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Full frame Vs APS-C: New article about the crop factor and pixel density
- Thread starter Robsphoto
- Start date
Ronni H
Senior Member
Hi,
I discovered this thread a little late - and I'm not going to read through all the angry posts, so here is what I think of the article.
I am an APS-C user and read you article with great interest even though it got way too technical/theoretical at some point. I am not taking offence by it whatsoever.
If I had written the article I would probably have made it "pop" a little more - at least make an interesting introduction instead of going straight to the point. Furthermore I would add a few samples showing the aps-c crop vs FF. Also maybe add something about why FF appear to have shallower DOF.
However to make the article more credible to all users you really should mention the APS-C benefits as well such as smaller and cheaper lenses and camera bodies. And some of the FF disadvanteges such as the fact that FF cameras are more "demanding" on lenses etc.
Otherwise the conclusion is more or less what I had concluded myself beforehand - so thumbs up from me.
--
Never bite the Apple...
Ronni
http://www.pbase.com/ronnihansen
I discovered this thread a little late - and I'm not going to read through all the angry posts, so here is what I think of the article.
I am an APS-C user and read you article with great interest even though it got way too technical/theoretical at some point. I am not taking offence by it whatsoever.
If I had written the article I would probably have made it "pop" a little more - at least make an interesting introduction instead of going straight to the point. Furthermore I would add a few samples showing the aps-c crop vs FF. Also maybe add something about why FF appear to have shallower DOF.
However to make the article more credible to all users you really should mention the APS-C benefits as well such as smaller and cheaper lenses and camera bodies. And some of the FF disadvanteges such as the fact that FF cameras are more "demanding" on lenses etc.
Otherwise the conclusion is more or less what I had concluded myself beforehand - so thumbs up from me.
--
Never bite the Apple...
Ronni
http://www.pbase.com/ronnihansen
Olaf Ulrich
Leading Member
While I think Rob's article is a failure indeed, Russ' decision to acquire an APS-C-format camera sure is not a symptom of it. To the contrary---I think Russ has taken a very sensible and well-educated decision. 35-mm format has its pros and cons, and APS-C format has its pros and cons. It boils down---as alaways---to which pros are most significant to you and which cons you can live with without losing sleep.
Regards,
Olaf
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Olaf Ulrich, Germany
Olaf Ulrich
Leading Member
With regard to exposure, it's the same on either. With regard to depth-of-field and diffraction, it's not.
When shooting with different-format cameras and using lenses with equivalent focal lengths (i. e. shorter focal length on smaller-format camera) so that angles-of-view are the same, then at the same aperture the smaller-format camera will yield more depth-of-field and also suffer more from diffraction. Compared to a 35-mm camera, to get the same depth-of-field with APS-C you'd have to open up the aperture by one f-stop (1.2 f-stops, to be precise, but that doesn't make any real-world difference) ... and if you do that then diffraction will also be the same again.
However this is purely academical musing. For practical intents and purposes, this one-stop shift will hardly make any difference in your results. And again, there's pros and cons to the matter; you cannot say which format has an advantage. With regard to some aspects, the smaller format is better; with regard to other aspects, the larger format is better. And with APS-C vs 35-mm, it's a subtle difference anyway. It's not so subtle when comparing vastly different image formats like, say, 1/2.5" digital point-and-shoot vs digital 36 × 48 mm medium format.
Regards,
Olaf
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Olaf Ulrich, Germany
Olaf Ulrich
Leading Member
True.
.
False.
As a matter of fact, sensor size is the only factor determining the effective degree of blur from diffraction. And contrary to common belief, pixel density has nothing to do with it.
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Both of you are confused.
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First: There is no such thing as a pixel-density-related diffraction limit . Instead, diffraction is always there, but in a continuous spectrum of degrees. You can only establish some kind of artificial 'limit' by defining a certain degree of diffraction blur that you are willing to accept.
