Re: [APML]: Focusing a Takahashi Epsilon astrograph (was: New photos)

[Wil Milan <wmilan@airdigital.com>]

The Astro-Photography Mailing List
------------------------------------

Great idea, Ben. I have a dial micrometer I use for other things;
I may be able to adapt it for this as well, at least for trying
it out.

Thanks!

Wil M.


Ben Gomes-Casseres wrote:
> 
> The Astro-Photography Mailing List
> ------------------------------------
> 
> Wil,
> 
> I notice that Gene mentioned the benefit of calibration numbers on his
> helical focuser. I picked up a little calibration gizmo in Japan for my Tak
> refractor, which has an r&p focuser, as you know. It's a dial micrometer
> that you attach with a bar to the focusing lock and the measuring pin rests
> against the front ring of the focuser. It then shows any movement of the
> focuser. Though I use a magnifier (ground glass at film plane) or the B&K
> focuser, I focus several times in a row before shooting and check the dial
> each time. That way I am sure that my "final" focus is not an outlier; the
> true focus is where the measurements converge to. This worked well for me
> on the solar eclipse, when it was very tricky to focus on fuzzy sunspots
> and the boiling limb. Something like this might help as an addition to your
> already-great focus when seeing conditions are poor (which doesn't happen
> in AZ, I'm sure...).
> 
> Regards,
> 
> Ben
> 
> -----Original Message-----
> From:   Gene Horr [SMTP:genehorr@swbell.net]
> Sent:   Friday, July 10, 1998 10:16 AM
> To:     astro-photo@nightsky.com
> Subject:        Re: [APML]: Focusing a Takahashi Epsilon astrograph (was: New
> photos)
> 
> The Astro-Photography Mailing List
> ------------------------------------
> 
> Wil Milan wrote:
> 
> > I have the rack-and-pinion focuser, and yes it is a challenging
> > instrument to focus.
> 
> My hat is off to you!  I have the helical which has two
> advantages:  Calibration numbers on the side and an extremely
> fine thread (not quite 1000tpi, but it sure seems like it!)
> The biggest negative is having to spin the camera forever
> for minor focus adjustments.
> 
> I have the 6X magnifier and it is very helpful for rough
> focus.  Instead of a knife-edge I use the Tak FM-60.  This
> is an extremely handy device for just about any film camera.
> It consists of a focusing screen about the size of a microscope
> slide with a miniature microscope.  Once you get rough focus
> you open the camera back and lay the screen across the film
> plane.  You then use the microscope to examine the star
> image when fine focusing.  It works GREAT!  The street
> price is ~US$200.
> 
> > I've uploaded a larger version of the North American - Pelican
> > image. See
> 
> http://www.airdigital.com/NGC7000_and_Pelican_Nebula_Tak_E130_Pro100_30m
> _Sunglow_Jun98_larger.jpg
> 
> VERY NICE!!!  I like how you were able to get a black background
> while still keeping fine detail in the nebulae.
> 
> Gene Horr
> genehorr@swbell.net

-- 
Wil M.      
mailto:wmilan@airdigital.com
Astrophoto web site: http://www.airdigital.com/astrophoto.html
---
"When I consider your heavens, the work of your fingers, 
the moon and the stars which You have set in place, 
what is Man that you are mindful of him, 
or the son of Man that you care for him?"  -- Psalm 8