The best sized lenses

Mitch · 4th August 2002, 05:35 AM

Hi guys,
I have a question for ya. If I got ahold of a 98mm big screen TV projection lens, would that be big enough to project a 14" LCD screen?
Its a PCX, so would this mess up the projection onto a flat projection screen? For that type of screen, I don`t know if a flat lens or a PCX is better.

Thanks for your help,
Mitch

xblocker · 4th August 2002, 12:33 PM

Mitch,
1. it depends of the focal lenght, which in your case should have minimum panels diagonal size (14")
2. as stated over and over , a single lens always have spherical abberations, which don't let you focus the complete image properly. So a single lens can only give a rough projection quality.

BTW, what do you mean with PCX vs plan lens?

xblocker

jason1971 · 4th August 2002, 03:05 PM

I think I'm going to need some clarification here. Do we need in all circumstances a lense with the focal length of the screen's diagonal, or is that only in the case of not using a fresnel lense to project the light path down. Please correct me if I'm wrong, but I have been working off the assumption that we use the fresnel to condense the light path down to a smaller size so that the lense we use to project the image is fooled into thinking that the image is actually smaller. I know this is basic stuff and I should know the answer for this, but I guess I just have to ask because I just may have completely gotten this wrong.

xblocker · 4th August 2002, 04:54 PM

jason1971,
the lens formula would allow you to make focal lenght smaller, but this is only a mathematical question. Lenses, the thicker they are, add more and more optical distortion to the image, so that they need specialized correction elements! Like fish eye objectives.
If you look at optical instruments, bigger objects need longer focal lenghts (opaque projectors, OHPs). Also big format photography uses longer FL due to this optical problems. Fresnel lens only does illuminate the image path and has no imaging tasks for projection.

xblocker

Mitch · 4th August 2002, 05:15 PM

What i mean is since the PCX has the curved lens, I didn`t know if it would screw up the image on a flat surface screen.
Wait a sec. Are you saying that for a 14" monitor, I need a lens with a 14" fl? And these correspond like this all the time for optimal performance? This is something I didn`t know...
I guess theres a lot I don`t know.

4th August 2002, 05:35 AM	#1
Mitch diyAudio Member Join Date: Jul 2002 Location: Indiana, USA	The best sized lenses Hi guys, I have a question for ya. If I got ahold of a 98mm big screen TV projection lens, would that be big enough to project a 14" LCD screen? Its a PCX, so would this mess up the projection onto a flat projection screen? For that type of screen, I don`t know if a flat lens or a PCX is better. Thanks for your help, Mitch

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4th August 2002, 12:33 PM	#2
xblocker diyAudio Member Join Date: Dec 2001	Mitch, 1. it depends of the focal lenght, which in your case should have minimum panels diagonal size (14") 2. as stated over and over , a single lens always have spherical abberations, which don't let you focus the complete image properly. So a single lens can only give a rough projection quality. BTW, what do you mean with PCX vs plan lens? xblocker

4th August 2002, 03:05 PM	#3
jason1971 diyAudio Member Join Date: Jun 2002	I think I'm going to need some clarification here. Do we need in all circumstances a lense with the focal length of the screen's diagonal, or is that only in the case of not using a fresnel lense to project the light path down. Please correct me if I'm wrong, but I have been working off the assumption that we use the fresnel to condense the light path down to a smaller size so that the lense we use to project the image is fooled into thinking that the image is actually smaller. I know this is basic stuff and I should know the answer for this, but I guess I just have to ask because I just may have completely gotten this wrong.

4th August 2002, 04:54 PM	#4
xblocker diyAudio Member Join Date: Dec 2001	jason1971, the lens formula would allow you to make focal lenght smaller, but this is only a mathematical question. Lenses, the thicker they are, add more and more optical distortion to the image, so that they need specialized correction elements! Like fish eye objectives. If you look at optical instruments, bigger objects need longer focal lenghts (opaque projectors, OHPs). Also big format photography uses longer FL due to this optical problems. Fresnel lens only does illuminate the image path and has no imaging tasks for projection. xblocker

4th August 2002, 05:15 PM	#5
Mitch diyAudio Member Join Date: Jul 2002 Location: Indiana, USA	What i mean is since the PCX has the curved lens, I didn`t know if it would screw up the image on a flat surface screen. Wait a sec. Are you saying that for a 14" monitor, I need a lens with a 14" fl? And these correspond like this all the time for optimal performance? This is something I didn`t know... I guess theres a lot I don`t know.

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