why still crop factor?

[BillBingham2]

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.

B2

 

[DNG]

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 !!!

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.

___________________________________________________________________________________________________

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.

 

[drew.saunders]

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!

 

[Monochrom]

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"

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?

 

[ronnies]

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.

Ronnie