what is your tip when using manual focus under f2.0?

No the little red square in the viewfinder flashes ( blinks) when the camera thinks focus has been achieved and then extinguishes.

Sorry, Smeggypants, but the instructions quite clearly differentiate between the red point which indicates where you are focusing and the green hexagon that indicates when focus is achieved when it stops flashing and the camera beeps.

It's actually quite hard to prove the point as the camera locks onto focus in virtually every situation, but the red light can be made to flash on and off whilst the green hexagon is still merrily flashing away and no focus has been achieved. I know because I've just done exactly that.

The beep also indicates in focus.... goes right back to the ME-F.

With some lenses the red square is as good as you will get. It's
unlikely that a 28mm f/3.5 can be turned precisely enough to get
the green hexagon at over 3m There's only 5mm on the
focusing scale between the 3m mark and infinity You'd
need some kind of micrometer adjuster

... so line up the orange marks and you have hyperfocal set anyway

Bret

Hyperfocal distances were set in the 1930's for large format cameras.... just not good enough for digitals especially on a screen.

I've been trying to sort out 24mm and 28mm lenses recently. They seem to have a massive field curvature which throws things at about 30m on the edge of the frame OOF so the best option seems to be set the lens to infinity as long as it's properly adjusted for infinity. Everything from about 7m to infinity then seems to be in focus and the edges are more acceptable.

That's not really true because don't forget that depth of field tables were issued for 35mm format lenses, assuming a different circle of confusion than large format lenses. The circle of confusion is a different figure for every format, we don't rely on large format measurements in any way.

A useful trick is to set up hyperfocal distance (or any other DOF requirement) for an aperture, say f8, but actually use f11 instead. This results in a more conservative estimate of the DOF available and allows for better qquality enlargements.

It doesn't work with 24/28mm lenses anyway.... possibly due to
field curvature. Mattmatic did post a link to an article on the
Phase One site showing how to correctly set up WA lenses on
digital.

What doesn't work Algi? Field curvature will only be a problem in the near field, or at wide apertures, so not really changing the usefullness of that red-coded f8 setting on the pentax manual focus WA lenses.

You can get an idea what I'm talking about from this post. link Look at the "1:1 (100%) RHS of frame Compare captured by a screen grab at 800 wide." = RHS of Bridge shot by Chinon 28mm. The bridge was 40-50m away I was square off it and focused on the centre. The RHS of the Chinon shot is very soft. I've not retried it with this lens, but I did with another lens. It was soft as well when focused on the bridge, but when I set the lens to infinity, the centre stayed in focus and the edge went a lot better indicating a massive field curvature. The curvature now being close to infinity.

You can see this on most distant landscape shots with a 28mm sharp in the centre at a distance, but soft at the edge at a distance, but when you look at the edge closer to the camera it doesn't look too bad.

I will take the 28 out at the weekend and do some landscapes to check this; f8 or so, focussed at 2.xm for hyperfocal, focussed at infinity and then again at f11. Let's see what happens (this will be with the K5).

Bret

My feeling is that decentering and just poor design may have as much to do with this as any field curvature. Chinon are not the greatest lenses. I've never seen such a problem with any Pentax wide angle lens, or Nikon for that matter.

I can't get anything approaching sharp at the edge of a Pentax 28mm A f/2.8

I've found the lens test I noticed it on. It was a Kiron 28-105mm Zoom I'll post a screen grab later.

I did try it with a Sigma 24mm f/2.8 and found that best set to the middle of the infinity symbol.

I'm glad I'm not trying to find a 28mm that's sharp at the edge of FULL FRAME 35mm

Something is muchly amiss here. There's no reason why a wide angle lens should not be sharp at the edges. Maybe stopped down for optimum results, but it should be sharp.

Do you have a problem with current wide angle designs?

Funny you should say that John, check this out on my new DA15mm.




It vastly improves on stopping down to f8 (although the soft band on the RHS is still just perceptible) but surely this ain't right?

that pic looks soft in the centre as well here . ????