[johnsmith808]

Let me get this straight. From what I understand, lcd's such as the new panny and sanyo, as well as sony hs60 all have automatic irises that adjust as the need may be, thus resulting in high on/off contrast ratios.


Dlp's on the other hand such as the Sharp DT-500 and Mitsubishi HC3000/3100 have an iris that one can set to a desired level, but then it just stays there and doesn't adjust automatically as the need arises, thus resulting in lower on/off contrast ratios.


What is up with this? Do dlp manufactures think that because of having a higher native contrast ratio that they can just leave it at that? Why haven't they incorporated an auto-iris system as well. Imagine that, higher on/off contrast and higher ansi contrast than lcd's. Or are dlp manufacturers and lcd manufactures working together to ensure that no one side completely obliterates the other. Or maybe it's just pure economics of "if we are making money, why bother improving our product but reducing our profit margins.


Maybe I'm missing something.

 

[Sasler]

Perhaps the DLP projectors wouldn't benefit that much from Auto Iris...


Just a wild guess, I have no hard facts to back up my hypothesis

 

[muzz]

It seems that most folks set the iris where they want it, and leave it.

I have read that numerous folks do NOT like the auto Iris anyway, because they find it distracting.

 

[CT_Wiebe]

The "Auto-Iris" used on LCD PJs are there because LCD panels cannot compete with the better CRs (Contrast Ratios) of the DLP PJs (which have inherently better black levels (especially the newer Darkchip 2+ and the Darkchip 3 models). The problem with the "Auto-Iris" is that it cannot compensate for good black levels if there are any very bright objects in the same scene (the ANSI Contrast measurement is the extreme case). Also, the auto-iris operation can be very distracting if it's not done right. A few of the newer DLP PJs have an "Auto-Iris" also.

Added NOTE: The DLP CR is, in part, due to the higher "fill" ratio of the DLP chip (DMD). The "fill" ratio is the measurement of the gaps between the pixels on the panels. The LCD panels have fill ratios of 50% to 65% (IIRC) whereas DLP fill ratios are closer to 90%. The newer DMDs also have a 12 degree tilt which also improves the black (absence of light) levels. LCD panels depend on the amount of light that leaks through the cross polarized filters (which aren't perfect).


The newer crop of LCD PJs have much better auto-iris operation than last years models. The newer LCD PJs also have improved LCD panels, which have better black levels than last years models, due to improved panel design. LCD PJs incorporate "Auto-Iris" in order to compete with DLPs - pure economics and marketing.


If you have any room lights turned on (or any source of ambient lighting) your CR will be degraded anyway. Under these conditions, there will be no significant difference between LCD PJs and DLP PJs and the auto-iris function is next to worthless. With ambient light (not shining on the screen) you will be lucky to get 800:1 CR (and usually a lot less - some more experienced AVS members have mentioned around 300:1 CR under those conditions).

PS - I still prefer LCD PJs because I can get the quality picture, and which fit in my LR/HT, that satisfies my needs and for the money I'm willing to spend. None of the current DLPs priced under $2K do that. This is, in part, because the new DLP light engine designs require either very low shelf mounting, or higher than normal ceilings

- neither of which fit my room.

 

[johnsmith808]

Thank you all for your replies.


CT_Weibe,


I appreciate your technical explanation on my question. What confuses me about this topic is that reviews often say that dlp's have better black levels than lcd's yet the on/off contrast ratio's are highly in favor of the lcd units. When people say better black level, it's difficult to determine if they are referring to lowest absolute black level in a scene with little to no light, or black level in mixed dark/light scenes(I guess that would be more ansi contrast).


Upon reading reviews for the Sony hs51a/60a, reviewers claim that it can reach black levels of .001 FTL, but yet claim that the blacks are not as good as DC3 machines such as the Optoma hd78dc3. See what I mean?

 

[CaspianM]

Auto iris is same as dynamic iris unless some one tells me otherwise.

On my HS60 I hardly can tell the iris is working if any. It handles the mixed scenes well.

The only time I can tell is when the bright part is low in percentage compared to black by dimming the white a bit. There is tweak you can decide how much the iris closes. It works well and no distraction whatsoever. HS60 even without iris puts my DLP (Sharp 10x with 2k CR to shame in CR).

 

[sethk]

The HD81 is the only FP projector I've heard of with a dynamic iris and it pretty much doesn't work too well. The processing and mechanical requirement require quite a bit of R&D and some DI iris designs are patented so you have to come up with something relatively unique from what I understand (or license it from someone else.) This is a reasonable barrier for some companies, but I would expect someone like Mitsubishi or Sharp could do it without a problem on their DLP units.

 

[CaspianM]

Sony calls it Auto Iris and Optoma/Sharp call it Dynamic. Technically all are DI and function same.

DI functions like a SLR exposure control without the time exposure change. It is all controlling the light output via diagram on a continues basis.

 

[johnsmith808]

If dlp's have these Auto Irises as well, why can't their on/off contrasts match or even surpass that of the lcd's, which have a much lower native contrast ratio? I thought the budget dlp's incorporated only and iris on or iris off setup, not one that changes with each frame.


Or maybe the lcd designers have just made far superior irises than their dlp counterparts. I mean if everyone is lying/exaggerating the on/off contrast ratios of their units, then why are the dlp's exaggerated contrast claims still far lower than the lcd's? Is their disproportionate exaggerating going on? Insanity!

