Thats not what I see leh... The lens is still the same lens with the same angle. Using 50mm on a 1.6x isn't going to give u the same background as the 85mm on a FF. Maybe you should try it out...?
Thats also the reason why for us Canon users the 50/1.2L on the 40D is not going to give you the same result as the 85/1.2L on the 5D i think?
What I want to say is that the 1.6x isn't actually the same as using an multiplier extender (which is why your aperture doesn't drop...) Its simply to make it easier for us to see what kind of FOV we'll get. Perspective however remains the same, depending on the lens. Using a 85 on a 1.6 and a FF will give you the same background distortion (bokeh). The sensor just can't take in as much so it CROPS the centre part out.
Aiyo... this damn thing confuses all the time...
I don't quite get you when you say "The lens is still the same lens with the same angle".
Field of view (FOV) is the result of not only lens but also sensor size. So what you can see (i.e. included) in the background depends on the focal length, sensor size and of course, your shooting distance.
A picture speaks a thousand words :
If a person has 3 cameras : a FF (e.g. Canon 5D) with 80mm, a 1.6x crop camera (e.g. Canon 40D) with 50mm and a compact camera at about 14mm and then shoot the same subject from the same position with the 3 cameras, he will end up with the same picture with the same composition and perspective. The FOV on the 3 cameras will be the same and therefore whatever is included in the background will be the same.
The above answers threadstarter's question. When you're shooting with 50mm on the Nikon D80, your focal length is still 50mm but because the image sensor is smaller than a FF, the field of view is the same with 75mm on a FF and, for the Canon 40D, the FOV is the same as 80mm on FF.
As said in the earlier post, what is included in the background will be the same for 35mm on FF, 22mm on 1.6x crop factor camera and about 6mm on a compact camera because all have the same 35mm equivalent field of view.
Canon users with the 50/1.2L on the 40D will get a slightly wider FOV than the 85/1.2L on the 5D because 50mm on the 40D has the same FOV as 80mm on the 5D. If 80mm is used on the 85/1.2L for 5D, then the FOV (foreground and background) will be the same as 50mm on the 40D. This are of course differences in Depth of Field and Bokeh as a result of the combination of actual focal length, sensor size and lens construction.
Using an extender (i.e. teleconverter) of course will result in a narrower FOV, resulting in less in the background seen because when you add an extender on a camera, the focal length is increased without any change in the sensor size but a longer focal length has a narrower lens angle of view. (Just sidetracking, the decrease in aperture F number when adding an extender is because F number is the diaphragm size divided by the focal length and so when focal length is increased with an extender without any change in diaphragm, the F number becomes larger in the denominator ……e.g. F/4 becomes 1/(4x2) =F/8 when a 2x extender is added. This is related to light lost for exposure as focal length becomes longer and it’s a little complicated but suffice to say that the total amount of light going into the lens is decreased proportionally but the diaphragm is unchanged as the FOV becomes narrower and the less light coming in through the lens get spreaded onto the same sensor surface area such that when a 2x converter is used, what was originally F/4 exposure becomes equivalent to an F/8 exposure).
Again a picture speaks a thousand words (for e.g. focal length is increased from 50mm to 80mm either with a longer lens or by a 1.6x teleconverter (assuming there is one although the norm is 1.4x and 2x):
In contrast, when the focal length is increased from 50mm to 80mm and the sensor size changes from a 1.6x crop factor to a FF, then narrower angle of a longer focal length lens will be exactly offset by the wider angle in the sensor larger by the same 1.6x factor and thus, the FOV remains the same.
In summary, 80mm on FF (e.g. Canon 5D) will be the same as 50mm on a 1.6x crop factor camera (e.g. Canon 40D) as far as foreground and background are concerned as long as they're shot from the same position to have the same picture and composition. Indirectly, it also means 80mm on the 5D has a wider FOV than 80mm on the Canon 40D and therefore more can be seen not only in the background but also foreground if shot from same position since the Canon 5D has a larger image sensor or just more in the background if standing nearer by a factor of 1.6x so that the foreground is the same with 80mm on the Canon 40D. 80mm on the Canon 40D afterall has a narrower FOV equivalent to 80x1.6 = 128m on the 35mm format on the FF.
Perspective in strict photographer terms means how relative distances and sizes are rendered in the picture and it is entirely determined by shooting distance and contrary to popular belief, not affected by focal length or sensor size. As I have said in my earlier post, it has to do with magnification factor.
If one object is 2m behind another and you shoot from 5m away,
If you use 50mm, your magnfication factors will be :
1st object which is 5m away : 50mm/5m = 50/50,000 = 1/1000
2nd object which is 7m away : 50mm/7m = 50/70,000 = 1/1400
So 1/1000 vs 1/1400 is 1400 : 1000 = 7 : 5
= 1.4 : 1 relative magnification size ratio
If you use 200mm, your magnificator factors will be :
1st object which is 5m away : 200mm/5m = 200/50,000 = 1/250
2nd object which is 7m away : 200mm/7m = 200/70,000 = 1/350
1/250 : 1/350 = 3.5 : 2.5 = &:5
= 1.4 : 1 (Same as earlier with 50mm lens.)
So if you shoot from the same position, the relative sizes of things in the picture will always be the same regardless of what focal length you use. So the perspective is the same for different focal length as long as the shooting distance is the same. The difference is only in the FOV (i.e. what is included or excluded in the foreground and background). Again, Bokeh and DOF are separate issues.
The confusion in perspective comes about because people stand at different distances with different focal lengths. Usually, longer focal length is used at much further shooting distance and as a result, distances seem to be compressed as relative size differences become less pronounced. This is caused by the further distance and, contrary to popular misconcepton, not by the focal length. Again, this can be shown mathematically :
Now instead of standing at 5m away in the earlier example, now stand at 10m away.
1st object which is 10m away : 50mm/10m = 50/100,000 = 1/2000
2nd object which is 12m away : 50mm/12m = 50/120,000 = 1/2400
So 1/2000 vs 1/2400 is 2400 : 2000 = 1.2 : 1 relative magnification size ratio
And the 2nd object is now bigger relative to the 1st object than when shooting at 5m away and therefore distance appears compressed. This can be easily seen that 2m difference as a % of 5m is greater than 2m difference as a % of 10m.
If the above object 1 and 2 are the same size, then the 2nd object will appear 1/1.4 = 0.71x the size of the 1st object for the first picture at 5m away. But when shot from 10m away, the 2nd object will apppear to be 1/1.2 = 0.83x the size of the 1st object. Of course in absolute terms, the 2 objects will appear smaller in the 2nd picture at 10m away than the 1st picture at 5m away.
If you stand very very far away such as 500m away, then the ratio would become almost 1:1 and the 2m distance difference between the 2 objects would appear almost nothing in the picture and they look like they're just next to each other and if they're same real physical size, then will appear the same size in the picture. This is true even if you use a ultra wide angle lens such as 12mm. That is why very distant objects appear next to each other in many landscape pictures even though the focal lengths used are very short while the distance in the foreground which is very near becomes very exaggerated.
To see that perspective is the same at 10m away for a 200mm lens and a 50mm lens :
If you use 200mm, your magnification factors will be :
1st object which is 10m away : 200mm/10m = 200/100,000 = 1/500
2nd object which is 7m away : 200mm/12m = 200/120,000 = 1/600
1/500 : 1/600 = 1.2 : 1
Same as earlier with 50mm lens. So perspective is the same again with different focal lengths as long as it's shot from the same distance (10m in this case).
The LCD displays the entire shot captured, including that 0.05x bit of extra image that u cannot see thru the viewfinder.
