FYI ~ DOF and focus
Friday, October 12, 2012 at 11:10AM ;)
DOF comparison • click to embiggenOn yesterday's entry, civilized ku # 2372-74, John Linn wrote:
... What I find irregular of the trio is the difference in depth of field. To my eye the images do not seem to go well together (although you did achieve balance). You have often stated the necessity of using one focal length in a body of work. How about consistency of focus depth? It almost appears the center picture was shot with a longer lens.
my response: First, a technical note, re: DOF. Many of you may already understand this technical point, but I bring it up and provide the picture comparison for those who don't. -
... Depth of field refers to the range of distance that appears acceptably sharp. It varies depending on camera type, aperture and focusing distance, although print size and viewing distance can also influence our perception of depth of field ... Note that I did not mention focal length as influencing depth of field. Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to magnify the subject when one is unable to get closer. If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length! read more here
When John mentions that he sees a difference in the DOF between the center picture and the left/right side pictures in yesterday's triptych - which he attributes to the apparent use of different lenses in the making of the pictures - what he is actually seeing is a visually apparent difference in DOF which, in fact, is not the case. This fact is readily observable in the side-by-side comparison of the center picture with that of the right side picture (center and right as seen in the triptych) when that picture is cropped to the same (relatively so) magnification factor as the center picture - take notice of the middle distance grave markers and the background buildings.
When the magnification factor is similar, so is the apparent DOF. Or, at least it is close enough for government work.
All of the pictures in the triptych were made with the same lens and aperture - 45mm @ f1.8. I achieved a higher magnification in the center picture by simply moving closer to the tree ... which brings me to what I believe is the real point of John's comment - the fact that he finds the triptych to be visually discordant ("the images do not seem to go well together") because of the apparent difference in the DOF which the pictures present.
That apparent difference is obvious. However, there is another difference which John did not catch or at least he didn't mention. There is also a distinct difference in the point of focus between the right side picture - the focus point is on the background - and that of the left side picture - the focus point is on the foreground.
All of these differences - apparently different DOF and actually different points of focus - are intentional.
Lately, I have been giving some thought to concentrating, albeit not exclusively, my picture making on that of making triptychs (something I have done in the past but something I have, over time, let slip away). However, in doing so, I want to break out of my former look and somewhat tradition triptych approach and my experimentation with making triptychs with apparent (or even actual) differences in DOF and points of focus is just such a break out attempt.
IMO, and to my eyes and sensibilities, it's working. The trick in this endeavor is to achieve a sense of overall visual balance when the triptych is viewed as a whole - most likely from a distance which allows the viewer to see the piece as a whole - and a sense of restless visual discord when the individual pictures are viewed in relatively close proximity.
The reason for overall visual balance should be visually / emotionally / intellectually apparent - I want the triptychs to work as all of a visual piece. My reason for visual discord is to: a) mimic how the eye views any given scene - it wanders here and there focusing upon different planes and details, and b) to play with and make obvious, (WARNING: Elitist Alert) to the thoughtful and informed mind, some of the inherent characteristics of the picture making medium, especially its capability to call attention to specific planes in a scene or of a referent, both with point of focus and degree of magnification.
In a nutshell, that's what I want to focus on.
gravitas et nugalis
Featured Comment: John Linn wrote: "So basically what you are saying is the thing that bothers me is what you were going for ... This may be a good example of what could be better appreciated as a large print rather than web image."
My response: Yes, and yes. However, you are not alone - very often what strikes many viewers of pictures as not right / perplexing / confounding and hits them in the eye like a big pizza pie is exactly "what I was going for". You know, like Paul Maxim* as an example.
*to this day, every time the wife reads one of Paul's comments on my blog, she asks, "Did you and Paul throw any punches at each other during your date?"
Reader Comments (2)
So basically what you are saying is the thing that bothers me is what you were going for.
This may be a good example of what could be better appreciated as a large print rather than web image.
Even at web size, the effect of viewing the 3 images from left to right is striking. I really felt as if I was being pulled forward when viewing the middle image, then I could visually "step back" when viewing the third image.