Not really much slower. Remember, the 35-105 starts out at the same
speed as the 35-70/3.6 and doesn't go down to 4.5 until it gets to
105mm. So the question is, what is its speed at 70mm?
It can't be calculated directly from focal length and front element
diameter. The FE clear diameter of about 46mm corresponds with f2.3 @
105mm and f0.76 @ 35mm. Clearly, this isn't like a simple prime lens
like the 50/1.8, with ~28mm FE so 50/28 = 1.78, or f1.8.
f3.5-4.5 is just over 2/3 of a stop and 70 is half way between 35 and
105, so it is likely that 70mm is roughly 1/3 stop slower than 35mm.
Playing with a '105' and OM-4 with the lens resting on a light tablet
seems to show slightly more drop from 35-70mm than from 70-105mm. So,
given that the '105' starts fractionally faster than the '70', my guess
is that the '105' is 1/3 stop slower than the '70' at 70mm. Of course,
it is slower yet beyond 70mm, but that is bonus territory anyway, as the
'70' doesn't even go there.
All the above is only a measure of focal ratio, not light trasmission.
The '105' has 16 elements vs. the 10 in the 35-70, so theoretically it
should have lower light transmission. But the '105' is a later design
which may have more efficient coatings. Anyway, my examples of the 2
lenses show the same reading on the light tablet wide open at 35mm.
As to weight, I don't feel the difference is significant. Hefting the 2
there is very little difference. On my little kitchen scale, the '70' is
the advertised 400g, but the '105 is more like 455 than the 470g in the
eSIF. However, the '70 hood is bigger and heavier, so the difference
with hoods is more like 40-45g. Size is also a toss-up to me, with the
'105' a bit longer and the '70' a bit fatter.
Final technical factor: The 'zooming' hood design of the '70' is a
brilliant solution to hood coverage for a zoom.
Touchy feely: 1 or 2 touch doesn't make much difference to me,
especially if I'm using only one zoom for some time, I just seem to get
used to it quickly. I guess I sorta prefer 1-touch, but it's not much of
a factor.
Esthetic: I think the '105' looks better on an OM-4 or PC than the '70'
does.
Overall, for me, the extra reach of the '105' wins out.
How's that for way too much esoterica about a simple lens choice?
Moose
John Duggan wrote:
The 35/105 is 1 touch and slower..
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