What defines the upper bound for FX resolution/pixel density?

Started 11 months ago | Discussions thread
falconeyes
Contributing MemberPosts: 764
Like?
100/200/500/700/1000 MPixels
In reply to jfriend00, 11 months ago

Hi John,

I do not read the thread, but here are my answers:

1. lens limit center, assuming a Non-AA camera:

The very best lenses today are diffraction-limited at F/4 (highest resolution at F/2.8). Using the Rayleigh limit at F/3.3 with 550nm (green), we obtain 1.1µm as lower limit for the pixel pitch. This corresponds to 700 MPixels.

However, only very few lenses today are this good in the center. But they already exist. Note that the Rayleigh limit requires sharpening to reveal pixel level details. It won't show up in MTF50 resolution figures, except maybe photozone as they do sharpen. Theoretically, lenses with peak performance around F/1.8 are feasible. But they haven't been developed yet for an FX image circle. So, theoretically, a Gigapixel FX camera is feasible.

And as a footnote, the above aren't hypothetical values. I've shot test charts onto Gigapan high resolution B&W film with ZEISS lenses and "pixel peeped" results under the micriscope. The level of detail revealed (F/4 center) was mind blowing, in the order of several hundred MP for sure.

2. lens limit corner:

Same argument, but I'd say only the very best lenses like the Nikkor 200/2G or new ZEISS 55/1.4 will have diffraction-limited corners at F/8 already (highest corner resolution at F/5.6). We obtain 2.6µm as lower limit for the pixel pitch. This corresponds to 130 MPixels.

Because resolutions of between 130 - 700 MPixels require selection of a dedicated lens and almost fixed aperture (much like the Nokia 41MP phone cameras), I will assume the following more practical limits in my discussion:

  • FX camera with interchangeable lens (D800E type): 200 MPixels. (2.1 µm)
  • FX camera with fixed lens (RX1 type): 500 MPixels. (1.3 µm)

3. AF limits:

Let me assume F/5.6 photography with 2µm pixels. A sharp focus requires nailing the focus plane with <=9µm focus error (cf. LumoLabs WP on image sharpness).

Current phase AF systems have a typical focus error of about 20µm (with AF fine tuning), contrast AF systems of about 10µm. The "industry standard" used to be 50µm.

Therefore, phase AF is good enough for 50MP, contrast AF for 200MP. Everything beyond requires progress in the AF department. In low light, that may not be feasible.

4. Motion blur limits:

Can be overcome with flash. Nevertheless, here is a result: camera shake moves the camera at 10 mrad/s (cf. LumoLabs again). With 50mm and <1µm blur, this corresponds to 1/500s. Or a 10x increase of the 1/f-s rule. Moreover, shutter-induced blur must be avided, probably excluding a mechanical shutter at >100MP. A shake reduction mechanism would help (4 stops would bring shake blur back to normal) but lens VR is not designed to work with 1µm precision. So, in this resolution limit discussion, I exclude VR.

5. Noise limits:

I'd say that noise at ISO200/D800E is just low enough to allow for the headroom required to sharpen lens softness (like at F/14 at 36MP). Noise scales with resolution (cf. DxO labs).

At 200/36, we need 1.2 stops better ISO, at 500/36, we need 1.9 stops better ISO.

Therefore, to make use of resolutions in excess of 100MP (200-700MP), a base ISO of ISO50 will be required. Note that the sensor itself will not make much progress, as quantum efficiency is >50% today not leaving much headroom. It will be challenging enough to maintain the noise performance with 1µm pixels.

Conclusion:

While near Gigapixel resolutions are feasible with FX from a theoretical point of view, my impression is that FX is "good for" resolutions around 100 MPixels (their eventual sweet spot). I assume higher than 100MP resolutions to become the speciality of larger than FX, or fixed lens FX, cameras. As both will go down in price too. Note the the digital rear cap lens (like Sony Q100) falls into my fixed lens FX category.

kind regards,

Falk

-- hide signature --

Falk Lumo

Reply   Reply with quote   Complain
Post (hide subjects)Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow