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10-17-2014, 11:56 AM   #76
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Thanks, ChristianRock. I'll need to go away and sit down for a while and wonder why somebody would use f/22 at 1/125 at ISO1600 on a 645Z when they could employ a tripod and use f/11 at 1/30 at ISO100.

10-17-2014, 12:00 PM   #77
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QuoteOriginally posted by Dartmoor Dave Quote
QuoteOriginally posted by dr clark:
Camera exposure: The relative exposure recorded by a camera. In a digital camera, this is how full a pixel is to a given reference level. Smaller pixels fill with fewer photoelectrons than do larger pixels. As ISO is raised, the reference level is reduced. For example, at ISO 200, the reference level is half the photoelectrons as at ISO 100. Thus, a "properly" exposed digital camera image records half the light at ISO 200 as at ISO 100.
I know I said yesterday that I was going to bow out of this thread. . . but c'mon! You can't get away with that nonsense. Innocent bystanders might get hurt.

A digital camera does NOT record half the light at ISO200 than it does at ISO100. It applies double the gain to the analog signal output from the sensor. The amount of light hitting the sensor is the same, given the same aperture and shutter speed.
I think what Clark is assuming there is that you are changing the shutter speed to account for the change in ISO, and he's calling that the 'proper exposure'.

I agree that he could have been more clear, but I don't think he thinks changing ISO directly changes the photon count Read his explanation of ISO.

Dr Clark:

...But you may say when I change ISO in my camera, I record different amounts of light (in an auto mode). Let's say you are working in aperture priority mode where you choose the aperture and the camera meters the scene and choose the exposure. Let's say you are at f/5.6 and 1/500 second at ISO 100. You change ISO to 200 and the camera changes the shutter speed to 1/1000 second. Thus, the sensor now records half the light. So the ISO change instructed the camera to shorten the exposure time, thus recording less light, and then instructed the camera electronics to amplify the signal from the sensor and digitize a smaller range (see ISO 100 and 200 in Figure 1). That amplification fools photographers that the pixel is full again (the 0 to 255 scale). So what the camera says is max signal (255 on the 8-bit scale) is actually changing with ISO. If sensitivity changed with ISO, the number of photons recorded would change and all the pixels in Figure 1 would be like the ISO 100 pixel: the pixel would be full.


QuoteQuote:
I think I finally understand the notion of "Total Light" now.
Good!

QuoteQuote:
...You guys think that the ISO selected in a digital camera is something to do with exposure, but it isn't.
No, no, no. ISO does not affect exposure or total light directly. It allows a photographer to use less exposure and total light because it adds brightening to the image after capture.

Last edited by jsherman999; 10-17-2014 at 12:07 PM.
10-17-2014, 12:06 PM   #78
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QuoteOriginally posted by jsherman999 Quote
No, no, no. ISO does not affect exposure or total light directly. It allows a photographer to use less exposure and total light because it adds brightening to the image after capture.
Now that sentence would be completely accurate if you just left out the words "Total Light".
10-17-2014, 12:14 PM - 1 Like   #79
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QuoteOriginally posted by ChristianRock Quote
Apparently EJ wants to take the pic at f22. Why, I have no idea. Because he loves equivalence, I guess. And diffraction.
The less you think about this doggy doo doo, the happier you'll be.
To a man standing in front of a beautiful scene with a camera, it's worth less doo doo.

10-17-2014, 12:27 PM   #80
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QuoteOriginally posted by Dartmoor Dave Quote
Now that sentence would be completely accurate if you just left out the words "Total Light".
Why?

Total light is (in part) derived from exposure. If you use less exposure, you use less total light.
10-17-2014, 12:27 PM   #81
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QuoteOriginally posted by normhead Quote
The less you think about this doggy doo doo, the happier you'll be. To a man standing in front of a beautiful scene with a camera, it's worth less doo doo.
+1 to that! Good to hear a voice of sanity. I'm outta here!
10-17-2014, 12:35 PM   #82
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Going out in the field with a 645Z to take Q shots

QuoteOriginally posted by clackers Quote
You and I are shoulder to shoulder.

You've got a 645Z, I've got a tiny, tiny Q.

I meter at 1/125s, ASA200, f8.

You set to 1/125s, ASA200.

Now, what should your aperture be?
Physical aperture, or f-stop?

If you want to try to use that 645z to 'match' the tiny Q in exposure, you just shoot with those same parameters - 1/125s f/8. Of course that would give you radically different images in terms of DOF, and if you were shooting low-light you'd really see the difference in noise. DR would be extremely different as well. (You'd do the same thing between the 645Z and your phone.)

If you wanted to match the little Q in Total LIght, you'd need to stop down the 645Z some gawd-awful amount and raise ISO to alow the shutter speed to be maintained. Then you might get close to the Q's tiny amount of Total light (and get images very close in IQ.)

Now - say you didn't want to match the Q's output, you wanted to match the 645Z's - what f-stop would you need to shoot on that Q to get the same total light?

