Lens focal length and sensor size

[Oriondk]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

 

[Tom Axford]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

A 50mm lens used on an APS-C camera with a smaller sensor will give a smaller field of view.

So, in terms of the field of view only, a 50mm lens on a FF camera will be roughly equivalent to a 35mm lens on an APS-C camera.

A 50mm lens on an APS-C camera will be roughly equivalent to a 75mm lens on a FF camera (for field of view).

 

[Oriondk]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

A 50mm lens on an APS-C camera will be roughly equivalent to a 75mm lens on a FF camera (for field of view).

Is that regardless of whether the lens is a full frame lens or and ASP-C lens?

 

[Sheacash]

Yes.

The focal length of the lens is a physical property. The effective length is after the crop factor is applied.

 

[FingerPainter]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

A 50mm lens on an APS-C camera will be roughly equivalent to a 75mm lens on a FF camera (for field of view).

Is that regardless of whether the lens is a full frame lens or and ASP-C lens?

It's "APS-C" not "ASP-C". APS-C stands for "Advanced Photo System - Classic". There were also APS-H and APS-P, which stood for "High definition" and "Panoramic".

To answer your question, it depends which way you go.

If you mount a FF or APS-C lens on an APS-C body they will both give the same Field of View (FoV). This FoV will be the same as that given by a FF lens of 1.5 times the focal length on a FF body.

However, if you mount an APS-C lens on a FF body, it may not give the same FoV as a FF lens on a FF body, because the APS-C lens' image circle (the area over which the lens casts light on the sensor) may be smaller than the sensor.

 

[Michael Fryd]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

 

[Oriondk]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

A 50mm lens on an APS-C camera will be roughly equivalent to a 75mm lens on a FF camera (for field of view).

Is that regardless of whether the lens is a full frame lens or and ASP-C lens?

It's "APS-C" not "ASP-C". APS-C stands for "Advanced Photo System - Classic". There were also APS-H and APS-P, which stood for "High definition" and "Panoramic".

--Well, Duh! I knew that. Must have been thinking about snakes, lol.
David

 

[Oriondk]

Thanks all. I think I have it. So if I have a Nikon DX, APS-C, camera and get a 200 mm DX lens it would be the same as having a 350 mm lens on a FF camera?

 

[Sheacash]

Thanks all. I think I have it. So if I have a Nikon DX, APS-C, camera and get a 200 mm DX lens it would be the same as having a 350 mm lens on a FF camera?

 

[Alex Ethridge]

I’m a little confused abou the relationship of lens focal length and sensor sizes between ASP-C and full frame cameras. If I buy a lens for an ASP-C camera and it’s, let say, a 50mm is that the same as using a 50mm on a full frame camera or is that going to give me a slight telephoto effect on the smaller sensor? I hope I’m framing the question right.

A 50mm lens used on an APS-C camera with a smaller sensor will give a smaller field of view.

Correct.

I just want to add this: It is the size of the sensor behind the lens that makes the difference in the part of the image that gets recorded by the sensor. The smaller the sensor, the smaller the angle of view that gets recorded by the smaller sensor.

So, in terms of the field of view only, a 50mm lens on a FF camera will be roughly equivalent to a 35mm lens on an APS-C camera.

A 50mm lens on an APS-C camera will be roughly equivalent to a 75mm lens on a FF camera (for field of view).

 

[dsjtecserv]

Thanks all. I think I have it. So if I have a Nikon DX, APS-C, camera and get a 200 mm DX lens it would be the same as having a 350 mm lens on a FF camera?

300 mm; the Nikon crop factor is 1.5. The field of view would be the same, but the images may or may not be equivalent in other ways, depending on other factors.

Note that the same would also be true if you used a 200 mm FX lens. It is not the designation of the lens that determines field of view, but rather the combination of lens focal length and sensor size.

Dave

 

[Michael Fryd]

Thanks all. I think I have it. So if I have a Nikon DX, APS-C, camera and get a 200 mm DX lens it would be the same as having a 350 mm lens on a FF camera?

 

[baloo_buc]

When smaller sensor digital cameras came out, marketing departments started to talk about "effective focal length", and "focal length multipliers". What they are really trying to do is to express angle of view in terms of the focal length your would need on a traditional 35mm film camera.

EFL is equivalent focal length not effective focal length.

 

[Michael Fryd]

When smaller sensor digital cameras came out, marketing departments started to talk about "effective focal length", and "focal length multipliers". What they are really trying to do is to express angle of view in terms of the focal length your would need on a traditional 35mm film camera.

EFL is equivalent focal length not effective focal length.

 

[baloo_buc]

I disputed that the lens will change the focal length once you put on a crop sensor camera. The only acceptable meaning of effective focal length is actual focal length.

 

[Michael Fryd]

I disputed that the lens will change the focal length once you put on a crop sensor camera. The only acceptable meaning of effective focal length is actual focal length.

--
Victor
Bucuresti, Romania

I don't think anyone was suggesting that the focal length changes when you move a lens between a full frame body and a crop body.

 

[Oriondk]

I want to thank all those who responded to my question. It was pointed out to me in a private message that since I have shot with a 4x5 and 6x6 in the past I should’ve already known the answer to this. You know what? He was right. I guess I’ve been out of this too long. I sure seem to be having a lot of DUH moments lately when it comes to photography. It has been over twenty years, though. I feel like I’m starting over.

 

[baloo_buc]

Be careful with words since some posters will imply just that because you used effective instead of equivalent (although I agree that equivalent refers only to angle of view).

 

[Leonard Migliore]

--Well, Duh! I knew that. Must have been thinking about snakes, lol.
David

Watch out with that. You know, the more you think about snakes, the more snakes you see.

 

[Leonard Migliore]

When smaller sensor digital cameras came out, marketing departments started to talk about "effective focal length", and "focal length multipliers". What they are really trying to do is to express angle of view in terms of the focal length your would need on a traditional 35mm film camera.

EFL is equivalent focal length not effective focal length.

But way back before anything was electronic or automated, there was an Effective Aperture Kodaguide (which cost 10 cents in 1948). It was one of many useful devices offered by Kodak to help them sell film. What the Effective Aperture Kodaguide did was let you calculate your exposure when you were doing macros. We didn't have like through the lens metering or stuff like that. We barely had metering at all. But with the Effective Aperture Kodaguide, you would know that when you set f/8 you really had f/11.

Anyway, there was effective aperture but, as far as I can recall, there wasn't an effective focal length and there certainly wasn't an equivalent focal length.