Ross Xpres 300mm f4.5 design

[Colin D]

I've got this lens, not looking to sell it, and wondered what design type it is. I'm starting to use it for still life shots and with some manipulation to the front element turning it into a soft focus lens. I've checked the catalogue on the camera eccentric site but am still none the wiser about what design it would be classed as. I have seen some people call it a Tessar design, but then others refute that as there was a patent problem using that design.

Apart from the fact that I have to dis-assemble it to put the f stop ring on the right way again because it reads in the reverse to the way it should I find it an interesting fast lens.

The following (poor quality compact digi) shots show that when it is wide open you can see two sets of three reflections, the third reflection at the back is extremely faint, with one of the spots having a blue colour cast (does that mean single coated?). When stopped down you can see two sets of two refections.

[Dan Fromm]

By both the VM's and P-H Pont's Ross chronologies your lens is post-WW II. Should be coated, should be a tessar type.

Recognizing tessars is easy. Pictures such as you posted are unfortunately no help at all.

Here's the test: unscrew one cell from the shutter. Hold each cell under a light bulb and count reflections. The front cell should have four strong reflections, one from each air-glass interface. The rear cell should have two strong reflections. If it really is a tessar type, it should have one weak reflection from one glass-cement-glass interface. If the myth is true and the real cell is a cemented triplet, it will have two strong and two weak reflections. The weak reflections may be hard to see.

[Colin D]

By both the VM's and P-H Pont's Ross chronologies your lens is post-WW II. Should be coated, should be a tessar type.

Recognizing tessars is easy. Pictures such as you posted are unfortunately no help at all.

Here's the test: unscrew one cell from the shutter. Hold each cell under a light bulb and count reflections. The front cell should have four strong reflections, one from each air-glass interface. The rear cell should have two strong reflections. If it really is a tessar type, it should have one weak reflection from one glass-cement-glass interface. If the myth is true and the real cell is a cemented triplet, it will have two strong and two weak reflections. The weak reflections may be hard to see.

Thanks Dan, the front cell certainly has four strong reflections, the rear cell has one strong reglection and one much weaker and smaller reflection at the rear. Does this last bit mean anything?

[Colin D]

Ok, next question about this lens. Does the f stop ring screw on or slip on? Someone has put it on back to front so that it works in reverse ie. @ f4.5 the lens is stopped down to f45, @ f45 it is wide open. If I can take the f ring off and turn it around it should fix the problem. The f ring is rigid and does not move with the barrel when I open and shut the blades. I've tried unscrewing it with my hands but it won't move, I've put a small screwdriver in the small gap between the ring and the barrel and tried to prise it loose but it doesn't move. I'm reluctant to force it too much for fear of doing damage. Any suggestions would be appreciated.

[Dan Fromm]

Thanks Dan, the front cell certainly has four strong reflections, the rear cell has one strong reglection and one much weaker and smaller reflection at the rear. Does this last bit mean anything?

It means (a) that you, like the rest of us, sometimes have trouble seeing a tessar rear cell's second strong reflection (hint, its at the rear surface) and (b) your Xpres is a tessar type.

Sorry, can't help with the mechanics.

[Colin D]

Cheers, thanks again Dan.

[Ian Greenhalgh]

I own half a dozen post-ww2 Xpres lenses, they are all Tessars. I think the only Xpres that had a triplet in the rear are the early ones when the Tessar patent was still an obstacle. There are also plasmat and dialyte type lenses with the Xpres name, the WA Xpres 4/5" is a plasmat, the process Xpres are dialytes. In my experience, Xpres lenses are always top quality.

[Colin D]

I own half a dozen post-ww2 Xpres lenses, they are all Tessars. I think the only Xpres that had a triplet in the rear are the early ones when the Tessar patent was still an obstacle. There are also plasmat and dialyte type lenses with the Xpres name, the WA Xpres 4/5" is a plasmat, the process Xpres are dialytes. In my experience, Xpres lenses are always top quality.

There was a very early 105mm f3.8 Xpres that went on e-bay recently, I considered it for a while, but I'm happy with my 300mm and still experimenting with it. I know Jim Galli suggests unscrewing the front element to get a softer focus, do you know if doing the same thing to the back element has any effect? If Jim is around he might be able to answer as well.

I finally figured out the f stop ring was screwed on and was able to get it off and flip it around to get proper readings .

[Marko Trebusak]

Collin, in Tessar design, the front light is air spaced two element design. And you shall increase the distance between those two. The rear cell is a cemented doublet. And increasing distance between it and front cell might get you somewhere. But not in the same direction ...

[Ian Greenhalgh]

With a Tessar, increasing the spacing between the two front elements does increase spherical aberration and give you a soft, glowy result. I did it with a 1930's Kodak Anastigmat 124mm, which was a fairly soft lens to begin with. Didn't have much success because the maximum I could unscrew the front element and still hold it in place with the threads wasn't enough to get enough of the desired effect. I couldn't be bothered getting the tools out and modifying it. I have seen pictures others made after modifying a tessar in this way though and they suggested it was a worthwhile experiemnt.