A Sticky for known issues and work-arounds

[Ben Denham]

Recent contributions to this forum have given me the impression that there are people out there who see it as their civic duty to draw attention to the pitfalls of DSLRs particularly when they receive any kind of industry endorsement (the discussion of Philip Bloom's interview with with House's Greg Yaitanes is a recent example of this).

In a previous thread it was suggested that we have a sticky that deals with known issues and work-arounds. I think this would be a great way of helping to generate more positive discussion of the creative possibilities and technical aspects of the camera by (hopefully) aleviating the need of the nay sayers to do their duty by drawing peoples attention to the camera's pitfalls.

It would also be a great first point of call for anyone who might be new to DSLR film making. To get the ball rolling I have drafted up the following. Please feel free add to or alter this list in any way.


Known Issues and Work Arounds

1. Moiré/Aliasing

What it looks like – A kind of superimposed “psychedelic” pattern often seen on clothing and in patterned background areas (brick walls etc.)

What causes it – the line skipping that reduces the information from a 21 mega pixel sensor down to a 2K image.

Work around – Moiré will not occur in out of focus areas of the image so shooting wide open or low apertures will often be enough to eliminate moiré in both foreground (clothing) and background (buildings) areas. Diffusion filters may also help to reduce moiré .

2. The “Jello” Effect

What it looks like – When panning the image wobbles like jello, more specifically the bottom part of the image is skewed off axis so that vertical lines become diagonal.

What causes it – Progressive capture means that each frame is formed by scanning the lines that make up the image from the top to the bottom of the sensor. If the camera is moved before it has finished scanning the frame then the lines that were scanned at the top of the image may not line up with those that are scanned at the bottom. It has been suggested that the Jello effect is made worst by the line skipping mentioned in the causes of Moiré.

Work around – Slow pans are much less prone to the jello effect. Also ensuring that you shoot with a shutter speed of 1/60 of a second or less might improve pans by introducing a “more natural looking" motion blur.

[Wayne Avanson]

Great idea Ben. it could also serve as a repository of knowledge for people considering buying a 5D2 so they know what they're getting before they buy.

Since there's loads of knowledgeable and experienced people posting here, it would be good to have them share their experience of workarounds from 'in the field experience'

[Bill Grant]

I get a flicker in certain frequency lights. I have not found a workaround for this nor figured out what causes it. It seems that certain lights just have a rolling flicker.
Example

Greg Humphreys at the White Mule 12/26/09 on Vimeo

[Don Miller]

Isn't the frequency 60 (in the U.S.)? Are you shooting 30p? I've never seen flicker at 30p 1/60th or 1/30th. But maybe I don't look hard enough.

[Ben Denham]

From what I've read Don is right. 1/60 second shutter speeds should cancel flicker in the US, (1/50 here in Australia and in the UK). I would love to know the technical explanation behind this, but this is probably more of a general problem that applies to all cameras rather that a specific DSLR issue.

Any more known issues and work-arounds? Any additions to Moire and Jello? I was thinking "Too much light" could be one.

3. Too Much Light

What causes it - shooting under bright lights or outdoors during thee day.

Why its a problem - Once your ISO is set to its minimum level (160 if you want to stick to optimal ISOs) you can only adjust your exposure by increasing the shutter speed, which will lead to unnaturally frozen images (no motion blur) or by closing down the aperture, which can lead to the moire/aliasing effects described above, (not to mention the fact that you also lose the shallow depth of field that is the strength of these cameras).

Work-around - Use Neutral Density (ND) filters. These filters are placed in front of the lens and reduce the amount of light that hits the sensor without affecting the colour cast of the image (although cheaper ND filters might not be so neutral and can affect colours).

[Rick Hill]

Originally Posted by Bill Grant

I get a flicker in certain frequency lights. I have not found a workaround for this nor figured out what causes it. It seems that certain lights just have a rolling flicker.
Example
Greg Humphreys at the White Mule 12/26/09 on Vimeo

I can't help but wonder if the lighting here is LED. I have seen more and more LED fill lighting for stages as a musician. It is quite possible these LED arrays (when dimmed - which probably uses PWM for dimming) may be using non-standard frequencies. LED's do not have to be sync'ed to the 60 Hz line frequency.

[Dan Brockett]

Any ballasted light can cause flicker as the ballast ages because the operating fequency of the ballast only has to be off but just a small amount to register as flicker on a camera.

I once shot in a Kinkos in Nashville where we were shooting Beta SP and a 16mm film of the same scenes. In post, we noticed that because the fixtures located all over the store had ballasts of differing ages and the store was really old, we were recording differing rates of flicker all over the store. In one wide shot, we counted ten different flicker rates in different zones of the store. Betacam's shutter was 1/60th and the 16mm camera was crystal sync, yet we had equal amounts of nasty flicker on the film camera and the Betacam.

Unfortunately flicker is an inexact science. Sometimes you can see it with your bare eyes and other times, only in the camera and when you do see it, short of dialing in a specific shutter angle with a clear scan function, there is not much that can be done. And there is nothing that can be done when you have a scene with multiple rates of flicker from different sources.

Dan

[Bob Hart]

It looks like at least one of the lights was running off a diesel generator. Was this an outdoors gig or generator power for lighting coming in from outside?

If it was a discharge type, it might have been on a magnetic ballast which would reproduce the frequency of the generator.

The waveform coming off the light is 60Hz but is hunting back and forth very very slightly with the generator governor????

[Bill Grant]

These were definately LED lights. I've not ever gotten the flicker on the A1 at this venue, just the 5D. I thought maybe it was the 30p but I brought it back after the 24p upgrade and got the same thing. So once I see it, it's there eh?
Bill
A1 in the same venue.
YouTube - Matt Corbin (Everyman Jones and the Stick People) - Yellow Daisy Heart