On 10/7/2014 12:32 AM, Stanley Halpin wrote:
On Oct 6, 2014, at 10:38 PM, P.J. Alling <webstertwenty...@gmail.com> wrote:
On 10/6/2014 9:33 PM, Bruce Walker wrote:
On Mon, Oct 6, 2014 at 9:23 PM, Stanley Halpin
<s...@stans-photography.info> wrote:
On Oct 6, 2014, at 4:26 PM, Larry Colen <l...@red4est.com> wrote:
P.J. Alling wrote:
and wonder of wonders it's got some interesting information for free.
http://www.luminous-landscape.com/techniques/pentax_645z_astrophotography.shtml
Excellent link, though I'm afraid that if I were to spend $10K on a 645Z, I
wouldn't have any money left over for the $500 astro mount.
I was surprised to find that there don't seem any lenses faster than f/2.8
available for the 645. Doing some quick web search, there don't even seem to
be any manual focus lenses faster than f/2.8 available.
There are adapters that support the use of Hassleblad etc. on the 645. Maybe
you can find the faster glass you need by going that route?
I always assumed that there isn't faster glass because there doesn't
need to be. The DoF on medium format is already razor thin compared to
35mm and APS-C and perhaps a 1.4 on a 645z would create a serious
focusing problem? Or ridiculously OOF portraits?
In other words, we have what's practical to sell, as with other
formats. Or am I way off base?
Not just DOF, but an f2.0 135mm would be quite large and heavy if built to
cover the 645 format, yet it would be the equivalent of a Portrait lens say
85mm on 35mm, (75mm actually). Fast glass makes in any focal length on 645
need a tripod, whereas Pentax build a system to be equally good as a hand held
field camera, as well as at home on a tripod in a studio. Traditionally medium
format lenses have been fairly slow. There are exceptions, but they are
exceptions.
Bruce, not to disagree with your point at all, but FYI a 645 135mm lens on the
645z would have an effective field of view equivalent to a 110mm lens on a 35mm
film camera. The “crop factor” is 0.8. So taking (many of) the actual lenses
available, the 645z has:
X 645 lens => equivalent to Ymm focal length on 35mm
25 => 20mm
35 => 28mm
45 => 35mm
55 => 44mm
75 => 60mm
90 => 72mm
120 => 96mm
150 => 120mm
200 => 160mm
I think you were basing your comparison on actual 6x4.5 film vs. 35mm film.
One other point about lens speed: the importance of wide apertures has
seriously diminished (except for very specialized niche applications that call
for shallow DOF) - the ability to shoot clean shots at ISO6400 or 12800 really
makes “fast” lenses a relic of the good old days when we had a choice of either
Kodachrome as God intended it to be at ISO 25 or of that new Kodachrome 64 that
was a serious compromise in quality.
Though I must admit that I prefer a fast lens to a slower one for the simple
reason that I have a brighter image to focus and compose.
Stan
Well yes I am, basing it on film vs film. From the past the future is
determined. Most lens design in the past was based on existing lenses
being modified from other formats.
Just for example why was 135mm the most popular long lens for 35mm film
for such a long time? It's a funny focal length. Doesn't match any
particular rule that I ever heard. Well it was the "normal" focal
length for larger a film format. There were lots of good 135mm designs
to base the new Long Lens design on. So it became a defacto standard.
Faster short telephotos were designed, but the 135mm focal length was
now engrained in the photographers mindset, so they were designed in
135mm. n
So really why aren't there "fast" lenses for medium format? Well in
addition to DOF, there's size, cost, for lack of a better word, (not
that there isn't a better word, but I can't think of one). "tradition".
--
I don't want to achieve immortality through my work; I want to achieve
immortality through not dying.
-- Woody Allen
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