Question about the camera buffer....

When doing long exposure time-lapse shoots where you are taking 20 second exposures with only one second between shots, is there ever going to be an issue where the buffer fills up? Or does the buffer continue to write to the card even if it has started the next exposure?
Hopefully I'm clear about what I'm asking. I want to know if I need really, really fast cards or will slower, less expensive cards work. I'm looking to purchase some 128GB cards to do all night time exposures and there is a huge difference in price when you start looking at write speeds.

I believe you'll be fine with slower cards, the images will be written to card while the shutter is open. Sandisk Extreme are 50% cheaper than Extreme Pro, but still reliable.

Thanks Tim. That's what I was hoping to hear. Any other input? I'd love to save the money and go with the regular Extreme cards instead of the costlier Extreme Pros.

The buffer won't be your problem there - using Long Exposure Noise Reduction (LENR) would be as the camera effectively takes a "blank" frame of the same duration as your real photo for each frame, but a single image takes less than 1 sec. to write out.

Jon wrote in post #17634906
- using Long Exposure Noise Reduction (LENR) would be as the camera effectively takes a "blank" frame of the same duration as your real photo for each frame

Thanks Jon, Yes I am aware of the in camera noise reduction. I have always turned that feature off.
Thanks ~

Reading photons off the surface of a sensor is a destructive process, in other words, once the capacity of a pixel well is measured, the photons inside are destroyed.

What I'm getting at here is that during the 20 seconds your camera is capturing the image, nothing is being written to the card, the actual write happens once the exposure ends and that takes all of a fraction of a second, just like an exposure of any other duration.

What will push your card is if you're shooting ten frames per second or recording video.

Kolor-Pikker wrote in post #17636863
Reading photons off the surface of a sensor is a destructive process, in other words, once the capacity of a pixel well is measured, the photons inside are destroyed.

What I'm getting at here is that during the 20 seconds your camera is capturing the image, nothing is being written to the card, the actual write happens once the exposure ends and that takes all of a fraction of a second, just like an exposure of any other duration.

What will push your card is if you're shooting ten frames per second or recording video.

Sure, but the point is once those pixels have been read they're in a RAM buffer and can be written to the memory card while the next frame is being captured.

tim wrote in post #17636916
Sure, but the point is once those pixels have been read they're in a RAM buffer and can be written to the memory card while the next frame is being captured.

Thanks Tim. I understand that the image is not written to the card until after the exposure ends. What I wasn't sure about was if the camera writes to the card WHILE simultaneously taking the next image. Thanks for the clarification.

SiriusDoggy wrote in post #17641592
Thanks Tim. I understand that the image is not written to the card until after the exposure ends. What I wasn't sure about was if the camera writes to the card WHILE simultaneously taking the next image. Thanks for the clarification.

Of course it does, that's why cameras have buffers in the first place. I didn't quite understand the question since it didn't dawn on me that you were asking something that I see as self-evident.

Starting some time around the release of the 30D (maybe a release before or after; it's been a while), Can on started putting "double-ended" buffers in the cameras; buffers that could write while being filled by the sensor. But the read and write were independent. And a single image wouldn't fill the buffer, so you wouldn't have to worry about being unable to take a shot because of a single exposure.