Short-Throw Projectors

[FredK]

Would appreciate any recommendations and comments regarding short-throw projectors.

I'm planning a 3 projector visual project utilizing a curved screen and Sol7. Space constraints essentially limit me to use of short-throws. I realize there is already some sketchy info here but am curious if anyone has anything new to add.

Thanks,

FredK

[BHawthorne]

The Optoma EX525ST is readily available and works great for me. I know a few others are using that model too here. Go with DLP projector and look for 0.6:1 lens throw.

http://img30.imageshack.us/img30/6317/dscf3753k.jpg

[dcutugno]

I'm going to use 3 Sanyo DWL 100 ,ST projectors widescreen 1280x800 each more fov and resolution.
I'm wayting to source them.

They cost a little more than the 525st...

[FredK]

Thanks for responding.....

The better resolution for the WXGAs (Sanyo) is intriguing. However, the way I see it is that the wider display format is more of a negative particularly in limited projection space requiring short-throws....that is, there is less vertical space "fill" than what the 4:3 aspect ratio XGAs would offer. Such I think is important for flight simming - sightseeing at high altitude, landings, etc. My thought is to go with WXGA but then run it in emulated 4:3 aspect ratio to capture the best of both worlds. I'm not sure how that actually would work regarding any issues with display quality, performance etc.

FredK

[BHawthorne]

Re: The 5:4 vs 16:9 issue...

16:9 is going to have some technical issues with the curvature of the screen. The wider you get with the projector aspect ratio per projector the more distortion and focus issues you get. You're goign to lose a lot of empty pixels off the top and bottom center of your projections with 16:9 with how projection geometry works out on a circular screen. It's really hard to explain what I mean by "lost pixels" without understanding how projecting onto a circular screen works. The projection bows in the center because of the circular arc of the screen. In use of 16:9 the bow is really pronounced, enough that you might lose about 20% of your pixel capability outside the regular pre-warp final picture area. I really suggest 5:4 vs 16:9. I got rid of my 16:9 because of the issues I mention. There are more disadvantage to 16:9 than advantage when it comes to circular screen projection. It goes against logic, but how the mechanics work out it's better with 5:4.

[IanH1960]

Brian,

Can you give a quick indication of the radius of your curved screen? Any thoughts as to how small it might be possible to go..

Also, do you use Sol7?

....thinking ahead to a new project.

Ian

[BHawthorne]

Brian,

Can you give a quick indication of the radius of your curved screen? Any thoughts as to how small it might be possible to go..

Also, do you use Sol7?

....thinking ahead to a new project.

Ian

I prefer to go by the name of Brad, but I've been called a lot worse I suppose. :lol:

Where you pick up or lose aspect ratio is not in your projector but rather how tight your screen curvature is. You can go a lot wider FOV with a screen constrained within a 10x10 foot room than a screen constrained in a 15x15 foot room. The destortion I mentioned in my last post is also more pronounced the smaller the area is for the screen. I wouldn't go any smaller than 10x10 foot because you begin to lose excessive amounts of "empty pixel" area. Don't think of projectors in terms of flat projection aspect ratio but rather what you can project into within the circular arc of a screen area within the capabilities of the lens throw. All circular projection will have "empty pixels", it's just that it's up to you how you end up doing your setup based on the curvature size and whatever height you end up using for the projection. The taller the projection and the smaller the room the more FOV you cover, but also the more pixels you lose in resolution. You need to find a good balance. For me it's a 13x13 foot room. I didn't mathematicly come up with 13x13 foot, it's just the room size I had available.

Keep in mind that the bow distortion I mention is largely irrelevant to the projection once using Sol7. It's just that you are losing sharpness in your projection because of the usable resolution left within the pre-warp area if you get too extreme with the FOV per projector.

[IanH1960]

Apologies Brad - don't know where I got Brian from!

Thanks for the information...

Ian

[FredK]

Brad -

Your 13 X 13 recommendation is reassuring! By dumb luck that is almost exactly the space I'm dealing with!

Did you ever try to run your 16:9 in 4:3? I would assume such would result in even greater loss of pixels because of the unused "dark space" (left and right) although I'm not really sure how the emulation works in that regard.

Thanks for providing your info - very helpful - anything else I need to know?

FredK

[BHawthorne]

To clarify what I mean about lost pixels, here is an uncorrected projection vs. a pre-warped Sol7 projection. Same exact perspective of camera. The "humps" are essentially "lost pixels".

Uncorrected:
http://img132.imageshack.us/img132/3070/dscf3769.jpg

Pre-Warped with Sol7:
http://img190.imageshack.us/img190/7302/dscf3770t.jpg

[dcutugno]

This is interesting as i was planning for widescreen projector but my room size is about little more 13x13 feet (4x4 meters).

