Printing resolution in line pairs?

[Alun]

I have a question - please don't flame me if I'm getting mixed up!  

I have downloaded an iPhone app called OptimumCS Pro which, unlike most other apps I've seen, gives you the optimal aperture setting based on lens choice/desired DoF/focus distance and print resolution which it expresses in line pairs/mm for a 10inch print.

http://www.GeorgeDouvos.com/douvos/Why_OptimumCS.html

The background information seems to suggest that aiming for >10 line pairs/mm is desirable. I use an Epson 4900 and print at A2 (in reality c. 22 inch x 15 inch) so how does this affect this aim (double?/half?).

Thanks in advance of your reply
Alun

[Ernst Dinkla]

I stick my neck out as an amateur photographer. Could be there has been no reply so far as we all wonder whether that fundamental relation between DOF, best lens aperture, print size, print resolution is something you take into account when taking a picture but in heavy tripod landscape photography or art reproduction. The LPpMM seems to suggest analogue film use too where we would think of PPI on print size. The gain in using the best lens aperture to squeeze some extra line pairs from your equipment most likely does compromise image quality in general most of the time, esthetically, exposure related, ISO related, moving objects and whatever. He has an app too for sensor dynamic range, ISO/noise, color depth?  It is a good thing to know which aperture of the lenses you use deliver the best overall frame sharpness but compromises will be made in any picture taken. When you insert the memory card in the PC deconvolution lens sharpening in RAW processing, noise suppression, crops, upsampling routines at print time and smart print sharpening all have their place too and give a wider choice in the camera settings than that formula suggests.

If I translate 10 LPpMM in 250 PPI then I say that is a good pixel number to print a 10"-25 cm wide print that will be viewed at 40 cm. I am not going to compute the eye resolution figures for a given viewing distance. I might the day they publish MTF figures for inkjet paper/ink/printer combinations. I guess my eyes will age faster than the MTF figures appear. I would not mind to print the image twice the size if the image content allows it and the wall needs it.

--
Met vriendelijke groet, Ernst

Dinkla Grafische Techniek
Quad,piëzografie,giclée
www.pigment-print.com

[irvweiner]

Ernst, I believe 10 lp/mm would equate to 20 lines/mm. Thus we are looking  at ~500 PPI, a line pair consists of 2 lines--the same as 2 rows of pixels.

irv weiner

[Ernst Dinkla]

You are correct. Then it will also hit the highest resolution possible on inkjet paper I think. More slack in using that app.

Edit: To put that in perspective the iPad 2 has a 132 PPI screen with a near 10¨ diagonal so about 8x6" size. The iPhone 264 PPI, smaller screen but beyond the resolution of the eye according the late Jobs.

I think the translation of 10 LPpMM to 250 or 500 PPI in a print is crude too in relation to DOF. If all the tricks in the book are used to prepare image content in the printing phase, Qimage - Lightroom, it would be interesting to see what rules for DOF can be brewed from that. For theory only and not based on Siemens stars.

--
Met vriendelijke groet, Ernst

340+ paper white spectral plots:
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
update april 2012: Harman by Hahnemühle, Innova IFA45 and more

[Alun]

Thank you Irv and Ernst for the replies - very helpful