Is the Printer DPI Really There

I needed a fine-pitch line scale target for evaluating depth of field of various macroscopic lenses, so I created and printed the bitmap graphic (dpi_1200_b.psd) shown below as an icon.

Section of the dpi_1200_b.psd are: - n:o 1 alternates with one line black & one line white - n:o 2 alternates with two lines black & two lines white - n:o 3 alternates with three lines black & three lines white. And so on up to the section 6.  The background underneath the section numbers is pure black. In case you like to test your printer please remember to change the DPI of the file without resampling to match the DPI of your printer, originally the DPI info in the file is 1200 dpi. zip-file containing dpi_1200_b.psd  for download.

You will need a x10 lupe or preferably a low mag microscope with polarization filters for evaluation.

Originally the graphic had only the lower part, but Lexmark Optra R+ (B/W laser, 1200 DPI by the spec) printed the section 1 and section 2 as the same, there was virtually no difference under microscopic inspection and no resolvable lines. So after some thinking I tried printing the graphic again but rotated at 90 degrees. This resulted some difference between the sections 1 and 2 and in the section 2 the line structure was visible but only faintly/partly. 

So I learnt that the Lexmark Optra R+ is not a true 1200 DPI printer. It can do 600 DPI with the settings print darkness: Normal and Smoothing: On. If the Smoothing is set to Off then it is only a 300 DPI printer. I tested this on various quality papers and on overhead transparency film, but the 1 line dither is not resolvable under powerful microscope.

Next I tried printing with Tektronix Phaser 450e (300 DPI dye-sub) with the three color CMY roll installed. Result was good, very sharp lines even in section 1. Surprisingly Tektronix also had a little problem with the bottom part of the graphic, section 1 and 2 printed much darker in the lower part than in the upper part of the graphic.

Conclusions so far

With both printers the line-patters that were parallel with the movement of the paper printed much better than the line-patterns that were in right angle to the movement of the paper. 

So, laser and dye-sub printers seems to have potential charging/heat control problems, line pattern that requires rapid on/off charging/heating may not print well.

A simple line pattern graphic seems to be quite good tool for evaluating the specified DPI capability of the peripheral printers.

Quality of the paper (or the printing media) matters, but what is good quality paper?