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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Red and the infraRED

Shawn Nelson said:
Okay so I was wondering yesterday. The still lense industry has obviously worried about this before (just see all the round screw on 486 filters at B&H). But why has the film industry never fixed this? Does film not have this problem? What about F900 or Viper? Surely they've gotten into heavy NDs and theyn wondered "Why does the black shirt look purple??"
Click to expand...
Picked up the same problems with Vipers on a feature shot late last year. Finding this thread very usefull
 
I got this nice email from Better light INc:

"We buy our filters from these folks, it’s available in 6.5 inch squares and they cut it to size for us, for a fee of course. The thicker the glass the more IR is cut off. Here is a link to the specific IR filters we use:

http://howardglassco.thomasnet.com/...s/schott-filter-square-glass-2/bg-38?&seo=110



You’ll note it is a Schott filter and here is a link directly to the same filter at Schott:

http://www.besoptics.com/html/body_schott_bg38_filter_glass.html



We would have to mark this item up too much to act as an agent for you but you can email both of them directly and see where it goes, I’m sure one or both of them can serve your needs.

I should mention that we get our filters in two different thicknesses, 2mm for daylight and 3mm for tungsten, and we occasionally double them up to a total of 5mm when there are special problems with IR contamination in certain colors, mostly red’s, green’s and warm brown’s. This doubling up refers to the use of our systems for fine art reproduction which is the most critically demanding application where color accuracy is concerned."
 
Dominic Jones said:
Yes, of course, that will be a factor - good thinking Rob!

So between that and Deanan's info, I guess that's just a growing pain for single CMOS sensors. The fact that Red doesn't employ an analogue gain that can be turned down is probably exacerbating the issue a little as well, at a guess.

Haven't heard stories of Genesis or Dalsa problems with IR though - can anyone comment on if they have similar issues or how they solve them if not?
Click to expand...

I certainly can't speak for Panavision, but as far as DALSA is concerned, we solved all previous minor issues relating to IR about 14-months ago.

I've attached a downconverted 2K image from a horror film that shot with the camera about a year ago now. No filtration, shot with a DALSA 4K prime lens. This shot is a rigorous IR test to put a camera through. Exposure was a best guesstimate by the DP, but everything holds great from the brightest highlight to the darkest shadow detail down in the charred bits of plastic. The little bit of saturated blue in the fire just to the right of center near the bottom is remarkable- I don't think I've ever seen that amount of color information captured on any other digital cinema camera when shooting flames/fire. If I can find more DPX files from the project, maybe I'll post them in another (more appropriate) forum.

I.

Illya Friedman
DALSA
Digital Cinema Division
www.dalsa.com/dc
 
Well it looks like my upload (my first) was resized to even a smaller/lower resolution by the forum. I guess I'll find another place to put the higher resolution version.

I.

Illya Friedman
DALSA
Digital Cinema Division
www.dalsa.com/dc
 
Gregorios said:
I just did a very quick test today with an ND9 Panchro vs. reg ND9 under HMI lighting at PS today. Mr. Koch had tipped me off earlier. I will post when I get the .r3ds tomorrow from Morning. Congrats on the nom.
Click to expand...

Hey Gregor

That is great. I'll look forward to your results.

Congratulations on your nomination as well!

Dylan Macleod, DP
Toronto, Canada
www.dylanmaceod.com
 
Illya,


That is indeed very impressive. I've shot a lot of fire, and a lot particularly with the Phantom. So I know how much of a torture test that is.
 
Okay, here's a test of the Rosco Hot Mirror filter I mentioned in post #87.

Zeiss 35mm superspeed @ T2.8 + Schneider ND1.8.
Meter reading: 7000FC flat disc, 6000FC dome
sun setting behind me


264_1205538804.jpg

without hot mirror filter - best exposure

264_1205538822.jpg

without hot mirror filter - best color
(note my camera & laptop bags sitting on top of the flight case in the lower-right corner)


264_1205538866.jpg

with Rosco hot mirror filter - best exposure

264_1205538884.jpg

with Rosco hot mirror filter - best color​
 
told ya.


GREAT test Michael! Thanks for doing it.
 
