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RED SPOTS appearing on footage (moiré pattern)

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Paul Wildman

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Hey there Guys and Gals

Been filming sunsets in cape town on my RED EPIC with a Canon 24-70 & 70-200. and this moiré pattern / red spots appeared over the footage.

Shooting at 5K Full Frame at 25fps REDCode 11:1

Ive attached two jpegs files for you to look at, it won't let me upload the .R3D Files. If you want to see them I can email them.

Not sure what or how it happened, cause on some of the clips they didn't show up, so was it the sensor or the lenses that created this moiré pattern?

Has anyone else experienced this before?
 

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What was your F-Stop? When it's really high you will see this. It's because of the extreme light hitting the OLPF. If you use ND and shoot with a normal T-Stop it shouldn't occur.
 
Jaimy Soares said:
What was your F-Stop? When it's really high you will see this. It's because of the extreme light hitting the OLPF. If you use ND and shoot with a normal T-Stop it shouldn't occur.
Click to expand...

I've heard this happens when shooting above like an F11 and are pointing into the sun...more pronounced on wider lenses.
 
Epic MX or Epic Dragon? If MX, this is a known issue with the OLPF back in the day, with light reflecting off of it weirdly. It wasn't corrected until Dragon, and the swap-able OLPF system (Skin Tone OLPF corrected it).
 
Shooting a bigger aperture and using ND is your best defence. This can still crop up in various flavours on most OLPF types and sensors - and its not just a RED thing, most cameras do it.

Metadata on your R3D shows F16, which is about as I'd expect for the appearance of this artefact.
 
Yeah, looks like the aperture at f/16 is waaayyyy high for shooting into the sun. Definitely a bummer, I know this has happened on more recent cameras as well though. If you can ND down in the future (even with a vari-nd) it'll help immensely.

That being said, if the cuts are fast enough in your edit I doubt most folks would notice.
 
There are a boatload of threads on this.

https://cse.google.com/cse/home?cx=004538409993496633550:nmlowi0wk0c

Enter the search term "red dot pattern" and you will have a couple of days worth of reading.

What you are seeing is, at small apertures, the light enters the lens, hits the OLPF, is reflected off the back element of the lens, then back on the OLPF in a repeating pattern that creates a series of dots that you see all over your footage.

It is an optical path problem which shows up at small apertures when shooting bright sources, like the sun, there is no way around it other than to stack up ND and try to shoot somewhere around f4 or below. With the aperture blades open, there is less chance for a black surface behind the lens element and reduces the mirror effect that is created with a small apertures.

David
 
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David Battistella said:
There are a boatload of threads on this.

https://cse.google.com/cse/home?cx=004538409993496633550:nmlowi0wk0c

Enter the search term "red dot pattern" and you will have a couple of days worth of reading.

What you are seeing is, at small apertures, the light enters the lens, hits the OLPF, is reflected off the back element of the lens, then back on the OLPF in a repeating pattern that creates a series of dots that you see all over your footage.

It is an optical path problem which shows up at small apertures when shooting bright sources, like the sun, there is no way around it other than to stack up ND and try to shoot somewhere around f4 or below. With the aperture blades open, there is less chance for a black surface behind the lens element and reduces the mirror effect that is created with a small apertures.

David
Click to expand...

Here's an interesting question -- does this sort of light reflecting happen with some of the higher-end cinema lenses? I know that there are tons of small differences for cine glass and wondering if this might be one of them.
 
Brendan_H_Banks said:
Here's an interesting question -- does this sort of light reflecting happen with some of the higher-end cinema lenses? I know that there are tons of small differences for cine glass and wondering if this might be one of them.
Click to expand...

It is a bit lens dependent and interestingly this happens on other cameras. It's largely due to either the OLPF, AA Filter, or Sensor Coverglass in most situations.
 
Phil Holland said:
It is a bit lens dependent and interestingly this happens on other cameras. It's largely due to either the OLPF, AA Filter, or Sensor Coverglass in most situations.
Click to expand...

Yeah the potential universality of it is intriguing. Was wondering if there's a type of coating that might reduce the effect if it's the rear of the iris flanges that is causing the issue...and if so if anyone already does it.

I got lucky and saw one of the threads David linked to a day before an EXT shoot and saved myself a headache later.

EDIT: clarity
 
Brendan_H_Banks said:
Here's an interesting question -- does this sort of light reflecting happen with some of the higher-end cinema lenses? I know that there are tons of small differences for cine glass and wondering if this might be one of them.
Click to expand...

Yes.
 
Brendan_H_Banks said:
Yeah the potential universality of it is intriguing. Was wondering if there's a type of coating that might reduce the effect if it's the rear of the iris flanges that is causing the issue...and if so if anyone already does it.

I got lucky and saw one of the threads David linked to a day before an EXT shoot and saved myself a headache later.

EDIT: clarity
Click to expand...


The red you are seeing is the general hue of RED's lowlight and Standard OLPF's The Skintone highlight OLPF which is decidedly more green, the effect is greatly reduced. The RED is also , in part, a reflection of the OLPF you have installed. The STH helps a couple of ways in terms of 1, general stop loss forcing you to open up and 2, it's color.

David
 
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Brendan_H_Banks said:
Yeah the potential universality of it is intriguing. Was wondering if there's a type of coating that might reduce the effect if it's the rear of the iris flanges that is causing the issue...and if so if anyone already does it.

I got lucky and saw one of the threads David linked to a day before an EXT shoot and saved myself a headache later.

EDIT: clarity
Click to expand...


Front ND can cause it's own problems as well.

If you lift the OLPF and shoot without it altogether you probably will not have any problem, but you should test that out before you decide to shoot without an OLPF. :)

David
 
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