Second: The sensor sizes of the A700 and A900 are different, therefore they will suffer from diffraction blur to different degrees. If you define a certain degree of blur as your 'limit' then the A700 will bump into that limit earlier (i. e. at a wider aperture, provided a good-enough lens) than the A900. The difference in f-stops is 2 × log2(1.53) = 1.227 f-stops because the A900's sensor is 1.53× as large as the A700's (in linear terms). As simple as that.
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The site you use obviously is teaching you a lot of nonsense because there is no such thing as a 'diffraction-free aperture.' Even if the diameter of the diffraction circle (the so-called Airy disk) is smaller than the pixel pitch it will still reduce sharpness.
The closest to a 'diffraction-free aperture' or a 'diffraction limit' you can come up with is the aperture where the lens aberrations get so bad that they obscure any diffraction losses---or, as seen from the opposite point of view, where the lens' aberrations become so small that lens performance is solely limited by diffraction rather than aberration. But that aperture is purely a property of the lens, not the camera; it is determined by lens quality.
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So you really believe that at these apertures and wider, those cameras cannot suffer from diffraction, and diffraction will set in only when stopping down beyond these apertures? Well then you're wrong. Unless the lens is introducing Seidel aberrations, both cameras will yield sharper images at f/8 than at f/9, and at f/5.6 even sharper images, and at f/4 yet sharper images still. And so on. And at the same aperture (and with ideal lenses), the A900's image will always be 1.227 f-stops ahead of the A700's due to the larger sensor size.
Regards,
Olaf
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Olaf Ulrich, Germany
zackiedawg
Forum Pro
That's precisely the rub about all of the rather preachy attitudes declaring one format to be the right one and the other to be the wrong one. Articles devoted to 'educating' APS-C users that they aren't gaining anything, and in fact are losing much, for not using full-frame, are entirely missing the point.
EVERYTHING involves compromise. Period. It's a matter of personal choice which compromises a person wishes to accept in order to get what they perceive as important features or benefits. Do I want to compromise by getting a full frame camera or compromise to get an APS-C camera? Full frame requires me to spend more, deal with a heavier and larger camera, and use heavier lenses...or not make full use of my sensor by cropping to get the length I want. APS-C requires me to compromise on lenses designed for full frame cameras ("The images captured with this lens will provide the “full view” that is seen by the camera") and of course overall resolution and potential high ISO capability from the much larger sensor.
As it happens, I prefer APS-C cameras, and enjoy the gains they are making with them. I like the smaller, lighter, cheaper camera bodies, and the available smaller and lighter lenses I can buy to go with them. I like having 750mm optical in a camera/lens combo I can walk 10 miles with in the hot sun and shoot handheld without getting tired. It's a personal preference. I'm willing to compromise other things a bit to get that. If full-frame cameras became more compact, would that solve the problem? No...because the lenses would still have to be huge. What would a 200-500mm lens look like in full frame? Or the other option would be to choose the crop frame mode on the FF camera...well, yes - if the FF cameras got smaller and lighter and dropped into my price range, and APS-C cameras were fading away, I guess this would be my only real option.
For now, I am thoroughly enjoying the progress being made in the APS-C market -and don't have any worries about the market disappearing any time real soon given how many APS-C cameras are sold each year compared to full frame or 4/3rds.
We have choices...pick the one you like. No need to tell others what they need to choose. That's the job for the Taliban. Until they take over, we'll be able to choose between full-frame, medium format, APS-C, 4/3rds, or various P&S sensors. And any number of brands too. Isn't life grand?
--
Justin
galleries: http://www.pbase.com/zackiedawg
OK Olaf I'm very happy to learn if I'm wrong. I wonder if you are too...
We agree that
(if we don't agree here please let me know because the next step depends on this last)
So we have an absolute length, say for example 0.01 mm, beneath which nothing can be resolved in the focal plane. I do not see how sensor size can therefore determine the effective blurring due to diffraction. The only thing which matters is the distance between one pixel and another.
This is what I think. You say
Please explain better how sensor size determined the effective degree of blur whereas pixel density does not.
We agree that
The magnitude of smearing due to diffraction will be an absolute length beneath which two points cannot be distinguished. This length is defined solely by the wavelength of light and the f number of the optical system. Sensor size and pixel resoution do not define this diffraction length.
