[Rondec]

The point of equivalence is that if you take a photo at 200mm f4 and iso 200 on a full frame camera, it will be nearly exactly the same as a photo taken at 135mm f2.8 and iso 100 on an APS-C camera -- assuming same tech in the sensors, say K5 and D800. Clearly this equivalence formula is only workable if you scale the iso between sensor sizes.

The biggest problem I have with equivalence is the way in which people use it -- mostly to prove that full frame is better. The goal of photography is not shooting super high iso or narrow depth of field, although those can be useful for certain images. The goal of photography is to take well exposed images and as far as I can tell, that is pretty much possible regardless of the sensor size used.

[Kunzite]

In practice even then they won't be "nearly exactly" the same unless - like DXOMark - you're ignoring aspects like image detail. That's why I said it's a good match for DXOMark, both being synthetic benchmarks. It's no better than assigning numerical scores.
And IMO in practice you would not try to use two formats to get identical results, but each format to its advantages.

[monochrome]

Or we could just let it go.

[falconeye]

you're ... rude. There is no such thing as a "35mm-equivalent base ISO".

I was rude because I tried to avoid the discussion. And I said so. Obviously I failed.

I won't argue with anybody, have better things to do. But I can give you this much:

The "35mm-equivalent base ISO" (assuming constant sensor tech) is a direct measure of (directly inverse-proportional to) the total amount of light a camera can capture at most before it clips. Call it its inverse light capacity, if you prefer. Equivalent base iso may be less understood than equivalent iso which in turn may be less understood than equivalent focal length. But things one doesn't understand do sometimes still exist ...

I think it is a rather helpful tool to understand camera performance (i.e., how clean images can become) and I invite everybody to familiarize with the concept sooner than later. Thanks and Happy Late XMas

P.S. cameras like the RX100 have 35mm-equivalent base ISO 600. IMHO, this is their weakest point when used in daylight. With better communication, there would be more pressure on vendors to release more capable cameras in a small form factor, including their ability to capture clean images. Therefore, the point I am making here may be less academic than it may appear to some.

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Last edited by falconeye; 12-27-2015 at 05:22 PM.

[blende8]

The "35mm-equivalent base ISO" (assuming constant sensor tech) is a direct measure of (directly inverse-proportional to) the total amount of light a camera can capture at most before it clips.

How do you establish/calculate this?

P.S. cameras like the RX100 have 35mm-equivalent base ISO 600.

And this is bad because ...?

[Zygonyx]

I was rude because I tried to avoid the discussion. And I said so. Obviously I failed.

I won't argue with anybody, have better things to do. But I can give you this much:

The "35mm-equivalent base ISO" (assuming constant sensor tech) is a direct measure of (directly inverse-proportional to) the total amount of light a camera can capture at most before it clips. Call it its inverse light capacity, if you prefer. Equivalent base iso may be less understood than equivalent iso which in turn may be less understood than equivalent focal length. But things one doesn't understand do sometimes still exist ...

I think it is a rather helpful tool to understand camera performance (i.e., how clean images can become) and I invite everybody to familiarize with the concept sooner than later. Thanks and Happy Late XMas

P.S. cameras like the RX100 have 35mm-equivalent base ISO 600. IMHO, this is their weakest point when used in daylight. With better communication, there would be more pressure on vendors to release more capable cameras in a small form factor, including their ability to capture clean images. Therefore, the point I am making here may be less academic than it may appear to some.

Just to make things clearer, do you apply the same coefficient as for "crop factor" in your reasonning ? If so, can you precise the ISO you are taking as "base" for 35mm ?

[Nicolas06]

I do not think that one does buy a 645Z because it has better high iso. Or even because it has more MP. This could be good reaons but looking at prices, you'd get almost the same with an FF.

To me you get an MF because overall it give better pictures. We may have difficulties to define better and it may not be more dynamic range, better high iso, more color deph. A 645D still get better picture despite being older and people would should old film camera with even larger format for the results they get.

To me, it simply look better and this might be more linked to the size of the sensitive area and maybe lenses than metrics of the sensor.

This of course is difficult to measure so we measure other things and having good results here help drive sales despite not being that important anyway. Well at least it make the camera more capable.

