Issues with a DA* 16-50

aemaeth · 04-24-2021, 07:20 AM

Hi all

So, a few yers ago I bought a used DA* 16-50, and it had the focus issue. I found here a guy that can fix this in the UK and I sent it to him to get it sorted, and it was mostly OK for a few years, but the issue is back.

But that is not whatis bothering me. I just realized that at 50mm, at 2.8 it looks qute "creamy" and it wasn't doing it before. I have a feeling that is doing it more and more.

I had a look at old pictures to check if I wasn't going crazy and I can clearly see the difference. I also checked with a DA* 55mm at 1.4 and at 2.8 and is sharp, no issues, so is definitely that lens.

The biggest question here will be if is fixable and if so, it won't cost me a fortune.

I will try to attach some crop pics to show this.

Attached Images

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**Bob 256** · 04-24-2021, 07:54 AM

What camera are you using it with? Are you using manual or auto focus?

Usually, critical focus is established by the camera in auto-focus mode, and there are camera adjustments which affect this but not lens adjustments.

Do the usual checks on your lens and look through it when it's off the camera. See if there is any dust or contamination in the lens itself. Check to see if the rear tab closes the lens as it should (sometimes this gets stuck and you're shooting all your shots wide open without knowing it and that will cause a "filmy" appearance). Make sure your lens is set to the "AUTO" aperture setting and not a fixed setting (again it might be set to a wide open setting and your camera will use that every time, adjusting shutter speed to match exposure requirements).

From your photos (assuming this is lens related), it looks like it could involve lens elements (maybe decentering) and might take a reputable repair shop to analyze. One thing you can do is use Liveview if your camera incorporates it, and take a shot after adjusting for critical focus manually (using image magnification, again if your camera has that). Then without touching the lens focus, switch to auto-focus and see if the camera re-adjusts the focus point. If it does, then you might be looking at your camera and not the lens in terms of needing attention.

Hope this might lend some help.

**sergysergy** · 04-24-2021, 08:19 AM

Does anything sound loose inside? Based on the first couple of pictures it looks more like a decentering or glass problem than a focus problem.

**caliscouser** · 04-24-2021, 12:32 PM

The 16-50 does get 'glowy' wide open at 2.8. But the center should be usably sharp.

Check your focus, is infinity focus still working? Try live view focusing as suggested.

Get a flashlight out and do a good inspection of the optics for any haze or fungus.

Shoot a distant landscape at 2.8 focused at infinity or the furthest point in the scene. It will be soft off center, but if it is worse on one side that suggests de-centering (which is not unusual for this lens)

aemaeth · 04-25-2021, 06:49 AM

Thanks both for all the reply!

The camera is a Pentax K5, and always AF since I'm not the great with MF.

I did check and no dust or anything on the cristals as far as I can see and can't hear anything loose on the lens itself.

I will give it a go to the critical focus, but haven't had any issues so far with the rest of the lenses.

Infinmit focus seems OK but I will try a second spin.

And I know is not the sharpest on corners, but the crops are of the center, and is not the greatest.

If I close the F to more than f5 there is no issue and at that point is beautiful.

IF the issue is with the lense, is it possible to fix it?

shyrsio · 04-25-2021, 02:17 PM

It looks suspiciously soft, especially for a * lens. I think maybe a drop has decentered some element inside. I've seen this with its bigger brother the 50-135/2.8.

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04-24-2021, 07:54 AM	#2
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,378	What camera are you using it with? Are you using manual or auto focus? Usually, critical focus is established by the camera in auto-focus mode, and there are camera adjustments which affect this but not lens adjustments. Do the usual checks on your lens and look through it when it's off the camera. See if there is any dust or contamination in the lens itself. Check to see if the rear tab closes the lens as it should (sometimes this gets stuck and you're shooting all your shots wide open without knowing it and that will cause a "filmy" appearance). Make sure your lens is set to the "AUTO" aperture setting and not a fixed setting (again it might be set to a wide open setting and your camera will use that every time, adjusting shutter speed to match exposure requirements). From your photos (assuming this is lens related), it looks like it could involve lens elements (maybe decentering) and might take a reputable repair shop to analyze. One thing you can do is use Liveview if your camera incorporates it, and take a shot after adjusting for critical focus manually (using image magnification, again if your camera has that). Then without touching the lens focus, switch to auto-focus and see if the camera re-adjusts the focus point. If it does, then you might be looking at your camera and not the lens in terms of needing attention. Hope this might lend some help.

04-24-2021, 08:19 AM	#3
sergysergy Site Supporter Join Date: Jan 2011 Photos: Gallery Posts: 5,175	Does anything sound loose inside? Based on the first couple of pictures it looks more like a decentering or glass problem than a focus problem.

04-24-2021, 12:32 PM	#4
caliscouser Site Supporter Join Date: Sep 2014 Location: SF Bay Area, CA Photos: Albums Posts: 1,037	The 16-50 does get 'glowy' wide open at 2.8. But the center should be usably sharp. Check your focus, is infinity focus still working? Try live view focusing as suggested. Get a flashlight out and do a good inspection of the optics for any haze or fungus. Shoot a distant landscape at 2.8 focused at infinity or the furthest point in the scene. It will be soft off center, but if it is worse on one side that suggests de-centering (which is not unusual for this lens)

04-25-2021, 06:49 AM	#5
aemaeth New Member Join Date: Apr 2021 Posts: 2 Original Poster	Thanks both for all the reply! The camera is a Pentax K5, and always AF since I'm not the great with MF. I did check and no dust or anything on the cristals as far as I can see and can't hear anything loose on the lens itself. I will give it a go to the critical focus, but haven't had any issues so far with the rest of the lenses. Infinmit focus seems OK but I will try a second spin. And I know is not the sharpest on corners, but the crops are of the center, and is not the greatest. If I close the F to more than f5 there is no issue and at that point is beautiful. IF the issue is with the lense, is it possible to fix it?

04-25-2021, 02:17 PM	#6
shyrsio Pentaxian Join Date: Apr 2016 Location: Tirana Posts: 780	It looks suspiciously soft, especially for a * lens. I think maybe a drop has decentered some element inside. I've seen this with its bigger brother the 50-135/2.8.