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.

9784297843

[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 (http://en.wikipedia.org/wiki/File:Tessar.png) 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.

[DerrickStone]

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.

Are these lenses still available in the market? I am looking to get exactly these lenses so from where I will get them? Please help..

[Colin D]

Are these lenses still available in the market? I am looking to get exactly these lenses so from where I will get them? Please help..

Derrick, they appear on ebay occasionally. When I bought mine 6 months ago the seller had two, there was one last week going for $900, might still be there because I don't think it sold.

[Colin D]

Collin, in Tessar (http://en.wikipedia.org/wiki/File:Tessar.png) 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 ...


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.

Thanks for your advice Trebusak and Ian, but now I am slightly confused. When I unscrew the front cell it has two elements to it (on the left of photo), they are unseparable so when you blokes talk about increasing the space between the front two elements I thought it would these two but they are held together. I've added a photo of the lens dismantled. Or do you mean increasing the space between the front cell and the rear cell. Going by the diagram on wiki for Tessar mine appears to be different as I can also unscrew the rear cell as one piece that has two elements (on right of photo) and another element (I think, must check tonight) is still in the barrel (middle of photo) behind the iris.

I think it would be a Tessar and I've just misread what you are saying.

98411

[Colin D]

Derrick, Here is the ebay link to the lens I mentioned. I don't know the true value of these but I paid somewhat less than this one. BTW the ebay listing is still in original condition with paint, mine isn't.

151007093140

[Dan Dozer]

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.

Take a look all around the outside of the barrel. I have a lens about the same era that has a very (and I mean very) tiny screw that screws in thru the outside of the barrel that holds the iris in place. Removing the screw if there is one may free up the F ring.

[Colin D]

Thanks Dan, the f stop ring eventually unscrewed off the barrel and I was able to flip it and screw back on the right way. I found taking the screw out of the barrel simply disengaged the iris blades.

[DerrickStone]

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 cheap hid kits (http://www.robustbuy.com/lighting-system-hid-xenon-kits-c-492_645_653.html) 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.

Are these lenses still available in the market? I am looking to get exactly these lenses so from where I will get them? Please help..

Ok Thanks for reply

[Marko Trebusak]

Thanks for your advice Trebusak and Ian, but now I am slightly confused. When I unscrew the front cell it has two elements to it (on the left of photo), they are unseparable so when you blokes talk about increasing the space between the front two elements I thought it would these two but they are held together. I've added a photo of the lens dismantled. Or do you mean increasing the space between the front cell and the rear cell. Going by the diagram on wiki for Tessar mine appears to be different as I can also unscrew the rear cell as one piece that has two elements (on right of photo) and another element (I think, must check tonight) is still in the barrel (middle of photo) behind the iris.

I think it would be a Tessar and I've just misread what you are saying.


The thing is, that construction of the barrel will vary from manufacturer to manufacturer. So if you can't increase the distance between the two elements of the front cell, you will not be abble to use it as Jim Galli and Mark Sawyer (http://www.largeformatphotography.info/forum/showthread.php?57385-Velostigmat-Series-II-Info-and-Images) describe. You can try the rear cell only, as front cell of Tessar is only ment to correct the abberations. The result will obviouselly be different. The other question is: is your objective Tessar after al? If rear cell isn't cemented doublet, then it's something else. Manufacturers used triplets at the back to walk around Tessar patent, but I didn't hear of Tessar clone with separated cell in the middle of objective, as that means completelly different design.

[Mark Sawyer]

Colin, as much as you've already disassembled the lens, I think you should just strip it down to the elements and see what it is, checking curvatures and any cemented elements. Some lenses that were in production for a long time, like the Xpres, may have been made with different designs at different times. (BTW, mark the rotation of the elements too, so you can get them back where they were.)

BTW, does anyone know what this lens was meant for? I usually think of the Xpres as a process lens, but Wray made a 300mm f/10 Lustrar process lens, and a 300mm f/4.5 Lustrar portrait lens.

