How many ftL?

Discussion in 'Projectors, Screens & Video Processors' started by keyser, Oct 25, 2004.

  1. keyser

    keyser
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    I´ve noticed over at the avsforum that many like really bright images and the high gain screens are popular, so I wonder what everyone´s opinion is over here. How many ftL do you guys prefer?

    If a direct view TV is about 35 ftL and a plasma more than that, why would anyone want a screen with only ... say 10-15ftL? I´m always impressed by the brightness when I see a good plasma or LCD flat screen.. why is that brightness not recomended with a projector?

    Also... any opinions on the Da-Lite high power?
     
  2. theritz

    theritz
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    keyser,


    There are two links in the FAQ at the top of the page to pdfs on screen design -the one that should answer your questions is Here , see Page 39........ the other pdf is about screen installation.

    These two documents are good stuff............... :smashin:

    Sean G.
     
  3. keyser

    keyser
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    Thanks for the link, I couldn´t reply earlier because my computer broke down.

    It says how bright this and that is, and what to shoot for in a home cinema. But not whats bad about... say a 30ftL projected image. Many knowledgable people recomend a picture of about 15ftL, which I don´t understand.
    What´s bad about an 100"+ picture that´s as bright as a direct view CRT?? The only thing I can think of is that it might reveal artifacts(compression artifacts in DVD´s etc, dithering in DLP), but with an LCOS projector and a good source(LOTR DVD) I can´t see what would be bad about a bright picture?

    Most that have seen a very bright picture(IF 7205, Qualia + gain screen) think it gives a "wow" poop look, not a "too bright my eyes are melting and I can see artifacts everywhere"... any opinions?
     
  4. Peter Parker

    Peter Parker
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    Apparently, the main reason for around 12ft lamberts (gated), was to reduce the flicker of the film passing through it. 50hz tv flicker is noticable via periferal vision, so imagine 24hz flicker. :)

    I find that too bright an image does reveal artefacts in much the same way as having the brightness set too high - you see stuff that you shouldn't see in dark areas especialy, and reduces the illusion of seeing film IMHO - it looks digital. I prefer a solid image with no unwanted motion artefacts.

    I have an HT1000 projecting onto a 1.2 gain screen 84inches wide, and I have an FL-Day filter in front of it, recalibrated to D65. This is the best image I have seen despite it reflecting only 10.5ft lamberts.

    I feel I have good contrast and image clarity, yet zero image noise. I've seen some good 8inch CRTs, and I still don't think I'm missing anything except for the pure black level they can produce. Reality is I'm also only achieving a 3rd of their contrast ratio, but the image is very smooth and filmlike, with good ansi, so pros and cons put me closer I feel. :)

    With lamp projectors, overall black level can suffer with too many lumens - you end up with grey/milky blacks, and that's still a failing of LCOS and LCD, though DLP is better in this respect. Depending on your image preferences, black level may not be an issue though - black level at the cinema generaly isn't that great either.

    When you watch a bright image, you may also see noisy backgrounds which are the pixels moving around as the image processing is trying to decide where the edges are. I find that very distracting, especialy when the backround is a solid object such as a wall, so given the choice, will prefer a darker image over a brighter one at the moment.

    With the advent of hi-def (hopefully artefact free), we may be able to have higher brightness and no artefacts, so then I could be converted. :)

    Gary.
     
  5. keyser

    keyser
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    "Apparently, the main reason for around 12ft lamberts (gated), was to reduce the flicker of the film passing through it. 50hz tv flicker is noticable via periferal vision, so imagine 24hz flicker."
    I do notice flicker with bright scenes at the cinema, but with digital projector there is of course no flicker so that won´t be a problem in the home cinema.
    So as you say the picture noise is the problem with too bright an image, do you notice this even with very good DVD transferes and DVI?

