20D & 30D reading CF cards size differently

gus · December 11, 2006

Thanks to waxy i have today picked up my 2 new 4 gig CF cards. Thanks for you effort mate.

Odd thing is that the 30D reads both as 999 shots in large jpeg & the 20D reads them both as 851 shots in large jpeg. I have done a format & was wondering how this difference occurs ?

gus · December 11, 2006

All is sorted...the 20D was set to 1600 ISO. I dont know why this occurs but its all sorted anyway.

ivar · December 11, 2006

gus wrote:

All is sorted...the 20D was set to 1600 ISO. I dont know why this occurs but its all sorted anyway.

That makes that big of a difference

interesting. Can one of the smarter folks around here explain me why?

TylerW · December 11, 2006

Higher ISO = noisier image.

Image noise is very hard to compress using the techniques that jpeg employs. As a result, higher ISO images result in larger file sizes, which results in less images stored on a single CF card.

gus · December 11, 2006

TylerW wrote:

Higher ISO = noisier image.

Image noise is very hard to compress using the techniques that jpeg employs. As a result, higher ISO images result in larger file sizes, which results in less images stored on a single CF card.

We may not be talking the same thing here. Im talking about when you first put the empty card in the camera & the number of shots you have comes up in the screen.

ie.. no images at all. Do you mean the camera sets aside a set volume of CF card according to what its settings are on in presumption of the incoming image ?

ivar · December 11, 2006

TylerW wrote:

Higher ISO = noisier image.

Image noise is very hard to compress using the techniques that jpeg employs. As a result, higher ISO images result in larger file sizes, which results in less images stored on a single CF card.

Yeah, that makes sense I guess. I just didn't think it would be that big of a difference. Thanks.

ivar · December 11, 2006

gus wrote:

We may not be talking the same thing here. Im talking about when you first put the empty card in the camera & the number of shots you have comes up in the screen.

ie.. no images at all. Do you mean the camera sets aside a set volume of CF card according to what its settings are on in presumption of the incoming image ?

Yeah, the number the camera shows is the number of files it expects to be able to save on the card. If it uses a bigger filesize to calculate the number, the number will go down for a given size card.

claudermilk · December 11, 2006

Makes perfect sense to me. The camera is expecting the file to be noisier & therefore larger. I'll bet Canon spent a bunch of time getting a feel for the file sizes the sensor produces at each ISO setting with each quality setting & created some kind of lookup table to use for displaying expected number of shots. I have yet to see where the original expeected number of images (about 109 on a blank 1GB CF for RAW on my 20D) matches what I actually get (typically about 120 give or take a half-dozen).

Richard · December 11, 2006

claudermilk wrote:

Makes perfect sense to me. The camera is expecting the file to be noisier & therefore larger. I'll bet Canon spent a bunch of time getting a feel for the file sizes the sensor produces at each ISO setting with each quality setting & created some kind of lookup table to use for displaying expected number of shots. I have yet to see where the original expeected number of images (about 109 on a blank 1GB CF for RAW on my 20D) matches what I actually get (typically about 120 give or take a half-dozen).

Yep. The mileage varies with the nature of the images you shoot, as some can be compressed smaller than others.

BTW, I just checked my 20D with a freshly formatted CF card and the number of shots remaining depends on the ISO. It was a 2GB card, and the numbers ranged from 530 (ISO 100) to 378 (ISO 3200) in large fine JPG and from 222 to 183 in RAW. Interesting...you learn something new every day.

JWright · January 1, 2007

Another interesting fact: The number of available images showing with an empty card is not necessarily the number of images you're going to get, all other factors being equal. My 20D shows 445 images available on a 4Gb card at ISO 100 (RAW). I recently shot an airshow at ISO 100 and was able to get about 100 more images on the card. This was all in RAW...

The amount of detail in an image has a direct bearing on the final file size of the image on the card.

gus · January 1, 2007

JWright wrote:

The amount of detail in an image has a direct bearing on the final file size of the image on the card.

Absolutely...take a shot of fire works & look at its size....it will be tiny as there is very little information in the photo.

20D & 30D reading CF cards size differently

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