PDF attached.Some of you may be aware I am finishing up a writeup on testing I did between the JVC X500, X70, X550 and X750 including contrast measurements, black level comparisons, and a comparison of the 4 projectors. In doing this testing, I became intimately familiar with the function of the dynamic iris and how it translates onto your screen. I felt that the information on the DI deserved its own thread since it is a wealth of information in itself and the DI behavior is not as obvious as one would think. I also investigated the dual iris system. I have attached a PDF white paper so to speak that hopefully many of you will find informative and open a discussion. Let me know what you think! I will also be posting this in my shootout thread. This is also attached as a PDF.
JVC Dynamic Iris Function Technical Writeup
I will attempt to explain the fuction of the Dynamic Iris on all JVC Projectors that feature it. The beginning sections are basic understanding of the iris system and the latter portions are more indepth and might be new information to some. I also conducted tests on the upper end models and their dual iris.
The X3/X7/X9 and X30/X70/X90 model years did not include a dynamic iris. The black level is set and fixed wherever you have the aperture setting. By lowering the aperture setting and closing the iris more, you are getting a darker picture, but gaining contrast and achieving a lower black level. In other words you are sacrificing brightness for increased contrast and better blacks.
The Dynamic Iris we will be discussing gives JVC projectors the ability to maintain peak brightess while increasing contrast and black level during dark scenes which is where we want to have the best black levels.
There are two menu settings for the iris:
: 0 to -15
When manual mode is used, the aperture is fixed (static) wherever you have it set. A setting of 0 results in the brightest picture, but the worst contrast, and the worst black level. A setting of -15 clamps the iris down decreasing brightness, increasing contrast, and providing deeper blacks.
Here is a graphic showing the iris at various settings:
Notice several things here. The “Max” aperture setting can not actually be set by the user. The iris will only clamp down this far when using Auto1 or Auto2 (A1 and A2). In Manual mode, you can select anywhere from 0 (fully open) to -15 (fully closed). Rather, I should say that -15 is the fully closed position when using Manual Iris mode. In A1 or A2 mode, assuming you set the aperture to zero, the range of the iris during use is from 0 to max.
Now, this is where things get confusing.
Lets assume you have the following settings:
Auto1 or Auto2
And lets assume these are your contrast ratios at each aperture position:
In this configuration, the range of your iris is from 0 to Max Closed. But this begs the question, when does the iris actually activate? And when it does, how far does it close? Well, its actually not too complicated…
-----When does the aperture close to the “Max Position”?
When in Auto1 or Auto2, regardless of where you have the numerical aperture set to (0 to -15), the iris will always close to the MAX position when displaying a fully black scene or image. I should note this is not exactly true, if there is some non-black content, such as a mouse pointer (if you are using a PC) or one small word of text that covers less than 2% of the screen, this will also activate the Max aperture. I use Vudu streaming service, and Vudu has a screensaver which is simply a black background with a small “VUDU” logo about 100x50 pixels and with this screensaver, the max aperture does engage with this screensaver. Anything more than this, and the max aperture will not engage…
Examples of scenes that will NOT engage the max aperture mode:
-Scenes in space (most scenes in Gravity for example)
-Very dark scenes such as Harry Potter Voldemorts army on the hill
-Interstellar when they leave the wormhole (very dark space scene)
-Space scene in Stars Wars 5, just after the yellow text flows by
That being said, my initial thoughts were…well…if I’m only getting 500,000:1 contrast during full black scenes, this is kind of a joke isn’t it? Well, not really. What I came to realize is that many movies have extended fade to black scenes, transitions, or scenes in total dark and the aperture makes a huge difference here. The reason (I am assuming) that the Max aperture does not engage at any level above this is because the bright parts of the scene would simply be too dim because the iris cuts down nearly all of the light. Next question then is…
---When the Dynamic Iris is engaged, but not displaying a fully black image or movie scene, how does it function?
There is another aperture position that is not in the graphic above that we have not touched on yet. We will call it for now “-17”. We all know that the DI does engage during those Interstellar and Star Wars scenes but we know the iris does not fully clamp down to the MAX position. During these dark scenes, the iris clamps down to a position just a tad past -15 to our fictitious -17 position. Essentially, during dark scenes that are not quite dark enough to activate the Max position, the iris will close just a tad past -15. Heres what I mean by that….
