Lens hood - do you use one?

Started Feb 18, 2013 | Discussions thread
Barrie Davis
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Re: Lens hood - do you use one?
In reply to HEA-45, Feb 18, 2013

HEA-45 wrote:

I rarely use a lens hood for my landscape shots. The main reason is the incompatibility with my graduated filter set (which I use constantly.) The second reason is simply a lack of necessity; experimentation has shown that hoods make little difference (with a careful shot setup.)

The hood exists to remove non-image-forming light from the periphery of the image.

Non-image-forming light is that part of the light passed by the lens which is inside its circle of coverage, but outside the rectangle of the format frame.

This light is always deleterious of image quality.. (reduces shadow contrast).. even if not noticed a lot of the time.

This superfluous light reduces shadow detail, and does so by two independent mechanisms..

1) ... by bouncing between lens elements and creating flare which transfers highlight illumination to shadow zones.. (ameliorated but not removed by efficient lens coatings)

2) ... by spilling unhindered onto the wall of the sensor chamber, and from there reflecting to the sensor itself. All sensor zones receive this light, but it affects the shadows most, as in (1) above. Again, it is ameliorated by painting the surfaces with matte black paint, but the absorption process is not 100% effective.

Preventing this non-image-forming light from entering the lens in the first place, by means of a good hood IS 100% effective.. The closer the edges of the hood crop to the image zone itself, without actually appearing in frame, the better. That is why the ideal opening of a lenshood is a rectangle of same aspect ratio as the sensor, that is, NOT a circle.

(Petal hoods are the compromise they have to be to provide some hooding on zoom lenses, which is most critical at the wide end. The ideal hood for a zoom lens would vary its acceptance angle in synchrony with that of the optics... but the best we have so far are the adjustable professional hoods made in bellows form..)

Final point:- It is particularly important to fit an efficient close cropping hood when using filters, despite any inconvenience.

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Regards,
Baz
"Ahh... But the thing is, these guys were no ORDINARY time travellers!"

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