On 18/07/2017 11:32, Richard Treen wrote:

What digital projector features would be most useful for tracing
artwork onto a large canvas?

Begin able to compensate to make a grid of straight lines straight and
orthogonal. Most lenses have some barrel or pincushion distortion
depending on where in their zoom range they are operating.

There is usually a golden optimum where most distortions cancel out
towards but not actually at the long focal length end.

Do more lumens mean the projector needs less room darkness to project
the image clearly?

Yes, but it probably doesn't matter if you aren't looking for use as a
movie projector. It is never going to work in bright sunlight and so
long as you can see the lines to trace it shouldn't matter.

Is the ability to rotate the orientation a standard feature of digital
projectors?

Some PC specific ones might but most are designed to work one way up.

Do standard projectors allow for aspect ratio adjustment?

I haven't seen one that wouldn't play anything from basic SD TV
resolution through 720p to 1080p and with the option to force aspect
ratio with crop or letterbox view. In fact we tricked a 1080p projector
with a DVD playing in HD 720p format into working at a much longer throw
so that it didn't interpolate pixels up damaging text quality.

Does the potential for image distortion vary much from brand to brand?

Enormously. In general the further from the screen the projector is the
closer to ideal paraxial rays the image projection becomes. Conversely
the closer to the screen you put it the more essential it is to have
everything dead square on centre line and a very well behaved lens.

There are a lot of mid range home cinema type projectors on Amazon.

There are also some pricey "Artograph" models with "keystoning" and
grid features
But are they so much different than the less art specific brands?

I reckon you need keystone correction on the vertical axis unless you
have a very tall projector stand. Keystone correction horizontally is
also available but I think is more of a feature than a benefit.

A PC can produce any test patterns you like or you could manually
superimpose a grid on the image you want to project.

--
Regards,
Martin Brown