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07-08-2018, 09:27 PM   #1
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Photo Megabytes - Autofocus - Manual Focus

I had someone take some Autofocus photos, and similar Manual Focus photos today. The autofocus photos were in the 6.4 - 7.6 MB range. The manual focus photos were 10.2 - 12.4 MB range. I am using a Pentax K-5.

Why the difference in size? I used my f/1.7 autofocus Pentax 50mm lens, and an old Focal 28mm f/2.8 lens.


Last edited by mroeder75; 07-08-2018 at 10:12 PM.
07-08-2018, 09:42 PM   #2
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don't have a K-5; but on K-3II it is the same size; regardless of autofocus or manual focus
07-08-2018, 09:54 PM   #3
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File size is all about what the sensor picks up and how it can record it. More complex scenes take more mbs. Take a photo with the cap on. Its all black, simple and will be incredibly small file. Take a picture of bright light dappled through a tree and the file will be big.
07-08-2018, 10:26 PM   #4
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QuoteOriginally posted by mroeder75 Quote
I had someone take some Autofocus photos, and similar Manual Focus photos today. The autofocus photos were in the 6.4 - 7.6 MB range. The manual focus photos were 10.2 - 12.4 MB range. I am using a Pentax K-5.

Why the difference in size? I used my f/1.7 autofocus Pentax 50mm lens, and an old Focal 28mm f/2.8 lens.
The higher the ISO, the larger the raw filesize will be.

Also, JPEGs will be bigger if there is more detail. If you take a photo of the moon, for example, there is nothing in the background, so the filesizes end up being tiny. But for most daytime shots, the filesize will be pretty consistent.


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07-09-2018, 12:47 AM   #5
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The JPEGs are compressed lossy. The RAW is also compressed losslessly, so the file size also vary by the content. If your autofocus made less sharp images (maybe in the background, count the sharp/soft pixels, not your real theme), then it may give you smaler files. Post two examples and we will examine.
07-09-2018, 05:30 AM   #6
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QuoteOriginally posted by mroeder75 Quote
I had someone take some Autofocus photos, and similar Manual Focus photos today. The autofocus photos were in the 6.4 - 7.6 MB range. The manual focus photos were 10.2 - 12.4 MB range. I am using a Pentax K-5.

Why the difference in size? I used my f/1.7 autofocus Pentax 50mm lens, and an old Focal 28mm f/2.8 lens.
Besides the ISO effects mentioned by others, your lenses might be causing this:

1) A wider angle lens will often create a larger file both by encompassing more objects in the scene and by typically having greater depth of field (more objects in focus).

2) A sharper lens (or sharper aperture) will create a larger file.

Can you post a pair of the "similar pictures"?

Last edited by photoptimist; 07-09-2018 at 06:13 AM.
07-09-2018, 05:59 AM   #7
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Little things like aperture selection will also make a difference eg the 50mm used at F1.7 will likely have lots of out of focus bokeh in the image. Little detail information present in the bokeh and this would allow the out of focus areas to be quite heavily compressed. Same scene (even with same focal length) but the lens has F2.8 widest aperture (or the F1.7 lens used stopped down) will create less oof blur and more detail than the F1.7 lens used wide open. So a somewhat larger file would be expected with the F2.8 image even for the same scene.

07-09-2018, 06:21 AM   #8
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I would only use identical pictures when looking at file size.
07-09-2018, 07:05 AM   #9
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^^This

QuoteOriginally posted by mroeder75 Quote
Why the difference in size? I used my f/1.7 autofocus Pentax 50mm lens, and an old Focal 28mm f/2.8 lens.
Even slight changes in what is included in the image can change the file size, so can many other factors as noted above.

To test: put the camera on a tripod and lock it in place. Take several images with the camera in auto-focus and then without moving anything take several in manual focus. I think you will find the image sizes to be nearly identical.
07-09-2018, 07:25 AM   #10
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I do not worry much about file size but I thank the OP for starting this thread it has been interesting and I have learned a lot.
07-10-2018, 12:44 AM   #11
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QuoteOriginally posted by Mikesul Quote
I do not worry much about file size.
Likewise but sometimes it surprises me just how much difference level of detail makes to compressed file sizes. A pixel shifted image in finalised JPEG format after the initial monsterous RAW file has come out of processing thru DCU and then Lightroom is surprisingly large - all that fine detail noticably restricts the JPEG compression routines.
07-10-2018, 06:59 AM   #12
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QuoteOriginally posted by southlander Quote
Likewise but sometimes it surprises me just how much difference level of detail makes to compressed file sizes. A pixel shifted image in finalised JPEG format after the initial monsterous RAW file has come out of processing thru DCU and then Lightroom is surprisingly large - all that fine detail noticably restricts the JPEG compression routines.
Oh, it is definitely interesting. i always enjoy learning more about how the equipment works.
07-10-2018, 07:24 AM - 1 Like   #13
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QuoteOriginally posted by southlander Quote
Likewise but sometimes it surprises me just how much difference level of detail makes to compressed file sizes.
In one batch of files saved to jpeg, files K-1 files can range from 600mb to 2.4 MP. All with the same jpeg compression and image size. How detailed the image is makes a huge difference.
07-10-2018, 07:49 AM   #14
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The point of compression is that it can use very little code for areas without information and so the file is smaller. If an image is full of details corner to corner it has to be recorded and a larger file results.
07-11-2018, 07:20 AM   #15
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Photos

Similar photos, but not identical.

The sharper one, #1257 is comprised of 6.51 MB taken with SMC Pentax-DA1:1.8 50mm lens.

#1269 is comprised of 10.3 MB, was taken with my old manual focus Focal MC Auto 1:2.8 manual focus lens acquired in 1983. These were sold at KMart, likely manufactured by Tokina.
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