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52K views 481 replies 93 participants last post by  mark haflich 
#1 ·
#352 ·
What I was interested in was if all these projectors added an achromatic lens element to counter the abberations, or do some of these lenses literally have no achromatic element in the assembly?


There was an old TI whitepaper article that explained it in depth written by the scientists that worked at TI in field of optics, and the paper was specifically aimed at telling the OEM's how to setup the optics to get the sharpest image. I posted the whitepaper about 3 years ago in here somewhere, but I can no longer find it and it appears TI removed or archived a lot of those old whitepapers.


Though debating is fun, I think this stuff is too in-depth to debate and you'd need to contact an expert in the field of optical lenses. The University of Arizona (as well as Tucson, AZ in general) has a high number of optics engineers and physicists that work in that general field, the area is referred to as "Optics Valley". You could probably find a professor to email on it if you are really bored :p


One thing I do remember is that It said the sharpest possible images were obtained by the longest throw lenses. If you look at the Sharp a900b, it has a pretty long throw. OR a cheaper sharp projector, the Benq w7000, also tends to have a longer throw then most of the similarly cheap DLP's.


Of course that was only one aspect of it, we know it's also refraction in the lens elements and the achromatic properties of the lens countering the aberrations (presumably). It wouldn't surprise me at all if different lenses have different sweet spots, but I think the complexity of lenses gets a little bit too insane, unless you want to spend months learning about it (probably more like decades). I kind of lost interest when I learned that there were like 10+ different types of achromatic lens elements and probably 500 different equations just for that purpose, I was like ok, I like to learn about this stuff to an extent, but at some point...
 
#353 ·
If the lens used in all projectors didn't have one or more such elements, one could not adjust the focus so that all three primary colors would be in focus at the same time. One projector manufacture had a lens used on all models of its HT projector for several years but was BADGERED by various posts here at AVS Forums into revising its lens design. Now it uses a very good lens which costs it less than the old lens. Chinese sourced instead of Japanese sourced. Point, is that anyone hear can tell if their lens contains achromatic elements by performing a really tough tough test, LOL, can you focus RGB so that they all are in focus at the same time. Of course without a lens diagram show besides the location of each element, its shape, and integration into a group comprised of two or more elements, AND the type of glass in each element, one can't positively identify it as a achromatic element. Also not to be sneezed at would be the coatings on the exit element to deal with chromatic aberrations at exit. The Wiki cite is rather easy to understand and is simplistic to the most casual of observers with an appropriate engineering background. English lit/ IT/computer types might have difficulty understanding it or any other fundamental element of life.


Batter up.



Cedia is coming up quickly than god. We are running out of inane subjects to discuss. Don't you guys ever watch your machines just enjoying content instead of contemplating what may come and how it will be built. I watched a baseball game last night and thoroughly enjoyed it even though the team I am routing for lost.
 
#354 ·

Quote:
Originally Posted by darinp2  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/320_40#post_23745973


This is the part I'm not seeing. The assumption of softening the image. Now I could be wrong and if so you or somebody else will probably show me the error of my ways so I will finally get it, but at this point I don't.


Are you assuming that the image will be softer and if so, based on the edge of the lens having less quality mostly? As I mentioned, somebody who actually measured MTF found higher MTF at the larger image end of the zoom, not the longer throw end. At least for 1 projector. I'm guessing they were measuring near the center of the image, but even there, why would the MTF go up at the end of the zoom that is generally thought of around here as the worse end for sharpness?


By anomoly size I mean things like bumps on the lens or cracks or divits in the surface of the lens that can be seen when it is put under a strong enough microscope. A lens may feel like it is flat, but isn't really down at the small scale that is relevant here.


To me this is related to why a 4K projector requires a better lens to resolve its pixels than a 2K (or 1080p) projector does. The anomoly size relative to pixel size seems relevant in both cases.


If the same lens was used for a 4K projector and a 2K projector, but the 2K projector was put at the long throw so that the center inch was used for 2K pixel width and the 4K projector used the center 2 inches, then in both cases the center inch would be used for 2K pixels. If the 4K chip was twice as wide with same fill ratio and related parameters, then would the sharpness on screen differ for the center 2K pixels for those two cases? If so, why?


If they don't differ, then for those center pixels zooming the 4K image to have a bigger exit image improved the quality for those pixels. I'll save the logic of that one for later in case that doesn't make sense, but it is related to the lens not being high enough quality for 4K if only 1" of it was used, but being high enough quality (at least for the center 2K pixels) if 2" of it was used.

Thanks. I appreciate it.


