Can someone teach me a few things about projector lenses?

[slashmaster]

I want to know a few things about projector lenses. Like are zoom lenses something to stay away from if you want a sharper image? Will long throw lenses give a sharper image than short throw? I have one of these http://www.javaphoto.com/Images/bandhclamshell.jpg it's problem is I can look at the center of the screen and get a very sharp image but the edges of the screen won't be so sharp, if I get the edge of the screen sharp the center wont be so sharp. I've tried using the same size lenses from 2 earlier bell and howell regular 8 projectors which are almost the same as this, but the results seemed to be about the same. The lens says on it "INCRELITE 1 INCH f/1.6 BELL & HOWELL MADE IN U.S.A." the diameter where it screws into the gate is 7/8" and the tip you turn with your finges is 1". Would I be able to use a lens from other projectors in that gate? Are lenses of that size poor quality? Anything else I can do to get a better picture?

[beamascope]

I don't have an answer myself. I was going to say it sounds like maybe an element in the lens is backwards but you say you've used other lenses with the same results so I doubt all of them have flipped elements. Any chance the film is not lying flat enough in the gate? Do the older model projectors you borrowed the lenses from do it also? Maybe the projector has been damaged/dropped in the past? Just guessing.

[BMasson]

If you are projecting Reg-8mm film, I would recomend a Bolex projector with one of their lenses. I like the M8 model, and use either the 15mm or 20mm lens. You should be able to nail one on ebay for about $30.00 or so. The glass supplied with the Bolex machines is a step above what you have now. As far as zoom lenses are concerned, I have one for my super-8 projector, and I am very happy with it. Again, it is a Kern lens made for the Boles SM8. (Super-8 model). I hope I have been of some help. Good luck with your projecting. Brad M

[slashmaster]

I don't have an answer myself. I was going to say it sounds like maybe an element in the lens is backwards but you say you've used other lenses with the same results so I doubt all of them have flipped elements. Any chance the film is not lying flat enough in the gate? Do the older model projectors you borrowed the lenses from do it also? Maybe the projector has been damaged/dropped in the past? Just guessing.

These lenses might be sealed, would be very hard to twist apart if that is even how they come apart, they look clean inside.
The older regular 8 projectors do it with all 3 of my lenses as well, but not as extreme because regular 8 is a smaller picture frame which will fit in the area I can get sharp better. I never dropped this projector, I already know about the allen screw that the gate shuts against which I can adjust in or out but that seems to be set about right.

[slashmaster]

If you are projecting Reg-8mm film, I would recomend a Bolex projector with one of their lenses. I like the M8 model, and use either the 15mm or 20mm lens. You should be able to nail one on ebay for about $30.00 or so. The glass supplied with the Bolex machines is a step above what you have now. As far as zoom lenses are concerned, I have one for my super-8 projector, and I am very happy with it. Again, it is a Kern lens made for the Boles SM8. (Super-8 model). I hope I have been of some help. Good luck with your projecting. Brad M

Thanks Brad, So you use a 15mm and 20mm lens in your bolex? What are each of them for? Is one a longer throw than the other? Do you adjust this lens by turning it in or out or does it have a gear rack? I'm trying to figure out if it will fit my B & H.

[BMasson]

The 15mm lens gives me a bigger picture. I project about 19 feet from my screen; so at that distance, the image is around 6.5 feet wide. With the 20mm lens, the image on the screen is 5.5 feet wide. Of course the 20mm lens gives slightly better contrast and resolution, because you are not blowing up the image as much. These lenses screw in and out for focus adjustment. At this moment, I don't have the lenses handy; otherwise I would measure the diameter for you. So I'm not sure if they would work in your B&H. Perhaps someone else could supply the answer to that question. This is part of what makes filming so interesting--It's just not a simple push-button operation.