Focal Length and EFOV

To get the most out of our camera gear it’s important to consider the focal length and EFOV of the equipment we use. As photographers the camera gear that we choose is less important than our knowledge on how to use it effectively. How we express our creativity through this artform called photography, is the most critical factor. Not the camera gear we own.

NOTE: Click on images to enlarge.

Nikon 1 J5 + 1 Nikkor 30-110 mm f/3.8-5.6 @ 34 mm, efov 91.8 mm, f/5.6, 1/125, ISO-800

Any photograph that we create captures a moment in time that will never happen again. There may be similar moments in the future… but not that precise moment.

Nikon 1 J5 + 1 Nikon 10-100mm f/4-5.6 @ 48mm, efov 129.6mm, ISO 800, 1/100, f/6.3

It can be a moment of joy. Or sadness. Or loss. Or connected to some other human emotion. It is the emotion captured in an image that touches us and moves us. From that perspective the camera that was used to create the image is irrelevant.

Nikon 1 V3 + 1 Nikon CX 70-300mm f/4.5-5.6 @ 300mm, efov 810mm, f/5.6, 1/1000, ISO-1600

It is easy to get fixated on camera gear and have endless and pointless debates about which format, brand or model is best. Our evaluation of what is best is based on our individual needs. I can’t tell you what is best for your needs. Nor can you make that determination for me.

Nikon 1 J5 + 1 Nikon 10-100mm f/4-5.6 @ 10mm, efov 27mm, f/8, 1/250, ISO-160

Some of us choose to use smaller sensor cameras. The reasons for that can be many and varied. If we are migrating from a larger sensor format to smaller sensor gear, it can be helpful to remind ourselves about lens focal length and EFOV (equivalent field-of-view) as these considerations can affect our creative approach.

OM-D E-M1X + M.Zuiko PRO 7-14 mm f/2.8 @ 7 mm, f/2.8, 1/2000, ISO-200

Focal length is an optical attribute of a lens. It has nothing to do with the size of the sensor that may be in a particular camera. For example, when I pick up my M.Zuiko PRO 7-14 mm f/2.8 zoom, I’m shooting with a 7 to 14 mm lens that gives me the depth-of-field characteristics  associated with those focal lengths. The optical attributes that a specific lens provides are not related to equivalent field-of-view.

OM-D E-M1X + M.Zuiko PRO 7-14 mm f/2.8 @ 7 mm, f/2.8, 1/2000, ISO-200

Some folks in photography related chatrooms sometimes make statements like “when you use a M4/3 lens at f/2.8 you’re actually shooting at f/5.6”. This is incorrect. We’re shooting at f/2.8. The difference in depth-of-field that we observe is due to the fact that we are using a shorter focal length lens compared to a full frame camera when achieving the same field-of-view.

OM-D E-M1X + M.Zuiko PRO 12-100 mm f/4 IS @ 16 mm, efov 32 mm, f/5.6, 1/30, ISO-200, HDR version

Regardless of the camera format, a shorter focal length lens will always deliver more depth-of-field at the same distance to subject and aperture, than a longer focal length lens does.

Nikon 1 J5 + 1 Nikkor 6.7-13 mm f/3.5-5.6 @ 6.7 mm, efov 18 mm, f/3.5, 1/30, ISO-1600

This is important for us to keep this in mind, especially if we are using smaller sensor cameras. During our trip to Ireland in 2019 we visited a number of churches and monasteries. In the image above you can see that deep depth-of-field was achieved even though I used an aperture of f/3.5 with my Nikon 1 J5. I used this aperture to take advantage of the deep depth-of-field characteristics that a focal length of 6.7 mm delivers. This helped me deal with low light conditions.

Belleek Castle Ireland, Nikon 1 J5 + 1 Nikkor 6.7-13 mm f/3.5-5.6 @ 6.7 mm, efov 18 mm, f/3.5, 1/15, ISO-3200

I had similar low light challenges when creating images at various locations inside Belleek Castle. In order to overcome the low light environment I was facing for the photograph above, I moved in tight to the foreground element. Shot wide open at 3.5 using a focal length of 6.7 mm, and used a shutter speed of 1/15. That photographic approach allowed me to keep my ISO at 3200. I knew from experience that ISO-3200 would still deliver a usable image.

