Can you clear something up for me

Abraxaz1 · 21 Apr 2018 at 22:46

Hi Guys,

My mum recently brought me a Sigma 35mm F1.4 art for my belated christmas present.

Currently its mounted to a APS-C (pentax K3ii) am i right in think that this lens is actually a full frame lens so I should be treating it as a 52 odd mm lens instead of a 35mm?

so confused as i want to buy a new prime lens for portrait photography /Travel and dont want to double up on either 35mm or 50.

cheers

Raymond Lin · 21 Apr 2018 at 22:56

Yes, the field of view is essentially a 50mm lens (52.5mm to be exact)

Abraxaz1 · 22 Apr 2018 at 07:52

Raymond Lin said:
Yes, the field of view is essentially a 50mm lens (52.5mm to be exact)

Ok cool,

Was looking at the 55mm f1.4 to join my other three primes (14mm f2.8 and 77mm)

So should look for something between 28mm and 35mm to cover the gap.

Too bad Pentax is like the syphilis of the third party lens world.

Snapshot · 22 Apr 2018 at 09:07

It's physically a 35mm lens whatever camera you mount it on. Full-frame only means it has an image circle large enough to cover the larger sensor. As Raymond says, it gives a field of view equivalent to a 50(ish)mm lens when used on an APS-C camera; it doesn't somehow magically become a 50mm.

Abraxaz1 · 22 Apr 2018 at 10:02

Snapshot said:
It's physically a 35mm lens whatever camera you mount it on. Full-frame only means it has an image circle large enough to cover the larger sensor. As Raymond says, it gives a field of view equivalent to a 50(ish)mm lens when used on an APS-C camera; it doesn't somehow magically become a 50mm.

Yes, what I was trying to figure out if it's getting me an equivalent off 50mm their is no point in me spending £600 odd quid on a 55mm lens designed for a apsc camera.

Not sure I could warrant that extra 3mm with the missus

Razor-BladE · 22 Apr 2018 at 10:31

Whatever the mount of the lens is, that's separate from the focal length of the lens.

A 55mm lens designed for an APS-C camera will still give the equivalent field of view as 82.5mm.

Snapshot · 22 Apr 2018 at 21:03

Abraxaz1 said:
Yes, what I was trying to figure out if it's getting me an equivalent off 50mm their is no point in me spending £600 odd quid on a 55mm lens designed for a apsc camera.

Not sure I could warrant that extra 3mm with the missus

You're still not getting it. A 55mm lens is a 55mm lens whatever you mount it on but, as Razor-BladE says, on APS-C it will give you the field of view close to an 85mm lens.

Abraxaz1 · 22 Apr 2018 at 21:36

Snapshot said:
You're still not getting it. A 55mm lens is a 55mm lens whatever you mount it on but, as Razor-BladE says, on APS-C it will give you the field of view close to an 85mm lens.

Yes if I get a full frame lens of 55mm will give me a field of view of 85mm. But is this the same for a crop sensor based lens? I would have thought a 55mm lens for a crop sensor would be 55mm on a apsc camera.

So the full frame 35mm is giving me on the Apsc a view of 52 odd mm.

Razor-BladE · 22 Apr 2018 at 21:38

Forget about if it's designed for FF or crop. Whatever the focal length of the lens is, times by 1.5 to get the focal length equivalent for a crop sensor.

Energize · 23 Apr 2018 at 17:48

Abraxaz1 said:
Yes if I get a full frame lens of 55mm will give me a field of view of 85mm. But is this the same for a crop sensor based lens? I would have thought a 55mm lens for a crop sensor would be 55mm on a apsc camera.

So the full frame 35mm is giving me on the Apsc a view of 52 odd mm.

Yes it's exactly the same for a crop based lens.

Your sensor has a crop factor of 1.5x so ANY lens you use on it is multiplied by 1.5 so a 55mm f/1.4 becomes a 82mm f/2.1 lens in terms of focal length and depth of field.