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Author Topic: Lumens Question Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-01-2014 04:08 PM                     You guys are also forgetting about throw distance. Longer the throw distance the dimmer the image and vice versa. Most home theater projectors only have one choice of lens as well so it may not zoom out enought to fill the screen. JVC and Sony home theater projectors have some of the best contrast ratios. True 10,000:1. You can not tell if they are on or off the blacks are so dark. Not just on/off wither. The JVC doesn't need a dynamic iris to get very high contrast ratios. The Sonys also have excellent black levels but they implement a dynamic iris to get as deep of blacks. This is the one area I believe home projecters hands down beat DCI pjs and even film. If playing mostly black and white movies black level is very important. Both aren't know to be the brightest either tho. Always a trade off. Make sure you do all the math before committing. For my home cinema I use a BenQ W7000 and its rated at 2,000 lumens. I use it on a 1.0 gain 1.75:1 10ft acousticaly transperent woven screen with a throw distance of 20ft. In high lamp mode im getting around 19 fl for 2D and only about 4fl for 3D when bulb had about 100hrs on. There is 1,300 hours on the lamp and theres a slight drop in brightness. Just some info to let you know what to excpect with such a projector. You might look into this company for a nice 3chip DLP projector thats cheaper than a DCI pj but plenty of choices. http://www.digitalprojection.com/ I believe some of the pricier models have 2.35:1 chips but not positive.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-01-2014 04:35 PM                     Throw has zero effect, in and of itself, on brightness. Light travels through air just fine. Light travels through no air too just fine. Anyone that told you otherwise is wrong. What MAY affect light as a function of throw (total lumen output) is the lens and its speed and its speed at a particular zoom position. However that is dependent on the particular lens one is using. As for contrast ratio. While it is true that a projector with a dynamic iris system can achieve a greater range if one were to measure only black or only white, a DCinema projector will have a greater range (ratio) if there is a mix of anything else. Put up a 50% checkerboard pattern and see which projector does better. The DCinema will win every time. The problem with dynamic iris for cinema use is if a movie is graded and one knows the detail in the image based on standard light levels, if one has a dynamic iris and the scene is on the dark side, then it will likely also kill any shadow detail as the entire image is lowered in output to get those blacks extra black. I've yet to see any digitally projected image to compare favorably to film with respect to contrast ratio (presuming both are set up properly and exhibiting what they are capable of). Of course, I still like the image off of film better too but that is an entirely different discussion of little point anymore.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-01-2014 10:53 PM                     Thanks for the info. Ive must of always been misinformed of distance in relation to light loss. Home Theater magazine reviewer Tom Norton would speak of the effect of light loss at further throws. And referring to the lens specs like you said. But anyways Like if you had a flashlight shinning on a wall and you walk backwards its intensity weakons. I could be way off base but not sure. Im definitely against dynamic iris's and there effects on the image which is why I like the JVC D-ILA HT projectors so much and ther high contrast. They truly have the deepest blacks that ive ever seen in an image digital or film. Reminded me of film whenever I demoed them for sure. Edit; I Think where my confusion was is keeping the distance in spec with the lens like you say above. I think that's what I had in mind. Thanks again for info  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-01-2014 11:14 PM                     The flashlight example is the flaw. Think of the flashlight reflector as the lens. It will create a "spot" of a certain size at a certain distance. When one walks backward, the spot grows in size so the brightness appears to be darker. The lumen amount (what is coming out of the flashlight) does not diminish...it is the area that the flashlight is being asked to cover is growing...at the exact same rate as the reflected light is diminishing. Now look at a projector. if our screen is 20-feet tall. Regardless of where our projector is, we will select a lens such that the image remains 20-feet tall. It doesn't matter if our projector is 50-feet away from the screen or a 100-feet away. So the area that the same quantity of light has to cover is the same...hence the throw has zero effect on light levels. I have found that for most manufacturers, the fastest lenses tend to be in the middle of the range. So that the longest lenses and the shortest tend to be less efficient on light. For zoom lenses, often, for any particular zoom lens, the light tends to be more efficient with the lens zoomed for the shortest focal length (largest picture). However, unless you have a Throw Ratio such that you have a choice of 2 or more lenses, this is moot since the projector and screen are going to be at a distance dictated by architectural considerations so you will be stuck zooming the lens to the size needed to fill that same 20-foot tall screen.