Answer this one question!

[Amin Sabet]

--
http://aminphoto.blogspot.com

 

[Lee Jay]

Am I correct in assuming, that a 20D, due to it's 1.6x crop factor,
actually uses "less" of the lens' glass...

No.

and therefore does not
"see" deteriorating edge IQ?

You meant less of an image's image circle above. Every pixel looks at the scene through the entire lens aperture.

The answer is sort of. In practice, there's virtually no situation in which a 1.6 crop camera will out-resolve a full-frame camera at equivalent apertures and angles-of-view, even in the corners.

--
Lee Jay
(see profile for equipment)

 

[Lee Jay]

Yeap, I think Neil has the same understanding as me. Just that he
is better at explaining himself than me. I still struggle to
understand how a FF body has 2.56 stop advantage over an
equilvalent 1.6x cropped camera.

2.56x advantage = 1 1/3 stop advantage.

yes, ok, but...

Because the sensor is 2.56x larger and at the same f-stop, it's
getting the same light per unit area. 2.56x the area, times the
same light per unit area = 2.56x more light.

yes, overall it gets more light - but that's only because it's bigger

And that's enough, and all that's claimed.

as i said before, how can a smaller sensor get more intense
light, which would equate to a difference in exposure

F-stop controls the light intensity at the sensor. Exposure calculations always include ISO.

imagine you have a white card. shine a torch at it. if the torch
covers the whole card, then the the whole card has (for arguments
sake) 1unit of light power at every point

now cut the card in half

the card is now 50% in size, and the torch hasn't changed

the card is still receiving 1unit of light power at every point,
but there is also 'wasted' light where the card area has been cut
away

Right.

the light is not more intense

Correct.

the only way the light can be more intense is if there is some kind
of modifier that focuses all the light that was on the 100% card
onto the card when it is half the size

therefore a card half the size would receive 2units of light power
at every point

surely just because the sensor is bigger doesn't mean the image
will be brighter. it just means that more of the image will be
seen (i.e. no "crop factor" on focal length)

And more total light will be captured.

personally i suspect it has something to do with the pixels being
larger, which makes them better 'capturers' of light. however are
the pixels proportionately the same size compared to the sensor on
each camera?

Nothing to do with the pixels.

e.g. on a piece of card 100cm square the pixels are 1cm square

on a 50cm square piece of card are they 0.5cm square?

because if the pixels are larger, they are able to capture more
light - therefore it has nothing to do with sensor size per se,
just pixel size

although this is just a whim - i may be wrong

The claim is not that either the focal length or the f-stop actually change when you change bodies.

The claim is simple. An example is, a 50mm f2.8 lens on a 1.6 crop camera will behave the same as an 80mm f4.5 lens would on a full-frame camera. These are both hypothetical lenses and we're equating their performance in terms of image quality (noise), depth-of-field, diffraction, and exposure. Now, exposure includes ISO, and the larger sensor camera will need to run at a higher ISO, say, 1000 on full-frame versus 400 on 1.6 crop.

It's no accident that a 50mm f2.8 lens and an 80mm f4.5 lens have the same physical aperture (50/2.8 = 80/4.5 = 18mm). Since they have the same angle of view on their respective cameras, and since they have the same physical aperture, they are providing their respective sensors with the same image. The larger sensor's image is larger, and therefore the light is more spread out (less "intense") but the final result is still a match in terms of noise, DOF, and diffraction, and you get the same shutter speed with each system.

So, 1.6 crop, 50mm, f2.8, 1/60th, ISO 400 = full-frame, 80mm, f4.5, 1/60th ISO 1000.

--
Lee Jay
(see profile for equipment)

 

[Eugene Powers]

That is because you need to read the whole idea behind it but as usual in these forums it gets separated in to small pieces and I don't think he explains it in layman terms.
Let's see if I can do it.

First, you have to understand that the smaller the sensor the wider the DOF is. Just like on PS cameras you just can't get shallow DOF because of the small sensor.

Second, in order to match DOF from FF to crop camera you need to stop down FF camera.

Third, if you stop down FF camera you get less light coming in so you need to increase ISO or slow down shutter to match the same exposure.

Understand now? It is all based on DOF. Joe just went backwards explaining exactly the same thing.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[Eugene Powers]

Please read to the end before you answer.

Is this a test? : )

Now, since the intensity of the light on the sensor is the same,
it will meter the same, but since the total amount of light is
more, the noise will be less.

Not true. 1Ds has the same light gathering capability as 5D and
1Ds2 and more than 30D, 400D yet it has more noise than any of
these cameras.

Eugene, obviously, I am talking about sensors of the same design
and generation. I mean, the new 1DIII has less noise than the 5D
sensor as well. It's a new generation of sensor.

Likewise, FF has even more than a 1 1/3 stop noise advantage
compared to Nikon sensors, and more than a 2 stop advantage
compared to Olympus sensors. That's a whole other argument.

Let's keep this argument separate for now. Jury is still out. I for one think and observed that 1D3 does not have less noise it's just masked better.

Thus, you must up the ISO by a factor of 2.56 to get the
same exposure (or, alternatively, reduce the shutter speed by a
factor of 1.6, or some equivalent comination of ISO and shutter
speed).

Not true. There is a small sensor inside the camera that determines
the exposure in the camera not the size of the main sensor. Your
statement above contradicts your answer to me about the gray card.

Not "not true". : ) If you shoot f / 2.8, ISO 100 on 1.6x and I
shoot f / 4.5, ISO 250 on FF, we will get the same shutter speed
and exposure.

True but it is also true for FF camera not just crop camera. If you stop down any camera you need to decrease shutter speed or increase ISO.

Your mistake is that you did not explain that you are only trying to match DOF between the two cameras. Once that is understood everything falls in to place. It is pretty basic.

So, for example, if I take a pic with a 1.6x camera at 100mm, f /
2.8, 1/100, ISO 100, I will get an equivalent image with a FF
camera taken of the same scene from the same location at 160mm, f /
4.5, 1/100, ISO 250. The two pics will have the same FOV, same
DOF, same exposure, and same noise.

True, but you also changed f/stop. I think I know at this point
what you are trying to say you just need to rewrite your statement
above. To include that 2 things need to be changed not just one.
For example putting camera in program mode and changing F stop from
2.8 to 4.5 will give different shutter speed but DOF will be the
same as on the 1.6x crop camera.

Again, you must up the ISO 1 1/3 stops as well. Then the shutter
speeds will be the same.

Now, if the total number of pixels is the same , then the noise
will be the same on a per-pixel basis as well. However, FF sensors
have more pixels, thus the per-pixel noise is higher, but the
total image noise is the same. So, the FF sensor gives a more
noisy, but more detailed, picture.

Not true. It depends on the camera.

Again, I just thought that was kind of obvious that I was talking
about sensors of the same design and generation.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my
photos. If you wish to use any of my photos for any purpose other
than editing in these forums, please ask.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[Amin Sabet]

Am I correct in assuming, that a 20D, due to it's 1.6x crop factor,
actually uses "less" of the lens' glass...

No.

and therefore does not
"see" deteriorating edge IQ?

You meant less of an image's image circle above. Every pixel looks
at the scene through the entire lens aperture.

Less of an image circle does use less of the glass despite looking through the entire aperture. If that's not true, please explain.

 

[Amin Sabet]

Am I correct in assuming, that a 20D, due to it's 1.6x crop factor,
actually uses "less" of the lens' glass and therefore does not
"see" deteriorating edge IQ?
--
Flemming

Flemming, regardless of what recent threads have said about crop vs full frame, and regardless of whether the exact terms you are using are correct per Lee, there are a couple things that should be clarified. First, lens performance often tends to suffer in multiple respects with further distance from the center of the lens. Hence all MTF curves show performance relative to this distance. Second, when utilizing full frame lenses on crop bodies, most professional reviewers note that the crop lenses enjoy a "sweet spot" effect by not using the parts of the lens which are most distant from the center. Lee and Joe are challenging these widely held notions, and have provided some limited evidence for their point of view, but by no means have either of them proven that full frame IQ does not suffer on the edges more often than crop. The reverse has also not been proven, but it is a more widely held belief.

