Question re. buffering long exposures.

[Loopy]

There might be a really obvious answer to this but I'm missing it so I'm prepared for the old :bonk:.

If I take a photo at 1/1000 sec or at 30 secs, the file size is the same yes? (I shoot in raw + jpg)

So how come it takes almost as long as the exposure to transfer the data to the memory card on a long exposure butfast shutter speeds are almost instantaneous?

Off to have my tea now, so will respond to any replies (hopefully) later.

Thanks
L

 

[johnsy]

Do you have long exposure noise reduction switched on? If so this will take a dark frame at the same exposure length to remove any *sensor noise from the final image (*generated by heat during the exposure).

 

[SparkUK]

^ What johnsy said.... You've two choices really, turn it off in camera (and probably have to run some noise reduction on your PC) or put up with it on looooooong exposures.

 

[Canonman II]

Check also to see if you have "High ISO noise reduction" on too. This and the long exposure functions really slow stuff down.

 

[Loopy]

Ah, that makes sense. I think I have all of those turned on.

 

[StewartR]

If I take a photo at 1/1000 sec or at 30 secs, the file size is the same yes? (I shoot in raw + jpg)

Virtually, but not quite.

Both RAWs and JPEGS are compressed - non-destructively for the RAW and destructively for the JPEG. The degree of compression which can be achieved depends on the amount of fine detail in the picture, and noise counts as fine detail. (Noice can't be compressed because it's essentially random.) So if one picture has more noise than the other - long exposure noise or high-ISO noise - then its files will be larger.

 

[Loopy]

Cheers. Makes sense. I don't mind the wait as long as I know why it does it and that I'm getting some benefit. That's another bit of knowledge I can add to my collection.