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When someone wants to compliment a 35mm sensor, he can say that it's [almost] as good as medium format. Medium format appears to be the gold standard where image quality is concerned.

But. I'm usually working with natural light using my lenses wide open, and the widest lenses that I've seen for Hasselblad or Leica S2 are f/2.8, which I consider very dark. Also, when I watch clips on youtube concerning medium format, people usually use those lenses with artificial lighting, which also confirms my impression that medium format cameras aren't as light sensitive as DLSR systems.

So my question is - let's say I'm working with 1D X and 85mm f1.2. Is there anything in medium format sector, that can beat that combination when working in low light conditions?

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F1.4 in a medium format would leave such a narrow DOF that you'd have to stop it down anyway, unless you want a person portrait to look like a macro ant photo. –  Michael Nielsen Feb 14 at 9:09
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Your impression is correct, medium format digital is geared toward the studio, high ISO performance is terrible, nothing in MF can get anywhere close to the performance of a 1DX and 85 f/1.2 in low light. –  Matt Grum Feb 14 at 10:22

4 Answers 4

up vote 5 down vote accepted

Theoretically if you keep the size of the entrance pupil and field of view the same then you will capture the same total amount of light regardless of the format.

If your medium format sensor in 1.6 times larger (which is the upper end available today, the Leica S2 you mention is only 1.25 times larger), then to match your 35mm DSLR and 85mm f/1.2 lens would require a 135mm f/1.9 medium format lens.

f/1.9 lenses are rare in medium format (mainly for weight reasons), the only current(ish) lens I know of is the Mamiya 80 f/1.9 - this lens can compete (in terms of total light gathered) with a 50 f/1.2 on a DSLR.

However even though the 80 f/1.9 lens transmits same total amount of light as a 50mm f/1.2 that doesn't mean the medium format system with this lens is as good in low light - this is due to the sensor being less efficient.

Medium format digital backs are most commonly used in landscape, architectural or studio photography where a certain amount of light is guaranteed by the use of a tripod or large artificial light sources. The sensors are optimised for size, producing accurate colours and fine tonal graduations as opposed to offering high sensitivity.

For this reason nothing commercially available today can match the low light performance of a 35mm DSLR.

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Things you need to consider is the change in DOF and FOV, just like when you convert crop frames to full frames. Lenses are built for a certain image circle and the performance of the optics is stressed more by having to project the rays into a smaller size. Medium sensors are large and makes easier to capture small details, and they collect more photons, which gives less noise. Note that it is not always true that the pixels are larger. Because the resolution is larger , too. So canon 5dmk3 and 6d has larger pixels. but remember when comparing cameras you need to normalize to the "same photo viewed at the same size", which means convert your lenses for FOV, aperture for DOF, and downsize to the same size.

Why is high ISO performance then falling behind, with better conditions? The market for medium frame is very small compared to apsc and fullframe DSLRs. This means it is far between a new model comes out with improved low light performance. Ad the customer base are not typically needing low light performance. However, this year a CMOS medium frame comes out where they addressed low light performance and battery usage, so it is more up to date like DLSR, who all made the switch around 7 years ago.

http://www.pdnonline.com/gear/Phase-One-Unveils-Fi-10189.shtml

Also note that in tests like this: http://www.luminous-landscape.com/reviews/cameras/2010_mini_medium_format_shoot_out.shtml

they show 100% crops, and you are not supposed to look at 100%. Especially medium frame is very high resolution and thus ends up with viewing size around 12.5%-25% on the mediums commonly used for DSLR photos (posters excluded). Noise suppressed very neatly in downscaling.

In that test they also test Canon 1dmk3 and found it wanting.

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Keep in mind that the sensor is much larger and thus much more light comes through for a given aperture due to the larger entrance pupil needed to produce an image circle that covers the sensor. All the low light advantages that a full frame sensor has over a crop sensor are much further compounded by the growth to a much larger sensor. Each pixel covers a much larger surface area and can accumulate far more light than the much smaller 35mm sensor can. Thus, you don't need as fast of apertures for light performance.

This is also why lenses designed for APS-c cameras can be so much cheaper and why point and shoot cameras can have very fast apertures and very long zooms while it would cost far more on a 35mm to do the same thing.

