Re: [APML]: focusing

[rlecker@juno.com (Ric L Ecker)]

On the Olympus cameras the prime focus of the telescope is not the same
as the viewfinder.  The foresure method is the knife-edge because it
takes any guess work out of focusing.  Wearing glasses, my eyes will
correct focus problems very quickly, which my not be the correct focus
for the camera.  Its easy to get great focus using wide field scopes and
using the cameras viewfinder with a magnifier but with higher focal
lengths focus becomes a problem even with a magnifier.  Knife edge at the
focal plane of the scope eliminated mistakes that bad eyes or ronchi can
cause.  The Ronchi's work but the camera eliminates one device from
messing thing up.............

ric ecker co-pres. of OPTAS
OPTAS homepage and picture of Hale-Bopp
http://members.aol.com/rlecker/ric.html

On Thu, 07 Aug 1997 16:05:13 -0700 Steve Bell <sb635@delphi.com> writes:
>
>Philip Perkins wrote:
>> 
>> 
>> I have an ingrained nervous disposition :-) towards anything that 
>takes the
>> role of focusing away from the camera itself (caveat - this could 
>just be a
>> personal hang up).  
>
>Gosh, Phillip, we actually agree on something! <G> I too always prefer
>to focus using the device that holds the film, namely, the camera. And
>once done, I hate to remove it for any reason before I begin the shot.
>
>> IMHO the only thing that is calibrated and guaranteed
>> to focus accurately is the manufacturer's own screen installed in 
>the
>> manufacturer's own camera (providing the camera is a high quality 
>marque).
>
>I've been fortunate to have purcahsed a used Nikon F2 that apparently
>has it's screen focus correctly calibrated to it's film plane focus. I
>think this is one of the primary reasons why camera focusing gets
>whatever bad rap it does, ie, out-of-calibration cameras.
>
>> But if you find focusing in such a manner difficult you may want to 
>try
>> direct screen focusing via a x15 magnifier  (first golden rule of
>> astrophotography - throw away the pentaprism:-)  There are cameras 
>that
>> allow you to do this.
>>
>
>Are there others besides the Nikons? I know the OM1 doesn't have a
>removable pentaprism.
> 
>-- 
>Clear skies,
>Steve Bell
>email: sb635@delphi.com
>Astrophoto page: http://people.delphi.com/sb635
>