why still crop factor?
Old 06-01-2014   #1
conradyiu
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why still crop factor?

I recently joined the Fuji system with x-e1 and the kit lens.

I used R-D1 with LTM lens and understood that there is crop factor as the sensor is aps-c size but lens is designed for 35mm format. However, as the Fuji lens should be designed and made for aps-c sensor, I think there should be no crop factor on the x-e1. If so, why their lens still used the 35mm format focal length and we need to convert it by timsing 1.5? Eg., the 23/1.4 why not being named as 35/1.4 directly?

I'm sure I am wrong and just would like to know why?
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Old 06-01-2014   #2
Fraser
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probably because that would be even more confusing as the "23" is the focal length of the lens which never changes no matter the crop factor, and also the lens still has the perspective of a 23mm not a 35mm.
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Old 06-01-2014   #3
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End of the day a 23mm lens will ALWAYS be just that, a 23mm lens. Crop factor & sensor size is a different thing altogether.

I mean, on a Ricoh GRD for instance it's a 6mm lens but equates to 28mm in 35mm format.
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Old 06-01-2014   #4
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Originally Posted by Fraser View Post
...and also the lens still has the perspective of a 23mm not a 35mm.
Hmmm... Given the 23mm on APS-C has the same AoV as a 35mm on full frame, one would assume that a user would stand at the same distance from the subject with both systems/lens. As such, the perspective would be identical for both lenses.
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Old 06-01-2014   #5
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Quote:
Originally Posted by goodtimes View Post
In fact, the perspective of the 28 mm remained exactly the same as with any film Leica, but what changed was that the overall angle of view was narrower, in this case the same angle as the one of a 35 mm.

Perspective has nothing to do with focal length or AoV. The only parameter that affects perspective is the distance to the subject. If a 23mm or a 28mm lens has the same AoV as a full frame 35mm due to sensor cropping, a user is going to, in all likelihood, be positioned at the same distance from a subject for the same AoV. Therefore the 23mm (1.5x crop), 28mm (1.33 crop) and 35mm (FF) lenses would all demonstrate the same perspective.
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Old 06-01-2014   #6
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Quote:
Originally Posted by conradyiu View Post
I recently joined the Fuji system with x-e1 and the kit lens.

I used R-D1 with LTM lens and understood that there is crop factor as the sensor is aps-c size but lens is designed for 35mm format. However, as the Fuji lens should be designed and made for aps-c sensor, I think there should be no crop factor on the x-e1. If so, why their lens still used the 35mm format focal length and we need to convert it by timsing 1.5? Eg., the 23/1.4 why not being named as 35/1.4 directly?

I'm sure I am wrong and just would like to know why?
Focal length is an inherent property of a lens, not dependent upon format size or the resulting angle of view. It is the combination of a focal length used with a particular format that results in an angle of view. It would not be sensible or correct to rename a lens to be a focal length other what it is.

The reason people continue to apply crop factor calculations is because they have become accustomed to thinking of angle of view in '35mm film camera lens focal length' terms. It's a convenient (if often confusing) shorthand.

G
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Old 06-01-2014   #7
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Originally Posted by Godfrey View Post
The reason people continue to apply crop factor calculations is because they have become accustomed to thinking of angle of view in '35mm film camera lens focal length' terms. It's a convenient (if often confusing) shorthand.

G
Older photographers have. Not many younger ones where 135 is foreign, like measuring weight in stone.
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Old 06-01-2014   #8
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35mm is an extreme wide angle on 6x9 cm and won't cover 4x5 inch at all: a 47mm is hard pressed. A "standard" lens on my 12x15 inch Gandolfi would be around 500mm. The "standard" on a classic Minox is 15mm. Everything depends on format. Giving "equivalents" is meaningless. Learn the diagonal of the format (the best definition of "standard", even if it is imperfect) and relate other focal lengths to that.

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Old 06-01-2014   #9
conradyiu
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Thanks a lot for so much information, so there is no images being cropped by the XF lens on the X-E1, right?
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Old 06-01-2014   #10
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Quote:
Originally Posted by conradyiu View Post
Thanks a lot for so much information, so there is no images being cropped by the XF lens on the X-E1, right?
Well, with a few unusual exceptions the image circle on any camera is cropped by a rectangle/square, otherwise you'd be shooting circular photos surrounded by black.

