| dracul |
| anyone? Can i use this shorter FL projection lens with the 320mm Double fresnel all behind the lcd? |
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| superdaveumo |
| This might work with a small LCD that you suggest. Haven't tried it myself. But, the specs seem ok. Again, don't know. It's $12. Just try it. Doesn't work, sell it on E-bay. |
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| Guy Grotke |
lenses from photocopiers can cover an 8.5" by 11" piece of paper perfectly with the lens midway between the object and the image. (1:1 copying) If you want to put the screen farther away, then the LCD to lens distance will shrink a bit. You might cover a 9" by 12" LCD (AKA 15" diagonal), or you might not.
But it should cover a 6.2" LCD just fine, with any throw distance you want.
The 75 mm diameter is not so great. You will have to tune the condensor system just right to get much light through the lens. With a lens fl of 9" and a throw distance of 132", you would have a LCD-to-lens distance of 9.66" (245 mm). I would use a pair of 220 mm fl fresnels in a split design. That would get the most light into that lens. |
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| dracul |
| quote: | | The 75 mm diameter is not so great. You will have to tune the condensor system just right to get much light through the lens |
I dont understand this. Why is it necessary to fill the back diameter of the lens. I thought the purpose was just to focus all the light from the fresnels to the objective.
What happens if i use a 135mm diameter triplet with the same FL?
So what diameter triplet do you recomend instead of 75mm diameter? |
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| Guy Grotke |
No, I think you get even less light through the B&L lens, since it is only 50 mm in diameter.
If you get the fresnels selected and adjusted correctly, then they can focus an image of the lamp arc right at the optical center of the projection lens. That gets the most light through the lens.
If you have the arc image focussed before the lens, then a lot of the light doesn't even hit the lens. Much of the rest of it enters the first lens element, but then hits the mounting tube.
If you have the arc image focussed past the lens, then most of the light ends up on the board the lens is mounted in.
The size of the arc image is a product of the arc and the distances:
image size = arc size * (fresnels-to-arc-image / arc-to-fresnels)
With a pair of 220 fresnels, a 24 mm arc gives you a 24 mm arc image. Should be easy to get that through a 50 mm diamter lens, but your LCD may also diffuse the light (to improve the viewing angle). In that case, the bigger the lens, the more of that diffused light gets through it.
I am sure you can get the copy lens to work fine. Just make sure you get the fresnels adjusted. |
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| dracul |
| quote: | | If you get the fresnels selected and adjusted correctly, then they can focus an image of the lamp arc right at the optical center of the projection lens. That gets the most light through the lens |
Ok but why did you say a 75mm diameter lens is not so good. If the arc is say 24mm on the back of the lens and centered then I imagine a larger diameter lens is better since there is no risk of light hitting the walls of the lens inside.
| quote: | | but your LCD may also diffuse the light (to improve the viewing angle). |
I have removed the AG layer so the diffusion should be less but are you saying even with the AG removed from the lcd it still diffuses the arc preventing the arc to be 24mm on the objective? |
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| Guy Grotke |
I didn't know you removed the AG layer. I did that with my 15" Proview and it changed my big diffuse blob of light into a beautiful arc image that I centered right in the middle of my lens. Screen Lux was doubled!
Using a bigger lens would probably not give you any more light. That only helps if you have a lot of diffuse light to capture. But you will get loads of light through the 75 mm diameter lens.
You need the 220 mm field fresnel to match your LCD-to-lens distance, but you could try to get a shorter focal length fresnel for the condensor fresnel. That would put the arc closer and capture more light. Or use a pre-condensor lens with a 220 mm fresnel. Either of these will get more light through your LCD, but will also make your arc image bigger. But with that 75 mm diameter lens, you can afford to double the size of the arc image. |
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| dracul |
| Ok. thanks so sounds like the plummer is your first recomendation in this case. |
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| shaggy473 |
| I bought the plummer lenses myself for my 5" PSone screen projector. Not complete, but have ran a test to check it out. Seems to work well. |
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| dracul |
| so you your projector done with the plummer lens? |
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| I_eat_flowers |
hi dracul,
i used this for a psone and it works perfect.
