[rollei_list] Re: Tell the tales of Triotars
- From: Georges Giralt <georges.giralt@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sun, 05 May 2013 18:56:17 +0200
Le 05/05/2013 18:41, Richard Knoppow a écrit :
----- Original Message ----- From: "Sanders McNew" <sanders@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Sunday, May 05, 2013 12:26 AM
Subject: [rollei_list] Tell the tales of Triotars
Apart from the obvious difference in aperture, can anyone speak to the
differences (if any) between the f/3.8 and f/4.5 Triotars? Does anyone
think they can see any discernible differences in how they render
images? The difference in speed seems slight -- why did F+H offer
both lenses? Is there any advantage to one over the other?
Sanders McNew
The answer may lie in the cost of the lenses. I suspect the f/3.8
was offered because it was closer to the f/3.5 lens on the Rolleiflex
but the Flex originally came with a slower lens. Another possibility
is the size of the shutter, the slower lens will fit a smaller
shutter. Kodak made the 127mm Ektar as an f/4.7 lens because the iris
in the shutter they used would not open wide enough for f/4.5 and did
the same thing with an f/3.8 Ektar for press cameras which is
essentially the same as the f/3.5 lens in the Medalist camera only
slightly longer in focal length and in a standard shutter.
Both Tessars and Triplets are best as slower lenses, perhaps
around f/6.3. At larger apertures they begin to lose sharpness at the
margins of the image. The f/3.5 and f/4.5 lenses are at their best for
overall sharpness when stopped down to around f/11.
You may know that the Triplet is the simplest lens that can be
corrected for all seven primary aberrations. They were difficult
lenses to design pre-computer because any change in any parameter
affects everything else. They also are very sensitive to element
spacing so require precision mounting.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
Hello !
Something puzzle me. I own an Agfa Isolette II which is fitted with a 85
mm F:4.5 Apotar lens. It is a 3 lenses lens design and use front
focusing (i.e; the front element unscrew for the focusing). This said,
it is a very good lens and has plenty of contrast and detail (to my
surprise).
As this lens dates as back as the early '60s I wonder what is different
from the Triotar lenses ?
Thank you to enlightening me ;-)
--
If the only tool you have is a hammer, you tend to see every problem as a nail.
Abraham Maslow
A British variant :
Any tool can serve as a hammer but a screwdriver makes the best chisel.
---
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