 

[CaspianM]

Or maybe the lcd designers have just made far superior irises than their dlp counterparts.

----------

That is correct.

Sony in this case has well advanced in DI and DI used in Pearl is probably the most advanced DI. Optoma needs some work but you know DI will be gone.


The native CR of DLP is better than LCD but not much better. You are believing everything you read. Early LCD's were way off in CR but they are close. How about 2000 vs 1300:1. That is not much when a CRT can do near 1000,000:1 and still I can make out the screen in total fade to black. Ansi contrast to my eyes is same as my DLP.

 

[johnsmith808]

So with your experience in both crt and digitals, would you say that the lcd units more closely resemble crt's? I would think that the more on/off you have the better, as all digitals today seem to be just fine in ansi contrast.


My experience in projectors is limited to a Benq pe7700 and a NecXG852, neither of which I have anymore. I felt the Benq had horrible absolute black, which promted me to sell it. Then I bought the XG(non LC), which had a tremendous picture, but I just didn't have the room for it in my living room. Also I kept running into problems with gamma and Moome card issues that I just didn't want to deal with it anymore.


So now that takes me to today. Of course I know that a digital within my price range could not compete in picture quality with the crt, but I just want to get as close as possible.

 

[CaspianM]



Quote:
Originally Posted by johnsmith808 /forum/post/0


So with your experience in both crt and digitals, would you say that the lcd units more closely resemble crt's?

Some say that digitals are better already but for me it is a matter of compromise mostly for watching film based movies. But LCD's have come neck to neck in color in this case Sony HS51A/60. Top lumen is a draw but I have a hi end CRT in great shape with only 1000 hrs on it.

In terms of smooth and dimensional PQ especially with SD DVD all digital lack and of course 1080i unconverted is for CRT land only. Blacklevel remains as the biggest obstacle for digital but Sony does 10k:1 which is best you can do unless go more expensive and get 50% better which is not a whole lot IMO compared to CRT with nearly 100K's:1.

 

[Josh Z]



Quote:
Originally Posted by johnsmith808 /forum/post/0


If dlp's have these Auto Irises as well, why can't their on/off contrasts match or even surpass that of the lcd's, which have a much lower native contrast ratio? I thought the budget dlp's incorporated only and iris on or iris off setup, not one that changes with each frame.


Or maybe the lcd designers have just made far superior irises than their dlp counterparts.

I think you're still assuming that a dynamic iris is a good thing. That's highly debatable.

 

[johnsmith808]

Well, I had a Benq pe7700 that had no dynamic iris and it just didn't cut it. I know the negatives of a DI, but for me and my budget, it's either 2000:1 contrast with no tricks or 10,000:1 contrast with tricks. Heck, I'd love to have a digital do 10,000:1 native, but I'm not that rich.

 

[fleaman]



Quote:
Originally Posted by johnsmith808 /forum/post/0


Well, I had a Benq pe7700 that had no dynamic iris and it just didn't cut it. I know the negatives of a DI, but for me and my budget, it's either 2000:1 contrast with no tricks or 10,000:1 contrast with tricks. Heck, I'd love to have a digital do 10,000:1 native, but I'm not that rich.

10,000:1 native (or dynamic) ain't gonna do you any good if you're watching in a typical living room (white walls, ceiling, etc.). Not that you won't see a difference between 1,500:1 and 10,000:1 in a white room, but it probably won't be much of a difference (unless it's a very big room).


Now, if you had a dedicated darkened surfaced HT room, then those contrast #'s are really gonna matter. But you said you weren't rich, so maybe you don't have a dedicated PJ room....


Fleaman

 

[johnsmith808]

Good point. Right now my living room is not completely darkened as far as furniture and carpet/wall etc. It has no ambient light sources though. I use the graywolf 1 screen which reduces light bouncing all around the living room.


But, I most likely will be moving within a few months, and I will dedicate one room for HT. Then, I guess I'll really see what projectors can really do. So I'm planning my purchase with that in mind.

 

[CaspianM]



Quote:
Originally Posted by fleaman /forum/post/0


10,000:1 native (or dynamic) ain't gonna do you any good if you're watching in a typical living room (white walls, ceiling, etc.).

Fleaman

I think you are confusing ANSI CR with ON/OFF CR.

In a scene with deep black such as a shot of night space, the color and reflectivity factor of room's walls are not important since there is not much light to scatter to wash out your black level. 10k:1 is on/off ratio in this case.


Ansi contrast is measure of relative white to deep black where you have a mix of bright and dark in a scene. That is where your room reflectivity plays a role in your overall contrast. That is ansi contrast and most PJ's are ranked about 100~500:1 CR. That is where you need to be careful with your room to take advantage of your pj's native ansi cr.

 

[georgeorwell]



Quote:
Originally Posted by Josh Z /forum/post/0


I think you're still assuming that a dynamic iris is a good thing. That's highly debatable.

Thus the reason you can turn it on or off....user preference.

 

[CaspianM]



Quote:
Originally Posted by georgeorwell /forum/post/0


Thus the reason you can turn it on or off....user preference.

Yup even with DI off CR is very close to DLP nowaday for LCD's. Look at it as an icing on the cake.

 

[johnsmith808]

So wouldn't retro-reflective screens be great for people in less than ideal rooms for the sake of ansi contrast? Of course as long as you're not wearing all white, sitting on a white sofa with white drapes behing you. I guess you could focus on the things in the room directly behind the sofa to reap the most gain, with the least amount of effort.