Photo Notebook


Cropping to digital zoom presets, keeping the aspect ratio.

“Focal length” Pixels (ref) Scale (1-dim)
28mm 8368 x 5584 1.00
35mm 6704 x 4472* 0.80
50mm 4688 x 3128* 0.56
75mm 3136 x 2096 0.37
90mm** 2603 x 1740 0.31
103mm*** 2280 x 1522 0.27
166mm**** 1408 x 939 0.17
333mm***** 704 x 470 0.08

* Cropping in Photomator and respecting original aspect ratio, the 35mm height is +2px and the 50mm height is -2px vs expected.

** The 90mm is featured on the Q3, not Q2, but I simply did 90mm/28mm ≅ 3.214x for the scale factor, and (1/3.214) * 8368px = 2603px.

*** I'm interested in 2280px width because I'm developing a new website media display standard max width of 1140px, so a 2x pixel density means exporting to 2280px width. I reverse approximated the focal length via (8368 / 2280) * 28mm ≅ 102.8mm.

**** I'm also interested in 1408px width because it's 2x the current website text width of 704px. So text-width photos (again, 2x pixel density) would be exported to 1408px width. Focal length again reverse approximated with (8368 / 1408) * 28mm ≅ 166.4mm.

***** Same story for 704px, just a perverse experiment.

I don’t get these crops automatically in Apple Photos or Photomator even when I take a photo with those crop lines on,01 so there isn’t any real reason to abide by these. These just seemed like convenient settings to try.

Question: If the full photo is a 28mm focal length, why do the specs call it a “Digital 35 mm compact camera, fixed focal length?” Is this a convention, or about the sensor size?

Cropping Limits

I am curious about how focus interacts with crop in shallow-DOF photos. Here are a variety of crops shown on a photo:

Here are each of those crops displayed at text-width.02

28mm (orig) [f1.7]

"35mm" [f1.7]

"50mm" [f1.7]

"75mm" [f1.7]

"90mm" [f1.7]

"166mm" [f1.7]

I am shocked to see that, at this small of a width, the “90mm” crop is totally usable.

Out of sheer curiosity, I cropped down to 1408px, the equivalent to an eye-watering 166mm zoom, and… it looks excellent. This is totally surprising and delightful. I assumed that the raw image pixels didn’t correspond to usable pixels, just a somewhat arbitrary binning of sensor data. But it completely works.

And since if something is worth doing, it’s worth overdoing, I went past the 2x pixel density and made a raw 704px width photo, which I guess would be 333mm.

"333mm" [f1.7]

To me, this finally looks blurry. I think this is because it’s now actually stretched on a 2x pixel density screen. To verify, we can display it 1/2 size03 to make it 2x pixel density again.

"333mm" [f1.7], displayed 1/2 size for 2x pixel density

Doing this, I realized I’m stupid and this is now just exactly a cutout of the “166mm” photo.

My tentative conclusion is that yes, you really can use each pixel that comes out of the camera.

Practical Limits

On the website, I anticipate exporting at two potential widths:

This means, when cropping, those are my realistic boundaries.04

Here’s what each of these crops look like at their intended display size.

Crop of 2280px ("103mm"), displayed at max 1140px [f1.7]

Crop of 1408px ("166mm"), displayed at max 704px [f1.7]

On a big enough screen, the bottom image should just look like a cutout of the top. I.e., they should be at the same scale.

This is, again, delightful because there’s so much room to crop.


  1. I think Lightroom might do it, but I haven’t been willing to take that plunge yet. ↩︎

  2. All crops are exported to 1408px width and displayed at maximum of 704px to allow a 2x pixel density. ↩︎

  3. Sizes are confusing. This cuts each of the width and height in half, so it feels like “half size,” though the area gets cut by 1/4. ↩︎

  4. There are also cover photos, which will probably be bigger. ↩︎