Someone did an experiment to see wether or not the 35mm 1.4's image circle would cover the area of a 35mm sensor and it didn't. I imagine the case is the same for most if not all of the XF lenses.
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Old 06-01-2014   #11
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Do you sometime wonder if WE are the only ones that think about these (which I do) things. Some of my friends have interchangeable lens digital cameras, some mention the 'crop factor.' But the only ones that really do are 35mm film photographers that have changed to digital. Maybe it is as Shakespeare said, 'Much Ado About Nothing.'
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Old 06-01-2014   #12
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The only APS-C sensor interchangeable lens camera I remember using the equivalent focal length would be the Ricoh GXR's APS units. 50mm, 28mm and 24-85mm.
But the lens is fixed to the sensor.

I imagine with camera that can use both APS and 35mm lenses (such as Canon and Nikon DSLR), stating the 35 equiv only will give headache to the support staff when customer came with confusion of why their 50 mm and "50 mm" lenses showed different view.
For the layman, it's easier for them when comparing lenses for different format.
For those who understand the technical side, it's the correct number.
Win-win
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Old 06-01-2014   #13
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Okay, hows about this: instead of using the term "crop factor," both the Fuji 23mm lens on its system camera body and the 35mm lens on its film body are 54 degree horizontal-angle-of-view lenses (1). We'll create the term "DHAOV" as an acronym. So, they're both 54 DHAOV lenses.

There; that sounds easier, no?

~Joe

(1) Assuming this approximation for a 35mm focal length lens: 2*Tan-1(18/35), based on the HAOV for a pinhole that's 35mm in front of a 36mm wide film frame. In practice, actual multi-element lenses will vary in their HAOV slightly, based on lens design, so in our new standard we'll use pinhole optics as the reference.

To find the pinhole-equivalent HAOV for any lens, use: 2*Tan-1(18/X), where X is the focal length as used on a 135-format film frame.
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Old 06-01-2014   #14
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Quote:
Originally Posted by charjohncarter View Post
Do you sometime wonder if WE are the only ones that think about these (which I do) things. Some of my friends have interchangeable lens digital cameras, some mention the 'crop factor.' But the only ones that really do are 35mm film photographers that have changed to digital. Maybe it is a Shakespeare said, 'Much Ado About Nothing.'
Indeed true.

I think in terms of normal, wide, portrait tele, ultra-wide, tele, and long tele, for whatever format. Once I know the normal, the rest is easy. For example,

Oly E-M1: normal is 25, so 15, 45, 12, 75, 150 mm fills out the rest.
Sony A7: normal is 50, so 28, 90, 20, 180, 300 mm.
Hassy 500CM: normal is 80, so 50, 150, 38, 250, — mm.

Plus or minus, of course.

G
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Old 06-06-2014   #15
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what ever focal length a lens is, it remains that focal length even when you're multiploying by a crop factor, period. focal length and fov are two different things. and don't forget to multiply the f-stop by the crop factor as well.
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Old 06-06-2014   #16
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Originally Posted by romi.gilles View Post
...and don't forget to multiply the f-stop by the crop factor as well.
No, the f-stop is the f-stop. Its value is a function of lens parameters only. What you are probably confused with is that for a comparison of same size prints from same AoV lenses across different sensor formats, your respective DoF appearance - in the magnified view only - will vary as if the f-stop were multiplied by the crop factor.
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Old 06-06-2014   #17
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Originally Posted by charjohncarter View Post
Do you sometime wonder if WE are the only ones that think about these (which I do) things. Some of my friends have interchangeable lens digital cameras, some mention the 'crop factor.' But the only ones that really do are 35mm film photographers that have changed to digital.
I have met kids who have never used a film camera in their life and still discuss crop factors. If there is a division it is more likely between people who do not understand technology and people who at least try to.
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Old 06-07-2014   #18
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When the focal lengths of lenses designed for 135 format film and 24 x 36 mm sensors is divided by ~ 1.5 one obtains a focal length for the Fujinon lenses that give a similar angle of view.

The angle-of-view for the Fujinon's is not cropped compared to lenses designed for the larger media area as long as the focal lengths differ by a factor or 1.5.

Just think about angle of view first and focal length second/sensor area second.
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Old 06-07-2014   #19
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Crop factor gives you a point of reference as to how the lens will render in a given format. The vast majority of customers can understand how a 24 lens renders on a 135mm camera the vendors use this so their customers understand what they are getting.

Sort of a universal translator if you will.

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Old 06-07-2014   #20
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Quote:
Originally Posted by craygc View Post
Perspective has nothing to do with focal length or AoV. The only parameter that affects perspective is the distance to the subject. If a 23mm or a 28mm lens has the same AoV as a full frame 35mm due to sensor cropping, a user is going to, in all likelihood, be positioned at the same distance from a subject for the same AoV. Therefore the 23mm (1.5x crop), 28mm (1.33 crop) and 35mm (FF) lenses would all demonstrate the same perspective.
Correct !!!