--Darin
I definitely agree that 4K requires better lenses. A lens that resolves 1920 lines may not resolve 3840 lines. An analogy is todays mega pixel DSLR's easily show weakness in some older lens designs that are mitigated to some extent with lenses specifically designed with those mega pixel cameras in mind (CA is one of the biggies that I've noticed).


As to the assumption of softening the image as you move out from the center of the lens....

First off, I am not an optical expert but I have some experience with 35mm lenses and I think similar principles are involved in projector lenses. I've attached two Nikon MTF charts for their well regarded 24-70 f/2.8 professional zoom lens (I've also attached Nikon's key to reading these charts). Notice how resolution and contrast vary (worsen) as you move away from the lens center and also notice that there is also considerable variation with zoom position. Of course some lenses perform better than others but generally speaking contrast and resolution degrade as you move from lens center (prime lenses being much better than zooms, etc). With todays 36 megapixel DSLR (Nikon D800) I can certainly see that the image softens and contrast lowers along the outer portions of the frame. I have never had (or seen) any lens where this did not happen (the charts shown are made at f/2.8.....stopping down the lens improves performance across the board but the outer portion will always remain lower than the central portion).


I'll also note that most of Nikon previous [tele] zoom lenses performed best at minimum zoom (sharpness and contrast fall off at higher zoom levels) but recently Nikon has introduced zoom lenses that are better at the zoomed end. So a lens can be designed to work at best either end of the zoom range....it may well be that the projector lens in the unit where MTF works best at short throw vs long throw.


One other comment.....The nikon D800 has 36 Megapixels in a 24x36mm area.....this far exceeds any 4K projector density of 8.3 Mega pixels. And with w DSLR lens the exit image is going to be a circle that is larger in diameter then the diagonal of the 24x36mm frame (the diagonal is ~43mm). In this case there is significant pixel density along the edges of the frame.


Many projectors have shift lenses......Nikon and Canon make these too.....a shift lens has to output a significantly larger image circle. Consider the 35mm system wherein the image circle must be at least 43mm for a non shift lens to avoid vignetting -- it needs to be much larger for a shift lens (the 24x36 mm rectangle must lie within the image circle to avoid vignetting and as the image is shifted the position of that rectangle relative to center of the lens circle changes). Sharpness, contrast, CA are all affected when the lens is shifted (as most projector owners have likely noticed when they use lens shift).


It would be interesting to measure MTF at various positions on the screen.....I may be full of hogwash but I do believe that MTF would vary more on the outer portions of the image relative to the center of the image (although I acknowledge the central portion is more critical that the outer portion).


One final thought for now...there are always exceptions to rules and generalities....I suspect that the unit with the higher MTF at the larger image end of the zoom is the exception.....




To clarify, the horizontal axis on charts below go from 0-22...however, the edge of the image occurs at 18mm - the reason the chart goes to 22 (or thereabouts) is to show corner performance (half the diagonal is roughly 22mm).



 
#356 ·

Quote:
Originally Posted by mark haflich  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/320_40#post_23747303


There is no lens that can resolve 3840 line pairs. Nothing even remotely close. You are not using the criterion of line pairs correctly. I think you are attempting to say resolve 3840 lines rather than line pairs.
Forgive my poor wording...you are correct...I'll fix the post....
 
#357 ·

Quote:
Originally Posted by mark haflich  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/330#post_23747108


The Wiki cite is rather easy to understand and is simplistic to the most casual of observers with an appropriate engineering background. English lit/ IT/computer types might have difficulty understanding it or any other fundamental element of life.


Cedia is coming up quickly than god. We are running out of inane subjects to discuss. Don't you guys ever watch your machines just enjoying content instead of contemplating what may come and how it will be built. I watched a baseball game last night and thoroughly enjoyed it even though the team I am routing for lost.

It appears there are a thousand different ways to do one thing in optics, so I wasn't sure if achromatic lens elements applied to ALL projectors.


Also, according to this article all it said was, "achromatic lenses will provide the best result when designing a projector", that almost implies that some cheap projectors do not use achromatic elements. "Since most projection systems utilize white light, using achromatic lenses will yield the best image." As complicated as optics gets, I doubt that many people in here know that much about lenses, they might know the very very very basics, but it's not really much because that is a seriously complicated field.

http://www.edmundoptics.com/technical-resources-center/optics/optics-application-examples/?&pagenum=6


I am not in IT, but thanks for asking :p
 
#361 ·

Quote:
Originally Posted by mark haflich  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/330#post_23745553


What is the screen gain?


All things being equal you will get the brightest picture at short throw and the greatest on/off contrast at long throw. The lens will perform best optically at long throw. The exit image is smallest at long throw and one uses more of the sweet spot of the lens. So if you have enough brightness which is a function of your screen gain. the curves of fallmoff in brightness as you migrate from short throw and fall off in on/off as you migrate from long throw are log curves and are not straight lines , so deciding to mount a midthrow is not a good choice because you lose much of the brightness and much of the on/off. Say about 30%. Pick your poison.

