Large chip 3-chip designs?

[Robert Jackson]

I was wondering if anyone would like to talk about why large 3-chip designs are impractical? I've been really curious about why there are so many 2/3" 3-chip designs and that seems to be the point where people stop considering a multi-chip design as practical.

I'm sorry if this is obvious. Light falloff in large prisms or just a size-related issue or something, but I thought it was probably something that had been given significant consideration by the Red designers and wanted to ask.

[Gopher77]

I think I had read a post by Gramme that answered that. You just can't push that much data through.

[Mark B.]

Alignments get seriously critical when you're dealing with huge pixel counts on three different chips... trying to match them up perfectly would be a pain.

[Graeme Nattress]

Bigger prisms would lead to all kinds of problems with the lenses, and the distance between the back of the lens and the sensors would increase further and lead to all kinds of issues, not least the cost of 3 sensors rather than 1. You'd not be able to use standard lenses, so you'd need to buy new, and that would be a pain.

With our approach, you get to use standard lenses and get a great picture.

Graeme

[Michael Brennan]

Not large format, but there is a 4 chip ccd 4k camera head made by Olympus that is quite good, it uses pixel shifting and existing 2/3 inch HD lenses.
Olympus have not made the camera available for sale.
Panasonic have introduced pixel shifting to their new 1920x1080 camera head.

A multi chip non bayer mysterium with pixel shifting could double resolution but would need custom lenses. In theory and ignoring cost of lens design(!) cost, size and compexity of shooting would be probably akin to shooting 65mm IMAX?



Mike

[Graeme Nattress]

Unless those chips where 65mm dimensions, I'd say not. There's no substitute for size.

Pixelshifting is an interesting technique, but the only paper I read on it showed a luma increase of root(2) or about 1.4. It does seem to get used to try for a 2x factor increase in resolution, for which I've not seen a scientific justification for.

Graeme

[Andrew M.]

Talking about 3-chip design.
What about 2-chip design, to increase dynamic range.
Can we have semi transparent mirror in front of the first sensor and second sensor next to it, one responding to lower light levels and the second responding to the higher light levels?

Alternatively, is there a way to read only one CMOS sensor, first fast, for the intense light levels and then slow for the low light levels?

I was thinking to use 120fps in 4 intervals.
We use first ¾ to read low light levels and ¼ to read high levels.
Then to combine it as a one 30fps frame with extra two or 4 stops dynamic range?

[Jeff Kilgroe]

Pixelshifting is an interesting technique, but the only paper I read on it showed a luma increase of root(2) or about 1.4. It does seem to get used to try for a 2x factor increase in resolution, for which I've not seen a scientific justification for.

I'm not a big fan of pixel shifting. It does work, kinda, sorta in many situations. It essentially "doubles" the luma info for each pixel in the CCD array and can give increased resolution with midtone details and it's partial to neutral and grey colors. I often wonder if pixel shifting is more of a way of cheating when shooting those B&W and grey scale resolution charts.

Pixel shifting is easily defeated with certain types of camera motion or movement of the subject. CCD resolution of the HVX was originally confirmed by shooting a res chart with wobulation. ...I think it was Steve Mullen who did this. Any benefits to pixel shifting also break down when the green content of a source image is far lower than the red and blue components. So, if you're shooting a scene with lots of reds, purples, shadows, etc.., you're not gaining the benefits of a shifted green sensor layer. Which also leads to another method of testing true resolving power of shifted CCD cameras -- shoot a res chart under red light or shoot as normal and only analyze the red CCD layer. Although, this may not be as accurate as wobulation because you would be introducing a luminance handicap by only dealing with red light or CCD info.

[Andrew M.]

So, if you're shooting a scene with lots of reds, purples, shadows, etc.., you're not gaining the benefits of a shifted green sensor layer. Which also leads to another method of testing true resolving power of shifted CCD cameras -- shoot a res chart under red light or shoot as normal and only analyze the red CCD layer. Although, this may not be as accurate as wobulation because you would be introducing a luminance handicap by only dealing with red light or CCD info.

But isn’t that the same true for Bayer sensors?
Misterium is just 3MP Red or Blue sensor.
Once there is an absence of Green its resolutions drops far below 4K format standard?

[baro]

Talking about 3-chip design.
What about 2-chip design, to increase dynamic range.
Can we have semi transparent mirror in front of the first sensor and second sensor next to it, one responding to lower light levels and the second responding to the higher light levels?

