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# Throw Ratio

When you're calculating the throw ratio of a projector to see if it will work with an anamorphic lense, do you:

(My screen is 138" at 2:35 ratio and the 16:9 image on screen is 110")

1. take the distance divided by the width of the 16:9 image (example: 14' divided by 96" = TR of 1.75

or

2. take the distance divided by the width of the 2:35 image (example: 14' divided by 126.9" = TR of 1.32

Thanks

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thanks
No problem
TR=(Distance to screen in inches)/(Screen Height in inches) * .5625 :
TR=D/H*0.5625

e.g. 12' throw distance, 54" tall screen:
TR=144/54*.5625 = 1.5

This formula takes the guesswork out of whether to use the 16:9 or 2.35 size, etc.
I always thought that the TD was based on the 16:9 image width since that is the native output of the projector.
It is GetGray just backed it out with the screen height making it exactly the same without knowing your exact 16/9 width within your 2.40 screen.
Easy to find though. Scope screen width x 0.75 = 16:9 width.
Not that easy Mark. We regularly have users call in with 2.4, 2.37, and 2.35 sizes. Scope screen width varies. Scope height is constant. Why I use my formula.
Quote:
Originally Posted by GetGray

Not that easy Mark. We regularly have users call in with 2.4, 2.37, and 2.35 sizes. Scope screen width varies. Scope height is constant. Why I use my formula.

And your formula is good too Scott.

In the end of the day, if they are using a fixed 1.33x lens, then 16:9 + 1.33x lens is 2.37:1 regardless if the screen is 2.35 or 2.40. The difference to perfect framing is just a few percent of over scan.
Agreed.
Ok, so if my scope screen at 2.35:1 is 52.1" tall, and I am at a distance of 14ft or 168" then I would calculate it this way:

TR=168/52.1*0.5625

TR=1.813

So my throw ratio with an Anamorphic lens would be 1.8x? The RS50 supports 2.0x is this acceptable or will I end up with noticeable pin cushioning or softness around the edges?

I want to make an informed decision on scope screen size and mounting distance before I commit to the install
Quote:

So my throw ratio with an Anamorphic lens would be 1.8x? The RS50 supports 2.0x is this acceptable or will I end up with noticeable pin cushioning or softness around the edges?

I want to make an informed decision on scope screen size and mounting distance before I commit to the install

Your throw is indeed around 1.8, and your pincushion will be 17mm, or 1.3% of the screen height. Not bad, OK etc.

But at the longer TR of 2.0 that you mention, the pincushion/height percentage is 1% (about 13mm): much better, less noticeable than 1.3%

My advice: go for TR=2 if you can.

Quote:

In the end of the day, if they are using a fixed 1.33x lens, then 16:9 + 1.33x lens is 2.37:1 regardless if the screen is 2.35 or 2.40. The difference to perfect framing is just a few percent of over scan.

Few 'scope movies are 2.37. Most are either 2.35, 2.39 or 2.40. What I do with my HD-100 is to use the MASK menu function to digitally clip the edges by 2.5% (5% also available, but this is too much). I believe this function is in all JVC projectors.

That way all four formats from 2.35 to 2.40 will fit into the mask (with some minor cropping around the edges). I then zoom the projector just a touch, to fit the width of the digitally masked area into my 2.37 screen. The height automatically fits. That way I never have to tweak the zoom to get rid of unwanted black areas across the top edge of the screen when showing the wider ARs of this 2.35-2.40 range.

The small amount of action you lose around the edges is neither here nor there. Directors shoot their movies for 2:1 cropping in commercial cinemas anyway, so cropping back a couple of percent is well within their target range and worth it, IMO. for the release you get from worrying about the last few millimeters of action you were never really expected to see anyway. You can use fixed masking too, which is another advantage: it's cheap.

BTW, I know this is heresy, but it works for me. A great movie is still great cropped by 2.5% all around. A rotten movie is still rotten, no matter whether you see all the action or not.
Quote:
Originally Posted by Aussie Bob

Few 'scope movies are 2.37. Most are either 2.35, 2.39 or 2.40. What I do with my HD-100 is to use the MASK menu function to digitally clip the edges by 2.5% (5% also available, but this is too much). I believe this function is in all JVC projectors.

