Roo's View

A while back I via Planet OTI I came across a home theater related post from Brooke that pointed at an article on screen size and viewing distance. To be honest, I’m not sure I agree with the actual data, or some of the conclusions that are drawn from it – but it did get me thinking.

Here is the screen size vs. viewing distance vs. resolution chart that I’ve replicated from an article on carletonbale.com.

I’d caution you to treat this chart as a set of guidelines, not scientific fact.  Your eyesight is also a big factor here, as well as personal taste.  For me the interesting point here is about the delta between 720p and 1080p.  If you’ve got a 92″ diagonal screen (as I do) with a primary seating position at about 11 feet and a second row at approximately 16 feet, then in my primary seating position I’m right on the edge of being able to see the full benefit of 1080p.

You can look at that in two ways.  1) The ‘full benefit of 1080p’ means that 100% of the possible detail delivered to the screen is visible to your eye.  2) At any point closer than that, you are able to see more detail than your system is able to deliver.  The real question is do you want to sit at least that close, or at least that far away?

Let’s consider a smaller, more common screen size.  A 50″ diagonal screen would mean to realize the full potential of a 1080p system you’d want to sit 6 feet away.  I doubt many people sit that close.  According to the chart at 15 feet away from the screen you are at the full potential of a 480p image.  Finally the 720p limit happens at about 10 feet.

Wait.  There is one more factor too.  What is your source like?  Standard DVD is effectively 720×480 (480p).  So while you might have been thinking “Gee, maybe I should sit closer to my nice shiny new 50″ screen” let’s think about this again.  At 15 feet away, which is farther than most would sit from a 50″ screen simply due to standard room sizes, you’re actually getting the full benefit of that DVD.

Now if we consider HDTV inputs, the two common formats are 720p or 1080i (which we can consider effectively 1080p for this discussion).  If you’ve got a satellite system, then for either HDTV format you’re probably receiving about 19Mbps.  Some providers are dumbing down HDTV and re-encoding to a lower bit rate still (as low as 8Mbps), people are calling this HD Lite.  Compare this to blu-ray which is offering bit rates of 25Mbps and better, combined with the fact that it is using more modern codecs (MPeg4, VC-1, H.264) which means higher quality images in fewer bits so the quality delta with blu-ray is pretty huge.  So what is all this technical mumbo jumbo saying?  The source image is going to play a big part in terms of how close you want to sit.  The majority of your content will factor in where your seating is.  Also, if you’ve gone an optimized to get the ‘full benefit’ from 1080p you’re going to really notice when that 1080i signal that is MPeg2 encoded from your satellite box is a low bit rate.

Summary – so while the original article might get you thinking that you want to get the ‘full benefit’ of the higher resolutions and you should sit closer or have a bigger screen, you will also want to strongly consider what your source will be. Screen size should be determined by a lot more than just resolution.

All 3LCD displays have the potential to have convergence issues. Since the 3 display panels are mounted independently, the manufacturing process has to install and align the 3 panels – and any of the other elements in the optical path such that the resulting image on screen shows perfect alignment of the red, green and blue pixels.

There is also chromatic aberration to consider as well. My impression here is that the Epson lens system doesn’t introduce too much chromatic aberration. The lens on my digital camera seems to have a bigger problem here, causing the blue mis-convergence my 1080UB has to seem worse than it is. I’ve also noted this in other peoples screen shots of their convergence issues.

There is plenty of debate over what is acceptable mis-convergence. The competing DLP projection technology tends to using a single DMD chip with a colour wheel. Using a single chip has both advantages and dis-advantages. There are 3 chip DLP projectors, which will have some of the same convergence issues. The recent Sony VW60 has a novel solution to this problem, allowing for adjustments via image processing to hide the effect of mis-converged panels.

Ideally a projector with perfect convergence would be best. It is a little frustrating to know that there are 1080UB units out there with better convergence than mine may have. However, in the bigger picture – convergence is not the only measure of the quality of a projector and there are certainly other variables to consider. The best advice is to worry if you can see the effect from your closest seating distance, test patterns will show it up much more obviously than video material which tends to hide this type of problem. At the 1080UB price point, there will be problems if you look at things under a microscope.

My 1080UB has relatively good convergence. The blue is off by less than a pixel, and red and green seem almost perfect.  It turns out that blue is a very difficult colour for people to see, so having blue mis-converged is much less of an issue than red or green. I can only see the mis-convergence by standing right up against the screen. Here is a picture from quite close up of the internal menus, excuse the poor quality of the picture this is the best after multiple attempts with my point and shoot digital camera:

For comparison here are a few that I’ve captured from AVSForum that demonstrate bad convergence:

In each of the above examples, there is an obvious mis-convergence. It was reported as clearly visible from the normal seating distance with test pattern material. Normal video made it more difficult (or nearly impossible) to spot.

Art Feierman of projectorreviews.com recently posted in his blog on the 1080UB convergence problems which have been a hot topic on the AVSForum of late. Seeing Art’s posting was the kick I needed to write this up, which I’ve been meaning to do for a while.

From everything I’ve read, Epson has provided people with great after sales service – replacing any units people feel are not good enough. Recently my $200 rebate arrived, so I’m quite happy with Epson in that I didn’t need to call the rebate center and chase my claim – another thumbs up on customer service in my opinion.

In summary – I consider myself satisfied with the convergence of the 1080UB I have, it isn’t perfect – but after spending some amount of time evaluating it, I have to honestly say that I cannot see it from any reasonable seating distance.