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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 :)

Fix IR in post?

So basically I always need an IR filter when shooting in direct light? Is it ok to shoot with 2nds stacked that have the IR filter combined?
 
You don|t want to use IR filtering, unless you stack a bunch of ND's in front of your lens and it can (and can not) be fixable in post to some extent, depending on your development methodology and subject @ hand.

Dull greens seems to suffer the most, but again, that is if you use a lot of NDs. It is not true that you should always use IR filtering, like it is totally untrue that RED is unuseable in tungsten. The two subjects are related, though.
 
Up to ND .9 you are fine with standard ND's anything including and above 1.2 you should use IR filters. If you use a seperate IR filter, especially with the mirror type, you should have that as the first filter, i.e. in front.
 
As a rule of thumb, that sounds good. But te way you develop the files, is at least as important as the filtering (not less, but...) :)
 
Abu Reno said:
I've never really shot excessively in the sun until yesterday. Is this something I can fix in REDCINE?
Click to expand...

No, you can't fix it, I'm afraid.

Heavy ND and other filtering does not stop IR, which will have improportionately higher level in relation to visible spectrum when it reaches your lens and sensor. This causes colour "bleed" and shifts, some of which wil be out of focus as your lens is not designed to focus IR correctly. The result is loss of contrast (MTF), colur shifts off IR reflecting objects, such as nylon and foliage, ghosting and blurring.

To prevent this you need to filter IR as the first thing before it hits any other filters or the lens. Mirrors, as opposed to absorbtion filters, tend to reflect as much IR as other spectrum, therefore effectively reduce IR and prevent its excessive levels.

As others mentioned, it starts becoming a problem around 1.2 ND of combined filtration (ND plus whatever other filters you may have).
 
hunterrichards said:
I love how the IR light "messes up" the image in the RED, but thats just me.
Click to expand...

It messes the image up in every camera, not just RED. :biggrin:

Yeah, sometimes it can be a desired efect. But then, you can add this effect in post, if you like it. You can't remove it once it's there.
 
Pawel Achtel said:
It messes the image up in every camera, not just RED. :biggrin:
.
Click to expand...

Not really. The IR cut filter in the RED is just a little too weak to take out enough IR light. You won't run into this other problem on other cameras of this caliber. IR cut filters are difficult to get "just right" and this is RED's first camera. If it's too strong, wide-angle lenses color vignette. If it's too weak, IR light gets through. So even though there are simple solutions [filtration] and it's ultimately not a huge deal... we still should call it as it is: a design oversight. If everybody knows it's a problem... it'll get fixed on the next cameras. If everybody downplays its importance... we'll all be strapping our IR cut filters onto the 5K. No use in candy-coating it. :)

As for filtration, I still recommend the Tiffen filter over the Schneiders. I've tested both the original short-run Schneider [too strong] and the current 750 Schneider [too weak]. The Formatt filter is fine - not quite as strong as the Tiffen, but it doesn't seem to cause issues.

Across the board, I'm unimpressed with the IR/ND filters. They either don't cut enough IR light or are simply too reflective to be used effectively.

As for fixing it in post... you won't be able to do it in REDCINE and it will take a notable amount of work in a proper DI suite with secondaries and headaches all around. Even then, it won't completely go away.

Ultimately it comes down to either accepting the purple... or using the filter. There is no middle ground.
 
You're absolutely right about the difficulties or even impossibility (depending on image content) to fix it in post.

But I dare to contradict regarding the filtering in the Red. The situation is different in a camera with a 35mm sensor from ordinary HDTV camcorders with 2/3 sensors. If you make the filter too strong behind the lens, you get problems with wide angle lenses on such a camera. I think it's a wise decision to make it strong enough for most situations (up to .9 ND) and leave it to us to add another filter in front of the lens if you need more.
I'm quite sure that folks would blame Red for the resulting color vignetting if they would have made it stronger than it is.

