Hi All,
This lens looks pretty neat:
http://www.surplusshed.com/pages/item/l3003.html
and the price is right, $11 🙂
But how do you know if it's suitable to project a 15" source? Is there a way to work out the maximum source size (LCD size) that this lens can project? They don't tell us the Field-of-View. Help me, I'm a little clueless 🙂
-Peter.
This lens looks pretty neat:
http://www.surplusshed.com/pages/item/l3003.html
An externally hosted image should be here but it was not working when we last tested it.
and the price is right, $11 🙂
But how do you know if it's suitable to project a 15" source? Is there a way to work out the maximum source size (LCD size) that this lens can project? They don't tell us the Field-of-View. Help me, I'm a little clueless 🙂
-Peter.
Although this Fujinon Lens has been used by many DIYers with great success here , it is not available any more from Surplus Shed
If you do a search for it in their db you will not find it.
I ordered this one last week
link
to do some experimenting. It does have an Iris filter which is not necessary for a projector but I will do some testing and see how it goes.
Cheers
If you do a search for it in their db you will not find it.
I ordered this one last week
link
to do some experimenting. It does have an Iris filter which is not necessary for a projector but I will do some testing and see how it goes.
Cheers
field angle
Nobody can tell you the field of view in terms of the number inches across the LCD, because you can project any size LCD just by moving it far enough from the lens!
If you know how far away the LCD will be from the lens, then you can calculate how many degrees of field angle you need. If this is a triplet, then it will have a useful field angle of 45 degrees. If you use a symmetrical duplet, then you get only 30 degrees.
Nobody can tell you the field of view in terms of the number inches across the LCD, because you can project any size LCD just by moving it far enough from the lens!
If you know how far away the LCD will be from the lens, then you can calculate how many degrees of field angle you need. If this is a triplet, then it will have a useful field angle of 45 degrees. If you use a symmetrical duplet, then you get only 30 degrees.
Hmm, 45 degrees you say? Now I'm a little confused.
At a certain well known online store, they're selling fresnels with a 317mm focal length, for use with 15" monitors. I worked out (I think my math is right 🙂) that if you put the triplet 317mm away from a 12" wide LCD/Fresnel, you need 51 degrees to see the entire screen.
At a certain well known online store, they're selling fresnels with a 317mm focal length, for use with 15" monitors. I worked out (I think my math is right 🙂) that if you put the triplet 317mm away from a 12" wide LCD/Fresnel, you need 51 degrees to see the entire screen.
field of view
Triplets work very well up to 45 degrees of field angle. That doesn't mean they can't do reasonably with a bit more angle. Symmetrical duplets (a pair of PCX lenses) are used in cheaper OHPs, and they get more than the optimal 30 degree field angle.
And there are other lens designs, like the metrogon, that work well up to 90 degrees of field! Those only take four lens elements. (They just don't capture as much light as a triplet with the same diameter, for photography.)
Are you sure those fresnels they are selling are 317 mm fl? Not 330 mm? 330 is much more standard, and would be a much better fit to a 317 mm fl projection lens.
Triplets work very well up to 45 degrees of field angle. That doesn't mean they can't do reasonably with a bit more angle. Symmetrical duplets (a pair of PCX lenses) are used in cheaper OHPs, and they get more than the optimal 30 degree field angle.
And there are other lens designs, like the metrogon, that work well up to 90 degrees of field! Those only take four lens elements. (They just don't capture as much light as a triplet with the same diameter, for photography.)
Are you sure those fresnels they are selling are 317 mm fl? Not 330 mm? 330 is much more standard, and would be a much better fit to a 317 mm fl projection lens.
Yep you're right, it's 330mm, not 317mm.
Now I'm getting a 60deg FOV (30deg for the half-view above).
An externally hosted image should be here but it was not working when we last tested it.
Now I'm getting a 60deg FOV (30deg for the half-view above).
field angle
>60 degrees of field angle
Okay, but that is what the upper fresnel is doing when it bends parallel light to a focal point Every kind of positive lens can do that, and you can get some extreme condensor lenses that have focal lengths shorter than their diameter.
But that is very different from a projection lens. A projector lens is never used with an object right at its focal length, because then the screen would have to be an infinite distance away. In the case of the 317 mm fl projection lens, lets assume you are pointing it at a wall 10 feet away.
