Need info on Rodenstock Imagon 200mm

[Jeff Searust]

Does anyone have this lens and have the diffusion disks? I would love to get some sizes on the disk holes.

 

[thisismyname09]

I just bought one of these (adapted to an RB67 mount). I haven't gotten it yet, though, and it only comes with one (the h=5.8, I think.) of the three disks. :\ When it arrives I can get some pictures/measurements for you.

 

[Jeff Searust]

Yes, mine is just like yours it sounds like.

I ran up a dozen blank disks on my lathe last eve, and drilled a couple of them with 12 and 24 holes spaced around a 33mm center hole-- (the 24 holer in 2 concentric circles). I am sort of more interested in the size of the holes and the size of the center hole. Also I am interested in where the disks fit. I made mine fit in the end of the lens where the filter was.

My disks seem to work fine, and I am really impressed with the look they give.

 

[thisismyname09]

You wouldn't happen to be interested in making another set of disks, would you?

 

[thisismyname09]

Arrived in the mail today.

I've got the H = 9.5-11.5 disk, as it turns out. They function differently than I thought. one "disk" consists of two circular pieces of metal with holes drilled through them. One piece rotates to vary the softness of the image:

The disk fits on the front of the lens like so:

The center hole on my disk is 15mm in diameter. The second ring of holes are 3mm in diameter. The third ring of holes are 2mm in diameter. Each ring consists of 12 holes.

 

[Jeff Searust]

yours looks different than mine...

Dead Link Removed

yeah-- I knew about the open and close bit. I was just going to make one with the holes open and then one with no holes. With each the same center hole.

the 15mm would make that about f-13.3-- I wonder if the h- numbers are the same as f stops-- and they compute it at f-9.5 with the extra light from the holes and then 11.5 with just the center open. I am wondering also about the silver bit on the front of yours, and if it is sized differently.

Must play more with this thing...

 

[thisismyname09]

The silver thing seems to be what holds the disks in, as the one I have isn't threaded in any way. It just snaps into the silver part, which screws into the threads on the front of the actual lens. I did some crude light testing with a metered prism. With my disk at 11.8, testing showed that it was about f/11. opening the disk to 9.8 appeared to be f/9.5. The difference in the calculated f/stop and the values i found experimentally may have something to do with the fact that the aperture is in front of the lens, rather than inside, allowing some light to enter at odd angles and still hit the lens. Just a guess, though.

While testing without the disk, the apertures on the RB67 shutter were a half-stop off from their actual values, since the 180mm mamiya lens's max aperture is 4.5, about a half-stop off from 5.6. Ignoring extreme precision, the apertures on the rb67 shutter seem close enough to be substitutable, so long as the disk isn't being used. I also found that using the disk and stopping down results in vignetting.

The picture in your post doesn't seem to be loading.

Edit: your picture's working now. I'd assume the differences between ours lies in the brand of adapter. Yours is blank whereas mine is labeled "Zork-Tubus" The lens itself seems to be the same, minus the silver thing on mine. In fact, it looks like the silver thing was added to the disk-holding ring, possibly to make it easier to screw on and off.