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false_Aesthetic
7-Apr-2012, 08:44
Hi,

The recent sale of a Canham lens shade got me thinking: What do they do exactly.

Lemme clarify. I understand that they stop light from hitting the lens and causing a flare but so does my hand (darkslide, shadow, etc).

Is there an added benefit for having the lens completely surrounded a shade or is it more for ease of use (not having a random hand appear in the corner of your image or freeing up that hand for other things)? I assume that they'd be quite useful in the studio since you could have stray light bouncing around and coming back at you but what about in the field?


Thanks

Old-N-Feeble
7-Apr-2012, 08:49
They help old folks like me with shaky hands. :)

E. von Hoegh
7-Apr-2012, 08:59
A proper lens shade functions by excluding any light that is not part of the image. A compendium type shade, with a mask that matches the aspect ratio of the format and extends a good ways in front of the lens is about the best balance of efficiency and inconvenience.

eric black
7-Apr-2012, 09:04
plus they can be observed on the set up of the shot to make sure they are not in the frame- helps to avoid those unfortunate shots that have a dark slide impinging into the picture by accident. A "French Flag" does the same thing but from the topside only- I use them for wider angle shots where a compendium shade doesnt seem to be offering much in the way of shading.

Brian Ellis
7-Apr-2012, 09:30
Your hand keeps sunlight or another source of direct light from striking the lens. A good lens shade (not those narrow little round things typically sold with wide angle zoom lenses for smaller formats) keeps all light except image-forming light from striking the lens. They're particularly useful outdoors when the light is bright but there's no direct sunlight. As others have said, for a variety of lighting conditions and a variety of lenses a compendium shade is probably best.

E. von Hoegh
7-Apr-2012, 09:35
If you want a demonstration of just how good a shade can be, watch any movie from the 1930s. Those lenses were uncoated, some had many air-glass surfaces (early varifocal lenses) and are surprisingly free of flare.

false_Aesthetic
7-Apr-2012, 10:10
Thanks. (Esp Brian for comparing hands to shade).

T

Leigh
7-Apr-2012, 19:48
Any lens projects a cone of light into the camera body.

The desirable portion of that cone lands on the film and makes a picture.

The undesirable portion hits the camera interior, including the inside of the bellows, and bounces around.
If any of that light lands on the film it causes fogging. That problem can be difficult to diagnose.

The purpose of a compendium shade is to eliminate all of that undesirable light before it enters the lens.
This is why the opening should be masked to an aspect ratio matching the film.

- Leigh

Frank Petronio
7-Apr-2012, 20:05
They also help keep dust, drops, and other junk off your lens and should you drop a lens with a shade attached, they will sometimes soften the blow.

A compendium is nice but I try to put at least a cheap metal screw-in wide lenshade on every lens just to help keep them cleaner and safer. The newer pincher lenscaps can attach even with the shade screwed in. Even if I have a bellows shade I'll keep the little one on anyway.

joselsgil
8-Apr-2012, 15:10
There is also the "cool look factor". :)

sun of sand
9-Apr-2012, 21:44
I use 4 leaf barn doors that I epoxy to filter rings
round shades would always leave me trying to block sunshine from hitting the lens anyway or would vignette when I forgot to check after movements

sun of sand
9-Apr-2012, 21:46
search robert zeichner
he did a homebrew shade that I never attempted but then one day after seeing a small barn doors I got one for each lens