Just got my first rolls of film back taken with my new used (mint)
Tamron 20-40, so I thought I'd share a few impressions and
semi-scientific observations.
Physically, the lens is a pleasure to use. Big and solid feeling, it
even damps the shutter noise further on my Elan 7 by virtue of it's
mass. It's now a satisfying muted business-like kersnick. (see I
told you this was going to be scientific!) One reviewer commented
that the zoom ring was too tight, and the focusing ring too loose. I
agree about the focusing ring, but like the zoom ring's feel.
Built-in flash is out of the question - the big lens leaves a shadow,
even without the lens hood on. No problem with my 420EX, though, even
at 20mm. It's a huge filter thread - 77mm - so I'm going to think
twice about getting lots of filters for it. The AF is audible, but it
is very quick. The sound doesn't bother me, especially in the kinds
of situations I will be using this lens in. I like the position of
the AF switch - at about 11 o' clock - it's easy to find without
looking, a natural position for my left index finger. The reverse
zoom ring direction doesn't bother me in the least. Tamron's lens
cap design deserves an award, with it's inner grip surfaces. This is
not trivial to me, and it's easy to use even with the big tulip-bladed
hood on.
My first rolls - mostly detail shots of some museum aircraft -
immediately got a "wow" out of me. *Very* nice and sharp.
Jump-out-at-you sharp. The lens gets a lot of sky in some shots -
gathers a LOT of light at its wide end - and I think I will need to
learn to compensate for that, a few shots were kind of washed out and
low contrast due to overexposure.
After using an f/4 lens for the last few months, I really noticed the
speed of this lens, (f/2.7) especially crawling around old aircraft on
a dark aircraft carrier hangar deck, even though I was using a flash.
It was like having breathing room again, and reminded me how much I
liked my old f/1.2 and f/2 FD lenses. I know speed isn't everything,
but it sure helps.
Now the interesting part to me is the nature and amount of distortion
at the wide end. I did a little experiment, comparing it with the kit
EF 28-90 I've been shooting with, and discovered some interesting
things. The experiment involved 8 shots taken off the fantail of an
aircraft carrier overlooking San Francisco Bay, with a mast in one
edge of the shot, and a distant staright horizon (SF) through the
middle. Of course any set of straight lines would have done. The 8
shots were: 28-90 @ 28mm, mast in L and R edge; 20-40 @ 28, 24 and 20
with mast in either edge.
The Canon 28-90 did not fare well in this department. The shots I
took with it at 28mm, showed nearly one millimeter of barrel
distortion at the center point, on a 4x6 print. That is, the mast
bowed out from the center of the photograph, and when I laid a
straight edge along it, touching at the top and bottom, the mast was
1mm away from the ruler at the center.
Now I don't have precise measuring equipment below 1/32 inch, so
there's some guesswork here, but the Tamron lens showed the following:
@28mm - about 1/3mm (1/64 inch?) *pincushion* distortion (bowed in
towards center) at the same point as above.
@24mm - same as above. No naked-eye perceptible increase.
@20mm - distortion *reverses direction* to very small - 1/3mm again -
*barrel* distortion.
I found this to be very intriguing, and wonder if it is characteristic
for ultra-wide lenses. I personally find pincushion to be less
disturbing than barrel, but the amounts here were very small, and not
disturbing at all. Obviously with enlargement it would be worse, but
still, the proportional amount is very good, I think.
Both lenses rendered a straight line across the middle well. Again,
this is very sloppy science, just eye and ruler.
I'm really very pleased with the lens so far, and look forward to
shooting slides with it to really get sharp, and find out how it
responds in different situations.
Anyway, hope this is of some interest to some, and if anyone wants
scans showing any of the above, feel free to write.
Cheers
Ken Durling
Website http://home.earthlink.net/~kdurling/
Alternate e-mail: [EMAIL PROTECTED]
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