Does increasing the zoom decrease PQ?

[tenebre6]

Exactly as the title?

I am trying to decide the largest screen i can use for my setup.

I used and online calculator and it suggested a 1.5x zoom on my projector. will this hurt PQ?

[Petra_Kalbrain]

Doubtful it will decrease picture quality unless you have a screen bigger than most people's wall height. It mostly depends on the projected size of the image.

[tenebre6]

Originally Posted by Petra_Kalbrain

Doubtful it will decrease picture quality unless you have a screen bigger than most people's wall height. It mostly depends on the projected size of the image.

I was looking at the 142" carada.... its certainly not bigger than my wall

[Big Daddy]

At high zoom levels, a projector can lose light output.

http://www.bambooav.com/information-...ctor-zoom.html

Optical Zoom

Optical zoom allows the projector to enlarge the size of a projected image by extending the lens to magnify the image, without forcing the user to move the projector or to suffer a decrease in the quality of the displayed image. Projectors boasting optical zoom capabilities can often enlarge the image by twice its size without a loss in image quality.

The primary benefit of this feature is that it allows for the projector to be placed at a further distance away from the screen without reducing the quality of the image. The added benefit of the screen being further away is that cables can be shorter, meaning less cost and less signal degradation.

Digital Zoom

Digital projector zoom functions by cropping the image and then enlarging the pixels to increase the size of the projected picture. This allows for the projector to be placed further away from the screen whilst projecting a larger image. The increased throw distance provides the user with greater flexibility when positioning their projector, but the down side is that the more an image is digitally zoomed, the greater the pixilation, and the greater the reduction in quality of the image. Furthermore, it is important to note that digital zoom can only make small changes to the projector’s throw ratio since factory lenses only allow for small variations in the throw distance.

When a projector’s specifications boast 1.3x digital zoom, remember that although you may be getting a 30% larger image, your image’s quality will suffer as the size gets bigger. A 1.2x optical zoom projector may be more expensive, but the image quality when zoomed in will be much greater.

[Anthony P]

Originally Posted by tenebre6

Exactly as the title?

I am trying to decide the largest screen i can use for my setup.

I used and online calculator and it suggested a 1.5x zoom on my projector. will this hurt PQ?

probably not.

If we were talking cameras then digital would be yes and optical most likely not. With a projector we are usualy talking optical zoom, so it should not be an issue. Now that being said it would depend on the lenses, with some there can be slight degradation at one extreme or the other and so it is best not to go to either extreme.

[Flatnate]

The issue here is less about large size resulting in noticeable loss of detail and resolution as much as it is light output and having a slightly dimmer picture as a result of the size. Remember, a 1080p home projector is within 4% of the same resolution as many 2K digital projectors installed on small to medium screens at your local cineplex. The kicker is the home projector is maybe outputting roughly 800 lumens, and theirs is outputting around 12,000 lumens.

So, on a 142 inch screen use a projection calculator and try to place your projector as close to the screen as the zoom lens will allow for making that size. Doing that will actually make a slight difference in brightness. Also run the thing in normal lamp mode (as opposed to econo) if your wallet allows it. Personally I think 142 inches is totally watchable for most home theater projectors at 2D but you are probably pushing it when it comes to 3D at that size.

[Anthony P]

Originally Posted by Flatnate

So, on a 142 inch screen use a projection calculator and try to place your projector as close to the screen as the zoom lens will allow for making that size. Doing that will actually make a slight difference in brightness. Also run the thing in normal lamp mode (as opposed to econo) if your wallet allows it. Personally I think 142 inches is totally watchable for most home theater projectors at 2D but you are probably pushing it when it comes to 3D at that size.

yes image brightness will be affected by screen size (and light output from the projector) but not by projector distance and zoom unless there is something real wrong with the environment (i.e. it is as Smokey as crowded bar in the 80's)
If the projector outputs X lumens and the screen is Y feet the image will have the same brightness if the projector is close enough to have the zoom at one end or far enough to have the zoom at the other end. The small difference in the distance that the light has to travel won’t make a difference with normal dust and stuff.

