9

Sometimes when attempting to shoot continuously (at high speed) with my Nikon D90, something appears to block the smooth interval between shutter releases.

I have it set up to take RAW and JPEG images together and the specification suggests it can take 7 continuous shots (with the caveat that this "may vary depending on conditions"). I'd like to understand what these conditions are so I can attempt to minimise them.

I realise disk throughput is a big issue so I'm always careful to wait for disk access to finish before starting to shoot. Beyond that, I've observed the following phenomena when holding down the shutter release in continuous mode:

  1. Sometimes it feels like the camera waits after each release until there is something either in focus or moving under the active focus area. I've tried setting focus (and everything else on the body and lens) to manual, but this still seems to occur.

  2. Sometimes after the first shot is taken there is a long pause (20+ seconds) then the next 6 shots are taken in quick succession.

  3. Sometimes it does exactly what I want and takes all 7 shots in quick succession at perfectly equal intervals (at roughly the 4.5fps quoted in the specification).

I can't tell what is causing these differences in performance. Can anyone explain?

5

Memory write speed is one factor so any delays during writing and the camera will have to slow down as the buffer isn't cleared fast enough.

It's worth noting that not all raws are the same file size. Nearly all manufacturers employ some form of lossless compression on raw files. The amount of entropy (randomness) determines how much compression reduces the filesize.

If the filesize suddenly goes up the camera won't be able to write the file quick enough to clear the buffer before the next frame so shooting slows down.

Of course this doesn't explain a 20 second delay, this may indicate a genuine problem with your camera, or more likely the card.

  • OK. I think I should set up a controlled test and try with a bunch of different cards to narrow down the problem. Thanks. – Ian Mackinnon Jan 19 '11 at 15:55
2

The 20 sec. delay sounds like a problem for sure. That aside, with all the options like D-Lighting, noise reduction and so on turned OFF, this is what the D90's buffer is capable of:

RAW +Jpeg fine = 7

RAW = 9

Jpeg fine = 25

Anything smaller and you can shoot till the cows come home.

So basically, RAW + Jpeg is the worst setting for shooting bursts. Even with a really fast card (30Mb/s), your buffer will be full after a about 4 seconds and your continuous shooting will start to lag.

RAW + Jpeg is about 15Mo per shot, so your fast card can only handle about two of your 4 fps.

However, shoot in RAW only and it'll be able to deal with about 3, which will extend the time you can shoot for.

And in Jpeg fine you should be able to shoot till your card is full without lag if you have a fast card.

2

If you are using the buildt in noise reduction this would result in less shots. It kicks in after ISO640 and uses a lot of the buffer memory for processing.

  • I'm not (ISO was 200-400 in my tests), but useful to know that it comes on automatically. – Ian Mackinnon Jan 19 '11 at 16:01
1

My suspicion lies with your memory card. If you try it with another card, do you get the same behavior?

  • I'm going to find some other cards and make a test. Thanks. – Ian Mackinnon Jan 19 '11 at 16:01
0

You've set the focus to manual, that's good. Also set a quick shutter speed and full aperture.

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