Quote:
Originally Posted by romi.gilles View Post
what ever focal length a lens is, it remains that focal length even when you're multiploying by a crop factor, period. focal length and fov are two different things. and don't forget to multiply the f-stop by the crop factor as well.
f/2 is f/2 regardless of the Focal Length OR the Sensor Size...
f/number is THE AMOUNT of light the lens can gather.

The relative DoF on larger or smaller sensors has to do with the "Circle of Confusion" (CoC) of the lens along with what size sensor it will be used on.
Smaller senors require smaller CoC to produce acceptably sharp images.
  • 35mm Coc = .030
  • APS-C CoC = .020 (1.5x smaller CoC, 1/stop more DoF)
  • 4/3 m4/3 Coc = .015 (2x smaller CoC, 2/stops more DoF)
So, because you can use an f/2 lens from a FF on an APS-C camera, the relative DoF now is f/2.8... BUT... It is still f/2 as far as Light Gathering Power.

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for example of OP Question to label lenses to 35mm terms....

6x6 cameras makers never used 35mm terms for their lenses... 75/80mm is a normal lens, because it has a larger image circle. and a lager CoC... Ergo, even thinner DoV....so an 80mm at f/2.8 has similar Dov as 50mm f/2 on a 35mm camera.
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Old 06-07-2014   #21
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Originally Posted by JoeV View Post
Okay, hows about this: instead of using the term "crop factor," both the Fuji 23mm lens on its system camera body and the 35mm lens on its film body are 54 degree horizontal-angle-of-view lenses (1). We'll create the term "DHAOV" as an acronym. So, they're both 54 DHAOV lenses.
Which is great if you use different cameras with the same ratio, such as the 2:3 ratio that Herr Barnack chose when he took a 3:4 ratio movie film, flipped it and doubled it. I've used film cameras in 2:3 (24x36mm), 3:4 (41.5x56mm, a.k.a. 6x4.5cm) and 4:5 (96x120mm, or 4x5") so do you use horizontal, diagonal or vertical angle of view? Since my Fuji X-E1 is also 2:3, it's easy (for me at least) to compare it to 24x36mm by applying the "crop factor."

Yes, it's a confusing mess. I've owned an 80mm wide angle, an 80mm "normal" and a 75mm telephoto lenses at the same time. Fortunately, I'm not confused (at least I pick the right lens for the right camera, I'm confused on many other things), so I'm happy!

Last edited by drew.saunders : 06-07-2014 at 08:11. Reason: speling errir
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Old 06-07-2014   #22
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Very interesting doubt.

Before apsc sensors ther were mainly film cameras with fixed or zoom focal lengths, based all in 24x36 film format.

Since all digital new media wasn´t in that full frame format they made the names to match the common knowledge of that 135 film format.

But now, the fact of apsc sensors is so spreaded that brands tend to use the real focal length of their lenses...for instance the new summicron for the leica T has the 23 clearly engraved in the barrel and so are many other brands that supose the custmores are enough trained to catch the new (real) info.
On the other hand full frame technology is only a margin of the actual digital cameras.

Perhaps some folk of 20 years will immediatelly grasp/understand the field of view of a 23mm lens without the need of making the mental conversion "as 35mm lens on 36x24 film" "or x1.5"



Quote:
Originally Posted by conradyiu View Post
I recently joined the Fuji system with x-e1 and the kit lens.

I used R-D1 with LTM lens and understood that there is crop factor as the sensor is aps-c size but lens is designed for 35mm format. However, as the Fuji lens should be designed and made for aps-c sensor, I think there should be no crop factor on the x-e1. If so, why their lens still used the 35mm format focal length and we need to convert it by timsing 1.5? Eg., the 23/1.4 why not being named as 35/1.4 directly?

I'm sure I am wrong and just would like to know why?
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Old 06-07-2014   #23
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Originally Posted by Monochrom View Post
Very interesting doubt.

Before apsc sensors ther were mainly film cameras with fixed or zoom focal lengths, based all in 24x36 film format.

Since all digital new media wasn´t in that full frame format they made the names to match the common knowledge of that 135 film format.

But now, the fact of apsc sensors is so spreaded that brands tend to use the real focal length of their lenses...for instance the new summicron for the leica T has the 23 clearly engraved in the barrel and so are many other brands that supose the custmores are enough trained to catch the new (real) info.
On the other hand full frame technology is only a margin of the actual digital cameras.

Perhaps some folk of 20 years will immediatelly grasp/understand the field of view of a 23mm lens without the need of making the mental conversion "as 35mm lens on 36x24 film" "or x1.5"

Having different angles of view on different formats for the same focal length is almost as old as photography. It's not something that came about in digital times.

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