[cgyed]

Hello,

While trying to "tune" the autofocus of the body of my K50, I realized that I have a big difference of sharpness between the same picture taken at different conditions :
Photo1 (55mm f/5.6)
Photo2 (55mm f/8)
The f/8 is really sharper.

The pictures has been taken with the camera stable on a table, and the front lens is the 18-55mm is clean.

On most reviews, this sharpness of this lens seems to be good, for exemple photzone with the DA WR version (mine is DAL WR) of the lens: Pentax SMC DA 18-55mm f/3.5-5.6 AL WR - Lab Test / Review - Analysis.

Do you think the f5.6 picture is corresponding to the actual and known quality of the lens ?

Thanks.

[LensBeginner]

Uh... yeah, that looks about right.

It's definitely not the ideal situation, at the tele extreme, wide open and - I think this also plays a role, and it jibes with my experience - at close distance.
It gets better going a little wider, stopping down a bit and/or focusing on a subject which is a little further away.

[Na Horuk]

Most lenses are sharper when they are stopped down one or two stops. F8 is often a sweet spot because it gives you really wide DoF as well (bigger DoF gives illusion of more sharpness, unless focus is perfectly correct).
With the kit lenses, it is often said to use it between 28 and 40 mm and around f8 for optimal sharpness.

Note if you go above f9 or so, diffraction will start to set in. This is noticeable as a general softness, especially if you go as far as f16. This is why it is not advisable to go above f12, because even though you get more DoF with higher F-number, you will lose much more sharpness.

Of course, sometimes you have to use a specific aperture, whether you need more light or you need more DoF. Depends on the priorities of that photo

[UncleVanya]

On mobile can't see the pictures to tell if there is exif data so forgive me if the answer is obvious. What shutter speed (s) and was SR turned off (for example with 2 second self timer mode)?

[cgyed]

Hello,

The shutter speeds were 1/25s (f/5.6) and 1/15s (f/8).
For these pictures, the shake reduction system was on. However, i tried before with 2s sec timer (to avoid any movement while taking picture) and the result was exactly the same.

I found this article : Pentax K-50: Performance
It says in the lens (kit) performance paragraph "With default settings in the camera I shot the lens at 55mm in aperture priority mode and wide open at f/5.6 and got the same results reported by Laura – images looked really soft."
Pictures are taken to illiustrate the text (55mm f/5.6 vs 55mm f/8), and obvious differences are shown, as mine.

[UncleVanya]

Hello,

The shutter speeds were 1/25s (f/5.6) and 1/15s (f/8).
For these pictures, the shake reduction system was on. However, i tried before with 2s sec timer (to avoid any movement while taking picture) and the result was exactly the same.

I found this article : Pentax K-50: Performance
It says in the lens (kit) performance paragraph "With default settings in the camera I shot the lens at 55mm in aperture priority mode and wide open at f/5.6 and got the same results reported by Laura – images looked really soft."
Pictures are taken to illiustrate the text (55mm f/5.6 vs 55mm f/8), and obvious differences are shown, as mine.

I ask because it might related to shutter shock, you may want to double check with both at the same shutter speed that you used but it may just be that soft. Which 18-55 - version 1 or 2?

[cgyed]

I checked and re-checked with different parameters (especially with same shutter speed), I always have the same result.

My lens is pentax DAL 18-55mm f/3.5-5.6 WR (gray ring).
Pretty sure it comes from the lens, the "softness" perceptible in the viewfinder.
From now, I'll just avoid the 55mm/f/5.6 combination.

[kh1234567890]

My DA18-55WR is not significantly worse at 55mm f5.6 than at any other focal length - Search: smcpda1855mmf3556alwr and 55mm and f5.6 | Flickr

[mikesbike]

I cannot see your pictures- they do not come up for me. But judging from comments- be advised that lenses in general often do not perform the same at close range focus as they might at farther distances.

The DA 18-55mm WR kit lens has received good reviews for its type and class of lens, including the one you show here from photozone. Actually, its worst performance according to the photozone test, is at 18mm wide open.

[kh1234567890]

I cannot see your pictures- they do not come up for me.

You should be able to see them.
















and many more ...

Edit - unless you mean the OP's pictures, I can't see those either. You can download them by clicking on the grey 'Validate and download ..' box on each of the two OP pages.

[Adam]

On most reviews, this sharpness of this lens seems to be good, for exemple photzone with the DA WR version (mine is DAL WR) of the lens: Pentax SMC DA 18-55mm f/3.5-5.6 AL WR - Lab Test / Review - Analysis.

The optics are the same, and your findings sound about right- you'll get a big bump in image quality by stopping down.