    "With lamp projectors, overall black level can suffer with too many lumens - you end up with grey/milky blacks, and that's still a failing of LCOS and LCD, though DLP is better in this respect."
    At the moment the highest contrast projector is an LCD, the Sony HS51. With up to 5000:1 contrast, I don´t think black level will be a problem even with a high gain screen? I imagine I´ll uppgrade from my IF5700, when hopefully an LCOS Sony with an dynamic iris will arrive that doesn´t cost a car and a kidney like the Qualia.
     
  6. Peter Parker

    Peter Parker
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    Hi Keyser,

    You'e right - we don't see any flicker with digital pjs, so it really isn't an issue. That should mean no limits for screen gain providing they don't introduce hot spotting or other artefacts.

    Some brighter pjs I've seen seem to have more visible noise (in backgrounds for example), and this seems more prevalent when they are brighter. It may not always be the case, but that's just my experience, even via hdmi and dvi (which have less video noise anyway).

    Sometimes, too bright an image will look harsh and digital, but again, it's all down to personal preference. I've seen Alan Gougers screen (pics over at avs), and that is a very bright image!! It looks more like a plasma, but I wonder how it fares with regards to image noise.

    I very very rarely see any artefacts via dvi from my htpc - it's something that I find distracting, and fortunately my set-up doesn't seem to have any - mind you, I am only get around 10.5ft lamberts from my screen, so that could be why. Some may find the image dim, as some prefer a much brighter and punchier image, so in that respect, we have to pick our poison so to speak. I don't know if I could live with the hoya filter on a unity gain screen though, as it may be too dim.

    The Sony HS51 certainly seems to have a good solution with the dynamic iris, which by all accounts works very well. It's real on/off contrats is only 1400:1 IIRC, but with the iris, the dynamic contrast is over 5000:1. Currently, DLP is approaching 4000:1 without a dynamic iris, so hopefully this time next year, we will see DLPs capable of 8000:1 or greater dynamic cr. That's in the ball-park of a good 8inch calibrated CRT. It'll be interesting how the black level compares though.

    A high gain screen will still elevate the black level if there's any light there, but again, the punchy image they can give may be more of an advantage than the greyer blacks.

    I'm wondering how the ansi will look with the HS51 - I don't think it will be as good as a DLP (wondering how the iris will sit with that kind of image), but hopefully someone over at avs will have the answer.

    If you can get a demo of some high gain screens, then you will know what you find acceptable. I have tried some Vutec Silver Star 6 gain material, and while it was very bright, the sample I had also seemed to introduce some kind of 'fixed panel noise' - as you moved the screen around, the 'noise' moved with it - I think it was the structure of the material that could be seen. Of course, 6:1 gain is quite extreme, and probably better suited to a crt, so lower gains may be more acceptable for digital. The high power gets a lot of praise over on avs, though many seem to have it for ceiling mounted pjs, thus only realising a gain of around 1.5. For its full gain of 2.8, you need to table mount the pj, as the screen sends lightback towards the pj.

    Gary.
     
  7. keyser

    keyser
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    Have you seen or heard anyone here at avforums that has the high power?

    The projectorcentral screen review reveals most of the screens except the stewards are lower gain than the stated number. So there´s really no cheap alternative to the stuidotek130, is there? Maybe the 1.5 gain Da-Lite(I forget the name), but I think I´ve read it´s quite prone to hotspotting.

    Didn´t the widescreenreview measure the ANSI contrast of the HS51?

    I wonder what the contrast of the SXRD chip´s are, do you think that if Sony use a similar design as the HS51 but with SXRD it will have similar contrast? Maybe even lower.. they are only getting 2000:1 out of the Qualia with an iris(although not a dynamic one) and they have a massive xenon lamp to squeeze some contrast out of.

    p.s. hotspotting must be very related to the brightness uniformity(is that the word) of the projector. If a projector is darker around the edges, the any gain will revelase it even more. Is that correct... and what projectors are have the most uniform brightness?
     