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-04-2014 12:45 PM                     I see your point. I think whats going on is in HT projectors many if not most don't come with different options of lenses; just the lens that comes with it. It has a required throw distance to be most effecient like you said. So your stuck. Most are only effecient in a very short range, hince my argument and have very little vertical and horizontal zoom so you have way less throw distance to deal with as opposed to with cinema projectors where you can just pick the required lens for the distance. Thats what im saying. The OP better make sure the BenQ projector he selects has the ability to change lenses. I did and experiment last night and moved my projector closer to the screen by roughly 10 feet and adjusted focus and it became much brighter. Much less deeper blacks too at the expense of brightness. After moving the projector back to its original mount you could clearly see how less bright it was. It really is about the lens like you said. Thanks again.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-04-2014 03:13 PM                     Is your projector of a fixed focal length? Most are not for home use...when you moved it...did you zoom the lens so the image was the same size?  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-04-2014 03:29 PM                     No it is not fixed. I should have added that i adjusted zoom as well so image fit the screen. Theres not much play though. If I were to go a few feet further back from my normal 20ft throw it would not be able to zoom out enough to fill the screen.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 04-05-2014 07:43 AM                     As Steve said, depending on lens characteristic, the difference in brightness with the same image size adjusted with a zoom lens is small. Typical behaviour is slightly brighter, with slightly less contrast, in the wide position, somewhat less bright, but higher contrast, in the tele position (larger distance). Even some cheap home cinema projectors may have a zoom ratio of more than 2.1, so you can double the distance while keeping the same image size. The brightness though will not vary much. Usually you can measure it, but hardly see it with the bare eye. If you are free to choose the position, you can of course still optimize for either brightness or contrast a little bit. But it is NOT distance in itself. A piece of window glass will usually eat more light than 100m of free air. - Carsten  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-05-2014 11:21 PM                     Thanks for the info. Yes the difference wasn't huge but was noticeable.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-06-2014 06:11 AM                        That long throw/long focal lenghts negatively affect image brightness vis-à-vis the optics is a misconception that seems to be prevalent and probably originated in Drive-In circles because there is some truth there with those exceeding long throws out in open fields. But the conclusion that the lens optics cause any bright degredation is incorrect -- yes, distances there can show some negative effect on brightness, but it has nothing to do with the optics of the lens vs distance -- it has to do with other factors: 1) the amount of moisture and the dust/dirt particles in the air over that long distance that light has to punch thru and 2) very long focal length lenses that are needed for those distances tend to be more inefficient and with more elements needed to achieve those focal lengths. Even zoom lens change efficiency as they travel thru the zoom range.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-06-2014 04:52 PM                     Thanks Frank. Good points. Appreciate all who responded. On a differenct note I still hold true that the best HT projectors have better contrast than any DCinema projector that I have personally experienced. Blacks that make a star field appear to float inside a black void is what im talking about. Not grey, or dark grey blacks, or even really dark grey but true black while retaining brightness. My single biggest thing I hate about D-Cinema is its contrast performance. If someone could reccomend a theater or projector that has the best contrast they have seen Id love to expereince what is considered the industries best. So far the best Ive seen has been Sonys DCinema pjs. Thanks again.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-07-2014 06:43 AM                     As I said before...put up a 50% checkerboard pattern...the DCinema projector will have superior contrast performance. HT projectors don't properly render contrast as they use a dynamic iris...they make a presumption that if most of the image is dark to lower overall brightness. So, if you have a lowly lit scene indoors (say by candle light)...then shadow detail will be lost in people's faces...a problem a DCinema projector will not have.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 04-07-2014 10:43 PM                     I agree the ones that must rely on dynamic iris's for there best contrast are infirior. The best JVCs do NOT implement a dynamic iris to achieve it's best contrast. I'm referring to native contrast performance like a check board pattern and such. I'd love to see DCI content thru one. http://procision.jvc.com/product.jsp?modelId=MODL029155&pathId=140&page=10  |  IP: Logged

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