Weird lenses for 4x5 TLR

[james_mitchell8]

<p>Hi y'all!</p>

<p>I just bought two lenses off of the auction site that supposedly were inside of an xray machine (one of the lenses says "xray critical part" on a sticky-label), and was wondering if, given a description of them, if anyone could hazard an educated guess or two at their general formula...</p>

<p>They're in a plastic shell with a set screw that moves their middle element forward or backward (presumably for in-situ focal calibration). The front aperture is 4" across, and the rear aperture is 5.25" in diameter, with the whole lens being right around 7" from front to back. The weird thing is that the back focal distance is really short: I haven't yet jerry-rigged something to let me test infinity-focus, but if I set the lens near the floor and focus on the ceiling light, even at that close distance the back-focus is maybe a centimeter if that. The only other two pieces of data I have are A) that reflections of the ceiling light are all in different colors (multicoating?), and careful angling shows 10 reflections, which I presume means at least five elements (two air-glass interfaces each?).</p>

<p>Anyway, I know it's a big long-shot, but if anyone felt comfortable speculating I'd love to hear theories.</p>

<p>Thanks!</p>

[john_cooper9]

<p>They sound like some XR lenses I bought off Ebay years ago. There have large apertures of 0.75 and smaller. They have no aperture blades and the back focus is very small - varying from 3 or 4 mm to closer to 20mm at infinity. I tried hooking them up to a Pen F body and a old Mercury 1/2 frame. This works to some degree since the longer focal lengths had a large enough image circle to cover 18x24mm. I don't see how you could use them on 4X5 at infinity.</p>

[chauncey_walden]

<p>I have several of these, Rodenstocks and Kowas. One of them, can't remember which one (maybe a Rodenstock XR-Heligon), will cover 4x5 as a macro lens with the subject at about 4 inches.</p>

[james_mitchell8]

<p>More Data:<br /> These are bright enough that I can hold them up to the window (now that it's daylight out) and look at the outside *through* a sheet of paper up against the back of the lens. With the paper up against the rear element (which is flat), I can make out everything, though it's fuzzy, and at about half a centimeter I can focus the cypress trees down the street through the paper. Image is roughly 5.25 inches, although the outside 1/4" or so shows signifiant distortion. I can focus my venetian blinds through the paper with it at about 2-3 cm from the rear element.</p>

<p>Ground glass: my Razzle came with a ground-glass in a riteway; I put this directly up against the back of the lens and it focusses most everything in the field of view (roughly whatever a 35mm lens on my Pentax covers), although lacking an extra pair of hands I can't stick a loupe against it to see how good the focus really is. It definitely vignettes the corners of the GG at "infinity", but my window blinds can easily fill the corners with the window (at about a yard away). The odd thing is that, unless it's just an accident of my not holding both straight up & down, when I focus the window blinds, the vertical frames on my window (sideways window which is half open, so the whole frame's currently divided into four segments) seem to curve towards the corners -- even with wide-angle lenses I've never seen a distortion like that.</p>

<p>Anyway, that's for the help; these definitely don't match the lenses above. I'll try to get a picture uploaded so it's easier to make out what I mean.</p>

<p>EDIT: I managed to put a loupe up against the GG, and the riteway holder seems to be too far away from the rear surface to focus properly: you can make it out at a "postcard" level of image, but nothing in the loupe is clear.</p>

[james_mitchell8]

<p>(sorry, meant to say "thanks" for the help, not "that's"; I have a picture to upload but I won't be able to put it up until this evening.)</p>

[james_mitchell8]

<p> first pic</p><div></div>

[james_mitchell8]

<p>2nd pic</p><div></div>

[james_mitchell8]

<p>FWIW, the screw adjustment seems to give me infinity or close thereto off of the GG-riteway.</p>

<p>Anyway, thanks for your time; if anyone can shed further light on this kind of lens formula I'd be all ears, as even with dagor77's awesome offerings I've never seen hide nor hair of anything like these guys.</p>

<p>(c:</p>

[erie_patsellis]

<p>It looks to me more like a CRT projection lens. Does it have any other markings?</p>