IMAX /IMAX 3D

[Larry Kelly]

I've been working with some colleges who are experienced in IMAX and IMAX 3D. We are collaborating in designing 3D IMAX solutions transitioning from film to digital. We will be testing a new mirror rig that we have been developing in hopes that we can capture both the wide field of view as well as the depth of field control that film has been able to provide but here is the problem.

The ARRI 65 has the sensor size but is heavy, large and expensive.
The Dragon has the resolution but has a small sensor in comparison
The Weapon sensor is slightly larger but still not in the ballpark of 65-15 but has more pixels, perhaps enough pixels to achieve what I am suggesting below.

1. Use 8K weapons on 3D rig.
2. Develop a PL to Hasselblad etc. speed booster to adapt the viewing angle to match 65mm as closely as possible.
3. Result is comparable depth of field, acceptable resolution, field of view which may feel more like film than digital.

This would enable a light weight, slightly less expensive alternative with enough resolution to crop to 4/3 IMAX and you gain a stop or so in the process.

Is this possible, practical or has it been considered already??

 

[Gavin Greenwalt]

I wouldn't go with a speed booster. There is plenty of really good, rediculously fast Full Frame/Vista Vision glass. The Alexa 65 is about 33% wider than W-VV. If you want that shallow DOF look then just take a slightly wider lens and use the much faster Full Frame lenses. I have a Mamiya and to tell you the truth it's kind of a total bummer these days to shoot with it. I like shooting film but my Full Frame 35mm with fast primes has the same DOF and is way lighter. Do we know which Mamiyas Arri is converting? Because I would wager they're probably going to be on average around F/3.5. You have ultra primes at F/1.3 and you're into shallower DOF at 41mm than F2.8 @ 55mm on Medium format.

The only reason Arri went with large format was because they didn't want to increase the density of their sensor which people are very happy with. You can already achieve the "65mm/70mm look" with existing lenses in 35mm. A Full Frame F1.3 lens has the save DOF as an IMAX lens at 2.8.*

*I think. Or at least it should be pretty close... right lens techs?

DOF: RED-VV has shallower with faster lenses.
FOV: Tie. Same with appropriate lenses.
RESOLUTION: Technically RED-VV with 8k vs 6.5k unless Arri employs some fancy debayer tech to level the playing field and RED doesn't respond. Probably a tie though for most films since nobody will be doing VFX at 8k.
IMAGE QUALITY: Up to personal preference and we don't know what tuning RED has in store for VV.

 

[Mike Nagel]

1. Use 8K weapons on 3D rig.
2. Develop a PL to Hasselblad etc. speed booster to adapt the viewing angle to match 65mm as closely as possible.
3. Result is comparable depth of field, acceptable resolution, field of view which may feel more like film than digital.

W 8K has a 1.28 crop factor to 65mm

DOF can be matched by adjusting any of the 5 parameters that determine DOF...

FOV can be matched by adjusting distance, but u can't match the perspective of larger formats...

 

[Gavin Greenwalt]

FOV can be matched by adjusting distance, but u can't match the perspective of larger formats...

Sure you can. You can adjust FOV by just changing your focal length. An 80mm and a 120mm will look exactly the same with the proper compensation in sensor size. Just like you can shoot the same perspective on a 2/3" ENG camera as a Super35mm camera with a different focal length.

 

[Mike Nagel]

Sure you can. You can adjust FOV by just changing your focal length. An 80mm and a 120mm will look exactly the same with the proper compensation in sensor size. Just like you can shoot the same perspective on a 2/3" ENG camera as a Super35mm camera with a different focal length.

yes, but then u will have an even harder time (or it will be impossible) to match the DOF, because u have to use (much) wider lenses... by moving the cam back u can use the same lens (same focal length, aperture, same DOF characteristics), but u won't get the perspective...

