Why are my teleconverter test shots soft, and how should I test lens sharpness properly?
Asked 1/21/2020
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2 answers
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I tested a 135mm manual-focus lens on a Canon 5D Mark II, first by itself and then with a Kenko Pro300 3x teleconverter, using a tripod and remote release. I made 1:1 crops of a barcode target and noticed that both images look soft, with the teleconverter version looking worse.
What kinds of issues could cause this softness in a setup like this? For example, could it be focus error, low contrast from exposure, camera vibration, or the teleconverter itself? Also, what should I include in a proper sharpness test to better identify problems such as center softness, edge softness, vignetting, or distortion?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
1
Just a crop at the center of the picture doesn't show possible problems of vignetting, additional softness on the edges, and distortion. The images aren't very well exposed either and this reduces contrast.
There are a few things to check if you want to make sharp pictures,especially with long focal lenses:
- shooting speed
- use of tripod
- remote trigger
- mirror lockup
Not knowing what you did makes it difficult to give an answer.
Also, I assume the autofocus was disabled, so how did you set the focus?
Originally by user75947. Source · Licensed CC BY-SA 4.0
user75947
6y ago
0
Generated from our catalog & community — verify before relying on it.
From the examples and discussion, the main issue can’t be identified as a single optical defect from a center crop alone. A center-only crop won’t reveal edge softness, vignetting, or distortion, and low/poor exposure can also reduce contrast and make images appear less sharp.
Likely contributors are:
- focus accuracy, especially with manual focus
- camera vibration, particularly with longer effective focal lengths
- the teleconverter reducing sharpness and contrast
- test method limitations
For sharper, more reliable test images, check:
- solid tripod use
- remote release
- mirror lockup
- sufficiently fast shutter speed when relevant
- careful manual focusing
A 3x teleconverter will usually make softness more obvious, so the softer result with the converter is not surprising. To evaluate lens quality better, shoot a more controlled target and include more of the frame, not just the center, so you can assess center vs edge performance, distortion, and vignetting as well as overall sharpness.
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UniqueBot
AI6y ago
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