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10-09-2014, 08:48 AM - 2 Likes   #46
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Who is this guy Northrop... or whatever?

It seems to me that he's being paid to "bend" the numbers against aps-c formats (or any other crop format).

But there are things that not even with a million dollars in sponsorship, can change: (Some physics laws!)

1) Lens speed (max aperture) is a mathematical formula given by the focal length divided by the effective max diameter. In real world situations, this max aperture is compensated for glass light transmission and lens to film (sensor) distance, giving a more standarized f/stop effective value.

The area on which the image projected by the lens (full frame, aps, micro 4/3 or whatever) has nothing to do. Lens effective aperture has to do with LIGHT TRANSMISSION, not with picture format.

The reason that you should multiply the f/stop by the magnification in a teleconverter, is because the projected image is ENLARGED (blown, etc) from the lens towards the film (sensor). Its the same principle of having a garden hose with a stream then press a finger on the spout to create a "fanning" effect. The same amount of water is released, BUT LESS WATER FALLS ON A GIVEN AREA AT THE SAME TIME. OTOH, how come we have to consider extension tubes for light loss, even though we are not changing the light path? One simple reason: YOU ARE INCREASING THE DISTANCE, THUS, LOOSING LIGHT THAT FALLS OVER A GIVEN AREA. You also loose light. (Inverse Law of Squares: For any given light, the intensity drops to 1/4th for every distance doubling. In this case, since distance from lens to sensor is increased, then light loss (intensity over a certain area) drops accordingly. http://hyperphysics.phy-astr.gsu.edu/hbase/vision/isql.html

2) Speaking about f/stop and "crap" factor, what matters is NOT the light gathering ability of THE WHOLE SENSOR. Of course, a larger sensor will have a larger light gathering ability, BUT ONLY AS A WHOLE. What matters, is how much light falls into a given area of the sensor, which for measuring purposes, should be equal. Think of it as rain (precipitation) measurements. Worldwide, the measurement of fallen rain is in mm per square meter. One millimeter per square meter equals one liter of water. This is given ALWAYS as how much water falls PER SQUARE METER along a given amount of time.

Read carefully the following to questions (stratements)
Lets compare a football field with your back yard.... under the rain!

1) (Question as Northrop??? states we should get a statistical answer that matters)

How much water rained over the football field and how much water rained over your back yard yesterday?

Obviously, the answer would be something like "The football field gathered about 2 times more water than my backyard", and this answer would be right for certain purposes, but none of them are related to what matters (in photography)

2) (Right question to evaluate the fallen rain over a certain time frame and over a certain area. Statistically valid for our purposes)

How much rain PER SQUARE METER rained over the football field and how much rain PER SQUARE METER fell over your backyard yesterday?

If the football field and your house are close together, there is only one possible answer: IT RAINED THE SAME AMOUNT OF WATER PER SQUARE METER OVER BOTH PLACES.

In shorter words: The only way to honestly compare exposure through a given lens and a certain aperture, is to compare similar situations. As I said before: THE SENSOR SIZE HAS NO PART here. What matters is the effective light transmission of the lens (f/stop) and the time frame during the actual exposure (shutter speed). PERIOD.

3) One last thing: Please, stop saying and arguing that depth of field comes from the sensor (negative) size and lens at a given aperture. Again, the sensor size has nothing to do here. Depth of field is from MAGNIFICATION, within a specific focal length and aperture, but taking into account the sensor/film size to determine the maximum size of the "circles of confusion" that draw the line between whats in focus and what is not. Pretty complicated right? No, just think like this: For a smaller sensor you need a shorter focal length to produce the SAME MAGNIFICATION (over the sensor). Using a shorter focal length produces SMALLER circles of confusion, thus the apparent sharpness gap increases accordingly. That is why the same picture taken with your full frame camera (at 40 mm f4 for example) has a visible and measurable depth of field compared to the same picture shot with your smartphone, who for the same magnification, is probably using a 3 mm focal length and f/4, giving you an almost "infinite" depth of field. Again, the sensor size has nothing to do. IS MAGNIFICATION WHAT MATTERS!


