Lens specs

I know I want a wide lens, for photos not video - now what do I look for when shopping online to tell which is better quality?

 

Thanks :)

Are we talking an interchangeable lens for a dSLR or something else? You need to be more specific. I've been at this for many decades and it still comes down to seeing what others say. Rarely will you find any numbers that tell you what you want to know, and sometimes it doesn't even come down to what people typically measure. Stick with well known quality brands and you'll usually be OK. Also remember, you usually get what you pay for. Smokin' deals on things nobodies ever heard of don't usually turn out well.

What is it that you want to do? What about your current gear is holding you back? These are the questions to start with.

I'm buying my first camera and lens combo - I want to be able to quantify if the lens is good or not.

 

Conrad - you seem to think it's not quantifiable and I just need to relate to word of mouth?

The first key number to look at is the focal length. This is the distance, lens-to-image sensor when the camera is imaging a far distant subject. Based on this value, we classify the lens into one of three major groups (wide-angle --- normal --- telephoto). To make this determination, you need to know what focal length is “normal” for your make and model camera. “Normal” will be a lens that approximates the way we humans view the world about us. If a “normal” lens is mounted, with the camera held in the horizontal position, its angle of view will be approximately 45⁰.

 

Finding out what focal length is “normal” for your lash-up requires you to make an investigation. It is unlikely that you will just stumble on this key fact. Technically, the focal length value that is “normal” will be a lens with a focal length about equal to the corner-to-corner measure of your cameras imaging chip. Another way to glean this key value is; your camera likely came with a zoom lens. This is a lens that allows you to adjust the focal length over a moderate span. Look at the specifications of your zoom. “Normal” will most likely be the center of the span of adjustment of your zoom lens.

 

OK, now that you have investigated and found “normal” for your camera, what next? Lenses with focal lengths shorter than “normal” fall into the wide-angle range. This will be a lens about 70% of “normal” or shorter. Likely the shortest (zoom out) setting of your zoom lens just reaches this boundary. Want a wider angle of view; select a much shorter lens to do this task. To know what telephoto lens to buy, choose one that is longer than the max (zoom in) of you existing zoom lens.

 

Some help on focal length ranges:

 

For the venerable 35mm full frame camera (FX) – 50mm is normal – wide-angle = 35mm or shorter – telephoto is 135mm or longer.

 

If you own a compact digital (DX) – 30mm is normal – wide angle is 20mm or shorter – telephoto is 75mm or longer.

 

As to quality (sharpness) you get what you pay for i.e. more expensive is better.

A few points . . . The quality of a lens is absolutely quantifiable. But, great photographs have been made with poor lenses and terrible photographs have been made with great lenses. As noted above, for the most part, you get what you pay for. I would add that, for the most part, if it comes packaged with the camera, it's not a great lens.

 

Giving advice on what lens to get is very, very, difficult. I don't know what you are trying to accomplish, I don't know what your skill level is.

Though you get what you pay for (hopefully) you can also assume that a lens that stretches capabilities will either cost more or perform worse, than an easier design. IOW, a super wide range zoom will probably cost you optical performance. As an example, I once tested an 18-270 mm zoom by a well known third-party lens company. It was the worst lens I'd ever seen, suitable only for tyros and web photos. It just pushed the boundaries too far. In spite of what I think, it's remains very popular, and with positive reviews. Not all kit lenses are bad either. The Nikon 18-70 that came with my camera many years ago is remarkably good, the equal of many of my fixed focal length lenses. Regardless, how you use it will always be the most important thing.

A few points . . . The quality of a lens is absolutely quantifiable. But, great photographs have been made with poor lenses and terrible photographs have been made with great lenses. As noted above, for the most part, you get what you pay for. I would add that, for the most part, if it comes packaged with the camera, it's not a great lens.

 

Giving advice on what lens to get is very, very, difficult. I don't know what you are trying to accomplish, I don't know what your skill level is.

The quality of a lens is quantifiable but it's generally not part of the specifications.

As indicated above, many cameras come with a "kit" lens, and often these are zoom lenses, which usually cover the range from medium wide-angle to short telephoto. For beginners I think this is a great way to learn about your camera, photography in general, and as you gain experience, you will be better equipped to make informed decisions about what to purchase to best fulfill your shooting interests...which may well change over time and experience. Many "kit" lenses are good lenses. By that I mean they are capable of handling many photographic situations well, produce photos as good as the photographer is capable of, and stand up to the care or abuse of being in relatively inexperienced hands. The lens doesn't make the photographer, but certain characteristics of lenses can facilitate a photographer more easily achieving his/her vision. I suggest not rushing to accumulate a stable of lenses until you are able to realistically define your goals, the expected benefits of a new acquisition, and what your budget can comfortably afford. Best of luck in your decisions and most of all have a lot of fun as you learn about photography.

DxO's database? - They haven't tested everything but a lot of lenses. I'd look at their sharpness rating (the infamous perceived megapixels). If I wanted to shoot film I'd look for a less distorting lens.

Being there I'd look up interesting lenses for all camera systems you are pondering and maybe start making up my mind from there on.

Which qualities of a lens define quality for you?

Whats your budget?

Which camera brands are you pondering?

Does weight matter?

What is your attitude towards tripods? - If you don't want to bring one you should really look for lenses with image stabilizers, if you didn't get a camera that does the same trick by moving it's sensor around.

