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 p.38 #4 · Voigtlander 35mm f/2 APO-Lanthar Review | |
Petegh wrote:
Firstly, most probably don't know that Lloyd suffers from presbyopia (farsightedness); combine this with the normal age-related decline in vision by your mid-fifties, means that in poorer light, he needs to focus wide open to get accurate focus.
Secondly, there only is ever one plane in actual focus in a 3D image, the rest of the image is out of focus to some degree - the acceptable extent to which depends on how fussy the shooter is, how big you intend to print etc. So, having your main subject intersect with that single plane of actual focus can matter in large prints (simply being within the depth-of-field is not enough to render your subject the sharpest object in the frame), and focusing wide open increases your chances of nailing that focused plane right on your subject (assuming the lens has no focus shift when you then stop down to shooting aperture).
Thirdly, Lloyd also noticed that with the Voigt 35 APO and the Voigt 65 APO, there was some focus creep with the helicoid mechanism when the lenses were pointed downwards for shooting, which may also be 'contaminating' his results.
As to the Lenstip findings - that the 35 APO's performance dropped off faster at close focusing lab conditions at smaller apertures v's the other 35's, I wouldn't read too much into that: I spose its possible that the unique aperture blade mechanism could be worsening diffraction (because the circular-saw shape may increase the surface area of 'edge' the light has to diffract around), but I doubt you'd notice a difference in the real world.
My own copy of the Voigt 35 APO doesn't appear to have any of the above problems either, but I'm probably a little bit less fussy than Lloyd. I am, however, getting randomly overexposed shots: if for example, I focus at f2, then shoot an aperture sequence at whole f stops, touching only the lens to change the aperture, I'm getting an overexposed image - often at f8 or f11. The EXIF data shows the f top as being correct, but there is an anomaly in the shutter speed; i.e. on a cloudless day, you would expect the shutter speed to double for every drop in aperture, but it drops considerable more than that on a single frame within the sequence - and that image is overexposed: any ideas anyone?...Show more →
The depth of field 'illusion' assumes that an image is viewed at 'normal viewing distance', which is usually taken to be that which allowws you to see the whole 'picture'. Thus a larger print is viewed from further away, and print size is not relevant. If you peer moore closely at part of the image the 'illusion' is lost.
You cannot'see what is included in DoF' by focussing stopped down as there is no real way of assesing how much unsharpness is acceptable by looking at a magnified view. So for a lens that doesn't have focus shift you should focus at full aperture on your most important point of sharp focus required, and accept the calculations that have stood the test of time for many many decades.
Having used Leica all my life for film, I avoided like the plague lenses with focus shift as they didn’t seem to me to be compatible with the ideals of an optical rangefinder. Even with magnified live view I cant be bothered to try and cope with it, nor those problems encountered with field curvature, whether induced or an original design 'feature'. But the search for lenses that WILL perform well in this regard on a sensor stack with a thick cover glass has shown it's simplest to stick with lenses designed for it, assuming that the designer knew what they were doing, which hasn't always been evident!
Gerry
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