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What is a “Fast” Lens? ~ Photography Tip

What is a “Fast” Lens? ~ Photography Tip


Examples of Nikon Fast Lenses

Nikon AF-S Nikkor 35mm f/1.8G DX Lens

Nikon 10.5mm f/2.8G ED DX Fisheye Lens

Nikon Zoom Super Wide Angle AF 17-55mm f/2.8G ED-IF AF-S DX Zoom-Nikkor Autofocus Lens

Nikon AF-S Nikkor 70-200mm f/2.8G ED VR II Lens

Nikon Zoom Telephoto AF Zoom Nikkor 200-400mm f/4 G-AFS ED-IF VR (Vibration Reduction) Autofocus Lens

Examples of Canon Fast Lenses

Canon Normal EF 50mm f/1.4 USM Autofocus Lens

Canon Telephoto EF 85mm f/1.8 USM Autofocus Lens

Canon Zoom Super Wide Angle EF 16-35mm f/2.8L II USM Autofocus Lens

Canon EF 70-200mm f/2.8L IS II USM Lens

Canon EF 500mm f/4L IS (Image Stabilizer) USM Lens

Fast lens, also called fast glass, are lenses that have a lower f-stop rating. Let’s start out with the standard zoom lens which comes with most cameras when purchased. They are usually rated something like f/3.5-5.6. What this means is in the widest setting you can set your f-stop down to f/3.5, but as you zoom in to the tightest zoom of the lens, the lowest you can set the f-stop will be f/5.6. In low light settings like a school gym, f/5.6 isn’t going to do so well.

A fast lens will have a lower f-stop rating, and it’s usually fixed for all zoom points of the lens.  A good example is a 17-35mm f/2.8 zoom lens. This lens can be set down to f/2.8 zoomed wide at 17mm all the way through to 35mm. f/2.8 is a wider opening, than f5.6 which will allow more light into the camera and will make shutter times faster – thus the name “fast glass”. This was always confusing for me before too. If you look at a list of lenses and you see, for example a 70-200mm f/2.8 and an 80-210mm f/4-5.6, they look like they should be similar, except the f/2.8 is always about 5x more expensive. This is because it’s bigger, has much more optical glass, and is a true professional lens. The faster lenses, with lower aperture settings will allow you to shoot a shallower depth of field and in lower light situations. And because they allow more light in, most camera will focus faster as well.

Now the fast glass zoom lenses are pretty expensive, but you can get the advantage of fast glass a little cheaper with a prime lens. A prime lens doesn’t zoom, it’s simply one fix length (i.e. 35mm, 50mm, or 85mm, etc.) The cool thing with this is, if you know a lens focal length you like (I like the 55mm for doing portraits), it’s light weight, relatively less expensive, and you can get very low f-stops (wider aperture equals more light quicker). Some prime lens come in f/1.4 which is like a cat’s eye, and can almost see in the dark.

Regular Zoom lenses

  • usually variable minimum aperture
  • not as quick to focus in low light
  • limited depth of field range
  • slower shutter speeds in low light
  • less expensive
  • light weight
  • good for travel

Fast Glass Zoom and Prime Lenses

  • fix minimum low aperture
  • shallowest depth of field = soft blurred background
  • good shutter speeds in low light
  • quicker to focus
  • a true professional lens

Special Thanks to @Jewelzdezine on Twitter for the question that led to this post.

Photo Tip Tuesday ~ If you have a photo tip or would like to have a photo question answered, send me an email. Also be sure to subscribe for free to this blog to receive ongoing great photo tips and inspiration!

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  • Julie

    woot woot! Great job! Thanks for explaining this! It really helped, albeit I don’t know if I could afford a lens like that! LOL!

    Also thanks for mentioning my name! These video tips are way cool. Hope to see more!

    @jewelzdezine

    [Reply]

    TJ McDowell Reply:

    Julie,
    There are some great fast lenses that are also cheap. For example, look at the 50mm f1.8 lens. It’s a prime, which means you can’t zoom in or out, but you can get shots in really low light, and at least for Canon, the lens is under $100. What a deal!

    [Reply]

  • Great overview. I would suggest you add the Tamron AF70-200mm F/2.8 Di LD (IF) Macro to the list. It is available in Nikon, Canon, Pentax, & Sony mounts. I just got mine recently and it is fantastic.

    [Reply]

  • Great overview Kent – I pretty much use all my lenses as wide open as possible for the correct exposure. The faster the better that is for sure.

    [Reply]

  • Just watched your fast lens video. Great and easy explanation. I need to invest in a faster lens and I love that you gave some examples. :o)

    [Reply]

  • Julie,
    There are some great fast lenses that are also cheap. For example, look at the 50mm f1.8 lens. It’s a prime, which means you can’t zoom in or out, but you can get shots in really low light, and at least for Canon, the lens is under $100. What a deal!

    [Reply]

  • Mark Kenney

    Loved the tip! Man I would love that f/2.8 lens… a little out of my price range now. I use a Canon 85mm f/1.8 for my sports shots (gymnastics) for now, and am awaiting the Canon 50mm f/1.4 to do more indoor shooting without a flash. Someday I’ll get that f/2.8 zoom. :)

    [Reply]

  • Hi

    Great explanation of Fast Glass/Fast Lenses. My favorite for portraits is a 100mm Nikkor Prime. It is a tad on the expensive side but I love it for Environmental or Studio Portraits
    Regards, Erik

    [Reply]

  • […] this lens is not considered “Fast Glass”, but don’t let that discourage you. A kit lens, used the proper way, will yield photographs […]

  • […] From a photography standpoint, it was also a good time to get out and play with my new Nikon 18mm-200mm lens. I definitely missed being able to open up to f2.8 since this new lens is a f3.4/5.6. (If you aren’t sure what that means, here’s an introduction to what aperture is and how it works.) but it’s a nice option for shooting in bright daylight and keeps me from having to change lenses all the time, since I only have one camera right now. The 18mm-200mm is also A LOT lighter than my faster glass. […]

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