  8. Peter Parker

    Peter Parker
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    I don't know of anyone here with a high power, but I think Tom (cigarman) over on avs has one (or had one). Most seem to like it, and I can't say I've heard hotspotting mentioned with it - probably because their pjs are ceiling mounted.

    I haven't read the w/s review of the HS51, so it may have measured the ansi. I'll have to have a look. I think the overall consensus that Ive picked up from avs is that the pj delivers what it intends to, and with no negatives atributed to the iris, so it certainly looks like does work, and work very well. Eclipse did hint at an iris or 3rd panel to modualte light output, but haven't delivered yet. I thought we may have seen a variable iris from one of the DLP manufacturers by now too.

    Lamp uniformity is a good point - I don't think it's a major issue though as it never seems to be mentioned, but I believe hotspotting is exascerbated by the screen gain due to it's directionality, so that tends to be the main cause. Screens with gain rob reflected light from escaping outwards, and concentrate it more towards the center, so I think even with a perfectly uniform light source, you'll still get hotspotting from a high gain screen. The dimmer the source, the less chance of hotspotting I think. A friend has a 7inch CRT with a 2 gain Stewart screen, and he doesn't get any hotspotting, but another friend was supplied with the wrong screen for his CRT, and that did cause some issues. As for pjs with the most unform brightness, I can't say - I've seen focus across the screen mentioned, but never the brightness. I think that is more of an issue with CRT due to the varying light output from the guns, but I could be wrong.

    Have you looked at Vutec screens? Retro can give you some info on them, so try contacting him. There are people like Ellie.co.uk, DRH screens and Harkness Hall who do screens and screen material, so they may be worth looking into.

    Screens can be a bit of a personal thing, but it's very hard to get a demo of the varying types, and screen samples don't always help very much due to their size, so it's difficult to choose. You can't go wrong with a unity screen, or gain up to 1.3 IMHO, but above that, I'd say try to get a demo. What pj have you got?

    Gary.
     
  9. ZeroEX

    ZeroEX
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    Gary,

    I don't mean to sound picky but I felt compelled to correct the above statement.

    The thing is, a correctly calibrated CRT actually has a contrast approaching infinity, at least thats how it looks when the numbers are worked through.

    To calculate on/off contrast based on the lumen output at 100IRE (max lumens) and 0 IRE (minimum lumen output) you simply divide the max lumen output by the minimum.

    A quick example for the Sony HS50 is:

    400 / 0.09 = 4444:1

    On the other hand a WELL SETUP CRT would have around:

    250 / 0 = infinity

    This is because a CRT outputs no light (at least at the screen) at 0 IRE. Skeptics may say that there is some light on the screen but even at say 0.01 lumens output you'd still be looking at 25000:1 contrast ratio rather than 8000:1 :)
     
  10. Peter Parker

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    Hi Zero,

    No - you're not being picky, and to be honest, I'd rather be corrected (albeit in a nice way :) ) than let incorrect info go unchecked.

    However! In theory, you're absolutely correct, but you'll often find that in order to keep some extra black level detail, a calibrator will up the black level (brightness) to allow it to be visible. This of course reduces the overall contrast ratio.

    Over on avs William Phelps had calibrated a CRT to around 8500:1 IIRC. It seems common practice to up the black level for detail at the expense of contrast.

    I'll see if I can dig out the thread for you.

    Gary.
     
  11. Peter Parker

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  12. ZeroEX

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    Yes, it seems CRT can use their black level advantage to create monsterous CR figures when in actually fact the laws of diminishing returns applies more than ever here.
    I bet that if you put a picture up on a CRT that had 10000:1 calibrated contrast and then had another identical CRT calibrated to 20000:1 alongside it for direct comparison, the general public would see very small to absolutely no differences in the pictures.
    Also to exploit CRT's to the fullest its critical to have a dedicated room with the dark walls that go with that. Whereas Digitals aren't don't have a black level that can be exploited to the same extent and so they work better with ambient light.

    On the other end of the scale and with regards to white level, its very difficult to raise contrast using 'brighter' projector because you have to overengineer to get incremental increases and this obviously mean an exponential price increase, so obviously increasing black level it the way to go.
     
