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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 :)

Any footage of the DSMC IR PASS OLPF (color) ?

Bjorn thanks for posting, been looking forward to seeing some footage from this.. previously i only saw the IR modified epics.. can you tell us what settings were used for this, is there any correction done to the image, such as desaturation?
 
Adrien oneiga said:
Bjorn thanks for posting, been looking forward to seeing some footage from this.. previously i only saw the IR modified epics.. can you tell us what settings were used for this, is there any correction done to the image, such as desaturation?
Click to expand...

We did some white balancing. Color picked on something white and adjusted ISO to taste. so no saturation or contrast altering. normal dragon color and redgamma4. we shot with nd3+6 in camera hur to get to a bit lower stops as it was a quite sunny day. the footage is quite rich just like normal dragon footage so alot more colors and contrast can be pulled out of it but as this was just a test i figured i just render IT flat.
 
I have shot some days now with the IR (color) OLPF. I used mostly a Tiffen 87 IR pass filter.
To my understanding "Color" means here more that the OLPF is designed for the color Dragon sensor. Even Björn delivered really exquisite examples, I stick for now mostly with B&W. But Visible and IR light mix explorations will follow. Currently I test one lens after the other which one works... (some fail, e.g. bright center)


You can find stills here: (In my "Random Images Album")
https://plus.google.com/+DrSassiLA/posts

OR a short clip in UHD:
https://www.youtube.com/watch?v=Fvl5-H-ulVQ

I might put some clips in a short, but it needs some more time -- it is so far just exploration. Fun stuff.
 
Love the stills. So you used the tiffen IR Pass to take out the remaining colour in the frame, rather than do it in post?
Scrolling down a bit, i notice that you mentioned being able to swap the OLPF with a 'mini portable clean room' ? can you explain?


Dr. Sassi said:
I have shot some days now with the IR (color) OLPF. I used mostly a Tiffen 87 IR pass filter.
To my understanding "Color" means here more that the OLPF is designed for the color Dragon sensor. Even Björn delivered really exquisite examples, I stick for now mostly with B&W. But Visible and IR light mix explorations will follow. Currently I test one lens after the other which one works... (some fail, e.g. bright center)


You can find stills here: (In my "Random Images Album")
https://plus.google.com/+DrSassiLA/posts

OR a short clip in UHD:
https://www.youtube.com/watch?v=Fvl5-H-ulVQ

I might put some clips in a short, but it needs some more time -- it is so far just exploration. Fun stuff.
Click to expand...
 
Thank you Bjorn, for explaining, that gives me a good reference to what is possible. . . I can't wait until I get my hands on one of these :)

Björn Benckert said:
We did some white balancing. Color picked on something white and adjusted ISO to taste. so no saturation or contrast altering. normal dragon color and redgamma4. we shot with nd3+6 in camera hur to get to a bit lower stops as it was a quite sunny day. the footage is quite rich just like normal dragon footage so alot more colors and contrast can be pulled out of it but as this was just a test i figured i just render IT flat.
Click to expand...
 
I would like to do a test where I filter away all the visible light so I only get IR. Does anyone know where I can find such filter?

From readin ont the web I found out that the disc from an old floppy disc works well as a "visual light spectrum filter" problem is I don't have any floppy disks and I don't think the surface of such would cover my lens fronts. So any thing that is of 6x6" or such would be preferred.


Another question....

I would like to shoot with two cameras with a beam splitter, one that records the IR image and one recording an identical image with normal filtration. As I understand IR has a different focus due to the different wave length of the light, anyone knows what the formula for that offset is or is it different from lens to lens?
 
Björn Benckert said:
Another question....

I would like to shoot with two cameras with a beam splitter, one that records the IR image and one recording an identical image with normal filtration. As I understand IR has a different focus due to the different wave length of the light, anyone knows what the formula for that offset is or is it different from lens to lens?
Click to expand...

It is different lens to lens. Some APO-chromatic lenses advertise that they are so well corrected across the spectrum that no compensation is needed for IR photography. But many lenses do have an IR focusing dot that tells you how far off they are. From that, you can calculate the necessary diopter adjustment needed. If you don't have an IR dot, you can measure it yourself. Shoot a focus target in visible light, then IR only and see how out-of-focus the IR-only target appears. Twist the focus until the visible light image appears to be similarly out of focus, and that tells you the general range you need to worry about. Re-acquire sharp focus for the visible-light target, then carefully step the lens with the smallest increments you can measure and notate until you've gone safely past the range found in the earlier step. Confirm that you have an IR image that's indeed as sharp for the IR-illuminated target as for the visible, and put your dot according to the number of ticks indicated by the sharpest IR-illuminated target.

You may need to repeat these measurements for each different filter you use, because different filters pass different spectra:

wrat_comp.gif
 
Björn Benckert said:
I would like to do a test where I filter away all the visible light so I only get IR. Does anyone know where I can find such filter?

From readin ont the web I found out that the disc from an old floppy disc works well as a "visual light spectrum filter" problem is I don't have any floppy disks and I don't think the surface of such would cover my lens fronts. So any thing that is of 6x6" or such would be preferred.


Another question....

I would like to shoot with two cameras with a beam splitter, one that records the IR image and one recording an identical image with normal filtration. As I understand IR has a different focus due to the different wave length of the light, anyone knows what the formula for that offset is or is it different from lens to lens?
Click to expand...

Depending if you want produciton quality or just to experiment, you can source IR pass plastics in large sizes cheaply. PM me and I'll fix you up with something.
Proper quality glass filters in PV sizes are a custom job, with a price tag to match...