--
http://aminphoto.blogspot.com

 

[joe mama]

Eugene, obviously, I am talking about sensors of the same design
and generation. I mean, the new 1DIII has less noise than the 5D
sensor as well. It's a new generation of sensor.

Likewise, FF has even more than a 1 1/3 stop noise advantage
compared to Nikon sensors, and more than a 2 stop advantage
compared to Olympus sensors. That's a whole other argument.

Let's keep this argument separate for now. Jury is still out. I for
one think and observed that 1D3 does not have less noise it's just
masked better.

With pleasure. I actually don't have any evidence about the noise performance of the Canon sensors vs other brands or the new 1DIII sensor.

Not "not true". : ) If you shoot f / 2.8, ISO 100 on 1.6x and I
shoot f / 4.5, ISO 250 on FF, we will get the same shutter speed
and exposure.

True but it is also true for FF camera not just crop camera. If you
stop down any camera you need to decrease shutter speed or increase
ISO.
Your mistake is that you did not explain that you are only trying
to match DOF between the two cameras. Once that is understood
everything falls in to place. It is pretty basic.

In fact, I did explain it further up in this thread:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23300792

I'll quote the relevant passage:

To get an equivalent image, we up the f-ratio by a factor of 1.6
(1 1/3 stops) to get the same aperture, anc consequently, same
DOF, and same total light. However, that light is spread over 2.56
times as much area, so the intensity of that light is 2.56 times less.
Thus, you must up the ISO by a factor of 2.56 to get the same
exposure (or, alternatively, reduce the shutter speed by a factor of
1.6, or some equivalent comination of ISO and shutter speed).

I also said it in this post (in this thread) as well:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23293680

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[Eugene Powers]

The claim is simple. An example is, a 50mm f2.8 lens on a 1.6 crop
camera will behave the same as an 80mm f4.5 lens would on a
full-frame camera. These are both hypothetical lenses and we're
equating their performance in terms of image quality (noise),
depth-of-field, diffraction, and exposure. Now, exposure includes
ISO, and the larger sensor camera will need to run at a higher ISO,
say, 1000 on full-frame versus 400 on 1.6 crop.

I have to disagree here. If you are trying to match DOF between the two cameras you are correct but if not these two lenses don't behave the same. At F4.5 regardless of the focal length you will get little less than twice the amount of light regardless of the camera.

It's no accident that a 50mm f2.8 lens and an 80mm f4.5 lens have
the same physical aperture (50/2.8 = 80/4.5 = 18mm). Since they
have the same angle of view on their respective cameras, and since
they have the same physical aperture, they are providing their
respective sensors with the same image. The larger sensor's image
is larger, and therefore the light is more spread out (less
"intense") but the final result is still a match in terms of noise,
DOF, and diffraction, and you get the same shutter speed with each
system.

Again, only if you are trying to match DOF otherwise not true.

Take 24-105 F4 lens for example. I don't care which camera you will put it on. Set AV mode at F4 and you might get 1/1000 but if you set it at F5.6 you will get 1/500. Again, regardless of the camera. The only difference would be DOF of 1.6 crop camera and FF. Noise is not really relevant here because you might have noiseless camera at low ISO, diffraction is not relevant here because at large apertures you can't really measure or see it with naked eyes.

Now let me explain what I mean is the difference between quantity and intensity.
Imagine square container of 100 sq. inches filled with water 1 inch high.
Imagine another container of 50 sq. inches filled with water 1 inch high.

Now, 100 sq. inch container will have more water in it but pressure per sq. inch is the same as 50 sq. inch container.
So volume is equal to quantity and pressure is equal to intensity.

