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03-29-2019, 01:58 AM   #61
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QuoteOriginally posted by zburatoru Quote
Not my experience! Very, I said very sharp from f2.8! It can be a very good landscape lens! But, strangely or not you have to refocus if you focused first on f1.4 if you want to shoot at f4, 5.6 etc
This is "focus shift", and is quite common with relatively simple, fast aperture lenses. See the following article:

What is Focus Shift?

From that article:

"Focus Shift and Fast Aperture Lenses

Most lenses prone to focus shift problems have very fast maximum apertures of f/1.0, f/1.2 and f/1.4 for one major reason – a big portion of the lens surface is used to transmit the light. Fast prime lenses with uncorrected spherical aberration will always have focus shift problems for this reason. In fact, any fast lens with spherical aberration problems will exhibit focus shift at different apertures. Slower lenses with maximum aperture of f/1.8 and smaller that also suffer from spherical aberration problems will have a much less pronounced focus shift, so it will not be as noticeable in images."


03-29-2019, 06:56 AM   #62
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QuoteOriginally posted by BigMackCam Quote
This is "focus shift", and is quite common with relatively simple, fast aperture lenses. See the following article:

What is Focus Shift?

From that article:

"Focus Shift and Fast Aperture Lenses

Most lenses prone to focus shift problems have very fast maximum apertures of f/1.0, f/1.2 and f/1.4 for one major reason – a big portion of the lens surface is used to transmit the light. Fast prime lenses with uncorrected spherical aberration will always have focus shift problems for this reason. In fact, any fast lens with spherical aberration problems will exhibit focus shift at different apertures. Slower lenses with maximum aperture of f/1.8 and smaller that also suffer from spherical aberration problems will have a much less pronounced focus shift, so it will not be as noticeable in images."
Thank you for the explanation! It really doesn't bother but you have to be careful when focusing...
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