Dazzla Said: "Yes filling the entire lens aperture will work with the 135mm FL triplet and yes filling the entire lens aperture of a singlet will work. But filling the entire lens aperture of all lens types wont work and more aberrations will be present"
I would like to se an example of non working setup filling the rear lens, (i did a example of non working setup with focusing at optical center).
by the way, where is Guy Grotke? 😀 he has very intersting things to show us also... Maybe he spends more time on DBG since he become moderator 😀
I would like to se an example of non working setup filling the rear lens, (i did a example of non working setup with focusing at optical center).
by the way, where is Guy Grotke? 😀 he has very intersting things to show us also... Maybe he spends more time on DBG since he become moderator 😀
Where am I?
Yes, I have moderator status on DIYBG forum, but I have had that for months and used it exactly once to delete a post at the poster's request. I spend much more time right here answering your posts and emails, Rox!
Where I really spend most of my time is on my full time job, writing verification software for a new VDSL chip design before it gets made into silicon.
Besides, there are other people on this forum who are doing a great job of answering your posts before I get to them. And I suspect some of them know a lot more about optics than I do. 😀
Your example of the symmetric duplet that is too small in diameter has nothing to do with where the arc image gets focussed. It just has too small a maximum field angle for the application. If you try drawing the same thing using a diameter that is large enough, you will see that focussing the arc image at the optical center gives you the largest field angle.
Yes, I have moderator status on DIYBG forum, but I have had that for months and used it exactly once to delete a post at the poster's request. I spend much more time right here answering your posts and emails, Rox!
Where I really spend most of my time is on my full time job, writing verification software for a new VDSL chip design before it gets made into silicon.
Besides, there are other people on this forum who are doing a great job of answering your posts before I get to them. And I suspect some of them know a lot more about optics than I do. 😀
Your example of the symmetric duplet that is too small in diameter has nothing to do with where the arc image gets focussed. It just has too small a maximum field angle for the application. If you try drawing the same thing using a diameter that is large enough, you will see that focussing the arc image at the optical center gives you the largest field angle.
and about post 73 you have something to coment?
about the simetrical doublet it was just a stupid example. It could be that the field angle is not sificent... maybe a wide angle projectio lens would be a better example...
now forget it, i would like to see a example with my ideal setup not working.
about the simetrical doublet it was just a stupid example. It could be that the field angle is not sificent... maybe a wide angle projectio lens would be a better example...
now forget it, i would like to see a example with my ideal setup not working.
response to message 73
I understand message 73, but it is based on something you said in message 75:
"I believe this thing i am calling 'small lens area working on small lcd area' is much important than the aberrations introduced by the lens when you are on the outer limit. "
I just don't share your belief, because I don't think the light from a single pixel really falls on a small area of the lens. In simple spherical lenses, the spherical aberration is the most significant problem and it gets much worse the farther the light path is from the center of the lens. We don't have any idea how well the 450 mm fl triplet is corrected, but I can tell you from my experience using the OSLO optical modelling program that the corrections of a well-designed triplet are usually made so the maximum aberrations occur at the center and the edges of the lens. Half way from the center usually has the best correction. The aberration at the center does not matter at all, because light going through the center does not get refracted to a different direction. So the edges are where the poorest performance is.
Another thing to think about: A projection lens for an LCD does not need to be very good, because the size of each pixel on the screen is so large. But it does need to have a large enough field angle to get the corners lit. Focussing the arc image at the center of the lens gives you the widest field angle. Focussing past the center may cut off some of the light from the corners of the LCD. Not enough to give you black corners, since the light from those pixels gets spread over a (ie. 60 mm) circle. But enough of that light can get blocked to make them dim.
But all of this is just speculation: There are too many unknown parameters for the 450 mm fl triplet. We could discuss this forever and never reach any conclusions. Somebody has to get one and make some measurements.
I understand message 73, but it is based on something you said in message 75:
"I believe this thing i am calling 'small lens area working on small lcd area' is much important than the aberrations introduced by the lens when you are on the outer limit. "
I just don't share your belief, because I don't think the light from a single pixel really falls on a small area of the lens. In simple spherical lenses, the spherical aberration is the most significant problem and it gets much worse the farther the light path is from the center of the lens. We don't have any idea how well the 450 mm fl triplet is corrected, but I can tell you from my experience using the OSLO optical modelling program that the corrections of a well-designed triplet are usually made so the maximum aberrations occur at the center and the edges of the lens. Half way from the center usually has the best correction. The aberration at the center does not matter at all, because light going through the center does not get refracted to a different direction. So the edges are where the poorest performance is.
