Hey all. In hunting for a slide projector to use for a 2.5" cheapie setup, I found that the surplus store around the corner from my office has a bunch of CRT projection lenses (at least, that's what I think they are) and 4" LCD's that accept composite video. Hmmm...

I am NO expert on optics, but holding the projection lens up in front of the LCD, I was able to see the whole LCD if I had my eye the correct distance away from the output or downstream side of the lens. To me, this suggests that the FOV of this lens should be sufficient for this application. If I moved my eye further from the lens, I could not see the whole LCD. If I moved my eye closer, I could see more than just the LCD.

Questions:

1) DOES my quickie in-the-store test suggest that the FOV of this lens is OK?

2) Other than buying it and building a light engine and trying to project something through it, is there a simple test to determine if this lens is suitable for projection?

3) Is focusing sunlight to a point the best way to determine the focal length of this lens? If so, exactly how should I do this? I'm thinking shine sunlight "backwards" through the lens, measure the length at which the sunlight gets focused to a point, and then that would be the distance I'd want between the LCD panel and the lens.


Thanks for any info or advice,

CRT projection lenses can "see" whatever their diameter is. They are designed to be very close to the screen. If you have a 6inch lens then it will see a 6 inch LCD. Be aware there are two types of CRT projection lenses. One type is optimized for curved CRT's and the other is optimized for flat CRT's. You'll need to track down what projector used that specific lens, and if the CRT was a curved screen or a flat screen. If you use a lens designed for a curved CRT on a flat LCD, you will have focusing issues on the corners of your projected image. Curt Palme deals in CRT projectors and may be able to help you if you need any information on your lens. Here is a link to his site. http://www.curtpalme.com/

OK, looking at more CRT projectors online, I can see that the lenses at the surplus shop are not CRT PJ lenses. However, they are almost 4" in diameter on the inlet side (maybe 2.5" dia on the outlet). I think I might just have to pick one up and experiment with it and a piece of white cardboard in front of my 19" LCD in the dark to just kinda see what happens.


Take it easy,

What happened is that I found out that I can't use this lens like I was hoping I might, which is no surprise. The focal lenth is too long for what I want to do.

I know that people have scored a CRT PJ lens cheap off eBay or surplus shed, but I'm having probs finding one. Any pointers? I guess I'll contact curt palme and see what he has to say about it.


Take it easy,

I have one it called a delta II they are on ebay some times I had three but I scraped two. The rear fl is .5" and the throw is large the lense is triplet and all pvc and it has a rear lens size of 4.75" a 4" LCD would be good. I have more in shipping than the bid cost. I don't realy need it you can have it cheep. I'll grap a photo

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Click to view attachment

Thanks a million for your kind offer. Curt Palme has hooked me up and there's a lens on its way to me from BC right now. I didn't even realize until I had sent the order that he is in Canada too (I'm in Toronto) which will happily negate the ridiculous cross-border shipping, customs, and brokerage fees. What's coming my way is an "HD 6" lens. I know nothing about it, except I stated my requirements and he replied with:


He replied immediately, was very friendly and helpful in sorting out what I need, and gave me what seems like quite a good deal.

Depending on how this project works out, though, I might wanna do a few more, so I might still come after you for that lens at some point!


Thanks again,