02-18-2011, 12:42 PM
[quote name='ThomasD' timestamp='1298028831' post='6217']
Well, I was thinking in terms of EV, where the f-stop is independent of the size of sensor you project the image on. Considering that the light is distributed over a larger area on FF changes the picture of course.
[/quote]
That is not totally correct either (if I understand your sentence correctly). The sensor for each camera spread the light over 1 image each. The FF sensor collects way more light per image. And the hole in the FF lens is a lot bigger, more light passes through with the same f-stop.
You can not look at things in terms of f-values, when you want to understand equivalences. Because, simply, with a smaller sensor light gets cropped off the sides, making the captured light "field of view" more narrow (by crop factor), you have to start looking at the lenses as equivalents by crop factor. And then the f-value changes.
Lets just take a 50mm f2 lens as easy example.
On FF, it has the field of view of 50mm.
It has an f-value of f2.
This means, it has an aperture of: 50/2= 25mm (that is what the f-value really means: focal length / aperture).
On APS-C, a smaller field of view gets captured. The aperture does not change.
Equivalent focal length (field of view) to FF: 50 / 1.5 = 33.33mm
Equivalent f-value to FF: 50mm / 33.33 = f1.5
As you see, with the same light "amount" (same hole size, same field of view captured), the f-value changes.
A hard thing to grasp for many Olympus forums, for some strange reason.
But, you may wonder, how come the exposure times then remain the same? That is because the ISO is messing things up. ISO says NOTHING about sensor sensitivity, it only says that if you use two different sensors, with probably very different sensitivities, the photographer gets roughly the same exposure time with the same f-value and an equivalent focal length. This is done by applying very specific amplification per sensor.
[quote name='ThomasD' timestamp='1298028831' post='6217']
Surely. Looking at all these non-L primes, one may well get to the point where a FF investment becomes cheaper than APS-C. That is, however, also true for Nikon, although Canon has a slightly wider choice of primes.
Any opinions about Canon's 28/1.8, btw? Reviews seem to indicate that one should better avoid that lens.
[/quote]
Measurements of that lens often show it not to be great (like on photozone), but users often praise that lens. There is a (strange?) difference between Nikon and Canon users on forums... Canon users usually are very critical about lenses, where Nikon users tend praise lenses regardless of how good they actually are. This says nothing about the quality of the lenses, just more about a strange culture difference. Since Canon users often praise that lens (28mm f1.8), it might actually be a nice photographic tool. Just know and understand its limits.
For this lens, I think fredmiranda.com is actually very informative:
http://www.fredmiranda.com/reviews/showp...t=2&page=2
And of course pixel peeper:
http://www.pixel-peeper.com/adv/?lens=37...none&res=3
Well, I was thinking in terms of EV, where the f-stop is independent of the size of sensor you project the image on. Considering that the light is distributed over a larger area on FF changes the picture of course.
[/quote]
That is not totally correct either (if I understand your sentence correctly). The sensor for each camera spread the light over 1 image each. The FF sensor collects way more light per image. And the hole in the FF lens is a lot bigger, more light passes through with the same f-stop.
You can not look at things in terms of f-values, when you want to understand equivalences. Because, simply, with a smaller sensor light gets cropped off the sides, making the captured light "field of view" more narrow (by crop factor), you have to start looking at the lenses as equivalents by crop factor. And then the f-value changes.
Lets just take a 50mm f2 lens as easy example.
On FF, it has the field of view of 50mm.
It has an f-value of f2.
This means, it has an aperture of: 50/2= 25mm (that is what the f-value really means: focal length / aperture).
On APS-C, a smaller field of view gets captured. The aperture does not change.
Equivalent focal length (field of view) to FF: 50 / 1.5 = 33.33mm
Equivalent f-value to FF: 50mm / 33.33 = f1.5
As you see, with the same light "amount" (same hole size, same field of view captured), the f-value changes.
A hard thing to grasp for many Olympus forums, for some strange reason.
But, you may wonder, how come the exposure times then remain the same? That is because the ISO is messing things up. ISO says NOTHING about sensor sensitivity, it only says that if you use two different sensors, with probably very different sensitivities, the photographer gets roughly the same exposure time with the same f-value and an equivalent focal length. This is done by applying very specific amplification per sensor.
[quote name='ThomasD' timestamp='1298028831' post='6217']
Surely. Looking at all these non-L primes, one may well get to the point where a FF investment becomes cheaper than APS-C. That is, however, also true for Nikon, although Canon has a slightly wider choice of primes.
Any opinions about Canon's 28/1.8, btw? Reviews seem to indicate that one should better avoid that lens.
[/quote]
Measurements of that lens often show it not to be great (like on photozone), but users often praise that lens. There is a (strange?) difference between Nikon and Canon users on forums... Canon users usually are very critical about lenses, where Nikon users tend praise lenses regardless of how good they actually are. This says nothing about the quality of the lenses, just more about a strange culture difference. Since Canon users often praise that lens (28mm f1.8), it might actually be a nice photographic tool. Just know and understand its limits.
For this lens, I think fredmiranda.com is actually very informative:
http://www.fredmiranda.com/reviews/showp...t=2&page=2
And of course pixel peeper:
http://www.pixel-peeper.com/adv/?lens=37...none&res=3