At some forum somebody told Ikegami made a 4 chip camera once with that purpose (the fourth chip only received a small fraction of the incoming light). Ever since I hoped I would hear some more about it without success. I would be curious to hear if anybody has more information on this.

[Graeme Nattress]

Some of the earliest tube cameras had 4 tubes, with one dedicated to luma.

Graeme

[baro]

Maybe this is what the poster meant, thank you.

[Hrvoje Simic]

Talking about 3-chip design.
What about 2-chip design, to increase dynamic range.
Can we have semi transparent mirror in front of the first sensor and second sensor next to it, one responding to lower light levels and the second responding to the higher light levels?


...been thinking about the same thing, and glad I'm not alone.
Is this possible, Graeme ?
Both sensors would have the same distance to lense, just the second one would be on a 90 degree angle.

What are the obstacles in achieving that ?

[Robert Jackson]

...been thinking about the same thing, and glad I'm not alone.
Is this possible, Graeme ?
Both sensors would have the same distance to lense, just the second one would be on a 90 degree angle.

What are the obstacles in achieving that ?

Didn't you just cut the light reaching both sensors in half? Maybe there are some carbon arc lamps left over from the production of Birth of a Nation that you can pick up cheap. ;-)

[Anders Holck]

The obstacles in achieving that, would be alignment.
With the single sensor you just have to make sure the sensor is at the right distance from, and is perfectly flat to the flange. If it's shifted a bit up or down, left or right or even rotated (around the optical center) wont affect image quality that much.

In your setup both sensors and the mirror must be alligned to perfection in all 6 axis. Not to mention you's have to double the processing power.

But the setup could work I guess, 3-strip technicolor worked in a similar way.
Simply not worth it, even if you got it to work.

[Robert Jackson]

But the setup works, 3-strip technicolor worked in a similar way.

By the time light passed through the Technicolor beam-splitter and filters, the effective ASA of the Technicolor stock was only 5.

Interestingly enough, this is exactly why Citizen Kane was possible. Shooting at Selznick’s sound stages, Gregg Toland was able to make use of the Technicolor lighting the studio had purchased to film ‘Gone With the Wind.’ Shooting Kodak Panchromatic Super-XX with an ASA of 160 and push processing it to 320 he was able to use that Technicolor lighting rig to allow his lenses to be stopped down until he had sufficient depth of field.

Sorry. Wrote a paper about that in film school. ;-)

[Hrvoje Simic]

The obstacles in achieving that, would be alignment.


Yeah, I was thinking that alignment could be a problem...
Here's a quick idea of a assembly principle:

1. Sensors are mounted on the identical plates
2. 90 degree frame with mirror slot is made from a universal precise mold
3. Plates and mirror are mounted on the 90 degree frame
4. Additional sensor's x&y axis per-pixel alignment is achieved electronically through cropping (with 10-50 unused pixels tolerance)

Processing power will be no problem in the future.
Robots today are capable in achieving that type of precision, which leads to the next obstacle - cost of r&d.

[Robert Jackson]

Yeah, I was thinking that alignment could be a problem...

You know, Fuji's solution with dual 'S' and 'R' photosites seems to work pretty well without a beamsplitter. The second set of photosites are each really small, but their intended use is in situations with hot highlights, so it doesn't seem to matter much. It takes a lot of processing power to combine the data, though, and the file sizes are really huge.

[Andrew M.]

Processing power is not a problem if we do prepare data directly on the chip in the hardware.
Two sensors will be specially manufactured so the output side of the first sensor (first 12 bits) will expect the other sensor to be there starting from bit 5 to 16 so it will just combine it in to the 16 bit sensor output instead 12 bit one.
Actually the first sensor (low light level one) will connect to the second sensor with 12 bits and second sensor will have 16 bit output ready.

1 2 3 4 5 6 7 8 9 10 11 12 -- -- -- --
---------1 2 3 4 5 6 7 8 9 10 11 12
=========================================
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Alignment, hmm… we have more problems with alignment then that in 3CCD prism splitter and they manage to align 3 sensors there via prism.
Though I like Omens electronic self alignment idea.
Now, we cut the light by half but we combine two sensors data so we get it back at minimum in the middle luminosity range.
Also, one sensor will be manufactured to be optimized for low light levels the second for the high levels and two will be matched together. So once you have one of them defective you have to change two of them. Alternatively the optimization could be done by mirror splitter itself, sending less light to the bottom sensor and more light to the side one.