1/lens fl = 1/object to lens + 1/ lens to screen
So the object to screen distance would be 353.8 mm. Using Pythagorean Theorum the distance from the lens to the corner of the screen would be 401.8 mm. So the half field angle would be 28.3 degrees and the full field angle would be 56.6 degrees. Of course that would give you a 129" diagonal image, so using such a short lens with a 15" LCD may not be such a great idea.
I am using a 571 mm fl lens with my 15" LCD projector. With a throw distance of 163 inches, I am getting a nice bright 94" image. And my projection lens field angle is only about 32 degrees. That's why I can get away with a cheap positive meniscus lens instead of a triplet.
>60 degrees of field angle
Okay, but that is what the upper fresnel is doing when it bends parallel light to a focal point Every kind of positive lens can do that, and you can get some extreme condensor lenses that have focal lengths shorter than their diameter.
But that is very different from a projection lens. A projector lens is never used with an object right at its focal length, because then the screen would have to be an infinite distance away. In the case of the 317 mm fl projection lens, lets assume you are pointing it at a wall 10 feet away.
1/lens fl = 1/object to lens + 1/ lens to screen
So the object to screen distance would be 353.8 mm. Using Pythagorean Theorum the distance from the lens to the corner of the screen would be 401.8 mm. So the half field angle would be 28.3 degrees and the full field angle would be 56.6 degrees. Of course that would give you a 129" diagonal image, so using such a short lens with a 15" LCD may not be such a great idea.
I am using a 571 mm fl lens with my 15" LCD projector. With a throw distance of 163 inches, I am getting a nice bright 94" image. And my projection lens field angle is only about 32 degrees. That's why I can get away with a cheap positive meniscus lens instead of a triplet.
lense help----me too
no message icon cuz i could't find one that looked stupid enough
Hi, I bought an old slide projector today thinking that even it I couldn't use any of the parts at least I could get some hands-on experience to help with all the theory I've been reading about.
The lamp is to weak even though it's 500 watts, (about a third of the nominal lumens suggested and only 3200k) but I thought maybe the condenser and objective lenses would be of some use.
The condenser is what I believe to be very standard, (it looks just like several I've seen used in these projects. The objective lense housing is about 3&3/8 inches long and 2&3/8 inches diameter the actual lense seems about 1&1/4 inches diameter. It is marked
COATED ANASTIGMAT f3.5 4INCH
I think that anastigmat may be another way to describe a triplet.
The LCD I plan on using is 5.6 inches nominal, (I haven't got it yet so I'm not sure)
ANY information would be helpful
Thanksthink
no message icon cuz i could't find one that looked stupid enough
Hi, I bought an old slide projector today thinking that even it I couldn't use any of the parts at least I could get some hands-on experience to help with all the theory I've been reading about.
The lamp is to weak even though it's 500 watts, (about a third of the nominal lumens suggested and only 3200k) but I thought maybe the condenser and objective lenses would be of some use.
The condenser is what I believe to be very standard, (it looks just like several I've seen used in these projects. The objective lense housing is about 3&3/8 inches long and 2&3/8 inches diameter the actual lense seems about 1&1/4 inches diameter. It is marked
COATED ANASTIGMAT f3.5 4INCH
I think that anastigmat may be another way to describe a triplet.
The LCD I plan on using is 5.6 inches nominal, (I haven't got it yet so I'm not sure)
ANY information would be helpful
Thanksthink
slide projector lenses
Are great for projecting slides. No good for anything much bigger. For a 5.6" LCD you might find a really big CRT projection lens, but I doubt it. I think you could use a surplus copy lens, like shown in this thread.
240 mm fl would give you a 65" diagonal image from 10 feet.
Are great for projecting slides. No good for anything much bigger. For a 5.6" LCD you might find a really big CRT projection lens, but I doubt it. I think you could use a surplus copy lens, like shown in this thread.
240 mm fl would give you a 65" diagonal image from 10 feet.
slide projector lenses
Thanks for the info. Is it because the surface area of the LCD is too large or is it the thickness of the panel?
Thanks for the info. Is it because the surface area of the LCD is too large or is it the thickness of the panel?
slide projector lenses
These lenses generally have a very short back focal length, so you have to get the LCD panel very close to the lens in order to get it to focus. With it that close to the lens, the field of view is restricted to something not much bigger than a slide. Maybe 1.5" at the most.
These lenses generally have a very short back focal length, so you have to get the LCD panel very close to the lens in order to get it to focus. With it that close to the lens, the field of view is restricted to something not much bigger than a slide. Maybe 1.5" at the most.
dismembering fresnels
I have a "rule of thumb" question only looking for a general answer if there is one.
