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#22
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What is this weird hatred of different focal lengths?
wrote in message ... On Sun, 09 Sep 2012 15:46:48 -0800, (Floyd L. Davidson) wrote: wrote: On Sun, 9 Sep 2012 13:51:59 -0700 (PDT), RichA wrote: On Sep 9, 1:43 pm, David Dyer-Bennet wrote: "Trevor" writes: Which is all rather amusing when you consider the more serious photographers used an 85mm lens and a 35mm lens combination far more often than anything in the 40-70mm range. If anything a 58 mm lens was a little better for portraits than a 50mm one at least, even if not by much. A fast 50mm is a much better lens now on a non FF sensor DSLR however IMO. A 58mm is great on a 1.5X DSLR for portraits :-) But does it behave the same way as say an 85mm on a FF for the same subject matter? The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Unless of course you use the 85mm of a full frame sensor, in which case it has to bend the light rays *exactly* the same as a 56.7mm lens does on a APS-C sized sensor. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. Right, but those which are bent more with a 58mm FF lens are not part of an APSC sensor image, so become irrelevent. The comparison should only be made with an 85mm APSC lens on an APSC sensor of course, or an 85mm FF lens on a FF sensor. Trevor. |
#23
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What is this weird hatred of different focal lengths?
wrote in message ... On Mon, 10 Sep 2012 09:59:23 +1000, "Trevor" wrote: wrote in message . .. On Sun, 9 Sep 2012 13:51:59 -0700 (PDT), RichA wrote: On Sep 9, 1:43 pm, David Dyer-Bennet wrote: "Trevor" writes: Which is all rather amusing when you consider the more serious photographers used an 85mm lens and a 35mm lens combination far more often than anything in the 40-70mm range. If anything a 58 mm lens was a little better for portraits than a 50mm one at least, even if not by much. A fast 50mm is a much better lens now on a non FF sensor DSLR however IMO. A 58mm is great on a 1.5X DSLR for portraits :-) That was my point. But does it behave the same way as say an 85mm on a FF for the same subject matter? The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Since you are only using the centre part of the focus plane on a non FF sensor, the "bend" should be the same for the area used. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. You really need to specify which you are talking about, which are APSC lenses and which are FF lenses as the image circle and thus the "angle" the light is bent is different for both types of lenses at the same marked focal length. And for FF lenses only, the image area actually used is smaller on an APSC sensor, and thus the part which is "bent" the most is outside the sensor area and becomes irrelevent. Of course if you ignore all specifics, almost any statement can be claimed to be correct! :-) Trevor. |
#24
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What is this weird hatred of different focal lengths?
On Wed, 12 Sep 2012 14:30:30 +1000, "Trevor" wrote:
wrote in message .. . On Mon, 10 Sep 2012 09:59:23 +1000, "Trevor" wrote: wrote in message ... On Sun, 9 Sep 2012 13:51:59 -0700 (PDT), RichA wrote: On Sep 9, 1:43 pm, David Dyer-Bennet wrote: "Trevor" writes: Which is all rather amusing when you consider the more serious photographers used an 85mm lens and a 35mm lens combination far more often than anything in the 40-70mm range. If anything a 58 mm lens was a little better for portraits than a 50mm one at least, even if not by much. A fast 50mm is a much better lens now on a non FF sensor DSLR however IMO. A 58mm is great on a 1.5X DSLR for portraits :-) That was my point. But does it behave the same way as say an 85mm on a FF for the same subject matter? The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Since you are only using the centre part of the focus plane on a non FF sensor, the "bend" should be the same for the area used. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. You really need to specify which you are talking about, which are APSC lenses and which are FF lenses as the image circle and thus the "angle" the light is bent is different for both types of lenses at the same marked focal length. No Whether or not a lens is marked for FF or C sensors has nothing to do with it's actual focal length, if both lenses are marked 100mm that is what they both are, and they both bend the light the same amount. The difference is the size of the circle of light they project, which has to do with the size of the glass lens and construction, not it's FL. My D700 shows NO difference in images if I use a Digital 50mm or a FF 50mm lens, but the circle of light shows smaller with the dig. lens. If I set the crop factor to c type in the camera, it simply ignores the larger area, if I set it to FF then I capture the circle, complete with it's dark area for the D lens. The pictures are of course identical except for the 'blow up' effect if I crop to the c size, which is called the crop factor. I can also crop the FF lens and get the exact same picture as the D lens. And for FF lenses only, the image area actually used is smaller on an APSC sensor, and thus the part which is "bent" the most is outside the sensor area and becomes irrelevent. Again, the sensor has nothing to do with the amount of bending of the light. A smaller focal length lens bends the light to a smaller size image, and usually creates more distortion. If I draw a schematic of a lens system, and draw a line from the perimeter of the subject through the objective of a long lens to the target, I will get a shallow angle. Then I do the same thing for a short lens, I will get a steeper angle. (This is the only thing BTW I said concerned me in my first post.) Now we take two sensors of different sizes, and place them to gather the same image, a large sensor for the long lens and a small sensor for the short lens, the fact remains that the shorter lens bent the light more, the proof being that the same objective size fills the smaller sensor. |
#25
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What is this weird hatred of different focal lengths?