Other brands like SONY and BenQ also offer an adjustable over-scan which also removes the slivers of black from 2.40:1 films. Personally, I just live with them as I prefer the sharper 1:1 mapping of 0 over-scan. Not that it stays that way once VS is used, however because still patterns just look better this way, so should motion pictures.
Quote:
 Originally Posted by Aussie Bob Your throw is indeed around 1.8, and your pincushion will be 17mm, or 1.3% of the screen height. Not bad, OK etc. But at the longer TR of 2.0 that you mention, the pincushion/height percentage is 1% (about 13mm): much better, less noticeable than 1.3% My advice: go for TR=2 if you can.
How are you calculating the pincushing/height percentage?

Also I am unclear on the throw ratio, when I say 1.8x, to me this means the projector has to zoom more, the closer it is to the screen the higher the throw ratio correct?

So what you are saying is move the projector closer?

Also what A-Lens can I user that will support 166" distance from the screen?
Quote:
 Originally Posted by Gotchaa Also I am unclear on the throw ratio, when I say 1.8x, to me this means the projector has to zoom more, the closer it is to the screen the higher the throw ratio correct?
The other way round. The longer the TR, the further the projector is away and the smaller the beam angles will be. Short throws increase beam angles resulting in more severe pincushion. Short throws also limit which A-Lens you can use as you have to fit the beam through the lens on its way to the screen. Having had a 1.3:1 TR and now running a 2.1:1, I would not recommend the shorter throw.
Quote:

How are you calculating the pincushing/height percentage?

I modelled it in an optical design program called Zemax. I also put out an Excel spreadsheet that does the same job without having to fork out \$4K for Zemax. It's free. PM me for a copy.

Quote:

So what you are saying is move the projector closer?

No, do what Mark says. TR is proportional to throw. The longer the throw, the larger the TR. For a TR of 2.0 from 1.8 you would be moving your projector back, not forward.

Quote:

Also what A-Lens can I user that will support 166" distance from the screen?

Any focusable cylindrical A-lens should be able to do that. Prisms don't do it so readily as they are fixed systems (unfocusable except by swapping correction lenses in and out)
Quote:
Originally Posted by GetGray

TR=(Distance to screen in inches)/(Screen Height in inches) * .5625 :
TR=D/H*0.5625

e.g. 12' throw distance, 54" tall screen:
TR=144/54*.5625 = 1.5

This formula takes the guesswork out of whether to use the 16:9 or 2.35 size, etc.

Sorry the guesswork remains. I just don't understand this math. I don't know what *.5625. I mean I know that .5625 = 9/16" but I'm just not getting this. Please help.

I will have a 100.25" 2.35:1 screen (92.25" w X 39.25" h). A-lens + either JVC RS60 or SONY VW90es. What is the ideal distance from projector lens to screen for best possible picture? What is my potential range. I would be very appreciative. Thank you. jvh
Quote:
Originally Posted by console

Sorry the guesswork remains. I just don't understand this math. I don't know what *.5625. I mean I know that .5625 = 9/16" but I'm just not getting this. Please help.

I will have a 100.25" 2.35:1 screen (92.25" w X 39.25" h). A-lens + either JVC RS60 or SONY VW90es. What is the ideal distance from projector lens to screen for best possible picture? What is my potential range. I would be very appreciative. Thank you. jvh

If you use your 16:9 screen width of 68.78" and divide your throw distance of 144" by that number, you get a throw ratio of 2.06.

144" / 68.78 = 2.06

So as to not have to wonder whether to use the 16:9 screen width or the 2.40 screen width, you just use the formula GetGray suggested:

144" / 39.25" * .5625 = 2.06

Note that 39.25 / 68.78 = .5625 (mostly).
GetGray's formula gives the same answer since your screen height doesn't change regardless of whether you are watching 2.40 material or 16:9 material - with it you just didn't have to decide which of the two differing widths to use.
Quote:
Originally Posted by CAVX

The other way round. The longer the TR, the further the projector is away and the smaller the beam angles will be. Short throws increase beam angles resulting in more severe pincushion. Short throws also limit which A-Lens you can use as you have to fit the beam through the lens on its way to the screen. Having had a 1.3:1 TR and now running a 2.1:1, I would not recommend the shorter throw.

Resurrecting this thread. I've been going through hell on getting my mind wrapped around TR for a CIH install, and I thought I would comment on some things I've learned (or think that I have learned). And toss out some questions.

First, all bets are off if you use zoom instead of an anamorphic lens in a CIH setup. You use a different set of calculations (I believe the calculators at Projector Central are assuming using zoom lenses if you choose a CIH ratio in their calculations). This tends to make your throw distance much deeper, and in my case basically ususable.

Second, there are reasons to use closer throws. If you plan on using a room with people standing up (Move, Wii, Kinect), closer TD makes it less likely they will block the picture.