So you say i will have problem with those? too much distorsion?:roll:

With 5:4 projectors are we not limited by the high? we will hit the floor or the top way before, than wide format i think, so will cover less lateral fov.

Those are my thought based on no experience at all, advice are welcome.

Those are some picture of my curved screen still in building made of some MDF sheet and then i will add the screen material made for projection in white i just bought...

http://img301.imageshack.us/img301/3729/img0012gy.th.jpg (http://img301.imageshack.us/my.php?image=img0012gy.jpg)
http://img30.imageshack.us/img30/9287/img0013ml.th.jpg (http://img30.imageshack.us/my.php?image=img0013ml.jpg)
http://img291.imageshack.us/img291/254/img0014uw.th.jpg (http://img291.imageshack.us/my.php?image=img0014uw.jpg)

[FredK]

Be sure to do the math....

First-off, XGA projectors are 4:3 aspect ratio not 5:4, unless I'm missing something else here.

I have approximately a 13x13 foot space to work with. My intent is to maintain a constant 7 foot radial from pilot eyepoint perpendicular to the screen to avoid perspective distortion (which is a separate issue from the projector distortion). That radial is about the maximum possible within the space. I am even planning to offset placement of the curved screen slightly to accommodate (left of center of cockpit).

Given those constraints screen size for each projector segment (3 projectors) calculates to about 68 inches wide x 51 inches high (calculated simply as linear width - curved arc width will be slightly wider). The 51 inches will just about fill the upper/lower view space from the pilot perspective for forward view. Such would be less for the wide perspective projectors since width would need to be the same to maintain a constant radial distance.

Your setup appears to have a flatter arc (??). Such is a workable solution but gets involved with "zoom" adjustments etc. resulting in a narrower actual FOV. That's the way I see the logic but perhaps others with actual in-place experience can comment on all that.

Nice job with the screen - what material are you using for the surface and how do you plan to attach?

FredK

[dcutugno]

Screen not yet completed so the arc must be defined, today the fabric arrived it's the same material that you will find in the pre-made screen that you can buy in stores.

But as i can't find a screen wide enough i have ordered a custom one 8,30 x 2,20 meters just to be sure to cover all and then cut or fold the excess.

[Airhogg]

To clarify what I mean about lost pixels, here is an uncorrected projection vs. a pre-warped Sol7 projection. Same exact perspective of camera. The "humps" are essentially "lost pixels".

The bow would be less pronounced with more of a direct projection vs the angle from projector on floor to higher screen.

[BHawthorne]

The bow would be less pronounced with more of a direct projection vs the angle from projector on floor to higher screen.

Yes, but that requires a long projection distance, plus a relatively flat screen. I have none of that in my build :lol:

[FredK]

Hi All -

After some thorough research I finally made a decision on my projectors....

Going with 3 Mitsubishi WD500U-ST's.

My logic:

Short-throw (non-mirror type), DLP, and WXGA are musts: That leaves only 4 possibilities: Mitsubishi WD500U-ST, Toshiba EW25U, Sanyo PDG-DWL 100, and 3M SCP740.

Of those the Mitsubishi had the lowest short-throw ratio (0.51) giving me some added flexibility. Also, the Sanyo and 3M models also had much lower contrast ratios, Mitsubishi the highest of all (2500).

Not the cheapest option compared with the LCD models.

Regarding WXGA, my configuration will allow for a completely level screen projection which will avoid complications with the arched pixelation reported here.

I am in the process of constructing my curved screen - hope to have the visuals running within a couple of weeks using Sol7.

Many thanks to all that provided input here and elsewhere! Such info and understanding is invaluable! Each of our installations has it's own set of unique issues so it is important to see the complete picture on all this (no pun intended).

Fred K.

[Sean Nixon]

Any progress updates Fred?

[FredK]

Have been busy with other priorities but have made some progress. Framework for the curved screen is completed (see photos). Note the support structures for the projectors...short-throw projectors do not have a zoom feature so my plan is to precisely adjust zoom by simply moving the projectors forward/backward on those rails.

I did purchase and have received one of the Mitsubishi's. I want to try it with the Sol7 software before I purchase the other two. Very compact and well-designed unit.

Will post further as project progresses.