The focus difference for IR is unfortunately totally lens dependent, so only experimentation will inform. Some older stills glass does at least have IR focus marks though.
 
John Marchant said:
Depending if you want produciton quality or just to experiment, you can source IR pass plastics in large sizes cheaply. PM me and I'll fix you up with something.
Proper quality glass filters in PV sizes are a custom job, with a price tag to match...

The focus difference for IR is unfortunately totally lens dependent, so only experimentation will inform. Some older stills glass does at least have IR focus marks though.
Click to expand...

Im just experemeting so what kind of plastic can I use something I can find in a near by... plastic store?

would it work to adjust backfocus on the camera for a given lens to make it focus correctly in IR only filtration?
 
Björn Benckert said:
Im just experemeting so what kind of plastic can I use something I can find in a near by... plastic store?

would it work to adjust backfocus on the camera for a given lens to make it focus correctly in IR only filtration?
Click to expand...

The Lee filters are plastic, but found at photo supply stores, not plastic supply stores.

Actually, I just realized that the whole focus adjustment question is a red herring. In the Good Old Days of film, the only light one could use for focus was visible light hitting the ground glass. Visible light focus was usually not close enough to IR focus because of aforementioned chromatic aberrations that we outside the range of the normal lens design. The IR dot helped people compensate by focusing visually and then manually shifting the focus of the lens so that it was in focus for the IR wavelengths.

Today, we focus based on the light that hits the digital sensor. The digital sensor can not only see light wavelengths that our eyes cannot, but it can present the full range of wavelengths that define the focus problem for that lens, in that scene, with whatever filtration you desire. In other words, focus on what the sensor sees, and you get the focus you want in post! No IR dots are needed, and certainly no backfocus adjustments are needed.
 
Thanks for the feedback.

http://www.red.com/learn/red-101/infrared-cinema

The filter (Here Tiffen 87) takes "all" visible frequency [human] out of the image. This results in a redish image. While the camera is set to "IR Color" the channels are pretty similar.

I find the term Color for the OLPF not really great in terms of communication. So far, all input I got was, that the "color" means here -- based on the used sensor, hence the Bayern needs a different OLPF than than the Monochrome.

To my knowledge, there is no glass based filter which can turn an image from color to black and white.

The problem to have visible light and IR at the same time is certainly given in the different refraction of the frequencies. (… remember that IR red dot on older lenses?) Each lens works differently. Some do a nice job with IR, and some not at all, e.g., some have a bright center spot in it. Hence my single lens test and focusing (literally) on IR only right now.

The clean room is a little foldable plastic "case"
http://www.kohglobal.com/Labproducts-clean room.html
The idea is, that one places all the stuff needed into that enclosure and switch on a little filter/fan combination. After a few minutes the air went several times through that little filter. The fan is then switched off. Then, rubber cloves on and change the parts. I use it to clean lenses and place filters to them as well. They produce as well a blower with filter, so one doesn't blow even more dust into the gear.

It is not expensive and I like to use it, even it feels a little bit claustrophobic. ;o)


Adrien oneiga said:
Love the stills. So you used the tiffen IR Pass to take out the remaining colour in the frame, rather than do it in post?
Scrolling down a bit, i notice that you mentioned being able to swap the OLPF with a 'mini portable clean room' ? can you explain?
Click to expand...
 
Last edited:
Michael Tiemann said:
The Lee filters are plastic, but found at photo supply stores, not plastic supply stores.

Actually, I just realized that the whole focus adjustment question is a red herring. In the Good Old Days of film, the only light one could use for focus was visible light hitting the ground glass. Visible light focus was usually not close enough to IR focus because of aforementioned chromatic aberrations that we outside the range of the normal lens design. The IR dot helped people compensate by focusing visually and then manually shifting the focus of the lens so that it was in focus for the IR wavelengths.

Today, we focus based on the light that hits the digital sensor. The digital sensor can not only see light wavelengths that our eyes cannot, but it can present the full range of wavelengths that define the focus problem for that lens, in that scene, with whatever filtration you desire. In other words, focus on what the sensor sees, and you get the focus you want in post! No IR dots are needed, and certainly no backfocus adjustments are needed.
Click to expand...

Yes true, but I want to shoot with a beam splitter (3D mirror rig with lined up set of cameras) IR going to one camera and normal filtration to the other with perfect focus same image on both, Then to be able to pull focus I would need the focus marks to correspond / be synchronized. So for that I guess adjusted back focus on the IR camera on the rig would be best practice, no? focus by image would work for fixed focus but to roll focus is a different deal.
 
Björn Benckert said:
Yes true, but I want to shoot with a beam splitter (3D mirror rig with lined up set of cameras) IR going to one camera and normal filtration to the other with perfect focus same image on both, Then to be able to pull focus I would need the focus marks to correspond / be synchronized. So for that I guess adjusted back focus on the IR camera on the rig would be best practice, no? focus by image would work for fixed focus but to roll focus is a different deal.
Click to expand...

I guess it depends how your focus system works. If you have a geared system (such as a dual WMD or a pair of Cinegears), then you can just initialize the IR system using a fixed (and lens-specific) offset and you are good to go. If you have an electronic system like Foolcontrol talking to an autofocus system, then you might have to us backfocus instead. Use whatever works and works best! (But in either case, you have the infinitely better situation than in days past, because you can see your IR image in real-time.)

BTW, if you are going with a dual-camera approach, you should look at dichroic filters as your beam-splitters: http://rmico.com/infrared-dichroic-filters

Using a dichroic filter, you will not lose a stop of light up front splitting the full spectrum of light into two halves, each of which then get partial spectra filtered away.
 
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