Diglloyd writes in his review of the 40 Zeiss Hartblei about stitching:
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While overall imaging performance is very high, with especially appealing color, attention must be made to subtle shifts in focus when shift is applied. This makes the Hartblei 40/4 less than ideal for quick shift-lens-stitching applications.
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As far as I understand it, there will always be a focus shift implied once a shift or tilt movement was applied. Therefore focusing can only be done after any movement. For stitching this means every single shot needs refocusing.
The Zeiss CFE 4/40 looks much better.
Cheers
Jan
@Jan:
I think that Diglloyd is not very clear in what he means with "focus shift". I suspect what he observed relates to field curvature.
As far as I understand it:
- the lens projects an image to the sensor.
- this projected image (and the focus in that image) does not change when you shift, you just use a different part of the image.
- if you stitch several images from different shift positions then you can capture a larger part of the projected image.
- but if a lens has field curvature, then the point of focus is different in the centre of the lens than further out
(and most wideangle shift lenses with big image circles have very relevant field curvature, the Hartblei too)
- so in the shifted image, it SEEMS as if the focus point had moved (although you did not touch the focusing ring of the lens).
- the problem to get an image that is sharp across the whole stitched image is difficult because field curvature gets more relevant.
So if you refocus every shot - that would be something like focus stacking to overcome field curvature? Never tried it, but I think it is not easy to get the transitions done right. Maybe refocusing would slightly change magnification? Has any one of you tried that?
Marc