[v_squared123]

Originally Posted by Big Daddy

At high zoom levels, a projector can lose light output.

http://www.bambooav.com/information-...ctor-zoom.html

I have a Sony vpl hw15 projector. I looked in the manual to see if it had a optical zoom or a digital zoom but it doesn't say, it just says something like zoom - 1.6:1. How do you know if your projector is optically zoomed or digitally zoomed?

[frogmort]

I notice a decrease in brightness and contrast on my pj if I adjust the zoom to where the picture is very large, but after I draped my walls and ceiling in black bedsheets, it helped reduce ambient light and made the image seem much more bright and contrasted.

[Big Daddy]

Originally Posted by v_squared123

I have a Sony vpl hw15 projector. I looked in the manual to see if it had a optical zoom or a digital zoom but it doesn't say, it just says something like zoom - 1.6:1. How do you know if your projector is optically zoomed or digitally zoomed?

Optical zoom requires a zoom lens and moving parts in the camera/projector. Optical zoom brings the subject closer. You actually see the lens moving when you press the zoom button or zoom ring. Optical zoom does not alter the image quality. Of course, this depneds on the quality of the lens and its coating.

Digital zoom was orginally used in video cameras and later on used in still cameras and projectors. Digital zoom is fake zoom. Digital zoom takes part of the image and enalrges it electronically rather that by using the lens. In digital zoom, a part of the image is cropped and is enlarged. As a result, the image quality suffers a lot.

In the good old days of film photography and film projection, we only had real optical zoom. In the age of digital, everything has become fake. You can't trust any image that you see. Although image manipulation was done with film photography, it was a lot more diffecult and time consuming to alter the image and the extend of alteration was very limited. This was normally the job of professionals or advanced photographers. With a digital camera and a computer, even a child can alter an image significantly.

Another unfortunate result of the so-called digital revolution is that it has become possible for a manufacturer to advertise that their photographic equipment is capable of so so zoom level, even if it has no zoom lens.

[Anthony P]

Originally Posted by v_squared123

I have a Sony vpl hw15 projector. I looked in the manual to see if it had a optical zoom or a digital zoom but it doesn't say, it just says something like zoom - 1.6:1. How do you know if your projector is optically zoomed or digitally zoomed?

for cameras/camcorders they usually have both and they will mark both because they are extensions of each other (i.e. if I zoom the image I see less of the surrounding in both cases because the image size is fixed). With projectors they don't usually give digital zoom since the two are opposite, the optical zoom will make the picture bigger (or smaller) (i.e. 8' or 9') but the digital zoom will mean you show more or less of it(i.e. the image will still be 8' but some of it will be truncated or not)

digital zoom on a projector is like digital zoom on the TV, it is used by black bar haters to make the image fit the screen by cutting out the rest of it.

[Flatnate]

Originally Posted by Anthony P

yes image brightness will be affected by screen size (and light output from the projector) but not by projector distance and zoom unless there is something real wrong with the environment (i.e. it is as Smokey as crowded bar in the 80's)
If the projector outputs X lumens and the screen is Y feet the image will have the same brightness if the projector is close enough to have the zoom at one end or far enough to have the zoom at the other end. The small difference in the distance that the light has to travel won’t make a difference with normal dust and stuff.

This may not hold entirely true on all projectors, and perhaps lens quality plays a HUGE factor in this as well.

Art Feierman recently posted a review on the Panasonic PT-AR100U and noticed some very large differences based upon the distance of the projector to the screen using various lens zoom settings. You can find it here: http://www.projectorreviews.com/pana...erformance.php

Basically he says this:

Effect of zoom on lumen output (Dynamic mode):

In all the talk above about lumens, remember that where you place your projector has a lot of impact on brightness. As with most projectors, for any given sized screen, the further back you place the projector, the less bright the image on the screen. This is both an optical design, and a physics thing, so not all lenses behave exactly the same.

