Focus infinity @ F22, should it be sharp in landscapes?

[Mr Whippy]

Shouldn't things at any 'landscape' distance be as sharp as they would ever be if my lens is at f22 and focus dial turned to infinity?
Setting it to infinity at f22 and building chimneys sharp against the sky at about 100m away are quite blurry (subtle bokeh on shiny bits etc)

This is an A77 Sony with it's kit lens.

Is there something obvious I am missing? Or is that quite normal?

I'm dialling the focus back quite a bit (half way to the 2m marker from infinity) to get things looking sharp at say 100m away using this technique.


Even stuff on the horizon maybe 4-5 miles away looks slightly soft... hmmmm

Dave

[markmullen]

At f22 you're risking diffraction making things less sharp again, stop it back to f13 or f16 and I bet you'll find things improve.

[RobDickinson]

No. f22 and infinity focus wont give you hyperfocal plane.

Remember half your plane of focus is behind the focus point, which at infinity is a long way away.

Depth of field also depends on focal length too so f22 at 400mm wont work, f8 at 10mm , 3-5m focus will work.

But f22 is way past diffraction limits for your camera, which is around f8.

[Mr Whippy]

Ah thanks for that guys!

I'd never read about diffraction due to narrow apertures on cameras before but that makes lots of sense.

I've just done a quick test this morning using hyper-focal focussing (ish) and f8/11 and it doesn't seem to make any difference moving up to 11 that I can tell from a quick look.


I'll be honest and say that I did some panoramic images last summer and couldn't even tell, but I suppose the higher pixel count of my newer camera means I can actually see the diffraction distortion now, where before I simply couldn't see it anyway? (D70s)

Hmmmm

Dave

[RobDickinson]

Yep as the pixels get smaller you see diffraction effects earlier.

Its never worse than a larger pixel camera, you dont loose anything, but you dont gain either past a certain point.

[Elderly]

Does this mean that to get the DoF you require for a specific scene using a FF camera, you will have to use a smaller aperture than you would on a smaller sensor camera, and so the ensuing diffraction will reduce the resolution, so negating the advantage of the larger sensor?

[Major Bloodnok]

RobDickinson said:

Remember half your plane of focus is behind the focus point, which at infinity is a long way away.

<pedant>About 2/3 of the depth of acceptable focus is behind the focal plane, 1/3 in front.</pedant>

Other things being equal, though (which they aren't), something at 100m away should be in focus at f/22 on a crop sensor at 50mm equivalent lens. as others have said, the problem in the OP's case is more likely down to optics.

[NJH]

There is an interesting thread on this issue over on dpr, with respect to the sample images from the D800 and the OM-D
http://forums.dpreview.com/forums/readflat.asp?for...

That thread also refers to this;
http://www.cambridgeincolour.com/tutorials/diffrac...

[Elderly]

and look here: http://www.nikonusa.com/en_US/o/Y6wrkA9OU_z04Ireaz...

Lesson 3 on Page 5.

[Mr Whippy]

Haha, that D800 manual is great.

Use live view to avoid mirror slap wobbling your images

They should have used an SLT type system

Dave

[Mr Whippy]

Major Bloodnok said:

RobDickinson said:

Remember half your plane of focus is behind the focus point, which at infinity is a long way away.

<pedant>About 2/3 of the depth of acceptable focus is behind the focal plane, 1/3 in front.</pedant>

Other things being equal, though (which they aren't), something at 100m away should be in focus at f/22 on a crop sensor at 50mm equivalent lens. as others have said, the problem in the OP's case is more likely down to optics.

Even at infinity focus?

I think that is where my assumption had gone wrong.

It is much better now if I simply roll the focus to what I know is about 45m, set f8 at 50mm (hyperfocal focus), and shoot using those settings.

Just bad process on my part... clearly wasn't an issue with older kit but these new mega density sensors force you to need to actively consider diffraction... more so the D800 by the looks of things!

Dave