Who's got a Nikon and Tokina 11-16 combo??

bbg404 · 30 Oct 2014

Evening all im looking for Nikon owners who use the Tokina 11-16 lens got a couple of questions regarding the focus ring position at the infinity mark!!

I'm sure this kind of questions came up before and not many people pay attention to the focus ring but I'm just interested

So for example if you set it at 11mm then focus on a lamp post down the the street and shows just before infinity you then look away refocus on the same lamp post now it'll say just past infinity do it again and it might say bang on infinity

HOWWWWW confused

sk66 · 30 Oct 2014

That's just the variability of autofocus, especially w/ a deep DOF. *IF* you had a very specific point/line of contrast you focused on every time it should be more consistent, but it won't probably be entirely consistent. I don't think it's uncommon for AF to stop at a slightly different point depending on if it's focusing out or pulling focus.

shapeshifter · 30 Oct 2014

At 11mm there is a massive depth of field so the focus ring could be in different places and be in focus. If you use 11mm on an object that is very close to the lens it will be in the same place or at least it should be due to a smaller depth of field. I have a 11-16 Tokina and a Samyamg 8mm. With the 8mm Samyang it is manual focus so I just put the lens a little bit off infinity and unless something is very close to the lens everything is in focus.That's how wide angle lenses work.

bbg404 · 31 Oct 2014

thank you both for replies I've heard this kind of explanation before, and a lot of people just say if there's nothing really close in the frame just leave it on MF and focus just before infinity

shapeshifter said:
With the 8mm Samyang it is manual focus so I just put the lens a little bit off infinity and unless something is very close to the lens everything is in focus.That's how wide angle lenses work.

My question now though is ..... if the AF thinks its in focus somewhere between just before to just after the infinity mark Why is most peoples common response with a wide angle to just stick it just before the infinity mark?????????? yet the AF sometimes chooses before on or after the infinity mark

Pistnbroke · 31 Oct 2014

perhaps you should study the depth of filed calcs here http://www.dofmaster.com/dofjs.html

You dont say what camera you are using but remember at 11 mm you are pushing the resolution of your sensor ..even if its 24mp ... if you halve the focal length you need 4x the MP for the same resollution.

bbg404 · 31 Oct 2014

Pistnbroke said:
perhaps you should study the depth of filed calcs here http://www.dofmaster.com/dofjs.html

You dont say what camera you are using but remember at 11 mm you are pushing the resolution of your sensor ..even if its 24mp ... if you halve the focal length you need 4x the MP for the same resollution.

Thanks will have a read of that today

It's a Nikon D5200 so 24mp like you said

Pistnbroke · 31 Oct 2014

Thanks ...main mistake Nikon users make if they shoot jpeg is not to up the shapness ...they all come out the factory soft ....all mine are at +9 does not affect RAW

bbg404 · 31 Oct 2014

Cheers I only shoot Raw

It's not really about image softness or not in focus its about the focus ring showing a different reading for infinity but on the same object

sk66 · 31 Oct 2014

Pistnbroke said:
You dont say what camera you are using but remember at 11 mm you are pushing the resolution of your sensor ..even if its 24mp ... if you halve the focal length you need 4x the MP for the same resollution.

???? Unless I'm misunderstanding what you're trying to say, this is just wrong...
MP's do not realistically affect DOF (sensor size does). And FL doesn't affect resolution (but aperture does).

sk66 · 31 Oct 2014

bbg404 said:
My question now though is ..... if the AF thinks its in focus somewhere between just before to just after the infinity mark Why is most peoples common response with a wide angle to just stick it just before the infinity mark?????????? yet the AF sometimes chooses before on or after the infinity mark

Because they don't know any better, they're lazy, or they don't have the time to focus manually...

There's a focus distance called the hyperfocal distance... it is affected by the FL, sensor size, and aperture. And when the focus is set to this distance the DOF extends from 1/2 way to the point of focus out to infinity. For your 11-16 set at 11mm, f/16, on a crop body the hyperfocal distance is ~1ft. So when the focus is set to 1ft the DOF extends from 6" to infinity.

The infinity focus technique is based on the fact that no matter how far beyond the hyperfocal distance you focus, the near edge of the DOF never goes beyond the hyperfocal distance. So 11mm/f16/APS set to infinity the DOF would be ~1 ft. to infinity. This is the same as the "focus 1/3 into the scene" idea. There is one problem to this though, "infinity" can vary with environmental conditions and it is possible to "over-focus;" which is why there is the focus just short of infinity recommendation.

BUT, something being w/in the DOF does not mean it is actually "in focus." There is only one distance that is actually ever "in focus"... the rest is just "acceptably sharp." My best recommendation is to use hyper-focus when there is something very close to you and you want it AND infinity reasonably in focus. All other times focus on the most important element in the scene that you want to actually be "in focus."