[pure-silver] Re: Repurposing Enlargers
- From: William Harting <wm.harting@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Mon, 12 Dec 2011 19:49:56 -0500
I used a screw mount nickel Elmar 50 as my enlarging lens for many
years and it was wicked sharp. Later I bought a camera to mount it on
and it was wicked sharp.
-bill
On Mon, Dec 12, 2011 at 7:04 PM, Gerald Koch <gerald.koch@xxxxxxx> wrote:
> Ctein's article mentions the problem of focusing the enlarging lens using
> white light and then looking are the plane of focus for blue light. IIRC,
> as given in the article this shift was several millimeters for sone lenses.
> This is in addition to any focus shift due to stopping down the lens.
> I still hold with the conventional idea that enlerging lenses do no make
> good camera lenses. This also works the other way around; camera lenses do
> not make good enlarging lenses.
>
> Jerry
> ________________________________
> From: Jean-David Beyer <jeandavid8@xxxxxxxxxxx>
> To: pure-silver@xxxxxxxxxxxxx
> Sent: Mon, December 12, 2011 6:36:39 PM
> Subject: [pure-silver] Re: Repurposing Enlargers
>
> Gerald Koch wrote:
>> Camera lenses have a curved field of focus.
>
> Surely not all of them.
>
>> So if your subject is in
>> the center of the image the edges of the image will not be in focus at
>> large apertures.
>
> This would be useful only if you could adjust the field curvature to
> suite the image in question and if the subject is at the center of the
> image to be made. There is no curvature that would be suitable for all
> images. You can isolate the background from the rest of the image if it
> is in a different plane from the center-of-interest by adjusting the
> aperture of the lens, even a flat field one.
>
>> This can be used to isolate the subject from the
>> background.
>>
>> Lenses for BW enlargement need not be designed to focus all colors on
>> the same plane. Ctein had an article on this focus shift somewhere on
>> the web.
>
> They tend to be designed to focus most wavelengths at the same point,
> though. It is not worth the money to design two series of lenses for
> enlarging: one for B&W and one for color. And if you use variable
> contrast paper, you need at least to have the green and the blue focus
> in the same plane.
>
> Focus shift is something else entirely. It has to do with the focus
> changing as a lens is stopped down.
>>
>> For LF use you may not see any problems due to the small amount of
>> enlargement.
>> Jerry
>
>
> --
> .~. Jean-David Beyer Registered Linux User 85642.
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