Why does a wide-angle adapter make my 50mm f/1.4 blurry at wide apertures?
Asked 9/23/2012
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2 answers
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I use a 0.45× wide-angle adapter on my Canon lenses. It seems reasonably sharp on my 18-55mm kit lens, but when I put the same adapter on my 50mm f/1.4, images are noticeably blurry at large apertures like f/1.4. If I stop the 50mm down to around f/5.6 or smaller, the images get sharper.
The 50mm is sharp by itself, and the adapter also seems fine on the kit lens. I was shooting still subjects with a tripod, good light, and manual focus.
Why does the adapter become blurry on the 50mm at wide apertures, and why does stopping down improve it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
4
All optics has their own disabilities, and the two lenses are so little blurry you cant notice it. Larger apertures gives more blur. The 50 mm lens you cant notice on its own, the wide angle converter adds so little blur that you cant see it on the small apertures, but the blur on F/1.4 multiplied with the blur on the converter is enough to notice it. Does the specs on the converter say something about what aperture range the optics is made for?
Originally by user11455. Source · Licensed CC BY-SA 4.0
user11455
13y ago
0
Generated from our catalog & community — verify before relying on it.
A wide-angle adapter adds another optical system in front of the lens, and every optical element introduces some aberrations or softness. At wide apertures, your 50mm f/1.4 is using more of the outer parts of its optics, where aberrations are usually stronger. Adding the adapter on top can make that softness much more visible.
When you stop down to f/5.6 or smaller, the lens uses a narrower central portion of the optics, which reduces aberrations and increases sharpness. That’s why the combination looks better stopped down.
So the issue is not that either item is “bad” by itself; it’s that the adapter and the fast 50mm do not work especially well together at large apertures. The adapter may also be better matched to slower lenses or a certain aperture range.
In short: wide-open, the combined optical flaws are easier to see; stopped down, they’re reduced.
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