View Full Version : Bausch and Lomb convertible lens question - how to use?

30-Jan-2013, 09:46
Hi everyone,
I am using a Bausch and Lomb convertible lens on my 5x7 (Protar VIIa). It looks kind of like this: http://www.ebay.com/itm/Bausch-Lomb-Zeiss-Protar-Series-VII-7-3-16in-11-3-16-Convertible-1493904-1493906-/260992622656?pt=Camera_Lenses&hash=item3cc45f6040 .

My question is, how do I use it properly? It's mounted to a lens board and the shutter is exposed when I remove the front element. I tried to focus when I unscrewed the front element, but my bellows seem not to be long enough. How can I use it for 3 different focal lengths? And what are the strange things on it that seem not to move (the "roll" on the top behind that dial (mine is a dial that shows numbers up to 150, with the arrow pointing at 150)? And the lever on the right (on the photo) - it doesn't move either.

Can anyone offer any advice?

Kevin Crisp
30-Jan-2013, 10:09
The recommended practice when using the lens converted (either of your two cells used alone) is to put the cell behind the aperture. Yes, that does leave the aperture blades exposed, and depending on bellows draw, you might not have enough. Single cells can be pretty bad unless stopped down to at least f:22. 32 or 45 is probably more like it, depending on the focal length, if you want the edges sharp. (I say depending on the focal length since a long single element with a lot of coverage may have your 5X7 sheet of film using the middle of the image, which helps.) I've had Zeiss versions that weren't sharp on the edges regardless of the aperture when used as single cells, but have had better luck with B&L versions as single cells. Combined I think you will find the lens is outstanding.

Single cells will show focus shift, which means if you focus carefully wide open or near it, then stop down, the lens is no longer in best focus. So use a loupe and double check focus when stopped down, you will probably find a little shift is in order. If you focus at f:22 and stop down to f:32 you won't notice the effect and won't need to refocus.

If lack of bellows draw prevents use of single cells, you can use the single cell on the front, which takes considerably less bellows draw. I doubt you will really notice a quality difference with this placement, and a number of people have suggested certain single cells perform best when used in that position. Again, stop down a lot and watch for focus shift.

All of the above may make it sound harder than it really is to use one of these, they are my favorite lenses and this will all become second nature. Good luck.

30-Jan-2013, 10:35
The tube on the top is the air cylinder that is used to create the shutter speeds. It doesn't need to move. The lever on the right is for cocking the shutter. If it doesn't move, don't force it. On a compur shutter, the lever is locked when in T or B. I'm not sure what happens on the Compound.


Dan Fromm
30-Jan-2013, 12:04
To expand a little on what Dan wrote, and writing with a B&L Compound shutter in front of me, note the slot with a pin in it that's below the lens. As you face it, the left end will be marked "M", the middle "B", and the right end "T".

The middle and right end give, respectively, B (bulb, the shutter opens when the release is pressed and stays open until the release is released) and T (time, the shutter opens when the release is pressed and closes with the shutter is pressed again). These speeds must be used with the shutter not cocked. Do not cock the shutter while the pin is at B or T unless you want to break it. If the pin is set to M (timed shutter speeds, set by the dial at the top of the shutter) and is cocked, fire it before moving the pin to B or T.

The shutter must be cocked (press down the lever that is at the right as you face the shutter, it has four screws) before it will fire on M.