(if we don't agree here please let me know because the next step depends on this last)
So we have an absolute length, say for example 0.01 mm, beneath which nothing can be resolved in the focal plane. I do not see how sensor size can therefore determine the effective blurring due to diffraction. The only thing which matters is the distance between one pixel and another.
This is what I think. You say
OK. but in that case an APS-C sensor with 4 pixels and an APS-C sensor with 100MP will have the same 'effective degree of blur from diffraction' according to you... which is difficult to believe, to saythe least.
Please explain better how sensor size determined the effective degree of blur whereas pixel density does not.
I never said there is - I used the term 'diffraction-free' aperture. The use, and positioning, of the quotes was deliberate. I couldn't be a*sed writing out their text in full - namely that what I mean by 'diffraction-free' aperture is the point at which one begins to notice the effects of diffraction - and that point will of course depend on whether you are looking at a 6x4 postard from 100 metres or a 100% crop on a PC at 2 cm.
This depth of field change is a result of changing your distance to the focus point. ie: the "further away you go from a subject for a given lens and aperture combination"
I understand the point of view that the adjustments you make to make aps-c look like full-frame result in a depth of field change, but there is no direct correlation between sensor size and depth of field.
Take a look here:
http://blog.townerjones.com/2008/09/back-to-basics.html
The first shot is done at 24mm, the second shot at 150mm. In the second shot, the photographer backed up far enough so that the statue looked to be the same size in the frame. It's almost an optical illusion, but the statues are about the same size in those pictures.
Edit - hey wow, purple!
Sol
Veteran Member
--
Sol
http://solarviewphotography.com/
'There would be so many more happy digital photographers in the world,
if the 100% zoom button on their computers, was permanently disabled.'
. . . . where is my 100% Lupe, anyways ??' -Sol ;-)
Sol
http://solarviewphotography.com/
'There would be so many more happy digital photographers in the world,
if the 100% zoom button on their computers, was permanently disabled.'
. . . . where is my 100% Lupe, anyways ??' -Sol ;-)
Olaf Ulrich
Leading Member
Agreed.
.
It's because when one resolution-limited system (such as a stopped-down lens) passes on a signal to another resolution-limited system (such as a sensor with a finite number of discrete pixels) then the resolution of the signal dropping off the end of the chain is not simply equal to the minimum of the resolution limits of the chain's indiviual elements. Instead, the resolution limits will interact in a fairly complex way. This always gets ignored in those foolish articles, essays, and webpages addressing pixel pitch and Airy disk diameters.
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No. The only thing that matters (for the degree of blur introduced by diffraction) is the distance from the left border of your frame to the right.
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Exactly.
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What is so difficult about it? Obviously you are confusing pixel resolution (or lack thereof, see your four-pixel sensor) with the degree of blur from diffraction. The pixel count of the sensor will provide a certain resolution; it will be higher with more pixels, or lower with less pixels. The effect of diffraction subtracts from that. The amount that gets subtracted depends on aperture and sensor size but not on pixel density---actually you can subtract significantly less than the equivalent of one pixel-to-pixel distance, and it will still make a visible difference.
In order not to make a visible difference, the amount subtracted had to be much less than a single pixel ... so with your hypothetical four-pixel sensor the loss wouldn't matter indeed. But note the emphasis on the word 'visible'! In mathmatical terms, even your four-pixel sensor would still suffer from diffraction, to the same (absolute) degree as a four-million-pixel sensor of the same size. Only in relative terms the loss from diffraction would the virtually zero because the original resolution is so low to begin with. However in real life there are no four-pixel sensors ...
So when two sensors have different sizes but the same (or almost the same) pixel pitch then the single pixel's contribution to the final image from the larger sensor will be less, hence less blur from diffraction. Basically the same is true when the larger sensor has the same pixel count as the smaller one. Then the individual pixel's contribution to the final image will be equal for both sensors but the (relative) loss from diffraction on the single pixel will be less for the larger sensor (remember: the absolute loss is always the same, no matter how big or small the individual pixel, as long as the aperture remains the same). Either way, the larger sensor wins, no matter what the pixel densitiy is.