And for Gods sake! If you lived on the East Coast (USA) and moved to the west... when someone asks you "What time is it?, do you answer... "Ehhh... its three o'clock but its really 7 o'clock!" I don't think so. (Only broadcasting companies that show the same programs to the whole country at the same time, state the "east" scheduled time plus one or two other time zones. But that is just because they are doing it at all the time zones AT THE SAME TIME).

So, if you live in California (or Oregon, or Washington state), set your watch for western time zone and forget about the east. Just switch back any time to take a trip back to the east coast.


Last edited by rburgoss; 10-09-2014 at 08:53 AM.
10-09-2014, 08:57 AM   #47
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OP Marcus seems to keep asserting(in at least 4 posts, despite valiant attempts to explain by many here) that somehow a "small sensor doesn't catch the same amount of light as a large sensor". And follows with the assertion that small sensors are therefore boosted, no good, a con-job by the manufacturers.

Well a little reading about why photographers invented the f/- would correct that mis-conception.

Also common sense- if that assertion were true, we would have needed a separate exposure meter or spotmeter for every format size.

And what about the old film ISO ratings? The manufacturers traditionally make a wide strip of film, publish a data sheet for it with its generic ISO rating, and then slit it up to make the various format sizes so the consumers can select that film in their preferred format.

Is it that we have a hiatus in optical physics when we gas-bag on about the pros and cons of digital 35mm vs aps-s?
10-09-2014, 08:58 AM   #48
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QuoteOriginally posted by rburgoss Quote
What matters is the effective light transmission of the lens (f/stop) and the time frame during the actual exposure (shutter speed). PERIOD.
I think we're on the same page actually - cheers.
10-09-2014, 09:04 AM   #49
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QuoteOriginally posted by JinDesu Quote
But that is exactly what a cropped sensor does. It physically cropped the image you received. Pacer above me makes good sensor with mentioning film.

I'm pretty sure that a D800 and a D7000 does not do anything fancy with their ISO calculations just because they have different sensor sizes. If they did, you would immediately notice a difference in the D800 crop mode vs the D7000 normal output.
JinDesu, I am with you on this point, and having trouble understanding marcusBMG's claim that when you use the D800 in crop mode you get less light per photon. To me the whole argument is about resulting noise level at a given ISO. I was convinced that I need a FF because I can't shoot with my K100D, K10D and k-7 in higher than ISO 1600 without much noise.....


Last edited by aleonx3; 10-09-2014 at 09:10 AM.
10-09-2014, 09:11 AM   #50
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QuoteOriginally posted by marcusBMG Quote
I think we're on the same page actually - cheers.
Sorry, but I believe you are taking my words out of context.

"If the football field and your house are close together, there is only one possible answer: IT RAINED THE SAME AMOUNT OF WATER PER SQUARE METER OVER BOTH PLACES.

In shorter words: The only way to honestly compare exposure through a given lens and a certain aperture, is to compare similar situations. As I said before: THE SENSOR SIZE HAS NO PART here.
What matters is the effective light transmission of the lens (f/stop) and the time frame during the actual exposure (shutter speed). PERIOD."


(The red section is what you deliberately deleted to take my words out of context)

Yes, I said that, but I also said that in order to be valid, such measurement of light should be given over THE SAME AMOUNT of sensor area, like in the football / backyard comparison example.

It takes a little more than a youtube video to bend or even try to change some laws of physics. An believe me, as I work in the editorial production business (book making), there is an old saying that goes like "the media will stand to whatever is put on it..." (which means, that any statement cannont be considered true just because it shows through some broadcast media...
10-09-2014, 09:13 AM   #51
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It always amazes me how many pages these posts generate. My image-geek never really 'gets' the equivalence issue - I understand the concepts but not the relevance. I get amazing images (yes cr@ppy ones too) with aps-c sensors, and while theoretically I could do an increment or two "better" at 36×24 I don't shoot with theoretical cameras. In fact spending more cash and carrying twice the weight would make me a poorer imager (in more ways than one) so the simultaneous equations break down quickly from my perspective.

That's all from me, enjoy your conversation
10-09-2014, 09:26 AM   #52
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QuoteOriginally posted by marcusBMG Quote
And at the same time much of the light transmitted through the lens is discarded, no longer hitting the sensor. Thats the moment at which the analogy pacerr gives falls down, I think. Taking a print from a neg is a completely different photographic moment to the taking of the pic.
So you're sayin' that if I dodge or burn areas of an image OUTSIDE of the cropped frame it would change the amount of light falling WITHIN the crop frame? And the issue addressed here is how any sensor utilizes the available light, not when it occurs during the photographic process.

