Infinity focus setting DAL 18-55 Supplied with KR


RMURPHY195

Link Posted 02/11/2011 - 12:45
Arrived at high point near Clee Hill (Titterstone) yesterday just as storm was approaching. Followed my old film camera practice of taking a few snaps quickly in case storm arrived too fast to set up properly (it did!) Usual practice is - onto manual, check exposure, set focus to infinity (ie turn focus ring to max) and off we go.

Disaaster! - image quality awful!

So I did some tests, the upshot of which is that if I point at a distant object (block of flats) and take picture with focus set to infinity, focus set to recommended distance, then autofocus, the results are acceptably sharp from the auto and recommended focus shots, but everything - and I mean from 20 feet away into the distance- is blurred when the focus ring is turned to its full extent! Tried again with shake reduction switched off, same result. All on a tripod of course.

Similar tests (infinity v. recommended focus) using older 200mm F4 and 28-80 lens from MZ5N did not show this trait (and gave sharper images anyway).

Lens at fault is the 18-55 DAL 3.5-5.6.

Question 1)Do I have a faulty 18-55 lens which just produces rubbish when the focussing ring is turned to its fullest extent, or is there something I should know?

Question 2)Can anyone recommend a better quality replacement, preferably that does not have this trait?

Whizzkiddwill

Link Posted 02/11/2011 - 13:00
Not sure if this is relavant but i have recently purchased a K-x with kit lens 18-55 DAL 3.5-5.6 When using manual focus i found the same and have found a slight tweak to the left (i think it full right for infinity) seems to sort the image out.

I have read that the kit lens is a cheaper quality version so assumed (I Know its wrong to) that this was one of the effects.

For recomendations i think the 18-55 DA 3.5-5.6 will be better but i'm new to Photography so i'd ask someone else to advise you. I've just joined here but i think someone will comment soon and sort you out,

and of course Welcome to the forum. (If i'm not too new to say that)

Will
Pentax K-x, DAL f3.5-5.6 18-55mm,Pentax-A 50mm f2, DAL f4-5.6 50-200mm, FG360FGZ
Last Edited by Whizzkiddwill on 02/11/2011 - 13:02

timothyw

Link Posted 02/11/2011 - 13:27
There's something you're missing- most lenses will focus past infinity.

This is for a number of reasons- mainly it's because it's difficult to calibrate a lens so that the stop is exactly on infinity focus, partly it's because lens components can expand in heat so shifting the infinity focus point. I think it also means lenses are more likely to be compatible with conversion tubes etc.

You'll find the same with pretty much any lens. If you want to set infinity focus, I'm afraid you need to focus on something far away. The moon is a good bet at night time.

Helpful

sterretje

Link Posted 02/11/2011 - 16:06
As timothyw explained.

The missing distance scale is possibly even a bigger drawback on DA-L lenses than the missing lenshood (as the latter can be solved easily). You found one issue, playing with hyperfocal distance is also a problem.

Even the more expensive DA18-135 does not seem to have a distance scale (stupid omission if I'm right).
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)

Helpful

RMURPHY195

Link Posted 13/11/2011 - 18:32
Ah well, its back to leaving on autofocus, or just keeping the 28mm SMC on!
Thanks to all for your info

davidstorm

Link Posted 13/11/2011 - 23:13
The DA L 18-55mm lens is excellent optical quality (take a look at the pictures by morpheus71 in the gallery).

Whizzkiddwill wrote:
Not sure if this is relavant but i have recently purchased a K-x with kit lens 18-55 DAL 3.5-5.6 When using manual focus i found the same and have found a slight tweak to the left (i think it full right for infinity) seems to sort the image out.

I have read that the kit lens is a cheaper quality version so assumed (I Know its wrong to) that this was one of the effects.

For recomendations i think the 18-55 DA 3.5-5.6 will be better...

The recommendation above is not necessarily correct as the DA L version is optically identical to the DA version. I have had excellent results with this lens which is sharp and typically 'Pentax' in terms of colour and contrast. I always rely on my eyes if focussing manually and have had no issues with the lens. I think the other guys above are basically correct in stating that many lenses focus past infinity and I would also guess that unless you are unlucky and have a 'bad' copy of the lens, there's probably nothing wrong with it.

Regards
David
Flickr

Nicola's Apartments, Kassiopi, Corfu

Some cameras, some lenses, some bits 'n' bobs

sterretje

Link Posted 15/11/2011 - 12:12
davidstorm wrote:
...
The recommendation above is not necessarily correct as the DA L version is optically identical to the DA version.
...

Which is not 100% correct to my knowledge The DA version is the first generation, the DA II / DA-L / DA WR are the second generation with improved optics.
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)
Last Edited by sterretje on 15/11/2011 - 12:13

OldTaffy

Link Posted 15/11/2011 - 15:20
RMURPHY195 wrote:
Ah well, its back to leaving on autofocus, or just keeping the 28mm SMC on!
Thanks to all for your info

Well, you could run your own test...

I have just checked the 18-55 DAL that was fitted to my own K-x, using some leafless trees about 100 yards away as 'near-infinity'. Set to midpoint (35mm) I found that:

(a) autofocus on distant trees, then switch to manual focus: the ridged focus ring can be moved about 2 mm further before reaching the mechanical stop. Difference in the viewfinder only just perceptible.

(b) in LiveView (with the image magnified as much as possible with successive presses of the 'INFO' button) best focus at about 100 yards was again a couple of mm short of the end stop. This was true whether I was in MF the whole time, or if I used Liveview AF before disengaging the AF into MF, to allow the focus ring to move. Again, the defocussing at the end stop was very slight.

If you find a big difference between infinity autofocus, in any mode, and the mechanical end-stop, I would think that you have good grounds for claiming a replacement lens.

BTW: I seem to remember that there is still a lot of ironstone ore in Titterstone Clee - enough to make compass bearings unreliable. Is it wise to be up there in a thunderstorm?

Take care,

Martin
A few of my photographs in flickr.
Lizars 1910 "Challenge" quarter-plate camera; and some more recent stuff.

OldTaffy

Link Posted 15/11/2011 - 15:47
An afterthought: I can recommend karma mechanic's method for checking the accuracy of autofocus. It was in the Lens Fine Tune Adjustment thread, on 21/07/2011.

Martin
A few of my photographs in flickr.
Lizars 1910 "Challenge" quarter-plate camera; and some more recent stuff.
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