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I was wondering is there a way to know if a lens will be good quality? I've recently discovered that the camera body isn't absolutely everything when it comes to image quality, but that the lenses also count. Are there specs like a camera body to determine image quality (and I don't mean aperture and the like)? Is there a way, before buying a new lens to know if it will be sharp, blurry, or lacking in general quality? Or is this just resolved by "you get what you pay for", and the expensive, good branded lens will just simply be better?

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  • \$\begingroup\$ If you were going to buy a new car, how would you know if it was good? \$\endgroup\$
    – Philip Kendall
    Dec 7, 2023 at 8:21

6 Answers 6

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You live in the era of: Reviews.

  1. Learn a bit about Lenses. Focal length, aperture, distortion.

  2. Define your objective for the lens. Portrait, landscape, night photography, macro.

  3. Narrow your options. Visit the manufacturer's website and identify the "lines". Let's say, "silver line" or "gold line".

  4. Use a website like https://www.dpreview.com/products/compare/lenses to compare two or three specific lenses.

Some specific tests you want to look at are sharpness tests:

They use, of course test charts for sharpness.

enter image description here

Here is an explanation of how the test is performed and the different charts they use: Sharpness, vignetting, and distortions.

But there are some other features you could need and compare, like autofocus speed, image stabilization, and build quality.

  1. Complement viewing a YouTube video. Sometimes you can find even a comparison between the two models you want.

Normally the options are Lenses from the same brand, Like Nikon, Canon, Sony, or third-party brands, like Sigma, Tamron, or Tokina. There are also cheaper brands that are probably not as reliable but interesting to consider.

  1. Do not think you will get the perfect option the first time. The truth is that you will be learning on the way. Learn to enjoy the ride.

  2. Use the search box to read some tips to define your first lens besides the kit lens: https://photo.stackexchange.com/search?q=first+lens

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Are there specs...to determine image quality (and I don't mean aperture and the like)?

Actually, max. aperture is one key way to get a hint. I wouldn't ignore it. Typically, the bigger/faster the max. aperture of a lens is, the higher-end it will be in relation to its peers. Also, if a zoom lens has a constant max. aperture, it's likely to be higher quality than an equivalent lens with a variable max. aperture. So, f/2.8 zooms are typically pro-quality lenses, as are wide-to-short tele primes that are faster than f/1.8, and telephoto lenses that are faster than f/5.6.

But also, nearly every line of lenses has a "pro quality" indicator in their nomenclature. Canon uses L (luxury), Sony uses G Master, Nikon's Z lenses use an S. This Q&A on nomenclature can delineate these for most brands. And most of these lenses will have four-figure price tags.

However. There are also some low-cost lenses that have good solid image quality, and lens design improves as newer techniques enter the arena. Currently, Canon is making a number of very good lenses at low cost using PMo (plastic molded) elements that greatly increases what they can achieve at lower cost. Learning how to read an MTF chart, and doing some research on testing data to see how well a lens bears out on the MTF theoretical performance can help you.

And have realistic expectations on performance by knowing how some optical designs are more difficult/expensive to achieve than others (e.g., wide angle lenses tend to be tougher to get right than longer lenses; faster lenses tougher to correct than slower). Everything is a tradeoff. And higher optical performance often comes at increased cost, weight, and bulk. Knowing what's sufficient and what you can afford may also weigh more heavily on you than how flat and high the lines are on the MTF chart. Overall value to you might beat out image quality.

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Take pictures with it! Rent it for a week or so and see if it does what you want.

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Even cheap lenses nowadays often perform favourably compared to lenses of a few decades ago. Computer-aided design processes help a lot. I'm not going to claim it's impossible to buy an unsatisfactory lens anymore, but by and large, modern lenses perform well in the use cases they are designed for.

Many lens manufacturers use product naming conventions that give a hint to the intended quality/performance levels of a lens. Sigma has its "Art" line, Sony has "G Master" lenses, Canon has "L" lenses, the best performers from Zeiss are probably the "Otus" line, etc.

I think actually this existing question on the site could be helpful for you:
What do all those cryptic number and letter codes in a lens name mean?

And a very, very crude "tell" when it comes to lens quality is if the aperture reaches f/2.8 or wider. These lenses tend not to be simplistic to design/produce – manufacturers have put some effort into these lenses, certainly to perform better than their "kit" offerings, for example.

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  • \$\begingroup\$ f/2.8 for a zoom. It's not all that impressive for a prime ;) \$\endgroup\$
    – Tetsujin
    Dec 8, 2023 at 19:06
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    \$\begingroup\$ Correct, but we don't have to worry about primes so much because they tend to be pretty reliable quality in any case. With exceptions :) \$\endgroup\$
    – osullic
    Dec 8, 2023 at 19:40
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Answering your question directly: to know whether any product is good for your needs you need to know:

  1. what are it's key characteristics
  2. how does your experience depend on it

Key optical characteristics of lenses are:

  1. strength of chromatic aberrations - affect high contrast scenarios
  2. geometric distortions - may affect sharpness in the image corners and whether you need to use additional editing to cancel them
  3. field curvature - affects how predictable the sharpness region is
  4. vignetting - affects the need for additional editing and added noise
  5. bokeh - affects how smooth and uniform the out of focus region look
  6. resolution - affects how contrast of image features depends on their size
  7. flare resistance - whether lens produces ghost image of strong light sources placed inside and outside of it's view

and also there are:

  1. reliability and speed of AF (DSLR's AF does depend on lens)
  2. build quality

While all of these characteristics could be quantifiable and measurable :

  1. you will easily find only subset of those
  2. they can be measured very differently
  3. you might not find important metrics for the lens you are interested in
  4. there is no direct way of knowing how those metrics translate to your experience
  5. user-supplied photos can be misleading because you do not know what kind of editing was applied

In general lens market is quite competitive, there are basically no terrible lens made by major OEMs (depends on price of course) so if you are a starting photographer you do not need to overthink it. One good way of knowing if lenses are good enough is to establish some baseline using sample photos for one lens and comparing others against it with technical metrics you can find.

However here are some technical resources which you can rely on:
https://www.opticallimits.com/
https://www.dxomark.com/Lenses/
https://www.the-digital-picture.com/Reviews/Comparison-Tools.aspx

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Also there are rules of thumb you can apply to get sharper output for less:

  1. Stop down. Most lenses are softer at their widest aperture and at the edges of the frame, and this is worse for inexpensive lenses. Stopping down a full stop or two usually cuts out the worst of this.
  2. Consider using some 'primes'. Zoom lenses (especially the better ones with fixed maximum apertures these days) are much better than they were 40 or 50 years ago, but it's just plain easier to make a good lens if it doesn't have to change focal lengths. There is less glass in a 'prime' (some people are weird about what to call that), which means there's less flare, less weight, fewer compromises, and fewer things to get wrong in production. Usually this means an inexpensive prime lens will perform like an expensive zoom for the same focal length at a fraction of the size and weight.
  3. Look into mechanical stabilization. Nobody's hands are as steady as they think and a cheap monopod or tripod can make pictures sharper than you think the lens can take.
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  • \$\begingroup\$ This doesn't really answer the question, "how can I tell if a lens is good quality?" I understand your oblique approach to the question, but even if OP could apply your suggestions, you haven't helped them determine if a lens is good quality. \$\endgroup\$
    – scottbb
    Dec 10, 2023 at 22:15

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