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12-19-2009, 03:25 PM   #76
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QuoteOriginally posted by Class A Quote
I thought I'd spoil the party a bit and mention that f/2.8 on APS-C corresponds to f/4.3 on FF. Suddenly that DA 40/2.8 looks even slooooower than it had before.
Maybe if your expectation of what kind of aperture you might need is based on prior experience with film, where ISO 400 was really pushing your luck. On any modern DSLR, ISO 1600 is at least as usable (and you don't need to change rolls to get it!), thus buying you back two stops. Toss in SR, and the DA40/2.8 is *far* more versatile than any 60/4.3 on film (BTW, I'm taking your word on the equivalence; I usually hear the figure given as more or less exactly one stop).

Obviously, none of that helps with respect to DOF control, but those are the situations where I was saying I'm generally happier with MF anyhow. Still, once again, I agree it would be lovely if Pentax were to put out a cheap fast normal AF prime. Who knows, I might even get one myself. But it's not like I feel incomplete without one.

12-19-2009, 03:40 PM   #77
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??? why is that? Why would the aperture be transformed? To my knowledge aperture is simply calculated from focal length/entrance pupil, both of which are lens properties and do not change with film/sensor format.
and

QuoteQuote:
The aperture speed, actual or rated/apparent, doesn't change at all. The same amount of light hits the sensor, just in a smaller area. I don't know where you got this from.
See any of the discussions on this forum or elsewhere about "equivalence" as it relates to comparing lenses and formats. The concept is actually quite sound, although somewhat non-intuitive. The basic idea being, in order to get the same image between APS-C and FF in terms of FOV and DOF, you need a focal length 1.5 times longer for FF (as we all know), but also an aperture about one f-stop larger on the APS-C camera. So a picture taken at 60mm and f/4-sh on FF would indeed be similar in FOV and DOF to a picture taken at 40mm and f/2.8 on APS-C. Now, if it were just about equalizing DOF, no would would really care, but the fun part is, this also more or less equalizes between formats in terms of the tradeoff between shutter speed, ISO, and noise. The 60/4 on FF would require you to shoot at twice the ISO as the 40/2.8 in order to get the same shutter speed. And by shooting the FF camera at twice the ISO, you pretty much neutralize the inherent noise advantage of the larger sensor. Meaning not only will your shots with the 60/4 and 40/2.8 have the same FOV and DOF, they'll also have the same level of noise for a given shutter speed (or same shutter speed for a given level of noise). Extremely clever way of looking at things; almost magic that it works out that way.

But it does break down a little when you try making appeals like the above, because while a 60/4 sounds silly slow, that's mostly based on our collective experience with film, or experience we've had from reading about film. Or from thinking of the that f/4 in APS-C terms rather than realizing that on FF digital, f/4 actually is just as "fast" as f/2.8 on APS-C. In other words, using our experience with f/4 on film and/or on APS-C against us, by making it seems like f/2.8 on APS-C digital is anything other than exactly what it is. Sort of like trying to depress who is already concerned about about the weight by telling them, "yeah, not only do you weigh 200 pounds, but that's 90718 grams". Doesn't change anything about what it means to weigh 200 pounds, just makes it sound worse.
12-19-2009, 03:51 PM   #78
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12-19-2009, 03:52 PM   #79
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QuoteOriginally posted by Marc Sabatella Quote
See any of the discussions on this forum or elsewhere about "equivalence" as it relates to comparing lenses and formats. The concept is actually quite sound, although somewhat non-intuitive. The basic idea being, in order to get the same image between APS-C and FF in terms of FOV and DOF, you need a focal length 1.5 times longer for FF (as we all know), but also an aperture about one f-stop larger on the APS-C camera. So a picture taken at 60mm and f/4-sh on FF would indeed be similar in FOV and DOF to a picture taken at 40mm and f/2.8 on APS-C. Now, if it were just about equalizing DOF, no would would really care, but the fun part is, this also more or less equalizes between formats in terms of the tradeoff between shutter speed, ISO, and noise. The 60/4 on FF would require you to shoot at twice the ISO as the 40/2.8 in order to get the same shutter speed. And by shooting the FF camera at twice the ISO, you pretty much neutralize the inherent noise advantage of the larger sensor. Meaning not only will your shots with the 60/4 and 40/2.8 have the same FOV and DOF, they'll also have the same level of noise for a given shutter speed (or same shutter speed for a given level of noise). Extremely clever way of looking at things; almost magic that it works out that way.

