RE: [William Optics] Re: WO reducer mark 3 and Megrez 90; problem with miss-shaped stars.
I have the same issue with my Megrez 90, still persisting with the WO M3
until funds allow the upgrade. I am not so troubled as I am using a ST8300
which is not a full sized chip
From: William-Optics@yahoogroups.com [mailto:William-Optics@yahoogroups.com]
On Behalf Of Mikael
Sent: 26 August 2012 14:08
Subject: [William Optics] Re: WO reducer mark 3 and Megrez 90; problem with
Hi and thanks for the answer! Astrophotography has been off-season here in
Sweden until now. I totally forgot about this post until a couple of days
ago when I had my astrophoto season premiere.
--- In William-Optics@yahoogroups.com, "inZet" <gsordiglioni@...> wrote:
> The correct distance is 56mm. This is easy on Nikon cameras 46mm
lens-to-chip distance, plus 10mm T-ring. On Canon, distance is 45mm so you
have to add a 1mm ring. If the correct distance is not set, you get diamond
stars at the edges of your image: but you get elonged stars in any case.
> With large sensors like those of modern DSLRs, field curvature at the
edges is a serious issue.
> The WO Type III corrects 80% of the field; the Televue TRF-2005 for 90%;
the Borg DG-L 0.85 #7887 you get a 100% corrected field.
> I own your same (amazing!) telescope and I bought the Borg. Never seen
round stars at the edges on user images taken with our telescope model and
the WO flatteners. With the Borg, they are perfect.
> --- In William-Optics@yahoogroups.com, "robert adamson" <j.r.adamson@>
> > Hi did anyone provide an answer to this query?
> > robert
> > From: William-Optics@yahoogroups.com
> > [mailto:William-Optics@yahoogroups.com]
> > On Behalf Of Mikael
> > Sent: 02 March 2012 15:42
> > To: William-Optics@yahoogroups.com
> > Subject: [William Optics] WO reducer mark 3 and Megrez 90; problem
> > with miss-shaped stars.
> > Hello. I have a Megrez 90 (621mm f/6.9) and a WO 0.8
> > reducer/flattener mark 3. I am having problems with miss-shaped
> > stars in the edge of my photos, see an example here.
> > <http://www.martenssonphoto.se/photo/m101_12.html>
> > I got the suggestion that I should try changing the distance between
> > the camera and the flattener. What is the appropriate distance
> > between the sensor and the flattener for my system?