Thx for that informative response; so I'll try to mount the projector as far back as possible which is approx 19ft from the 120" screen from the sounds of it.


Still haven't figured out the screen material, but thinking of either of these ones:


- Stewart StudioTek 130

- JKP Affinity HD Progressive 1.1


To provide background on where the screen will be going, the Theare room will be dedicated with one small window (2' x 3' covered w/ shutters) adjacent to the back row seats. Ceiling will be painted black, Carpet will be a midnight blue, and walls a dark grey. Any preference on which screen would work best with the VPL500ES?


THanks in advance!
 
#362 ·

Quote:
Originally Posted by darinp2  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/330#post_23745717


Hi Mark,


Hope you are feeling well.


The above seems to be the prevailing wisdom, but I wonder whether that is accurate. A while back somebody asked me about seeing higher MTF at short throw and whether I thought that made any sense. I thought about it a little bit and decided that there could be some logic in it.


If the exit image is smallest then it has the highest density of pixels per inch of lens cross section. No lens is perfect, so let's consider an exit image that takes up 1" horizontally at lens exit and a lens imperfection with exactly 1 pixel width under those conditions. If you change the zoom so that the exit image uses 2" of lens horizontally at exit then that same lens imperfection is only 1/2 of 1 pixel width.


I know there are multiple lens elements, this could be much more complicated, and a smaller image may use a better part of the lens (depending on lens shift), but I think using less of the lens could cause worse images instead of better.


Consider a more extreme example of a 10" wide lens. Now if you shoot a 1920x1080 image through that lens at full width the anomolies at full width will be much smaller compared to the image than if you tried to shoot that same image through just the center 1" of that lens.


Seems like the same kind of principle as it being more difficult to make a small lens of the same pixel resolution as a large lens.


What do you think?


Thanks,

Darin


I think thar discussion ignores where the lens is sharpest considering the use of vertical lens shift. As one puts more of the image towards the glass extremities, the image tends to get less sharp at those points.
 
#363 ·
I would choose between the Stewart snomatt 100 (gain of one) and the JKP Affinity 1.1 gain. Given your screen size, you could use some gain and I would choose the JKP 1.1. You could use the 130 for the extra gain considering your long throw mount but to me the 100 is a better fabric than the 130 making the screen disappear when lit up. But I don't know about how happy you would be with the brightness.
 
#365 ·

Quote:
Originally Posted by rcohen  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/360#post_23749393


I am unsure of screen gain, screen size, or projector placement. So, I ordered the projector first, and got a bunch of different free screen samples I can tape on the wall. Once I can experiment with the projector, it should help with all these decisions.

Great strategy! Just projecting onto the wall will definitely help you decide on the screen size that is best for you, and the samples are also very helpful to decide on the screen material.
 
#366 ·

Quote:
Quote:
Quote:

Originally Posted by rcohen


I am unsure of screen gain, screen size, or projector placement. So, I ordered the projector first, and got a bunch of different free screen samples I can tape on the wall. Once I can experiment with the projector, it should help with all these decisions.

Great strategy! Just projecting onto the wall will definitely help you decide on the screen size that is best for you, and the samples are also very helpful to decide on the screen material.

+1. That is a good way to finalize your screen size / choice.

Quote:
I would choose between the Stewart snomatt 100 (gain of one) and the JKP Affinity 1.1 gain. Given your screen size, you could use some gain and I would choose the JKP 1.1. You could use the 130 for the extra gain considering your long throw mount but to me the 100 is a better fabric than the 130 making the screen disappear when lit up. But I don't know about how happy you would be with the brightness.

Add the new JKP HD Pro 1.3 and the Stewart Cima Neve 1.1 materials to the list Mark posted there, to check out.
 
#368 ·

Quote:
Originally Posted by Geof  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/330#post_23747290


To clarify, the horizontal axis on charts below go from 0-22...however, the edge of the image occurs at 18mm - the reason the chart goes to 22 (or thereabouts) is to show corner performance (half the diagonal is roughly 22mm).



Thanks Geof. Given those charts I wonder what they would look like with an infinite zoom range (like we essentially get) and the zoom setup so the edge of the image is at 15 mm. I see the MTF getting better for the middle there (even as it gets worse for the edges) going to wide zoom. I wonder if that is related to the factor I brought up.


Where I said anomolies it may have been more clear if I had said lens imperfections, which every one of these lenses will have down at the microscopic level.