[Bruce Allen]

Totally agree, guys. A quick question though - why couldn't you also just make every second filter in the R, G, B Bayer matrix have a bit of ND / darker filter added to it as well? Sony did a R, G, B, E sensor, why can't someone make a filter that goes something like R, darkG, B, darkR, G, darkB? Or a R, G, B, ND filter, for that matter?

Bruce Allen
www.boacinema.com

[Graeme Nattress]

At that point you're trading dynamic range for resolution, and introducing a much more complex demosaic algorithm.

Graeme

[baro]

Both sensors would have the same distance to lense, just the second one would be on a 90 degree angle.

What are the obstacles in achieving that ?

I don't think you can make it easily work with a mirror as you show on the picture. At least I never saw such a setup. Maybe one reason for this is that the light coming out on the other side of the mirror should be quite perpendicular to the surface of the mirror glass. And the front should be perdendicular as well to make it symmetrical .So after all you have to use a gigantic cube shaped prism with a beam splitter surface inside similar to a 3CCD beam splitter. And now again you get all the disadvantages of the big prism.

[Ace]

You could have a 45 degree mounted mirror that rotates at a few thousand rpm, reflecting to each sensor as it spins a revoloution.. the speed of the mirror RPM would = mechanical shutter speed.. thats how i would do it anyway.

[Andrew M.]

Rotating mirror is very good solution but it adds to the complexity and cost.
Bit more of brain storming here and maybe we will come up with some good simple solution.

As to the alignment (just thinking loud here) what about pixel shifting.
I couldn’t believe that I said that.

Seriously though, if we shift second CMOS Bayer pattern sensor by one pixel down and one right, relative to the first sensor we are getting double the resolution. Are we getting ½ of luminosity doing this?
And then the absence of green in the picture will not influence the outcome as bad as usually does for Bayer pattern sensors.
We have to balance between getting 16 bit dynamic range and higher resolution.
Whatever we loose in terms of luma we gain it back by combaining this two sensors data in to the one from bit 5 to 12 (not from 1 to 4 and 13 to 16)
Even if we get 8K virtual sensor resolution out of this pixel shifting I will downres it down to 4K on the output sensor anyway.

The first 4 bits (1-4) of low light will not be coming from the second (high luma sensor) so no extra resolution here, also last 4 bits (13-16) of high luma will not come from the first sensor so no extra resolution on highlights.
Do we need extra resolution at very low and very high luma levels?
Though from bit 5 to 12 we will get double kick in terms of resolution.

16 bit dynamic range is the only thing that is inferior on the CMOS, as compare to the film now.
We beat resolution of the film.
We beat the focus sharpness capability over the film.
Now if we bit the dynamic range then film is dead.


Just to simplify the discussion.

FIRST SENSOR is the low light sensor, this is the one servicing bits 1 – 12 and it is the one plugged to the second sensor 12 bit input port.

SECOND SENSOR is the high light sensor servicing bits 5 – 16 and it is the one that has 12 bit input port to take data from the first sensor and it has 16 bit output port.

As to the connection between these two sensors, we do not want to have more of data processing added to this sensors, especially to the second one that have to do some bits ORs or ANDs on the data. We can connect these two sensors not on the final bit data bus coming out of them but just straight on the row and columns of the CMOS photosensors, so the second sensor will have ability to address the first sensors photo cells like its own.
Just a thought that may simplify the design.
On the other hand, splitting processing power between these two sensors may be desired, so pre massaging the data on the first sensor before sending it to the second one could be very beneficial.
This reminds me the human eye construction.
The picture data received by our eye is pre processed on the retina before it is sent to the brain.
http://en.wikipedia.org/wiki/Retina
Can we learn anything from the nature here?

But let’s focus on the mirror design. Any other ideas?

[Hrvoje Simic]

You could have a 45 degree mounted mirror that rotates at a few thousand rpm, reflecting to each sensor as it spins a revoloution.. the speed of the mirror RPM would = mechanical shutter speed.. thats how i would do it anyway.


Acehole,
I like this idea.

In this solution the mirror would be reflective on both sides, and one revolution would cover 4 frames.