Having said that, don't feel bad everybody who doesn't own a 35-mm-format DSLR camera! The margin by which it wins over a APS-C-format camera in terms of diffraction blur is minuscule, and in 95 % of the cases it gets completely obscured by other real-world effects affecting (read: reducing) image quality which usually are one or two orders of magnitude greater than the difference of diffraction blur between APS-C and 35-mm formats.
Regards,
Olaf
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Olaf Ulrich, Germany
Dave Oddie
Veteran Member
And some old lenses are not so great. As to Olympus being nowhere Sony is not much better but I am not sure of the point of your remark anyway.
It is what it is what counts not what you think it is meant to be. On an aps-c camera it gives the f.o.v of a standard lens, on FF it gives a wide angle view and that is all there is too it. If you have no use for a standard lens f.o.v then you won't want a 28mm on an aps-c camera or a 50mm lens on a FF camera.
Sigma brought out their 30mm F1.4 as a standard lens for their 1.7x crop sensor. It can't be used as a wide angle because it is an aps-c only lens. It gives a 51mm f.o.v equivalent on a Sigma d-slr and 45mm on a Sony aps-c. Is this mean to be a wide angle as well? No. It was designed to give a standard lens f.o.v on aps-c.
So are Sigma wrong to think of their 30mm lens as a standard lens?
For you they may well be but I take a lot of landscapes as well and I found the 35mm & 21mm better.
Well I did say for me but anyone who likes the idea of a standard lens on FF can get the same f.o.v by buying a 28mm (or Sigma's 30mm) lens for their aps-c camera.
It is only not well suited to my needs on FF. It is well suited to my needs on aps-c. I could not have a lens line up that worked on both formats equally well. Of the two formats it is considerably cheaper to assemble a lens set up that is suitable for my needs on aps-c.
I am not anti-FF. I am pro aps-c for the above reasons. The two are not mutually exclusive points of view. Unfortunatley some people think aps-c is redundant because they can crop a FF picture.
Dave
Olaf I have trouble following you, I'm sorry. It may be just me but I have a feeling that when someone cannot explain clearly and simply with an example then it's likely they are confused or mistaken. This is my impression from what you write.
I am from the old school, Airy disk diffraction limit =1.22.lambda.f-number, this I can understand. This places an absolute limit on what can be resolved in the focal plane. A sensor with greater pixel resolution than this limit gains little. This is all independent of sensor size.
These are facts Olaf. Verifiable, testable and very well known.
--
http://mike2008.smugmug.com
I am from the old school, Airy disk diffraction limit =1.22.lambda.f-number, this I can understand. This places an absolute limit on what can be resolved in the focal plane. A sensor with greater pixel resolution than this limit gains little. This is all independent of sensor size.
These are facts Olaf. Verifiable, testable and very well known.
--
http://mike2008.smugmug.com
Phixel
Veteran Member
The first Alpha Mount digital SLR cameras were not 35mm format, they were all APS-C, so you are wrong on this point. There is a good argument to be made that the 35mm format is a later adaption of film size lenses to a digital body.
The term already exists and is exclusively used by camera manufacturers (they never use the incorrect term "cropped"), but too many old timers refuse to accept that APS-C size is a format unto itself and attempt to show their contempt of it by calling it "cropped".
You and others can argue the syntax and the scientific accuracy of that statement or others that approximate it but it is effectively truth.
Your truth, but not fact. The correct way to understand the difference between camera formats is Field of View. This concept has been around a long as photography has been around.
Or rather it is truth enough for people that need to learn of these related concepts. And there are MILLIONS that now or will eventually own cameras that these ideas are alien and confusing.
It appears to me that YOU are adding to their confusion.
It needs to be explained in simplistic terms that are understandable from a beginner’s standpoint. The way I look at it is that if people are willing to read on a subject and that they are interested in the subject, they have a right to discuss it no matter how much it has been mulled over before. If they are knowledgeable enough to contradict a point of view then what they read was not sophisticated enough for them. But that certainly does not make that writing without value.