But it does break down a little when you try making appeals like the above, because while a 60/4 sounds silly slow, that's mostly based on our collective experience with film, or experience we've had from reading about film. Or from thinking of the that f/4 in APS-C terms rather than realizing that on FF digital, f/4 actually is just as "fast" as f/2.8 on APS-C. In other words, using our experience with f/4 on film and/or on APS-C against us, by making it seems like f/2.8 on APS-C digital is anything other than exactly what it is. Sort of like trying to depress who is already concerned about about the weight by telling them, "yeah, not only do you weigh 200 pounds, but that's 90718 grams". Doesn't change anything about what it means to weigh 200 pounds, just makes it sound worse.
I appreciate the detailing of the subject for readers who might not be informed, but I believe simply talking about all of that leads to gross misinformation. For example, the "better noise advantage" of a full-frame sensor is not some mathematical constant like a crop factor of 1.5x, it changes from camera to camera. Further, you have the same DOF in a 40/2.8 lens on FF as you do in a 40/2.8 on APS-C, it's just that the image has been cropped. But OOF things are just as OOF on FF as they are on APS-C. It's really that simple, and even talking about trying to make equivalences like that needlessly complicates things.

A lens on an APS-C sensor acts 100% the same exact way as if you put it on a FF 135-format sensor, and produces the same exact image, it's just that a smaller portion of the image is picked up by the smaller sensor.

12-19-2009, 04:13 PM   #80
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QuoteOriginally posted by wallyb Quote
I appreciate the detailing of the subject for readers who might not be informed, but I believe simply talking about all of that leads to gross misinformation. For example, the "better noise advantage" of a full-frame sensor is not some mathematical constant like a crop factor of 1.5x, it changes from camera to camera.
True, but there *is* an aspect to it that scales well with sensor size. That is, for a given sensor technology, the size of the sensor really is the determining factor, and it tends to trump other factors (ie, even the worst FF sensor outperforms the best APS-C sensor).

QuoteQuote:
Further, you have the same DOF in a 40/2.8 lens on FF as you do in a 40/2.8 on APS-C
Actually, you'd end up with *less* DOF on the APS-C camera if you compared that way, because you'd need more magnification to reach the same print size. Being in or out of focus is not an objective trait of the image as recorded on the sensor - it depends on the amount of magnification performed before you see it and also on your viewing distance and visual acuity. That is to say, print both images at 4x6" and there will be things that appeared sufficiently in focus on the FF camera but won't any more on the APS-C because you've magnified the image more. I'm not familiar enough with the DOF formulas to know how much of an effect it has, but it's definitely real and pretty obvious just in comparing a single image at different sizes.

But given that we're comparing images of different FOV, it hardly seems worth comparing DOF in this way in the first place. That's the point of equivalence - to allow you to figure out what lenses will actually produce the same image in *all* respects, not just one or two.

QuoteQuote:
It's really that simple, and even talking about trying to make equivalences like that needlessly complicates things.
No, it really simplifies them, as then you don't have to say, "well, it's the same DOF on the sensor, except I wonder how much that changes because of the larger magnification required to get to the same print size, plus it's a different FOV so I wonder how I should factor that in to my thinking, and oh by the way, the FF camera has less noise so I wonder how to factor that in also". If you're only concerned about one of the many picture-taking parameters, then by all means, you can focus on just that, but real pictures almost always depend on all of them.

QuoteQuote:
A lens on an APS-C sensor acts 100% the same exact way as if you put it on a FF 135-format sensor, and produces the same exact image, it's just that a smaller portion of the image is picked up by the smaller sensor.
Right, and because of that, the actual image you end up with is very different. The idea of of equivalence is to tell you what lens would have produced the *same* image, not the image that would-have-been-the-same-if-it-weren't-and-had-been-taken-with-a-camera-with-better-high-ISO-capability.

