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07-25-2016, 05:56 AM   #16
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QuoteOriginally posted by Wild Mark Quote
Good question

Pentax FA 28mm f2.8 = 18.5MB
Pentax F 28mm f2.8 = 18.2MB
Pentax A 28mm f2 = 19.9MB
Pentax M 28mm f2.8 (late model = Pentax A 28mm f2.8) = 17.9MB
Pentax M 28mm f2.8 (early model) = 19.6MB
Pentax K 28mm f3.5 = 22.3MB
Pentax K 28mm f2 = 22.8MB
Vivitar 28mm f1.9 = 21.6MB
Pentax M 24-50mm f4 = 20.0MB
Tokina ATX 28-85mm = 19.7MB
Tokina ATX Pro II 28-70mm = 19.6MB

I am curious about the file sizes of the images.


Is the "resolution" of a lens reflected in the file size? Larger = better?
Or are there other variables between lenses including actual FL (i.e <28mm or >28mm) or possible lack of infinity focus as has already been mentioned in this thread or centre and edge performance variables?.
Is the camera sensor in this test "under-resolving" what the lenses should be capable of?


Perhaps I should have posted this in the beginners help section but as this test is being done and evaluated I have posted it here.


Many thanks for doing the testing and for any answers.


Last edited by Skodadriver; 07-25-2016 at 05:56 AM. Reason: Small change in text.
07-25-2016, 07:02 AM   #17
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QuoteOriginally posted by Skodadriver Quote
I am curious about the file sizes of the images.


Is the "resolution" of a lens reflected in the file size? Larger = better?
Or are there other variables between lenses including actual FL (i.e <28mm or >28mm) or possible lack of infinity focus as has already been mentioned in this thread or centre and edge performance variables?.
Is the camera sensor in this test "under-resolving" what the lenses should be capable of?


Perhaps I should have posted this in the beginners help section but as this test is being done and evaluated I have posted it here.


Many thanks for doing the testing and for any answers.
JPEG is a image file compressed by keeping the least amount of information about the image that captures the strongest visual details in the image.

To a first approximation, the size of a JPEG file for a given value of the JPEG quality setting (e.g., 3-stars), is a function of the amount of detail in the RAW sensor data of the scene. The greater the amount of variation in pixel-to-pixel brightness differences, the less the algorithm thinks it can discard whilst preserving the structure of the scene.

In general, images of simple scenes, low-contrast scenes, out-of-focus lens settings, optically-poor lenses, and low-ISO be smaller than those of detailed, high-contrast, sharply focused, high ISO, with a high-resolution lens.

If the sensor underresolves the lens, the effects on file size would depend on whether the sensor has an antialiasing filter or not. If there's an antialiasing filter, then all lenses that match or exceed the sensor resolution would have similarly large file sizes. If there's no antialiasing filter (Wild Mark didn't say if the AA simulator was on or off), then file size for an extremely detailed image would continue to grow somewhat for the sharpest of the sharp lenses (because such lenses would resolve sharp details such as telephone wires, backlit twigs, or text on signs as having perfect high-contrast step-changes in brightness between adjacent pixels).

In the case of these tests, Wild Mark took pictures at the same ISO of the same scene with the same attempt at focusing the scene. Thus any differences in file size would likely come from differences in the sharpness of the lens in resolving the entire feild of the image.

(P.S. Of course, there's a bunch of technical details and clever processing by which the camera decides what information to keep and what to discard. I'm sure every camera manufacturer has their own clever tweaks for interpreting the raw sensor data and adjusting the JPEG compression to get the best looking picture with the fewest artifacts in the least file space possible. Also, I'd not be surprised if some lenses such as those with speckled, "busy", or soap-bubble bokeh can create largish files if the bokeh have a lot of details in them.)
07-25-2016, 07:09 AM   #18
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I can say the AA simulator was turned off It would seem true that the higher the MB size the less CA although this was not exactly the case. The K28/2 and A28/2 had the least CA and perhaps best distortion control. Perhaps this allowed for more detail to be captured in the edges and corners ????