[Nicolas06]

How do you establish/calculate this?



And this is bad because ...?

Basically what he is saying is that at iso 100 on a RX100 you get the same quality rougly as iso 600 on an FF (and 300 on APSC) So you get more dynamic range, more color deph with the bigger sensor. And even with a tripod an RX100 will not match the quality that you can get out of an FF handled because you have much more latitude with the FF than the 1" sensor.

If at least the RX100 had some low isos settings like 12, 25 and 50 isos, you would get that quality back when there enough light. Because you would be likely to shoot at f/4 or f/5.6 instead of f/8 f/11 anyway due to diffraction and added deph of field on the RX100, there would be many occasions were even handled you could do just that. But this is not possible so you miss that possibility. At best you use a tripod, shoot a few frames and merge them to get some quality back.

[blende8]

Thanks Nicolas.

But is it that simple?
Is it just a matter of sensor area?
Not also of sensor quality/technology?

[Rondec]

Thanks Nicolas.

But is it that simple?
Is it just a matter of sensor area?
Not also of sensor quality/technology?

All of these formulas assume the same level of technology. If you start comparing a Canon sensor to a Sony sensor, things fall apart to a certain extent with regard to the formula, because a 6D doesn't have the same performance at iso 200 that a K3 has at 100.

[Simen1]

I also have a specialist degree that utilizes a lot of math and physics, but my education doesnt make me more right then others. The math we are talking about here are on the level that 12-14 year old kids learns.

I just disagree in using equivalent ISO in comparisons. When some sensors have larger well depth then others then it just means they have larger pixels. Max charge per unit area is usually not that different between sensors. Less photon noise means larger sensor, holding all other factors the same. When medium format gives a different visual feeling its can be partly because of higher DR, but in the case of 645Z its almost the same as many other cameras.

[Rondec]

My feeling is that people shoot medium format because (1) they print bigger (2) they like the glass that is available for it and (3) they have found the image files to allow for more processing without looking over processed. I don't know how close the D810 is to the 645Z in real world shooting, but my guess is that for landscapes and studio shots, it is still a little distant.

[Nicolas06]

Thanks Nicolas.

But is it that simple?
Is it just a matter of sensor area?
Not also of sensor quality/technology?

Sure ! This would be sensors with similar technology. Say Sony BSI 1" vs Sony FF BSI for example. Now because say D810 has iso 64 mode and even more dynamic range, the gap would not close but even widden.

This is just that it get you rough ideas of what to expect. Basically a K30 + 16-45 is going to cost no more and to perform as well as a RX100 for picture quality rougly. I don't say exactly but quite similar. But everybody will praise an RX100 and will criticize the K30 + 16-45.

Of course the key will be the K30 would accept many more lenses if needed and get better ergonomics but would be much bigger to get arround. That's the interrest of theses equivalences things to quickly get a rough idea of what to expect from a given device.

[blende8]

All of these formulas assume the same level of technology.

Ok,
lets say we have the 36 MP Sony FF sensor.
We cut out the middle of it to get an APS-C sized one.
Now we shoot the same scene.
Since on the APS-C sensor more light hits a single pixel, it has a higher equivalent base ISO?

[Nicolas06]

I also have a specialist degree that utilizes a lot of math and physics, but my education doesnt make me more right then others. The math we are talking about here are on the level that 12-14 year old kids learns.

I just disagree in using equivalent ISO in comparisons. When some sensors have larger well depth then others then it just means they have larger pixels. Max charge per unit area is usually not that different between sensors. Less photon noise means larger sensor, holding all other factors the same. When medium format gives a different visual feeling its can be partly because of higher DR, but in the case of 645Z its almost the same as many other cameras.

- Max charge is different on different sensors that's for sure.
- if you have more pixels, you can average them together this decrease noise and give you better results. This isn't going to work that well for dynamic range but it will work fully for color deph and high iso performance.
- the look of a MF camera come much more because you use different lenses to get the same picture than from the dynamic range or high iso. This is just that to get the same framing you'll use a 24mm on an APSC, a 36mm on an FF and a 47mm on a 645Z. The focus transitions will be different