Like I said, it's not very intuitive at first, and pretty much everyone resists the idea at first, but it's quite sound and simplifies an awful lot of thinking when comparing between different formats.
12-19-2009, 04:33 PM   #81
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QuoteOriginally posted by Marc Sabatella Quote
True, but there *is* an aspect to it that scales well with sensor size. That is, for a given sensor technology, the size of the sensor really is the determining factor, and it tends to trump other factors (ie, even the worst FF sensor outperforms the best APS-C sensor).
I wouldn't agree that's something inherent in the design. It's fully possible for an APS-C sensor to outperform a FF sensor -- just make a bad FF sensor. It's not as black and white as that.

QuoteOriginally posted by Marc Sabatella Quote
Actually, you'd end up with *less* DOF on the APS-C camera if you compared that way, because you'd need more magnification to reach the same print size. Being in or out of focus is not an objective trait of the image as recorded on the sensor - it depends on the amount of magnification performed before you see it and also on your viewing distance and visual acuity. That is to say, print both images at 4x6" and there will be things that appeared sufficiently in focus on the FF camera but won't any more on the APS-C because you've magnified the image more. I'm not familiar enough with the DOF formulas to know how much of an effect it has, but it's definitely real and pretty obvious just in comparing a single image at different sizes.
No, you wouldn't end up with less DOF. You'd have the same DOF, it would just appear different because of the crop factor. If you had a theoretical 1500x1500 pixel FF sensor, and took a picture with a lens, then put that same lens on a 1000x1000 pixel APS-C sensor and took a picture, you would have an exact crop of the FF image. It just appears that the DOF is "smaller" because the *cropped* image has been blown up, due to high pixel density. This is the whole point I'm trying to make on how people get confused... And being in or out of focus is an objective trait, and has to do with the distance that other subjects are from the focal point. combined with the lens aperture used. It has nothing to do with sensor/film size, at all.

QuoteOriginally posted by Marc Sabatella Quote
But given that we're comparing images of different FOV, it hardly seems worth comparing DOF in this way in the first place. That's the point of equivalence - to allow you to figure out what lenses will actually produce the same image in *all* respects, not just one or two.
You will never get the same image, because the sensor size is different. Period. When you start "making up for the differences", like using a 35mm lens on an APS-C digital body to be the rough equivalent of a 55mm lens on full-frame, you start confusing yourself and getting the math wrong.

QuoteOriginally posted by Marc Sabatella Quote
Like I said, it's not very intuitive at first, and pretty much everyone resists the idea at first, but it's quite sound and simplifies an awful lot of thinking when comparing between different formats.
I would assume people resist it because much of the explanation you've just given is scientifically wrong. This is a very confusing subject to some people, but you just have to think of it as simply a crop. Because that's all it is. Don't try to equalise everything, because you will never reach an equilibrium.

Last edited by wallyb; 12-19-2009 at 04:44 PM. Reason: Changed use of larger/smaller
12-19-2009, 05:38 PM   #82
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QuoteOriginally posted by Marc Sabatella Quote
Like I said, it's not very intuitive at first, and pretty much everyone resists the idea at first, but it's quite sound and simplifies an awful lot of thinking when comparing between different formats.

It's even simpler to not make comparisons in the first place and just take pictures instead.
12-19-2009, 05:51 PM   #83
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QuoteOriginally posted by Damn Brit Quote
It's even simpler to not make comparisons in the first place and just take pictures instead.
thaaaaank you....

12-20-2009, 06:22 AM   #84
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QuoteOriginally posted by Ben_Editct Quote
Why would the aperture be transformed?
Marc has already explained this well. Thanks Marc.
For those that remain unconvinced, try reading the wikipedia article on DOF vs format size.

Basically, DOF is controlled by the aperture diameter. If you change the focal length (in order to obtain the same FOV on different formats) you also need to change the f-ratio in order to get the same aperture diameter again (as the f-ratio is defined by focal-length/aperture-diameter).

QuoteOriginally posted by wallyb Quote
Further, you have the same DOF in a 40/2.8 lens on FF as you do in a 40/2.8 on APS-C, it's just that the image has been cropped.
We are talking about "equivalent images", i.e., how to take an image on a crop camera that is identical to one taken on an FF camera. If you want to do this, you need to adjust more than just the focal length.

