[audiobomber]

Note that DxOMark uses a 10 log ratio, i.e., a doubling of the signal corresponds to +3dB, not +6dB. Shifting left three times would hence correspond to +9dB, not +18dB.

True, I never thought of that.

[starbase218]

What if we agree that anyone can use a theory if it suits his or her personal needs, without presuming that that theory is "the truth" (even though it might be), and trying to persuade others to agree to it.

I may have made the same mistake myself actually, in this thread: https://www.pentaxforums.com/forums/136-pentax-q/299146-how-would-you-sell-someone-pentax-q.html. But if so, I am trying to learn from it.

[audiobomber]

What if we agree that anyone can use a theory if it suits his or her personal needs, without presuming that that theory is "the truth" (even though it might be), and trying to persuade others to agree to it.

I don't think that's the right answer. If all beliefs are equal, there is no truth, and no one learns anything. Photography is not religion, it's science. There is a correct answer.

[wombat2go]

Note that DxOMark uses a 10 log ratio, i.e., a doubling of the signal corresponds to +3dB, not +6dB. Shifting left three times would hence correspond to +9dB, not +18dB.

I think in the engineering, SNR has to be 20 log (S/N)
Noise has many contributors and they have to be added as noise equivalent powers , or else they have to be added in quadrature if they are treated as voltages, for example voltages read from a sensor, or voltage levels that have been digitised through the ADC.

I looked at some simple photodiode specs and the junction noise is quoted as NEP in units of [Watt/sqrt(HZ]
for example: http://www.vishay.com/docs/81521/bpw34.pdf

Considering a stand alone ADC, its quantization noise is 20 log ( 2^N * sqrt(12) )
I think wiki has it right: https://en.wikipedia.org/wiki/Quantization_%28signal_processing%29

So I think it is incorrect to state signal-to-noise as 10 log (Brightness ratio) in a photographic image.

[starbase218]

I don't think that's the right answer. If all beliefs are equal, there is no truth, and no one learns anything. Photography is not religion, it's science. There is a correct answer.

That's not exactly what I'm saying.

[Pål Jensen]

Yes, and they all get images with a different DOF and different level of image noise as a result.

Or are you telling me that m43 shooter and the m43 shooter are getting the same DOF when using the same exposure parameters?

Are you telling me that I can print as nice an image from the m43 camera as I can from the medium format camera?

1) yes
2) No. But are there any particular reason why they should? Lenses for different formats are never truly DOF equivalent as DOF is dependent on focal length, aperture, focus distance and subject magnification.
3) No. And that's why some use MF cameras. They don't use them in order to be "equivalent" to a smaller format.

And this is the point of various formats. Equalize, to the extent it is possible at all, a cellphone with a 645 (to make the principle extreme) makes only sense for those who doesn't grasp what this is about.

[starbase218]

2) No. But are there any particular reason why they should? Lenses for different formats are never truly DOF equivalent as DOF is dependent on focal length, aperture, focus distance and subject magnification.

Firstly, I get the impression that you don't care much for the creative possibilities you get with a shallower DoF. You seem to think that the purpose of a large aperture is only to get acceptable shutter speeds in low light, while not saturating the image with noise due to having to increase the ISO. Am I right?

Secondly, what is subject magnification in this regard, and why does it affect DoF? I thought subject magnification itself is only dependent on focal length and focus distance?

The reason I am interested in the DoF capabilities that a system (body + lens) can offer me is that I want to use shallow DoF in my photos, to e.g. emphasize my subject. For example, I think micro4/3 is a great system: relatively small and lightweight, lots of choice in bodies and lenses. But I also think that if I go that route, I wouldn't be able to apply the same shallow DoF to my photos, unless I get closer to my subject. But then it's not the same photo anymore in the first place.

