A Curious Thing - Lens-hack Question

[nelsonfotodotcom]

SO, I purchased a JML 6.5" f/8 from Don Bryant. It's a nice chunk of metal and glass, holding it now having received it moments ago in the post.

I'm eyeballing this thing, opening and closing the diaphragm, when the question pops into my head: Wide open, there's still a lot of opening to be had... is it possible to have a lens like this tweaked to open beyond f/8? If not, why not? What is prohibitive? I'm even thinking it might be fun to yank the diaphragm out of it altogether....

Now, I'm new to the LF lens racket, so pardon me if this is an elementary issue and one which might draw a roaring "STUPID!" from many, but I figured I would ask. I've picked up quite a bit thus far just by reading these forums, so, hoping to learn another thing or two about a thing or two.

Danke!

C.

[Dan Fromm]

Craig, manufacturers usually limit apertures to protect users from themselves and to preserve their reputations. It is often the case that forcing a larger aperture than the manufacturer intended just kills image quality far off axis. But since your lens more than covers 4x5 and you're shooting 4x5 this may not be a major problem.

In other words, since you own the lens now there's no reason why you shouldn't remove the diaphragm or break it (or maybe not) trying to get it to open wider.

[nelsonfotodotcom]

Dan, howdy!

I've got a query into Grimes' crew to see what it would cost me to have mounted in shutter or at least to have it placed in a decent board for its size and weight. I'm not the least bit mechanically inclined, so the hacking would not take place by my hands, but at some point it might be interesting to have it altered, if possible, to see what happens.

Thanks for the input. Seems on par with Rick Oleson's advice over on my board.

Best,
Craig

[nelsonfotodotcom]

Also occurs to me that these process lenses would have been set for sharpest output, hence the high minimum aperture. I love the look of the old, fast lenses, the wild OOF, etc., so that's what got me to wondering about the potential in this one.

Again, thanks.

[Jim Galli]

Actually the JML process lenses are sought after for that. Machine whatever is stopping the diaphragm so that it can open all the way and then you will observe a very softish performance from a normally super sharp lens. Or so I've heard.

[nelsonfotodotcom]

Jim - you wouldn't happen to know what potentially could get FUBAR if I open this thing up, or what exactly would be needed? The cells unscrew from the diaphragm, leaving the center free to disassemble. Worried I'd end up when tension devices and/or aperture leaves all over the place.

Single locking screw, by appearances, on the threaded portion which would take a retainer or flange. I'm assuming once the is removed, the rest will unscrew, revealing another screw that is visible within the diaphragm barrel. I image that might be a stop of some kind, perhaps the key to opening the diaphragm, fully.

Ideas? I'd be willing to shoot some images if needed as examples.

C.

[Jim Galli]

No I haven't done one and truly don't know. OK, just went out and looked at both my 6" and my 8 1/4". The 6 inch you take the front group out of the barrel and then the aperture ring slides right off. You can see the slot that would have to be enlarged to make it open wider. The 8" is similar but there is a retainer behind the aperture ring that comes unscrewed and then the rign slides off. Same thing, expensive machine work. That slot would have to be milled.

[nelsonfotodotcom]

The ring is locked in on the 6.5" - must come out like the 8".

I might tinker with it later. In the midst of assembling some Dremel stuff in order to make a board for the JML so I can at least see what it does at f8.

Thanks, Jim, for checking.

C.

[lenser]

You might also check with Carol Miller at Flutot's Camera Repair in Whittier, Ca. She does some truly amazing things at extremely reasonable prices:

www.Flutotscamerarepair.com

[nelsonfotodotcom]

Thanks.

After a little work with the Dremel, the lens squeaked its way into that old lensboard I had. Had to sand a bevel into the back of the board to allow the rear element room to bolt down, and had to remove the bottom lensboard nut to get the assembled lens and board into the camera. Once everything screwed back into place, she's a-ready to go, I do believe. Looks sharp to me. Will shoot a sheet or two past her tomorrow. Time for bed.