Re: [APML] Red filters and the need to focus

[Brian larmay <power_windows4789@yahoo.com>]

Hi Bill,
I was going to wait for more replies, but I think ill
step in regarding the calibration process and what I
have done so far.

Ive calibrated the 105mm already for H-a work using
the 2 hole mask.
This is the only lens in question.
Would that calibration already be enough for this #23?
filter?
Do I even need to worry about calibration since its
not an H-a filter?

Ok.. maybe im just lacking some sort of understanding
as far as the differance between H-a and non H-a

So ok....Ive calibrated that lens..is that where I
should use it at with any type of filter in the red
spectrum?

Pardon my lack of understanding.

One more clear night and a moon thats at 97.1% ... I
might just go for it since my clear nights are rare
and have some results tonight of the Orion complex.
I think I might really be pushing my chances, but
hey.. why not eh' it will be warmer tonight in the mid
teens<g>.

Brian


> Brian larmay wrote:
> > 
> > Does anyone know whether I need to calibrate my
> lens
> > for a deep red filter that is not H-a?
> > 
> > Im guessing mine is a #23 since there are no #'s
> on it
> > besides R-2.
> > Customer support is auomated and offers no help.
> > 
> > When does one ned to calibrate, and when does one
> not
> > need to calibrate?
> 
> Brian,
> 
> I just ran a series of tests using an #82A filter to
> focus through and
> then I substituted an Ha filter before starting the
> exposure. This was
> at prime focus so that may have made it more
> critical ? or less so
> depending on who you talk to :^) this was on an f/4
> optical tube that is
> nortorious for being picky in this regard. But
> actually determining the
> exact point of focus with a camera lens is pretty
> easy using a label and
> a two hole mask and then doing a series of shots to
> determine where the
> best focus really is. John Mirtle has some
> information on this on his
> web site IIRC.
> 
> But I think the real answer to your question is ...
> yes. It will make a
> difference.
> 
> 
> Regards
> 
> Bill
> 
> 
> -- 
> William R. Mattil	|                              
> wrmattil@ix.netcom.com	| http://celestial-images.com
>      
> (972) 399-4106		|
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