Re: [APML] Nikon DW-4 help

["mstecker" <mstecker@dslextreme.com>]

Hello Emmanuele:

It is very difficult to get a good focus with the Nikon DW-4 unless you are
myopic with excellent close vision.  I only used mine to frame the object
and used a much higher power magnifier to focus on the stars (you also could
use a knife edge focuser).  Like all visual focusers used with cameras, you
must first focus the DW-4 on the camera's screen and not the object you are
photographing.  The ground glass spot in some of the Nikon screens works
best.  Do not try to focus on the Freznel, microprism or split image line.
I focus on the camera's screen in daylight with no lens or telescope on the
camera.  You can either mark or tape the DW-4 focuser to set the correct
camera/eye setting.  This should never be changed unless your eyesight,
camera or DW-4 device changes.  Then when doing your viewing the system will
be calibrated correctly and all you will have to do is focus with the knob
on your telescope.  Again the DW-4 will not give you a good focus unless you
have exceptional good vision.  It is far easier and more accurate if you use
a higher magnification or knife edge system.


Michael Stecker
mstecker@dslextreme.com

My Web Site:
http://www.homestead.com/mstecker/index.html (INDEX)
http://www.homestead.com/mstecker/astrogallery.html (Astroimage Index)
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----- Original Message -----
From: "Emmanuele Sordini" <vega@ulisse.it>
To: <astro-photo@seds.org>
Sent: Sunday, August 25, 2002 4:17 AM
Subject: [APML] Nikon DW-4 help


> Dear all,
> just back from vacation, I've got a question to pose to the whole list
> about correct focusing with the Nikon DW-4 magnifier.
> Some weeks ago I tried to use it for prime focus photography with a Nikon
> F3 (with red-dot, D-type focusing screen) and a 8" SCT: when framing, the
> field seemed correctly in-focus, but when I got my slides developed stars
> did have very cool donut-like shapes. So, here is how I proceeded.
>
> Since one can focus both by turning the DW-4 pipe and through the scope's
> focus knob, I thought the most correct way was to block the DW-4 and use
> only the scope's knob. The DW-4 body has a vertical white line on its
back,
> and its turning part has a small white dot which, I suppose, should be
> brought to perfect match in order for the focus on the film plane to be
OK.
> Here's what I noticed:
>
> 1) When the dot and the line were aligned by turning the magnifier's pipe
> clockwise, then by no means could I get the stars in the magnifier to look
> properly focused by turning the scope's focus knob.
> 2) When I turned the DW-4's pipe clockwise _all the way_ down, the star
> field looked as crisp as I could ever want, but the actual shots did not.
>
> What am I missing here? Could it be my fault (most likely) or perhaps a
> flaw with the DW-4? Any suggestions/links will be highly valued.
> Please note that the DW-4 (used) was bought some months ago in San
> Francisco by a friend of mine, so I guess I can't do much about it if it
> happens to be the DW-4. It is in overall good condition, except for
> slightly twisted hooks, which make attaching it to the camera not so
smooth
> an operation: however, once mounted, it stays firmly in its place.
>
> Thanks
> Emmanuele Sordini
>
>
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