In this particular case, there was one unusual aspect. Going from close (wide-angle) to distant placement (telephoto) resulted in a loss of brightness to the tune of more than 50%! That is unusually high, with other projectors sporting lenses similar in range (2:1), more typically around a 40% drop, and some even less.

Effect of zoom on lumen output (Dynamic mode):

Zoom out: 2051
Mid-zoom: 1819
Zoom in: 1347

As a result, this projector may be blindingly bright when, say, ceiling mounted close to the screen, but if you set it at the telephoto end of the zoom, brightness drops to near average. For example, if you were also considering the more expensive Epson 5010, while the Epson isn't as bright overall, if you put both in Dynamic, and place both at the maximum range of the zoom, then at that point, the Epson might even be a touch brighter, even though as you place them closer, the Panasonic PT-AR100U will then exceed the output of the Epson, until there's a very real difference at the short end of the range.

I know he has posted the effect of zoom and distance on measured lumens for several other projectors as well; none of them being this pronounced. Still, given the quality lenses on most consumer projectors it must make a significant impact if he is quoting typical measurements of around 40% light loss on a 2:1 lens from the closest to the furthest range that most projectors throw.

[Anthony P]

Originally Posted by Flatnate

This may not hold entirely true on all projectors, and perhaps lens quality plays a HUGE factor in this as well.

Art Feierman recently posted a review on the Panasonic PT-AR100U and noticed some very large differences based upon the distance of the projector to the screen using various lens zoom settings. You can find it here: http://www.projectorreviews.com/pana...erformance.php

Basically he says this:

Effect of zoom on lumen output (Dynamic mode):

In all the talk above about lumens, remember that where you place your projector has a lot of impact on brightness. As with most projectors, for any given sized screen, the further back you place the projector, the less bright the image on the screen. This is both an optical design, and a physics thing, so not all lenses behave exactly the same.

In this particular case, there was one unusual aspect. Going from close (wide-angle) to distant placement (telephoto) resulted in a loss of brightness to the tune of more than 50%! That is unusually high, with other projectors sporting lenses similar in range (2:1), more typically around a 40% drop, and some even less.

Effect of zoom on lumen output (Dynamic mode):

Zoom out: 2051
Mid-zoom: 1819
Zoom in: 1347

As a result, this projector may be blindingly bright when, say, ceiling mounted close to the screen, but if you set it at the telephoto end of the zoom, brightness drops to near average. For example, if you were also considering the more expensive Epson 5010, while the Epson isn't as bright overall, if you put both in Dynamic, and place both at the maximum range of the zoom, then at that point, the Epson might even be a touch brighter, even though as you place them closer, the Panasonic PT-AR100U will then exceed the output of the Epson, until there's a very real difference at the short end of the range.

I know he has posted the effect of zoom and distance on measured lumens for several other projectors as well; none of them being this pronounced. Still, given the quality lenses on most consumer projectors it must make a significant impact if he is quoting typical measurements of around 40% light loss on a 2:1 lens from the closest to the furthest range that most projectors throw.

I don't know anything about this guy , his set-up, tools or this projector. If there is something really wrong with it, then maybe it can make a difference but even then it will most likely be with image quality more than brightness. BUT in reality there should not be a difference unless there is an issue with the projector. The rules of physics don't support his conclusion.

Let's go back to basics. A projector has a light source that makes an extremely bright image, that image goes through lenses, if you are tight or wide the difference will be the distance between the two lenses but it still need to pass through the exact same lenses. The lumens (or candela if we use metric) should not be any different for the image as a whole if you are tight or wide since the light passes through the exact same path and the loss will be exactly the same due to the quality of the materials. Now that image grows as it gets farther and it will hit the screen at a given size, that is when we talk Foot-lambert fL or (candela per meter square in metric). Since the output is exactly the same (let's say X Candela) and now the area is the same (meter squared) you should get the exact same brightness (candela per meter squared). Now the only issue is that the light will cross the room and air can have some refraction due to dust or smoke particle. So in a Smokey room, that can be an issue (the same way that it is hard to see far in the fog) but most people won't use a projector in that environment and in a normal room there is usually not enough crap in the air to make a measurable difference at such a small difference in distance.

