Wow, good to know... I'll have to inspect the Tokina more... I have a 15-35 F2.8 RF on the way here, so that will be my new "Go-To" lens for wide angle shots (too bad the monsoon is basically over now). One of the main problems I've noticed living in Utah is you simply are far more limited in areas to stand to get compositions you want. You have cliffs, fissures, drop offs, etc... Many of the Arches simply only have a small handful of areas as good vantage points.
As far as diffraction goes, what I was "trying" to do was buy more shutter speed as I didn't own any ND filters at the time. This was for lightning shots. I've kind of figured out if you can get to a full second on interval timer, while not being as any insanely high F stops, then you kind of strike a balance between time vs aperture to hopefully get some of those daytime lightning shots (the most challenging!!). Currently I have a 6 stop ND, which does take the brightness down a bit of the lightning strike, but it noticeably increased the number of keepers on the last storm we had roll through.
Previous to owning an ND filter, the Tokina, even with the one B+W polarizer I own, would still force me to be in that F16-F22 range. So on one hand you get the lightning, on the other hand you will give up some fine detail on whatever else is in the photo.
I think for those wanting to chase lightning, a 3-Stop - 6-Stop ND filter is kind of the sweet spot, but being aware of what your particular lens is going to do when it comes for anything above say F14 is probably a wise move. Luckily most lightning compositions are going to be mainly of the entire sky, and yes I suppose one can do a composite utilizing the best aperature for any larger forground objects. I personally am old school and like to try to just get ONE shot of everything, but old habits die hard right!?
John Sheehy wrote in post #19281797
Does the Tokina's pupil have a weird shape when stopped down to f/16, so that it is not very round (more like a slit, or a sharp triangle), or is it smaller than it should be (a little harder to eyeball)?
The normal relationship between the amount of light getting through (due to assumed f-number) and diffraction assumes a circular aperture, and as this shape gets further from a circle, the more diffraction you get for the amount of light getting through. Most people never look at stopped-down apertures and wouldn't know how round they are stopped down. The area of the aperture is also probably not what it's supposed to be if it is not round, too. The inability to accurately control the shape and size of the aperture at very small apertures is probably a major reason why short-focal-length lenses often have a low upper limit on f-ratio.