Belleek Castle Ireland, Nikon 1 J5 + 1 Nikkor 6.7-13 mm f/3.5-5.6 @ 6.7 mm, efov 18 mm, f/3.5, 1/25, ISO-3200

When using smaller sensor cameras we continually need to think in two concurrent photographic realities. For example, we may be shooting at an equivalent field-of-view of 18 mm in full frame terms…. but may be using a focal length of 6.7 mm to do so. A short focal length often allows us to use a more wide open aperture to achieve the deep depth-of-field we may need for a given photograph. Using a more wide open aperture can allow us to use a lower ISO value, which in turn gives us more available dynamic range and colour depth.

Purakaunui Falls, Nikon 1 J5 + 1 Nikon 6.7-13mm, f/3.5-5.6mm @ 8mm, efov 21mm, f/8, 1/4, ISO-160

When I first made the transition from full frame gear to using Nikon 1 it took me some time to adjust my shooting technique. No doubt there were situations when I likely stopped my 1 Nikkor lenses down more than was actually needed.

Nikon 1 J5 + 1 Nikkor 10-100 mm f/4-5.6 @ 10 mm, efov 27 mm, f/5.6, 1/640, ISO-160

I was so used to stopping my full frame gear down to f/8 or f/11 for landscape images it had become a habit, which I initially, and mistakenly, carried over to my Nikon 1 kit. To make better use of smaller sensor cameras I had to consciously remind myself of the depth-of-field characteristics of shorter focal length lenses.

OM-D E_m1X + M.Zuiko PR 40-150 mm f/2.8 @ 150 mm, efov 300 mm, f/2.8, 1/1000, ISO-200, subject distance 725 millimetres

These two concurrent photographic realities also come into play when we want shallow depth-of-field in our images. When using a smaller sensor camera our approach involves using a longer focal length lens to get the composition we desire. Using a longer focal length reduces depth-of-field. Fortunately the minimum focusing distance of many M4/3 lenses is quite short which gives us a lot of composition flexibility.

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 @ 150 mm, efov 300 mm, f/2.8, 1/400, ISO-400, Kenko 10 mm and 16 mm extension tubes used

To achieve even shallower depth-of-field we can use an extension tube in combination with a longer focal length lens. An extension tube further shortens our minimum focusing distance.

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 @ 150 mm, efov 300 mm, f/2.8, 1/400, ISO-400, Kenko 10 mm and 16 mm extension tubes used

Regardless of the camera format we happen to own, we can achieve the deep or shallow depth-of-field we want with our photographs. The key is to understand the optical attributes of the actual focal length of the lens we are using.

Tairua, New Zealand, Nikon 1 J5 + 1 Nikkor 10-100 mm f/4-5.6 @ 26 mm, efov 70.2 mm, f/5.6, 1/320, ISO-160

Technical Note:

Photographs were captured handheld using camera gear as noted in the EXIF data. Images were produced from RAW files using my standard approach in post. Crops are noted. Photographs were resized for web use. This is the 1,169 article published on this website since its original inception in 2015.

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5 thoughts on “Focal Length and EFOV”

  1. Hello there.

    I have been reading a bit about the proposition of aperture ‘equivalence’ recently because I sensed confusion and doubt about my own knowledge and understanding.
    There are well known websites and YouTube channels owned and operated by some established and credentialed photographers who have expressed a different understanding than that of a Micro Four Thirds camera and lens manufacturer that I contacted today.
    Disclosure policy of this company does not give me the freedom to name or quote the individual who provided me with this information.
    I will paraphrase: The light capturing capability of a lens is not affected by the size of the sensor within the camera.
    An f1.8 aperture is an f1.8 opening for light, no matter the mount.


  2. Thank you for this posting. I have to admit that even after using Olympus for 2-1/2 years I still need to be reminded of how this works. I used Nikon full frame for many years and the old thoughts and habits are hard to overcome.


    1. Hi Joel,

      When I first made the switch to small sensor cameras it also took me a while to adjust my technique and how I assessed an image opportunity. I found it was helpful for me to not think about efov at all and just focus on the focal length of the lens I was using.


  3. Thanks for such a succinct post. Just had a major “ah-ha” moment re depth of field and focal length. There is so much noise around sensor size and little attention to optics! Thanks. Have a coffee.

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