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03-06-2014, 07:00 PM   #61
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Another myth on sensor area. Bigger sensor does not mean more light because a sensor is useless without a lens in front of it LOL! With a lens in front you now have a f-stop to consider. A f-stop is a f-stop no matter which format. Sorry but that's a very common myth that is spread in forums.

03-06-2014, 09:21 PM   #62
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F-ratio vs. entrance pupil

QuoteOriginally posted by dtmateojr Quote
Another myth on sensor area. Bigger sensor does not mean more light because a sensor is useless without a lens in front of it LOL! With a lens in front you now have a f-stop to consider. A f-stop is a f-stop no matter which format. Sorry but that's a very common myth that is spread in forums.
Oh, my.

OK, some quick basics. First, terms: There's the linear aperture, sometimes called the virtual aperture, and that's the entrance pupil diameter. Then there's F-stop (or F-ratio), which is what we know as f/2, f/4, etc, and it can also be called the relative aperture, and it's the quotient of the focal length and the virtual aperture.

Now, we know that, for example, if you shot say 70mm at f/2.8 of a FF sensor, because of the 1.5x crop, to get the same FOV with an aps-c sensor and the same shutter speed, you would need about 46mm @ f/2.8. So:
70mm f/2.8 FF == 46MM f/2.8 aps-c (To keep shutter speed and FOV the same.)
(Let's just assume for the sake of this comparison that the sensor tech between them is same-gen, like the K5 & D800.)

Now, are the images produced by each combo above (70m f/2.8 FF & 46MM f/2.8 aps-c) exactly the same? No, the FOV and shutter speed will be the same, but the noise will not - the FF image will have about a stop advantage. (the FF shot will have about 1.3 stops less DOF, too, something equivalence tells us and you can confirm with any DOF calculator.)

Now, why exactly does the FF image show less noise, if the sensor tech (the pixel tech) and the F-stop are the same? Because although the F-stop/relative-aperture stayed the same (f/2.8,) the virtual aperture did not.

Remember, the F-ratio is just the quotient of the focal length and virtual aperture. In other words, the linear aperture is = FL / F-stop.

So, we have:
FF: 70mm / 2.8 == 25mm linear aperture (entrance pupil)
aps-c: 46mm / 2.8 == 16mm linear aperture
See that? For the same FOV and F-stop and shutter speed, we actually have a wider pupil, a larger linear aperture with FF, bringing more light onto the sensor - resulting in less noise (and less DOF.) Or, as Joseph james puts it: "..The same relative aperture (f-ratio) will result in the same density of light falling on the sensor (exposure) for a given scene luminance and shutter speed for all systems, whereas the same virtual aperture (entrance pupil) will result in the same total amount of light falling on the sensor for a given shutter speed (as well as same DOF for a given perspective, framing, and display size)."

Now, if you're paying attention you see that this also means that if we do not want less DOF with the FF shot - if we want to match both the FOV and DOF of the aps-c shot (hey, it happens... maybe ) then you would stop down the FF combo, giving you:
FF: 70mm / 4.375 == 16mm linear aperture (entrance pupil)
aps-c 46mm / 2.8 == 16mm
And we would have equivalent images - same FOV, DOF, shutter speed, and noise, assuming you boost ISO a stop with the FF combo to match shutter speed. (although not equivalent sharpness there, probably.)

So, to say 'an f-stop is an f-stop on any format' is wrong in exactly the same way it's wrong to say 'a focal length is a focal length on any format'. Or another way to put it - it's right as long as you're willing to compare completely different images

.

Last edited by jsherman999; 03-06-2014 at 09:44 PM.
03-06-2014, 09:51 PM   #63
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LOL! Because you are assuming that light does not diminish as the square of the distance (e.g. focal length). A f-stop is a f-stop mate. ROFL! It's the same. OMG! Can't believe I have to explain that to you.
03-06-2014, 10:01 PM   #64
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QuoteOriginally posted by dtmateojr Quote
LOL! Because you are assuming that light does not diminish as the square of the distance (e.g. focal length). A f-stop is a f-stop mate. ROFL! It's the same. OMG! Can't believe I have to explain that to you.
Oh, my, again. Did you understand what I wrote above with regard to linear aperture vs. relative aperture? Did you understand the equivalence reference? Because 'an f-stop is an f-stop on any format' is about as relevant as saying 'focal length is focal length on any format.'