  13. Peter Parker

    Peter Parker
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    I have to agree with you there. :)

    Not many realise the room itself is a big contributor to the final image - especialy for ansi contrast figures. The perceived black level of the screen is only ever going to be as dark as the room will allow - any ambient at all and your black level floor has risen and the max possible contrast has dropped.

    Black level is definitely the way to go for overall contrast instead of just putting in a brighter lamp - I was measuring the contrast ratio on my DLP pj when I noticed I still had some mirror activity and therefor some unnecessary light being shone onto the screen when 'black' (I use the term loosely :) ). Once corrected, the lumen figure at 'black' was obviously lower, but the CR went up considerably. It doesn't take much of a drop to realise a larger increase in CR.

    Although DLP has better ansi than CRT, it still seems that on an overall evaluation, pros and cons, CRT image quality is still the leader, but for Joe Public, the convenience and image quality from digital is good enough. I think there have been quite a few threads regarding percieved differences with increasing contrast ratios, and it did seem to be harder to tell after 4000:1 IIRC. I'd like to see something in black and white to confirm it though.

    Gary.
     
  14. Mr.D

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    Few things.

    The foot lambert values are for peak white level: normally measured of a 100IRE window pattern.

    23ft/lamberts (I think) is the ideal recommendation for a broadcast crt monitor however in practice no ones ever found one that can output that amount of light without blooming or throwing itself out so in practice you aim for 20ft lamberts and you can go as low as 16 and still get a monitor to pass calibration.

    Now the peak white point and even the black level is not the whole story. Its more important that the display can render an acceptable intensity range within its contrast range if you like (Gary's point about CRTs often requiring a little bit of energising above dead black to render intensities correctly in the low end)

    Now when you go to the cinema and watch a projected bit of film the blacks are not entirely black (in fact if you went on absolute black level ...as some rather mutton headed individuals on the AVS forum do it wouldn't compare favourably with a really good LCD most likely). However film can describe way more intensity variation than video (exact figures escape me but its along the lines of 1000 intensity variations between dmin and peak white compared with 100 for the same image on video, HD doesn't improve over this particularly).

    Now its the intensity variation that gives an image its depth not just its coarse on -off range. So film can get away with a raised black level because your eye can see so much more intensity variation leading down to the blacks if you like.

    Now with video the intensity variations are much less subtle (not across the entire range but certainly in the high and low end ..this is where a telecine operator earns his money when they transfer from film to video , they essentially decide which areas of the image range to transfer over as best as possible and which areas they can sacrifice to get the whole image into video in an acceptable form...its normally the low end and the high end and the midtones get the priority). The net result of this is that to produce an acceptable image video needs black as black as possible and white as high as possible to spread out the remaining intensity variations as much as possible to give the appearance of having a decent intensity range.

    An analogy would be the difference between a beautiful fine art print of a photograph with lots of subtle tonal variation compared with a harsh photocopy of same.

    Unfortunately the contrast range figures are often bandied about as a comparisson of one unit with another. Once you have a healthy contrast ability its more important about what the unit does with the intensity variations on the material itself.
     
  15. ZeroEX

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    When you talk about colour intensity you are referring to ANSI contrast aren't you?

    If that is the case then a DLP would be considered king since most have over 200:1 compared to a liquid coupled 9" CRT rating of around 100:1. It is of course incredibly important to have a black room or 'cave' otherwise these figures are never obtainable.
    Your right on the money of figures mean very much less when considering subjective picture analysis but because were talking on a forum and objective analysis is important and this is where the specs and figures play a more important part. According to my sumisement above DLP will have a 'better' colour intensity than CRT's due to their higher ANSI rating when in actual fact its the other way around in most cases. Why? Because the CRT has a higher on/off contrast ratio.
    All this can be confusing and highlights just why we need to view machines of varying specification to see what real world difference these have.
     

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