Fred

[BHawthorne]

Looks like a good build. Certainly a lot more permanant of a screen build than mine. :)

[Sean Nixon]

I've sourced a reasonably priced projector, the BenQ MP522ST. Here are the main specs:

Display Technology DLP® by Texas Instruments
Native Resolution XGA (1024 x 768)
Resolution Supported VGA (640 x 350) to SXGA (1280 x 1024)
Brightness 2000 ANSI lumens
Contrast 1000:1
Image Size 27.5" to 300"
Throw Ratio 0.9:1

It's not as short as the Optoma at 0.9:1 versus 0.6:1, will this present a problem to me? My available width is 15ft, I have plenty of space depth wise.

How do the other specs compare?

Thanks

Sean

[orwell84]

!5 feet of throw distance? Throw distance and projected image size are the factors you want to consider. The projector people website has a calculator to figure this out. 15 feet of throw distance is a lot. I looked at this projector, but will probably vgo with the Optoma you mentioned. It gives and 8 foot wide image at about 5 feet of throw distance. This is about all the space I have.

[Sean Nixon]

My throw distance will be somewhere around 6-8ft. It's the width that's 15ft (the width of the screen). I plan to use 3 projectors/TH2G/Sol7/curved screen.

[orwell84]

Check out www.markuspilot.com. He has a good description of a 3 projector setup with dimensions that are similar to yours.

[BHawthorne]

!5 feet of throw distance?

Yep, short-throw has good points and bad points. The lens is a bit extreme on the short-throw, but to get the projection height I wanted within a reasonable room size short throw or mirrors are required. I don't want to screw with first surface mirror mounting and alignment, so that limited me down to short-throw. Roughly I have my projectors currently mounted around 6 foot throw distance at the moment. That allows for plenty of projection height to ensure immersion factor is there. The extreme short-throw lens is what accentuates that bow in the curved screen, so there are trade-offs here. There are plenty of examples of people using mirrors but that is another layer of alignment and mounting headaches to deal with. I'd rather keep things simple as possible. As is there are several layers of complexities to deal with in this new hobby projection technology. I didn't want to add anymore more valiables than I had to into the design.


Check out www.markuspilot.com. He has a good description of a 3 projector setup with dimensions that are similar to yours.

Yep, looks pretty comperable to mine. Using both Sol7 and a simular triple mounting configuration. A bit more permanant of a screen design though. My screen design is a lot cheaper and can be taken down in about 15 minutes notice. While the room is a dedicated gaming room, I wanted the ability to put up and take down the screen as needed. Painters drop canvas works great for my current needs. It's good to see different examples of screen design. Depending upon your goals you have several potential design options.

[Spatate]

And what about a short throw combined with a fresnel lens that you curve?

Sol7 would correct the distortion no?, wouldn't allow it to use less than 3 projectors?

[BHawthorne]

And what about a short throw combined with a fresnel lens that you curve?

Sol7 would correct the distortion no?, wouldn't allow it to use less than 3 projectors?

How would you encorporate an fresenel lens into a projection setup?

[Spatate]

How would you encorporate an fresenel lens into a projection setup?

Here's my idea...

http://www.mycockpit.org/photopost/uploads/2560/fresnel.png

[BHawthorne]

Here's my idea...

http://www.mycockpit.org/photopost/uploads/2560/fresnel.png

Hrrrm, anyone want to buy me an optical quality fresnel lens so I can test this and post the results? Xmas broke me for this month. :smile:

On a related note, optical mylar sheet is also capable of convex and concave anamophic shaping. I have the mylar from an old back projection big screen tv someplace to also play with as a shapable first surface mirror.

[kelvinlars]

Really very good idea..

[Spatate]

Fresnel is not very expensive.... here's a supplier

http://www.3dlens.com/shop/fresnellens.php

Cheers :-)

[BHawthorne]

Fresnel is not very expensive.... here's a supplier

http://www.3dlens.com/shop/fresnellens.php

Cheers :-)

Yes, but there is a difference between optics quality and just a generic fresnel. There is also a difference between first surface mirror and generic mirrors also. You lose sharpness and clarity through mirrors that aren't first surface and you lose optical clarity and sharpmenss through fresnels that are not optic grade.

[Spatate]

Yes you are probably right... Since i haven't tested this setup i can't argue.. but spending $30 to MAYBE save $1,000 in another projector.. might be worthed!

[BHawthorne]

Yes you are probably right... Since i haven't tested this setup i can't argue.. but spending $30 to MAYBE save $1,000 in another projector.. might be worthed!

Problem is, like anything simpit, someone needs to take the first experimental steps and document it though. ;)

IMHO, the mylar first surface film sounds more plausible.

[cjellwood]

Hi all,

Any chance someone can hit me with the Sol7 software price?

thanks
Chris

[FredK]

A single computer license for Sol 7 software is 450 Australian Dollars.

[Airhogg]

Wouldn't 2500 lumens through a fresnel lens melt your retina's??? :shock: