AV News 192 - May 2013
Brightness
You'll see this measured in lumens. Again in my opinion many projectors are
too bright, resulting in burnt out highlights and 'grey' shadows, so unless you're
going to be showing your work where there is significant ambient light, or in
very large venues, I would have thought that 2000 lumens was the absolute
maximum you would want. This is getting a bit harder to find as projectors get
brighter to satisfy the home cinema market where ambient light is apparently
quite common. The BenQ and Optoma mentioned before are both 1800
lumens which is why I had them on my shortlist.
Contrast
This is closely linked to brightness, except in this case the higher the better. If
you look at specifications you'll find contrast ratios ranging from about 500:1
up to a massive 32,0000:1 in some of the Epson machines. Unfortunately
there's a lot of horsemeat in the burgers. Firstly, I think contrast must be
measured on a logarithmic scale and the much greater numbers only give a
modest increase in contrast. Secondly I've discovered that some
manufacturers simply quote 'contrast' while others call this 'full on/full off' or
'dynamic contrast' and also quote an 'ANSI' contrast ratio which is always
much much lower. For example the Optoma HD33 has a dynamic contrast ratio
of 10,000:1 and an ANSI contrast ratio of 500:1. Always try to find out the ANSI
ratio if possible as this seems to be more realistic. Having said that, it really is
important to minimise the amount of ambient light falling on the screen. It
doesn't matter whether the projector has 10,000:1 or 1,000:1 contrast - turn on
a light and you can hardly tell the difference between them. Even one
emergency exit sign can degrade the contrast dramatically making your
pictures look washed out.
Focal length, throw range, zoom
You need to have some idea of the size of room the projector will be in and the
size of screen that will be used. That's easy if you're just considering your living
room at home, but of course once you take it out you have no control over
either of these two variables. In general, it's an advantage to have as longer
throw range as possible as that means the projector can be sited further back
to minimise blocking the view of the audience. Unfortunately, there is a trend
for 'home cinema' projectors to have quite a short throw range to fit smaller
rooms. Fortunately some retailers such as ProjectorPoint provide a 'screen
size calculator' on their website, where you just select one of the projectors you
are interested in, slide the projector back and forth until it fits the screen size
you have, and hey presto, you have the maximum and minimum distance the
projector can be from the screen.
Lens shift
You would think that if you point a projector at a screen the lens would be in
line with the middle of the picture. Oh no it isn't! Most projectors project an
image upwards, which is actually quite an advantage as the picture is raised
making it more visible for the audience. The degree to which this happens
varies a lot. With some projectors it's hardly noticeable while with others the
lens is roughly in line with the bottom of the image.
Page 10