What next when the hyperfocal is wrong?

According the Lord of math, the hyperfocal distance of my 50mm lens is
25 feet at F/11. Supposedly everything from 25 feet to infinity will be
in focus. Unfortunately you can't tell if this is the case until you
examine the image on a computer.
Last week, I shot a wedding where I wanted the couple at about 25 feet
and a church at infinity plus all in between to be focused. I didn't get
the measuring tape out but I have a fair idea of how far away 25 feet is.
The picture is OK. The foreground is sharp but the church in the
distance is not as sharp as I'd have thought it would be considering the
maths of the matter. I reasoned any smaller than F/11 and the image
would start to lose sharpness and produce vignetting.
Anyway... Can someone offer a suggestion as to why the technical details
were right and the results with my 20D off? The same image from my 5D
was spot on. Have I missed something with the crop factor or are there
other considerations when the lens is on 1.6 crop camera?
Douglas

Dmac

Re: What next when the hyperfocal is wrong?

...
The hyperfocal distance for a 20D with 50mm @ f11 is 38.3 feet. This is
the minimim distance at which you could focus while maintaining a far focus
limit of infinity.
If you focused at 25 feet (20D + 50mm @ f11) your near limit of acceptable
sharpness was 15.1 feet, while the far limit was only 71.6 feet.... this may
have resulted in your church softness.
To get a far limit of infinity to cover the church, you would need to focus
at the hyperfocal as mentioned above. This focus distance would also give
you enough DOF to cover your subject with a near limit of 19.2 feet.
Different CoC (circles of confusion) must be considered for these cams, due
to their different sensor sizes and their need to be enlarged by different
amounts to get to the same size print. A 20D has a CoC of 0.019, while the
5D is 0.030.
Naturally the above comparisons are based on the same subject distance,
where is reality these would be different between the two cams if you wished
to compose the same within the frame. Moving closer to the subject with the
5D would mean a whole new set of calcs whould have to be made and these
would pretty much resemble the 20D near and far limit results.

POTD.com.au

Re: What next when the hyperfocal is wrong?

In article <VObhg.4273$ap3.1744@news-server.bigpond.net.au>,
Dmac@this.group says...
Ah, to have HF markings on your lens... God bless 'em old manual focus
lenses. I was actually using this method of focussing at a German Bazaar
I attended on the weekend. I simply put the infinity sign at the marking
for my aperture and made sure that the subject was within the distance
indicated at the other marking for that aperture.
Interesting that you are getting different results with the same lens on
different DSLR's...
--
http://www.nikongear.com/

Re: What next when the hyperfocal is wrong?

Presuming your couple were at 25 feet and the church was near enough to
infinity, then the hyperfocal distance - your focus point - should be 50
feet. Focus on 50 feet and the dof will extend from half the HD, i.e. 25 ft
to infinity, at the correct stop, of course. If you focused on 25 feet then
there's your problem. Dof when focused at 25 ft and f/11 extends from 13.5
ft to 174 ft, so the foreground and couple will be sharp, but the church will
probably be outside the 174 ft limit (from Dofmaster calculator).
From the DofMaster website calculator for APS-sized sensors with a CoC of
0.025mm, focusing on 50 ft at f/8 will give a dof of 22.6 feet to infinity.
If you focused directly on the couple for maximum sharpness (which is what I
would do), and wanted the church in as well, then your HD is 25 ft, the point
you focused on, and the aperture to extend the dof to infinity will be
f/13.5. This would also extend the dof in front of the couple to 12.4 feet -
so your total dof would be 12.4 ft to infinity when focused on 25 ft, which
obeys the rule of acceptable sharpness from half the HD to infinity.
But, as I well know, doing this in your head while shooting a wedding is all
but impossible.
Did you not think of using the 'A-dep' function on the camera?
Colin D.
--
Posted via a free Usenet account from http://www.teranews.com

C J Donoghue

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