75 mm is great when all the light pass thru. the more light passes the brighter is your projection.
just my 2 cents. |
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| dracul |
| so what size of image on the screen are you getting at what distance are you viewing ? |
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| jbelk |
| Guys, sorry to crash this tread but I'm out of the diy lcd projector for a while due to a family crisis. I have 2 two 18” F.L lenses for sale one is a diyprojectorcompany lens the other I got from ebay it’s a Bessler opaque projector lens. Both lenses are in mint condition. If anybody interested make me an offer my email is jbelkhadir@yahoo.com. I rather sale them to a diyer than put them on ebay. Thanks! |
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| pceng |
i also bought one of these plummer lens from ss.
i just wanted to ask what the condition were the lenses in from the other folks who purchased one?
the one i received has some scutta on the inside and outside surfaces. ....:(
i realize that these are surplus but i doubt if this will be useable without showing the defects on the screen. |
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| Guy Grotke |
What you think is a dirty lens, may just be anti-reflective coating. Sometimes the coating is uneven and grainy looking, but the lens still works fine. (Or it could be mold.) It may not pass quite as much light as one with less gunk, but you would be hard pressed to measure the difference even with a light meter.
Chips and cracks will affect the image, but not the way you would think. They don't show up as a visible artifact on the screen. Instead, they just send some rays off in the wrong directions, so your image is not as sharp as it should be. For example, the contrast would be decreased so black areas (ie. the screendoor pattern between pixels) would be not be very dark. This is because the surfaces of the lens are not in the plane of the object (the LCD) or the image (the screen). Rays from each pixel strike all parts of the lens and then get refracted back to a single point on the screen. If defects in the lens block some of those rays, it just results in a dimmer point on the screen.
Try the lens before rejecting it. I bet it works fine. |
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| pceng |
hi guy,
i have been lurking about for several months now to get up to speed and not ask too many stupid questions. i have read a lot of your posts and respect your opinions. thanks for your contributions to this forum.
some of the defects do look like they could be fungus. some kind of look like water spots. these are on the inside surfaces so i guess i would have to disassemble it and clean them up. any recommendations on what is safe to use? i would prefer common household cleaners if possible.
i will try it out before cleaning first just to make sure that cleaning would be necessary. |
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| Guy Grotke |
I would try lens cleaning solution, like the kind of stuff they sell for cleaning eyeglasses. The issue would be that it could be a water-soluable lens coating, so it would not be difficult to clean the coating right off.
But the worst you could do with even alcohol or detergent solution, would be to remove the coating and end up with a clean uncoated lens. First try cleaning the last surface of the lens (the glass surface that faces the screen). If you remove lens coating from there it does not matter.
Start with a lens cleaning tissue or clean soft cloth with condensation from your breath. If that doesn't do anything, try distilled or deionized water, then try dishwashing detergent in warm water. If some point gives you a fairly clean-looking surface, stop there, rinse with distilled water, and dry it.
If you have a lens coating intact, you will be able to see a slight color tint when you look at the lens from an angle.
Whatever works on the last surface should work on all the rest. The Surplus Shed websight says that Plummer copy lens comes apart with retaining rings, so you can get to all the surfaces. Make sure everything is DRY DRY DRY before you reassemble it, so you don't get condensation inside. |
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| dracul |
guy grotke,
Can you please give me your opionion on this lens
this is what i bought. Will it work with a 17 inch lcd perfectly? Did I get a good deal? 6 elements baby!!!! Thats got to be sharper then a pro triplet from LL. I was told clear diameter inside capture ring is 2.4 inches.