QuoteOriginally posted by wallyb Quote
You will never get the same image, because the sensor size is different.
You can compensate for the different sensor size by adjusting the focal length to get the the same FOV, f-ratio to get the same DOF, ISO to get the same shutter speed. The maths is not difficult and has been done many times.

QuoteOriginally posted by Marc Sabatella Quote
Maybe if your expectation of what kind of aperture you might need is based on prior experience with film, where ISO 400 was really pushing your luck.
I've never used a film SLR. I find the term "fast lens" a bit unfortunate nowadays because I see the advantages of wide aperture lenses in the DOF control they offer. Yes, they also let more light in, but as you say with modern DSLRs shooting in low light can often more easily be had with higher ISO settings and in contrast to using wide apertures, one still has usable DOF.

QuoteOriginally posted by Marc Sabatella Quote
...you pretty much neutralize the inherent noise advantage of the larger sensor.
As it becomes clear from your later statements, a larger sensor has no noise advantage (it has a dynamic range advantage; the noise advantage only comes into play when one is able to use FF lenses whose APS-C equivalences do not exist, such as a 85/1.4). Anyone arguing this please check out this thread "low-noise-benefit-ff-vs-aps-c-equals-zero".

QuoteOriginally posted by Marc Sabatella Quote
But it does break down a little when you try making appeals like the above, because while a 60/4 sounds silly slow, that's mostly based on our collective experience with film, or experience we've had from reading about film.
An equivalence is an equivalence. It doesn't break down for some cases. In order to get an image with an APS-C (say 1.5 crop) sensor that is equivalent to one made with a 60/4 lens using an FF sensor, you need a 40/2.67 lens. Make the FF lens a 60/2.8 and your APS-C lens needs to be a 40/1.86.

QuoteOriginally posted by Marc Sabatella Quote
Sort of like trying to depress who is already concerned about about the weight by telling them, "yeah, not only do you weigh 200 pounds, but that's 90718 grams".
I see it as saying to someone "Yes, you can state your weight is 0.091 tons, but that doesn't make you lighter my dear. Your weight is still 91kg." We are basically saying the same thing, except that I believe that many people mistake an APS-C f/2.8 with the FF f/2.8, i.e., think they can get less DOF than they can really get.

Scale this down to P&S sensor formats and then suddenly pretty much everyone knows how difficult it is getting thin DOF on such cameras even though the lenses often are specified as f/2.8 as well. Their FF equivalent f-ratio is much higher.

QuoteOriginally posted by Damn Brit Quote
It's even simpler to not make comparisons in the first place and just take pictures instead.
Why didn't you take a picture instead of making this comment?
12-20-2009, 06:49 AM   #85
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QuoteOriginally posted by Class A Quote
We are talking about "equivalent images", i.e., how to take an image on a crop camera that is identical to one taken on an FF camera. If you want to do this, you need to adjust more than just the focal length.
If you want to talking about making images in different formats equivalent, then what you and Marc explain is basically correct. However, it is the mere notion of trying to 'equivalise' them that leads to so much confusion, misinformation, and wasted posts on photography forums. That is where my disagreement lies, along with the definitions of terms and correction of things about aperture ratings that I outlined above.

Thinking of an image from an APS-C sensor as nothing more than a cropped version of the same scene in a larger format removes all this confusion, because that's all that it is.
12-20-2009, 08:23 AM   #86
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QuoteOriginally posted by Class A Quote
Marc has already explained this well. Thanks Marc.
For those that remain unconvinced, try reading the wikipedia article on DOF vs format size.
But this does not explain, why you suddenly transform the 40/2.8 into a f/4.3 lens - not at all.

That was all I wanted to get an explanation for. The DOF discussion does not serve that purpose.

Ben
12-20-2009, 08:42 AM   #87
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Heated thread...

Did anyone answer the OP's hood question... I didn't see the answer

Just wanted to add that the price at B&H is $359, then you get a $100 visa card back as rebate, so it's actually $259 in the end
12-20-2009, 11:15 AM   #88
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QuoteOriginally posted by commo Quote
Heated thread...

