Why no 40mm pancake (or similar)?

Started Feb 9, 2018 | Questions thread
Holistic Photog Contributing Member • Posts: 719
Re: Mount specs probably
1

uRebel Rob wrote:

Astrotripper wrote:

I don't know too much about optics design, but here's a little trend that might explain that.

Mount / Flange distance / Pancake lenses

MFT / 19.25 mm / 14, 17, 20 mm
EF-M / 18 mm / 22 mm
EF / 44 mm / 40 mm
EF-S / 44 mm / 24 mm
Sony E / 18 mm / 16, 20 mm
Leica M / 27.8 mm / 28, 35 mm

Pentax K / 45.4 mm / 21, 40, 43 mm

The 70mm/2.4 is pancake. And although rated as an ASPC, it works okay on FF too. On a cropped sensor, that's 105mm FFE.

Nikon F / 45.5 mm / 28, 45, 50 mm

And add the discontinued samsung NX

Samsung NX / 25mm / 16mm, 20mm, 30mm

Do you see the trend? There are no pancake lenses that have significantly longer focal length than the flange distance of the mount they are designed for.

... (except for the pentax 70mm) ...

That's probably not a coincidence.

But yeah, the easiest pancake is around the flange distance, but Pentax has both the 21mm and the 70mm, both pretty far outside the normal range. Canon's EF-S pancake "cheats" a little, as it allows the lens to go into the camera body (and why you can't use canon EF-S lenses on FF bodies).

Pentax is known for it's pancakes, and it's going to be hard to match/beat the ~ 0.5x to 1.5x the flange distance range that they have.

Obviously I omitted collapsible lenses that are only pancakes when collapsed.

So if you are hoping for a pancake short telephoto, I'm afraid you're out of luck.

Based on pentax's 70mm pancake FL being about 1.5x its flange distance, and applying it to m43's flange distance (and heavy rounding): 1.5 * 20 = 30mm. I think a m43 pancake 30mm lens is possible, but 40mm might be outside the flange distance's possibilities.

I think they can make pancakes either a little (maybe 50%) above or below the flange focal distance if they limit the max aperture (i.e. make it a slower lens). I believe the further away from the FFD you go, either wider or longer, while still keeping a pancake shape, the slower you have to make the lens.

So, I believe the fastest pancake lenses can be made right around the FFD.

At least that's been my observation. Since I'm not an optics expert, I can't explain why this is.

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