IQ wise, at least that's what I think the OP is trying to achieve... ;-)

 

[Larry Kelly]

Thanks for the input guys, I'm not the camera or lens expert in this team but it seems to me that taking into account the aspect ratio of the IMAX which is i believe 4/3 there is a significant crop factor with the 2/1 sensor ratio of the dragon or 8K weapon. For this reason I'm thinking that the closest emulation to the aspect resolution to the 65-15 film would require some sort of optical wizardry like the speed booster. With out it you would have a significantly shallower depth of field and possibly lacking in that large format feel that you get in the Science park 3D IMAX theatres. That said I will take your suggestions to our IMAX guru and see what he says.

 

[Gavin Greenwalt]

yes, but then u will have an even harder time (or it will be impossible) to match the DOF, because u have to use (much) wider lenses... by moving the cam back u can use the same lens (same focal length, aperture, same DOF characteristics), but u won't get the perspective...

Matching the DOF is pretty easy. And besides people aren't trying to "match" DOF they will just judge it by eye until it looks good. If I told you an "80mm lens on Super 35 at F1.8" and told you to "draw a circle the size of the Bokeh for a point light 30' from camera with the focus set to 10 feet" I am fairly confident no living DOP could guesstimate a precise bokeh diameter. And even if they could... even fewer could do the same test on a 70mm IMAX format. Also the math is incredibly easy. If you double the FOV then you halve the F-stop and it should match. So a 100mm @ F5.6 will have the same bokeh diameter all else being equal as 50mm @ F2.8. F2.8 literally means the aperture is 50mm/2.8 = 18mm Aperture. 100mm / 5.6 = 18mm aperture. If anything DOPs are far more familiar with FOV for Super35/FullFrame 35 than they are with IMAX FOV. So if there is any "matching" it's going to be DOPs trying to figure out what a "50mm equivalent is on IMAX" not IMAX cinematographers trying to figure out an equivalent S35 or FF35 lens to their regularly used lenses.

Once you introduce a speed booster you will be experiencing a quality drop since it's one more piece of glass that wasn't integrated into the lens' design. It also means you would have to unnecessarily use larger heavier medium format glass. There is no reason except for resolution to shoot medium format considering how slow most medium format lenses are. An alternate way to look at it is to think of a really nice fast F1.3 Master Prime *as* a medium format lens with a speed booster built in since it's more than twice as fast as most MF glass. And as luck would have it, in the case of motion, you can find higher resolution Full Frame sensors than IMAX sensors.

 

[Christopher*Seguine]

Do we know which Mamiyas Arri is converting? Because I would wager they're probably going to be on average around F/3.5. You have ultra primes at F/1.3 and you're into shallower DOF at 41mm than F2.8 @ 55mm on Medium format..

No Mamiyas, Hasselblad HC or HCD all the way, same ones IMAX re-houses. Most are T3.5, but the 100 is T2.2

The only reason Arri went with large format was because they didn't want to increase the density of their sensor which people are very happy with. You can already achieve the "65mm/70mm look" with existing lenses in 35mm. A Full Frame F1.3 lens has the save DOF as an IMAX lens at 2.8.*.

well getting more life out of the 765 lens series is probably a factor too, and there is a 110mm T2.1 in that line.

DOF: RED-VV has shallower with faster lenses.
FOV: Tie. Same with appropriate lenses.
RESOLUTION: Technically RED-VV with 8k vs 6.5k unless Arri employs some fancy debayer tech to level the playing field and RED doesn't respond. Probably a tie though for most films since nobody will be doing VFX at 8k.
IMAGE QUALITY: Up to personal preference and we don't know what tuning RED has in store for VV

You forgot sensitivity, those are some pretty big pixels on the Alexa65 - 8.25 micron vs Weapon's 5 micron, plus 12bit log arriraw vs 12 bit linear raw with redcode.

 

[Phil Holland]

Hi Larry,

Couple things to clear up. IMAX supports Aspect Ratios of up to 1.43:1, at least the shot on film IMAX productions. IMAX Digital productions are 1.9:1 typically, which is also the DCI Standard and also the Aspect Ratio of Weapon 8K Dragon. The Alexa 65 is a 2.11 Aspect Ratio.

True IMAX film productions are/were shot on 70mm 15-perf. The Alexa 65 is closer to 65mm 5-perf.