A very condescending statement, and ironic since you are the one that does not have an understanding of FOV and focal lengths or different sized camera formats.
Yes ,you are right, cropping is another factor in favor of a 35mm format camera. I never have to crop that severely, so that not an issue for me, but I can see it's value to some.You state that there are only two compelling reasons to go full frame dSLR (your words…full frame…and I agree with the FF part. The first is essentially the need to print large. I would challenge that as I see all those pixels as the ability to significantly crop for compositional purposes.
-Phil
Dave,
When looking at what Rob did in the bird photo, am I correct in using another term "up-sampling" rather than cropping. If I understand this correctly, when you up-sample, the computer via the editing software creates pixels that were not captured by the sensor. If this is so, isn't a photo taken by an APS-c sensor actually superior to a photo that has been up-sampled from a FF sensor to create a similar FOV image since the APS-c image is what was optically captured? I hope I am explaining this so you can understand my question!
When looking at what Rob did in the bird photo, am I correct in using another term "up-sampling" rather than cropping. If I understand this correctly, when you up-sample, the computer via the editing software creates pixels that were not captured by the sensor. If this is so, isn't a photo taken by an APS-c sensor actually superior to a photo that has been up-sampled from a FF sensor to create a similar FOV image since the APS-c image is what was optically captured? I hope I am explaining this so you can understand my question!
Olaf Ulrich
Leading Member
That's your problem, not mine. So no need to apologize.
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Okay---please take into consideration that English is not my native language. And then ... some topics just are complex. Earlier in this thread I said, an explanation is good when it's simple and correct. In order to be correct, an explanation mustn't fall below a certain degree of complexity when the topic to be explained is complex. So an explanation should be as simple as possible and as complex as required. But of course maybe someone else who is better with words than I am may find a simpler wording to (correctly) explain the same.
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That is all correct. Still you don't fully understand it.
No matter what the sensor's pixel resolution might be, the resolution of its output will always be below the absolute limit that you just have sketched out above. The higher the sensor's pixel resolution is, the closer the output gets to that upper bound. To actually reach the upper bound, the pixel resolution would need to be infinitely high---which of course is impossible. Still, a higher-resolving sensor will yield higher-resolution output. Always.
Of course, in the presence of diffraction, the relation between pixel resolution and output resolution is not linear (that means, doubling the pixel density won't necessarily double the output resolution)---but let's save that twist of complexity for another day ...
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Yes indeed. But not well understood, obviously.
Regards,
Olaf
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Olaf Ulrich, Germany
Well Olaf, you really need to be more direct and more simple. You are making really very simple things more difficult then they need be and nhot explaining anything in more than very vague hand-waving terms.
The effect of diffraction is directly observable with any high MP dslr. Try shooting a scene at f/40 and f/8 with an A350 and see the difference.
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http://mike2008.smugmug.com
The effect of diffraction is directly observable with any high MP dslr. Try shooting a scene at f/40 and f/8 with an A350 and see the difference.
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http://mike2008.smugmug.com
Olaf here we have a clear example of the resolution degradation associated with high f number.
If you do not follow what I am saying after a while it becomes impossible, I'm sorry I cannot show you where you are going wrong as you do not explain well enough to see what the error even is. You are 'not even wrong', to coin a phrase.
All the best.
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http://mike2008.smugmug.com
If you do not follow what I am saying after a while it becomes impossible, I'm sorry I cannot show you where you are going wrong as you do not explain well enough to see what the error even is. You are 'not even wrong', to coin a phrase.
All the best.
--
http://mike2008.smugmug.com
Olaf Ulrich
Leading Member
Umm ... okay, point taken.
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So it's what I called 'artificially defined limit of degree of blur that you're willing to accept.'
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Sure. But are you aware what the conceptual difference is, with regard to the comparison of pixel densities of different sensors, between a postcard (at any distance) and a 100 % view on the monitor (again at any distance)? I'm afraid you're not. Most aren't.
Regards,
Olaf
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Olaf Ulrich, Germany
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