Also, of course they don't use bigger sensor systems to be equivalent to smaller sensor systems. That would be a waste of investing in a bigger sensor system. Who says the goal of equivalence is to create equivalent photos? It's not, at least not to me. I think the goal of equivalence is to find out at which settings two different systems can shoot the same photos. Because if you know that, you also know what extra capabilities the bigger sensor system has. So you can choose a system to fit your needs, and then stop thinking about equivalence and just get accustomed to the system. E.g. what does 10mm mean, and can I get a sharp image handheld at 1/20 at that focal length? What does f/2.8 mean? What does ISO 400 mean? Etc.

So yeah, who says the goal of equivalence is to create equivalent photos? I guess that's what it comes down to.

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Last edited by starbase218; 07-25-2015 at 01:45 AM.

[Class A]

So yeah, who says the goal of equivalence is to create equivalent photos?

Nobody says that.

But it makes a great straw man argument.

[Rondec]

Nobody says that.

But it makes a great straw man argument.

Then why do people show up on the Q forum to tell them how slow their lenses are? The goal of equivalence is to prove that no system is as good, or small, or as fast as a full frame system.

[starbase218]

Then why do people show up on the Q forum to tell them how slow their lenses are? The goal of equivalence is to prove that no system is as good, or small, or as fast as a full frame system.

If you are referring to what I wrote in a certain topic on the Q forum, I only wrote it in response to reh321 saying it's equivalent to a 1400mm lens, without losing any light. I thought that was misleading. I mean, saying it's like a 1400mm lens is already applying equivalence, right? To my mind, if you apply it to focal length, you have to apply it to aperture too, because aperture (well, the f-number anyway) is a formula: f divided by some number. And f is the focal length, and you just said that's like 1400mm. The end result of the formula is the diameter of the actual opening in the lens. That doesn't change. So in order to make the math work, if you say it's like a 1400mm lens, you are also saying it's like an f/26 lens. Although ISO kind of loses its meaning in that respect. That's why I spoke of relative ISO performance. But ok.

You don't HAVE to say it's like a 1400mm lens though. In which case you can just dismiss all of this.

Also, I didn't tell anyone how slow his or her lens was. Telling someone how slow a lens is implies an opinion. I did not state that. It was interpreted as such, but that was not my doing. In fact I was surprised that f/26 seemed to be interpreted as some kind of offensive language or something.

Btw, according to DXOMark, the Q10's indicated ISO actually differs a great deal from the measured ISO (http://www.dxomark.com/Cameras/Pentax/Q10---Measurements). ISO 3200 is really just above ISO 1600. So you have to take that into account as well when comparing noise performance.

edit: so, actually, if the above holds true, ISO 100 / f/2.8 / 1/100 will not get you the same exposure on a Q10 as it does on, say, a K-3. I still like my Q10 though.

[Rondec]

If you are referring to what I wrote in a certain topic on the Q forum, I only wrote it in response to reh321 saying it's equivalent to a 1400mm lens, without losing any light. I thought that was misleading. I mean, saying it's like a 1400mm lens is already applying equivalence, right? To my mind, if you apply it to focal length, you have to apply it to aperture too, because aperture (well, the f-number anyway) is a formula: f divided by some number. And f is the focal length, and you just said that's like 1400mm. The end result of the formula is the diameter of the actual opening in the lens. That doesn't change. So in order to make the math work, if you say it's like a 1400mm lens, you are also saying it's like an f/26 lens. Although ISO kind of loses its meaning in that respect. That's why I spoke of relative ISO performance. But ok.

You don't HAVE to say it's like a 1400mm lens though. In which case you can just dismiss all of this.

Also, I didn't tell anyone how slow his or her lens was. Telling someone how slow a lens is implies an opinion. I did not state that. It was interpreted as such, but that was not my doing. In fact I was surprised that f/26 seemed to be interpreted as some kind of offensive language or something.

Btw, according to DXOMark, the Q10's indicated ISO actually differs a great deal from the measured ISO (Tests and reviews for the camera Pentax Q10 Measurements - DxOMark). ISO 3200 is really just above ISO 1600. So you have to take that into account as well when comparing noise performance.

edit: so, actually, if the above holds true, ISO 100 / f/2.8 / 1/100 will not get you the same exposure on a Q10 as it does on, say, a K-3. I still like my Q10 though.