If focused on the extraction of an Aspect Ratio of 1.43:1 you get:
Alexa 65 = 4436x3102 (36.6x25.58mm)
RED Weapon 8K Dragon = 6178x4320 (30.89x21.6mm)

If focused on the 1.9:1 Aspect Ratio:
Alexa 65 = 5888x3102 (48.58x25.59mm)
RED Weapon 8K Dragoon = 8192x4320 (40.96x21.60mm)


Do remember you have access to faster lenses on the VistaVision+ format of RED Weapon 8K Dragon and higher frame rates as well. (Weapon 8K = 60 FPS at 8K, Alexa 65 = 28 fps at maximum resolution)

Just a couple of numbers to poison your mind.

 

[Mike Nagel]

Matching the DOF is pretty easy. And besides people aren't trying to "match" DOF they will just judge it by eye until it looks good. If I told you an "80mm lens on Super 35 at F1.8" and told you to "draw a circle the size of the Bokeh for a point light 30' from camera with the focus set to 10 feet" I am fairly confident no living DOP could guesstimate a precise bokeh diameter. And even if they could... even fewer could do the same test on a 70mm IMAX format. Also the math is incredibly easy. If you double the FOV then you halve the F-stop and it should match. So a 100mm @ F5.6 will have the same bokeh diameter all else being equal as 50mm @ F2.8. F2.8 literally means the aperture is 50mm/2.8 = 18mm Aperture. 100mm / 5.6 = 18mm aperture. If anything DOPs are far more familiar with FOV for Super35/FullFrame 35 than they are with IMAX FOV. So if there is any "matching" it's going to be DOPs trying to figure out what a "50mm equivalent is on IMAX" not IMAX cinematographers trying to figure out an equivalent S35 or FF35 lens to their regularly used lenses.

Once you introduce a speed booster you will be experiencing a quality drop since it's one more piece of glass that wasn't integrated into the lens' design. It also means you would have to unnecessarily use larger heavier medium format glass. There is no reason except for resolution to shoot medium format considering how slow most medium format lenses are. An alternate way to look at it is to think of a really nice fast F1.3 Master Prime *as* a medium format lens with a speed booster built in since it's more than twice as fast as most MF glass. And as luck would have it, in the case of motion, you can find higher resolution Full Frame sensors than IMAX sensors.

Dude, I'm not trying to "match" anything, the OP is... ;-)))

yes, distance and focal length have a reciprocal relationship in the DOF equation, so u're saying u're using aperture to then "match" DOF... well, if the "reference DOF" on large sensor was already with a very wide aperture, then u have no chance... unless u're telling me u're using Kubricks 0.95 f-stop lens and u can open the aperture that wide to match the DOF... ;-))) the only other DOF deciding parameter u have left now is CoC...

Obviously, additional "problems" u could potentially have with ur approach when having to use wider lenses can be increased CA, lens distortion and a higher min aperture when going lower in focal length, e.g. < 18mmm (which would make it impossible to match DOF)...

U can NEVER completely re-create what large sensors do on smaller sensors (u will always lose at least one IQ factor, and may it just be resolution), otherwise nobody would have ever been shooting 35mm over 16mmm and 65/70mm over 35mm................... ;-)

 

[Michael Tiemann]

Gavin and Mike,

I think you are both right. Namely, that the whole FOV/DOF thing is a complete red herring, because obviously all a lens does is cast an image on a focal plane, and clearly speed boosters/teleconverters can reduce or shrink the image to make identical renderings (of FOV/DOF) on smaller or larger sensors for whatever benefit that might be. A 21 T1.0 lens with an image circle of 18mm is equivalent to a 42 T2.0 lens with an image circle of 36mm is equivalent to an 84 T4.0 lens with an image circle of 72mm, provided you can properly record the same percentage of each image circle with your sensors.

