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Evaluating the New William Optics FLT 132mm

Started by dan janosick, 02/03/2007 05:18AM
Posted 02/03/2007 05:18AM Opening Post
I was finally able to set up the WO flt-132mm the other night for a couple of quick snapshots. I took a 3 second shot of Aldebaran on a modified dslr. I cropped the star image so we could see it clearly. I am wondering what is causing the dark lanes at 120 degree angles? Is the normal, I checked optical aberations on the net and I do not beleive it is pinched optics? But would love this group to offer insights.

Daniel Janosick

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dan janosick's attachment for post 35623
Posted 02/03/2007 05:19AM #1
I also shot the near full moon.

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dan janosick's attachment for post 111315
Posted 02/03/2007 07:11AM #2
This is an air spaced lens, yes? When you look through the front of the lens can you see three little spacers at 120 degrees? That could easily cause what you saw. If so, nothing at all to worry about.

- Jared
Posted 02/03/2007 08:43AM #3
>>I am wondering what is causing the dark lanes at 120 degree angles?>>

The lens spacers are in the optical path.

Posted 02/03/2007 01:19PM | Edited 02/03/2007 01:20PM #4
Yes those are the lens spacers. But perhaps a bigger question
is why there is so much light out there to make a dark spike.
I might suspect the lens has some turn-edge or roll-off right
at the edge.

If you can make two more images of a star like that.
But set 5mm inside best focus, and another image 5mm outside
best focus, it would be very instructive. Some of us over
have been doing this Roddier test on our telescopes.
You would probably need a tracking mount (drive) to do it --
maybe you are using one already.

Another approach would be to somehow mask off the outer
2mm of the lens, and see if the spikes go away, and whether
images suddenly seem much sharper. Maybe get a cardboard
and cut a 125mm hole in the middle.