How can I tell if my Pentax DA 18-135 is defective or just soft at some settings?
Asked 8/19/2016
5 views
2 answers
0
My Pentax DA 18-135 gives inconsistent results. Some images are very sharp, but others look noticeably soft, and a few are extremely blurred-looking. I’m trying to figure out whether this is normal lens behavior at certain apertures or focal lengths, or whether my copy may have a problem.
For example, one shot was taken at ISO 200, f/4.5, 1/2000, RAW, with a little sharpening in post. The soft area I’m seeing is from a crop near the lower-left portion of the frame. Focus was set with the center point on a distant mountain.
What’s the best way to test whether the lens is behaving normally?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
2
Most lenses are at least a little softer wide open, and you should expect some variation across the zoom range as well. Try looking through your archive and comparing different shots taken at specific apertures to see how consistent the issue is. Are all the shots at f/4.5 similar in sharpness, or do they vary a lot? How about f/8? If you can keep the focal length constant as well, that'll give you even better information.
Consider buying a focus target for a few bucks and using it to get better data. You'll know for sure that the lens has a problem if you can get it to produce varying results under the same circumstances, so it's useful to be able to measure the degree of softness as you hold other variables (aperture, distance, focal length) constant.
Originally by user4262. Source · Licensed CC BY-SA 4.0
user4262
9y ago
0
Generated from our catalog & community — verify before relying on it.
Some softness can be normal, especially wide open, and sharpness can vary across a zoom lens’s focal range. A single soft frame doesn’t prove the lens is defective.
The key is consistency: test the lens under controlled conditions and keep variables fixed. Compare images shot at the same focal length, same subject distance, and same aperture. Then check whether results are repeatable.
A good approach is to review your archive or make a simple test series:
- shoot the same subject repeatedly
- keep focal length constant
- compare f/4.5, f/8, and other apertures
- look for whether all shots at one setting are similarly sharp or whether sharpness varies unpredictably
Using a focus target can help a lot, because it gives you a repeatable subject and makes focus errors easier to spot.
If the lens produces very different sharpness under the same conditions, that suggests a problem. If it’s consistently softer wide open and improves when stopped down, that’s more likely normal behavior.
Recommended products
UniqueBot
AI9y ago
Your Answer
Related Questions
How does the Pentax DA 18-135mm compare to the 18-55mm for sharpness and image quality?
Is strong color fringing at f/1.8 normal on the Pentax DA 50mm f/1.8?
Pentax DA L 55-300mm is very soft at 300mm — faulty lens or user error?
Why does my Pentax K10D autofocus miss focus, and how can I test for back-focus?
Is the Pentax DA 35mm f/2.4 AL a good starter prime for street and night photography on a K-50?