where's the image on my Bausch & Lomb 24" aero tessar?

<p>I've recently started experimenting with old lenses, and I just bought this B&L aero tessar, but I can't find the projected image anywhere. I've never had a lens with this long of a focal length, so that could be the problem. I haven't been able to find an image anywhere out to about 4 feet from the lens. Am I missing something? I tried searching the archives, but found nothing. Any input would be appreciated.<br>

Thanks!<br>

mark</p>

<p>What camera do you have this on? What format?</p>

<p>Larry</p>

<p>It's not on a camera yet--I'm planning on building a camera around it. I'm trying to test the lens by building a mini-darkroom (think film changing bag) around it and projecting the image on to a piece of translucent paper. This method has worked for me with everything from magnifying glasses to 12" LF lenses, but I can't get it to work with this lens. Thanks for asking for clarification.</p>

<p>I would mount the lens near a window pointing out to bright daylight inside of a dark room. Hold a piece of paper behind the lens and move it back and forth to find the focus. Infinity should be about 24" behind the aperture. Tessar is a standard lens design, with no retrofocus, so the focal length of the lens is literally the distance from the aperture to the film at infinity. Unless you have a camera that will extend over 20 inches, you will need some kind of elaborate extension setup just to reach infinity focus. To get closer focus than infinity, you will need even more extension... but this depends on the format and the kinds of shots you want to do.... portraits, macro, etc. </p>

<p>Mark, this is going to be a HUGE camera! You will probably need metal rails to support the front standard and allow it to move smoothly and have some frames to support the bellows so they don't sag into the image area. You should post pics when you finish it!</p>

<p>Patrick</p>

<p> I was thinking that because that is a super long lens the extention will have to go almost 2 feet out from the film plane.</p>

<p>I believe this lens was for Recon Air Craft from the 40's and 50's</p>

<p>Thank you Patrick and Larry for your info--it was very helpful. I'm starting to wonder if maybe my lens is not "all there." I also thought I should be able to see an image around 24" behind the lens, but when I tried your suggestion there's nothing there--in focus or not. When I look through other lenses in my odd assortment of LF lenses, the image looks heavily "jumbled", but when I look through this lens, it looks like I'm looking through a pair of minimally corrected eyeglasses. Is that typical for a 24" lens? I kind of thought that the image would be harder to recognize when just looking through the lens. It doesn't look like there's anything missing from the lens, but maybe there is and that's the problem. (The front optic is about 4" in diameter, the rear optic is about 3.5" in diameter, and the front to back distance from the front to rear optic is about 2"--is that about right for 24" Tessar design?)<br>

Thanks again to both of you for your replies.</p>

<p>Hold the lens in front of your eyes. If you see an erect image slightly reduced in size then the lens is missing a positive element. If the image is not clear and the lens acts a strong magnifier and holding it at arm's length produces an inverted image, then the lens is missing a negative element. If the lens is complete, looking through it will produce a slightly magnified, erect image of nearby objects and holding it approximately 2 feet away from a wall opposite an open window should produce an inverted image of the window view. The effective focal length of any multi-element lens depends upon the focal lengths of the components as well as the spacing between them. Good luck with your testing.<br>

FWIW, these lenses were also popular among amatuer astronomers who deisred to build "richest field" telescopes.</p>

<p>Thanks Mike--helpful information. My lens seems to fall in the first example--an erect image slightly reduced in size, held both right at my eye and held any distance away. It seems I would need a positive element. How difficult is this to get for a lens like this? If the answer is not simple, is there a resource you can point me to?</p>

<p>Hmm... I don't know much about these kinds of cameras, but on small cameras, lenses are split into two sections, one section in front of the aperture/shutter and the second section behind. The aperture needs to be at the focal center of the lens, where the image crosses over itself or else it will vignette the image at smaller sizes. It is not impossible to imagine someone pulling off the big shiny front section of the lens (which might be the first 3 elements connected in a housing) and leaving the rear element still mounted to the other side of the aperture/shutter. </p>

<p>Since it's been a while since this lens was made there are not likely to be any spare elements around. Still, you might find a repair shop with a damaged one, but one with the element you need intact. Kind of a long shot. Just google and see what turns up.</p>

<p>I'm having trouble even finding a photo of what this lens is supposed to look like, much less finding spare elements. Does anyone know if it's possible to use some type of generic element to complete the lens enough to use it?<br>

Thanks!</p>

 

<p>I have extra front cell assembly of the lens you spoke about, B&L 508mm, the iris diaphramin is in the rear cell assembly, if you have th company name in the ring around the glass you have the front cell</p>

<p>OK, I had put this project on hold for a few months since I couldn't find a rear cell assembly. But then I realized that a simple magnifying glass could probably act as the positive element Mike spoke about. It worked, but I could see a pronounced ghost image around my subject. Could this be because of the low quality of the magnifying glass ($1 special even though it is made of glass) or the lack of anti-reflective coating or both? Any thoughts on where to find a simple, large (4") well made glass lens with an AR coating? Thanks!</p>

 

<p>Well when you find the lens you may try to mount a coated UV filter to it. This may be your coating for the element. Just a thought.</p>