12" EF Projection Lens

[Hagadin]

Hey all,

I'm not a large format photographer, I'm a tinkerer, but I have a question I was thinking you guys would have no problem answering. I'm thinking of purchasing a Bausch & Lomb Balopticon C magic lantern projector with a 12" EF lens. The idea is to replace the slide holder with a slide holder of my own that contains a little 3.5" LCD screen so I'll have a really neat antique as my movie projector. I don't know anything about lenses however and wanted some clarification on whether or not the lens that appears to come with the projector is an appropriate one for a distance of 15'-20'. What size screen would I have at that range?

Thanks in advance for your responses!

[Dan Dozer]

While techinically the lens might work, the resolution on the wall/screen will likely be not what you are expecting. The old magic lantern lenses are usually petzval lenses and I would think that your projected image would be fuzzy around the edges and only in focus in the center.

I think that your much greater problem, and I'm sure that others will say this also, is that your image from your LDC screen is likely to be not nearly strong/bright enought to project an image that is usable or visible especially at that long of a distance. It might not even be bright enought to project an image only just a few feet.

[Hagadin]

Actually I will be stripping the backlight off of the LCD screen and using that 600w Mazda Edison bulb. Should be good enough to project 20' in daylight with all the lights in the house on.

sorry to hear about that petzval lens, though. Although I thank you for using the name so I can do some research and see what i'm up against now. :)

Edit: So I found this after a bit more digging on your forum. Sorry I missed it before.

http://www.largeformatphotography.info/forum/showthread.php?t=63183

The post appears to be about a 15" B&L lens of the same type (I'm guessing) and they're calling it a triplet. Would I be correct in thinking that a triplet would better suit my purpose than a petzval?

[eddie]

The B&L 12 inch EF lens may in fact be a triplet.

[Jim Jones]

Actually I will be stripping the backlight off of the LCD screen and using that 600w Mazda Edison bulb. Should be good enough to project 20' in daylight with all the lights in the house on. . . .

May also be good enough to fry the LCD screen.

[Hagadin]

The operating temp of the LCD screen is up to 60C, but I've read that I really don't want to operate it over 40C if I want any kind of longevity. Since I have to put in a 12V rail for the LCD screen anyway I've decided to put in a couple of computer fans along with it. My suspicion though, and I won't know until the balopticon is in my hands, that I won't really have clearance for the fans around that big 600w monster bulb. I shall see.