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Rear Projection on 35mm

rear projection 35mm

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#1 Anna Biller

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Posted 30 October 2014 - 05:06 PM

I'm shooting some car scenes where I want studio lighting on the actors, so I'm thinking rear projection might be the best way to go. A model for the look I want is the driving sequence near the beginning of Bunuel's BELLE DE JOUR (starting at about 11 minutes into the film). One DP I spoke to said he thinks those shots were done on a process trailer, but to me they look like rear projection. Any thoughts on how those scenes were shot would be greatly appreciated.

 

We're shooting on 35mm, and I was wondering if anyone has had experience shooting on 35mm and projecting the background plates on LCD or DLP?  Are there issues with flicker when shooting in this way? And does anyone have advice on which type and size of screen to use?


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#2 Albion Hockney

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Posted 31 October 2014 - 10:55 AM

If you want to do rear projection and achieve a look that is realistic you need a really great projector and strong source material. I think it doesn't matter too much what you are shooting on yourself (digital or film)....someone else might chime in and say some technical stuff with 35mm I am not aware of but I couldn't really see any difference existing.

 

As for screen size I'd think you want something pretty large in size as to get a bit of distance between your talent and the backround. For the projector I'd say you want atleast 1080p (2k or 4k would probably be better) and you will want something very bright ....at the very least 5000lumens

 

there are specfics of the screen type too for sure, I did this once many years ago and I had a good talk with a rental house about what screen to use as there are several options in materials....I'd talk with the rental house about that part.


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#3 Phil Rhodes

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Posted 31 October 2014 - 11:28 AM

All of this depends on how large the projection will be in frame, whether it will be (or has to be) in focus, and how specifically it will be referred to. 

 

There isn't a huge difference on paper between doing it on 35 or HD, other than the fairly enormous issue of being able to see exactly what you're getting in the latter case. You should be able to see any flicker in the viewfinder in either case. A TFT projector is less likely to produce unacceptable flicker than a DLP, but either might, and you should certainly test with both camera, projector and video playback device you'll be using to ensure everything's OK.

 

Colour may be a problem, which, again, you can probably only really determine by testing.

 

I would not do this on 35mm without tests, unless I had people supplying the projection equipment who were willing to guarantee me on their mother's lives that it would not give trouble.

 

P


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#4 Anna Biller

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Posted 01 November 2014 - 05:18 PM

Thanks for your suggestions!

 

If you were shooting the scene, how bright a projector would you go with? I read somewhere that 25,000 lumens was an idea to be aimed for, but that's not in our budget. I was wondering if 10,000 lumens would be bright enough. 

 

What would be a large screen size? 10' x 14', or larger?

 

Some of the background scene will have to be in focus, because there is a car tailing the car in front that must be seen through the rear window.

 

I don't think I have the budget to do tests really...that would involve the renting the studio, lights, the car, the screen, the crew, etc. and it's just not feasible for us to do that without at least trying to get the "real" footage out of it. 

 

Is there a way to adjust the frame rate of the projector to be in synch with the camera, or to synch them together somehow so there would not be an flicker?


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#5 David Mullen ASC

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Posted 01 November 2014 - 06:25 PM

You really need to test, but it doesn't have to involve the car in the test, a face in front of a screen would do. Perhaps you can drag the camera over to the video projector rental company and do the test there.

 

It may be possible to use a smaller projector and screen and scale up the results on paper to figure out what you really need but I don't know how precise that would be.

 

With most digital projectors, flicker is probably not going to be an issue but it is still a risk not to test unless you have some fancier flicker meters to measure the screen with, assuming your 35mm camera has an adjustable shutter angle anyway so that you can do something about it.

 

You also have to factor in that most projectors are close to daylight balance and will create blueish image in a 3200K setting unless you pre-grade your footage with an orange cast to correct it for tungsten (the best way to be sure that you are close to the right amount of orange is to shoot your plates in daylight balance but with an 85 filter on the lens to make it orange.  Or just light the actors with daylight balanced fixtures -- LED's, HMI's, etc.)  You could try taping a glass 85 camera filter to the projector lens but you'd lose output and there may be some heat danger, I don't know.


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#6 Phil Rhodes

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Posted 01 November 2014 - 08:10 PM

I think if one were to test with a projector other than the final one, there would be a significant risk of there being differences in how the output is refreshed, potentially affecting flicker. Colorimetry is also likely to alter unless it uses the same type of lamp. 

