Re: "normal" focal length of *ist-D?

[Joe Wilensky]

Actually, the first 50mm f/1.4 Super-Takumar, released with the 
Spotmatic in 1964, was Pentax's first 50mm lens. But for more than a 
decade after that, the fast 1.4 Takumars and K-mount SMC's were 50mm 
lenses, while the co-existing f/1.8 standard lenses were 55mm. This 
lasted into the K era until the M series lenses standardized both the 
f/1.7 and f/1.4 normal lenses at a 50mm focal length. I don't know 
why, though. I don't think it was easier to design the f/1.4 lenses 
at 50mm, since at least a few other SLR manufacturers (like Minolta) 
made their early fast lenses in the 58mm focal length.

Joe



Well, first off lets straigthen out a misconception here.

The screwmounts came with a 55mm because that gave a 1:1 (life 
size)image in the viewfinder. In those days that was a "feature". 
But it kind of turned out that folks kind of perferred having a 
normal "normal" lens which for 135 was a 50mm. So starting with the 
srewmount 50/1.4 SMC Takumar Pentax used 50mm for their normal lens. 
As far as I know no Pentax camera has a 1:1 viewfinder image with a 
50mm lens, they all show a smaller than life size image varying from 
slightly (ME Super)to a whole lot less than life size (ZX series).

Now the istD has a 95% viewfinder magnification that is the same as 
an MX. BUT, the screen size is only 2/3rds of that of a 135 film 
camera. So I would estimate that you would need about an 82mm lense 
to give a life size viewfinder image, so a 77/1.8 limited or 85 
ought to be close.

Anybody with the istD want to check that out. Simply mount the lens, 
look through the viewfinder then blink the other eye a few times. 
The image should not change size much with a lens that give a 1:1 
viewfinder image.

Though it beats me why it should matter.



Paul Ewins wrote:
There was a discussion in the last few weeks about "standard" lenses,
which came to the conclusion that the 55mm focal length matched the
magnification of the spotmatics and K series viewfinders, while the 50mm
focal length matched the M and later series cameras. Would someone who
has bought an *ist-D care to relate what the "standard" focal length is
for it? By matching I mean that what you see in the viewfinder is the
same magnification as the outside world, so that if you keep you're left
eye open while looking thorough the viewfinder with the right it all
looks the same. Just put a 28-70 on it and change the focal length till
it looks right! I would prefer to have a fast prime to a slow wide zoom,
so I would like to know whether to look for a 28/2, 31/1.8 or 35/2. I've
got a 24/2, but it will probably be just a little too big to keep on the
camera normally.  Thanks,
 Paul Ewins
Melbourne, Australia