Proper filtering is part of our craft!
 
thanks brook, im so greatful for your input
and can you tell me then if your unimpressed with the ir/nd
what setup do you recommend.
i have been following all your advice and appreciate the time you put in
i have tiffen ir+nd's but i dont believe theyre the new tiffen hot mirror
and i also have pancro irnd's shipping to me.
after reading all your tests i would love to have this clarified
im lost with how the pancros got the ghost and alot of what was said in this thread about how 1.2 and above needs the ir filter and all of what everyone said seems to conflict.

thank you
 
Brook, I respectfully disagree.

It is always better to filter IR before the lens than after. The reason is that IR is then not bounced around the optics. I strongly feel that, although not always convinient, it is far better to rely on external IR filter than expect a "miracle" filter in front of the sensor. Even if there was such "miracle" filter, it would be much more effective in front of the lens.

In that sense, I think that Red has made sound decision to put only mild IR filtration on the sensor.

I shot hundreds of time lapse sequences using high end DSLR's with heavy ND filtration - all suffering from heavy IR contamination. It is common problem and it is always going to be an issue for cameras that have high sensitivity.
 
I respectfully disagree with your respectful disagreement. :) I still personally feel that the built-in IR cut filter is just a bit too weak. I understand that it was a safety decision to prevent color vignetting on wider lenses... but they're just south of the sweet spot. While it's certainly better to be too weak than too strong in this case... I'd rather have "perfect" over too weak. :)

I personally find the IR pollution bothersome with just about any ND in place. I've also been in situations [generally under significant foliage] where the IR pollution has been an issue with no ND in place. This isn't a game that I have to play with other digital cinema cameras and I'd love to see it "fixed" on the next camera.

Adding an additional filter wouldn't really bother me [just put it in and forget about it...] if it wasn't for the fact that I cannot use a polarizer and ND in an LMB-5 on the RED. I need an LMB-15 or a three-stage conversion for the LMB-5.

Furthermore, since there is no three-stage equivalent of the LMB-4, I'm stuck with a clamp-on adapter for a round ND [to keep the IR and polarizer in the mattebox itself] or I have to grab a three-stage conversion. Since both of these add depth to the mattebox, it becomes an issue on extremely wide lenses.

So it's not the fact that I have to add a filter that causes issues, it's that my mattebox choices have to change to make up for a camera handicap. That's why it becomes a big deal. Proper filtration may be part of our craft... but to me, the camera's IR sensitivity is a bug - not a feature. :)
 
Skip, it is visible on on-set monitors... though it's not quite as easy to determine on the onboard monitors because of their slightly skewed black point.
 
paintthetownred said:
thanks brook, im so greatful for your input
and can you tell me then if your unimpressed with the ir/nd
what setup do you recommend.
i have been following all your advice and appreciate the time you put in
i have tiffen ir+nd's but i dont believe theyre the new tiffen hot mirror
and i also have pancro irnd's shipping to me.
after reading all your tests i would love to have this clarified
im lost with how the pancros got the ghost and alot of what was said in this thread about how 1.2 and above needs the ir filter and all of what everyone said seems to conflict.

thank you
Click to expand...
If I was buying filters from scratch, I'd buy a .3-1.5 ND set from Schneider and Tiffen's Hot Mirror.

The Pancros are good filters, but they do require some hand-holding to avoid inter- and intra-filter reflections. I've actually seen the filters cause scary reflections within themselves. They definitely do the best job of cutting the proper amount of IR light as far as IR/ND combos go... but they can be a pain in the butt on set.

Everybody will conflict here because a lot of these choices are personal and aesthetic. There is no "right" answer here. Ultimately whatever you [or somebody] prefers will be the right filter for them. It's filmmaking - sometimes the "best" is not the best. :)

So shoot with your filters and take a look at the footage. If you don't see the pollution or see it and don't care... great! You own the right equipment for yourself.
 
OK Brook, I partially agree with your respectful disagreement with my respectful disagreement. :ranting2: LOL

I have same practical problem of not having enough stages in my LMB-5, which I agree is one of the most loveable matte boxes around. But I see it as a pactical issue.
banghead.gif


From technical point of view, and convinience aside, you will always get a better end result by filtrating IR first, not last.

You see, the engineer takes the better part of me
clown.gif
 
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