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What in the world are these three dark lanes!

Started by dan janosick, 02/15/2007 07:07PM
Posted 02/15/2007 07:07PM Opening Post
A few weeks ago I posted a thread about dark lanes every 120 degrees around bright stars on my new refractor. Many well referenced people told me they are the spacers , but I carefully checked and there in no sign of any spacers in the light path in any way.
I was then told that they might be piched optics by some others. The manufacturer told me the exact process and I backed each of the three screws out 1/8 turn. The resulting image showed no improvement.
I have attached an image taken through this scope with a dslr. Can anyone offer an explanation before I send this scope back for a full refund from the manufacturer.

Attached Image:

dan janosick's attachment for post 35798
Posted 02/16/2007 05:27AM | Edited 02/16/2007 05:30AM #1
Daniel - I think it is pinched optics as the others have said. Most of the WO scopes have a push pull cell design, but the coll. screws are on the SIDES of the cell, not on the front like most designs - so if the screws are too tight you would probably get this effect. To get to them, you have to unscrew the dew shield, and slid it off, or back (depending on model). There you will see the screws. Try backing off each just a SLIGHT bit. I did this with my 105 and it improved the image (although I never had what you see in your photo's - mine was just severly mis-aligned). My 110 TMB is right on and does not show any anomalies.
Posted 02/16/2007 08:31AM #2
It is very simple for you to find the source of these three spikes. If they originate in the objective plane, then simply point your telescope to a bright star (use Polaris since it won't move during the test). Place the star in the middle of the eyepiece field. Now remove the eyepiece and place your eye in its place. Look up toward the objective and you will see the lens filled with light from the star. It should be evenly illuminated all around. Any obstruction around the periphery(spacer, cement or other) will be instantly visible as a dark shadow. When you can see these shadows, try shining a flashlight into the objective from above and looking again from the focuser end to see if you can see the cause.

Judging from the even illumination of these shadows, i would guess that it comes from either the spacers or the pads on which the lens rests. It is not as likely that the lens is being pinched, but strange things can happen with optics.

Posted 02/22/2007 01:41PM #3
I took your image and labled the three effects that are shown (glow from turned edge, spacer shadows and diffraction from each of the 6 edges of spacers).


Attached Image:

RolandC's attachment for post 111835