[iasonis]

Hello, I finally recieved my lens pentax 31mm f1.8 limited lens today and was very excited, until I got to testing it. I cant seem to get it to focus, even autofocus seems to come out flurry. Possibly 1 in 10 shots come in clear, but not better than my kit lens 18-55 al 2. I really enjoy the low light ability and the focal length is nice for what i need it for....except i cant focus even manually its hard. Is it just me??? Or is this lens faulty. I posted 5 pictures, the first is with my kit lens, the other 4 are from the 31mm. Thanks much for helping.

ps these are the best of the shots i took with the 31mm

Attached Images

         

[iasonis]

This is a close up of my cat with the kit lens, thanks again

[Zav]

Hard to say anything without the exif data.

[iasonis]

sorry, here it is:

1st pic iso 400 18-55 f6.7- 1/180
2nd pic iso 400 31mm 1.8 -1/15
3rd pic iso 400 31mm 1.8 1/6
4th pic iso 400 31mm 2.0 1/20
5th pic iso 400 31mm 3.5 - 1/30

[Peter Zack]

EXIF data has been stripped from the images (according to PhotoME) What shutter speeds, ISO SR etc? But if the focus ring is stiff and the AF motor isn't turning the focus, then you have a problem. Return it to the seller and get a new one.

Edit. pretty slow shutter speeds and basically wide open. 1/6th is not going to give a sharp image wide open. This is camera shake IMO. SR on/off? What camera? You're comparing the first (flash shot??) at 1/180th against some very slow shutter speeds. The exposures in 1 and 2 are fairly similar with drastically different shutter speeds.

[iasonis]

my camera is a k20d. I can manually turn the focus ring, it is pretty smooth but not loose. The first pic with the kit lens was not a flash shot.SR was on for all shots. Most of the shots were taken in full green mode, the camera chose those settings for some reason. I manually change them but just cant get it focused. Maybe its me but it seems 10000 times harder to focus the 31mm than my kit lens

[Duck Dodgers]

Are you getting focus confirmation from the camera? If so, I'd say it's camera shake (handheld at too slow a shutter speed).

[iasonis]

here is a pic of the kit lens 18-55 to compare it to

18-55 at 18 iso 400 f5.6 1/45
the next is 31mm 400 f2.0 - 1/180

[Zav]

sorry, here it is:

1st pic iso 400 18-55 f6.7- 1/180
2nd pic iso 400 31mm 1.8 -1/15
3rd pic iso 400 31mm 1.8 1/6
4th pic iso 400 31mm 2.0 1/20
5th pic iso 400 31mm 3.5 - 1/30

Do you really expect the FA31 wide open (or nearly wide open) to be as sharp as your 18-55 @ f6,7? and have a similar dof?
The dof is so narrow that you just can't see it properly (2nd picture the sun umbrella seems to be in focus).

[iasonis]

So its definitely not the lens then? In full green mode its chosing these settings, auto everything. Also when I manually try to focus it i feel that the ring wont let me turn it enough, it only goes so far then stops...i guess this is normal , sorry this is my first time trying to manually focus a lens.

[Zav]

If you want to make the most of the FA31, I suggest that you take a little time to learn the basics of the photography. :-)
Especially how to deal with the aperture.

[iasonis]

Maybe I am not being clear, it is stuck on 1.8 unless i put it into full manual mode. Auto doenst seem to focus at all. For that I would just have gotten an older lens cheaper. Anyway thanks for trying to help.

[Mike Cash]

Maybe I am not being clear, it is stuck on 1.8 unless i put it into full manual mode.

You mean you can't put the camera in Av mode and choose some aperture other than f1.8?

Excuse me if I inadvertently insult your intelligence with the question....but are you aware of the role aperture choice plays in depth of field?

[Peter Zack]

There seems to be some confusion of the various controls. shutter speed has nothing to do with focus. So if you are at 1/8th or 1/500th (or any other speed), it has no bearing on the focus at all. Just how much action you can capture and reduction of camera shake.

If the camera is in auto focus mode, then you should not be able to focus the lens manually very easy. Actually you shouldn't try to turn the focus ring at all with this lens. The camera body's AF motor is engaged and you are pushing against the motor. You could easily damage the camera. The DA18-55mm lens has a quick shift feature allowing you to do this but the 31mm Limited does not have this feature. You must turn the camera's AF switch to manual to use manual focus.

[NaClH2O]

Iasonis:
Here is what I'd do.
1) put the camera in AV mode, you can change aperture with the rear thumbwheel. If you look thru the viewfinder you can see both the aperture and shutter speed change as you change aperture. Try keeping aperture between 5.0 and 11.0 for outside shots this should give you enough dof and provide you with enough speed so that the camera SR can handle it. Speed should be 1/60 or above. If it is significantly below that bump up the iso.
2) Place the AF/MF switch to MF and practice turning the focus ring while looking thru the viewfinder. Pick a nicely defined object to focus on (back porch door for instance) As you turn the focus ring watch the door go from out of focus to in focus back to out of focus. Turn the ring back the other way, but slower. Keep doing that while watching thru the viewfinder, as you turn the ring slower and slower you will see a moment when your focus object pops into focus. When that happens, stop turning the focus ring and take your picture.

NaCl(hope that helps)H2O