This is a comparison test between the three different level anamorphic lenses and the zooming method for creating a cinemascope picture. The lenses in a test are Isco3/Schneider Cine-digitar XL, Prismasonic HD-5000R and the uncoated single prisms.
Isco3 has two achromatic, ar-coated cylindrical lenses with a focus correction ring. This lens is widely considered as a reference to all lenses, and this is also the reason why it was taken into this test.
Prismasonic HD-5000R has two ar-coated achromatic prisms combined with the focus correction element.
The third 'lens' is two single prisms with no ar-coatings. It represent the DIY approach, and in addition to zooming method, for many it is the first step towards to scope world.
A common assumption is that the all prism based lenses loose to cylindrical design both in sharpness and CA performance, as well as the brightness and contrast performance. This test shows how the good quality prism lens challenges the 'king' isco3. Also this test shows is it worth to start with a ‘DIY’ route, and how is zooming method managing with the lens setups.OTHER EQUIPMENTS IN A TEST
The projector in this test is a high brightness Panasonic PT-DW6300ES WXGA DLP projector with 2 lamps. It has specified to have maximum brightness around 6000 ansi lumens. In this test it was running with only one lamp in a high contrast mode (mechanical iris close). This was enough to form a picture of good brightness in a pretty small testing room (throw distance 3.3 meters). On the other hand the light output is good to be high enough so that especially with the contrast measurements, the slight room condition changes, if such happen, will not affect to the results. The right side of a projected picture was used in screen shots. It is very clean and absolutely free from any kind of color fringing. On the other hand, since the chromatic aberration of lens attachments mainly occurs on horizontal sides, this area instead of the horizontal center shows the differences best .
The test pictures were thrown to the matte painted white wall. Because the light meter is measuring the values in front of the ‘screen’, it does not matter what are the screen properties.
The room is an ambient light controlled, but the walls are not very dark. This makes the ANSI contrast results worse than in the room of black walls. However, this test is not for defining projector’s absolute performance, but comparing the different scope setups to each other.
The used light meter is AMPROBE LM-120 with specified resolution of 0.01 lux.BRIGHTNESS, CONTRAST (on/off), CONTRAST (ansi)
All of these measurements are very sensitive to the following things, and the extra attention was paid for them. Optics has to be absolutely free from dirt and especially from grease. Before the tests all the optics were carefully cleaned with Isopropanol, which is a very good solvent for the grease. Secondly, in order results to be comparable, the room, projector and the light meter conditions have to be unchangeable during and between all the tests and setups. The room and projector’s conditions were tested to be unchangeable every time after changing the setup from one to another. This was done by measuring both full ON and full OFF values from the same spot of the same test pictures (without the lens and with same throw ratio).Brightness
The brightness (full ON) measurements were done with the following test picture.http://www.prismasonic.com/images/te...FWFwguages.jpg
There are 9 spots from where the results are collected, and the mean (average) is calculated from the samples. In order results to be most comparable to each other, the final results are presented in lux*m^2=lumen. Due to this the mean value of light meter result is yet multiplied by the active picture area. The standard deviation of the 9 sample values is informed similarly in lumen.
In order to get the scope aspect to all 4 setups, for the zooming method measurements the picture was vertically compressed 33% by the projector. Also since Prismasonic can be internally adjusted to ‘pass mode’, this was added to the measurements. As for a reference to this also the uncompressed 16:9 picture without the lens (pass mode for isco+sled) was tested.
The Projector’s throw distance is the same for all measurements (3.3 meters). All the lens setups were measured with a 2.4 throw ratio (zoom factor). The used throw ratio for zooming method was 1.8, because with this ratio the active picture size is about the same as with the lens setups.
Here are the results of the brightness measurementsIsco 3
Mean: 444 lm
Standard deviation: 38 lmPrismasonic HD-5000R
Mean: 427 lm
Standard deviation: 38 lmDIY lens
Mean: 364 lm
Standard deviation: 41 lmZooming method
Mean: 415 lm
Standard deviation: 53 lm--------------------------------Pass mode, ISCO+SLED
Mean: 453 lm
Standard deviation: 32 lmPass mode, HD-5000R
Mean: 438 lm
Standard deviation: 31 lmContrast (ON/OFF)
The ON/OFF contrast is defined by the ratio of the maximum brightness and the minimum brightness. This measurement uses the mean results of brightness measurements as ON values in lux. In addition to this, with each setup the full OFF values are measured from the full black picture.
The three measurement points in picture diagonal were taped to the wall. These measure spots for each setup are determined from the 3 squares (left-down, middle, and up-right) of the corresponding brightness measurements setup. The mean OFF value is calculated from the samples, after which the contrast (on-off) can be calculated.