Third, my question about the pincusioning effect is this--do you start to add significant pincushion if you go closer than the manufacturer specified minimum throw, or do you have this issue even if you are within the specs? Let me check my knowledge on this one--does this have something to do with how much of the lens is used? Can the quality of the lens affect the severity of the pincushion? I guess I'll also PM Aussie Bob for his spreadsheet.

EDIT: I would do that but he has PM'ing turned off. Bummer. Wonder what would be the problem with just posting it. Lots of spreadsheets here. Anybody else have it? He was a regular poster and hasn't posted since early January so I'm not thinking I can expect to get it from him any time soon.

EDIT 2: I guess if I'm planning on using a curved screen, his calculator may not take that into account anyway.
Postng short questios in every thread in the forum won't get you much participation I don't think. The expectation is that you have read the thread, generally, and have something to add clarify, or ask a new topic.
Quote:

Can any one tell me that how to calculate the exact throw ratio?

For example, the answer to this question was #5 in this thread. But if you need clarification or don't understand something already posted, let us know and someone will try to help.
Quote:
Originally Posted by GetGray

Postng short questios in every thread in the forum won't get you much participation I don't think. The expectation is that you have read the thread, generally, and have something to add clarify, or ask a new topic.

For example, the answer to this question was #5 in this thread. But if you need clarification or don't understand something already posted, let us know and someone will try to help.

Were you responding to me? The newest post besides mine was about 2 weeks older and the line you quoted does not even exist in this thread.

I still had some unanswered questions I was hoping would get a response though.
No, was not replying to you sorry. Maybe a been a spammer, or he deleted it. The post is gone. He was posting in every thread in the sub-forum.
Quote:
Originally Posted by turls

First, all bets are off if you use zoom instead of an anamorphic lens in a CIH setup. You use a different set of calculations (I believe the calculators at Projector Central are assuming using zoom lenses if you choose a CIH ratio in their calculations). This tends to make your throw distance much deeper, and in my case basically ususable.

If working off the 16:9 image width, the same method of TR calculation is still relevant. The part you need to make sure of is that you have enough zoom to cover the 1.33x needed.

Quote:

Second, there are reasons to use closer throws. If you plan on using a room with people standing up (Move, Wii, Kinect), closer TD makes it less likely they will block the picture.

Would have to think about that one some more...That really comes back to image size, not TR.

Quote:

Third, my question about the pincusioning effect is this--do you start to add significant pincushion if you go closer than the manufacturer specified minimum throw, or do you have this issue even if you are within the specs?

All HE A-Lenses add pincushion. It is a bi-product of their optics. The longer the throw, the less you have.

Quote:

Let me check my knowledge on this one--does this have something to do with how much of the lens is used? Can the quality of the lens affect the severity of the pincushion? I guess I'll also PM Aussie Bob for his spreadsheet.

See above. His spread sheet is available in the DIY section of the 235 sub forum.

Quote:

EDIT: I would do that but he has PM'ing turned off. Bummer. Wonder what would be the problem with just posting it. Lots of spreadsheets here. Anybody else have it? He was a regular poster and hasn't posted since early January so I'm not thinking I can expect to get it from him any time soon.

See above.

Quote:

EDIT 2: I guess if I'm planning on using a curved screen, his calculator may not take that into account anyway.

I'm sure his calculator was designed to work out the pincushion so you can work out how much curve is needed to correct it.
Aussie Bob is not currently allowed to participate here on AVS, thus the no PM issue. I have a new version of his calculator, but it would not be appropriate to post without his permission.
Hi. In terms of the pincushion ratio, does it work like "deltaE" that if it is below certain%, human eye cannot really detect it?
If that's the case, what would that % be?
Like I think in the above example, will a 1.3% (17mm) vs a 1% (13mm) make a difference? I am assuming that the mm refers to the maximum distance - minimum distance across the screen. If that's the case, the 4mm (0.16") difference seems pretty tough for anyone to notice across a 52.1" High screen??
The only times you'd really notice pincushion is for still images and (TR pending) maybe end of movie credits as they scroll.
Cool that's a nice tip! Thanks.
Sorry I am resurrecting this thread however I have a question on understanding Throw ratio and I am getting a AR2 lens.
The AR2 lens has a throw ratio minimum of 1.4 my current throw ratio is 1.8.
I'd like to understand which scale the minimum is i.e. 1.4 is min and 2.0 is max? or 1.4 is min 1.0 is max etc..
The lower the number, the closer the projector is (will be) to the screen and the worse the pincushion will be. A longer throw (say 2.1:1) may also present require you to further rotate the prisms which may or may not be possible with the AR2.
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