But you are also both correct--and this is the far more important point--that the character of the lens is really what people are looking for. The character may first be sorted by FOV and DOF, but things quickly get down to bokeh, contrast, resolution, etc., and this becomes both a function of the lens and the imaging system. There may well come a day when a whiz-bang lens material[*] makes it possible to do have zero CA, perfect MTF, etc., across a small sensor, and that might end up imaging better than conventional MF glass on a large sensor. But in the mean time, knowing the characters of the various systems is like knowing which paint brush to use, not only which color, and today, the large glass/large sensor systems do have observably different character than small glass/small sensor, beyond what the FOV and DOF numbers indicate.

[*] http://www.wired.com/2012/08/new-flat-lens-could-revolutionize-cameras-as-we-know-them/

 

[Gavin Greenwalt]

Otherwise nobody would have ever been shooting 35mm over 16mmm and 65/70mm over 35mm................... ;-)

Well, that was when the playing field was completely level because of chemistry. It used to be that if you got Kodak stock it was essentially identical just cut to different sizes. That's true of Alexa/Alexa65 since it's just a larger cut but the ALEV sensor has been a real trooper for the last 5 years where as Dragon is a pretty brand spanking new sensor (for better or for worse). It would be like comparing Super16mm Vision 4 to Super35 reversal. A couple generations of technology can make up the difference in size. Just like a modern APS-C lens can "out perform" a lot of Full Frame lenses from the 90s.

One thing to keep in mind is investment. Cooke, Nikon, Canon and Zeiss have invested a LOT of money into refining Full Frame lenses. It's true that CA and distortion are more challenging on a smaller sensor but they also have spent an order of magnitude more resources on perfecting the optics on a lens like the OTUS 50mm than Hasselblad has spent working on their 80mm. And probably the best performing low light sensor in the world today is a Full Frame sensor (A7S) not a medium format sensor. The A7S sensor would scale up really nicely to medium format but sometimes consumer technology outpaces niche tech. Medium format is definitely niche.

 

[Mike Nagel]

Well, that was when the playing field was completely level because of chemistry.

absolutely, that's the great thing for us living in the golden age of cameras... so many options and sensor size is just one of many factors that contribute to the IQ...

IMO, the image fidelity of the sensor is more important than the actual physical size...

 

[Larry Kelly]

Thanks for the education on IMAX sizes Phil. Ok, so what many of you are saying is an 8K sensor in a weapon can potentially produce a similar look and feel as IMAX film cameras due to the superior glass compared to the current lenses used on IMAX film cameras even with the floor to ceiling goodness of the IMAX format?

 

[Mike Nagel]

Thanks for the education on IMAX sizes Phil. Ok, so what many of you are saying is an 8K sensor in a weapon can potentially produce a similar look and feel as IMAX film cameras due to the superior glass compared to the current lenses used on IMAX film cameras even with the floor to ceiling goodness of the IMAX format?

IMO, the look and feel that I always want when I go and see movies in IMAX is due to the large image plane capture... and that relates to FOV and the inherent perspective and DOF (at that perspective). You will only get that on large sensors. That is what makes IMAX to me such a different experience, and it can be very underwhelming when it does not deliver... like Nolan's Interstellar which - for me - was a disappointing experience in IMAX... (not a format issue, the way he used it for IMAX release)

W 8K has 1.28 crop to 65mm and 1.7 crop to 70mmm capture... u won't get that unique look and feel of the larger formats...

but, as Gavin has pointed out, u will get much cleaner, prettier images due to the vastly improved capture process nowadays (glass, sensor, etc)... so aesthetics will be better.

and turning the other way, comparing to S35 or even Dragon 6K capture - u will have that unique look and feel... it all depends what your reference is... ;-)))

 

[Gavin Greenwalt]

Yes. Also keep in mind that IMAX is rolling out their new projectors now and they're dual 4k projectors. So any camera that can resolve 4k resolution in the near future will be delivering the maximum resolution that IMAX can project with their new Dual 4k DLP Laser Projectors.

Also keep in mind that most IMAX films these days are feature films that are shot on Super35 and finished in 2k. So just upping to 8k aquisition and 4k mastering will look sharper and more IMAX-y than Avengers Age of Ultron.

