• Tech Staff

    a long throw / zoom lens will create a narrower beam so that's a major factor..  of course the far/near edges will be very different.

  • Not an answer to your question but a recommendation, this lens is amazing. Talking angles (ratio 4:3, reference bottom of projection) 68°. And not a single pixel streched.

    best r

  • the other way around - 22°

  • @reinhard I lust after that lens. It's SO expensive, but I have two projectors that can use it! 

  • @gertjanb I think you are talking about ending up with a trapezium shape because you are projecting from an angle, not just using lenses to change aspect ratios right, where the projection angle is not perpendicular a situation where you might have used keystone?

    In general you can have a good idea of the minimum resolution you need based on screen size and audience viewing distance, these numbers are so the audience cannot see your pixels, people have their own formulas but you can check this http://carltonbale.com/wp-cont.... From this you can calculate the maximum size your pixels should be. In the case of an offset projection angle you can calculate the the different between the pixel sizes for each side of a screen, the angle gives one side of the screen a bigger distance to the proejctor. If this falls within your pixel size range then it should be ok. You will also notice a colour and brightness dropoff over the surface with low angles.

  • @Fred 

    even if you are keystoning/mapping your image to fit it back into a rectangle, your pixels are not going to be square. I think Gertjan is asking about the distortion within the individual pixels. if you're projecting at an angle then the image creates a trapezoid shape, and each pixel is going to be a tiny version of that trapezoid. (roughly)

    different lenses will cope with angled projection in different ways. a basic rule that i have experienced is that the wider the throw, the more pronounced the trapezoid. i regularly use Sony UST beamers with 0.27:1 lenses and these need to be pretty perpendicular to the screen, but can go super-close and throw about 500mm-1m above the machine. I also use Optoma ST machines with 0.5:1 lenses - also with an asymmetric throw, these also chuck the image about 1m above the machine (at a 6m wide image). Beamers with symmetrical throw lenses (widest I've found is the Sanyo LNS-W10 that is 0.8:1) tend to have physical lens shift that will give you more options for image placement. by the time you get to 1:1 throw ratio, the trapezoid is less apparent if you need to hit the screen at an angle. so i guess the longer the lens, the more acute angle you can hit the wall, but also the further from the wall you need to be to get your image big.

    i'm doing a gig next month with a couple of Sony VPL SW536 machines in a tight space at the back of a stage. i'm thinking of angling one of them at about 60 degrees to the wall and i know its going to splay out massively and will need lots of izzymap, but the image doesn't have to be super clean, so big, out of focus pixels at the far edge will be acceptable.

  • Tech Staff

    I ran across this thread while looking for something else: https://community.troikatronix...

  • Hello @dbini,

    Seeing you've some experience with Optoma ST machines. I'm doing a project for which I'll use an Optoma ST 0.5:1. We are thinking of angling it at between 60&70° to the surface. Have you any idea what angle would be a no go - even with mapping?

  • @msanii

    i'll test the setup for you over the next couple of days and post some results here....

  • @dbini 

    looking forward, thanks.

  • i had a play around with an Optoma ST with an iPhone taped to it to use the spirit level - 1m from the wall so the image is 2m wide. here's some sketches of the results - not to scale. i wouldn't push the projector much further than 24 degrees from horizontal because the keystoning gets excessive and brightness starts to fall off. but up to 24 degrees i reckon mapping is no problem. i dropped it to -21 degrees, which - using a little table as a stand - got the image onto the floor. the top edge started to get a bit small and bright. i regularly prop this machine up with its front paws on the floor, so that the bottom edge of the image is also on the floor, and map it back to rectangular.i guess thats at about 16 degrees. i hope this helps....

  • Hi @dbini

    I wasn't able to respond earlier but thanks so much for this. The projector has an offset of 115%. So I figure when placed perpendicular to a surface 3m away (blue lines in drawing) the projector offset produces a projection angle of 9.6°. If I then incline the projector 24° (red lines) I'd in reality be obtaining a projection angle of 33.6°(9.6+24).