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[OM] Alternate Paradigm [was Harbingers of Spring]--macro FL and shutter

Subject: [OM] Alternate Paradigm [was Harbingers of Spring]--macro FL and shutter speed for hand held shots
From: usher99@xxxxxxx
Date: Fri, 6 Sep 2013 15:37:37 -0400 (EDT)
Shoot and Run Moose writes


>>Here are some close-up and macro shots from the last couple of 
months, all shot
>>hand held.
>><http://zone-10.com/tope2/main.php?g2_itemId=8184>

>>I've actually posted many C-U/Macro shots over the last year plus, 
but may not
>>have made it clear that virtually all are
>>hand held. These samples of using the extension tubes, for example, 
were done
>>without a tripod.
>><http://zone-10.com/tope2/main.php?g2_itemId=4514>

>>>>>The biggest drawback is shutter speed for unmoving subjects. The 
excellent IS
>>>>of the E-M5 is a big help, but I'm often
>>>>working at ISO 3200 in the shade.


Oooo, missed those. S&R Moose likes the loooong FL macro and it does 
work very very well to simplify the background.
Must see the mft ext tube PZ14-42 set up which worked  MUCH better than 
I would have expected.  Must be a tiny kit.

Got me a thinkin. Always read that long FL requires higher SS handheld 
as it increases the magnification so moderate change in FL at same mag 
shouldn't make that much difference, no?

Thinking about the extremes at a 600mm FF equivalent FL must play some 
role
as lateral motion would be exagerated at that longer working distance.
So what gives?


  At high M the distance from the sensor plane to the image = the sum of 
the image and object distances or: [(1+M) + (1+1/M)] f = [(1+M)**2 / M] 
f where M is the magnification and f the focal length. Since the image 
is magnified by a factor of M this means if we shift our view laterally 
by a distance of a/M (where a is again the sensor pixel width) we will 
shift the image by one pixel on the sensor. So the angle required for 
this 1 pixel shift is:

(a/M) / {[(1+M)**2 / M] f} = a/[f (1+M)**2]. This is exactly the same 
as the non-macro case above except for the factor of (1+M)**2 - and in 
fact the earler results is just the limiting case for small M.

Bottom line is that the 1/f rule is STILL valid for macro (contrary to 
my original  impression), but must now be modified by multiplying f by 
the factor of (1+M)**2. So for example at 1:1 (1+M)**2 =4 and the 
shutter speed for sharp handheld imaging needs to be 1/4th as long as 
would ordinarily be the case for the focal length.  This ignores a 
purely rotational shake and that would be substantially altered by the 
center  of rotation.  Suspect the
(1+M) factor is not squared but linear if the center of rotation is the 
exit pupil but not sure I  can prove that (esp at work)

Macro Mike



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