Friday, February 27, 2009

F-Stop Friday: F5.6, The Friendly F-Stop

Good Evening Everybody,
Well welcome to my almost midnight post today at DigitalProTalk. Is anybody still awake?? I've been at a keyboard for 12 straight hours wrapping up my presentation I'm giving at B&H on Sunday. I hear from the boys in New York that it's going to be quite the crowd. The room holds about 70 to 80 people but I hear we have 104 registered for the presentation. I'm really looking forward to it and I'm kind of curious how I’m going to get through my 400 slide PowerPoint in five hours. I've got it --- nobody gets “potty” breaks we just go straight through:~)

Anyway, my apologies for the very late post today. My first priority was to get the PowerPoint done for my presentation on Sunday. I was planning to finish a little bit earlier today, get the DPT post up much earlier, but things are what they are.

I thought I would do another episode of our F-Stop Friday Series because it gives you some insight into why I do what I do when I'm shooting my images. So without any additional whining from me about being at the computer all day let's get right to it.

F-Stop Friday: F5.6 - The Friendly F-Stop
Back in the old film days F8 was my favorite, friendly F-Stop. With a medium format camera F8 gave us plenty of depth of field for the candid images we were shooting. When you look at the numbers below, you may not think so. But as most of us have migrated to digital 35’s, the wider equivalent focal lengths that we used on those cameras give us more depth of field at the same aperture than we had in the old film days.

Here is how that works:
An 80mm lens on a 6x6 medium format camera is equivalent to a 50mm lens on my 5D mark II and a 35mm lens on my 40D.

Now let’s look at the DOF (depth of field) numbers. The depth of field at 10 feet at F8 when shooting my 80 mm Distagon lens on my Hasselblad was 8.57-12ft or a total DOF range of 3.43 feet.

When shooting the equivalent focal length, a 50 mm lens, on my Canon 5D Mark II, my depth of field at 10 feet is significantly more 7.77-14 feet or a total DOF range of 6.28 feet.

Now look what happens to the DOF on the APS sized sensor cameras like the Canon 50D. The equivalent focal length lens is about 35mm. So on a Canon 50D fitted with a 35mm lens focused at 10 feet with the aperture at F8 we have quite a bit of depth of field 7.28-16 feet or a total DOF range of 8.69 feet.

That's why it's so easy to get by with F5.6 on our digital 35s. We actually end up with even more depth of field our full frame digital SLR and even more depth of field on our APS sized sensor cameras like the Canon 50D.

Following this logic further - we can see that we can actually shoot the Canon 50D at 35mm optic focused at 10 feet at F4 and actually have more depth of field that I was getting at with my Hasselblad fitted with its 80mm lens. I always thought it was interesting that so many film photographers as they transitioned to digital 35s continued to shoot at the same F8 aperture they used on their medium format cameras. Many didn’t even realize that they were increasing their depth of field tremendously.

That means that with our digital 35s, we can shoot a full 2 F-stops wider for the same depth of field as in the film days with the medium format cameras. That means that we need less light to make the image. This is a benefit to us, especially if you're using your on-camera flash and bouncing off of a side-wall to bring the light in from that off-camera direction that I've talked about so often here at DigitalProTalk. Combine that with our new high ISO cameras and we have all kinds of photographic possibilities open up to us. HOORAY!!

If you want to have some fun with this depth of field logic yourself, let me point you to Don Fleming's on-line depth of field calculator right here. You too can play around with a different focal length lenses on the different camera bodies and may find yourself amazed at what you discover.

The bottom line is this - I find that F5.6 gives me plenty of depth of field for all of my wedding day flash candids. As long as I shoot with the focal length between 24-50mm I’ve got plenty of depth of field to capture the action, and I'm assured that even if the auto focus misses a bit I'm still covered by my depth of field.

Hey gang that about wraps it for me today. We've got an early wake-up call tomorrow so I’ll see on the flip side of the weekend. Have a good one and remember even pixels buy their cameras at B&H Photo&Video. Adios, -- David


  1. Amazed. . .and kicking myself for having so many out-of-focus pictures last weekend when there was an easy fix:)

    Very cool!!

  2. There is a very cool little iPhone app called PhotoCalc which has a DOF calculator, sunrise/sunset info, Flash Exposure calc, and a few other goodies.

  3. Without the science and math behind this, I've been using 5.6 for most of my shooting too for a more practical reason.
    Until recently, my most used lens was a Tamron 28-200, which gives all kinds of flexibility in range from subject, and it had a top Fstop of 5.6.
    Being pretty lazy, I found that I could simply put my camera in Manual, set to 5.6 and then just worry about the shutter speed to control my exposure.
    Without even thinking about it I found that 5.6 gave me pretty good DOF, and generally made my shooting easier, because I knew my Fstop wouldn't change through the range of the lens.
    Some of my friends would disagree with me citing the traditional use of F8, etc. but form a practical stance, when you're busy shooting and not wanting to have to fuss too much, I just found the f5.6 to be very convenient, and yielded nice results.

  4. I never really thought about this since I switched to digital - interesting post, David! So how was your presentation at B&H?