[Andrew M.]

And what is the speed equivalent on rotating mirror?
1/250 1/60?
We have to stop rotating when taking shoot of the frame.
This have to be some kind of electrically polarized plate rather then actual rotating mirror.
What is the speed on Misterium while reading ? 1/60 I presume at 60fps

[jbeale]

Stopping the mirror and then restarting twice per exposure presents some mechanical difficulties. With the right kind of sensor you could imagine shifting the pixels electronically in sync with the mirror rotation to accumulate the image as the mirror rotates, but this may be impractical for several reasons.

I wonder if it is possible to have a two-layer sensor, sort of a simplified Foveon design, with the top layer being a regular Bayer-type array as is used now, and then beneath that is a low-sensitivity layer that picks up a dim trickle of photons not absorbed in the top layer, but enough to give you a few more bits (= stops) of dynamic range in the highlights.

You might even not have to actually run any more pixels per second through the A/D, if you have some switch at each pixel so only the top layer is read, unless it has reached full-well status, in which case you switch over and use the bottom pixel and left-shift the result by X bits. This would be a step towards a native "log-output" sensor (like film, and the human eye) as opposed to the linear sensors like all the CCD and CMOS chips I'm aware of so far.

[Ace]

Acehole,
I like this idea.

In this solution the mirror would be reflective on both sides, and one revolution would cover 4 frames.

Actually I was talking about rotating from a 45 degree angle, so that it doesnt flip at any time. It just spins on one axis and the tilt determins the direction of reflection.

Also, why would you need to stop the mirror? Do film shutters "stop" to expose a frame on camera?

[Andrew M.]

LCD shutter or electronically activated reflection mirror could be used instead of mechanical shutter.
But I think the best idea is to use half reflecting mirror.
This way the first sensor that needs more light is the one right behind the mirror.
The second sensor that works only for mid and high light intensities is gathering light from semi-reflective surface. I guess we could experiment with altering electrically the reflective factor of the mirror so for 1/60 of the second the mirror is fully reflective and for another 1/60 of the second mirror is not reflecting at all, but this will cut the light quantities to both sensors and it is good for the second sensor but not good at all for the first one.
Any other idea how to direct the low light levels to the first sensor and high levels to the second one at the same time?
LCD shutter, rotating parabolic mirror that flips from one sensor to the other without rotation distortion…more key words needed….

[Bruce Allen]

At that point you're trading dynamic range for resolution, and introducing a much more complex demosaic algorithm.

Graeme

Yes, exactly! I'd rather have a 3K camera with high dynamic range... Introducing a much more complex demosaic algorithm is okay too as long as computers keep getting faster.

Bruce Allen
www.boacinema.com

[Graeme Nattress]

We picked the sweet spot for today, but all this stuff is interesting discussions for the future.

Graeme

[Andrew M.]

Just talking to the other people around here about intrinsic characteristic of the CMOS sensors, looks like there is a blind time spot where sensor is shunted to clear the photocell charge for next frame exposure.
Each CMOS is different so I can’t speculate on the Misterium design, but if there is a blind time for Misterium, this time could be used for the second sensor to gather the high intensity light. So electronically triggered mirror would be a nice option for this.

Another option is to create light memory turbocharger that will extrapolate intensity of the light based on the current curve of the charge voltage increase. So once the first sensor is shut out of light and the second sensor is receiving the light, the first sensor will be extra turbo charging its photocell based on the ramp up of voltage.

[Bruce Allen]

We picked the sweet spot for today, but all this stuff is interesting discussions for the future.

Graeme

Agreed! It's so cool having talks about ideas for improving dynamic range and not feeling that our comments are disappearing into a corporate black hole. I like small companies that respond to their customers. It makes me want to live off of cans of soup for months so I can afford a share in a Red One. Actually, that, combined with working straight through NAB, might just get me there... Anyway, enjoy NAB and good luck.

Bruce Allen
www.boacinema.com

[Thom Steinhoff]

You could have a 45 degree mounted mirror that rotates at a few thousand rpm, reflecting to each sensor as it spins a revoloution.. the speed of the mirror RPM would = mechanical shutter speed.. thats how i would do it anyway.

Very interesting idea, though as graeme said, they have the best solution to date.