 

Flicker would probably be visible in an unloaded camera through the viewfinder, but I'd consider it a very dicey approach to assume that the colour would be anywhere near daylight. On video at least, many of them appear minty-greenish. All kinds of esoteric light sources are used for video projectors.

 

The cheapest way to test it would be to look at it through an unloaded camera for flicker, and take some stills using the proposed stock for colour. That might get you most of the way there. There are special considerations (which can ruin yours and others' film) about having motion picture stock processed as stills, so beware.

 

As to brightness, you'd have to spot meter it, ideally while projecting a static test image of a representative field of grey. You can't assign a number of required lumens without knowing the geometry. Project a given number of lumens on a larger screen, it'll look dimmer than on a smaller screen. What you need will change depending on the sort of footage you're projecting, the speed of the film, the lighting conditions, etc.

 

P


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#7 Anna Biller

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Posted 02 November 2014 - 06:52 PM

Hmmm...lots of things to consider. Thank you Phil, David, and Albion for your invaluable suggestions.

 

The color does worry me, now that you guys mention it. Isn't there a way of putting a filter of some sort on the projector lens without cutting too much of the light?  Or is there a way of testing the color temperature of the projector with a meter, so that the footage can be timed to compensate?


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#8 David Mullen ASC

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Posted 02 November 2014 - 07:09 PM

You could try camera correction filters taped to the projector lens, I just don't know what the heat is like right there, I'd hate to crack an expensive glass filter.

 

Digital projectors also have some range of color temp adjustability in their menus.

 

Sure, a color temp meter can read the light from the projector, it may be easier if it is projecting the image of a grey card. You can use that reading to balance the light on the foreground but I'm not sure how you use that reading to color-correct the footage, going into a color-correction session knowing that the projector image is, let's say, 6000K, doesn't necessarily tell an colorist how to adjust the image.  Hence my suggestion to shoot the footage pre-filtered if possible with an orange 85 filter but the camera set to daylight, then you'd know that your projected footage would be closer to tungsten balance.  Or if this is previously shot footage, take it into the colorist's room but also bring in a grey scale shot under white light and then with an orange 85 filter on the camera so he has a neutral and an orange reference, then he can time the original footage to match the amount of orange on the grey card shot. 

 

But even then, you'd still need to tweak the lighting on the set to match perfectly.  A digital still camera may be a good reference for that.


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#9 Phil Rhodes

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Posted 02 November 2014 - 07:23 PM

Personally I'd hope to have something like a Blackmagic HDLink in the chain, so the image could be tweaked on set. But then I'd be shooting video and lighting to a monitor...

 

If a DSLR is a reasonable reference (which is not something I can talk about as I've never done it) that might work with an HDlink or other LUT box or digital processing device. Certainly it'd be easier than optical filtering, although I have seen that done on video projectors. If you play the footage back using a PC, you may find the graphics card's driver software has some colour correction capability built into it, perhaps including curves.

 

Some video projectors (and monitors, and outdoor LED display screens, and so on) may end up needing to look practically sepia in order to render anything like correctly on camera. A lot of news sets, which often have lots of video displays of various types, look terrible in person, with all the video looking brownish to the naked eye. Don't be surprised if your projection looks terrible on set in order to look correct in the final image.

 

P


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#10 Ali Walker

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Posted 03 November 2014 - 06:40 PM

I definitely wouldn't shoot this scene in 35mm. The quality of lamp in the projector is your first issue. You would need a Barco/Christies DLP projector for decent light output and true 24p etc. Some projectors don't run at 24p (especially 99% of consumer ones- even if they say so 23.98). Then  if you can't afford those projectors (rentals are very expensive), you will have issues with colour depending upon the type of projector used etc etc etc. If you have to shoot 35mm for this then use an old 35mm film projector- you'll get the look you're after and a much better quality light output. But I would still shot this digital!


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#11 Anna Biller

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Posted 03 November 2014 - 06:48 PM

Hi Ali, well, the rest of the film is going to be shot on 35mm so it has to be shot on 35mm. The thing about 35mm projectors is that 1, usually the lamps are not bright enough for rear projection, and 2, I can't even find one in all of Los Angeles for rent! (Not even an ordinary one). The great thing about the digital projectors is that the lamps are so bright. I remember reading somewhere that the projectors used for rear projection back in the day were special projectors with fantastically bright bulbs that were only used for that purpose. (Although I've read elsewhere on this forum about someone using a regular 35mm projector for rear projection). I'd also have to find one of those old motors to synch camera and projector together. It would be so much fun to shoot it that way, but where can I get the equipment?? I did call about a DLP projector, and they are outrageously expensive. 


