Newbie lens question

[LandCruiserPhil]

What is the difference between a 50MM fixed lens and 50MM with my 18-135mm zoom assuming F stop are equal?

A 50mm fixed is called out a lot as a do everything lens and Im trying to understand why I would need one when I have 50MM covered with my zoom.

Thanks

 

[Theoretician]

Assuming an equal f-stop, there wont be a lot of difference between a decent zoom lens at 50mm and a 50mm prime. The prime will be smaller, lighter, and the optics will probably be better corrected, and the lens will probably be more durable and weather resistant, but most of the direct use attributes would be the same.

The odds of a zoom matching the max aperture of a prime are pretty dang low, though, so the discussion is pretty much just a thought experiment.

In sunlight, photographing a landscape, it'd be pretty difficult to tell the difference between an iphone and an SLR with a prime 50. Around the campfire the following night, you'd probably be able to pick out the differences between the SLR/zoom and SLR/prime.

 

[LandCruiserPhil]

Assuming an equal f-stop, there wont be a lot of difference between a decent zoom lens at 50mm and a 50mm prime. The prime will be smaller, lighter, and the optics will probably be better corrected, and the lens will probably be more durable and weather resistant, but most of the direct use attributes would be the same.

The odds of a zoom matching the max aperture of a prime are pretty dang low, though, so the discussion is pretty much just a thought experiment.

In sunlight, photographing a landscape, it'd be pretty difficult to tell the difference between an iphone and an SLR with a prime 50. Around the campfire the following night, you'd probably be able to pick out the differences between the SLR/zoom and SLR/prime.

Thanks that was my assumption.

One more The cost difference between a prime 50mm 1.4 and 1.8 given the Canon EF brand is ~double, is it worth it? Would I be better off learning more about what I own and the answer will become clear in the future?

 

[verdesardog]

Just get the 1.8 it will probably suit you fine for many, many years. Even if you are doing low light photography there isn't much difference between 1.8 and 1.4.

 

[Theoretician]

Seconded. The nifty fifty is cheap enough, and the difference between f/1.4 and f/1.8 small enough, that if you don't know that you need the extra half stop of light then don't worry about it. Use that money on insurance for your gear so you feel more willing to ABC.

 

[Kerensky97]

Many people report that the f/1.4 isn't as sharp as the f/1.8 anyway. F-stops aren't a measure of lens quality so you can have an f/1.2 with crummy build quality and low quality glass that will give you muddy low contrast images. But the background will be more out of focus and bokeh is most important right?!

Going back to the original question I think that's the main benefit of prime lenses, their simplicity makes it easier for lens manufacturers to produce quality at a low price point. The zoom lens can take the same picture but all of the lenses and mechanisms to allow it to do many focal lengths means that it's more difficult to do 50mm f/x well. You're more likely to have a soft image, less contrast, chromatic aberration, lens distortion without dropping a ton of money for a top end designed piece of glass.
It's like you need a tool to turn a screw on your vehicle. In one hand you have a normal, properly sized screwdriver; in the other you have multi-tool with a screwdriver tip built into the handle.
Both will do the job and the multitool will do a lot more (include scaling fish and sewing leather!!!), but have you ever tried to turn a screw with one of those off balance multi-tools? It's a PITA. It does tons of jobs but that doesn't mean it does them well.

 

[nwoods]

Kerensky touched on the real answer. The prime lens with faster Aperature will have better low light performance, generally sharper image quality, and MUCH better depth of field control. This gives you the ability to blur the background and foreground of a shot. The canon 1.8 is considered one of the best deals in the lens world, and periodically goes on sale (factory rebates), and has been nicknamed "The nifty fifty". It's also a pretty good portrait lens

 

[Deleted member 96197]

A lot of good points have been made here, but to the original questions, two points. The F-stop might be equal if you set them both high enough, but your zoom is not going to give you the fast aperture range of the 50mm prime (dof and low light performance as referenced above). Secondly even if you are shooting with the aperture equal, a well built prime will in nearly every case be sharper than a well built zoom, yes there some amazing zooms on the market, but only the very top few from each manufacturer come close to the sharpness of a decent prime.
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Additionally one of the things that has made the nifty fifty the go to lens for so many people for so long is 50mm on a full frame camera, or 35mm on a crop sensor is essentially distortion free. No significant wide angle distortion or telephoto compression, so when you take a photo at that field of view it tends to just look right to people, and for that reason until the recent era of cheap zoom kit lenses, nearly everyone started shooting with a 50mm prime.
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For all new photographers, especially people who have only dealt with their kit lens, even an upgraded kit lens, I always recommend picking up a nifty fifty, or 35mm, to get a feel for shooting with a truly sharp and fast lens, trust me it will be a different expereince than your 18-135. (I realize canon doesn't make a cheap 35mm option, so my comments about distortion will be a bit off, you will be closer to 85mm on a crop sensor canon, which will give you a bit of telephoto compression and it will act more like a portrait lens). You shouldn't be out more than $200, which it why it's considered pretty much the best investment you can make early on.

 

[Deleted member 96197]

Many people report that the f/1.4 isn't as sharp as the f/1.8 anyway. F-stops aren't a measure of lens quality so you can have an f/1.2 with crummy build quality and low quality glass that will give you muddy low contrast images. But the background will be more out of focus and bokeh is most important right?!

Going back to the original question I think that's the main benefit of prime lenses, their simplicity makes it easier for lens manufacturers to produce quality at a low price point. The zoom lens can take the same picture but all of the lenses and mechanisms to allow it to do many focal lengths means that it's more difficult to do 50mm f/x well. You're more likely to have a soft image, less contrast, chromatic aberration, lens distortion without dropping a ton of money for a top end designed piece of glass.
It's like you need a tool to turn a screw on your vehicle. In one hand you have a normal, properly sized screwdriver; in the other you have multi-tool with a screwdriver tip built into the handle.
Both will do the job and the multitool will do a lot more (include scaling fish and sewing leather!!!), but have you ever tried to turn a screw with one of those off balance multi-tools? It's a PITA. It does tons of jobs but that doesn't mean it does them well.

Great analogy to the multi tool