Tokina 12-24 Test Shots - Technical Analysis Invited

[leek]

I finally found time to take some test shots with my new Tokina 12-24 today.

I took all of the following shots with the D70 mounted on a tripod and with self-timer delayed shutter.

So that you can appreciate the context of the crops, here's the scene that I took (with minor post-processing):



Here are 4 centre crops at different apertures. All shots were taken at 12mm focal length, at 200 ISO with the D70 mounted on a sturdy tripod and using the self-timer to activate the shutter. No polariser was used for these shots (see later). Also no PP applied to crops:


1/1250 @ f4

1/320 @ f9

1/100 @ f16

1/60 @ f22

I don't really feel qualified to analyse the optical characteristics of these crops and would therefore invite the pixel-peepers amongst us to let me know what they think regarding sharpness, CA etc. Personally, I'm quite confused as the F4 shot seems to be the sharpest

Earlier in the day I took some shots further up the Lane Cove River with a CPL mounted... At 12mm, the filter causes some quite pronounced vignetting.



Is there any way of minimising this vignet? A better quality CPL perhaps?

[Glen]

John, maybe an ultrathin cpl, though I would try first. See if Birddy has one in that size or try Mainline Photographics at Crows Nest. Try and test first as it may not cure anything.

The first shot seems dark in the bottom left corner

[sirhc55]

John - with my aged eyes the f/4 does seem to be the sharpest but this is well within the context of most lenses having the sharpest images at f/4 thro f/8.

[big pix]

yes that is the edge of your filter which will show when using 12mm........ you need an ultra thin cpl filter.......

[birddog114]

Yes, thin CPL filter from Hoya and B+W (3mm) costs nearly 1/3 the price of that lens.
I'm sure Nikon 12-24 does not have this issue with standard 5mm CPL filter.

[gstark]

John,

Do you have crops at f5.6 and f8?

The contrast seems to have dropped very sharply at f16 and f22, and it cetainly seems somewhjat soft at those apertures as well.

I'd like to see what this lens does at the more moderate apertures.

[Antsl]

You are right, the Tokina 12-24mm lens is very sharp wide open which is why I like it. Most lenses do get softer at the smaller apertures and this is because of a condition called the diffraction of light. What happens is that light will bend about an object, whether it be our sun (hence the reason why astronomers can observe stars behind the sun) or a human hair.

As we use smaller apertures what happens is that there becomes more perimeter of the actual metal aperture for the smaller surface area letting light through; the nett result is that at the very small apertures some of the light is bent away from its usual direction, thereby softening the image.

[stubbsy]

Yes, thin CPL filter from Hoya and B+W (3mm) costs nearly 1/3 the price of that lens.
I'm sure Nikon 12-24 does not have this issue with standard 5mm CPL filter.

Correct. I have the standard Hoya CPL on my nikkor 12-24 and no vignetting. Of course I paid a touch more for the lens than John did for his Tokina.

[leek]

Yes, thin CPL filter from Hoya and B+W (3mm) costs nearly 1/3 the price of that lens.
I'm sure Nikon 12-24 does not have this issue with standard 5mm CPL filter.

Correct. I have the standard Hoya CPL on my nikkor 12-24 and no vignetting. Of course I paid a touch more for the lens than John did for his Tokina.

Yes... let me see... $660 for the lens + $200 for an ultrathin filter... I still think I'm better off Either that, or all my 12-24 shots will be displayed in pano-format

[leek]

John,

Do you have crops at f5.6 and f8?

The contrast seems to have dropped very sharply at f16 and f22, and it cetainly seems somewhjat soft at those apertures as well.

I'd like to see what this lens does at the more moderate apertures.

Didn't take any at those apertures this time Gary, but I'll pop out again soon for another test...

[thaddeus]

Most lenses do get softer at the smaller apertures and this is because of a condition called the diffraction of light. What happens is that light will bend about an object, whether it be our sun (hence the reason why astronomers can observe stars behind the sun) or a human hair.

Great explanation, thanks!

[Onyx]

Fark, diffraction noticeably sets in between f/9 and f/16 shots - I suspect you'll get the sharpest image at f/11 or so.

I'm not terribly impressed by the chromatic abberation present in the crops, esp since they're crops from centre of frame, but I guess considering its price it's decent value glass - and there's always a software fix.

John, if you zoom in to say 14mm or so, until the vignetting disappears, and train yourself to use this field of view, you'll save from having to upgrade to a thinner CPL filter.

[dooda]

One trick that I do sometimes if you have to be wide open, or if you only notice the vignette after, is to clone it out. I find the corners fairly easy to clone out without being noticed (people don't generally linger on the corners much).