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To all,
Based on a special area using the Meteor Capture
Calculator by Ulrich Beinert and Roger Sinott ( http://members.aol.com/ubeinert ) I
have come up with the following efficiencies for the Pentax 67:
f/2.4
f/2.8 f/4.0
f/5.6
Areal Coverage (square degrees)
45
mm
64.5
32.9 6250
55
mm 52.8
26.9 4185
75
mm 78.9
38.7
2250
105 mm
76.7 56.3
27.6
1146
165
mm 35.7
17.5
463
It appears the 75 mm f/2.8 just squeezes by the 105
mm f/2.4. Goes to show how important the f-stop is in capturing
meteors. However, as noted by the 45 mm f/4.0, areal coverage is very
important too. The 75 mm f/2.8 is a new aspherical lens. I'm
not sure how it performs astronomically speaking, but I'll be testing it during
the meteor shower assuming clear skies. Has anyone tried this new
lens? If so, how is its performance (i.e., what's the most efficient
f-stop)?
I'm not so sure how well the 105 mm f/2.4 lens
will perform wide open. I would suspect not very well, but I used it
last year at f/4.0 with Comet Ikeya-Zhang and saw no noticeable
degradation. At the very least, it might be worth stopping down to
f/2.8. I'll likely be using the 75 mm f/2.8 wide open just to see how well
the aberrations have been corrected with an aspherical lens. However, just
to be on the safe side I'll shoot some at f/4.0. The 45 mm f/4.0 wide open
does have some nasty aberrations near the edge, but probably acceptable if
cropped out; otherwise, I would recommend shooting at f/5.6. Wide open,
the 55 mm f/4.0 has some aberrations at the corners but not near as bad as
the 45 mm f/4.0. All my shots will be guided from a very dark
location.
I hope this helps in some of your decision making
over the next week.
...Wade...
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