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Comment by falcrist | Hacker News Reader

That's a bit of an odd title. This is a mirrorless camera.

I always found it interesting that medium format cameras generally don't have the fastest lenses. The fastest autofocus primes I see are f/2.8 and f/4, which are roughly equivalent in speed to an f/1.6 or f/2.3 respectively. I'm sure the quality is better, but I'd love to know why manufacturers don't seem to be pushing the aperture as hard with medium format as they do with full frame.

Of course, I'd love to play around with one of these... Even if it would be massive overkill for anything I'm doing.

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>but I'd love to know why manufacturers don't seem to be pushing the aperture as hard with medium format as they do with full frame.

For one because the DoF would be so small as to make focusing almost impossible wide open...

This is true. I have an 80mm f2.8 from a 6x9cm camera that I mounted onto a recessed 4x5 lens board. Wide open the depth of field is so insanely shallow that it's tough to focus even under a dark cloth.

I have a 110mm f/2.8, it took me several weeks of experience with the lens and camera system before I could confidently get accurate focus. But I think that the shallow DOF is a point in its favor, because if you can get good focus at f/2.8 you're going to get a very sharp image at f/11.

That, and the sheer amount of glass you'd need would make for an excellent workout session every time you went shooting.

Say, a 250mm f/1.4 with an image circle large enough to be useful on 6x9 would be quite the beast (and impossible to focus on my Texas Leica.)

You've got computers to focus for you, for the reasonable price of adding a motor strong enough to move all that glass ;)

> why manufacturers don't seem to be pushing the aperture as hard with medium format as they do with full frame.

It's usually a lot more expensive to manufacture larger aperture lenses, for one, and the more the aperture increases the more your focus is going to be razor sharp (1.8 on medium format will mean your focus fully open will probably be only a few mms deep in short distance) so the applications are very limited. And for further away subjects then you won't see much difference anyway. Digital sensors have variable ISOs and not too much noise even at several thousands of ISOs now so you could take pictures in the evening even with a narrower aperture.

Oh, no doubt it would be expensive, but medium format digital cameras already tend to be prohibitively expensive for anyone who doesn't have an urgent professional use for one.

If you can do without AF then most of the cost is just the back. You can totally shoot digital MF economically if you're open to not using the latest greatest back.

I paid about 1.5K total for my back, body and lens, to provide one anecdote of how cheap it can be.

> The fastest autofocus primes I see are f/2.8 and f/4, which are roughly equivalent in speed to an f/1.6 or f/2.3 respectively. <

Can you elaborate on that? What do you mean by "equivalent in speed?"

Equivalent to ƒ/1.6 and ƒ/2.3 on a "full frame" sensor.

Similar depth of field and total light gathered.

I'm aware that sensor size doesn't change depth of field, however if you compensate the focal length to produce the same field of view on both sensors, you then need to compensate the aperture to arrive at the same depth of field.

So a 50mm f1.4 on a full frame sensor would be roughly equivalent to an 85mm f/2.4 on one of these digital medium format sensors.

The best way to look at total light gathered is to talk about the aperture diameter, not f-ratio. The f-ratio is what it is; it doesn't make sense to multiply it or divide it to 'compensate' for different aperture diameters. You should just use the aperture diameter at that point.

And an f/4 for any size format will be gathering the same amount of light per sensor area. It's just that the sensor area is larger on larger formats, so the total amount of light (but not light per pixel!) is more. This is why telescopes have such wide apertures; they're limited by total amount of light.

The amount of light per area at the sensor is directly proportional to the area of the aperture and inversely proportional to the focal length. That's why we use the f-number, which is a ratio of focal length to aperture diameter.

Please note that the f-number doesn't indicate total light hitting the sensor. It indicates total light per unit area at the sensor. Thus, for the same f-number, a larger sensor will gather more light.

All of this info can be found in the wikipedia page: https://en.wikipedia.org/wiki/F-number

> I'm sure the quality is better, but I'd love to know why manufacturers don't seem to be pushing the aperture as hard with medium format as they do with full frame.

Wide open, the lens is less sharp and you are going to have large portions of the image out of perfect focus. At that point there is no point using MF, you might as well use a smaller camera.

My personal experience... I mostly use a 110mm f/2.8 prime, and when I shoot wide open it's beautiful, but at that aperture I'm definitely not getting near the sharpness that the system provides.

But all of this applies to full frame with an f/1.4 85mm lens as well, yet even f/1.2 isn't that rare in the full frame world.

That is incorrect, it does not apply to an f/1.2 full-frame lens, because you cannot switch to a smaller format. At least not without spending an exorbitant amount of money.

I said it applied to an f/1.4 lens. In that case, you'd have to switch to an APSC f/0.95 lens. Those exist, but only in manual focus... and they're only around $500

If you're shooting MF at f/2.8 on a 110mm lens with ~0.5x crop factor, you'll get similar results to shooting 55mm at f/1.4. So, not much advantage to making MF lenses with larger aperture.

If you're shooting f/1.4 on a full-frame camera, and swap to APS-C at f/0.95, you're not getting similar results. An f/0.95 is a somewhat extreme lens design and will have noticeable aberrations wide open. At least, the f/0.95 lenses that I've seen.

For the same reason, you rarely see LF lenses that open wider than, say, f/5.6 or f/4.

There is a Fuji G 110mm f/2 prime which is autofocus. Its image quality is sublime.

I don't really get the obsession with fast lenses, shooting wide open suits a fairly limited range of subjects, and generally lens performance is terrible wide open. I have some Zeiss Planar f/1.4 lenses for 35mm, and I basically never shoot wider than f/5.6. Also never really shoot wider than f/8 on medium format Zeiss CF lenses. But I don't shoot stuff that needs fast lenses I suppose.

In broader photographic terms (outside of full-frame / mirrorless), f/4 is fast.

I suspect that people shooting medium format aren't as interested in having awesome bokeh and a super fast lens with a lower number, and instead care about lens performance in general.

There are number of reasons as you can imagine. Those lenses would be enormous (think 10lb lens + camera). It is very difficult to manufacture large lenses (with high quality), requiring a complete change in the tooling. It would also be labor intensive and thus only a very limited quantity can be made. At f/1.8, the lens price would probably be you just directly paying the technicians salary plus overhead.

So you want like the medium format equivalent of a Noctilux, but with autofocus?

I'm surprised something LIKE that doesn't exist, but I'm thinking more of f/1.2 equivalent glass.

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