Depth of field

I don't claim to be a professional photographer, but the photo bug has hit me pretty hard over the past half-dozen years. I've pulled the trigger enough times, with enough cameras, on enough different subjects, and in enough conditions, to learn a few things. One of which is you'll almost always shortchange yourself and under-utilize your camera if you just leave it on full auto mode.

 

At the upcoming Mothapalooza event, John Howard - an absolutely topflight photographer - and I are going to teach a photography seminar. That one will focus on moths, especially, and the use of flash, obviously. Much to the incredulity of all involved in the planning, Mothapalooza is SOLD OUT! 120 people coming to Ohio's Shawnee State Forest for a weekend of learning about and finding moths! Who'd a thunk it?

 

I'll also be conducting another photo seminar, this one more focused on plants, at this July's Midwest Native Plant Conference in Dayton. That event, too, is rapidly filling but space is available. There's all manner of cool stuff happening over the course of that weekend - details are RIGHT HERE.

 

One of the important variables that can be controlled by the photographer is depth of field. This relates to your camera's F-stop, which determines how wide the lens' aperture is. The smaller the F-stop number, the wider open the lens is, and the less depth of field. Ironically, the higher the F-stop number the smaller the lens aperture, but the greater the depth of field. Examples follow. Both photos were taken in full manual with a Canon 5D Mark III outfitted with Canon's excellent 100 mm macro lens. No tripod was used (I know, I really should), nor was any sort of artificial flash or light employed (I am increasingly becoming anti-flash when possible).

 

The beautiful Bird's-eye Primrose, Primula mistassinica, shot along the shores of Lake Huron on my recent NettieBay Lodge excursions. This image was made at the following settings:

f/7.1
1/100 exposure
ISO 200

Note how the flowers look nice and relatively crisp - especially the center blossom, which is what I was focused on. But the basal rosette of leaves, some six inches below and on the ground, are quite blurred and out of focus.

This shot was taken from the identical position as the former, but note how the leaves are much sharper, as are the peripheral flowers. We can even see the leaves' midveins, and denticulate serrations along the margins. Those details were certainly not detectable in the previous image.

So, what changed? A radical reconfiguring of the camera's settings, as follows:

f/32
1/100 exposure
ISO 4000

Note the shutter speed remains the same as the first photo, but shutting the aperture down to a tiny f/32 (as small as it will go) requires much more light. And therein lies the rub. You must slow the shutter speed WAY down to compensate, which will make holding the camera (sans tripod) steady enough for a clear image very difficult. Or, you can use flash, but that (in my opinion) seldom gives as pure and natural-looking a shot, OR you can bump the ISO up. And it's the latter that I did, all the way up to 4000 to achieve a decent image but one that allows the depth of field to be vastly improved. ISO is the digital equivalent of film speed (remember the olden days of Kodak in 100, 400, 800 etc. film speeds?).

Tiny F-stops and low light situations are where the Canon 5D really shines, as it'll go up to massive ISO numbers with little loss of quality. It's necessary to experiment with each camera to see how far you can push the ISO before loss of quality/graininess/digital noise become too problematic.