Now if this guy measures stuff in a smoke filled room, that could explain it and there could be an effect on brightness, if this guy is sticking his meter near the lens and so he ends up getting wrong numbers because the image coming out when in tight is smaller than in wide, then it is just bad measurements and the guy being an idiot because if both those images grow to the same size by the time they get on screen, then the brightness will be the same. The simple thing that he does not give image size and does not measure image brightness in foot lamberts should be enough to show that he does not know what he is talking about

[Flatnate]

Originally Posted by Anthony P

I don't know anything about this guy , his set-up, tools or this projector. If there is something really wrong with it, then maybe it can make a difference but even then it will most likely be with image quality more than brightness. BUT in reality there should not be a difference unless there is an issue with the projector. The rules of physics don't support his conclusion.

Let's go back to basics. A projector has a light source that makes an extremely bright image, that image goes through lenses, if you are tight or wide the difference will be the distance between the two lenses but it still need to pass through the exact same lenses. The lumens (or candela if we use metric) should not be any different for the image as a whole if you are tight or wide since the light passes through the exact same path and the loss will be exactly the same due to the quality of the materials. Now that image grows as it gets farther and it will hit the screen at a given size, that is when we talk Foot-lambert fL or (candela per meter square in metric). Since the output is exactly the same (let's say X Candela) and now the area is the same (meter squared) you should get the exact same brightness (candela per meter squared). Now the only issue is that the light will cross the room and air can have some refraction due to dust or smoke particle. So in a Smokey room, that can be an issue (the same way that it is hard to see far in the fog) but most people won't use a projector in that environment and in a normal room there is usually not enough crap in the air to make a measurable difference at such a small difference in distance.

Now if this guy measures stuff in a smoke filled room, that could explain it and there could be an effect on brightness, if this guy is sticking his meter near the lens and so he ends up getting wrong numbers because the image coming out when in tight is smaller than in wide, then it is just bad measurements and the guy being an idiot because if both those images grow to the same size by the time they get on screen, then the brightness will be the same. The simple thing that he does not give image size and does not measure image brightness in foot lamberts should be enough to show that he does not know what he is talking about

I think I may actually email him for clarification on his testing methods of zoom on measured lumen output. I am positive that I have read his page on testing methods on his site; but it has become so comprehensive I'm having a hard time finding it. Upon further examination, he has taken some kind of measurement on a near, mid, and far zoom setting for every projector review posted. A few more from his site.

The Epson 5020 in Dynamic mode was:
Zoom out: 2142
Mid-zoom: 1890
Zoom in: 1438

My JVC RS20 in Cinema 1 mode was:
Zoom out (closest position - wide-angle): 775 lumens
Mid-zoom: 672 lumens
Zoom in: 550 lumens

Being that Art has been a speaker at Infocomm and professionally reviewed nearly everything I can think of from the Sony VPL-VW1000 to the Optoma HD20 I'm a little leary about just writing him off on this subject. I've emailed him once before and found him prompt, friendly and happy to clarify. I really want to get to the bottom of how he comes up with these numbers.

[Flatnate]

Okay did a little more browsing over at Projectorreviews.com and found a not too technical a write-up that addresses some of the zoom vs brightness question. Essentially it says, when a projector's lens is in full wide angle mode (largest image from a given distance), more lumens make it of out the lens than in full telephoto (furthest distance). Full telephoto at the furthest distance means less lumens out of the lens but better contrast. I'm still a little unclear on how he is taking his various brightness measurements.

http://www.projectorreviews.com/advi...sLensThrow.php

Home Theater Projector Brightness, Zoom lenses and Throw Distances
What's this all about?

When shopping for your home theater projector, of course brightness - lumens, are one of the most obvious specs you see. The interesting thing, is that depending on how/where you set up your projector, brightness can vary by almost double!