I wasn't referring to you specifically. I think it is a reaction to people mounting, say a 50mm f1.4 lens on a Q, and then assuming that they have a 280mm f1.4 lens. Well, it is a 50mm f1.4 lens, whatever sensor size it is mounted on and that is most appropriate to say. But when equivalence folks show up, they need to emphasize the fact that the lens is really slow on the Q and often the conversation goes from there to denigrating the whole Q model as not worthy of real photography.

[starbase218]

I wasn't referring to you specifically. I think it is a reaction to people mounting, say a 50mm f1.4 lens on a Q, and then assuming that they have a 280mm f1.4 lens. Well, it is a 50mm f1.4 lens, whatever sensor size it is mounted on and that is most appropriate to say. But when equivalence folks show up, they need to emphasize the fact that the lens is really slow on the Q and often the conversation goes from there to denigrating the whole Q model as not worthy of real photography.

Ah, ok. You're right, it is still a 50mm f/1.4 lens. Nothing can change that. Equivalence is just an attempt of communicating the abilities of a lens on one platform (sensor size), using another platform as a reference. But when you apply it, I think you must apply all of it, including f-stop, etc.

[Rondec]

Ah, ok. You're right, it is still a 50mm f/1.4 lens. Nothing can change that. Equivalence is just an attempt of communicating the abilities of a lens on one platform (sensor size), using another platform as a reference. But when you apply it, I think you must apply all of it, including f-stop, etc.

I suppose. The hard part for me is that like it or not, cameras with smaller sensors do end up with a size advantage on the telephoto end. But folks who are really strong full frame proponents completely discount it completely because the lens apertures are slow with regard to equivalent apertures.

A full frame camera with a 70-200mm f8 lens is going to be quite a bit bigger than a Q with the 06 zoom (never mind the fact that such a lens does not exist). Of course, if you would create a 70-200 f2.8 equivalent lens for the Q, it would be huge, but I don't see any of the Q users clamoring for such a lens.

[Class A]

The hard part for me is that like it or not, cameras with smaller sensors do end up with a size advantage on the telephoto end.

It is not the size of the sensor, though, that provides the "tele boost".

The real reason is the sometimes insanely high pixel-pitch of these sensors. An FF camera would have to have 389MP to match the pixel-pitch and hence "reach" of the original Q.

That tells you, BTW, how taxing the Q is on lenses. Any imperfection of the lens is magnified big time. Even a very decent lens like the FA* 200/2.8 isn't up for that. Not wide open.

You may say you don't care whether it is sensor size or pixel-pitch that provided the "reach" and you'd have a point with respect to real world offerings (many small sensor cameras have very high pixel-pitch).

BTW, I'm happy for anyone who is happy with a Q. I fully understand that compactness and Q-tness are desirable factors. Horses for courses. I never joined a thread uninvited to tell people how slow their lenses are. However, if someone gets their numbers mixed up, I'll point it out. It seems to be the small format people who take offense at "f/26“ rather than me or someone else intending to poop on someone's parade.

[starbase218]

I suppose. The hard part for me is that like it or not, cameras with smaller sensors do end up with a size advantage on the telephoto end. But folks who are really strong full frame proponents completely discount it completely because the lens apertures are slow with regard to equivalent apertures.

A full frame camera with a 70-200mm f8 lens is going to be quite a bit bigger than a Q with the 06 zoom (never mind the fact that such a lens does not exist). Of course, if you would create a 70-200 f2.8 equivalent lens for the Q, it would be huge, but I don't see any of the Q users clamoring for such a lens.

Actually, if you look at Canon's 70-200/4, that's nearly the same weight as the Pentax 50-135/2.8. Size is also not far off, although the Canon is longer. And when the first is used on a fullframe camera, and the second on an APS-C camera, they are more or less "equivalent" to each other, at least in terms of AoV and DoF ranges.