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Black spikes on stars thru refractor

Started by chuck p , Feb 03 2007 11:16 AM
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19 replies to this topic

#1 chuck p

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Posted 03 February 2007 - 11:16 AM

Hi all,
I need help with the way my stars look. Here is a example.
I've had several people tell me that it is pinched optics or the spacers or baffles in the tube. It's taken with a Rebel XT and a WO FLT 110 f7. Any comments will be appreciated. Someone did send a pic and it looked just like my stars and he said it was pinched optics.
Chuck

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  • 1400848-black spikes.jpg

#2 LLEEGE

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Posted 03 February 2007 - 12:32 PM

Are the spikes in the same location as the cork spacers?

#3 chuck p

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Posted 03 February 2007 - 01:50 PM

I'd have to check it out next time I image. I rotated my focuser so I don't know what position they were in. I can see them so I will check next time. Thanks.

#4 anat

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Posted 03 February 2007 - 05:00 PM

Could it be due to the pinched optics?
http://www.aozc64.ds...collimation.htm

#5 Refractor6

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Posted 03 February 2007 - 05:20 PM

If it is indeed pinched optics Chuck in the book "Star Testing Astronomical Telescopes" refer to the top left image on page 149 on it's effect on the diffraction image at high power in a refractor. If this is what you see you indeed have pinched optics. I've seen this very pattern in a achro refractor and it's pretty obvious to identify and seperate from other possible issues.

If not then it is probably the 3 spacers causing artifacts which shows up as 3 indent type notches in the outer ring of a round slightly out of focus diffraction image at high power which shows 3 clean spikes on bright stars observed on lower powers.


----------------

Stan

Takahashi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6.45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP

#6 KaStern

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Posted 03 February 2007 - 05:36 PM

Hello Chuck,

I bet it is the spacers. You can investigate this by applying a mask that
is perfectly round and only masks about 3mm round the lens so that
there are no spacers in the light anymore. Take another picture if
there are spikes left.

Regards, Karsten

#7 Refractor6

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Posted 03 February 2007 - 06:12 PM

Chuck I was just reading on another astro forum and looking over someones image of the same type of artifact taken with there 132 mm refractor that looks very similar to your image/artifact posted here.

It appears the concensus there is the spacers are in the light path causing the black spikes.


-----------------

Stan

Takahashi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6.45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP

#8 DCS

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Posted 03 February 2007 - 06:33 PM

It appears the concensus there is the spacers are in the light path causing the black spikes.


Seems like you should be able to check for this by looking through the scope with no EP in place. If there is an obstruction you would then be able to see it directly.

-Pete

#9 tboss70

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Posted 03 February 2007 - 07:12 PM

Chuck,

On my NHNG Vic told me it wasnt "pinched optics". He gave me instructions on how to eliminate the problem. In my case for the NHNG i just had to very slightly loosen the collimation screws after the scope and set outside in the cold. This solved my problem however I would call WO for specific instructions on what the problem may be.

Im not sure what the technical details are for "pinched optics" but Vic said that wasnt the case on mine.

#10 jrcrilly

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Posted 03 February 2007 - 07:32 PM

Chuck,

On my NHNG Vic told me it wasnt "pinched optics". He gave me instructions on how to eliminate the problem. In my case for the NHNG i just had to very slightly loosen the collimation screws after the scope and set outside in the cold.


You may have misunderstood Vic. That's the classic example of correcting pinched optics. It would have no effect on any other problem.

#11 chuck p

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Posted 03 February 2007 - 07:47 PM

I do have an email into WO so I'll probably know something on Monday. It could also be the camera. I will try rotating the camera and try a mask if the sky ever clears.
Thanks All

#12 LLEEGE

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Posted 03 February 2007 - 07:58 PM

It's not the camera.

#13 tboss70

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Posted 03 February 2007 - 10:41 PM

John C, I did not misunderstand. See for yourself, from the MAN himself.
http://www.cloudynig...77/Main/1316589

#14 hub

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Posted 03 February 2007 - 11:54 PM

I had the same problem crop up with a Stellarvue 80/9D. It was indeed pinched optics. Vic ran me through the same cure that Todd mentioned. Worked like a charm.

John

#15 Refractor6

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Posted 04 February 2007 - 12:00 AM

I had the same problem crop up with a Stellarvue 80/9D. It was indeed pinched optics. Vic ran me through the same cure that Todd mentioned. Worked like a charm.

John


Like I say John a high power star test and study of the diffraction image will reveal all to understanding what it truly is and then take it from there.


------------------

Stan

Takahashi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6.45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP


-------------

#16 jrcrilly

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Posted 04 February 2007 - 01:45 AM

John C, I did not misunderstand. See for yourself, from the MAN himself.


Yup. You didn't misunderstand, he said it. Dunno why he would have said such a thing; I was presuming that he knew better. Sorry!

#17 chuck p

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Posted 04 February 2007 - 09:53 AM

I just looked down the tube again. I can see light where my focuser draw tube comes in and can see the adjusting screws which are placed at 120 degrees apart. The baffles don't come out far enough to block this. Can stray light be getting in and causing this.
Chuck

#18 lineman_16735

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Posted 04 February 2007 - 10:17 AM

I still think it is lens spacers. It is a classic case of spacers intruding into the light path. I have no such problem on my ZS 110. I wonder if the cold temps have in a sense pushed the spacers into the light path? Do you have a point source you can take an image of indoors under more moderate temps?

#19 spaceydee

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Posted 04 February 2007 - 01:42 PM

I would contact William Optics on it since it is their scope. If you look at the stellar images inside and outside of focus what do you see? I'm troubleshooting something similar on one of my scopes (not necessarily the same thing) and the current theory on it is pinched optics. I have spikes on one side of focus and indentations on the other. I would contact WO for help if it bothers you.

#20 glassman

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Posted 04 February 2007 - 10:47 PM

I have just exactly this issue in my orion 100mm ED. It's the spacers which stick out into the clear aperture just a fraction of a millimeter. Solution would be (as previously suggested) a perfectly circular mask - diffraction is a swine ain't it!

Of course many of our friends in the newtonian club believe that curving the spider vanes cheats physics and eliminates diffraction. :roflmao:
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