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InfraRed Zooms

 

I’ve been looking into sources for zoom lenses that have been coated for InfraRed shooting - or how difficult it would be to coat lenses for it.  

We did a shoot recently using Panasonic LT’s with the IR-cut filter removed, as well as a Canon ME20 (mostly in visible light mode and at ridiculously high ISO, but it also easily flips out the IR-cut filter with a simple menu selection).  

The issue is when using IR LED’s that are in the shot (or any source that gives off a decent amount of IR)… you get some pretty bad internal reflections, because the lenses are coated for the 350-750’ish nm range - and we’re letting the higher wavelengths get to the sensor.  

So I wanted to gather sources and info on coating lenses for IR reflections.  
Say a 24-290, 18-85 or a 19-90 cabrio, just as some examples of what could be needed.  

Prime lenses were somewhat better (less elements) but still not immune.  
It only takes one internal “mirror” to give an annoying / offset of a hotter IR source in the frame. 
But the show would really need a few zooms so that’s the main goal. 

In this case, any lens darkening due to the coating would be trivial  - we have plenty of IR light to light for it.  

Any help / resources greatly appreciated. 

mdp 

Mark Doering-Powell, ASC
LA based DP 

Mako Koiwai
 

Lots of info here: https://kolarivision.com/the-science-of-infrared-hotspots/

Stopping down typically makes it worse.

Read about their special anti-reflection coating.


makofoto, s. pasadena, ca

 

Mako writes:
Lots of info here:  https://kolarivision.com/the-science-of-infrared-hotspots/
Stopping down typically makes it worse.
Read about their special anti-reflection coating.

Great info.  Thanks.
That HSK filter seems to do the trick at the sensor level, but judging from what I saw and how the reflections moved with pan/tilt and zoom, the worst reflections were within the zoom elements - and it was only one element in particular.  That’s what made me wonder if coating at least that one offending element would do the trick (this was a 19-90 cabrio). 

Or if any pro lenses exist for larger sensors that have already coated for this.  

mdp 

Mark Doering-Powell, ASC
LA based DP 



Mark H. Weingartner
 

Or if any pro lenses exist for larger sensors that have already coated for this.
Might be worth a call or email to Dan Sasaki at PV Woodland Hills - I know that PV has done military contract stuff in the past and they’ve done a number of odd night-vision things that would have been very IR touchy.



Mark Weingartner, ASC
DP, VFX Supervisor, and Stereographer
Los Angeles based
vfxmark@...

Cigarettes make the sun come up
Whiskey makes the sun go down
And in between
We do a lot of standing around


http://www.schneiderentertainment.com/links/WEINGARTNER%20Full%20Client%20Resume.pdf
Represented by Schneider Entertainment Agency

Evolve Films
 

On 29-Aug-18 6:22 PM, Mark Doering-Powell, ASC via Cml.News wrote:
I’ve been looking into sources for zoom lenses that have been coated
for InfraRed shooting - or how difficult it would be to coat lenses
for it.
I have done a lot of work shooting IR. There is a fundamental issue with
zoom lenses that in most cases make them unsuitable for use with infra
red illumination. It comes back to the fact lenses are designed and
optimized for visible wavelengths. The much longer wavelengths of near
infra red, 0.75–1.4 µm means that the spacing between lens elements is
not optimized for the wavelengths used with IR illumination.  Given zoom
lenses have many more elements than prime lenses this causes more
issues, often halos, flares and generally soft images. So I generally
stay clear of zoom lenses for this reason.

There is also an issue caused by internal reflections from the interior
of the lens barrels when IR light is reflected where visible light is
absorbed. Again causing flares and halos and  central spots.

I find that generally simpler the lens design the better the results. I
my experience often older prime lenses give best results, especially
early Zeiss prime series or older (FD series) long (300mm plus) Canon
prime still lenses seem to work quite well. (possibly because of simpler
coatings or barrel design)

It is also advisable to use IR band pass filters in front of the lens to
block visible light and only allow the specific IR wavelengths you want
to pass.

There is a website that contains a lot of information re IR/UV shooting
for stills and video. https://www.lifepixel.com/

Mark Lamble ACS DP Evolve Films Woodend Australia

FYI I have no association with lifepixel but have used their services.

circle_of_confusion@...
 

On Fri, Aug 31, 2018 at 09:27 PM, Evolve Films wrote:
There is also an issue caused by internal reflections from the interior
of the lens barrels when IR light is reflected where visible light is
absorbed. Again causing flares and halos and  central spots.
I second this, go with the most simple optical design lenses you can find and you'll be better off than with more complicated.  With the hotspots your only practical solution generally is to change your angle in relation to the angle of light entering the lens, but that may not be possible depending on what you are shooting.

Good luck!


Illya Friedman
President
Hot Rod Cameras
Burbank, CA
www.hotrodcameras.com