Canon: fps and metering?

GadgetRick

Ok, this is (imo) a strange one.

So, playing with my 50D the other day because I noticed a, "problem," I seemed to have occasionally at a shoot I was doing the other day. I was shooting sports and used AI Servo and high speed bursts. Every so often I'd hit the shutter button to shoot a burst and the first frame would seem to take longer to cycle than it should then all frames after that would fire away happily at the max fps on my 50D (I didn't measure it but it sounded correct).

Anyway, I was playing around and noticed a strange thing. If I'm shooting at something dark, the camera shoots at a speed much lower than the 6.3fps the 50D is capable of. When I shoot at something reasonably-well lit, it fires away happily at 6.3fps. Hmm...

So I tried different things such as shutter speed, metering modes, etc (shooting full manual, btw). Seems to always do it. I called my friend who has a 7D and asked him about it. He tried it on his 7D and the same thing happened! Double hmm...

To me, this makes no sense. If I'm shooting manual--which I was--the camera should happily fire away in full burst speed when AF has locked on, right? This doesn't seem to be the case.

Anyone know what's happening or why it works this way?

ziggy53

Several things come to mind. First both the Canon 50D and 7D have 2 different burst speeds. Make sure that you are not changing it accidentally.

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 both cameras have 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"

final_alarm

ziggy53 wrote: »

Several things come to mind. First both the Canon 50D and 7D have 2 different burst speeds. Make sure that you are not changing it accidentally.

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 both cameras have 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"

Ziggy is on to something with his comments on the 7D for sure. Mine does the same thing as your friends 7d in really low light. If i switch to manual focus it will happily fire away at full speed. If know there is some custom settings to adjust the auto focus priority i have never played with it.

canonthen

I shot my 7D in front of Rick at full manual, including focus in high speed shutter. It performed exactly how Rick mentioned. Noise reduction always is disabled but just to be safe I shot in low ISO anyways.

S even with everything set to manual, will the light metering still affect the burst rate? Kinda kills the whole manual setting then.

Jekyll & Hyde

GadgetRick wrote: »

Every so often I'd hit the shutter button to shoot a burst and the first frame would seem to take longer to cycle than it should

J: It's the Autofocus.

H: When shooting in AI Servo, the camera still operates in a loose "Focus Priority" mode (not as strict as "One Shot" though).

J: Lower light/lower contrast or poor tracking are the main causes.

H: You'll also sometimes notice a framerate slowdown mid-burst if AF gets lost.

J&H

GadgetRick

Ok, this is making some sense. Like Abe mentioned, no noise reduction and I've also tried manual focus. Seems to be an AF issue. Just checked, and that's exactly what it is. If I put it on One Shot focus, it fires away happily. If I switch to AI Servo, it fires happily at something well-lit but slows down at darker subjects.

Well, I guess it's good I learned this! Thanks for helping clear it up!