Depth of Field

Lately, I’ve been chatty on G+, mostly in photography and amateur radio circles. Recently, I gave myself a major kick in the pants that I very much appreciated. My sincere thanks to +Don de la Rambelje, a birder and photographer for guiding me to see my error.

Don had posted a picture of a bird using his favorite lens, Siggy, a Sigma 300-800mm f5.6. I commented on how narrow the depth of field was in that picture, literally deep enough for the bird to be in reasonably sharp focus and everywhere else muted. That picture, WHAT’S IN A NEYME, led to a discussion of a problem I’ve been having getting clear, sharp shots of birds in flight with my Tokina 400mm. As a result of that discussion he posted a chart showing just how thin the depth of field was on Siggy at various f-stops. For that particular picture, the depth of field was a mere 0.7 meters, or 27.6 inches! As I recall, the bird was 34 meters away from him, yet everything before the bird was blurred and everything past the bird was blurred. He nailed it, that bird was nice and sharp, with feather details, etc. very clear.

That paragraph right there explains the sum total of my issue. Studying the chart for Siggy’s depth of field made me want to go bang my head against the wall.

My 400mm is an older lens from my film days, meaning that while it works with my DLSRs, it is a completely manual lens. That is to say, the only part of pictures with that lens controlled by the camera is the shutter speed, ISO and white balance. No focus control and no aperture control. It’s still my favorite lens even while being the most frustrating to use at times.

On that lens are guides that just aren’t on any of the more modern lenses any more, at least not any that I’ve looked at. Only my older lenses include these setting guides.

My old manual 50mm lens, showing the depth of field markers.

My old manual 50mm lens, showing the depth of field markers.

My old 80-200mm manual lens, showing the depth of field markings.

My old 80-200mm manual lens, showing the depth of field markings.

My old 135mm telephoto showing the depth of field marks.

My old 135mm telephoto showing the depth of field marks.

My beloved old 400mm telephoto, showing the depth of field markers.

My beloved old 400mm telephoto, showing the depth of field markers.

I had been using this lens by setting the focus manually to infinity. Even though I knew what depth of field was, and how it varied with the f-stop, I would still look at the lens, set the infinity symbol on the right-most mark. I’d set the camera to manual focus and shoot. Notice the error there? I totally ignored the left mark which tells me where my in-focus range begins.

The result?

My bird shots were rarely in focus…because as you can see from the above image for the 400mm that would make my depth of field clear and sharp starting somewhere beyond 300 feet and most of those birds were well within 300 feet, not past it. Indeed, most of the time I would shoot with f/5.6 for maximum shutter speed in order to freeze the bird’s motion. Again, referring to the above image, you can see that with the f-stop set to 5.6 and infinity set to about where the 5.6 line would be…the depth of field starts way out there, easily 800 feet or more.

No wonder I couldn’t get the image nice and sharp…I was consistently focusing past the birds. All the while I was pleased with myself for figuring out how to avoid having to focus on the fly while tracking the flying birds…one less variable to worry about.

In short, my focusing was for the birds. (Sorry, bad pun, I know, but I couldn’t resist including it.)

This is a great lesson for me to revisit the basics, and to do so hands-on experimentation if at all possible, on a regular basis. I try to read my camera manual once a year for several reasons, including re-discovering features the camera has and finding new things to try or play with so I don’t get stuck in a rut using just the features of the camera I’m familiar with. You’d think that if I was doing that, I’d revisit the basics as well, right?

Turns out…that would be a mistaken assumption. I would come up with projects to try out various camera settings and learn to use them, but I wouldn’t just go out and play with what I already knew. Not like that. Oh, I’d go out and take pictures that involved this or that camera setting and think about them as I did the shoot, but I didn’t revisit things like the depth of field markings on the old lenses. I knew they were there, but I’d been spoiled by the autofocus and various tricks I used to set the focus automatically then move the camera to take the actual picture. For example, I’d focus on a distant object, then switch to manual focus and not touch the focus again. Yup, totally ignoring the depth of field other than “it’s out there and not going to change.”

For so many things, that works. But for some things, like these bird shots, it didn’t. It wasn’t until Don showed me Siggy’s depth of field tables that I realized what was going on and why my pictures weren’t coming out nice and sharp even though I would have sworn I was doing everything right.

Now I know, and this is one way to make sure the lesson sticks, learning it like this.

I can’t wait to get out and try shooting birds again. This time, though, I’m paying attention to both sides of the depth of field markers!! Like I should have been doing all along.

Thanks, Don!


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One Response to “Depth of Field”

  1. Bill Says:

    I have since found that these indicators still exist on many prime lenses, just not so much on zooms.


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