Beginner I Purchased a Canon 50mm EF f/1.8 STM lens recently...........

sparker

sparker

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Simon
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I purchased a Canon 50mm EF f/1.8 STM lens recently for my 70D but I am a little confused by the field of view. I took two images, one with the 50mm and one with an 18-135mm EF-S lens set at 50mm and there was very little difference in the field of view of the two images. I was expecting, given the x1.6 crop factor, that the 50mm EF lens would give me around about the same as the EF-S lens set at 80mm but this wasn't the case. Am I misunderstanding the maths?

Many thanks
Simon
 
sparker said:
I purchased a Canon 50mm EF f/1.8 STM lens recently for my 70D but I am a little confused by the field of view. I took two images, one with the 50mm and one with an 18-135mm EF-S lens set at 50mm and there was very little difference in the field of view of the two images. I was expecting, given the x1.6 crop factor, that the 50mm EF lens would give me around about the same as the EF-S lens set at 80mm but this wasn't the case. Am I misunderstanding the maths?

Many thanks
Simon
Click to expand...

Yes. Because the '50mm' of the 18-135mm zoom also has the x1.6 applied to it hence both are around 80mm equiv on FF.
 
The only thing of significance is the "EF-S" - means the lens is only usable on a crop sensor body (ie. EF-S). The EF lens is usable on both full frame (EF) & crop sensor (EF-S)
 
No, you are confusing the crop factor, and or format equivilencies.
On the same camera with the same frame/sensor size behind the lens, a lens is a lens is a lens, and an 80mm lens from an MF camera remains an 80mm lens, whether its on that Medium Format 120 roll-film camera it's native to, on a 35mmm SLR or on a 'Full-Frame' Digital SLR or a 'half frame' APS-C sensor DSLR, on a Micro-Four-Thirds sensor camera, a 110 Instamatic or a micro-sensor action-cam or smurfone... what alters the angle of view you get is the width of the sensor behind the lens; the lens dont change. Same width sensor, same focal length you get the same Angle of View, no crop-factor to be applied.
The crop factor is an 'equivalence' to the focal length of lens that delivers an 'equivalent' angle of view, on a different format/sensor size. In this case it dont apply, 'cos the sensor is the same. and the focal lengths are the same.
Side note having mentioned Medium-Format 120 roll film; This is 6cm wide; and commonly cameras have traps that may put either a 4.5x6cm frame on the film, a 6x6cm 'square' frame, or a 6x9cm frame, and on some cameras, the frame is interchangeable, so that you can take more pictures per roll, or get bigger, higher quality negatives. Either way, the lens on the front, commonly an 80mm, gives the same Angle-of-View on the focal plane.. its just that when you put the smaller frame behind it, you mask or 'crop', hence 'crop-factor', more or less off the sides of your photo... BUT the lens does not mystically change focal length when you put a bigger or smaller masking frame behind it; it remains what it is, and any other lens of or set to that focal length should deliver the same AoV.
Make sense?
 
Teflon-Mike said:
No, you are confusing the crop factor, and or format equivilencies.
On the same camera with the same frame/sensor size behind the lens, a lens is a lens is a lens, and an 80mm lens from an MF camera remains an 80mm lens, whether its on that Medium Format 120 roll-film camera it's native to, on a 35mmm SLR or on a 'Full-Frame' Digital SLR or a 'half frame' APS-C sensor DSLR, on a Micro-Four-Thirds sensor camera, a 110 Instamatic or a micro-sensor action-cam or smurfone... what alters the angle of view you get is the width of the sensor behind the lens; the lens dont change. Same width sensor, same focal length you get the same Angle of View, no crop-factor to be applied.
The crop factor is an 'equivalence' to the focal length of lens that delivers an 'equivalent' angle of view, on a different format/sensor size. In this case it dont apply, 'cos the sensor is the same. and the focal lengths are the same.
Side note having mentioned Medium-Format 120 roll film; This is 6cm wide; and commonly cameras have traps that may put either a 4.5x6cm frame on the film, a 6x6cm 'square' frame, or a 6x9cm frame, and on some cameras, the frame is interchangeable, so that you can take more pictures per roll, or get bigger, higher quality negatives. Either way, the lens on the front, commonly an 80mm, gives the same Angle-of-View on the focal plane.. its just that when you put the smaller frame behind it, you mask or 'crop', hence 'crop-factor', more or less off the sides of your photo... BUT the lens does not mystically change focal length when you put a bigger or smaller masking frame behind it; it remains what it is, and any other lens of or set to that focal length should deliver the same AoV.
Make sense?
Click to expand...

It made sense to the OP in post 5 ;)
 
sparker said:
Thank you. I understand the maths and I NOW understand the application. A 50mm lens is always a 50mm lens, the FOV changes only with the sensor.
Click to expand...
That is it, exactly. Some people would use 5000 words to try to explain it, but that's it in less than twenty words.

(The only other thing you need to be aware of is that, sometimes, specifications mention the "full frame equivalent" focal length. That is never an issue with interchangeable lenses, but it can be for compact cameras and bridge cameras. For example Nikon advertise the Coolpix P1000 as having a 24-3000mm optical zoom, but in the small print it clarifies that that's the full-frame equivalent, and the actual focal length range is 4.3mm to 539mm.)
 
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