 

When lenses get sold or advertised you only read focal length (range) aperture (range) and maybe if it has built in OIS + some cryptic claims about the construction (like "aspherical, extra low dispersion glass, apochromatic", AF motor type, made for shutter priority or not). Those tell close to nothing; an inexpensive Sigma "Apo" zoom punches in a different league than a Leica "Apo" prime.

 

Going by brand name gets you nowhere. - A few exceptions, like Fuji's digital camera systems or Phase One's aside, manufacturers have been around for many decades and their, a lifetime ago, on film, "awesome" stuff doesn't necessarily play well on digital sensors.

The quality of a lens is quantifiable but it's generally not part of the specifications.

 

Actually . . . There are plenty of things in the specs that can clearly indicate quality . . . A 16-500f5.6-11 lens is not likely to be of high quality and it's right there in specs. Not all f2.8 lenses are the best but most are far better than average. The same goes for f1.8, f1.4 and f1.2 lenses. Right there in the specs. Variable max apertures are USUALLY not as good as fixed max aperture lenses. All right there in the specs.

 

But, the most important information needed before answering a question like this is about the intended use.

Ed, I'm not sure what you mean by the specs. Do they rate corner sharpness, contrast, etc. At one time Modern Photography used to run tests on various lenses and rate the sharpness (lp/mm) contrast, etc, as Excellent, very good, good, etc. I based my purchase of a Kiron 28-210mm on those test results since most of them were Excellent and was very happy with the lens.

I am suggesting (and I'm not sure why since the OP hasn't come back and told us anything that will help answer his question) that things like the maximum aperture, zoom range and the fact that the lens is either fixed or variable aperture are in the specs and are a clear indication of the quality of a lens. You can also see the number of elements and the construction material both of which will indicate quality as well.

 

Not everybody needs all of these or that quality lens. When I resumed my interest in photography in the late 80's, I can remember be very happy with lower priced lenses that allowed me to build a larger kit faster. Not one of those lenses would meet my standards today. I don't know about the 28-210 that you are talking about but I am pretty sure that I wouldn't be taking it to shoot weddings. Not that great pictures (as I noted above) can't be taken with it. Those tests in MP didn't turn up many dogs but many were made.

Actually . . . There are plenty of things in the specs that can clearly indicate quality . . . A 16-500f5.6-11 lens is not likely to be of high quality and it's right there in specs. Not all f2.8 lenses are the best but most are far better than average. The same goes for f1.8, f1.4 and f1.2 lenses. Right there in the specs. Variable max apertures are USUALLY not as good as fixed max aperture lenses. All right there in the specs.

 

But, the most important information needed before answering a question like this is about the intended use.

 

There is nothing in the specs that say about quality of the lens. Nothing about sharpness, resolution, MTF, Nothing about distortion. Nothing about aberration. Nothing about vigneting or ligh fall off.

So . . . WTF . . . You don't like my responses. I don't care. What have you added to the discussion? If you have an opinion, throw it out here . . .

 

Yes, the fact that the manufacturer makes an f2.8 lens, means that this lens is VERY LIKELY to be sharper, have higher resolution, better MTF, less distortion, fewer aberrations ("ED" glass or aspheric elements), less vignetting and falloff. Wide to tele zooms are FAR MORE LIKELY to suffer from these effects more than two, or three, to one lenses.

 

All of this, will allow the OP to have a better idea of what he shopping for online. READ HIS QUESTION! He wants to know what to look for when shopping online. He does not ask about ANYTHING that you brought up.

 

Over and out . . .

@kevg: I agree with the above comments that:

- in general (there exceptions) you get the quality you pay for

- what you consider to be 'wide angle' (or 'ultra wide angle') depends on your camera (crop sensor or full-frame) and the kind of photos you want to take

 

I suggest choosing a camera type first (taking the price and sensor crop factor into account) and then deciding on a focal length (prime lens) or range (zoom) that enables you to take the type of photos you want to take with it.

 

On my old Canon 40D (with a 1.6 crop factor) I have an 18-55mm lens. The 18mm is wide enough for me (landscapes, city scenes and indoor photography). When I switched to a Canon 6D (Full Frame, no crop factor) I decided to go with a Tamron 24-70mm lens which had good reviews and gave me roughly the same focal range. The equivalent 'Canon' lens got even better reviews but the price was way above my budget. Both lenses are my 'walkabout' lenses with just enough wide angle that I need. But other people take much more 'sweeping' photos of beaches and landscapes with (roughly) 10mm-20mm lenses that generally fall into the ultra-wide' category. Given the price of these 'specialized' lenses and the limited use I'd make of one my 'walkabout' does the job well enough.

 

After that, it's well worth looking at some lens review sites such as Dxomark.com. Lenses that are consistently ranked highly at different sites and are within your budget are probably the ones you should consider. I also think it's worth searching photo sites like Flickr and 500px for photos taken with both the sensor crop factor and the lens (or at least the focal length) that you have in mind. That should give you some 'real life examples' of photos that you could take with the camera and focal length you have in mind. You can also look at shorter (more wide angle) focal lengths to see if these might better suit your needs.

 

Some non-technical aspects of 'quality' that spring to my mind are:

- compatibility with your camera (same make or 3rd party lens designed for your make)

- optical resolution (sharpness)

- lack of distortion

- autofocus (accuracy and speed)

- weather & dust resistance

- weight

 

A final thought: it's also worth considering what you're going to do with your photos. If you're to be printing high-resolution A3-size photos then 'sharp details' will probably be more important than if you're publishing on digital platforms. These days, post-processing software allows you to correct and enhance digital images (lens distortion, sharpness, etc.) at least up to a point.