One thing to keep in mind is that the image is not focused as it passes through the front of the lens, so center pixels on the screen don't just use their corresponding spot as they exit the front of the lens. What I wrote earlier may have given a different impression, but I still think that the factor of lens imperfection size to average pixel size may be relevant here, with that factor possibly getting worse as we use less of the lens surface (use longest throw).


--Darin
 
#369 ·

Quote:
Originally Posted by mark haflich  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/360#post_23748271


I think thar discussion ignores where the lens is sharpest considering the use of vertical lens shift. As one puts more of the imge towards the glass extremities, the image tends to get less sharp at those points.
Such as that those of us who use a retro-reflective screen and put the projector a little overhead and behind may be using a sharper part of the lens than those who mount their projector high up on the ceiling.



We know that the edges of the lens may not be as good as the center (and generally won't be), but that does not automatically lead to the longest throw giving the best images. There can be multiple factors at work that have to be weighted against each other.


This could get especially complicated if one place in the throw range gives the sharpest images for the center pixels but not the sharpest toward the edges of the image, since pixels near the center of the screen tend to be more important than edge pixels for normal viewing.


BTW: I'm not saying I know where the best throw positions are, but I think it may be more complicated and not quite match the general wisdom around here.


--Darin
 
#370 ·

Quote:
Originally Posted by kraine  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/360#post_23751714


One lucky guy in France today








Kraine,


Are you getting to play around with one of these today? If so, what are your impressions? I'm especially interested in how 1080p blu-rays look up scaled.


Mike
 
#372 ·

Quote:
Originally Posted by hifiaudio2  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/270#post_23728970


255 I believe. Been quite a while since I tested (and I don't have it anymore).



Hifiaudio2 ( and SOWK )


You are correct, with contrast at 88 ( iris off ) , its is just arround to begin to clip at 250-255. ( with auto iris on, the clip will occur with contrast at 96 - max. typical )

If you want it to clip arround 235 ( with iris off ) , you can turn contrast up to about max.



dj
 
#374 ·
It will be REALLY interesting to see how the VW500ES compares to the VW1000ES. Really, if the contrast and sharpness are even close, i don't see the point of getting the VW1000ES. That's an extra $10,000 at least.


From the hands on reports so far (including Cine4homes detailed report), the brightness calibrated is almost the exact same. The native contrast is 20% less, BUT you can adjust how far the iris opens and closes in a new menu, so really, i would just clamp it down that extra bit and be good. The only thing that concerns me is the lens sharpness. But that's a large premium to pay, if its $10,000 MORE than the VW500. The VW1000 has a wider color space, and a sharper lens. but the VW500 has many cool features that are not on the VW1000 YET (mastered in 4K, autocalibration, new motionflow modes, previously mentioned iris tuning, possibly it has brighter 3D than the VW1000 if Sony implements its lamp pulsing tech, and probably cheaper lamps). Maybe some will come with the update? hopefully it does for VW1000 users.


If the VW1000 is still 25K, i would have a hard time justifying that purchase over the VW500 unless the lens and contrast are REALLY crappy. I can't see the contrast on the VW500 being much worse than my VW95, which i'm happy with.
 
#376 ·

Quote:
Originally Posted by whitetrash66  /t/1438597/sony-vpl-vw500es-sxrd-4k-projector-ifa-berlin-2013/360#post_23754783


It will be REALLY interesting to see how the VW500ES compares to the VW1000ES. Really, if the contrast and sharpness are even close, i don't see the point of getting the VW1000ES. That's an extra $10,000 at least.


From the hands on reports so far (including Cine4homes detailed report), the brightness calibrated is almost the exact same. The native contrast is 20% less, BUT you can adjust how far the iris opens and closes in a new menu, so really, i would just clamp it down that extra bit and be good. The only thing that concerns me is the lens sharpness. But that's a large premium to pay, if its $10,000 MORE than the VW500. The VW1000 has a wider color space, and a sharper lens. but the VW500 has many cool features that are not on the VW1000 YET (mastered in 4K, autocalibration, new motionflow modes, previously mentioned iris tuning, possibly it has brighter 3D than the VW1000 if Sony implements its lamp pulsing tech, and probably cheaper lamps). Maybe some will come with the update? hopefully it does for VW1000 users.


If the VW1000 is still 25K, i would have a hard time justifying that purchase over the VW500 unless the lens and contrast are REALLY crappy. I can't see the contrast on the VW500 being much worse than my VW95, which i'm happy with.

If I hadn't had a 1000 for almost 2 yrs now, and were looking for a new pj this year, I think I would go the route you describe. The main choice, I would think, is between the VW500 (or 600--don't yet know what its US label is) and the top of the line JVC's. I'll bet they both look very, very good. (Still happy, though, that I did bite for the 1000!)
 
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