I'm actually curious about what specifically you disagree with, I cant really tell from your response.

Here, before you answer - an external source that fleshes out and expands on what I just said. Do you disagree with that?

.

03-06-2014, 10:23 PM   #65
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I'll read that lengthy post later but I don't think that will change anything

Let me simplify (again) for you. The simplest "lens" is a pinhole. Do you think that a pinhole in a full frame is brighter than a pinhole in aps-c? Think really hard about it. Really hard lol!
03-06-2014, 10:40 PM   #66
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QuoteOriginally posted by dtmateojr Quote
I'll read that lengthy post later but I don't think that will change anything

Let me simplify (again) for you. The simplest "lens" is a pinhole. Do you think that a pinhole in a full frame is brighter than a pinhole in aps-c? Think really hard about it. Really hard lol!
Can you explain why that's relevant to your earlier point, and how it's specifically relevant to the point I made regarding relative vs. virtual aperture?

Listen, I really want you to read the links I provide, don't blow them off. In this and the other threads I made the effort to explain things, and then provide links that back up what I'm saying, and I feel like you don't bother really reading what I'm saying *or* reading the links, judging by your responses - I feel like I could be arguing with someone who's really, actually, just trolling.

Part of the reason I provide links is because it's sometimes hard to just accept what some random person you don't know says in a forum like this. Understood. Read the links. Joseph James, Bob Newman (bobn2), Sheehey, the DxOMark link - these are PhDs, and they either work or have worked in the imaging or optics industry. Accept their word if you don't trust mine.


.
03-06-2014, 10:52 PM   #67
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Why is it relevant? Because we now move to step 2 of this oversimplification. If the pinhole is too near the sensor it wont illuminate the whole sensor. So what do you do? You move it farther away from the sensor. The bigger the sensor the farther the pinhole. Absorb that for a moment and maybe we wont need step 3

---------- Post added 03-06-14 at 11:06 PM ----------

I'm going ahead of myself here but here's the spoiler: a full frame actually gets lesser light vs smaller sensors. This is very visible in the form of vignettes where a full frame lens in a full frame sensor loses up to 2 stops of light near the corners. The same lens on an aps-c will chug along quite happily.
03-06-2014, 11:08 PM   #68
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QuoteOriginally posted by dtmateojr Quote
Why is it relevant? Because we now move to step 2 of this oversimplification. If the pinhole is too near the sensor it wont illuminate the whole sensor. So what do you do? You move it farther away from the sensor. The bigger the sensor the farther the pinhole. Absorb that for a moment and maybe we wont need step 3
I'm not able to see how you even read my post, or the link, based on this ^^. But I have hope that you're coming to a salient point! For the sake of brevity, and to prove you're not just in it for the troll, why don't you lay out all your steps and we'll see what we've got. Falk Lumo once used a very neat pinhole cam example to show how lens cost can decrease as sensor size increases, so yours may be a thought experiment that might hold interest if not relevance here

EDIT: you answered:

QuoteQuote:
I'm going ahead of myself here but here's the spoiler: a full frame actually gets lesser light vs smaller sensors. This is very visible in the form of vignettes where a full frame lens in a full frame sensor loses up to 2 stops of light near the corners. The same lens on an aps-c will chug along quite happily.
That has *nothing* to do with what I wrote, is not relevant to the point I was making, and is in fact only true if you have a lens that does not fully cover the image circle... ?!? Why on earth are you talking about shooting a sub-par or aps-c lens on FF here and using that as an example for anything? I also don't even see how it relates to *your* original point.

.


Last edited by jsherman999; 03-06-2014 at 11:27 PM.
03-06-2014, 11:16 PM   #69
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Ok let's assume you understood all points above. Moving the pinhole away from the sensor reduces light intensity. Since a bigger sensor needs the pinhole farther away it follows that the sensor is receiving less light. How do you compensate? Make the pinhole bigger. The distance of the pinhole to your sensor is your focal length. The size of the pinhole is your aperture. The ratio is your f-stop. And that is why you are believing in a myth.
03-06-2014, 11:36 PM   #70
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QuoteOriginally posted by dtmateojr Quote
Ok let's assume you understood all points above. Moving the pinhole away from the sensor reduces light intensity. Since a bigger sensor needs the pinhole farther away it follows that the sensor is receiving less light. How do you compensate? Make the pinhole bigger. The distance of the pinhole to your sensor is your focal length. The size of the pinhole is your aperture. The ratio is your f-stop. And that is why you are believing in a myth.
Ah, so your pinhole isn't really a pinhole anymore, it's morphed into an actual diaphragmed linear aperture that can vary. Is it possible you're about to agree completely with what I just wrote here?