Continuing your idea, though, if money was no object, I would think it would be cool to have the rotation axis of the mirror motor pointing directly down the barrel of the lens. Then you could have the top mirror (resting) be for the optical tap, then left right and bottom are the three chips or even get more drastic and have no optical and have six chips even spaced around the barrel, giving you the ability to have 2 sets of 3 (giving you more dynamic range maybe?)

Cool idea. I'll stick with my Red One, though, as it has no moving parts!

Thom

[Hrvoje Simic]

We picked the sweet spot for today, but all this stuff is interesting discussions for the future.

Graeme

E-xactly. Hence the community.

Thinking ahead is what made 4k.
RED's recognition of the power of idea input is another brilliant move. Disregarding the sea of ideas is like locking the countless doors to possible future. Personally, I can't stop thinking ahead and ideas come all the time. That's what got me to all this advanced multimedial expression tools in the first place.
I'm sure many people here also appreciate this open channel for that endless flow.

We'll keep the flow running as long as you guys are listening...

[Michael Brennan]

At some forum somebody told Ikegami made a 4 chip camera once with that purpose (the fourth chip only received a small fraction of the incoming light).

If we are talking about the same camera, the primary purpose of the 4th chip was to avoid a European import duty that was defined as "3 chip ccd cameras".

So Ikegami built a 4 chip ccd camera!


Mike

[baro]

Great info. Do you happen to remember the model name?

[Evangelos Achillopoulos]

Hello to all Red forumers…

I’m new here, am just reading for months now…

I decided to register, I haven’t reserve any Camera but in Greece am the evangelist (no it’s not coming from my name) of the digital era of Cinema for many years so it’s coming…

Graeme I have tried in my FT 2K your demo plugins and they are quite nice.

I have played a little bit with a Foveon sensor the Fx17-78-F13D few months ago from Alternative Vision and it was awesome the results even though I use it only in 1280/720 in 24fps in a four pixels to one configuration and the images where stunning. We where experimenting in our Lab in order to build a scanner… This sensor doesn’t need to de-mosaic and their resolution is far better than typical CMOS one chip in the same pixel count.

I was wondering do you thing to use same technology like this in the future cameras.
I thing the quantities that you gone to order from Foveon they will justify such an R&D for them.

For further reading www.foveon.com read under technology.

I will soon be one of your RED users since I will order one after NAB for my Rental/2KDI business…

Best regards and remember a start is half of everything…

[Graeme Nattress]

We had a discussion on the foveon stuff elsewhere, but there are real issues using it:

it doesn't have the fps for 4k.
Too low a resolution, just 2.5k at the moment.
Lots of colour issues / noise due to the aggressive matrix we need to get the colour right, so on and so forth.....

Graeme

[Andrew M.]

Hello, Evangelos, welcome to the forum.
There is many articles that I posted links to it here on this forum, comparing CMOS, Fevon and CCD. One good one, you can find on the Dalsa website is here:
http://www.dalsa.com/dc/documents/Image_Sensor_Architecture_Whitepaper_Digital_Cinem a_00218-00_03-70.pdf

In short, as per current state of technology, you can pack more photo-sensors per mm on CMOS sensor then on Fevon. All three technology developers are investing a lot of money in improving the characteristics of these sensors but as of now, if you want the speed and low heat dissipation the CMOS is bit more advanced. After all, if you pack 20 photo-sensor in place of one in Fevon you have 20 pixels to work with instead of one.
CMOS technology in the labs is pushed as far as 48MP and when Fevon will get even half the way there CMOS will be at 128MP. CMOS has its own problems to overcome as well but so far CCD and CMOS are technologies where the most R&D money is invested in.

[Graeme Nattress]

That's a good paper from Dalsa.

Graeme

[Dean Gough]

Amazing I sign up to Reduser.net and first thread I read is about an item I've been experimenting with for a while now.

The semi transparent mirror you are talking about is a pellicle (see attached)

410

411

412

Pellicles are very thin nitrocellulose membranes bonded to lapped aluminum frames. Ghost images are eliminated by the thinness of the membrane, as the second surface reflection superimposes on the first surface reflection. The uncoated pellicle reflects 8% and transmits 92% throughout the visible and near infrared regions. They are approx 2 mcrons thick.

The transmittance/reflection ratio of the pellicle determines how much light goes to the second sensor.