That's right - a projector placed in one position in your room, might do 350 lumens, but placed more optimally, it could produce as much as 700 lumens. Sound easy? Not! There are always trade-offs. Before I get into all of this, let's be clear up front:

The purpose of this piece is to improve your understanding of the impact of positioning a projector, the lens it has, and your need for achieving a level of brightness. While the information here, may cause you to change some of your installation assumptions, it is unlikely that you will make totally different choices in projector, screen type, or whether you ceiling mount or shelf mount a projector. These decisions will all have some, but minor impact on your overall theater, and its performance.

OK, back to brightness, first, this two to one range of brightness isn't true for all projectors. The huge shift in brightness occurs with projectors that are exceptionally flexible in placement, by virtue of wide range zoom lenses.

When a projector's lens is in full wide angle mode (largest image from a given distance), more lumens make it out the lens. In full telephoto, less lumens.

Many projectors for the home, (mostly 3LCD and LCoS types) now offer 2:1 zoom lenses. That is a placment range from closest to furthest, of 2 to 1. Perhaps, for a 100" diagonal 16:9 screen, that might be from 10.5 feet to 21 feet away.

If you mount it 10.5 feet from the screen, you will get almost double the lumens as mounting it 21 feet back.

There is no straight simple formula, because different lens designs will have some impact on the actual amount of change, but, let's say that with a 2:1 lens, it will be close to a doubling.

If, on the other hand, the projector has a far more limited lens, say with a zoom ratio of 1.2:1, then, the change in brightness from one "extreme" to the other, becomes minimal, and not a serious consideration.

Now, most of the DLP projectors have limited zoom lens (1.1:1 to 1.3:1), so there isn't much to concern ourselves there, but with the 3LCD, and LCoS projectors, where all of them seem to have at least 1.5:1, and most are around 2:1, where you place the projector can matter a lot.

Consider, the reason you get a 2:1 zoom on most of these projectors, is to allow the flexibility not just to ceiling mount the projector, but to give you the option of mounting the projector on the rear wall of your room. The projectors with wide range zoom lenses means that probably 90+% of people can rear shelf mount.

And, rear shelf mounting can save money, in terms of length of cables as well as installation costs - as it's harder to get power to most ceilings, and if you have fairly high ceilings, working up there means ladders or scaffolding. For most, shelf mounting is just plain simpler and less expensive.

For most people that are shelf mounting their projectors, they will find their zoom lens nearer to the middle of the zoom range, or further back. As a result the actual brightness will probably be a little less than we quote, since we measure with the zoom at mid range.

The only reason this may be important, is for discussions of what is bright enough to meet your needs, screen size, type, etc.

If getting more lumens tempts you to ceiling mount, no problem at all. You get to enjoy any extra brightness. Of course there are trade-offs to everything. The closer the lens to the screen, the more optical distortion in the ends and corners (I'm talking very, very minor stuff). There will also be a smaller "sweet spot" for sitting, with higher gain screens. For that reason, as an example, Stewart FilmScreen's Firehawk (which I own), comes in two versions, one for closer in positioning of the projector, and that one has less gain (less brightness back to your eye). Again, its another small difference, but a consideration if you are being thorough. Interesting - you mount closer for more brightness, but then need a screen that is less bright to maintain a wide viewing cone (angle). Overall, closer is still brighter, but such offsetting issues do tend to limit the importance of placement, in terms of brightness.

The bottom line, is either ceiling or shelf mounting will work fine, with only minor advantages and disadvantages.

[v_squared123]

Originally Posted by Big Daddy

Optical zoom requires a zoom lens and moving parts in the camera/projector. Optical zoom brings the subject closer. You actually see the lens moving when you press the zoom button or zoom ring. Optical zoom does not alter the image quality. Of course, this depneds on the quality of the lens and its coating.

Digital zoom was orginally used in video cameras and later on used in still cameras and projectors. Digital zoom is fake zoom. Digital zoom takes part of the image and enalrges it electronically rather that by using the lens. In digital zoom, a part of the image is cropped and is enlarged. As a result, the image quality suffers a lot.

