[Digitalis]

Corner/edge performance at f5.6 is really unacceptable. Since when do we evaluate lens performance based on center resolution alone?

I agree, the corner/edge performance leaves a lot to be desired. However you were stating that the peak of sharpness from the DA15 is seen at f/8 - this is clearly not the case, to obtain the best overall performance from the DA15 one needs to compromise and stop down to f/8 - which is hardly where it performs at its best - though if you use central compositions with the subject at the centre of the image, the corners softness isn't such an issue - Which is an argument users of the sigma 30mm f/1.4 have been using for years. When it comes to lens performance evaluation it is dependant on the focal length and the subject being photographed, which is an important factor with lens selection.

I'm sorry, you totally lost me there...a 'loose lens" ??? "Fall off the mount" ??? No idea what you are trying to say.

I was referring to your statement-

all lenses loose sharpness when the aperture gets too small.

- it is spelt "lose" not "loose"

[newmikey]

I was referring to your statement- - it is spelt "lose" not "loose".

I was referring to your statement

My humblest apologies for this grave mistake and I can see where this led you to emphasize this obvious mistake and ridicule it. Considering the fact that English is merely my third language I should possibly not be posting on this forum in the first place. May I cordially invite you to join us over at http://www.pentaxforum.nl and share your opinion on this lens? (In Dutch please)

However you were stating that the peak of sharpness from the DA15 is seen at f/8

What I literally said was "With UWA, shooting between F8 and F11 should be enough to benefit from extreme DOF and get the best sharpness out of the lens.". I cannot see how you would willingly misquote me on that or take that text as implying that I was referring to a "peak of sharpness", whatever that may mean to you.

When I refer to "best sharpness out of the lens" that means the lens. Not the corner or the center but the whole thing. All things considered between f5.6 and f8 the center takes a hit of 4.5% while the border and corner performance both shoot up by over 13% resulting in an overall performance increase of slightly over 6%. That would lead me to believe the lens performs better at f8 but I may have mixed up my numbers, you never know.

[Lowell Goudge]

if you are considering comparing a K5 to full frame, and the canon 17-40 mm lens, you need at least to go to 12mm on the wide end.

start with this, if you want to go as wide.

but personally i do not like to go that wide with landscapes, unless you want to add a foreground subject. ultra wide lenses tend to make the background insignificant,

I like longer lenses to bring the background out

as for flairless lenses in ultra wide i find the samyang lenses, 8mm and 14mm lenses very very good

[Kaiowas]

Common misunderstanding: all lenses loose sharpness when the aperture gets too small. F22 is way to small and will not get the most out of the lens' theoretical performance. With UWA, shooting between F8 and F11 should be enough to benefit from extreme DOF and get the best sharpness out of the lens.

Example: I saw you purchased the famous DA15. At F11 its DOF ranges from 75cms to infinity when focussed on something 2 meters away. Online Depth of Field Calculator.

That's true, losing significant sharpness after a certain aperture is normal, i should have wrote "best possible" sharpness @F22 maybe. Maybe there are lenses that perform far better @F22 than others. The reason for me asking about this is to get as nice sunbeams as possible, so the criterai is to still be able to get as much sharpness as possible across the border @F22.

Generally i agree, F8 seems to be the best for the DA15mm, I dont see a reason to use F5.6 for a little bit center sharpness and losing much more relative overall picture sharpness for landscape, forest, etc, pictures with a lot of objects, when my goal is to shoot an overall sharp image. (losing 95 LW/PH center versus gaining 241 LW/PH Border)

[rparmar]

DA12-24 is the best choice. Usable straight from f/4. Optimal sharpness. Better IQ overall than DA15, especially edges and corners. Who buys a wide angle to have only the centre sharp?

Field of view much the same as that Canon 17-40mm you referenced. A lot wider than DA15. And the ability to go to near normal at 24mm is very useful.

DA15 better for flare and more compact. But if you are comparing to FF that can't be an issue!

[rparmar]

but personally i do not like to go that wide with landscapes, unless you want to add a foreground subject. ultra wide lenses tend to make the background insignificant,

I like longer lenses to bring the background out

A good point. I use ultrawide for interiors where there is no choice. For landscapes I think the whole ultrawide thing is a rather old gimmick. It turns mountains into molehills and presents an entirely unrealistic view of the world.

I currently shoot on a system where my widest lens is FOV equivalent to 28mm on 135. That's as wide as I need for outdoors. And sometimes a telephoto is perfect for landscapes too. Really depends on your eye and what you are doing.

[Digitalis]

I use ultrawide for interiors where there is no choice. For landscapes I think the whole ultrawide thing is a rather old gimmick. It turns mountains into molehills and presents and entirely unrealistic view of the world.

I agree, however there are some subjects that just scream for a wide angle lens:


Pentax K5IIs - DA15mm f/4 ASPH

[ManuH]

I agree, however there are some subjects that just scream for a wide angle lens:

Wow that's a really beautiful picture.

I like the DA 15mm a lot because it's wide without being too extreme.

That said I still regret selling my 12-24mm, it was such a good lens with reasonable flare control. It's more versatile than the 15mm and you "only" lose the size. But it's not that big for a zoom, it's only the front element that makes it look like big. I still have the 15mm and the 8-16mm. As Digitalis said it's a brick compared to the DA 15mm and worse you cannot attach filters as easily as the 15. (and the 49mm filter thread is a bonus because Pentax was wise enough to standardize their primes on that size, I think only the DA 14mm and FA 31mm have a different thread size, which is understandable considering the FOV and the speed).