We measured the black level on a JVC X500 at a Manual aperture setting of -15 to be about 0.8 Lux, and then we measured the black level with the aperture in Auto mode to be about 0.75lux during non-total black scenes like Interstellar or Star Wars which is slightly darker than the -15 maual setting. In fact, regardless of where you have the numerical aperture setting, when using A1 or A2, those dark scenes will always close to that -17 position (again, unless the scene is total black). Doesn’t matter if you have it set to 0 on A1 or -15 on A1, the wormhole scene in Interstellar will always have a black level of 0.75 lux.
Essentially, your best black level during movie content that is not fully black is going to be equal to or very close to using a manual setting at -15.
Now, we begin to see the advantage of the Dynamic Iris versus a projector without a DI. Lets assume we have a DLA-X500 with a DI and an X500 without a DI (just bare with me) and we need to get at least 12foot-lamberts onto our gigantic screen. Lets assume the projector without the DI needs to have the aperture set to zero to get those 12fL and our black level is going to suffer at a measurement of 3 lux as previously stated. With the X500 that has the DI, we can leave the aperture at zero, retaining our 12fL during bright scenes and set it to AUTO so that for our dark scenes, we aren’t stuck with a 3lux black level. The pj with the DI will clamp down to -17 during dark scenes and to MAX during fade to blacks.
This is main advantage of the DI in my opinion…good blacks AND still being able to fill a big screen with enough light…Without a DI you would need to choose between getting enough light or having good blacks…
But there is more…
----The difference between A1 and A2 Mode
Auto1 and Auto2 do not differ in the mechanical function of the iris at all. They function exactly the same in that regard. Where they differ is in the way they “treat” the image.
When using Auto1, the projector modifies the image slightly, focused on creating a more contrasty image…It takes the dark parts of the image and makes them even darker and the bright parts even brighter by boosting them. In my opinion, this results in many of the dark areas being too dark and you lose much detail. To some, the image may appear darker but this is just image treatment.
Auto2 focuses on gradation and preserves the image more naturally applying very little image treatment and maintains more of the original image.
As I delved more into the Auto modes, I eventually noticed something wonky was happening…When leaving the aperture at -15 and setting it to A1 or A2, we noticed that the images were not being treated the way we had seen before. We switched from -15 to -6 and suddenly the image was being treated more. We went from -6 to zero and the image was being treated even more.
What we discovered was, based on where you have the numerical setting, also depends on how much the image is artificially treated.
Last but not least…given all of the above information, we can determine the following. On the left are examples of some possible aperture and iris settings and to the right are the black levels and possible aperture positions. For example, When set to Auto and -8, the Aperture can fluctuate from -8 to Max, the peak lumens are 1,000 and the max contrast is 500,000:1. The examples below are assuming your projector has a native CR of 50,000:1, a dynamic CR of 500,000:1, and a peak lumen output of 1,300lumens. These contrast, black level, and lumen numbers are fairly reflective of the measured output of the DLA-X500
Key and Notes:
Black Image BL
– The black level – in lux – of a totally black scene or image as described above
Dark Scene BL
– The black level – in lux – of a dark scene that is not a total fade to black. See above for description.
– This is the peak output of the projector in lumens.
-----X700/X900 and X750/X950 Function – Dual Iris
Things go even further because the X7** and X9** models feature a DUAL Iris system whereas the X500 and X550 models feature a single Iris.
In the dual aperture projectors, there is a front iris and a back iris, both of which are adjustable.
When you set the iris to MANUAL, and you start moving the slider from 0 towards -15, you are manually adjusting both irises. Now, I do not claim to be an expert on the dual iris system as the rear iris or the light engine iris is not visible without taking the projector apart, but it seems like with every click, the front iris closes one click and with every 2 clicks the rear iris moves. When set to Auto 1 or Auto 2, the rear iris stays fixed wherever you have the numerical setting but the front iris still functions dynamically as described already in this paper.
The effect of this is that when using the Auto1 or Auto2 settings, the best dynamic contrast ratios are actually achieved with the aperture set to 0. When using A1 or A2 and setting the iris to -15, you actually have a slightly worse dynamic CR. However, native contrast (MANUAL mode) is still best with a -15 setting. In other words, your best dynamic CR is achieved in Auto mode with the aperture at zero. Your best native CR is with the aperture on Manual at a setting of -15 but this results in reduced light output.
Please look at my other threads, mainly the X500 vs X70 vs X550 vs X750 shootout thread, to see an example of this where I have listed the measured contrast ratios for each projector, noteably the dynamic CR’s for the X750 which is the only one on that list with a dual iris.