That said, note that in actuality, most current medium format sensors do not have as good of low light sensitivity as the smaller DSLRs for other technical reasons. Even though they have more surface area to pick up light, the sensitivity of that surface area is significantly less sensitive than a good 35mm sensor. That could change in the future though as newer medium format sensors come on the market.

You also don't need the same aperture for bokeh either since the image circle is so much larger and that makes lenses appear wider than they would on a 35mm. Since you can use a longer focal length from closer up, you get compensation for the amount of depth of field you get despite the smaller aperture.

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Whilst true in theory, today's digital medium format cameras/backs are designed for different conditions than 35mm DSLRs and often have dramatically worse sensitivity than 35mm sensors (though this may change soon with new CMOS sensors from Sony). –  Matt Grum Feb 14 at 10:08
    
Good to know. Up voted your answer already but I'll also update mine to clarify that. –  AJ Henderson Feb 14 at 13:33
    
The Phase One IQ250, at least, produces very clean images at ISO 6400. There's no reason to believe that the Hasselblad 50C back or the upcoming CMOS Pentax 645 would fare much worse. (Even if one assumes that Phase One is doing "magic" NR with their back, ISO 3200 should still be okay in the others. And Pentax has been pretty darned good at NR so far.) –  user2719 Feb 14 at 21:02
    
@StanRogers it's not just the ISO. If all things were equal, I'd shoot at lowest iso available, with the lens open as wide as possible. The stuff that I read basically says that medium format lenses do let more light through, but that that light has to be distributed around a large sensor, so in terms of light transmition, f/2 on medium format equals f/2 on 35mm sensor. My question is: let's say we are taking pictures with 100mm f/2 with 35mm sensor vs medium format. Will the two require the same exposure times to get the same picture if everything else is the same? –  Arsen Zahray Feb 15 at 13:12
    
Assuming the same iso, yes the same exposure is required, however that is because iso is a calibrated sensitivity to make it so. In real terms of sensitivity only two things matter, the level of noise the sensor produces and the surface area of the sensor (ie how much light actually hits it) because the light is randomly distributed you can use it either to increase low light performance (by keeping the number of photons that registered above the noise) or to increase resolution (by making smaller sites that only get sufficient light due to the size.) –  AJ Henderson Feb 15 at 16:28

Sorry but some of your information in the other answer is plainly wrong. Sensor size has no impact whatsoever on the amount of light coming into the camera. The pixels may be bigger on a larger sensor but it doesn't enable them to gather more light, that's impossible. If I used a hand held lightmeter and it gave a reading of 1/125th & f2.8 at ISO 400,then that exposure would be exactly the same on a dslr, medium format, large format or even a compact camera. To answer the original question medium format cameras are excellent in controlled environments i.e tripod, lighting, careful focusing. DSLRs are still better in low light high action environments.

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what do you think ISO is? –  Michael Nielsen Feb 14 at 9:10
    
The resulting photo would be exposed the same, so you are correct there. But what happens inside the camera, on the sensor, is that larger photosites gather more light. –  Esa Paulasto Feb 14 at 10:00
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-1 "If I used a hand held lightmeter and it gave a reading of 1/125th & f2.8 at ISO 400,then that exposure would be exactly the same on a dslr, medium format, large format or even a compact camera" Exposure is light per unit area, increase the area (by making the sensor larger) for the same exposure and you increase the total amount of light captured. –  Matt Grum Feb 14 at 10:11
    
Too expand on what Matt Grum is saying, you are confusing light sensitivity with a standard way of grading it. Traditionally, the size of each pixel on a medium format piece of film was the same size as that on a 35mm piece of film, thus, the same amount of light was needed for a given surface area at a given ISO. The medium format had larger surface area but also had larger number of "pixels" (pigments in the film). More light is still entering the camera, but more light was required to generate an exposure. –  AJ Henderson Feb 14 at 14:02
    
On digital, that changes, the photosites can be larger on a larger sensor for a similar resolution, sure they also up the resolution of a medium format, but the size of each pixel is still larger. This allows them to collect more light since the same amount of light hits per area for a given aperture and focal length. All other things being equal, 10 photons hitting a sensor instead of 5 is easier to read. The ISO of the camera is then set accordingly so that meter values still read out properly, but you would be able to go to a higher ISO before noise is a problem. –  AJ Henderson Feb 14 at 14:04

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