Re: f/32 testing

[T3D Greg Erker <erker@xxxxxxxxxxxxxx>]

>If anyone has the time, I'd be interested in hearing of a comparison.
>Just plug the figures in my post into MAOFD and see what happens.

  I asked so I'll put the numbers in. (I used MACmaofdW by the way.)

I entered an and af and various f-numbers and got the resulting
geometric resolution (rg) and diffraction limited resolutions
(rd).

I played with the "film plus lens res" to convert John's lpmm numbers
in to resolutions (minutes of arc) and got the following conversions
60 lpmm = 1.1, 42 lpmm = 1.6, 30 lpmm = 2.3, 21 lpmm = 3.3 and
15 lpmm = 4.6.  I hope I converted these correctly.

I didn't know the res of John's film so I used two numbers for
the combined film + lens res: 40 and 60 lpmm. This res is
shown in the table as r40 and r60.

The table shows two "summations of all res. in quadrature"
for the 40 and 60 cases (called s40 and s60):

an   af    f#   rg     rd    r40   r60   s40   s60
--------------------------------------------------
490  628   16   2.41  0.61   1.7   1.1   3.0   2.7
490  628   22   1.75  0.84   1.7   1.1   2.6   2.3
490  628   32   1.20  1.23   1.7   1.1   2.4   2.1
490  628   45   0.86  1.73   1.7   1.1   2.6   2.2
490  628   64   0.60  2.46   1.7   1.1   3.1   2.8

So for the nearest and farthest targets the spreadsheet
says that f/32 is best and that the res is between 2.1
and 2.4 moa (based on my film res assumptions).

John wrote:

>At f/32, I can make out the 15 and 21 lpmm at all five distances.
>At the 550 distance, I can additionally make out 30 lpmm.  At f/45
>I can make out the 15 and 21 at all distances but the 30 at none.
>At f/64 I can make out _none_ of the test targets' lines!  I _can_
>still read the f/64 setup information tag I put under the targets.

  The 15 and 21 targets are 3.3 and 4.6 moa based on my conversion
and thus should be visible if the "sum" resolution is 2.1-2.4.
The 30 target is 2.3 lpmm and John wasn't able to see it on the
near and far targets. So the spread sheet calculation may be
optimistic.

  At f/64 the spreadsheet says the res is between 2.8 and
3.1 so the 15 lpmm target should still be visible. It wasn't
so again the spreadsheet is suspected of being optimistic.

For the in-focus target:

an   af    f#   rg     rd    r40   r60   s40   s60
--------------------------------------------------
550  551   64   0.00  2.46   1.7   1.1   3.0   2.7

  At this aperture the res is below 3.0 (calculated)
yet John couldn't see the 21 lpmm target which is
3.3 moa or the 15 lpmm target which is 4.6 moa.
Again the spreadsheet is too optimistic.

  This all assumes that I converted John's lpmm numbers
to moa's correctly. If not the conclusions are suspect.

Greg E.


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End of TECH-3D Digest 141
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