Image size with Canon 18-55 and quantaray 300 lense

[RASphoto]

Hello all this is my first post so wack me around if im in the wrong area. I have a 300d Dig Reb. Under the large capture setting with the canon 18-55 lense the files come out about 5 mb. I got a deal on this Quantaray 70-300m lense so decide to get it and try it out, its a brand new lense. When I switched and took shots at about 250-275 zoom the pictures came out pretty well but the file sizes were only around 1.5 mb under the same largest setting (NOT RAW). Is this cause of the Zoom or maybe the lense? Any help much appreciated.

Bob

[vvizard]

5MB was large for the "large jpeg" setting I think. Mine usually comes out at 2-2.5MB on the 10D. What ISO-settings where you using? Are you sure the quality for the large-setting was the same both times? Try shooting the same subjects with them, with the rebel-lens set to 55mm, and the other on 70mm so you can try getting mostly the same composition.

If the resolution of that last zoom is real crappy, maybe it was easier to compress due to the fact that there was less details.. Still I think 5MB for a large jpeg sounded awfully large.. That's nearly the size of what a RAW-file should be

[G3]

Try this...set your 18-55 on 55 and take a shot of something. Then, using the same settings and lighting set your 70-300 on 70 and shoot the exact same subject. Keep the camera in the same position for both shots. The file sizes won't be exactly the same, but I bet they'll be a lot closer. Better yet, try it again using RAW for both shots. The size of the jpeg file is going to depend on how much different data is recorded in the pixels. In other words, a subject that has a lot of the same color is going to produce a smaller file than a subject that has a lot of samller amounts of different colors and detail. It's more the subject and compression ratio that determines the files size than anything else.

[RASphoto]

thanks for the info I will try that. I just looked and a few shots taken with the canon lense and they all are about 5 mb. that does seem large for not being on the RAW setting,

thanks again,

Bob

[vvizard]

I haven't looked as much into this on the 10D as I did on my previous (and first) camera, but on that one, the filesize nearly doubled when I used long exposures (15-30sec) on night-shots. (which I take a lot of). Could that be a reason for you getting such large files? (Although I haven't verified if the 10D also gives larger files for longer exposures)

[robertwgross]

Extremely long exposure time or high ISO yields high color noise. High color noise yields more randomness of the data file, and that makes it less compressible in RAW, which means a larger file size.

Short exposure time with a clean subject and low ISO will yield low color noise, which yields less randomness of the data file, and that makes it more compressible in RAW, which means a smaller file size.

---Bob Gross---