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IR-CUT or HOT MIRROR for ND filters ?

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Jack Colquitt

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I read lots of thread about that, but nobody gave the final answer (if there is one !)...
so when using screw-in ND filter (regular or variable), are the HOT MIRROR better than IR CUT filters ?
Because sometimes, it's not really discreet to have a large mirror on front on the lens ! ; )

And, for you, what is the best HOT MIRROR (Tiffen, Formatt...), and also the best IR CUT filter (Hoya, B+W, Heliopan...) ?

Thanks.
 
IR Cut and Hot Mirror filters are essentially the same thing. They are all reflective and mirror-like, some more than others and that depends on the formulation used to block IR.

I've had the best luck with Formatt and Pancro. B+W (Schneider) and Tiffen do pretty well too.

Variable ND filters don't usually get along with hot-mirror or IR filters or just about anything else in front of them in the optical path. They are not truly ND's, but stacked polarizers.
 
Yep Formatt or Pancro. Format make two Hot Mirrors using different IR cut frequency.
 
Ok... Fromatt or Pancro for HOT MIRROR.
And what do you think about IR/UV cut ?
Like the HOYA, B+W, or HELIOPAN ?

@ Jeff Kilgroe
You mean that using an IR / HOT MIRROR with an variable ND is useless, and we can't fight the IR pollution in this case ?

@Dave Blackham
How can we define the good frequency to use ? Except in buying both filter... ; )
 
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Id need to check with filters we use. One cuts more IR than the other so I think if you need to run some tests to see what suits you needs.
 
Thanks for the links.
But on Epic / Scarlet MX sensor, the IR pollution start at 680 or 720nm ?
 
From my tests the IR pollution on Epic is from well below the visible spectrum, not on the cusp. The built in OLPF/IR cut works nicely close the deep red / near IR but lets a band of slightly deeper IR pass. A 720 cut should work fine, but I'd test its effect on deep reds, as the shape of its transmission curve will affect the rolloff from red to IR.
 
Sorry for distraction / off topic, I just thought this stuff really should be on some kind of a Red Wiki page, you know. Forum is great and helpful, but searching for some very certain stuff in old threads sometimes not exactly easy, as a result you have people asking questions, that often have been already discussed and resolved. I don't know if such centralized knowledge base already exists, but it wouldn't hurt to set up one, obviously you can update those wiki pages when things change (new sensors etc). Call it "tips from Redusers" or some like that. Lots of guys, who are just starting with Red will appreciate that, as I may imagine. Just saying.
 
John Marchant said:
From my tests the IR pollution on Epic is from well below the visible spectrum, not on the cusp. The built in OLPF/IR cut works nicely close the deep red / near IR but lets a band of slightly deeper IR pass. A 720 cut should work fine, but I'd test its effect on deep reds, as the shape of its transmission curve will affect the rolloff from red to IR.
Click to expand...

In practice the 720 IR cut seems to work fine but Ive not done a scientific test and looked at the curve. The deep reds which we were looking for on one project were satisfactory to my eye with 0.9 ND but Id like to test against other IR filters. I think 680 would not be good for most of our work if there are deep reds that could be affected by it.

I agreed too would be good to get all this stuff in readily accesable some place on this board.
 
And what do you think about IR/UV, like the Heliopan, B+W or the Hoya ?
I use UV filters to protect my lenses since so many year, that I completely forget if it's usefull or not !! ; )


@Dave Blackham

Strange, because if you look at the PDF on your link, and on BH, there is 2 different Formatt hot mirror :
- BF 82IR680 / Formatt 82mm Hot Mirror Infra-Red 680 (maybe 680nm)
- BF 82HM4 / 82mm Hot Mirror (maybe 720nm)

But you're surely right... I will using this IR filter on a variable ND, for documentary.
So maybe, if I "trust" your tests, the better is to take a 720nm...
better than nothing and good enough for most works, and it can keep at least deep red
if by chance I meet this kind of color... like the Red Cross by example !! ; D

But, if you're making any test with other IR "wavelength", please, tell us...


@Vadim Bobkovsky

+ 1 !!
Google is may be my friend, but now, I can stand no more this pal !!! ; )
I feel like Indiana Jones, reading thousand posts (really !!) each week only to get "simple" answers which experimented people like you surely already knows...
I learned a lot, and I'm really grateful about Reduser, and all of you who have the patience to help - again and again - ignorant like me,
but I'm sure a wiki (like Eyeon did for Fusion in example) can be reaaaaaly more simple in many ways for a lots of dumb and too frequently asked question...
 
Jack Colquitt said:
Ok... Fromatt or Pancro for HOT MIRROR.
And what do you think about IR/UV cut ?
Like the HOYA, B+W, or HELIOPAN ?