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#12 Phil Rhodes

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Posted 03 November 2014 - 07:16 PM

DLP projectors often look brighter than 35mm projectors, even when the 35mm device has a more powerful lamp (or at least a lamp that consumes more power). The DLP devices in a proper D-cinema projector, or even lower-end ones, are often larger than a 35mm film frame, with consequently larger lenses. This provides for a lower effective f number through the complete optical setup with increased brightness as a result. Also, and perhaps more significantly, DLP and TFT projectors don't have a shutter, so they don't waste so much light blasting it into the back of a shutter.

 

I don't think you need to look for a brand name like Barco or Christie, although you could be more sure of a projector which uses a Xenon lamp, which at least has a reasonable spectral output to begin with. It still wouldn't be a certainty, though, because there may be a significant amount of filtering in the projector to ensure its images look appropriate to the eye which may or may not work well on film.

 

The flicker issues caused by a projector may be entirely unconnected to the frame rate of the video, too. DLP projectors in particular may create shimmer regardless of the source frame rate because of the low level details of how they work.

 

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#13 Ali Walker

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Posted 03 November 2014 - 07:39 PM

Have you tried cinemas? They may have old digital projectors knocking about in projection room. I have done this before, but Christies supplied the kit along with a technician, and the biggest issue you may have is real 24p. Yes the light output is very powerful but some of the cheaper units like Sony have naff quality of light and you'll end up building rig to flag the ambient light. They filmed large parts of Oblivion wth DLP projectors and no lights for a global illumination look. What about keying the background in?


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#14 Anna Biller

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Posted 04 November 2014 - 07:03 PM

Thanks again everyone for your suggestions. I did think about keying the background in, but what i love about rear projection is the ability to direct actors in front of the background image so I know exactly what I'm getting. I also love the look of rear projection. I did find a reasonably priced DLP projector in Florida (5 times cheaper for the same projector in Los Angeles), but I have to find out if they will ship it here for the rental. So is the consensus that a 24P DLP projector is the way to go?


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#15 Freya Black

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Posted 05 November 2014 - 08:47 AM


If a DSLR is a reasonable reference (which is not something I can talk about as I've never done it) that might work with an HDlink or other LUT box or digital processing device. Certainly it'd be easier than optical filtering, although I have seen that done on video projectors. 

 

I hope I'm not muddying the waters but I wondered if it would be worth trying this out with a 24p video camera of some kind first to get an idea of the potential issues or even if it might be in some way comparable. It seems like a would be a good way of getting more experience with this kind of thing even if it was just a Canon 5D or a HVX200 or something and a cheap consumer projector of a similar type to what you are expecting to use. This seems like it might give you more of an eye for potential problems down the line.

 

Perhaps you could even use such cameras on set alongside the 35mm camera to get an idea if there are going to be issues too.

 

Of course that doesn't preclude the 35mm camera having it's own special issues with whatever the setup is but it might get things most of the way there at least.

 

Freya


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#16 Anna Biller

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Posted 11 November 2014 - 01:26 PM

Does anyone have any opinions on whether to shoot the plates on film or digital? I was thinking to shoot them on film and transfer to digital to project, but is this the best way?


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#17 Phil Rhodes

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Posted 11 November 2014 - 02:13 PM

I've seen 35mm film shot using digitally-acquired plates. The back projection for Oblivion was shot on Epics, but the movie was F65. It depends heavily - as do all the things we've discussed here - on exactly what the content of the scene is, and what function the back projection is required to perform.

 

Is this a faintly-visible horizon out of a ship's porthole in the background of a scene, or is it two thirds of the frame with a requirement to look photorealistic?


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#18 David Mullen ASC

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Posted 11 November 2014 - 07:17 PM

Just shoot them digitally, for one thing, most of the time camera will be focused on the subject, not the projected image, but second, if you are shooting the scene on film, that will provide the grain structure over the image, you don't really need grain also in the background on top of the overall grain.  And third, with the plate being projected on a frosted screen material, it would be hard to tell the difference between film or digital anyway, so if digital plates are easier and cheaper, do that.

 

It's also easier to edit the plates to the lengths needed.


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