DB mount

[tim810]

Hi All,
I have a friend who has a lens I am interested in, the only problem with the lens is it is in DB mount. Is there anything I could do to make this lens work on a standard Cambo lens board. Maby even have it remounted in a copal shutter??? I can probably get the lens for a song and just want to see if I would be able to use it. BTW it is a Sinar 355 Symmar.
Thanks again
Tim

[Patrik Roseen]

The DB mount includes the aperture but not any shutter mechanism. The shutter mechanism is supposed to go behind the lens board. This way the sinar camera has the same shutter for all lenses basically, which makes the cost for adding new lenses cheaper since they do not require individual delicate shutters. The aperture within the DB-Mount is usually operated from the back of the lensboard, which makes it difficult to use on any other lensboard.

What you can do is to unscrew the lens elements from the DB mount, and screw them into a 'normal' shutter. I believe the 355 Symmar should go into a Compur Electronic #3 (?) http://www.schneideroptics.de/archiv/pdf/symmar_5.6.pdf

[Pete Roody]

Many lenses mounted in DB mounts are direct fits for Copal shutters (0,1 and 3). If the serial number is for a late model 355 symmar, then it would most likely fit a copal 3 directly. An early vintage lens may or may not.

Sinar shutters are selling for less than a copal 3 and maybe you could rig it to fit the cambo front standard. This would allow the use of other barrel lenses.

[tim810]

I have the 355 convertable in hand it has an aperture ring from f6.8-64. The elements unscrew nicely and I have a copal 3 in front of me (from my 240 caltar). The elements interchange and by putting the 240 in the db mount it focuses as it should. The 355 fits nicely in the copal 3 and all works well on this end. My question is how do I change the iris from the db mount to the copal 3 and make it so the apertures match up. Oh and the 240 is f5.6-45. Any help would be great. I feel I will use the 355 more than the 240 and can wait to find a copal 3 for the 240. I would really like to start using the 355 soon.
Tim

[Patrik Roseen]

You are not supposed to change the iris.
The copal-3 shutter which has up to now been housing the 240mm should have on it an aperture scale (5,6..8..11..)

When you insert the 355mm lens you need to put a new aperture scale on the copal-3 shutter so that the opening of the iris will correspond to the correct f-stops for the new lens (6,8..8..11..)

BTW, if there is an aperture scale on the DB-Mount, you can measure the diameter of the aperture opening for each f-stop, then adjust the size of the aperture opening on the Copal-3 to this size and mark the corresponding f-stop on your own home made aperture scale and put on the copal-3. Be careful not to damage the aperture blades while measuring.

Do a search on this forum and you will find lots of information about this (It's quite common procedure)

[Struan Gray]

The ratio between 240 and 355 is close enough to the square root of two that you can almost certainly get away with using the aperture scale for the 240 and simply adding a stop. That is, if the scale says 'f8' it is really f11 for the longer lens. Similarly (mutatis mutandi) if you use the 240 in the DB mount.

I'm assuming that your caltar is a normal plasmat (Caltar-II S or N or something like it). If it's a tessar or one of the cheaper triplet Caltars you will have to do your own aperture calibration. As Patrik said, there are many threads on the subject here if you search. A bit of masking tape and a pencil and you're ready to go.

[tim810]

Last night I did just as you recommended and took out the calipers and measured the diameter of the apreture as it corresponded to the scale. Than I just took notes as to what the new apretures would be. It ended up being basically one stop difference. I am going to call SK Grimes today and see if I can get a new scale made.


Thanks everyone!!
Tim

[Pete Roody]

You might want to check with Schneider for the scales. They can supply scales for some of their lenses.

http://www.schneideroptics.com/service/contact.htm

Last night I did just as you recommended and took out the calipers and measured the diameter of the apreture as it corresponded to the scale. Than I just took notes as to what the new apretures would be. It ended up being basically one stop difference. I am going to call SK Grimes today and see if I can get a new scale made.


Thanks everyone!!
Tim