The amount of light that passes through an aperture is a constant. How much of that light you choose to capture isn't moderated by the size of the cropped area -- unless of course you stack exposures as in HDR for instance but that isn't a single exposure.

We may only use a fraction of the TOTAL light passed through the aperture, especially when using FF lenses with small sensors, but the intensity of the light falling within the cropped frame doesn't change. Unless we adopt round "negatives" as a norm, there will always be light "wasted" by the circular projection of the lens but that doesn't detract from the illumination on the sensor regardless of its relative size or shape.

Consider a cone of light projected by a full frame lens with four small sensors occupying their own discrete areas at the plane of focus. No one of them would capture ALL the light, but each would receive the light needed for a correctly calculated exposure - and none would "steal" light from another.

The light requirement of a sensor, whether CCD, CMOS, film or photo paper, is determined by its sensitivity (defined by ASA/ISO standards) not the amount of light "wasted" by falling outside of the area of the sensor's surface.
10-09-2014, 09:34 AM   #53
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If you have 16 photosites arranged in a square. Then you take away the outer row of photosites. Why would that affect the number of photons that fall onto the inner photosites? If the exposure drops one photon on each photosite, it doesn't matter whether there are 4, 8 or 16 photosites, and it doesn't matter if some photos fall outside of the photosites.
The reason why FF sensors were traditionally better is because they are a more premium product, using the latest, top notch technology. They also had bigger photosites, but this is no longer the case with modern cameras, since technology is pushed to the limits.

10-09-2014, 09:37 AM   #54
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We have digressed rapidly away from my OP, which was to make the point that if you wish to talk or think in terms of full frame/35mm equivalence relative to a crop factor camera, the crop factor needs to be applied to the aperture as well as the focal length. This is merely arithmetic at the end of the day. The f stop is the focal length divided by entrance pupil. To use the example of the 70-200mm f2.8 and work backwards, f2.8 tells us this has an entrance pupil of approx 71mm. Now on apsc we say that this is equivalent to 105-300mm. The entrance pupil is a physical aspect of the lens and can't change - it is still 71mm. 300mm divided by 71mm gives us the full frame equivalent = f4.2. My impression from some of the responses is that some are trying to cling to an inner notion of "no its still f2.8!" which of course it is and always will be 70-200mm f2.8. But: OR 105-300mm f4.2 fullframe equivalent.

In his video Northrup discusses, with sample pictures, how this is all interlinked with ASA. Since I'm getting out of my depth, not having the technical knowledge to discuss the inner workings of digital cameras, if you would like to take up particular points about these interesting discussions, I suggest you do so with him. However I can't personally see how smaller sensors can match ASA on a smaller photon count ie fewer total photons hitting a smaller sensor) without some internal adjustment (asuming other aspects eg MPx are the same).

Last edited by marcusBMG; 10-09-2014 at 09:49 AM.
10-09-2014, 10:01 AM   #55
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QuoteOriginally posted by marcusBMG Quote
We have digressed rapidly away from my OP, which was to make the point that if you wish to talk or think in terms of full frame/35mm equivalence relative to a crop factor camera, the crop factor needs to be applied to the aperture as well as the focal length.
As explained already, that is true *only* for DOF purposes. For all other purposes, the aperture is the same regardless of what size sensor you are using. If get your light info from a light meter and you shoot ISO 100 1/200 with a 50 1.7 on a full frame body, you don't suddenly have to shoot ISO 100 1/80 with the same lens mounted on an APS-C. It's still an f/1.7 lens as far as the exposure calculations are concerned, not a f/2.8 lens all of a sudden. Equivalent f-stop is for DOF only. Nothing else.
10-09-2014, 10:08 AM   #56
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QuoteOriginally posted by marcusBMG Quote
I can't personally see how smaller sensors can match ASA
One of my old ref books Brandt:"The Photographic Lens" has a section 5 on light transmaission and brightness,
however it is a bit more advanced and does not directly cover your mis-conception.

