[APML]: APML: Wind and seeing

["Martin C Germano" <mgermano@gte.net>]

Wil,

>> Bob Fera wrote:
>> 
> > I, like many other astrophotographers, am of the opinion that you can't
>>have too much mount -- my C-11 sits on a AP 1200. Given that, I'd
>>definitely recommend the 900 over the 600. I previously owned a G-11 and
>>felt that it was inadequate for shooting with a C-11 (fine for visual,
>>though). The slightest amount of wind was enough to give it  and the
>>autoguider fits.
> 
> I don't shoot when gale-force winds are blowing :-), but under more
normal conditions I've experienced no such problems with a C11 on a G-11
mount.
> 
> I *have* had the experience of high winds playing havoc with guiding even
though the winds were *not* blowing on the mount. In that case the
guide-star jitters were due to the wind howling over the hill behind me
(the "hill" was actually the top of a mountain ridge; I was located just
below the top). The extreme turbulence caused by the wind cresting over the
peak
> above caused jittery guide stars and erratic guiding, looking very much
like mount vibration, but in fact the mount was in still air. (That was an
AP mount with an smaller scope, but it wouldn't have mattered if it was
Palomar 200" mount; the motion was due to the air moving, not the mount.)
> 
> As a practical matter I've found that when strong winds are blowing the
seeing will be so poor that it's not worth bothering with narrow-angle
photography. Even when wind on the mount is not a factor (as above), the
star images will balloon to the point that the photo will never be
outstanding.
> 
> Wil M.

Bob Fera was just voicing a fact of life for Mt Pinos, where it can be
windy AND have *good* seeing. As a long time (1976) photographer from the
Mt Pinos (California) parking lot, I have quite often experienced good
seeing and high (est 15-30mph) winds. At nearby Pine Mt (due south across
the Lockwood Valley, known for its terrible seeing) some of the best seeing
I have ever experienced occurred with the wind howling 50 feet over my back
at the ridgetop.

Conversely, at another mountaintop ridge I frequent (Figueroa Mt), the
seeing is most often fair to poor when the wind blows. I guess the real
reason we like to "over-mount" our tube assemblies is for stability when
the wind strikes our unshielded telescopes, as is unfortunately a way of
life in our Southern California mountains. *Bad* seeing will cause problems
whether the wind is blowing or not. I guess we just have to take what we
get out in the field, as my experience with wind verses seeing is a mixed
bag in the Southern California area.

Martin C Germano
Thousand Oaks, Calif
mgermano@gte.net