At first reading I thought this was normal conditions but then noticed it's sun setting with very warm light plus 6 stops of ND. From earlier in the thread it sounded like an ND 1.8 would be the equivalent of adding 6 stops of IR or the equivalent of an IR pass filter, right?
 
"adding" isn't the right term since the amount of IR always stays the same. You are effectively just shifting the ratio between visible light and IR. So as you decrease and the visible light the IR becomes more apparent. The problem is the IR is always there, and in areas where visible light is weak the Ir can still provide exposure lifting the blacks, or color shifts.
 
Michael Morlan said:
Okay, here's a test of the Rosco Hot Mirror filter I mentioned in post #87. Zeiss 35mm superspeed @ T2.8 + Schneider ND1.8. Meter reading: 7000FC flat disc, 6000FC dome, sun setting behind me
Click to expand...

Excellent test Michael, it looks like that tells the story. I was thinking of doing something like this myself, but no need now! The Rosco mirror is suprisingly affordable, all things considered, what is your judgment on its optical quality (flatness etc.) ? Your picture with the Rosco filter looks fine, at a small size anyway. Hopefully, anyone making the stronger ND filters will offer a version that has the hot mirror filter built-in.
 
dewaldaukema said:
Picked up the same problems with Vipers on a feature shot late last year. Finding this thread very usefull
Click to expand...

As was mentioned before CCD cameras like the Viper don't have this issue.

The purple cast you see in Viper images is caused by clipping of the green channel.
This happens when you overexpose highlights. The green ccd is more sensitive than the blue and the red one. It is then overloaded while the blue and the red still have some room.
Thus the purple hue.
 
Willem Nagtglas said:
As was mentioned before CCD cameras like the Viper don't have this issue. The purple cast you see in Viper images is caused by clipping of the green channel.
Click to expand...

I don't know the Viper, but with regard to CCD cameras generally I think it just depends on the IR filter used. I have a CCD videocamera with no internal IR filter. It is advertised as sensitive to IR out to about 1000 nm, and I have tested that and confirmed it is true.
 
An ND filter from Schnider with IR cut built in would be the best choice as far as I can tell. Are they going to make them? One would assume that under all conditions you'd want your ND to be filtering across the spectrum into IR anyway.
 
jbeale said:
I don't know the Viper, but with regard to CCD cameras generally I think it just depends on the IR filter used. I have a CCD videocamera with no internal IR filter. It is advertised as sensitive to IR out to about 1000 nm, and I have tested that and confirmed it is true.
Click to expand...

I don't want to stray too much off topic, but I wanted to address the Viper issue based on problems I encountered in a test. The purple cast was very noticable and according to Philips Natlab (the camera supplier) it was caused by overloading the green channel.

Regardless of this issue, do you know of any IR problems with CCD videocameras similar to CMOS sensors? What effect has the prism block in this?
 
ND w/IR CUT:

It wouldn't be hard to create an ND with IR cut since the cut happens in the dichroic coating on the surface.

It's conceivable that Rosco could do a dichroic treatment on existing filters from Schneider and Tiffen (although their chamber typically works on larger circles of glass that are then cut down to final shape.)

Alternatively, Schneider and Tiffen could develop a dichroic process along with their heavier ND's. I imagine they would charge a premium for that.

Rosco Hot Glass Flatness:

The Rosco glass appears to be quite flat from my test. (Read, I walked to the end of my garage and shot a picture of a fluorescent bulb reflected in the filter. There doesn't appear to be any deviation from that rough test.

I can't speak for parallelism.

Also note, the Rosco glass is like a piece of picture glass, roughly half the thickness of a Schneider matte-box filter. Rosco can make thicker versions. It is cut and the edges mildly finished but I plan to take mine to the local fuzed glass studio I frequent and grind a better edge and rounded corner.

BOTTOM LINE:

The Rosco Hot Glass filter serves my needs quite nicely and can be ordered from any Rosco dealer in any shape. My 4x5.65" was $53 before taxes/shipping.

Michael
 
Does anyone have a link to the rosco hot mirror?

Sorry im confused Michael is it just a hot mirror filter or is it a hot mirror/ND filter. Or did you use ND and just have the hot mirror as a filter in front of it?

If it is just a hot mirror how many stops does it effect?

thanks
 
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