Experiments are being conducted with a pair of 2/3" Bayer CCD's, output of cameras is 8 bit RGB. The exact set up is still going through changes.

I have also explored briefly the other item of discussion, a rotating mirror, not to increase dynamic range but to increase frame rate. Imagine a 45 deg rotating mirror shutter as in a Arri 435 (or similar). The mirror not only provides the shutter function but in its closed cycle reflects the image to the optical system for the eyepiece, replace the eyepiece assembly with a sensor and you now can have two sensors capturing images 180deg apart or twice the frame rate.

All we have to do now is deal with the flood of data ;)



Talking about 3-chip design.
What about 2-chip design, to increase dynamic range.
Can we have semi transparent mirror in front of the first sensor and second sensor next to it, one responding to lower light levels and the second responding to the higher light levels?

Alternatively, is there a way to read only one CMOS sensor, first fast, for the intense light levels and then slow for the low light levels?

I was thinking to use 120fps in 4 intervals.
We use first ¾ to read low light levels and ¼ to read high levels.
Then to combine it as a one 30fps frame with extra two or 4 stops dynamic range?

[Andrew M.]

Dean, this 8% reflection or bit more will be more then enough to capture extra 4 bits of highlights. As to the second sensor to get higher frame rate, I think the CMOS is fast enough to go even 800fps, it is the data processing that is the bottleneck here.
So two chips or one, you have to get this data out somehow and process it.
The best is to advance CMOS technology so it will get 16 bit dynamic range.
For now if we want to beat the film we have to use two sensors.

[baro]

Hi Dean. That would be a great way to increase dynamic range. For a seamless integration of the two images from the brighter and the dimmer image, theoretically you would need the two transmission graph to be the same shape ( that is true when your goal is to increase the resolution too). As you experimented with that thing, you may have some experience if the small differences in the transmission shapes has a bad effect in practice on the resulting picture. Or can you apply an optical filter in front of some of the imaging devices that corrects the transmission function so that the two shapes are identical?

[Dean Gough]

The project was originally started because of my interest in HDR imaging. Most Digital Cinema cameras (notice I didn't say video cameras) seem to have around 9 - 11 stops of dynamic range and bit depths ranging from 10 to 16.

I don't see any reason this could not be extended to 14 - 16 stops (film is considered 11 - 12). From a purely visual stand-point you're not going to see the extra dynamic range on the screen because of the eyes inability to distinquish large variation in brightness but from a Post perspective the extra latitude may be useful. Same as an original camera negative may capture 11 stops of information but only a small part is ever seen on the screen.

CMOS is definitely fast enough, Vision Researchs Phantom HD camera does 1000fps at HD resolution. Useful but not for your typical Digital Cinema requirements. Thats actually what I like about RED, it has a great practical feature list without going overboard (read as adding unnecessary expense)

Anyway probably getting way of the subject of 3 chip cameras here. My 2 cents worth is that single chip cameras are here to stay and have more than enough quality capability for Digital Cinema use. There are so many other factors which effect the initial captured and displayed image. The digital still market which have used large single CCD and CMOS sensors for years, there are many instances 6 -8 Mpixel cameras have out performed 10 - 12 Mpixel units.

I've seen some pretty awful films shot on 35mm as well. Content is King.


Dean, this 8% reflection or bit more will be more then enough to capture extra 4 bits of highlights. As to the second sensor to get higher frame rate, I think the CMOS is fast enough to go even 800fps, it is the data processing that is the bottleneck here.
So two chips or one, you have to get this data out somehow and process it.
The best is to advance CMOS technology so it will get 16 bit dynamic range.
For now if we want to beat the film we have to use two sensors.

[Dean Gough]

Increasing the dynamic range was the primary goal.

One of the reasons I chose the 92/8 pellicle was because the graphs are very flat in there response. I am only experimenting at low resolution (640x480x8bit RGB) as proof of concept.

Now if I had access to a couple Mysterium sensors I could take it to the next level :)



Hi Dean. That would be a great way to increase dynamic range. For a seamless integration of the two images from the brighter and the dimmer image, theoretically you would need the two transmission graph to be the same shape ( that is true when your goal is to increase the resolution too). As you experimented with that thing, you may have some experience if the small differences in the transmission shapes has a bad effect in practice on the resulting picture. Or can you apply an optical filter in front of some of the imaging devices that corrects the transmission function so that the two shapes are identical?