On Tue, 11 Sep 2012 16:38:51 -0800, (Floyd L. Davidson) wrote:
wrote: On Mon, 10 Sep 2012 20:04:27 -0800, (Floyd L. Davidson) wrote: The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Since you are only using the centre part of the focus plane on a non FF sensor, the "bend" should be the same for the area used. Trevor. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. Not to cover a smaller sensor it doesn't. You are wrong... the 58mm lens bends the light more to match the smaller size of the smaller sensor. http://www.pbase.com/flintstonestudi...me_things_work Your cited page does not confirm your claims. Yes it does. Please go to http://www.tawbaware.com/maxlyons/calc.htm where you can scroll down and find a calculator for "Angular Field of View". That is the angle at which the lens bends the light! No it ain't! That is the combination of the sensor size and the lens, that creates an image with a certain field or angle of view. These combinations have infinite variables. A short lens bends the light to a smaller size which can match the size of a smaller sensor, giving possibly the same image (angle of view) as a long lens which doesn't bend the light to such a small pattern and therefore covers a larger sensor. Set the focal length to 85mm and the crop factor to 1.0, which will give a horizontal angle of 23.9 degrees, a vertical angle of 16.1 degrees and a diagonal of 28.6 degrees. Now change the focal length to 56.667mm and the crop factor to 1.5. Same angles! You think that parallel light waves coming through 2 different FL lenses have the same angle of refraction?????? AND that they produce the same size images on DIFFERENT size sensors means the same thing????? Which means they would produce DIFFERENT size images on the SAME sensor, and that proves they are the SAME angle????? I think not. |
#26
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What is this weird hatred of different focal lengths?
wrote:
On Tue, 11 Sep 2012 16:38:51 -0800, (Floyd L. Davidson) wrote: wrote: On Mon, 10 Sep 2012 20:04:27 -0800, (Floyd L. Davidson) wrote: The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Since you are only using the centre part of the focus plane on a non FF sensor, the "bend" should be the same for the area used. Trevor. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. Not to cover a smaller sensor it doesn't. You are wrong... the 58mm lens bends the light more to match the smaller size of the smaller sensor. http://www.pbase.com/flintstonestudi...me_things_work Your cited page does not confirm your claims. Yes it does. Please go to http://www.tawbaware.com/maxlyons/calc.htm where you can scroll down and find a calculator for "Angular Field of View". That is the angle at which the lens bends the light! No it ain't! In fact, it is the maximum angle. It is the angle that the edges of a scene have to be bent at. Note that light rays from the center of a scene are not bent at all for rays going through the center of the lens. That is the combination of the sensor size and the lens, that creates an image with a certain field or angle of view. These combinations have infinite variables. And that defines the maximum angle required. A short lens bends the light to a smaller size which can match the size of a smaller sensor, giving possibly the same image (angle of view) as a long lens which doesn't bend the light to such a small pattern and therefore covers a larger sensor. If the long lens bends the light to cover a larger sensor then it *necessarily* is bending it *more* than is required to bend a light ray to cover a smaller sensor. The *fact* is that for the same framing on different sized sensors, the ratio of the focal lengths and the sensor dimensions (crop factor) will be the same. Set the focal length to 85mm and the crop factor to 1.0, which will give a horizontal angle of 23.9 degrees, a vertical angle of 16.1 degrees and a diagonal of 28.6 degrees. Now change the focal length to 56.667mm and the crop factor to 1.5. Same angles! You think that parallel light waves coming through 2 different FL lenses have the same angle of refraction?????? AND that they produce the same size images on DIFFERENT size sensors means the same thing????? No body said "the same size images"! Pay attention to detail! They produce the same framing of the image, *on different sized sensors*, which clearly also means different size images. This is not rocket science... Which means they would produce DIFFERENT size images on the SAME sensor, and that proves they are the SAME angle????? I think not. Then it's time you actually started thinking about it. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
#27
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What is this weird hatred of different focal lengths?