[IanG]

The Xpres was the standard Ross camera lens, it's not a true Tessar type lens at all, however as it states the Patent it's a 5 element design which was an improvement on the original Tessar design.

Ross made a separate series of f10 Apo Process lenses. The lens the OP has is in fact a 12" / 305mm Xpres designed to cover 10x8", they were also available in Compur/Compound shutters to special order.

Ian

[Colin D]

Ok, there are only two cells with cemented elements, so I might try unscrewing the rear cell to see what that does. Unscrewing the front cell didn't appear to make any discernable difference.

[Marko Trebusak]

Collin, are you sure that the front cell is cemented? From the picture on first page, one would think that theat is a two lens air spaced cell. The problem might be unscrewing the front element. Just depends on the barell construction. If your front cell unscrew together, that doesn't mean you would not be abble to separate the front two elements. You might need special tool to do so.

[Ian Greenhalgh]

The front definitely won't have a cemented element, it will be two air-spaced elements. Most likely there is a retaining ring to remove from the back of the front cell in order to be able to get at the elements.

[Louis Pacilla]

Ok, there are only two cells with cemented elements, so I might try unscrewing the rear cell to see what that does. Unscrewing the front cell didn't appear to make any discernible difference.

Hey Colin

I don't believe that your front cell is a glued group. Sometimes the rear element of the front group is the element that separates from the front element of the front air spaced group. Particularly if the Tessar design is not originally built to add diffusion. Yours was NOT made in this way and many Tessar designs that are not meant to be separated for diffusion have the design like yours. Where the rear element of the front air spaced group is the one that unscrews from the front element .

If you look at the arrow that I drew on the front group of your posted photo. Check and see if the is the sign of a smallest gap between the painted black cell (inner cell of the front the group) and then the brass threads which are part of the (front element) cell to the outer element of the air gap front group.

See if you can get the black painted (Inner element) cell to break free from the (front element) brass cell. There should be a inner set of threads that the inner cell (black painted) attaches to the front cell (brass).

If you think what I said may be true you may want to get a pair of rubber pads and a little lubricant . add a tiny bit of lubricant to this tiny gap & not a lot. Add a little more lube & let it sit a few more minutes. Wipe the access lube off the the front cell so you can get a grip on both sections with the rubber pads. Now try and break the threads free and you should be able to break them apart. Let's hope.

BTW- from the looks of it you defiantly have the correct front cell (Air spaced) and NOT two glued groups. Let us know if this works out.

[Colin D]

Now I understand, my ignorance is showing :P, I'll give that a try.

[Ian Greenhalgh]

I agree with Louis. I checked my 8 inch Xpres and it looks the same inside as yours, there is no slotted retaining ring, so I reckon it is the piece that Louis arrowed that unscrews. I can't see another way of doing it on mine, no little grub screws, no rings, nada.

[Colin D]

I've put some lubricant around the join but it is stuck fast even after a few hours. The lens is in good condition making me reluctant to use any excessive force to loosen the thread, I'll see how it is in the morning.

[Colin D]

It still won't budge. The gap between the first element and the front element is minimal so I wonder if the lubricant is even reaching the thread. On the weekend I might try mor mechanical methods to loosen it. Apart from the softer focus thing, I'd like to clean the interior glass which has a very small smudge in the middle of one of the elements that shouldn't affect images but still it annoys me.

[Colin D]

The latest development on this saga. Today I had another fling at working this out and think I might have succeeded. If I have got this right, the front element actually unscrewed at the very front. If you look at Louis's diagram, the thread for the front element is where the botton of the arrow starts, that is at the opposite end to the pointy bit, you can make it out on the photo. However, the cell that Louis points to still exists and appears to have two air spaced elements to it, this I have not been able to move.

To see if I had discovered how to make this a soft focus lens ala Jim Galli style I unwound the front element to the last couple of threads; on the ground glass it appears to have a soft focus quality, with a very narrow point of sharp focus. Tomorrow morning I am takng a still life shot of two lens elements in low light to see how it looks.

And I was able to clean out a small faint blemish that bugged me even though it was not matrial enough to really worry about.