http://cgi.ebay.com/ws/eBayISAPI.dl...AMEWA%3AIT&rd=1
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| Guy Grotke |
| Sorry, that URL is not working for me. Post the eBay item number, and I will have a look at it. |
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| Guy Grotke |
That Gerogon is not a process lens, it is a very good color-corrected enlarger lens. It has a focal length of 360 mm and a maximum f-stop of f9. That means the clear aperature is only 360/9 = 40 mm. You see how the middle of the lens is much smaller than the outer lenses? You may have a difficult time getting much light through this lens. (That does not matter for an enlarger, since you can just increase the exposure time.) You will have to use a brightview LCD, or an LCD that you can remove the antiglare layer. Then adjust the fresnel distances perfectly to get the arc image right at the center of the lens.
The Rodenstock website I have used to look up lens data does not have the Gerogon. I think it is obsolete.
http://www.prograf.ru/rodenstock/largeformat_en.html
So I don't know the maximum angle of coverage for this lens. But I think the chances are good that it will cover a 17" LCD. I bet it could cover a an 11" by 14" print from an 8" by 10" negative. You can use the usual equations to calculate the distances to do that, and then determine the angles to the corners of both. Do the same calculation for a projector and see if the required angles are the same or less.
In summary, I think you will get a perfectly-focussed image from corner to corner but you will have to work very hard to get it bright. Let us know how it works out. |
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| dracul |
| The seller told me the clear glass aperture inside the capture ring is 60mm. Another words with the aperture wide open at f/9 there is 60mm diameter glass that is clear to allow light to pass through. So are you saying if you had a 360mm FL lens with a 2.8 max aperture you would have a 128mm diameter ? |
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| Guy Grotke |
The "clear aperture" may be very different from the diameter of either of the outer lenses. Lenses that have an adjustable aperture (like this one) usually put it right in the middle. Decreasing the size of the aperture makes it focus sharper and also makes the amount of light getting to different areas of the film more even. But it does that by blocking the extra light that would have fallen in the center of the image.
Like I said, that is fine for photography because you can just increase the exposure time. Not useful for projection, unless you think your screen image is too bright!
Anyway, "clear aperature" is always focal length/f-stop. The internal light path may be physically larger or smaller than that, but the light path can be converged or diverged by the outer lenses before it gets to the most narrow opening inside the lens. The f-stop numbers take that into account, so you can use any lens with the same focal length and f-stop setting and you will get the same amount of light to the center of the film. |
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| dracul |
| damn so sounds like i have to desist and eat a negative feedback. Am I blocked for buying temporarily when getting a negative feedback as a buyer? |
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| Guy Grotke |
No, you don't get blocked, but the seller can post exactly why he gave you the negative feedback. You then get to post a reply to that. Some sellers then may choose to reject your bids, but that is not automatic. If you can come up with an adequate excuse, and have lots of positive feedback to balance it out, then eventually the sellers will "forgive" you.
If you do fail to buy the item that you bid for, then you will cause the seller a loss in the amount he spent for the auction as well as his time to create the auction posting. I suggest that you go ahead and buy the lens so you can give it a try. You might be very happy with it. It will certainly give you a very sharp image. We just don't know how bright or how wide the object field will be. The only way to find out is to try it!
If you later decide you want to go with a different lens, you can sell it on eBay. So you will not get stuck with it. |
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| AustynSN |
| If you don't want negative feedback, or the lens, then I'd suggest contacting the buyer, explaining that you made a mistake and the lens wasn't what you needed and (This is the most important part) offer to cover his ebay costs. Your loss for a lens you don't need should be quite a bit less, his/her unfair loss to eBay will be nonexistant, and you'll not receive negative feedback. If (s)he doesn't like that idea of course, you should then still complete the transaction. (And of course, leave positive feedback for him/her. Be it for shipping you the lens, or accepting a consolation payment). Even if you do have to buy the lens, you could always just turn right around and sell it on eBay yourself. |
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