04-06-2012, 09:14 AM
(This post was last modified: 04-06-2012, 09:17 AM by Brightcolours.)
[quote name='Plochmann' timestamp='1333691598' post='17341']
I'm writing this in response to a trollish comment on another site's forum. The post was on the announced Voigtlander 17 0.95. Though many Mft users are happy with the prospect of owning one, someone made the comment that the f-stop was only so fast because the puny sensor is so small that it needs less light. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/huh.gif' class='bbc_emoticon' alt='
' /> I think an f-stop is just an f-stop and sensor sizes are not part of the equation. But maybe I'm wrong. Can 4/3 lenses be faster because the imaging circle is smaller and therefore more focused? But then why aren't point and shoot cameras ridiculously fast? And then we have really fast ff lenses. But I can't think of any super fast medium format lenses. And I also notice that rangefinder lenses tend to be faster, does the shorter flange depth help with this f-stop equation? Any experts?
[/quote]
I do not understand how you can write a response to a to us unknown comment. Why not post a link to the "comment", so we can see you interpret it right?
4/3rds lenses can NOT be smaller because they are "more focussed", that is just nonsense. They can just be smaller because of the small imager circle. What is so hard to understand about that, though?
Now lets look at the lens in question. It is a 17mm f0.95 lens, according to the manufacturer. If one were to make a 17mm f0.95 lens for for instance 135 format, the image circle would have to be MUCH bigger. In case of such a wide angle lens, it is not a question of just making it 2x as big, as on 4/3rds it is not very wide angle at all. So... the only reason that 17mm f0.95 is possible for the money and size is indeed because of the small sensor of 4/3rds, and no other reason.
Now what does 17mm f0.95 mean? It means the lens gives (on 4/3rds) a similar field of view as a 34mm lens on 135 format, also known as "full frame" 35mm. It also means that the aperture is 17 / 0.95 = 17.9 mm. A 34mm lens with the same aperture will have a f-value (focal length / aperture ration) of: f1.9
Not very impressive, is it? Simply put: a 17mm f0.95 lens is equivalent to a 35mm f2 or f1.8 lens on full frame.
Simply put: it is easy to make a short focal length lens for 4/3rds with big focal length / aperture ratio, because on 4/3rds 17mm is not very wide angle at all. It crops so much that the image circle is very small, and the glass elements design and manufacturing is relatively cheap. It is all about the view angle captured by the sensor/film.
An f-value is an f-value. Is an f-value. Sure. However, an angle of view is not an angle of view. F-values ONLY say something about the ratio between focal length and aperture. They mean nothing more to us, the photographer. What does matter to us:
The angle of view
The size of aperture (which determines the depth of focus)
And maybe, just maybe, the amount of light reaching the sensor.
In all 3 points above, the 17mm f0.95 is equivalent to a 35mm f2 lens on FF. Or a 24mm f1.4 lens on APS-C. 35mm f2 lenses (135 format) and smaller and lighter than the voigtlander 17mm f0.95, though.
For 135 format (FF) there are also 35mm f1.4 lenses. An equivalent for 4/3rds or mft would have to be a 17mm f0.75 lens.
You also state that range finder lenses tend to be faster? I have no idea where you got that from. Which range finder lenses are so fast that there are no SLR equivalents for? The fastest I know is the very expensive Leica 50mm f1 and f0.95. For SLRs there are the Canon 50mm f1's..... I have not heard about a range finder 85mm f1.2, nor a 200mm f1.8...
Another point: there ARE compact digital cameras with very fast f-ratios. Only possible because of their super tiny sensors.
I'm writing this in response to a trollish comment on another site's forum. The post was on the announced Voigtlander 17 0.95. Though many Mft users are happy with the prospect of owning one, someone made the comment that the f-stop was only so fast because the puny sensor is so small that it needs less light. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/huh.gif' class='bbc_emoticon' alt='
' /> I think an f-stop is just an f-stop and sensor sizes are not part of the equation. But maybe I'm wrong. Can 4/3 lenses be faster because the imaging circle is smaller and therefore more focused? But then why aren't point and shoot cameras ridiculously fast? And then we have really fast ff lenses. But I can't think of any super fast medium format lenses. And I also notice that rangefinder lenses tend to be faster, does the shorter flange depth help with this f-stop equation? Any experts?[/quote]
I do not understand how you can write a response to a to us unknown comment. Why not post a link to the "comment", so we can see you interpret it right?
4/3rds lenses can NOT be smaller because they are "more focussed", that is just nonsense. They can just be smaller because of the small imager circle. What is so hard to understand about that, though?
Now lets look at the lens in question. It is a 17mm f0.95 lens, according to the manufacturer. If one were to make a 17mm f0.95 lens for for instance 135 format, the image circle would have to be MUCH bigger. In case of such a wide angle lens, it is not a question of just making it 2x as big, as on 4/3rds it is not very wide angle at all. So... the only reason that 17mm f0.95 is possible for the money and size is indeed because of the small sensor of 4/3rds, and no other reason.
Now what does 17mm f0.95 mean? It means the lens gives (on 4/3rds) a similar field of view as a 34mm lens on 135 format, also known as "full frame" 35mm. It also means that the aperture is 17 / 0.95 = 17.9 mm. A 34mm lens with the same aperture will have a f-value (focal length / aperture ration) of: f1.9
Not very impressive, is it? Simply put: a 17mm f0.95 lens is equivalent to a 35mm f2 or f1.8 lens on full frame.
Simply put: it is easy to make a short focal length lens for 4/3rds with big focal length / aperture ratio, because on 4/3rds 17mm is not very wide angle at all. It crops so much that the image circle is very small, and the glass elements design and manufacturing is relatively cheap. It is all about the view angle captured by the sensor/film.
An f-value is an f-value. Is an f-value. Sure. However, an angle of view is not an angle of view. F-values ONLY say something about the ratio between focal length and aperture. They mean nothing more to us, the photographer. What does matter to us:
The angle of view
The size of aperture (which determines the depth of focus)
And maybe, just maybe, the amount of light reaching the sensor.
In all 3 points above, the 17mm f0.95 is equivalent to a 35mm f2 lens on FF. Or a 24mm f1.4 lens on APS-C. 35mm f2 lenses (135 format) and smaller and lighter than the voigtlander 17mm f0.95, though.
For 135 format (FF) there are also 35mm f1.4 lenses. An equivalent for 4/3rds or mft would have to be a 17mm f0.75 lens.
You also state that range finder lenses tend to be faster? I have no idea where you got that from. Which range finder lenses are so fast that there are no SLR equivalents for? The fastest I know is the very expensive Leica 50mm f1 and f0.95. For SLRs there are the Canon 50mm f1's..... I have not heard about a range finder 85mm f1.2, nor a 200mm f1.8...
Another point: there ARE compact digital cameras with very fast f-ratios. Only possible because of their super tiny sensors.