So, 1.6 crop, 50mm, f2.8, 1/60th, ISO 400 = full-frame, 80mm, f4.5,
1/60th ISO 1000.

And so is FF 80mm F4.5 1/120 ISO 2000 and FF 80mm F6.3 1/60 ISO 2000 and I can go on and on.

Yes, for matching DOF only on crop and FF cameras. Otherwise pointless argument.

--
Lee Jay
(see profile for equipment)

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[Eugene Powers]

but it got broken in to so many pieces that people got confused eventually.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[joe mama]

The claim is simple. An example is, a 50mm f2.8 lens on a 1.6 crop
camera will behave the same as an 80mm f4.5 lens would on a
full-frame camera. These are both hypothetical lenses and we're
equating their performance in terms of image quality (noise),
depth-of-field, diffraction, and exposure. Now, exposure includes
ISO, and the larger sensor camera will need to run at a higher ISO,
say, 1000 on full-frame versus 400 on 1.6 crop.

I have to disagree here. If you are trying to match DOF between the
two cameras you are correct but if not these two lenses don't
behave the same. At F4.5 regardless of the focal length you will
get little less than twice the amount of light regardless of the
camera.

I'm not sure where you're disagreeing with Lee. What you and he said is both correct.

Yes, for matching DOF only on crop and FF cameras. Otherwise
pointless argument.

Again, I'm unclear on what you are saying. Not just for DOF, but for everything. 50mm, f / 2.8, ISO 100 on 1.6x produces the exact same image as 80mm, f / 4.5, ISO 250 on FF. Same FOV, same exposure, same shutter speed, same DOF, and, for the same output size, the same noise.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[joe mama]

but it got broken in to so many pieces that people got confused
eventually.

The second link I gave you:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23293680

was only my second first post in this thread and pretty darned near the top!

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[Eugene Powers]

Are you saying that crop factor camera "sees" all of the glass in the lens including corners?
The answer could be only Yes or No.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[joe mama]

Second, when utilizing full frame lenses on crop bodies,
most professional reviewers note that the crop lenses enjoy a
"sweet spot" effect by not using the parts of the lens which are
most distant from the center.

Actually, the whole of the optics are used, but I, myself, am unclear of the specifics, so I'll let Lee Jay answer that.

Lee and Joe are challenging these widely held notions, and have
provided some limited evidence for their point of view, but by no means
have either of them proven that full frame IQ does not suffer on the
edges more often than crop.

No one denies that FF does not suffer on the edges, but certainly no more so than cropped cameras do. The evidence is pretty overwhelming:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

The reverse has also not been proven, but it is a more widely held belief.

Yes, it is. A lot of widely held beliefs are wrong. A large part of the reason that people have this particular wrong belief is that, while people have gotten accostumed to the idea of multiplying the FL by 1.6 to get an equivalent image on FF, they fail to realize that they must also multiply the f-ratio by 1.6 as well.

Thus, people have been comparing FF edges with cropped edges at the same f-ratio. That's as silly as using the same FL and then comparing sharpness. Clearly, if one took a pic of an object at 100mm from the same position with both a FF and 1.6x camera, the 1.6x camera would most certainly have more detail. Likewise, the edges of a 1.6x camera will be sharper, and it will vignette less (if using FF glass), if the FF camera uses the same f-ratio.

People need to understand that, just as you use 1.6x the FL on FF as 1.6x, you also use 1.6x the f-ratio, and 2.56x the ISO. It is the failure to understand that key point that causes all the confusion.

That's the mission Lee Jay and I are on.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[Eugene Powers]

The claim is simple. An example is, a 50mm f2.8 lens on a 1.6 crop
camera will behave the same as an 80mm f4.5 lens would on a
full-frame camera. These are both hypothetical lenses and we're
equating their performance in terms of image quality (noise),
depth-of-field, diffraction, and exposure. Now, exposure includes
ISO, and the larger sensor camera will need to run at a higher ISO,
say, 1000 on full-frame versus 400 on 1.6 crop.