wrote in message ... On Wed, 12 Sep 2012 14:30:30 +1000, "Trevor" wrote: wrote in message . .. On Mon, 10 Sep 2012 09:59:23 +1000, "Trevor" wrote: wrote in message m... On Sun, 9 Sep 2012 13:51:59 -0700 (PDT), RichA wrote: On Sep 9, 1:43 pm, David Dyer-Bennet wrote: "Trevor" writes: Which is all rather amusing when you consider the more serious photographers used an 85mm lens and a 35mm lens combination far more often than anything in the 40-70mm range. If anything a 58 mm lens was a little better for portraits than a 50mm one at least, even if not by much. A fast 50mm is a much better lens now on a non FF sensor DSLR however IMO. A 58mm is great on a 1.5X DSLR for portraits :-) That was my point. But does it behave the same way as say an 85mm on a FF for the same subject matter? The 85mm lens bends the light rays less than the 58mm lens does, that might make a differance... you need to try it! Since you are only using the centre part of the focus plane on a non FF sensor, the "bend" should be the same for the area used. No matter what sensor you have, an 85mm focal length lens bends light at less of an angle than a 58mm lens. You really need to specify which you are talking about, which are APSC lenses and which are FF lenses as the image circle and thus the "angle" the light is bent is different for both types of lenses at the same marked focal length. No Whether or not a lens is marked for FF or C sensors has nothing to do with it's actual focal length, if both lenses are marked 100mm that is what they both are, Who said otherwise? One is necessarily designed for a bigger image circle though. and they both bend the light the same amount. NO, because one has a bigger image circle than the other. The difference is the size of the circle of light they project, which has to do with the size of the glass lens and construction, not it's FL. If you rearrange that so as to realise the size and construction is a *consequence* of the required image circle, then correct. My D700 shows NO difference in images if I use a Digital 50mm or a FF 50mm lens, but the circle of light shows smaller with the dig. lens. Exactly. If I set the crop factor to c type in the camera, it simply ignores the larger area, if I set it to FF then I capture the circle, complete with it's dark area for the D lens. The pictures are of course identical except for the 'blow up' effect if I crop to the c size, which is called the crop factor. I can also crop the FF lens and get the exact same picture as the D lens. Right, so what? And for FF lenses only, the image area actually used is smaller on an APSC sensor, and thus the part which is "bent" the most is outside the sensor area and becomes irrelevent. Again, the sensor has nothing to do with the amount of bending of the light. But it DOES affect what part is used!!!! A smaller focal length lens bends the light to a smaller size image, and usually creates more distortion. Focal length has nothing to do with "image size" at the sensor. Pehaps you are just being sloppy again with your terminology? And distortion of course is not just about smaller focal lengths, unless you are talking about fish eye's. If I draw a schematic of a lens system, and draw a line from the perimeter of the subject through the objective of a long lens to the target, I will get a shallow angle. Then I do the same thing for a short lens, I will get a steeper angle. (This is the only thing BTW I said concerned me in my first post.) Now we take two sensors of different sizes, and place them to gather the same image, a large sensor for the long lens and a small sensor for the short lens, the fact remains that the shorter lens bent the light more, the proof being that the same objective size fills the smaller sensor. Hard to even tell what you are trying to say here. But drawing the ray diagrams for both size sensors on both size lenses is a good start. It would certainly show you need a steeper angle for a given FL to fill a bigger sensor image circle. Trevor. |
#28
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What is this weird hatred of different focal lengths?
You really need to specify which you are talking about, which are APSC lenses and which are FF lenses as the image circle and thus the "angle" the light is bent is different for both types of lenses at the same marked focal length. No Whether or not a lens is marked for FF or C sensors has nothing to do with it's actual focal length, if both lenses are marked 100mm that is what they both are, Who said otherwise? One is necessarily designed for a bigger image circle though. and they both bend the light the same amount. NO, because one has a bigger image circle than the other. WRONG! The bigger image circle contains MORE IMAGE AREA. Anyway, you guys do what you want, I'm done wasting my time. |
#29
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What is this weird hatred of different focal lengths?
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#30
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What is this weird hatred of different focal lengths?
RichA wrote:
On Sep 11, 3:19*pm, David Dyer-Bennet wrote: Thre is no flattening effect or compression caused by focal length. Perspective (which technically means the relationships between objects in the rendered image) is controlled by camera location. *If you take a photo from the same place with the center of the frame pointing exactly the same direction with a 24mm lens and 600mm lens, and crop the 600mm angle of view out of the center of the 24mm image, the perspective will be the same. So, if we have two objects in a frame, at different distances from the camera and we just frame them in a 500mm lens and then a crop from a 50mm lens shot, the appearance between the two subjects in the images will appear identical in both shots? No "telephoto compression" will be visible making the two objects in the 500mm crop seem closer to each other? Yes. The composition will be the same. That is, the size of the two object will have the same relationship. If the nearer object appears to be twice as tall as the far one, that will be true for both images. -- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) |
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