A better source may be a search to get tutorials on optics classes, I find them useful for the theory.
Do some reading.
10-09-2014, 10:09 AM   #57
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QuoteOriginally posted by marcusBMG Quote
We have digressed rapidly away from my OP, which was to make the point that if you wish to talk or think in terms of full frame/35mm equivalence relative to a crop factor camera, the crop factor needs to be applied to the aperture as well as the focal length. This is merely arithmetic at the end of the day. The f stop is the focal length divided by entrance pupil. To use the example of the 70-200mm f2.8 and work backwards, f2.8 tells us this has an entrance pupil of approx 71mm. Now on apsc we say that this is equivalent to 105-300mm. The entrance pupil is a physical aspect of the lens and can't change - it is still 71mm. 300mm divided by 71mm gives us the full frame equivalent = f4.2. My impression from some of the responses is that some are trying to cling to an inner notion of "no its still f2.8!" which of course it is and always will be 70-200mm f2.8. But: OR 105-300mm f4.2 fullframe equivalent.

In his video Northrup discusses, with sample pictures, how this is all interlinked with ASA. Since I'm getting out of my depth, not having the technical knowledge to discuss the inner workings of digital cameras, if you would like to take up particular points about these interesting discussions, I suggest you do so with him. However I can't personally see how smaller sensors can match ASA on a smaller photon count ie fewer total photons hitting a smaller sensor) without some internal adjustment (asuming other aspects eg MPx are the same).
A place like DXO Mark measures certain things -- SNR, dynamic range, etc. What they find is that for an equalized viewing/printing size and same generation sensor, full frame cameras have a little better than a stop better dynamic range and SNR compared to an APS-C sensor. This does not mean that you get different exposures using a smaller sensor than for a larger sensor. If you are shooting at f2.8 iso 200 and 1/80 second on both formats, you will get the same exposures -- that's the whole point of iso.

If you are shooting at low-ish isos, you will not see much difference between the formats. Certainly at iso 1600 and below and printing less than , say 30 inches on a side, APS-C is going to perform well enough that you won't see a significant difference between the output of a current gen APS-C sensor and a current gen full frame sensor. It is at the extremes that you will see the difference and only if you are willing to accept less depth of field in your photo.

All of this ignores the basic issue of photography which is making images with color, light and subject -- noise and detail are probably secondary to all of these things in the end.

(shot at 22mm f11 equivalent)

10-09-2014, 10:09 AM   #58
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Lets keep trying this in terms anyone can understand, no matter how stubborn they may seem to be.

Lets do a fast comparison. Lets say our cameras are like cargo trucks and its sensors can be considered "payload capacity". Of course, different size trucks will have different cargo capacity, as a whole; but what about if the measured capacity is not total and its considered as per unit of volume (not total volume)?

Lets say... we are not interested on how much weight it can carry, or how many boxes can fit in the cargo area. Lets say, we would like to know how much weight (or volume) can they carry per box used... what size is the box? It doesn´t matter, because all of them are using the same size box.

Photo lenses are measured like that. On how much light they can shed over a given area. It doesn't matter if the total available area is 1 sq mile or 1 sq foot. We need to know how much light falls into 1 sq inch... that's it!

Last edited by rburgoss; 02-03-2015 at 05:04 PM.
10-09-2014, 10:11 AM   #59
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I just took a quick look at the entry on film speed over at Wikipedia. I have a admit up front that I'm no expert in optics so much of the math is lost to me; however, the size of the medium (film / sensor) doesn't seem to matter at all when determining ASA/ISO. So there.
10-09-2014, 10:23 AM - 1 Like   #60
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Well, the whole thing is pretty useless for most people shooting APS-c as they've never ever shot 135 film or digital FF. The best thing would be if people not in need of comparing "equivalence" just would stop doing it. There simply is no real need for it. If minimal depth of field is your biggest wish nothing will beat large format film cameras, so forget digital.

As an example of why the equivalence often is broken in practice is that the advantage of a bigger sensor gets completely diminished as soon as you start cropping pics to the equivalence of aps-c. So for me when shooting sports where I often end up cropping even at 200-300mm to get the right composition I would end up with the same result with FF, unless I get equally bright longer lenses.

---------- Post added 10-09-14 at 07:26 PM ----------

About the aperture equivalence the same thing applies, if you shoot with the lenses stopped down you don't have to care about lenses max aperture equivalence relative to sensor size at the same image composition.
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