I'm working on replacing the projector in an art gallery setup where an image is projected onto the inside of a curved surface (about 90 degrees' worth of surface). I never saw how the old projector was set up. This is not my design: I'm installing what I've been handed. In particular, this design uses a 16:10 projector to project a sort of a moving painting that uses less than the width of a 4:3. The extreme sides of the image are black.

Please don't critique that idea. It's what I've been handed and cannot be changed.

It's been suggested that if any of the extreme side areas project any light onto that concave surface, opaque tape could be used in front of the sides of the lens to blank those areas. There will NEVER be any images in those areas.

My question is, will this result in a sharp edge or a fuzzy edge? It shouldn't matter because the tape won't be cutting off any part of the image. It will just be ensuring that no light will go from the black section of the image to the surface. As in, you know, black through an LCD is not completely black. Even though it doesn't really matter, I like to understand what will happen, what I'll be dealing with.

Thanks.

Unless the mask is in the focal plane of the lens, I don't think that the masking will be fully sharp. The question is: Will the masking be sharp enough?

You can do some quickie experimentation with black construction paper or black poster board. Note that, even with black stock, there will be a certain amount of reflected light that you'll need to manage.

I don't like applying something directly to the lens because the reflected light will be tightly coupled to the lens and this will result in lowered contrast.

Consider a two stage approach: Place one mask close to the lens and a second, larger mask in front of the first, spaced as far as you can tolerate.

Can you frame the screen area with black?

Full disclosure: I don't have a projector handy that would allow me to fuss with this and I've never tried any of these techniques.

Most masking borders use velvet- I don't know how you cold cause the edge to be absolutely crisp when it's projected onto the screen and mask unless it was rear-projected and the edge was on the backside of the screen and the viewers were on the other side.

The projector comes down out of the ceiling on a lift. There's about two inches of space in front of the lens in which to put any masking. There is absolutely no other place in the light path to put any kind of masking.

The space outside the image can't be masked because that's the wall that's supposed to give no hint that anything is or might be projected onto it.

I don't think that tape on the lens is the way to go. If you need to twist the lens in order to focus, I think that you'll go crazy trying to align the masking and getting the focus right. You may be able to design a clip-on mask that can be adjusted independently of lens rotation.

Another point to watch out for is "shimmy" of the mask started during the projector drop or due to air currents.

Rather than attempting to mask sharply to the image edge, could you mask to the edges of the curved surface? Rather than black borders around the image, changing to a color similar to the curved surface or its complement, would give a shimmering effect.

Our ability to help has been limited by you not posting the projector's brand and model number.

Have you contacted the manufacturer, to find out if they offer a masking element for the lens?

I think if this were a real threat, we'd always have to worry about having to refocus the projector after lowering and raising it a few times. I've never seen that be a problem.

It's an art thing. An image is projected on a wall, laterally concave in shape, with nothing on the wall at all. So, no.


I don't think so. When I ask about whether an edge near the lens will result in a sharp edge on the... in this case, wall, the way optics work doesn't vary from brand to brand.

Tape was suggested by the person who created the artwork, who researched and selected the projector. This person is savvy enough to have suggested if it existed. Remember, I'm not specifying anything. I'm just installing it.

My "shimmy" comment was addressing the mask, not the projector assembly.

While it's not quite the same as a projector lens system, mask a flashlight near its lens. Are the results satisfactory?

I just came back from Disney.

Every.single.projector. In that place had masking. Granted this is Disney and can have anything made with a swipe of a pen. However I highly DOUBT they are the ones making the masking system.

I would be looking on the commercial side more then the residential side. I would call DPI.

Worst case, find someone with a 3D printer and have it made

ghetto fabulous way.. find the plastic lens cap and take an exactoknife and cut out what you need.

Nothing ghetto about it. This is the most clever thing in all of the posts here.



That would be a great idea if they made the projector I have to use. Remember, it's been chosen and given to me. I don't want to name the brand because it's reputable so I don't expect junk, and I don't want to even hint at the artist because this is not about the artist.

That's a great idea, too. Won't happen. Schedule won't allow. It's art, you know, so it has to be done yesterday.

You mention visiting Disney. I hear he's not looking so good these days....

I was involved in a tourist information access system for Epcot years ago and learned from Disney employees that everything they did was high pressure, get it done yesterday, and when it's done your job is done because the group that did that project breaks up.

Masking on everything? SURE! I can see them controlling light using cardboard because the price is right and it'll do the job. THIS WEEK.

Good idea to order a couple spare lens caps -- just in case the first attempt does not work out.

One also might get lucky and find a jar cap that is a convenient size.

No, but the lens does. One brand may have some provision for masking while another won't.

I'm not sure how you came to think I was implying that.

Does the radius of the wall's curve match that of the projected image?

Ah. I had no idea you were talking about whether the lens was built in a way that allows mounting masking to it. I was asking about fuzzy edges, which is an optical thing. Sorry I missed your point.

You didn't say you were not just talking about the optics.

No. The radius of almost every projected image I've ever seen is infinity. That is, the surface onto which the image is projected is flat. Like a screen, for instance. In this case the radius is about seven feet. The shape of the space is cylindrical, with the center line being vertical.

Not into photography, eh? How do lens filters mount? Usually, it has a threaded ring that mates with the front of the lens- that's why I asked about asking the manufacturer if they offer a masking element. WRT an opening cut into a lens cap is that you may have an umbra and penumbra, which will make it look like there's a problem when there really isn't- it's just one of the phenomena that occur when an object is placed in front of a light source.

You didn't say you were not just talking about the optics.


When someone asks about masking, the brand IS important because somewhere, someone offers a product for achieving that and since all lenses aren't the same, it would need to be brand-specific.



Infinity? Maybe for long throw, but a 7' radius isn't going to work with that type of lens. The image is focused on a plane at some distance from the lens and just like capturing an image, the lens has a limited depth of field. Because of this, a projector that's near its inner limit of useful distance to the screen may be in focus at either the edge or center, but not at the other when projecting its image onto a flat surface. The whole reason curved screens are used is so the viewers will be able to see things in focus when they turn their head or rotate, without their eyes needing to refocus as they turn. The problem- if they're not at the correct locus for the curve, it won't be in focus as it should be and if the lens isn't right for the curve, ditto.

How far from the screen is the projector to be mounted?

Remember- the elements of a lens aren't flat, which means they naturally distort the image to some extent. They have corrective elements, but those only work when the lens assembly can focus at a specific range of distances- anything inside or outside of that and spherical aberration occurs. Also, the colors don't have the same wavelength, so it's possible that the same kind of rainbow effect may be seen that's visible with DLP TVs- the colors don't focus on the same plane.