Lens Board Thickness prevents proper lens mounting

[CCLA]

Hello,

I finally was able to purchase a lens for my Sinar F2 camera. When I received the lens it was mounted in a lens board that is about 2mm thick. In addition between the shutter and the lens board there is a spacer which is about .76mm thick. When I tried to mount the lens on the Sinar board I noticed that it was thicker (it is about 4mm thick). After mounting the lens on this board I noticed that the rear element did not screw in as far as it could go (even after removing the spacer) because the locking ring interferes with it (on the thin board the rear element screws in about 4 and a half turns whereas in the thick board it only goes about 3 and a quarter).

I assume this will make the lens unusable with this board, so I have a few questions. Why the two different thicknesses of the boards? Does Sinar provide thinner boards? Do I need to use the spacer?

One final observation, the original lens board is flat while the Sinar board seems to be a reverse-recessed board (see here: https://www.photrio.com/forum/threads/sinar-f1-4x5-outfit-in-case-many-extras-325.137851/


thank you for any help

claudio

 

[CCLA]

Also, the lens I have is a Nikkor 75mm F4.5. Will I need a recessed lens board for this lens? How can you determine is a lens needs a recessed or regular lens board?

claudio

 

[jim10219]

What kind of bellows do you have for it? I don't think you'll need a recessed lens board for a 75mm lens if you have the bag bellows, but I could be mistaken. You might have to put both the front and rear standards in front of the tripod mount on the central rail to get them close enough though. But with a sturdy tripod, that shouldn't cause any issues (and keep the rail from showing up in the pictures). But a recessed lens board certainly wouldn't hurt with a 75mm lens, other than making the shutter more difficult to access (and possibly making the cable release problematic). The best way to tell how it would look like with a 75mm lens is to put about 81mm of distance between the back of the front lens board and the front of your ground glass (that's your lens's published flange focal length). If your standards will compress that far, then it should work. If not, then you might need some bag bellows, or if there's other hardware in the way, then you'd definitely need a recessed lens board. With the regular bellows, you might not be able to do much in the way of movements even if it does technically work.

If you need to, you can shave down the back of the lens board a bit to thin out the board to allow your lens to mount properly. All of my lens boards came with a lip around the edge of the hole where the lens mounts and there the metal is about half as thick. So I've never had your issue. You can buy them premade like this too. Several generic makers do this as well, and for a decent price. Check that auction site for some examples. That might be a better and cheaper route to go than having to DIY a solution or take it to a machinist.

 

[shutterfinger]

The post you link to in your initial post in this thread shows a spacer of some type attached to a Sinar lens board with 3 screws, what do you have once the three screws are removed, a standard lens board and a spacer?
Does the 75 have a mount ring or a mount flange?

 

[CCLA]

The camera in the post I linked is actually the camera I bought so I have both the bag and the regular bellows. I did follow the instructions and found out that the distance between from the front of the lens board to the ground glass is around 82mm. So for a regular lens board without the spacer it would be around 72mm since the spacer is 10mm. I guess a recessed lens board would allow more movement with the regular bellows when focused at infinity, although I could always switch to the bag bellows in the situation. I guess I will look for a board that is thinner.

As for the current lens board, if you were to remove the three screws you would have a regular lens board with a hole as big as the plastic disc (the spacer) onto which the shutter is attached.

 

[shutterfinger]

Mount ring, flat on both sides or rounded on one? Was the lens designed for a mount flange by chance?

 

[CCLA]

Rounded on one side.

 

[Dan Fromm]

Claudio, you've been a bit confusing. Will the lens mount properly on the board with spacer shown in the link you provided?

To use a short lens on your camera, it is best to mount the tripod mounting block in front of the front standard. One of the pictures in the link you provided shows it between the standards. I believe that the F1/F2's minimum extension is 38 mm, not the greater distance that you measured.

 

[shutterfinger]

I would turn down the mount ring rounded side 1mm to 2mm or turn down the mount board 1mm to 2mm about 5mm wider than the mount ring whichever will provide the most rigid mount.
A Dremel with a sanding drum or a flat file will do the mount ring or a mortising bit in a Dremel in a router base for the lens board or have a machinist do it for you.

 

[Ian C]

Here is a table of shutter-mounting dimensions for various modern shutters. It includes specifications for minimum and maximum board thickness.

http://skgrimes.com/lens-mounting/to-lensboard

 

[CCLA]

I finally bought a new thinner board. The board I had originally is similar to the following one (albeit a different hole size):

Thick Board.

claudio

 

[Nokton48]

OK Here is the deal.......

That board "forward mounts" certain lenses, so the the rear cell of the lens does not poke into the blades of the Sinar Mechanical Shutters. At the factory Sinar would "forward mount" these lenses so the rear cell was 1mm from the front of the shutter blades. That is the optimum position. I've done this many times myself in my workshop. A precise procedure.

With a longer lens it would also be easier to access the shutter controls, with gloved hands.

No sweat with a 75mm and Sinar, but you have to reconfigure the camera to bring the two standards very close together. Bag bellows helps if doing movements. If you have a regular bellows you can bring it around to the front and use it as a shade.