Did anyone answer the OP's hood question... I didn't see the answer

Just wanted to add that the price at B&H is $359, then you get a $100 visa card back as rebate, so it's actually $259 in the end
ummmm...not exactly....you only get that $100/lens cashback rebate thingy if you buy the lenses at the same time, same invoice as a K-7. D'oh!!
12-20-2009, 12:26 PM   #89
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It occurs to me that some of us old-time Pentax owners need to change our paradigm about the 50mm 1.4 or 1.8. These lenses were dirt cheap because they were the kit lenses of their day. Almost no one bought an SLR without one, and they were manufactured in huge volumes.

It also seems to me that the SLR also held a different place in the market back then. Many people I know who owned a film SLR have opted for some digital replacement other than an interchangeable lens SLR. I'm sure that someone with a better finger on the pulse of the industry can confirm or refute this, but it seemed that when I went to weddings, graduations and other events in the film days, there were SLRs around far more necks than today. People today seem awed by a digital SLR.

The 50mm is becoming a lens for enthusiasts, sold at volumes commensurate with a lens for enthusiasts to fit a camera for enthusiasts. We should probably expect the price to reflect the consistently decreasing volumes and increasingly specialized market.
12-20-2009, 12:37 PM   #90
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QuoteOriginally posted by wallyb Quote
I wouldn't agree that's something inherent in the design. It's fully possible for an APS-C sensor to outperform a FF sensor -- just make a bad FF sensor. It's not as black and white as that.
Let me put it this way: make an FF sensor, then take that *exact* sensor and crop it to APS-C format. There is a very real and completely predictable effect on noise that is attributable to sensor size. Whether *different* sensors will *also* affect the results is another matter.

QuoteQuote:
No, you wouldn't end up with less DOF. You'd have the same DOF, it would just appear different because of the crop factor.
DOF is nothing but appearance. Saying the DOF appears different means DOF *is* different.

QuoteQuote:
And being in or out of focus is an objective trait, and has to do with the distance that other subjects are from the focal point. combined with the lens aperture used. It has nothing to do with sensor/film size, at all.
Simply untrue. Would suggest you read up the subject, with particular reference to the term "circle of confusion". DOF is *not* simply a function of the image as taken - it is also a function of the *viewing* of the image.

QuoteQuote:
You will never get the same image, because the sensor size is different. Period.
Not sure what you mean by this. You can get an image with the same field of view, the same DOF, the same shutter speed, and the same amount of noise. Whatever other difference you think might be attributable to sensor size, it's isn't going to be reflected in an of the above, so I'd question what relevance it has.

Seriously, this idea of equivalence is real. Like I said, takes a while to wrap your head around it, but it is completely 100% scientifically verifiable.

QuoteQuote:
When you start "making up for the differences", like using a 35mm lens on an APS-C digital body to be the rough equivalent of a 55mm lens on full-frame, you start confusing yourself and getting the math wrong.
Not if you the idea of use "equivalence" - used correctly, it *will* yield the correct answer. And that's what makes it valuable.

QuoteQuote:
I would assume people resist it because much of the explanation you've just given is scientifically wrong.
No, it is not. Like I said, I suggest you do some reading on the subject. This is *not* something in which there is even the slightest room for debate. Arguments against the idea of equivalence are flat earth arguments.

QuoteQuote:
you just have to think of it as simply a crop. Because that's all it is.
Yes - and a crop that has major consequences on field of view, DOF, and noise. Feel free to try to guesstimate those ffects if you're unwilling to work through how equivalence works, but once you understand it, the guessing game is over, so that's kind of nice. It's not relevant veryoften, snce I don't shoot FF, but it relevant when I start wondering about eventual upgrades and wish to think about what kind of results I could expect from an FF camera and what kind of lenses I'd need to achieve those results (in terms of giving me any improvement in noise for a given shutter speed). The way it works out for me, there is basically no benefit in FF - in order to see any improvement, I'd need lenses much larger and more expensive than I have any interest in.

Last edited by Marc Sabatella; 12-20-2009 at 12:54 PM.
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