The results are as follows:Isco 3
Contrast (ON/OFF): 944Prismasonic HD-5000R
Contrast (ON/OFF): 964DIY LENS
Contrast (ON/OFF): 917Zooming method
: (TR 1.8)
Contrast (ON/OFF): 839
--------------------------------Pass mode, ISCO+SLED
Contrast (ON/OFF): 870Pass mode, HD-5000R
Contrast (ON/OFF): 915Contrast (ANSI)
The ANSI contrast is defined by the ratio of maximum brightness again divided by the minimum brightness. However, this time the minimum brightness is measured from the following picture, where there are both white and black areas in a picture.http://www.prismasonic.com/images/te...erboard4x4.jpg
The values of white areas were so close to the values measured from the full white picture so that this once again uses the mean results of brightness measurements as full ON values in lux. However, the measures of black areas differ much from the full OFF values due to many reasons, which are for example the projector's technology, projector’s optics, wall and ceiling reflections, the reflections introduced by the anamorphic lens. In this measurement we only are interested in the reflections introduced by the anamorphic lens, supposing that everything else maintains constant during the measurements of all setups.
There are four measurement points from left-down to up-right (black boxes in picture diagonal). While measuring these blocks one has to be very careful in trying to avoid blocking the white blocks as little as possible. It is also important to position oneself with a light meter as similarly as possible in each setup. The mean value is again calculated from the 4 samples, before defining the ratio.
The results are as follows:Isco 3
Contrast (ANSI): 86Prismasonic HD-5000R
Contrast (ANSI): 87DIY LENS
Contrast (ANSI): 76Zooming method
: (TR 1.8)
Contrast (ANSI): 88
--------------------------Pass mode, ISCO+SLED
Contrast (ANSI): 99Pass mode, HD-5000R
Contrast (ANSI): 98Conclusions
Due to 33% extra active resolution a good quality anamorphic lens increases the brightness to the scope picture. The brightness increase would have been more significant if the 2.4 ratio would also be used with the zooming method measurement. However, since it is ZOOMING method, it was reasoned to use the throw ratio, which introduces the same height to the scope picture as to full panel 16:9 picture without zooming. Also as mentioned before, with 1.8 throw ratio, the picture size from the same throw distance was about the same as with the lens setups.
The on/off contrast was better with all the lens setups compared to the zooming method. However, in the ansi contrast measurement the zooming method was a winner with a very small margin to Prismasonic and Isco.
In the lens setups the Isco 3 and Prismasonic HD-5000R were very equal in all measurements. Isco created a brighter picture but in the contrast measurements Prismasonic was slightly better. However, the results were so close to each other so that the margin of error could have flipped the results, especially in case of ansi contrast measurement. The ‘DIY’ lens was performing clearly worse in every section.
The following graph represents the measured air-glass reflection curves in % for the 4 samples of Prismasonic HD-5000 series prisms, picked from the manufacturing batch after the AR-coating process.GEOMETRICAL DISTORTION AND GRID DISTORTION
With all a-lens setups the geometrical as well as the grid distortion (side-to-side linearity) are very much the same. The geometrical distortion for the horizontal expansion lenses is a pincushion type distortion (sides are taller than the center). These both distortions are directly dependent on the throw ratio. With the throw ratio of 2.4 the geometrical distortion for all lenses is around 1.8 %, while with the throw ratio of 1.8 it is around 2.7%. Accordingly with throw ratio of 2.4, the grid distortion for all lenses is around 9%, and with the throw ratio of 1.8 it is 17%. A curved screen with an appropriate curvature radius corrects both of these distortions, and that is why there is a good reason to use one with the lens.SCREEN SHOTS
The screen shots of 4 different setups are shown below. The source material is the following 1280 x 720 picture.http://www.prismasonic.com/images/te... shot eye2.jpg
The 'eye box' is located to the horizontal side of the screen, where the chromatic aberration mostly appears. The throw ratio for the lens setups was again 2.4, thus allowing to use enough zoom for zooming method to enlarge the picture to the same size as with the lens setups. Also for the zooming method, the test picture was compressed vertically 33% by the projector.
The isco screen shot shows, why the lens is considered as a very good product. The absence of CA combined with a great sharpness can well be observed from the shot. However, the amount of an anamorphic stretch is dependent on the throw ratio and the throw distance. Thus the focus sweet spot for this setup resulted only around 1.3x stretch instead of intended 1.33x. That is the reason why the 'eye box' is narrower than with the other setups. The correct 1.33x stretch factor was achieved with the throw ratio of 1.8 from this projection distance.
Prismasonic HD-5000R screen shot shows a very good sharpness as well. There exist a small amount of chromatic aberration, which can be seen in white vertical board bars next to black background (max contrast edge), but not very well inside the real picture area, (which also has pretty high contrast edges). It is good to note that LCD projectors normally have more color fringing than this due to the panel misalignment. Prismasonic lens is variable so the correct aspect ratio can always be adjusted.
The DIY lens screen shot differs most from the others. This amount of softness and CA clearly affects to the picture clarity. Without the focus correction optics the horizontal and vertical lines cannot be focused simultaneously, and the sweet spot locates in between thus compromising both the vertical and horizontal sharpness. Also without the proper CA correction the amount of color fringing makes a clear degrease not only to the white board bar but to real picture area as well. However, it is good to note that the test picture window locates on the side, where CA mostly appears. On the horizontal center the picture would be cleaner.
The zooming method represents as the reference for the lenses, when it comes to CA and sharpness. The pixel grid can be noticed better mostly because the vertical pixel density is now around 33% smaller. It is good to note that seeing the pixel structure better does not necessarily mean sharper picture. The fact is that there is no information in a pixel border even if it looks very precise.
EDITED 29.9: The Brightness units are now correct, Thanks HogPilot!