Another factor to consider is the camera applying the lens profile for the FA28 (only just thought of that).

I will ponder these results some more and maybe re-test with a more interesting and challenging scene sometime. I will also endeavour to do a series with 20mm lenses at the same time (SMC Takumar to FA20/2.8 + some zooms minus the A20/2.8).
07-25-2016, 07:36 AM   #19
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Another factor to consider is the camera applying the lens profile for the FA28 (only just thought of that).



That may be a good point! If the camera can apply some specific "fixes" for known deficiencies in a lens, the output would be better probably than a similar "quality" lens that has not been recognised.

---------- Post added 07-25-16 at 07:55 AM ----------

QuoteOriginally posted by photoptimist Quote
JPEG is a image file compressed by keeping the least amount of information about the image that captures the strongest visual details in the image.

To a first approximation, the size of a JPEG file for a given value of the JPEG quality setting (e.g., 3-stars), is a function of the amount of detail in the RAW sensor data of the scene. The greater the amount of variation in pixel-to-pixel brightness differences, the less the algorithm thinks it can discard whilst preserving the structure of the scene.

In general, images of simple scenes, low-contrast scenes, out-of-focus lens settings, optically-poor lenses, and low-ISO be smaller than those of detailed, high-contrast, sharply focused, high ISO, with a high-resolution lens.

If the sensor underresolves the lens, the effects on file size would depend on whether the sensor has an antialiasing filter or not. If there's an antialiasing filter, then all lenses that match or exceed the sensor resolution would have similarly large file sizes. If there's no antialiasing filter (Wild Mark didn't say if the AA simulator was on or off), then file size for an extremely detailed image would continue to grow somewhat for the sharpest of the sharp lenses (because such lenses would resolve sharp details such as telephone wires, backlit twigs, or text on signs as having perfect high-contrast step-changes in brightness between adjacent pixels).

In the case of these tests, Wild Mark took pictures at the same ISO of the same scene with the same attempt at focusing the scene. Thus any differences in file size would likely come from differences in the sharpness of the lens in resolving the entire feild of the image.

(P.S. Of course, there's a bunch of technical details and clever processing by which the camera decides what information to keep and what to discard. I'm sure every camera manufacturer has their own clever tweaks for interpreting the raw sensor data and adjusting the JPEG compression to get the best looking picture with the fewest artifacts in the least file space possible. Also, I'd not be surprised if some lenses such as those with speckled, "busy", or soap-bubble bokeh can create largish files if the bokeh have a lot of details in them.)



Thank you for this, very informative. Nice large JPEG image files from the camera at around 20 MB though.


If I align my own opinion of my Pentax 28mm lenses with the file sizes quoted, the later "M" and optically same "A" 28mm lenses are not the best performers. On the basis that file size does reflect image output quality to a degree of course.


I sold my copies of these and kept the early M28 F2.8, the M28mm F3.5 and the Vivitar 28mm close focus F2.8 as my albeit untutored view of the performance of the others at towards infinity was not good.


The Vivitar had a MFD advantage and seemed sharper and the M 28mm F3.5 seemed to provide better images at the same apertures than the M and the A.


Of course my copies of these lenses may not be working anywhere near as well as they had when new.

07-25-2016, 06:00 PM   #20
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QuoteOriginally posted by Skodadriver Quote
If I align my own opinion of my Pentax 28mm lenses with the file sizes quoted, the later "M" and optically same "A" 28mm lenses are not the best performers. On the basis that file size does reflect image output quality to a degree of course.
I think you have made a well informed decision there if my basic testing and copy variation is considered to be representative of what you would expect under a range of conditions. The testing has certainly consolidated in my mind the superiority of the K28/2 and, to a smaller extent, the A28/2. In regards to the latter, the lens shines as a compact WA - something the K28/2 is not known for
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