stella_h

Mike, That's a good point. That would be an easy and less costly way to get to A3. For some images that softness would be perfect. I am a sucker for the crispness of ambro and tintype though. Thanks. Allan, that is a great idea. As the element configuration at the base is obviously intended to project the small sized image outwards onto a wide screen, I'm wondering if even removing that element might be all that is needed? It's at times like this I wish I could get my head around Physics and Maths better. I have to learn by physically trying things out what most people can with paper and pencil. Something struck me as odd when I was looking at it though. I had placed an object in front of the lens and was looking in through the back of the lens, quite close to the lens and the focussed object was sharp. As I moved backwards the object appeared out of focus (as one would expect) but as I backed away even further the object came back into focus. I'm not sure if this is what would normally happen with a multi element lens and was just more noticeable due to the large lens size, whether this is particular to projection lenses or whether I'm just being daft. I've been struggling to get a large enough area in total darkness to experiment with it. I'll have await the arrival of my camera obscura tent, I think. I don't want to destroy the lens but I'm buoyed from having yesterday managed to strip a process lens, clean it and put it's disassembled iris back together successfully, so feel it's worth a try. I need to get a bigger lens wrench, that's for sure. It's definitely worth attempting. Thanks for the idea. Stella

Thanks Mike, I believe the lens came from a training simulator projector. And thanks for the link. I did stumble across Ian Ruhter's van camera a while ago when I started researching camera obscura. Crazy guy, huh? I'm puzzled as to why each image costs upwards of $500, I'm guessing it's his road crew and travel expenses factored in. But making images beyond 14x11, for me, it is pretty much essential to be pouring your own emulsions, cost wise. And in ULF size wet plate and pinhole aren't an easy combo because of the length of time of the exposures. Still, it's all part of the territory. Photography is never without trade offs. Thanks for posting. Stella

Thanks Dan, I'm not worried, it's all learning. I actually really like the lens and was quite amazed that as close as I was to the back of the lens the image still looked likely to be nearing the 10x8 inch coverage. It will still get used and I'll learn a lot in the process. Thanks for your help. Stella

<p>Hi John,<br> When I tried it earlier using tissue paper in the place of groundglass the focus point was virtually touching the lens when the lens was in 'projecting out' position. When I turned the lens around to use it backwards focus was a few inches away from the lens but (being so close) produced a small image circle. I'll try a different set-up tomorrow though and see if I can achieve better.<br> I noticed something strange earlier just when looking through the lens. Having the lens pointed at a subject and me close to the back of the lens the image was sharp, as I backed away the image lost focus but as I kept backing away it came into focus again. I have to say I thought that was quite mysterious. I need to set up a longer bellows to follow the full projection I think.<br> Thanks for responding to the post.<br> Stella</p>

<p>Hi Dan,</p> <p>Thanks very much for your response. Just from experimenting with it just now it seems that the focusing ring does very little (at the distances I've been experimenting with). It looks to be an immensely heavy macro lens. So I'm thinking you might be right. Coverage seems to be somewhere between 5x7 and 10x8. Not exactly what I had in mind. I wonder though if the lens configurations could be altered to get the coverage I want?</p>

<p>Ah-ha, I've just freed the focussing ring. I can go back to my walk-in bellows. I am still very interested in any advice you large format users have on using such a beast of a lens though. Somehow I'm guessing I'll probably need to fabricate a lens hood too? All advice will be greatly appreciated.</p> <p>Thanks again.</p> <p>Stella</p><div></div>

<p>Hi everyone,</p> <p>Apologies if I am posting this in the wrong place but it looked the most likely category for my query.<br> To be as concise as I can, I'm wanting to build a camera obscura with a lens as opposed to a pinhole. I have acquired a projector lens that I am told came from a training simulator projector. As I was looking for something that would cover either 20x30 or 30x40 inches it seemed the lens could be a good idea. (It wasn't very expensive so worth the punt). The lens diameter is 14cm and the length 26cm. There is no shutter, of course, and no iris, and no other identifying information. If I can figure out a way to post a photo (sorry, newbie problems) I will. There are multiple lens groups inside and the lens comprises an inner cylinder that holds the lenses and an outer cylinder that has a grooved band that I thought would be a grip for focussing but it doesn't seems to move. (Although strangely enough, I thought it did when I first picked it up - I may have been mistaken or there may be some kind of locking mechanism?) I mocked up some giant bellows just to look at the focussing distance and was surprised that when I was behind the lens with the flange plate nearest me, focus using tissue paper as a ground glass was almost touching the back of the lens. As it's a projector lens I then turned it around (flange plate furthest away) and found focus on tissue paper several inches behind the lens. Either way of course not the large image circle I was looking for.<br> <br> Would anyone be able to tell me if this is likely to be just a focus issue and larger images will be attainable once I figure out what is going on with the focussing outer cylinder? Or am I missing something really obvious to everyone else and that it won't be possible to use a projector lens of this sort in the way I'm trying to?<br> <br> I very much appreciate any help or insight anyone can offer. I shall now go away and see if I can find out how to post a photo.<br> <br> Thanks a lot.<br> <br> Stella</p>