In the good old days of film photography and film projection, we only had real optical zoom. In the age of digital, everything has become fake. You can't trust any image that you see. Although image manipulation was done with film photography, it was a lot more diffecult and time consuming to alter the image and the extend of alteration was very limited. This was normally the job of professionals or advanced photographers. With a digital camera and a computer, even a child can alter an image significantly.

Another unfortunate result of the so-called digital revolution is that it has become possible for a manufacturer to advertise that their photographic equipment is capable of so so zoom level, even if it has no zoom lens.

Optical zoom would be me twisting the lens cap to make the image bigger or smaller and digital zoom would be using the zoom-in function of the projector where the black bars of a cine scope movie would be removed and i can also change the scope of format from 4:3 to wide,etc. Is that the difference? And if so, according the earlier post above using the digital zoom function of the projector would mean you would lose pq clarity as opposed to using the optical zoom of the projector by twisting the lens. Is that correct as well?

[v_squared123]

I hope I have it right otherwise I'm very confused with the difference of digital zoom and optical zoom

[v_squared123]

Originally Posted by Flatnate

Going from close (wide-angle) to distant placement (telephoto) resulted in a loss of brightness to the tune of more than 50%!.

I'm trying to understand what would be the best placement for my Sony vpl hw15 projector. It's about 24 feet away and I have it zoomed out making a 120 inch image approx. I do this so I don't lose any lumens and therefore have a brighter image as opposed to making the size large and losing brightness.

BUT I'm confused now bc I thought I was helping my picture by doing that now it seems there could a better solution. And this talk about wide angle lenses and telephoto lenses has me lost. Do projectors have both types of lenses? Or does it just mean how the projector is setup, ie. close to the screen is a wide angle type of lens and farther away is a telephoto type of lens? I think I'm more lost than before typing this. Help?

[Flatnate]

Originally Posted by v_squared123

Or does it just mean how the projector is setup, ie. close to the screen is a wide angle type of lens and farther away is a telephoto type of lens? I think I'm more lost than before typing this. Help?

You got it right there man. It really is how it is set up. Its all the same lens, it is just the lens on the projector is considered a zoom lens with a large range . So placing the projector as close to the screen as the lens will allow will produce the brightest picture, and placing it as far back as the lens will allow will produce a slightly darker image, but with a little better contrast. A mid-range distance is probably best. This all has to do with the way the optics of the lens in the projector works. Oh and just to clarify we are talking about the optical zoom here, meaning the optics of the projector (twisting the lens adjustment by the lens cap as you say) and not messing with settings on the projector that essentially just display part of the image at the expense of cropping stuff off.

Quick Edit:

The calculator at Projector Central says that for the VPL-VW15 has a 1.6x manual zoom lens (what you twist by the lens cap). The lens throw calculator on the site states that you have a placement range between 12 feet 1 inch and 18 feet 4 inches to produce a 120 inch diagonal picture. So positioning the projector at 12 feet 1 inch would produce the brightest possible image for that projector.

[v_squared123]

Originally Posted by Flatnate

You got it right there man. It really is how it is set up. Its all the same lens, it is just the lens on the projector is considered a zoom lens with a large range . So placing the projector as close to the screen as the lens will allow will produce the brightest picture, and placing it as far back as the lens will allow will produce a slightly darker image, but with a little better contrast. A mid-range distance is probably best. This all has to do with the way the optics of the lens in the projector works. Oh and just to clarify we are talking about the optical zoom here, meaning the optics of the projector (twisting the lens adjustment by the lens cap as you say) and not messing with settings on the projector that essentially just display part of the image at the expense of cropping stuff off.

Quick Edit:

The calculator at Projector Central says that for the VPL-VW15 has a 1.6x manual zoom lens (what you twist by the lens cap). The lens throw calculator on the site states that you have a placement range between 12 feet 1 inch and 18 feet 4 inches to produce a 120 inch diagonal picture. So positioning the projector at 12 feet 1 inch would produce the brightest possible image for that projector.

Thank you for clearing this up for me