrel lenses. With larger lenses the mounting can be unwieldy to the point of being downright scary (especially if you have concrete floors as I do). That's when it's time to invest in a lens board. The medium and smaller sizes generally work better.