I have read that altering the size of a fresnel lense will alter fl.
shorter or longer?
Or is it more complicated than that.
thanks
I have a "rule of thumb" question only looking for a general answer if there is one.
I have read that altering the size of a fresnel lense will alter fl.
shorter or longer?
Or is it more complicated than that.
thanks
condusing fl with f#
It doesn't change the focal length when you change the size, because the focal length is the distance to the point where all the parallel light going in the rough side focuses on the smooth side. (Assuming a positive lens.) Even if you block out or remove parts of the fresnel, the light through the rest of it still goes to the same place.
It does change the f number, which is defined as (focal length) / (lens diameter). This is the measure of light gathering capacity commonly used for photographic lenses. Not so important for fresnels used in projectors.
It doesn't change the focal length when you change the size, because the focal length is the distance to the point where all the parallel light going in the rough side focuses on the smooth side. (Assuming a positive lens.) Even if you block out or remove parts of the fresnel, the light through the rest of it still goes to the same place.
It does change the f number, which is defined as (focal length) / (lens diameter). This is the measure of light gathering capacity commonly used for photographic lenses. Not so important for fresnels used in projectors.
fl & f
Thanks Guy
I'm sure I read the fl thing on some diy projector site I've been checking out a lot of them even ones that are no longer active. One of the problems with these kind of discussions is that along with the people that have done significant research and testing of their ideas you have people who think that they are knowledgable. For someone like me it's not always easy to tell the difference.
Thanks again for the correction.
Thanks Guy
I'm sure I read the fl thing on some diy projector site I've been checking out a lot of them even ones that are no longer active. One of the problems with these kind of discussions is that along with the people that have done significant research and testing of their ideas you have people who think that they are knowledgable. For someone like me it's not always easy to tell the difference.
Thanks again for the correction.
How good is this
Hi
Anybody have an opinion on the condenser setup from my dismembered slide projector. since it's already mounted and all I would have to do is locate the rest of the optics, (and maybe a real lamp) and I'm ready to rehouse it. It's only for a 5.6" that I'm playing with as a learning experience.
thanks
Hi
Anybody have an opinion on the condenser setup from my dismembered slide projector. since it's already mounted and all I would have to do is locate the rest of the optics, (and maybe a real lamp) and I'm ready to rehouse it. It's only for a 5.6" that I'm playing with as a learning experience.
thanks
Attachments
condensor lenses
You could give either or both of those condensor lens a try. Put them up to your lamp and look at the cone of light they send to a piece of white paper or a nearby white wall. If you can get some arrangement to generate a cone that fits your lower fresnel's size and focal length, then you could use that in your projector.
Protect your eyes if you have a bare MH lamp running! Snow blindness is not fun, and it could be permanent damage...
You could give either or both of those condensor lens a try. Put them up to your lamp and look at the cone of light they send to a piece of white paper or a nearby white wall. If you can get some arrangement to generate a cone that fits your lower fresnel's size and focal length, then you could use that in your projector.
Protect your eyes if you have a bare MH lamp running! Snow blindness is not fun, and it could be permanent damage...
my condensors & lamp
Hi, I'm going to post some pictures with hope of a second opinion. Please before you decide to lecture me about the lamp quality not that this is only a prelimanary setup. It's the setup as it was in the old slide projector except for where I've bent the aluminum framing. I'm thinking that this will be enough to test with once I get the 5.6" lcd and triplet lense.
I have tested with this setup and a picture printed out on plain white paper between the two fresnels and focused with a lense yanked off of an old film/photo to video transfer device. It showed a picture but obviously not a very good one.
One of the things is that I'm not expecting perfection with this so called "high resolution" display. I have deciphered the manor in which many of the sellers are determining the resolution of these units and the only thing high was them.
OK from the top
Hi, I'm going to post some pictures with hope of a second opinion. Please before you decide to lecture me about the lamp quality not that this is only a prelimanary setup. It's the setup as it was in the old slide projector except for where I've bent the aluminum framing. I'm thinking that this will be enough to test with once I get the 5.6" lcd and triplet lense.
I have tested with this setup and a picture printed out on plain white paper between the two fresnels and focused with a lense yanked off of an old film/photo to video transfer device. It showed a picture but obviously not a very good one.
One of the things is that I'm not expecting perfection with this so called "high resolution" display. I have deciphered the manor in which many of the sellers are determining the resolution of these units and the only thing high was them.
OK from the top
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