Focus Fallibility: Lens Test Fallacies

Paul Furman wrote:
Alfred Molon wrote:
In article 122465f9-3e52-4411-b3d6-4f240fe66274
@x35g2000hsb.googlegroups.com, Don Stauffer in Minnesota says...

Admittedly an LCD screen is far, far from resolution needed to judge
focus.

But you can zoom down to pixel level and precisely adjust focus.

Not quite that close. From what I've seen the D300 zooms closer after
taking the shot than in live view.

I *think* the D300/D3 zoom to 1:1 pixel view in LV mode. The LCD is
also much higher resolution than any other current dslr with LV.
The aperture set when entering LV is "held" until LV is exited, so you
can set f2.8, use that for focusing on the LCD. Or you can set aperture
- quickly exit and re-enter LV mode, and get a real DOF preview.
It's excellent for critical focus / tripod work. I've found LV useless
for anything else so far.
In review, the D300/D3 zoom way past 1:1 - looks like about 400% view.
They can be programmed to go to 1:1 (or other selected magnification) by
clicking the center of the 4-way selector once centered on the active
focus point, click again to return to previous view.

Alfred Molon wrote:
Here is an interesting article by Dave Etchells:


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--
Ray Fischer

Alfred Molon wrote:
Here is an interesting article by Dave Etchells:
http://www.slrgear.com/articles/focus/focus.htm

I found it interesting that according to him manual focus through the
viewfinder is not precise enough, while manual focus through live
preview on an LCD screen delivers the best results.

Very interesting article! It explains something which has been
baffling me for months.

I'd noticed that some of my shots, all perfectly in focus at the
centre, somehow seemed to be much better at the edges than others, for
no reason I could discover. I struggled with tripods, spot auto focus,
very careful manual focus, and I simply couldn't reproduce the edge to
edge sharpness of my best shots reliably.

I was beginning to think maybe there was some slop in the zoom, so the
lenses inside didn't always line up the same way. But that article
explains it. The best focus for easily visible edge to edge sharpness
can't be achieved reliably with autofocus, nor is there any manual
viewfinder or LCD method which is nearly good enough.

The kind of methods he used can't be exported from the lab. There are
other things it's hard to get right outside the lab with portable
tools, such as exposure and white balance. So camera makers offer
cameras which can do bracketed exposure runs and bracketed WB runs.

Does anyone offer bracketed focussing?

--
Chris Malcolm DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

In article , Chris Malcolm says...

I was beginning to think maybe there was some slop in the zoom, so the
lenses inside didn't always line up the same way. But that article
explains it. The best focus for easily visible edge to edge sharpness
can't be achieved reliably with autofocus, nor is there any manual
viewfinder or LCD method which is nearly good enough.

If you had the patience to use manual focus with a pixel-level zoomed
LCD, you'd get almost perfect results.

The kind of methods he used can't be exported from the lab. There are
other things it's hard to get right outside the lab with portable
tools, such as exposure and white balance. So camera makers offer
cameras which can do bracketed exposure runs and bracketed WB runs.

Does anyone offer bracketed focussing?

Not that I know, but could be done by a change in firmware I guess.
Another option is to simply take a few shots and walk back and forth a
bit between the shots.
--

Alfred Molon
------------------------------
Olympus 50X0, 8080, E3X0, E4X0, E5X0 and E3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

Alfred Molon wrote:
In article , Chris Malcolm says...

I was beginning to think maybe there was some slop in the zoom, so the
lenses inside didn't always line up the same way. But that article
explains it. The best focus for easily visible edge to edge sharpness
can't be achieved reliably with autofocus, nor is there any manual
viewfinder or LCD method which is nearly good enough.

If you had the patience to use manual focus with a pixel-level zoomed
LCD, you'd get almost perfect results.

You've never tried that, have you?

Lessee, zoom, center, zoom, center, zoom, center, zoom, center, focus,
whoops, bumped the camera, unzoom, unzoom, unzoom, center, zoom, zoom,
center, zoom, adjust focus, zoom, center. Press shutt... Now where
did they all go?

--
Ray Fischer

Alfred Molon wrote:
Here is an interesting article by Dave Etchells:
http://www.slrgear.com/articles/focus/focus.htm

I found it interesting that according to him manual focus through the
viewfinder is not precise enough, while manual focus through live
preview on an LCD screen delivers the best results.
It would be interesting to see how well rangefinders are able to focus.
Optically they have the advantage of a large base, but the mechanical
coupling of the lens focus position and the camera body seems error prone.

-- Hans

I was having serious difficulty with the autofocus of my
Canon 30D until I discovered that the focus point size of the
central focus point is three times as big as the size of the
marked square, 9 times the area. Once I knew that, everything
made sense and I no long have unexpected out of
focus shots.

Doug McDonald