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Re: [OM] IMG: Sunrise, Moonset

Subject: Re: [OM] IMG: Sunrise, Moonset
From: John Hudson <OM4T@xxxxxxxxxxx>
Date: Mon, 20 Oct 2014 09:57:52 -0300
Does "embiggen" convey any greater meaning than "enlarge" in the context of the subject under discussion ?

jh


On 10/20/2014 8:09 AM, Chuck Norcutt wrote:
I'm sorry you cant embiggen it because there's no larger image behind it available to the general public. And showing you (in particular) a full pixel version wouldn't prove or disprove anything. That shot was done handheld with the 5D and no IS on the lens. What's its actual resolution? I have no idea. I only know that it meets my own criteria for a shot planned to be printed at 8-10" high at full frame size. It wasn't intended to be cropped to show the detail of the foreground flowers (although it might suffice for that). If I really wanted to do that I'd have taken a different photo... just as you did with the weather vane. I consider a hyperfocal shot to be a purposeful, landscape shot. It's meant to be displayed as I framed it in the viewfinder. If it serves a second purpose that's fine but was not the intent.

Your comments about hyperfocal distance and CoC lead me to believe that your understanding of such is only partial. You say: "ALL DoF calculations and tables rely on assumptions about the CoC..." Your comment about the use of tables making assumptions about CoC is quite correct. The same holds for DoF markings on lenses and, unfortunately, most DoF calculators. They all assume a CoC of about 30 lines/mm for 35mm size images. However, a good DoF calculator makes no such assumptions. It allows you to define the desired CoC. I find that 30 lines/mm is adequate for my own usage when working with the 5D. But working with the E-M5 with its 4/3 sensor requires 60 lines/mm to account for the 2X print magnification over 35mm. Maybe your own criteria require 40 lines/mm for 35mm size and 80 lines/mm for 4/3. Whatever it is can be readily determined with a good DoF calculator that allows entry of the CoC as a parameter.

The following DoF/hyperfocal calculator will allow entry of a specific CoC if you scroll all the way to the bottom of the list of cameras.
<http://www.dofmaster.com/dofjs.html>

For my own use I don't carry a calculator but do carry a small card with hyperfocal distances that I have calculated for just a couple wide angle focal lengths. The characteristic of these little custom tables is that they use only one aperture (the diffraction limit for the sensor size)... about f/11 for a 5D and about f/5.6 for an E-M5. Then I calculate the hyperfocal distance. The parameters that I used for the 24mm shot on the 5D would have been f/11 and hyperfocal distance of 5.65 feet. But I make no attempt to be that precise in setting the focus distance. What I do know is that, if I focus at less than 5.65 feet I will miss infinity. I don't depend on focusing scales since most lenses don't have them and those that do may be hard to interpret with any precision. But I can estimate 6 feet fairly accurately and then add a foot or two to be on the safe side. If I end up focusing at 8 feet the near focus will be 4 feet instead of 1/2 of 5.65. But that rarely matters whereas missing infinity does.

This is not really finished but I've got to end it here now. We're traveling to Florida after having sold our New York place to await the completion of the South Carolina house. This laptop is shared with SWMBO and it's now her turn. :-)

Chuck Norcutt


On 10/19/2014 6:22 PM, Moose wrote:
On 10/19/2014 1:02 PM, Chuck Norcutt wrote:
Here's a little hyperfocal math at work showing the you can trust them
numbers.  The closest plants in this photo are about 3 feet away from
the camera.  Note that "infinity" is in focus.  Canon 5D, 24mm at f/11
with lens focused at 6 feet.  This is actually a 2-image pano.
<http://www.chucknorcutt.com/Mt%20Rainier/pano%208552-8553er.htm>

Lovely @ 5x10" on my screen. But of course, being Pixel Peeper Moose, I
kept looking for where to click to embiggen it.

ALL DoF calculations and tables rely on assumptions about the CoC, as
you know well. And they all have their roots in opinion polls. Folks
showed a bunch of prints to another bunch of folks, asked which were
sharp and tallied the results. That's why you set the viewing size in
making the calculations.

Here's why I don't have and/or don't trust them numbers.

1. Right off the bat, I'm in trouble, because my 20/10 vision is an
outlier; I don't have the same opinions about what is sharp as the average.

2. The world has changed. We, at least the pixel peepers among us,
routinely view images at magnifications never dreamed of in film days
(the movie Blowup not withstanding), if only because grain the size of
golf balls isn't that interesting.*

I rather routinely take crops of rather small parts of an image and
present them at 8.5x11" on my screen, larger or smaller for various
viewers on their screens.

Take the example I just used. Lets say I decide to do a gallery or book
of the weather vanes I shot over the years. (Farfetched for weather
vanes, but two of my three books have come from images collected from
over the years.) I have a good shot of this one, in focus. I've added it
to the existing comparison.
<http://www.moosemystic.net/Gallery/MPhotos/BayArea/Miscellaneous/AngelMoon.htm>


Had I used hyperfocal for 'good enough' focus, it would be soft at this
size. Taken with the 14-150 @ 150. Had I had the 70-300 at the time, I
wouldn't have needed such a crop, but that's part of the point: I
didn't, but shot for the best result, no matter what as yet unknown use
I might put it to.

3. I said it before. My µ4/3 lenses don't have DoF markings, anyway, nor
do any zooms I know of. This shot was taken casually, when I parked in a
tiny village and was about to walk to a store to pick up a custom order.
How am I to make all these calculations in any reasonable time frame? I
don't even know for sure how far away the vane is.

I've tried using manual focus to find the middle between extremes, but
the results have been mixed, at best. Usually to my eye, not right for
either end.

A couple of shots in a few seconds, and I'm done and on my way.

Directly On Focus Moose

* OK, another disclaimer, if only for me. Kodak made a special reversal
film, originally for spy planes, I believe. We used the commercial
version back when. It seemed grainless and somehow like the subject ran
out of detail before it did. :-)   Slow, very tricky to process, etc. As
far as I know, no one was using it for regular photography. But for huge
enlargement on a rear projection screen, amazing.


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