But it might be quicker for you to flesh out exactly what the 'myth' is that I believe, because again, it's not clear from what you write. (Although more & more I'm starting to think that you just didn't really read what I wrote, and I wish you would take the time to do that.)

.
03-06-2014, 11:38 PM   #71
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If you do not resize the pinhole then the bigger sensor will obviously receive less light. And yes, pinhole sizes do vary :-p

---------- Post added 03-06-14 at 11:40 PM ----------

Explain why a D3 is a full stop better than K3. Better in what?
03-06-2014, 11:57 PM   #72
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QuoteOriginally posted by dtmateojr Quote

[/COLOR] Explain why a D3 is a full stop better than K3. Better in what?
I'll challenge myself to be succinct without leaving important things out or oversimplifying terms: Better in noise performance, because low light noise is determined by the amount of light hitting the sensor. The amount of light hitting the sensor is determined by the linear aperture (pupil) diameter. It's the larger sensor that enables the larger entrance pupil diameter because of the longer focal lengths required for the larger sensor to have the same field of view at the same f-stop (linear aperture diameter = focal length / f-stop).

But you know this, because I already laid it out here, and Dr James laid it out here.

Looking forward to continuing this in the morning CST, night!

.

Last edited by jsherman999; 03-07-2014 at 12:06 AM.
03-07-2014, 12:06 AM   #73
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QuoteOriginally posted by jsherman999 Quote
I'll challenge myself to be succinct without leaving important things out: Better in noise performance, because low light noise is determined by the amount of light hitting the sensor. The amount of light hitting the sensor is determined by the linear aperture (pupil) diameter. It's the larger sensor that enables the larger entrance pupil diameter because of the longer focal lengths required for the larger sensor to have the same field of view at the same f-stop (linear aperture diameter = focal length / f-stop).

But you know this, because I already laid it out here, and Dr James laid it out here.

Looking forward to continuing this in the morning CST, night!

.

Clearly you did not understand my very elementary explanation. I will stop here. It's futile explaining to you. Carry on with your beliefs. I would rather trust my degree in physics and optics.
03-07-2014, 12:18 AM   #74
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QuoteOriginally posted by dtmateojr Quote
Clearly you did not understand my very elementary explanation. I will stop here. It's futile explaining to you. Carry on with your beliefs. I would rather trust my degree in physics and optics.
You received your degree between the 23rd of February and now? vv

QuoteOriginally posted by dtmateojr Quote
I'm a physics major.... I major in optics and dsp. .
03-07-2014, 12:24 AM   #75
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Finally managed to read that link you posted. I stopped at this:

The concepts of, and connections between, total light, DOF, and noise, are much more easily understood in terms of aperture rather than f-ratio, especially when comparing different formats. While the same f-ratio will result in the same exposure (where exposure is the density of light that falls on the sensor -- photons / mm˛), regardless of the format, the aperture diameter, together with the shutter speed, determines the total amount of light that falls on the sensor, where the same total amount of light falling on the sensor results in the same noise in the photo, for equally efficient sensors. In addition, for a given perspective, framing, display size, viewing distance, and visual acuity, the same aperture diameter will result in the same DOF.

Clearly, that does not take into consideration the intensity of light which is affected by distance. It is very easy to see the big flaw in that explanation. If you consider only the total amount of light as the variable that affects noise then I would have to ROFL. Do you do flash photography? Do you know what a guide number is?

---------- Post added 03-07-14 at 12:25 AM ----------

QuoteOriginally posted by jsherman999 Quote
You received your degree between the 23rd of February and now? vv

Is that an insult?

---------- Post added 03-07-14 at 12:29 AM ----------

Sorry but I do think you are trying to insult me. From now on you are in my ignore list. I feel like talking to a coconut here.
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