.
10-17-2014, 12:38 PM   #83
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This is all pretty weird. People use terms like "exposure" loosely, meaning something far different from what I mean. Proper exposure is obtainable on any format, regardless of size, although to hear people talk about it in this thread, it is virtually impossible on small sensored cameras, because there just isn't enough "total light." That's just crazy. Obviously when you push iso up and shoot in low light, smaller sensor cameras will struggle, but in general, you have as little trouble getting proper exposure with a Q as with a D600. End of story. Total light is irrelevant.

10-17-2014, 12:47 PM   #84
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QuoteOriginally posted by normhead Quote
The less you think about this doggy doo doo, the happier you'll be.
To a man standing in front of a beautiful scene with a camera, it's worth less doo doo.
You can stand in front of a beautiful scene with a camera and still appreciate what's going on underneath it all. Science & understanding is not doo-doo, it's a wonderful, interesting, sometimes-practically-useful thing.


Taken 2 days ago with iphone. Didn't worry about Total Light, just... light

.

---------- Post added 10-17-14 at 01:53 PM ----------

QuoteOriginally posted by Rondec Quote
... but in general, you have as little trouble getting proper exposure with a Q as with a D600.
Yes!

QuoteQuote:
End of story. Total light is irrelevant.
No, no, no, no, no.

Sigh. Two steps forward, two steps back. I'm in a Sartre play.
10-17-2014, 01:44 PM   #85
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QuoteOriginally posted by ChristianRock Quote
Apparently EJ wants to take the pic at f22. Why, I have no idea.
I didn't define the picture that someone else wanted to take.

QuoteOriginally posted by ChristianRock Quote
And diffraction.
Diffraction has the same influence at equivalent shots. The person who defined the picture defined it as a very-diffraction-limited picture.
10-17-2014, 01:48 PM   #86
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Total light is not irrelevant (both total light gathered and total light projected - in another thread I was grilled because people meant one type and I was talking about the other).
Equivalence is not irrelevant.

They're just not all that they're cracked to be. They're references, and once you know them, just don't think about them and go and take pictures. You know what your DOF is and you know how far you want to push your ISO levels, so you just work within your parameters and you forget about equivalence completely because when you're out shooting pictures you're not supposed to be thinking what these would look like with a different system. If you're out shopping for a new system, or if you think what system you have can be used for what purpose, sure, think about equivalence and what DOF/exposure latitude you want, then once you have a system and a purpose for it, just go out and use it.

Some people turn it into a "my format is better than your format" argument, like "my car has a V8 engine, yours is just a V6, pfffffffft". Whatever. My car gets me comfortably to work and does what it needs to do, thank you very much.

---------- Post added 10-17-14 at 04:53 PM ----------

QuoteOriginally posted by ElJamoquio Quote
I didn't define the picture that someone else wanted to take.
No, but you defined how you would do it with your equipment. You basically decided to do the equivalent of the other person, instead of using the same exposure, which is what a real photographer in a real situation would probably do.

QuoteQuote:
Diffraction has the same influence at equivalent shots. The person who defined the picture defined it as a very-diffraction-limited picture.
So you're saying that the sensor size defines the diffraction level of the lens? That's the first time I've heard that.

Anyway, diffraction levels at f22 vary from lens to lens, use of LD, APO or ED glass, optical formula, etc etc etc. And you'll see there's no equivalence for those things. You won't see an APS-C lens with twice the amount of elements for APS-C to compensate for equivalence to 135mm...

Last edited by ChristianRock; 10-17-2014 at 01:53 PM.
10-17-2014, 02:04 PM   #87
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QuoteOriginally posted by ChristianRock Quote
No, but you defined how you would do it with your equipment. You basically decided to do the equivalent of the other person, instead of using the same exposure, which is what a real photographer in a real situation would probably do.
I listed 'same picture required' as a major and likely invalid assumption.

QuoteOriginally posted by ChristianRock Quote
So you're saying that the sensor size defines the diffraction level of the lens?
I'm saying that sensor size is roughly irrelevant, all else the same, and the impact on sharpness of a lens from diffraction tracks with DOF rather than aperture divided by focal length.

So diffraction tracks with equivalence.
10-17-2014, 08:12 PM - 1 Like   #88
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I trust any new Pentax full-frame will have a setting to adjust for 'Equivalence' on the mode dial, and be able to meter for 'Total Light', as well as Matrix, Centre-weighted and Spot.

Those features are obviously what serious photographers can't live without nowadays.
10-17-2014, 08:56 PM   #89
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QuoteOriginally posted by rawr Quote
I trust any new Pentax full-frame will have a setting to adjust for 'Equivalence' on the mode dial, and be able to meter for 'Total Light', as well as Matrix, Centre-weighted and Spot.

Those features are obviously what serious photographers can't live without nowadays.
I'm pretty sure many of Pentax cameras have features like this already.
FI If using "Landscape" mode on K-S1 or Q-S1 they will most likely give different exposure settings for the same scene.
And the camera will use "equivalent focal length" when setting shutter speed for avoiding camera shake in images.

Last edited by Fogel70; 10-17-2014 at 09:09 PM.
10-17-2014, 08:56 PM   #90
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It'll be easier for the uninitiated, that's for sure.
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