Canon 7D high speed continuous shot problem

Mark1616

There is something weird going on with my 7D when shooting in high speed continuous drive.

Basically in low light/under exposed situations it will not hit the 8fps, probably not even making 4fps.

To test this I've gone for manual focus (takes out any focus release issues), manual exposure so shutter speed is up over 1/2000s so can attain the 8fps and then shot. If I point at a correctly exposed or over exposed area then it will fire off as expected, if then somewhere less bright it will slow the shooting right down.

I've tried a settings reset to make sure nothing funny is going on but still no joy.

Any ideas?

ziggy53

The things that can affect burst speed are:

• Shutter speed, longer shutter speeds result in a slower burst rate.
  
• High-ISO noise reduction, at the strong noise reduction setting it has a noticeable effect on the burst rate.
  
• I think that the 7D has the ability to detect light flicker and implement a strategy to prevent the flicker from affecting AF and metering accuracy. I believe that would affect the speed to first shot and that the burst rate might also be affected. (I could not immediately find the reference however.)
  
• Do not use AI Servo for static subjects. AI Servo, by design, samples subject motion and will try to calculate future prime focus based on the sampled speed and rate of change. The effect on static subjects is unpredictable focus behavior. One-Shot AF is correct for (relatively) static subjects.

On the 7D, and only the 7D I believe, the new metering system can slow down the frame rate to favor AF accuracy. There is even a vague reference in the 7D User Manual. (Bottom of page 93.)

http://media.the-digital-picture.com/Owners-Manuals/Canon-EOS-7D-Owners-Manual.pdf

"In low-light areas or indoors, the continuous shooting speed may become slower even if a fast shuttter speed is set"

Dan7312

I just did a test with my 7D.

Manual Focus
Stabilzation off
Manual Exposure 1/2000 sec F5.6
High speed drive.
Raw capture

With the lens cap on frame rate is very slow
With the lens cap off frame rate is very fast.

If everything is manual why is this?

I can understand the calculations to find edges for AF and and light level for AE might take longer to do with low-light, but if everything is manual those calculations are not needed.

So it looks like when everything is manual the 7D is doing all the calculations needed for the auto settings, but then throwing them away before firing the shutter instead of just firing the shutter when the button is pressed.

Sometimes fly-by-wire isn't all it's cracked up to be.rofl

ziggy53 wrote: »

The things that can affect burst speed are:

• Shutter speed, longer shutter speeds result in a slower burst rate.
  
• High-ISO noise reduction, at the strong noise reduction setting it has a noticeable effect on the burst rate.
  
• I think that the 7D has the ability to detect light flicker and implement a strategy to prevent the flicker from affecting AF and metering accuracy. I believe that would affect the speed to first shot and that the burst rate might also be affected. (I could not immediately find the reference however.)
  
• Do not use AI Servo for static subjects. AI Servo, by design, samples subject motion and will try to calculate future prime focus based on the sampled speed and rate of change. The effect on static subjects is unpredictable focus behavior. One-Shot AF is correct for (relatively) static subjects.

On the 7D, and only the 7D I believe, the new metering system can slow down the frame rate to favor AF accuracy. There is even a vague reference in the 7D User Manual. (Bottom of page 93.)

http://media.the-digital-picture.com/Owners-Manuals/Canon-EOS-7D-Owners-Manual.pdf

"In low-light areas or indoors, the continuous shooting speed may become slower even if a fast shuttter speed is set"

ziggy53

The Canon 7D appears to have closely tied the AF system with the exposure system. While there do seem to be benefits to this method in good light, it obviously does not seem to be a benefit in really poor light.