On Wed, 8 Jan 2003 18:59:53 +0000, David Littlewood <david@nospam.demon.co.uk> wrote:

>In article <3e26562e.9611772@newsstand.cit.cornell.edu>, Neuman -

>Ruether <d_ruether@hotmail.com> writes

>>On Wed, 08 Jan 2003 09:21:17 +0000, Moldy

>><elim(underscore)oldman@hotmail(dot)com> wrote:

>>>I have just got a screw in hood for a lens on which I mount a UV

>>>filter. Which order should I place the filter and hood.

>>>

>>>Lens | Filter | Hood - Will this cause vignetting?

>>>

>>>or

>>>

>>>

>>>Lens | Hood | Filter - Will the added distance between the front

>>>element and the filter affect the picture?

>>>

>>>The lens is 28mm focal length with a 52mm filter size if this is of

>>>any relevance

>>Lens | Filter | Hood - otherwise, the filter is not

>>shaded or protected. Whether or not the combination

>>will vignette depends on the design of the lens, the

>>thickness of the filter rim, and the design of the

>>hood (the hood is the most likely to introduce

>>vignetting). If your camera has DOF preview, you can

>>easily check for vignetting by focusing to closest

>>distance possible, setting the aperture at the smallest

>>stop possible, and while holding in the DOF preview

>>button, look at a bright subject area placed in a

>>corner of the VF to see if the corner is darkened.

>>If you VF does not have nearly 100% coverage, though,

>>this will not be definitive (moving a finger around

>>the edge of the shade extended very slightly inside

>>the shade edge while doing the checking can indicate

>>if there is a likely problem). If this is too awkward

>>or impossible, shoot one picture of a smooth-toned

>>subject occupying the entire frame, with focus at

>>minimum and with the lens at the smallest stop.

>>BTW, if the 52mm filter will fit onto the hood, it

>>is likely the shade will vignette in any case [with

>>the 28mm lens for the 35mm format], unless the lens

>>front element is considerably smaller than the 52mm

>>filter ring...

>Vignetting (whether internal or external) is normally at its worst at

>maximum aperture. Particularly with a wide-angle lens, the image of an

>external obstruction may become visibly sharper on stopping down, which

>may create the appearance of it being worse.

Yes - but at most middle to wide stops, the visible

effect of the vignette is minimal, and generally

acceptable; only at the smallest stop is the vignetting

shade really objectionable. In reality, virtually all

lenses (at least the short and medium FLs...) vignette

at their widest stops due to just their physical

structure, and adding a bit more with a shade is

generally not very important...

>In my experience checking for vignetting by looking through the

>viewfinder is much more difficult than seeing it on film. This would be

>even more the case if the lens were stopped down.

No - when well stopped down, the abrupt darkening of

the viewfinder corners caused by a vignetting shade

(or even lens structure) is quite evident with short

FL (for the format) lenses when viewing a bright

subject area... BTW, more awkward, but the technique

used for large format for checking coverage can also

be used with 35mm: with the lens stopped down to

minimum, look through the front of the lens for

the VF screen corner (this takes a light shining into

the VF and illuminating the corner of the VF to

work) - if the corner is visible from the front, there

is no sharp vignette; if not, there is...

>Also, the best check for vignetting should IMO be at infinity focus.

>When focussed close up, the image on film (or focussing screen) is only

>a central fraction of the normal image circle* and you are likely to be

>missing the obstruction.

>* A 35mm lens may serve as a decent macro lens for larger formats

In this you are (generally) quite correct - I must have

been asleep when I wrote the reverse (though this is not

always true - some lenses [mostly zooms...] show a wider

field of view at closest focus rather than at infinity

focus...).