[pure-silver] Re: Chromatic Aberration of Enlarging Lenses
- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
- To: PureSilverNew <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 28 Apr 2006 01:34:37 +0200
I achieve the best focus by focusing with white light only. Then, I swing
the MC filters into the optical path for the exposure. Focusing with Y/M
light creates a focusing problem, due to the chromatic aberration of the
human eye, which gets worse towards red. Focusing with white light seems to
fix that. However, the use of a blue filter turned out to add no benefit to
the white-light focus in any of my tests.
With some people the chromatic aberration of their eyes is so bad that they
cannot focus on red light at all. If you have a red-LED alarm clock, try to
focus on the timing display and the surrounding area at the same time, it
might be difficult to do. This is worse in dim light, because your eye's
aperture is around f/2 in dim light. In bright light, it gets up to f/8 and
you get the benefit of depth of field.
Another example is a newer model-year VW's instrument panel (dash board).
The designers decided to use blue and red together in the displays. The two
colors are at the opposite extremes of the visual spectrum. Hard to focus on
both. IMHO, that's an ergonomic faux-pas by VW.
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
On 2006-04-28 02:10, "Steve Nicholls" <gl1500@xxxxxxxxxxxxxxxx> wrote:
> Tim Rudman wrote:
>>
>> My Peak focus finder has a blue filter for this reason. I was never
>> convinced that it made any visible difference. I know others who dismiss the
>> idea (in print) and some who swear by it.
>> Tim
>>
>>
> Just further to this thread -- i actually printed through the blue
> filter as well as focusing with it in the optical path. In my set up I
> now have the blue filter sitting on teh back element of the enlarging lens.
>
> :) the other possibility is my eyes are shot !! They aren't by the way.
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