[AZ-Observing] Re: DLSR Focusing
- From: Chris Schur <comets133@xxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 4 Jul 2007 12:49:16 -0700 (PDT)
Jimmy, those 2.5x right angle viewers are not good
enough by a long shot. They will get you close but
you still will have half your photos out of focus
enogh to ruin an 8x10. I have the canon expesive one,
and while the optics are not in question, the low
magnification is. There are two ways around this.
One, is preffered by many accomplised astro imagers,
is to take a 1 second exposure of a nearby star field,
then zoom in on the back of the cameras LCD at full
magnification and examine it. Then take another. and
another. After about four or six shots youll have
absolutely perfect focus. Now thats the best way.
Heres an "almost" best way. Get a 6x30 finder scope
and refocus in the daytime to be able to see your
ground glass through the back of the camera sharply.
focus on the etched squares. Now at night you can be
more certain of a critical focus. Its hard to point
into a camera eyepiece but you MUST have at least 6 -
8x magnification to focus properly.
Third $$$$ option, buy maxim dslr, and get the control
cable from hap griffin cables. Then you can watch the
action on the big laptop screen.
I hope these suggestions help. Here is an example of
a dslr image I recently took using an 8x finder to
focus:
http://www.schursastrophotography.com/xtiastro/m7b.html
Good enough for you?
Chris
--- Jimmy Ray <jimmy_ray@xxxxxxx> wrote:
> I'm looking for the group's opinion on DLSR focusing
> when taking
> astrophotos. I find that when I have the camara body
> mounted in prime focus
> (Canon XTi to a 8" or 11" SCT) it is dificult to
> assess focus and to date
> the results haven't been "stellar". I was looking at
> the Canon magifying
> angle finder "C" which has 1.25x and 2.5x and runs
> about $180 delivered.
> Other options or tricks?
>
> Jimmy Ray
>
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>
>
Take Care,
Chris
Astro: http://www.schursastrophotography.com
Robotics: http://www.schursastrophotography.com/roboticsmain.html
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