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08-30-2011, 03:11 PM   #16
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QuoteOriginally posted by Lowell Goudge Quote
for the record, SR does not fully apply to macro work.
Quite so, for the reasons stated. I'm not sure where the cutoff is; my rule-of-thumb for handheld shooting is that a working (subject-to-lens) distance of 2x focal length is definitely too close, and 5x FL is definitely SR-able. In between is a grey area.

And your mileage may vary depending on how palsied or stoned you are. Also, SR may be ineffective when you're in a bouncing moving vehicle. Avoid closeups in the back of a pickup truck rolling down a rocky road after drinking a jug of absinthe, eh?

08-31-2011, 12:07 AM   #17
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QuoteOriginally posted by RioRico Quote
...after drinking a jug of absinthe...
Ah, if consumed neat - the situation improves proportionally by the amount of dilution with water. However it would require experimentation over many weeks to find your own level of comfort.

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08-31-2011, 06:24 AM   #18
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Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm. I must be having a brainf*rt because I'm just not grokking part of this I'm still a bit befuddled by the idea that the mm of the reversed lens wouldn't alter the appropriate SR setting to use. So I drew a diagram to explain why - yes it's a bit simplified but hey hopefully it gets the idea across.

AFAIK, The MM of the SR you set basically tells your sensor how much it should move to compensate if there's a wobbly photographer. Which differs according to the lens used because of the degree of view of the lens. So, using the diagram, 3 examples with a photographer doing the same physical wobble:
  • 100mm
    • 100mm has a very small degree of view, a device to bring a small distant degree of view focused onto a close-by sensor plane
    • a wobble on a small field of view far away means that the whole image transferred onto the sensor moves a lot.
    • ie the projection of the bunny on the sensor is now on the left rather than the right because of the wobble
    • and SR has to deal with that by moving the sensor - quite a move
  • 28mm
    • 28mm has a huge degree of view, a device to bring a huge degree of view focused onto a close-by sensor plane
    • a wobble on a huge field of view far away means that the whole image transferred onto the sensor moves a tiny bit.
    • ie the projection of the bunny on the sensor has shifted a pixel or two because of the wobble
    • and SR has to deal with that by moving the sensor - a tiny tiny move
  • 50mm
    • 50mm has a normal degree of view, a device to bring a normal degree of view focused onto a close-by sensor plane
    • a wobble on a normal field of view far away means that the whole image transferred onto the sensor moves a bit.
    • ie the projection of the bunny on the sensor has moved a bit but not a huge amount because of the wobble
    • and SR has to deal with that by moving the sensor - a bit of a move


Now onto reversing. I thought that a reversed lens works opposite to a normal lens, it is a device to stretch a close-by sensor plane out to differing field of views depending on the mm. The stretch is greater with smaller mm (because smaller mm means wider field of view)
  • 100mm with 50mm
    • The reversed 50 (set at infinity) delivers an image of the sensor plane (the focus point) to infinity at its field of view, which is normal. The normal 100mm lens then takes a small slice of that infinity and delivers that to your sensor.
  • 100mm with 28mm
    • The reversed 28 (set at infinity) delivers an image of the sensor plane (the focus point) to infinity at its field of view, which is wide. The normal 100mm lens then takes a small slice of that wider spread infinity and delivers that to your sensor.
    • I think this is the crucial bit. Because you've reversed a 28, the sensor plane gets spread onto a wider field of view than were it a 50. Therefore your eventual degree of view is smaller - the 100mm doesnt change but the 28 has "spread it out" "stretched" it more because of its greater degree of view.
    • It's a bit like taking the bunny in the 100mm top example and stretching it/making it bigger. The viewfinder/at the sensor would therefore be filled with less of the object, so it's like a smaller degree of view.

Personally I doubt SR would work for macro because the degree of compensation that'd have to be required. Equivalent to a 2000mm lens or something - too much for the sensor to handle?

Last edited by Nass; 05-08-2017 at 08:20 AM.
08-31-2011, 08:05 AM   #19
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Here is the fundamental lens diagram showing how a light from a particular angle is focused on the sensor.


The angle, "alpha", shown represents the camera's wobble; the distance the image moves across the sensor, Y, is proportional to the distance from the lens to the sensor. The key thing is that it doesn't matter what the focal length of the lens is if the image is in focus.:

if an image is in focus, camera wobble leads to image displacement proportional to lens-sensor distance.

Adding a reversed (or non reversed) lens to a primary lens creates a "new lens" with a different focal length but it is the distance of that "new lens" from the sensor that affects the wobble-image displacement relationship & not the focal length of the "new lens". Rather, the new focal length changes the relationship between image magnification and how far the lens is from the sensor.


Last edited by newarts; 08-31-2011 at 08:13 AM.
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