Pentax DA L 55-300mm is very soft at 300mm — faulty lens or user error?
Asked 8/31/2012
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2 answers
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My Pentax DA L 55-300mm becomes extremely soft at or near 300mm, even in the center of the frame. I tested it on a Pentax K-5/K-r using Live View contrast-detect AF, and the problem seems worse at the long end. Stopping down helps only a little.
I’ve also found the issue is intermittent: sometimes the lens looks normal, but after staying near 300mm, sharpness degrades badly with visible aberrations. Zooming out and back in often seems to clear it up. Below about 150mm there’s no obvious problem, and around 150–200mm it’s only somewhat soft.
I’ve ruled out simple camera shake as much as possible, including testing on a stable surface. Is this likely a technique issue, or does it point to an internal mechanical fault in the lens?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
2
There seems to be a problem with my DA L 55-300mm lens:
Pentax K-5 with Pentax DA L 55-300mm @ 300mm.
Av, 1/320s f/5.8 ISO 125. 100% crop from center.
If it didn't do it before and it does it now then somethings broken - probably. But, you know that.
Is that hand held or on a tripod? At 1/320s and 300mm you are on the reasonably comfort bottom limit of what can be hand held wit reasonable care without stabilisation. (ie you can get to say around 1/150th with super stable hand, good experience and care and Ninja breathing).
IMPORTANT:
- If using with a tripod **turn the antishake off* !!!
- If using without a tripod, turn it on.
That certainly is not pretty and I'd hope for far better from even a consumer lens, properly used. Full zoom is going to be less than its best setting. So you could start out by giving it a less challenging task to see if it is grossly broken or works OK at some settings.
I don't know the specific lens but at about say 150 mm, f/11 and on a tripod, I'd expect it to do about as well as it is capable of. That would give slightly under 1/100s at the same ISO as above, so you'd want a tripod or have the camera solidly held on a stable mount. (I chose 150mm as the ~ geometric mean of 55 and 300mm - and longer zooms usually work at about their best around mid range.
These enthusiastic user reviews suggest that your should give better than that.
Originally by user6263. Source · Licensed CC BY-SA 4.0
user6263
13y ago
0
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That level of softness is not normal for this lens, especially in the image center. A 300mm consumer zoom may be weaker wide open at the long end, but it should still perform much better than your samples.
First, rule out technique: at 300mm, camera shake is easy to introduce. If testing on a tripod or stable support, turn shake reduction off. On Pentax, using the 2-second self-timer is helpful because it also reduces vibration via mirror lock-up behavior. If hand-held, keep stabilization on and use a faster shutter speed.
If you still get results like this, especially if the problem is intermittent or the lens used to be sharper, that strongly suggests a fault. Since zooming out and back in temporarily fixes it, an internal mechanical issue is likely—possibly wear or damage affecting alignment or focus/zoom mechanics. That would also fit the increased aberrations you’re seeing near 300mm.
So: this is probably not normal user error alone. If careful testing still shows the issue, the lens is likely faulty.
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UniqueBot
AI13y ago
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