However Mike and I disagree. And that is that you can get the exact same look and feel on Full Frame/Vista Vision as 70mm. It's simple physics. An F1.3 50mm on VV will have the same look and feel as an 80mm at F2.8 on IMAX. There just *aren't* any good cinema lenses for IMAX that can deliver shallower depth of field or a superior image to a quality Full Frame lens IMO.

 

[Mike Nagel]

However Mike and I disagree. And that is that you can get the exact same look and feel on Full Frame/Vista Vision as 70mm. It's simple physics. An F1.3 50mm on VV will have the same look and feel as an 80mm at F2.8 on IMAX.

it is... until physics meets reality ;-)

so if your reference shot at 80mm is already full open @ 1.3 u won't match as your 50mm won't have the required max aperture...

if - in ur specific example - u can't open the 50mm to 1.3 because of exposure problems, again u won't match the look...

it's all these funny tests we did 5 years ago with 7D vs 5D and those are the issues u will run into... besides that u capture less resolution...

there are examples where it will work, like ur examples, but that does not mean it will work all the time... besides that the wider required aperture on smaller sensors will make the image softer (with most lenses)... another difference...

There's a reason peeps are buying the W 8K sensor... ;-) again, level playing field Dragon 6k vs. Dragon 8K... and lenses will be better (for a while) on Dragon 6K but peeps are buying the larger format...


so I'm not disagreeing with you on the logic (excluding the difference in resolution capture), what we have is a case of theory vs. practical application...

 

[Gavin Greenwalt]

if - in ur specific example - u can't open the 50mm to 1.3 because of exposure problems, again u won't match the look....

Sure it will you just apply ND like every DOP has done on every shoot since the beginning of time. Set your Aperture for your creative DOF and then use ND to control your exposure. Not to mention we would expect that the smaller sensor would be less sensitive so its native ISO would be lower. As you said smaller pixel wells means less sensitive. So it naturally cancels itself out.

And lenses like the OTUS can out-resolve Alexa 65's 6.5k sensor wide open. We aren't talking about APS-C (and even then try and tell ARRI that their master primes are sub-par to a Hasselblad's), full frame lenses are plenty large to avoid most of the physical limitations of designing an extraordinary 16mm or even S35 lens.

 

[Mike Nagel]

Sure it will you just apply ND like every DOP has done on every shoot since the beginning of time. Set your Aperture for your creative DOF and then use ND to control your exposure. Not to mention we would expect that the smaller sensor would be less sensitive so its native ISO would be lower. As you said smaller pixel wells means less sensitive. So it naturally cancels itself out.

And lenses like the OTUS can out-resolve Alexa 65's 6.5k sensor wide open.

okay, we are running in circles now... ;-) all arguments mentioned already...

just a last thing: I'm always comparing apples to apples, meaning (theoretically) same sensor to same sensor, just a different size of that sensor... Dragon 6K vs. Dragon 8K.

if u're now bringing in different sensor technologies, then this gets mood very soon as I would always shoot on the S35 Alexa than on the FF 5D MK III...

not because of FOV and perspective but because of color rendition and DR... the overall aesthetics factor, as mentioned before.

So why do u think Nolan still (partially) shoots 65/70mm ? because he can't "match the shot like u" on 35mm.... ? ;-)))))))))))

Are u saying that if I drop u off in palm Springs with a 7D and a Canon Zoom that a week later when I pick u up I would see the next "Lawrence of Arabia" in all it's 70mm glory ? ;-)

 

[Gavin Greenwalt]

OK I just ran the numbers. To match an IMAX 100mm a VV Weapon would need to be a 60mm. That means a Hasselblad 100mm which is Hasselblad's fastest prime would be an F2.2.

100mm/2.2 = 45mm aperture.
60mm/ X = 45mm => 60mm/45mm = x = F1.3.

So the Otus F1.4 would be only a nearly imperceptible smidge less shallow on the depth of field. But would be shallower than an Alexa 65 by a mile. Also the Otus as I said can resolve 20+ megapixels. 6.5k is only 21 megapixels so the Otus should be able to at least match the Alexa 65 for resolution. The Otus also has nearly no CA and nearly no distortion. So it's sharp enough. It matches DOF. It matches field of view and it's lighter and smaller.