@ Jeff Kilgroe
You mean that using an IR / HOT MIRROR with an variable ND is useless, and we can't fight the IR pollution in this case ?

@Dave Blackham
How can we define the good frequency to use ? Except in buying both filter... ; )
Click to expand...


IR Cut and Hot Mirror are technically the same thing. I have not used the Hoya or Heliopan IR filters, so can't comment. I use Hoya ND filters with my RPP 300 drop-in tray and I have some other screw-on Hoyas for SLR lenses and those have been great, so I would be willing to try their IR filters.


IR filters with a variable ND may not be useless, but you're combining stacked polarizers with another reflective filter. The variable ND should go behind the IR / Hot Mirror filter. My best advice is to TEST, TEST and TEST again.


720nm seems to be fine on the EPIC. I have great luck with the Formatt filters on EPIC. Mine are all 720nm 4x5.6 size. I alter ND filters by job, but the main ones I never go without are: Hot Mirror, ND.3, ND.6, ND.9, IR+ND 1.2, IR+ND 1.5, IR+ND 1.8.
 
I'm using the Formatt Hot Mirror ND Combo filters. I did many tests against the IRND filters from others and really where the difference is clearer is in the .9-1.2 and up range.
 
IR Cut and Hot Mirror are NOT the same thing. An IR Cut is generally an absorber of IR, or heat, while a Hot Mirror is just that -- a reflector of heat. They function differently and as such yield different results with different artifacts and issues.

The RED cameras are affected by IR issues in ways different than other cameras. I would say that for severe IR issues, a Hot Mirror must be used. A good example of this would be the suspenders-and-a-belt filter set from Tiffen, the HMIRND (Hot Mirror Infrared Neutral Density).

Check out the AbelCine EXPO: Filters for Digital Cinema that I just Livestreamed earlier this week. We did a bunch of live tests of IR issues with a variety of cameras including a RED EPIC. The complete presentation video is archived for viewing on Livestream.

http://new.livestream.com/abelcine/FiltersExpo
 
To add to this topic, here's my quote from the Red Quick Reference Guide:

Infrared Protection
Using deeper neutral density (ND) filtration can introduce a reddish color cast to your image. This is Infrared Contamination. It is hardly noticeable at 0.3 (1 stop) and 0.6 (2 stop), however, around 0.9 (3 stop) it becomes slightly visible and the color cast becomes more apparent as you use deeper (darker) ND filtration. While it is possible to color correct the color cast in post, many prefer to get a more natural and accurate color balance in camera. To counter the effect of the infrared color cast contamination I recommend using either: ND filtration with the addition of a Hot Mirror in the front-most filter tray, an “IRND” filter, or a Hot Mirror/ND filter.
Personally I recommend IR protection when shooting with ND iltration at around 0.9 or 1.2 and anything deeper.
Click to expand...

Take a look at the images in that PDF and you can visually see what the effect is on the color chart and why/when you should protect yourself from IR.
 
Phil Holland said:
I'm using the Formatt Hot Mirror ND Combo filters. I did many tests against the IRND filters from others and really where the difference is clearer is in the .9-1.2 and up range.
Click to expand...

The Formatt Hot mirror was not in the AbelCine video. Do you use the Hot Mirror stacked on the ND or does each ND have it's own coating? Also - does the Formatt exhibit that green tinge? I like Formatt's idea of broad spectrum attenuation, but felt they were limited by the lack of Hot Mirror in the shoot.
 
Mitch Gross said:
IR Cut and Hot Mirror are NOT the same thing. An IR Cut is generally an absorber of IR, or heat, while a Hot Mirror is just that -- a reflector of heat. They function differently and as such yield different results with different artifacts and issues.
Click to expand...

While that is true by definition, the reality differs somewhat. I've found most all the IR cut filters I've tried to be reflective, especially those with higher neutral density values. There is only so much that can be done in terms of known materials and glass formulations or coatings for absorbing IR wavelengths. Stacking IR cut filters can still lead to nasty results.

IR does affect the RED cameras differently than most other cameras on the market. But that isn't to say other cameras / sensors are not affected or film stocks are not affected. IR filtration has been around for a long time. It's somewhat weird I suppose, but I own a couple cameras that exhibit very similar IR anomalies to what the RED One exhibits. One of them is the Canon PowerShot G9 point n shoot. Odd, but it can duplicate most all the same IR issues when shot side by side under the same conditions.

IR artifacts can also differ with lens selection and how different lenses transmit that portion of the spectrum. I always found that intense IR through my Cooke 18-100 would give me very noticeable halos around objects that emitted or reflected a lot of IR. those halos were far more pronounced with that lens than with most any other.
 
I've had good luck with the 680 Hotmirror... I've liked the Platinum IRND's but they don't cut the proper range for Red like they do Alexa or F65
 
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