So, why is focus shift so serious now?

[Vickko]

So, why is "focus shift" so serious now?

It seems that with digital, it is a big deal.

Is it because of the ability to get instantaneous results, that you now can determine that your shots are affected by focus shift?

I wouldn't think that a digital sensor made focus shift any worse, just faster to determine.

..Vick

 

[jpberger]

2 reasons-- first, film emulsions have some depth (not very much, but some) whereas all the photo sites on a sensor are at the same depth- thus more actual focus shift.

second, looking at digital files at 100% is equivalent to looking at film with a microscope so it's much easier to see focus problems.

 

[Vickko]

hmmmm. Thank you

 

[MCTuomey]

my very favorite lenses exhibit focus shift

i guess that's serious

old buddhist saying: time spent pixel peeping is subtracted twice from a man's life ...

 

[Vickko]

I would think all lenses exhibit focus shift, as it wasn't something that the designers optimized for.

I just find it interesting that it has come up as one of the "serious flaws" when evaluating lenses.

 

[ampguy]

so we don't get surprised when we pickup or develop our negatives and get images we thought were in focus, but look like this:

(photo courtesy of mfogiel)

 

[Vickko]

Wow, that image is just spooky.

There was a Japanese horror film, whose premise was if you got imaged with a fuzzy face, you'd be next on the "hit list".

Vick

 

[Freakscene]

I would think all lenses exhibit focus shift, as it wasn't something that the designers optimized for.

I just find it interesting that it has come up as one of the "serious flaws" when evaluating lenses.

Focus shift is caused primarily by uncorrected spherical aberration. Those aberrations have been among the highest priorities for correction for lens designers ever since cameras have existed.

All lenses have focus shift - it you observe anything, however, depends on whether the shift is larger than the increase in depth of field when you stop down.

Marty

 

[ferider]

It's not so serious.

If it would be a real problem, and not only an issue observed when shooting center-focus'ed rulers, people would complain about field curvature as well ....

 

[ampguy]

interesting

interesting

omoshiroii katta, I wonder if they used the word "bokeh" in the film

Wow, that image is just spooky.

There was a Japanese horror film, whose premise was if you got imaged with a fuzzy face, you'd be next on the "hit list".

Vick

 

[David Hughes]

In the digital camera world they spend a lot of time stirring up problems in the interests, it seems to me, of making people abandon their old digital cameras and buying yet another one.

Wasn't the monster in the horror film called "Bokeh" or something similar?

Regards, David

 

[DubilUC]

2 reasons-- first, film emulsions have some depth (not very much, but some) whereas all the photo sites on a sensor are at the same depth- thus more actual focus shift.

second, looking at digital files at 100% is equivalent to looking at film with a microscope so it's much easier to see focus problems.

In addition to this, many digital sensors have a smaller circle of confusion than film. So not only will the effective depth of field be thinner on digital than on film (this is VERY evident using the same lens at the same aperture between my M6 and gf-1), a focus shift that was considered acceptably sharp on film may appear soft on digital.

 

[varjag]

Before, people were rarely able to print that large as to notice much of the effect.

 

[Sonnar Brian]

It is much easier to see pixel peeping than scanning negatives or using a 15x loupe.

I like using the M8 to shim lenses, I can pick the exact optimization point a bit more easily. Found the pre-war Sonnars 5cm f1.5 do quite well optimized for F2. F1.5 is fine, F4 is really close.

 

[sevo]

Live view may also have some impact on the public awareness of focus shift and other stopping-down related phenomena - LV is marketed as WYSIWYG, but it is generally done fully open (to keep the sensor cool at lowest sensitivity). The majority of implementations on DSLRs do not even permit a DOF preview during live view, and none I am aware of do default to it.

Previously, people would use the DOF preview to get as close to the final outcome as they could, noticing the focus shift in the process - now, many use LV under the impression that this is more accurate, and may be surprised by the focus shift and DOF changes in the recorded image...