SIGMA 18-35mm APS-C QUESTION

[Alejandro Sellinger]

Hi All,
I have a question about a APS-C lens advertised as "35mm Equivalent Focal Length: 28.8-56mm"

I understand the crop factor of my 24mm FF lens is equivalent to a 38.4mm on a APS-C sensor based on the attached chart I attached.

When I see "35mm Equivalent Focal Length: 28.8-56mm" it looks like the math is going backwards.

I understand people on here say "the focal length is the focal length" but I'm just wondering because I would like to understand before purchasing new lenses what lengths it is. My question isn't from sensor to sensor. Basically, I have one question that I think will make me understand.

If I have a 24mm FF lens, what focal length would I set the SIGMA 18-35mm APS-C for the exact same framing on the same camera?

Thanks,

Alejandro

 

[David W. Jones]

If I have a 24mm FF lens, what focal length would I set the SIGMA 18-35mm APS-C for the exact same framing on the same camera?

Thanks,

Alejandro

24mm

 

[Sam T]

I think this will be helpful http://abelcine.com/fov/

 

[Dan Kanes]

This comes up like every single day.

take a 35mm prime and the 18-35

put them up on the camera one at a time.

same thing.

just forget about crop factor and think about sensor coverage and field of view.

take a sigma 24-35 and an 18-35

at 35 ,same lens
at 24 ,same lens

the difference is : diameter of projection is coming from the back of the lens to the sensor.

a "full frame" lens guarantees it will cover a 36x24 imaging area.

some lenses have crazy huge image diameters - Nikon 14-24 comes to mind. It's image circle is enormous.

 

[Alejandro Sellinger]

Thanks guys! I get it now. so its basically the same math as finding the crop factor, just backwards to find the framing equivalent. so "the focal length is the focal length" is true through all lenses.

Thanks again!

Alejandro

 

[Andre W.]

*removed*

 

[Jacek Zakowicz]

Now take a 24mm FF lens on a FF camera, and then put a 24mm APS-C built lens on an APS-C camera, put them side by side and you should have a similar FOV. Key word there is similar.

Nonsense. Please do not confuse things. 24mm lens on FF camera will have 1.6x the angle of view of 24mm lens on APSC camera.
Regardless what format the 24mm lens was designed for. The angle of view has nothing to do with the lens and everything to do with the sensor size. Larger sensor=larger angle of view (field of view) The lens has to cover of course...
To me 1.6x is not "similar" to you it may be....