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03-15-2012, 10:32 PM   #1
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posting pictures question

I'd like to post some pics taken with my Super Takumar 135mm f/3.5 lens so I can get a sense of the quality of its performanace from other users. Having only 4x6 prints to scan, save, and upload, I'm wondering if there's some way to get them on PF at a larger size - 8x12, say - so the lens can be fairly evaluated. I know I could scan at 72 psi and just blow them up, but that would present quite a lousy view of the lens' ability. I thought of scanning the prints at a higher resolution. I can get a large, sharp display of them in Photoshop that way, but they would end up being displayed at 72 psi (I believe) and showing at 4x6 here anyway - not much of a view. No resolution pro here, so any suggestions much appreciated.

03-16-2012, 08:08 AM   #2
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Nothing you do is going to change the number of pixels per inch displayed by any of our monitors. Most monitors display somewhere around 100ppi (seldom as low as 72ppi any more); the new iPad's "retina" display has over 300ppi. None of this is under your control. All you control is the number of pixels you feed to our monitors. Since most of us are viewing in windows that are somewhere around 800-1000 pixels wide, you should scan your prints at whatever ppi setting it takes to yield that number of pixels. Fewer pixels and the image will appear small within our windows; more pixels and it will appear too large to fit in the window. The ppi setting you scan at is important for the purpose of getting the desired number of pixels but after that, this information is completely ignored. Our monitors work in pixels, period; the number of pixels they can display per inch is fixed in the hardware.

So, for a 4x6" print in landscape orientation, if you want it to come out 900 pixels wide, you need to scan at 150ppi (900 pixels divided by 6 inches equals 150 pixels per inch). You could scan at a higer resolution then downsize in postprocessing and get exactly the same results - a picture that fills our windows. But scanning at 72ppi then upsizing would indeed give poor results.
03-16-2012, 02:52 PM   #3
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Scanned/Uploaded/Attached

Thanks Marc for your clear and concise explanation. Identifying this ST 135 3.5 was a subject last week on the Pentax SLR Lens Discussion forum. I'll attach a couple of scans on a new thread in that forum ("A Good Copy Of This Lens").
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