I have to disagree here. If you are trying to match DOF between the
two cameras you are correct but if not these two lenses don't
behave the same. At F4.5 regardless of the focal length you will
get little less than twice the amount of light regardless of the
camera.

I'm not sure where you're disagreeing with Lee. What you and he
said is both correct.

Yes, for matching DOF only on crop and FF cameras. Otherwise
pointless argument.

Again, I'm unclear on what you are saying. Not just for DOF, but
for everything. 50mm, f / 2.8, ISO 100 on 1.6x produces the exact
same image as 80mm, f / 4.5, ISO 250 on FF. Same FOV, same
exposure, same shutter speed, same DOF, and, for the same output
size, the same noise.

Let's make it clear.

Yes, above statement is correct as long as you include DOF. If you don't include DOF there are many more combinations of shutter speed/aperture to get the same results.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my
photos. If you wish to use any of my photos for any purpose other
than editing in these forums, please ask.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[Amin Sabet]

No one denies that FF does not suffer on the edges, but certainly
no more so than cropped cameras do. The evidence is pretty
overwhelming:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

Joe, I don't think those data are that overwhelming, and the widely held beliefs I cited are widely expressed by a number of experts, not just yahoos like me. Also, I would not expect a sweet spot effect, if such a thing exists, to be evident when using an EFS lens. Please note that I am not challenging you or Lee, and I am a believer lens equivalence as you define it. I also find that full frame has pretty much made all my lenses better for one reason or another, I am simply pointing out that when you go up against widely held expert opinion, the burden of proof is on you.

--
http://aminphoto.blogspot.com

 

[joe mama]

Again, I'm unclear on what you are saying. Not just for DOF, but
for everything. 50mm, f / 2.8, ISO 100 on 1.6x produces the exact
same image as 80mm, f / 4.5, ISO 250 on FF. Same FOV, same
exposure, same shutter speed, same DOF, and, for the same output
size, the same noise.

Let's make it clear.
Yes, above statement is correct as long as you include DOF. If you
don't include DOF there are many more combinations of shutter
speed/aperture to get the same results.

Perfect. We are on the same sheet! : )

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[joe mama]

No one denies that FF does not suffer on the edges, but certainly
no more so than cropped cameras do. The evidence is pretty
overwhelming:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

Joe, I don't think those data are that overwhelming, and the widely
held beliefs I cited are widely expressed by a number of experts,
not just yahoos like me.

Check this out:

http://www.naturfotograf.com/D2X_rev06.html

Most certainly not by a "yahoo", yet he does not take DOF equivalent pics. On the other hand, he is aware of this issue:

"The depth of field (DOF) is significantly different, as indeed should be the case since the 200 mm lens has less image magnification. The foreground of the test scene shows this clearly. We cannot compare image qualities here due to this fact, it wouldn't be fair."

So, people look at the pics, at the same f-ratio, and make erroneous conclusions. It's because the "experts" never compared different formats at equivalent f-ratios that these misunderstandings take place.

Also, I would not expect a sweet spot effect, if such a thing exists, to
be evident when using an EFS lens.

Absolutely correct, except that some cropped glass may cast a considerably larger image circle relative to the sensor than does FF glass. For example, the 60 / 2.8 macro works on the 5D with extension tubes.

Please note that I am not challenging you or Lee, and I am a
believer lens equivalence as you define it. I also find that full
frame has pretty much made all my lenses better for one reason or
another, I am simply pointing out that when you go up against
widely held expert opinion, the burden of proof is on you.

I completely accept that fact. I no more expect people to merely take my word, than I will take the word of others. That's why I explain the theory, work the math, and post the pics.

If you'll recall, Galileo was put under house arrest for saying that the Earth was not in the Center of the Universe. Fortunately, my difficulties are somewhat less. : )

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.

 

[Eugene Powers]

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

Not only it is a bad test but total waste of time because he used two totally different lenses.

