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Lens hoods, Grazing flare and Contrast
I am a reader of your Zeiss ZF Lenses review and enjoy it a lot. I have the Zeiss ZF 25/2.8, 35/2, and the 100/2 Makro-Planar. How necessary would you say it is to use the hoods with these lenses? The hood for the 100 macro is certainly impressive but is a pain to use. — Jackie S
Most of the time it is not necessary. Grazing (non image forming) light cutting across the front element is the main issue. If you pay attention to such conditions and block that light, you'll be fine. Often you can see any problems in the viewfinder. However, what you're paying for with the Zeiss ZF line is in good measure the exceptional contrast and color, precisely areas which will be degraded under challenging lighting conditions.
Remember too, that most lens hoods are compromises: they are shaped in a way that does not allow them to optimally block all extraneous light: round lens hoods are good examples here. The lens hoods for the ZF 18/3.5 Distagon and especially the 21/2.8 Distagon have much more complex shapes which are more effective at blocking non image forming light, especially important for wide angles, where it may be difficult to avoid a bright light source just outside the frame.
When shooting in infrared, flare control is massively important with most lenses, so be sure to always use lens hoods in that case.