The Good and the Bad of Big Glass Depth of Field

Greetings all! I am finally getting back on my feet after the month from hell. Once all the adrenaline and excitement wore off from the race and party I started realizing what a toll it all took on my body. Even with my customary week off relaxing (yep, no running, and no work on Project Auuunoold) I still couldn’t shake the aches and pains. The next week started and I was beginning to get concerned. Figured I’d start the rebuilding process this week … back on the core to get the body fixed up and stretched and a little biking for cardio is starting to work their magic. Still not ready to run yet but due time, due time. In the meantime, thought I’d toss out a quick post.

Tonight’s topic is that very tricky subject of Depth of Field (DoF). To be honest, this is one of those photography topics I am trying to get a better understanding of – primarily because I’m constantly fighting it out in the field especially with the Beast. My quick and dirty definition of DoF is the measurement of how much distance will be in focus (sharp) for a given set of exposure, glass and camera specs. I still have a lot of learning to do on this subject so there will not be any expert advice here – I’ll certainly come back on this subject once I get read up on it some more. The good, or the bad depending on your point of view, is that you can see the effect pretty easily.

Take a look at some shots from a shoot Linda and I took back in July. We were out at Jubilee and due to lack of birds was spending my time on anything else I could find that had wings.

So there I was with my standard birding setup which consists of the Beast (200-400mm) coupled with the 1.4 Tele on the D7000 (1.5 crop sensor).  These shots were taken at around the 3.6 to 3.8 m range hand held… and people wonder why I continually workout.  These dragonflies were all over the place darting to and fro so I decided to get a little small subject focusing practice in.  When the subject is smaller than the central focus region, the glass tends to walk a lot, especially the long glass.  So there I stood happily shooting away.  That happiness lasted until I got home and started assessing the output.  Notice anything glaring wrong with the first shot?

The right wings are nice and crispy, but what the hell is up with the left side?  Was that particular wing moving at the time … doubtful, they tend to move both sets of wings in unison from what I have experienced and the 16oo ISO would have compensated for that anyway.  The problem is in the focus parameters.   My depth of field is not encompassing the full thickness of the subject.

I was fighting the glass to keep it on target and firing away on fast multi-shot so there were plenty of other examples to explore.  Hit the jump to see more examples of DoF.

Here’s another shots of the same setting.

Ahhh, the left wings are now more crispy, but wait a minute, what the hell happened on the right side.  It’s as if I had flipped the image.  So what is really happening here?  The culprit is really the depth of field I have to work with.  Ummm, clarify that, the culprit is a result of poor execution, but the element of difficulty is the small depth of field (or amount of distance in the image that can be sharp).  There are a number of free depth of field calculators on the web which makes it pretty easy to determine what DoF is for any given setting.  This one was pretty nice (link here) since it allowed me to enter my exact telephoto distance.

Parameters:

  • Crop Factor 1.5 (Nikon)
  • Aperture 5.6 – lowest I can go with the Teleconverter on
  • Glass Focal Length – 550mm (yummy)
  • Focus Distance 3.6m

Want to guess what the DoF is for this setup?  How does 1 centimeter hit ya?  So according to this calculator (and confirmed by two others on the web) I have a whopping 10mm to work with.  There is easily that much play in just my arms trying to keep that glass on target.  The fact that any side is in focus is a surprise.  The expectation should really be closer to the following shot which managed to put BOTH wings out of focus and instead get the head and weed stalks it was clinging to.

Fortunately, I “lucked” out and got a few shots that looked a little better.  Here the left side, body and most of the right wing is in focus – not perfect, but I’ll take it.

I almost took the two “one sided’ shots and stitched them together to get the perfect shot but who could shave in the morning looking at a cheat.  If you bought that last line you might want to lower your standards a bit since we take a more liberal approach to the art around these parts – Lightroom and Photoshop, the great equalizers.  Anyway, thought you might be interested in an aspect of photography you might not be aware of.  If nothing else, makes me feel a little better about cards full of screw ups.

In closing, this is another shot I took while we were out there.  It gives you a little feel for the depth with the band of clarity that runs almost the width of the dragonfly – you can see the wing tips fading out a little but you can take that width and run it across the picture.  Of all the bad things with the big glass when it comes to DoF, there are plenty of good things about it that make it worth lugging it around – that includes the obvious reach, but it has a wonderful effect of throwing the background to cream pretty quick.

Hold the presses, I just had a great idea for a new camera feature (Nikon, are you listening?)  They should have a DoF bracket mode that works like the Exposure bracketing, but in this setting it simply walks the focus forward and backward a set amount for a given set of shots – same way the bracketing changes exposure setting slightly different on each of the shots in the sequence – this would be awesome – set it to creep back and forth across say 5 shots changing the focus point forward and back a centimeter or more depending on the focus distance.  I’d use that in a heartbeat when shooting the smalls.  You saw it here first boys and girls and I’m gonna demand my royalties if it pops up on a camera after this.

Okay, before you race to the comments and ask, I think the first dragonfly is a Widow Skimmer.  I always get these things confused with Damselflies but according to our friends at Wikipedia, damselflies tend to keep their wings together at rest where dragonflies will tend to keep them perpendicular – something new everyday around here.  The last one .. hmmm that was a toughie.  My best guess at this time is it looks closest to another skimmer called a Blue Dasher.  Probably a safe bet since they are one of the most common skimmers in North America.

Hope you enjoyed!

4 thoughts on “The Good and the Bad of Big Glass Depth of Field”

  1. It is, I think, a tragedy that my brother would search, utilize and then recommend online calculators for Depth of Field without asking if I had a nomogram to do same. I am like a prophet in the desert.

    Nice sequence of photos, though, that really demonstrate the effect. Dragonflies are a perfect subject for this with their intricate but planar wings, assuming you can capture them at just the right angle. BTW, does Linda have any words to offer on your new “luck shot” approach to macro photography?

    Ron

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  2. Ummm do you have a depth of field nomogram? that takes into effect the crop sensor of my specific camera? …If so, do I have to put on a cloak and chant while using it (hehehe)

    These dudes were a little skittish that day which made it tough to find one at the right angle, but you are right, they are probably one of the few planar insects with wings – butterflies are darn hard since they keep flapping their wings which are compounded by being so much larger than their bodies. Just occurred to me there is another big advantage of big glass macro – there is no way I could have gotten our 105mm close enough to take that shot without scaring them away. Chalk that up to another “good”

    As far as words of wisdom go I think appreciation for actually admitting there might have been some luck involved is the first step in reconciliation (note, I purposely quoted that figuring someone would jump on that).

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