Another thing to think about: A projection lens for an LCD does not need to be very good, because the size of each pixel on the screen is so large. But it does need to have a large enough field angle to get the corners lit. Focussing the arc image at the center of the lens gives you the widest field angle. Focussing past the center may cut off some of the light from the corners of the LCD. Not enough to give you black corners, since the light from those pixels gets spread over a (ie. 60 mm) circle. But enough of that light can get blocked to make them dim.
But all of this is just speculation: There are too many unknown parameters for the 450 mm fl triplet. We could discuss this forever and never reach any conclusions. Somebody has to get one and make some measurements.
i have received very interesting information from the manufacturer about this triplet but am workin on it yet, í´ll keep you informed, i can advance you that my thoughts are getting warm... bad news for some sellers...
by the way, i would never focus the arc so far that it starts to losse light out of the barrel. The key for me is to focus where the outer light ray (arc edge) fills the rear lens.
just would like to ask you the same question i asked to dazzla but did not reply; if the aberrations are minimal on the center, why do you focus so far on the optical center? if you focus direcly on the lens, i guess the used area would be minimal ever, isn´t it?
by the way, i would never focus the arc so far that it starts to losse light out of the barrel. The key for me is to focus where the outer light ray (arc edge) fills the rear lens.
just would like to ask you the same question i asked to dazzla but did not reply; if the aberrations are minimal on the center, why do you focus so far on the optical center? if you focus direcly on the lens, i guess the used area would be minimal ever, isn´t it?
Final nail in the coffin!
Here is the end of the "focus point for arc image" discussion! I just looked up one of the websites selling the 405 mm fl triplet:
http://www.diyprojectorcompany.com/catalog/product_info.php?cPath=23&products_id=69
They give the barrel length as 159 mm and the lens inner diameter as 135 mm. I made a full-scale drawing of this lens with a 60 mm wide arc image focussed at the center of the lens, and a 60 mm wide arc image focussed at the third lens. Then I projected rays from the upper edge of each of these arc images to the upper barrel at the first lens edge. This shows the maximum field angle the lens can support with 100% of the light getting through the lens. In the drawing below (not very accurate) the arc images are in red, the field angle with the arc image at the center is in blue, and the field angle with the arc at the last lens is in green.
If you focus the arc image at the center of the projection lens, you get a field angle of around 49 degrees. If you focus the arc image at the far lens, then you get a field angle of around 26 degrees. A 17" LCD with a 528 mm distance between the LCD and the lens, needs a field angle of 44.5 degrees. If you get the arc image focussed right at the optical center of the projection lens, then this lens should work perfectly for a 17" LCD. If you focus the arc image at the far lens, then the corners will be dim.
I think we are done now...
Here is the end of the "focus point for arc image" discussion! I just looked up one of the websites selling the 405 mm fl triplet:
http://www.diyprojectorcompany.com/catalog/product_info.php?cPath=23&products_id=69
They give the barrel length as 159 mm and the lens inner diameter as 135 mm. I made a full-scale drawing of this lens with a 60 mm wide arc image focussed at the center of the lens, and a 60 mm wide arc image focussed at the third lens. Then I projected rays from the upper edge of each of these arc images to the upper barrel at the first lens edge. This shows the maximum field angle the lens can support with 100% of the light getting through the lens. In the drawing below (not very accurate) the arc images are in red, the field angle with the arc image at the center is in blue, and the field angle with the arc at the last lens is in green.
If you focus the arc image at the center of the projection lens, you get a field angle of around 49 degrees. If you focus the arc image at the far lens, then you get a field angle of around 26 degrees. A 17" LCD with a 528 mm distance between the LCD and the lens, needs a field angle of 44.5 degrees. If you get the arc image focussed right at the optical center of the projection lens, then this lens should work perfectly for a 17" LCD. If you focus the arc image at the far lens, then the corners will be dim.