The truth is that crop sensor does not see all of the glass in the last element of the lens.

There was thread here few months ago about why crop factor lenses could not be made much smaller than FF lenses in which I was involved but I can't find it now. It should explain why.

The reverse has also not been proven, but it is a more widely held belief.

Yes, it is. A lot of widely held beliefs are wrong. A large part
of the reason that people have this particular wrong belief is
that, while people have gotten accostumed to the idea of
multiplying the FL by 1.6 to get an equivalent image on FF, they
fail to realize that they must also multiply the f-ratio by 1.6 as
well.

Thus, people have been comparing FF edges with cropped edges at the
same f-ratio. That's as silly as using the same FL and then
comparing sharpness. Clearly, if one took a pic of an object at
100mm from the same position with both a FF and 1.6x camera, the
1.6x camera would most certainly have more detail. Likewise, the
edges of a 1.6x camera will be sharper, and it will vignette less
(if using FF glass), if the FF camera uses the same f-ratio.

People need to understand that, just as you use 1.6x the FL on FF
as 1.6x, you also use 1.6x the f-ratio, and 2.56x the ISO. It is
the failure to understand that key point that causes all the
confusion.

That's the mission Lee Jay and I are on.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my
photos. If you wish to use any of my photos for any purpose other
than editing in these forums, please ask.

--
Eugene

The only time a smaller sensor with the same pixel count is superior to a larger sensor (aka higher pixel density) is when you are focal-length limited.

Lee Jay

 

[peteb]

At least as far as the front element goes.

http://forums.dpreview.com/forums/read.asp?forum=1032&message=21528198

In the above post I outline how it is obvious that the outer edge of a lens impacts the light at the center of the frame.

The point of a lens element is to capture as many photons as possible from an object and refract them back to a single point. If you didn't use the outside edge of an f2.8 lens to do this it wouldn't be an f2.8 lens any more. This should hold true for all the optices at least back as far as the aperture blades. the f-stop of a lens is fixes regardless of the size of the image circle. It is a function of the focal length and aperture size ratio. Since no 2 properties are being affected, neither can the third.

Second, when utilizing full frame lenses on crop bodies,
most professional reviewers note that the crop lenses enjoy a
"sweet spot" effect by not using the parts of the lens which are
most distant from the center.

Actually, the whole of the optics are used, but I, myself, am
unclear of the specifics, so I'll let Lee Jay answer that.

Lee and Joe are challenging these widely held notions, and have
provided some limited evidence for their point of view, but by no means
have either of them proven that full frame IQ does not suffer on the
edges more often than crop.

No one denies that FF does not suffer on the edges, but certainly
no more so than cropped cameras do. The evidence is pretty
overwhelming:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23296470

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23297008

http://forums.dpreview.com/forums/read.asp?forum=1029&message=23301485

I mean, that's pretty hard core evidence to the contrary.

The reverse has also not been proven, but it is a more widely held belief.

Yes, it is. A lot of widely held beliefs are wrong. A large part
of the reason that people have this particular wrong belief is
that, while people have gotten accostumed to the idea of
multiplying the FL by 1.6 to get an equivalent image on FF, they
fail to realize that they must also multiply the f-ratio by 1.6 as
well.

Thus, people have been comparing FF edges with cropped edges at the
same f-ratio. That's as silly as using the same FL and then
comparing sharpness. Clearly, if one took a pic of an object at
100mm from the same position with both a FF and 1.6x camera, the
1.6x camera would most certainly have more detail. Likewise, the
edges of a 1.6x camera will be sharper, and it will vignette less
(if using FF glass), if the FF camera uses the same f-ratio.

People need to understand that, just as you use 1.6x the FL on FF
as 1.6x, you also use 1.6x the f-ratio, and 2.56x the ISO. It is
the failure to understand that key point that causes all the
confusion.

That's the mission Lee Jay and I are on.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my
photos. If you wish to use any of my photos for any purpose other
than editing in these forums, please ask.

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