Re: Q FOR THE OPTICAL GENIUSES
- To: alt-photo-process-l@usask.ca
- Subject: Re: Q FOR THE OPTICAL GENIUSES
- From: Richard Knoppow <dickburk@ix.netcom.com>
- Date: Fri, 27 Apr 2007 14:10:41 -0700
- Comments: "alt-photo-process mailing list"
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----- Original Message -----
From: "BOB KISS" <bobkiss@caribsurf.com>
To: <alt-photo-process-l@usask.ca>
Sent: Friday, April 27, 2007 6:42 AM
Subject: Q FOR THE OPTICAL GENIUSES
DEAR LIST,
This is for those who REALLY know their optics.
I have a 210 mm Goertz gold dot Dagor and a 210 mm
Schneider Apo
lens. I want to do some EXTREME close up photos of dried
leaves, seeds, et
alia, on 8X10 to make contact PT/PD (see it IS on topic).
I know that both
of these lenses will cover the 8X10 format at this bellows
extension and I
am using this focal length to keep from having to stretch
my bellow as much
as I would with a longer focal length lens.
**********NOW MY QUESTION: Which of these two lenses would
give me better
results in terms of detail and contrast at this
magnification (between 5X
and 10X)?
CHEERS!
BOB
Please check my website: http://www.bobkiss.com/
Its guess work without testing, however, the Dagor is
completely symmetrical so it is optimum at equal subject and
film distance, i.e., unity magnification. If the Schneider
lens is an APO-Symmar, its optimised for infinity. The Dagor
will be similar to a process lens, that is, optimised for
around 5:1 to 1:5. The Gold Dot series of Dagors are coated
and have only four glass air surfaces so they have very low
flare. The Schneider lens has more surfaces but is probably
multi-coated.
Be careful of blur due to diffraction at small stops,
remember that the _effective_ stop at close distances is
smaller than at infinity. This affects diffraction blur as
well as exposure.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com