I think we are done now...
Attachments
Dazzla; Rox in your example pic you aren't focusing thelight at the centre of the lens
yes, your drawings are with perfect bulb, but mines are with arc lenght at optical center as you have teach me to do. Anyway is stupid example.
just would like to see finaly the setup with my ideal teory (fillng rear lens) not working example. And would like also a reply to the question why don´t you minimize the rear lens area (you could focus exacly there so minmal area and minimal aberrations would be used at center.
Ok i give up with convincing anybody about where to focus with the field lens. I´ll just place the bulb somethng closer to the rear lens than you (if the 550mm field is done by 3dlens) and everibody will be happy.
about triplet field angle, the information manufacturer told me is less than 40 degrees of max field angle the lens was designed for, that has sense if you refract the lines something in your pics GG. Your field angles are considered like if the barrel had no lens, like if it only was a tunel.
Thanks for your help. GG/Dazzla
yes, your drawings are with perfect bulb, but mines are with arc lenght at optical center as you have teach me to do. Anyway is stupid example.
just would like to see finaly the setup with my ideal teory (fillng rear lens) not working example. And would like also a reply to the question why don´t you minimize the rear lens area (you could focus exacly there so minmal area and minimal aberrations would be used at center.
Ok i give up with convincing anybody about where to focus with the field lens. I´ll just place the bulb somethng closer to the rear lens than you (if the 550mm field is done by 3dlens) and everibody will be happy.
about triplet field angle, the information manufacturer told me is less than 40 degrees of max field angle the lens was designed for, that has sense if you refract the lines something in your pics GG. Your field angles are considered like if the barrel had no lens, like if it only was a tunel.
Thanks for your help. GG/Dazzla
anyway, it is great this forum. You can find very interesting people. I don´t know who is correct in this (you or me, i guess you 😀) but the most important thing is that you have defended your teory perfectly.
hope we can learn much more in the future, who knows what strange things can i try to convince you 😀.
hope we can learn much more in the future, who knows what strange things can i try to convince you 😀.
Guy Grotke, have you heard of this?
Another thread reminded me of this. I saw a 'how to' on a site that had something to do with projectors, (sorry, that's all I remember). It showed how to build a plexi or some other type of clear tank into a prism that was filled with water and seemed to be used to correct keystone problems with a projector mounted on a high ceiling.
Does this make any sense?
Thanks
Another thread reminded me of this. I saw a 'how to' on a site that had something to do with projectors, (sorry, that's all I remember). It showed how to build a plexi or some other type of clear tank into a prism that was filled with water and seemed to be used to correct keystone problems with a projector mounted on a high ceiling.
Does this make any sense?
Thanks
keystone
No I have not. I think keystone correction is much more of an issue for tiny commercial projectors. I can't imagine mounting a DIY-size projector on the ceiling!
The best solution for our projectors is just to design them for long-throw, so you can put them on a counter or shelf at the back of the projection room, in line with the center of the screen. Then you don't have any keystone distortion, you get less noise from fans, it's easier to make adjustments and do maintenance, and you see less disturbing light leakage.
And best of all, no stiches on your head from walking into the $%#*&^ thing. 😀
No I have not. I think keystone correction is much more of an issue for tiny commercial projectors. I can't imagine mounting a DIY-size projector on the ceiling!
The best solution for our projectors is just to design them for long-throw, so you can put them on a counter or shelf at the back of the projection room, in line with the center of the screen. Then you don't have any keystone distortion, you get less noise from fans, it's easier to make adjustments and do maintenance, and you see less disturbing light leakage.
And best of all, no stiches on your head from walking into the $%#*&^ thing. 😀
Re: Guy Grotke, have you heard of this?
Is this what you were referring to? http://home.c2i.net/ahustvedt/lens.html
justme said:
Is this what you were referring to? http://home.c2i.net/ahustvedt/lens.html
mike, do you understand how this works? iám triyng to find a ligh path but don´t see it, could you try to post a pic?
Rox, the end result of a an anamorphic lens is to magnify in one direction only. There's a light path diagram here.
http://members.shaw.ca/quadibloc/other/aspint.htm
http://members.shaw.ca/quadibloc/other/aspint.htm
- Status
- Not open for further replies.