Massive projector lens

Hello all,

First time posting here, but i need some advice.
I acquired this massive piece of plastic and glass for allmost nothing ( ~10$ ). The seller told me that it`s about 9-10cm diameter ( 3.5-3.9 in ). Perfect for my 5x7 homemade box-in-box paper-negative camera. ( Will post it when it`s done :) )

https://i.imgur.com/SlOYcaGh.jpg

To my surprise this thing has a diameter of 14 cm ( 5.5 in ) and a focal length of about 380-420 mm ( 14-16.5 in ) resulting in a f2.8 aperture.

The question would be : is this usable with a negative that`s 5x7 ? ( the diameter is grater than the negative width ). I was hoping for a f4..something for portraits..
I could build a much larger box camera for this, as i can get paper as big as 20x24in but i`ll run into some other problems.

I also have a few enlarger lenses i plan on using : Eskofot ultragon 150 and 210 mm f/9, zeiss apo-germinar 240,360,450 mm f9. All have f-stops, and thredead mounts. This one has neither.

You might get a better response to this on the lens forum.

I think this would be excellent for portraits. My favorite 5x7 portrait lens is 12", but a couple more wouldn't hurt. I would at least give it a try.

It would be interesting to figure out how many elements it has, and whether you could saw into the side and add waterhouse stops.

@DrewBedo : lens forum seems more for "real" large format lens, But i`ll give it a shot, thank you.
@mdarnton : Seems to have 3 lens/groups ( i can see some edges inside the lens ).

I`m planning a box for it ( box camera ), format will be a little bigger than 5x7. Paper is 7x9.5in. It has a focus adjustment ( the gearing on the right moves the massive lens inside a plastic barrel ) so the box will not need focusing.
i`ll dismantle it this weekend. the lens tube is plastic, and has screws, so it can be opened, the case also can be split in two. I`ll post pictures :).

Do you happen to know where that lens came from?

Guy that sold it to me said something about a automatic projector.
I think it's from some sort of large overhead projector. Judging by the size, something that would be used in a atrium classrom.

I collected quite a lot of projection lenses. Yours is a TV projection lens type. It typically has really short flange distance, with softness and color fringes wide open . Best for experimentation and shooting in black and white. Most focal lengths are typically 140mm f/1 (around 140mm diameter). Since you said this is a 380-420, it sounds hard to believe but it could have happen. I would love to see more pictures before making more accurate assessment.

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Originally Posted by renditiont

I collected quite a lot of projection lenses. Yours is a TV projection lens type. It typically has really short flange distance, with softness and color fringes wide open . Best for experimentation and shooting in black and white. Most focal lengths are typically 140mm f/1 (around 140mm diameter). Since you said this is a 380-420, it sounds hard to believe but it could have happen. I would love to see more pictures before making more accurate assessment.

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the focal length is measured empirically : set the lens on a support, looking at something far away ( 250m in my case ). Use a ruler and a matte screen, once the image forms on the matte screen, measure with the tape distance form lens to screen. It gave accurate results for all the other lenses i have ( that have focal length written on them :) )

I`ll get some more images. There is nothing written on it :(.

Also i plan to use this only with paper negatives, so no problems with colour fringing.