Optimal aperture position?

Started 2 months ago | Discussions thread
ProfHankD
ProfHankD Veteran Member • Posts: 6,819
Side-by-side images with laser-printed apodizer

fferreres wrote:

ProfHankD wrote:

There are really three issues for printing:

  1. Optical transparency of unprinted areas. This is where inkjet doesn't do so well, because the material needs a coating to hold the ink.
  2. Optical density and continuity of the printed areas. Inkjet makes relatively smooth shades, while laser output tends to be clumpy and less continuous (discrete particles of toner). Laser toners vary wildly, but some can produce higher transmission density than any inkjet will give; some (mostly older) lasers also produce solid-shaded regions that have markedly higher density at the edges than in the middle of a region, which makes them unusable for making apodization masks.
  3. Spectral blocking. Organic dye is generally transparent in NIR, so you need pigmented ink for an inkjet. Most black laser toners are pretty good, but it does vary. Ideally, you want carbon black in the ink/toner.

Thanks! I feel little dumb as it had not occurred to me I could just make different sizes and print all of them on one sheet. It's obvious, unless after it's mentioned. Are there any other fun shapes to play with that make sense /only work near the aperture (I liked the black spot in middle to leave a lens with the most aberrated part only too)?

Do you know if there's any name for a tool to cut perfect circles? I guess I will start apreciating lens centering after this experiments.

None of this is particularly difficult, but the printed masks tend to be pretty miserable quality. Here's an example shot of a Christmas tree (out of focus) using a laser-printed 300DPI apodizer vs directly shooting at f/1.7 using an old Minolta Rokkor 50mm f/1.7:

Notice that the apodized OOF PSFs look rather grainy, contrast is dramatically lower, and there is still deformation of the OOF PSF by vignetting (and the above is a roughly APS_C crop). In other words, you see problems #1 and #2 described above plus the vignetting I also warned about.

Now I have to make it clear that LED Christmas tree lights are NOT good point sources, so some of the flaws above are due to that. For comparison, here's the same scene shot with the perfectly apodized Sony STF 100mm (and uncropped FF):

From the above you should note that the circles that have a dark ring around a bright core are the result of lenses on the LEDs interacting with the apodization... the very smooth ones are what you get from better approximations to point sources.

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