In reading reviews of the 5D, I understand it is much brighter than the 20D due to the full-frame sensor configuration. However, I've heard one drawback is the magnification factor is much less than the 20D (~75% vs. ~95%). I may be wrong with the exact figure because I'm going from memory, but I know it was a significant difference.
My question is - What exactly is 'magnification factor' with regards to a viewfinder? I know this is not speaking to the amount of the image seen in the viewfinder vs. recorded on the sensor. What, then, does it mean exactly?
Dblais wrote:
In reading reviews of the 5D, I understand it is much brighter than the 20D due to the full-frame sensor configuration. However, I've heard one drawback is the magnification factor is much less than the 20D (~75% vs. ~95%). I may be wrong with the exact figure because I'm going from memory, but I know it was a significant difference.
My question is - What exactly is 'magnification factor' with regards to a viewfinder? I know this is not speaking to the amount of the image seen in the viewfinder vs. recorded on the sensor. What, then, does it mean exactly?
The magnification is a comparison of the way we see things through the viewfinder and in real life on A NORMAL LENS.
A magnification of 1:1 means that the scene seen through a viewfinder is equal to that in real life for a 50 mm lens (we should use a 42 mm lens = length of diaginal of sensor/film, but these are not that widely available, so we use a 50 mm lens, which is a common focal lengt). When you look with your left eye through the viewfinder with a 50 mm lens attached, you see everything at the same scale as with your right eye looking at the scene itself.
The 5 D has a 70% magnification, so everything is shown 30% smaller than in real life using a 50 mm lens.
On the 20D, canon (as all other manufacturers) still uses a 50 mm lens for the measurement, which is incorrect, the 50 mm is not a normal lens, it is a telelens. Canon should use a 28 or a 35 mm lens for the calculations... If you take this into account, the real magnification of the 5D is about 56%,...
Yes, the 5D views 96% of the the 24m x 36mm frame and a magnification of 0.71x.
The viewfinder of an SLR needs to be able to show not only the focus screen, but also the electronic display of information such as speed, apeture, flash status, exposure compensation, etc. In order to keep the prism assembly smaller yet still be able to display all this 'stuff', the magnfication of the viewfinder is smaller than full size.
Since the 20D focusing screen is smaller, it can cram the data display into the viewfinder and preserve a higher magnification level in the finder.
Flappie - For you and other 5D owners, do you consider this smaller magnification an issue? Does it bother you at all? My thought would be that you would get used to it and eventually not even notice it.
Assuming you frame your pictures the same using the 2 different cameras, using different length lenses, say a 100mm on the 20d and a 160mm on the 5d. The image would still be bigger in the viewfinder of the 5d than the 20d.
So I would say ... the magnification factor is irrevelant. Viewfinder size is what matters.
Fluffy wrote:
Assuming you frame your pictures the same using the 2 different cameras, using different length lenses, say a 100mm on the 20d and a 160mm on the 5d. The image would still be bigger in the viewfinder of the 5d than the 20d.
So I would say ... the magnification factor is irrevelant. Viewfinder size is what matters.
It is absolutely not irrelevant, because size and magnification are related. For a same angle of view (eg 50 mm on 20D and 85 mm on 5D, the 5D will have a 25% bigger magnification), that's the only that is important.
And yes, for me it is important, the bigger the magnification, the more you are capable of judging the focus or intervene with MF (very important for macro work)
Flappie wrote:
On the 20D, canon (as all other manufacturers) still uses a 50 mm lens for the measurement, which is incorrect, the 50 mm is not a normal lens, it is a telelens. Canon should use a 28 or a 35 mm lens for the calculations... If you take this into account, the real magnification of the 5D is about 56%,...
5D: 36mm frame width x 0.96 area viewed x 0.71 magnification = 24.5mm apparent focusing screen width
20D: 22mm x 0.95 x 0.9 = 18.8 mm apparent focusing screen width
20D focus screen is 77% of linear measurement of 5D, and 62% of the area measurement of the 5D. BOTH focusing screen size and apparent magnification are important in the viewfinder!
