How can I compare lenses objectively, and what differences should I expect between a 50mm f/1.4 and an 18–55mm kit lens?
Asked 6/9/2013
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I want to make more informed lens-buying decisions instead of relying only on reviews and opinions. Are there reputable sources that compare lenses with measured data such as sharpness or distortion? Also, are there simple real-world tests an amateur can do to judge lens quality?
As a concrete example, I have a Canon 50mm f/1.4 and an 18–55mm kit lens on a Canon T3i. When I took a quick handheld photo of the same subject with both, the images looked very similar to me. I understand focal length and aperture at a basic level, but I’m unclear on how to evaluate things like distortion and depth of field, and how much of the perceived difference between lenses is actually visible in practice.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
8
Sooo. Several questions here.
- For sites with lens reviews, see Where can I find reviews of lenses?. These generally do measure, as your example, distortion.
- As with any qualitative test you can do yourself, these reviews focus on aspects which are easily measured. And they probably do a better job of those measurements than you can with your own test. (I'm not sure exactly how a "Turing test" would apply, as we are not trying to determine if the lenses are sentient.)
- Depth of field is flat-out the same for any two lenses with the same aperture and focal length. This isn't a quality issue.
- You can learn to see some common lens characteristics (flaws, artifacts, compromises). I've written a long answer detailing the most visible of these at What image-quality characteristics make a lens good or bad?
- And, finally, I've flagged this as a duplicate of What are the standard tests available to quantify lens parameters?, because I think that covers a lot of what you're asking.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—good lens review sites do publish measured comparisons for things like sharpness, distortion, vignetting, and other optical behavior. Community answers specifically recommended tools/reviews like DxO Mark and The-Digital-Picture.
A quick handheld snapshot often won’t reveal much, especially if both images were made under similar settings and viewed casually. Many lens differences only show up in controlled comparisons: same framing, same focus point, steady support, and close inspection.
Key point: depth of field is determined by focal length, aperture, and subject distance. For two lenses used at the same focal length and aperture, depth of field is essentially the same—it isn’t a “quality” rating of one lens versus another.
The biggest practical difference between your two lenses is maximum aperture. At 50mm, the kit lens is much slower than the 50mm f/1.4, while the prime can open much wider. That gives you more background blur potential and better low-light capability. When both are stopped down to the same aperture, differences may be much smaller, which is why your coffee-cup test looked similar.
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