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[OM] Re: Shift lenses

Subject: [OM] Re: Shift lenses
From: hiwayman@xxxxxxx (Walt Wayman)
Date: Mon, 05 Jul 2004 17:21:11 +0000
I'm too dumb to figure out this trigger-whatever stuff.  And when I fold paper, 
it usually ends up being an airplane that won't fly.  So, I resorted to a 
method more suited to the simple-minded:

I just put an OM-4 on a tripod, stuck on the 35 Zuiko shift, took note of what 
was at each edge of the viewfinder, then replaced it with a 35/2 Zuiko.  At a 
distance of 10 feet, the 35/2 actually covers about a six-inch wider field than 
the shift lens.  Shifting the shift lens in any direction actually DECREASES 
the field of view so that the 35/2 then covers nearly a foot wider field at 10 
feet.  This hands-on, with-the-gear experiment makes a lot more sense to me 
than mysterious calculations and folded paper.

What am I missing?  I hope we're not confusing coverage with field of view.  To 
me, field of view is what you get on film, what you see through the viewfinder 
or on the ground glass, regardless of the image circle the lens may project, 
a.k.a. its coverage.  And I do know about coverage.  One of my favorite MF 
lenses is a super-sharp 90/5.6 Caltar.  It will cover the 5x7 in. format, but I 
use it on my 6x9cm baby Graphics.  Talk about cherry-picking the center out of 
an image!

Walt, often Clueless, but eager to be instructed


--
Everybody has a photographic 
memory. Some people just don't 
have any film. 




-------------- Original message from "Piers Hemy" : -------------- 
> 
> John Lind's mention of Markerink's web site was the opportunity to have 
> another browse - and not just for IR (or UV) photography. It's recommended. 
> In doing so, I found that at 
> http://www.a1.nl/phomepag/markerink/shifcalc.htm Willem has attacked a 
> question which has arisen on the list in the past months, namely "Is the 
> angle of view of the 24mm/35mm shift lens greater than the normal 
> 24mm/35mm?". 
> 
> Olympus describe the 35mm as having an image circle equivalent to that of a 
> 24mm - but that is misleading. The specs in the Sales Info File say: 
> "35mm shift AoV 63 degs (83 degs with 62mm image circle)" - this suggests 
> that it is just the image circle which is bigger. 
> "24mm shift AoV 84 degs (100 degs at max shift)" - this says something 
> different! 
> 
> In truth, as Markerink discusses with applied trigonometry aplenty, the 
> angle of view of a shifted lens (in the direction of the shift) *is* greater 
> than the angle of view of a normal lens of equivalent focal length. 
> 
> Visualizing how this can be is not easy - but it occurred to me there is an 
> obvious way to show the effect, using two sheets of office paper. No pen, 
> protractor or ruler needed. You don't even have to be able to count. 
> 
> 1 Fold one sheet of paper in half across the long side to find the 
> midpoint of the long side. Unfold it and make one fold from the midpoint on 
> one side to each corner on the opposite side. The angle between the two 
> diagonals is the angle of view of our notional normal lens. 
> 
> 2 Fold the other sheet of paper along a diagonal, from corner to 
> corner - the angle at the corner is the angle of view of a notional shift 
> lens, fully shifted. 
> 
> 3 Now put one sheet of paper over the other, and you will see that the 
> angles are different. The first "normal" lens has a wider angle of view 
> than the "shift" lens, but they both cover the same subject plane. In other 
> words, a fully shifted 35mm lens has the same coverage (parallel to the film 
> plane) as a 24mm normal lens. 
> 
> That had been bugging me for months. Thanks to John Lind (again) for the 
> pointer that put it to rest! 
> 
> Piers 
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