Time to see a shrink!

[Abitconfused]

Why would any n o r m a l photographer want both of these?


Nikon 17-55 at f/7.1, 57mm... Sharp!


Sigma 18-35 at f/4.5, 32mm... Sharp

Nikon D7100

[James G]

Please define 'normal'

[TonyW]

I thought "normal photographer" was an oxymoron. And a carburetor repair person working in this day and age, especially on diesel engines, must be struggling for business.

[IzzieK]

I am wasting time trying to read that sign. You do not need a shrink -- one needs an ophthalmologist to figure out what it says. Maybe "normal"?

[Abitconfused]

Normal (ORIGIN: French or Latin normalis made according to a square...). Normal is the guy who just wanted to get through life without being noticed. Normal photographer... one who uses the AUTO setting and wonders why some buttons on the camera have an odd little +/- written on them.

[Greg Lehey]

Nikon 17-55 at f/7.1, 57mm.

I'm impressed by the focal length. How did you manage it?

[IzzieK]

Err...something is wrong with the first picture that says

Nikon 17-55 at f/7.1, 57mm... Sharp!

because your EXIF said you used 38mm focal length not 57mm...

[Abitconfused]

I think the focal length may vary depending on the program used to view it. Obviously the 17-55 is a DX lens so the FOV is 1.5X that stated on the lens. Can this explain the discrepancy? Also, DXO gives a modest sharpness rating to the 17-55 but even the compressed image above is quite sharp. The original is extremely sharp. I think f/7.1 is the sweet spot for this lens but I haven't done science on it.

[revi]

There is no discrepancy, just two ways of reporting the focal length.
Looking at the EXIF data, I see:
Focal Length = 380/10 mm ===> 38 mm
("real" focal length) and
Focal Length in 35mm Film = 57
("apparent" focal length)
Which corresponds exactly to a crop factor of 1.5...

The crop factor has nothing to do with the type of lens you use, it only depends on the camera sensor.
(i.e. it doesn't matter whether you use a DX or FX lens). And, I don't know of any lens that shows FOV
information (FOV is expressed as an angle, not as a length, unless you specify at what distance you measure
FOV...)

[xpatUSA]

I think the [stated] focal length may vary depending on the program used to view it. Obviously the 17-55 is a DX lens so the FOV is 1.5X that stated on the lens. Can this explain the discrepancy?

Ed, to avoid a bit of confusion, how about ignoring the second number in any statement of a lens setting? (but not of a zoom range). That second number is useless to any n o r m a l person because it's just implying how a scene might look if you took your DX lens and plunked it onto an old film camera or a Nikon D700. Better to take what's written on the lens (where it says f=nn) as said and just live with it in the knowledge that, with an APS-C size sensor, you get what you get.

I have a Sigma 50mm DG (FF) macro lens. In my mind, it is never anything but a 50mm lens. I don't think of it as a 75mm lens when it is on my 1.5 crop SD1 camera and certainly not as a 85mm lens when it is on my 1.7 crop SD14. Equally, when I am shooting close-up at 1:1, I do not think of it as an effective 100mm lens (focal length + the extension needed to get close).

I think of focal length only as the point where rays from afar converge behind the lens when it is set to infinity - because that is what is stamped on the lens. Nothing else should be described as just "focal length" without some weasel words like "equivalent" to go along with it.

Bit of a rant, that . . sorry.

Nice sharp shots, by the way - my long-gone Nikon D50 always seemed a little soft to me, even with the 60mm micro-Nikkor on it

[Manfred M]

+1 to what both Urban and Ted have written.

When people write about the "equivalence" of various lenses on different sensor sizes, they are ONLY referring to the focal length impact. They are ignoring equally important factors like depth of field, which also impacted.

The only issue to worry about is what a specific focal length will do with the camera you are shooting with. An f/1.4 50mm lens is exactly that, regardless of which camera you are shooting with. If you framed your image to be the same size with a 50mm lens on a full-frame camera and a 1.5x crop frame camera at the same aperture setting, the depth of field would be one stop larger; i.e. the f/1.4 DoF on crop frame would be the same as if you were shooting at f/2.0 on the full frame camera.