defocused antares in scorpius has double diffraction rings

chris shaw · Post by **chris shaw** » Thu Aug 12, 2004 2:44 pm

Dear all

Maybe you can help: Last night while viewing an out-of-focus Antares at about 300X, I noticed that embedded WITHIN Antare's diffraction rings is another dimmer, smaller airy disk with it's own diffraction rings. It was almost like having a smaller ripple within a larger ripple in a pond.

Is this Antare's companion star? If so, why can't I resolve it in-focus but am able to resolve it out-of-focus? If this is true, then I can use this defocused method to 'spot' faint companion stars which would otherwise be invisible in focus!

Anybody experienced this before? I hope its nothing wrong with my optics to cause me to see another smaller airy disk diffraction rings embedded within Antare's larger, brighter diffraction rings.

Hope this makes sense.

Chris

ChaosKnight · Post by **ChaosKnight** » Fri Aug 13, 2004 9:07 am

http://www2.odn.ne.jp/~ccr61210/www2.od ... tar99.html

Post by **weixing** » Fri Aug 13, 2004 10:31 am

Hi,

Last night while viewing an out-of-focus Antares at about 300X, I noticed that embedded WITHIN Antare's diffraction rings is another dimmer, smaller airy disk with it's own diffraction rings. It was almost like having a smaller ripple within a larger ripple in a pond.

I don't think what you see is the Antares's companion star. May be you should try the same star test on other bright star to see whether it give you the same pattern.

Have a nice day.

chris shaw · Post by **chris shaw** » Fri Aug 13, 2004 10:42 am

Dear YW

That's what Dr Clay Sherrod thinks. He suspects my new Maksutov from Meade may have resonant diffraction problems - caused by what, I don't know. I don't think its bad collimation, do you? I have tried this OUT-OF-FOCUS technique (for star test) on other stars and I have never seen this before!

I received another email from Joe Shuster of the LX200 webgroup and it says:

Antares has a relatively dim companion that's a real challenge primarily due to the contrast in brightness. I suspect that the dilution of defocusing takes the "dazzle" out of Antares. People who give advice on collimation always advise against using double stars just for just this reason. (Many folks forget that stars like Antares and Polaris are double and then struggle with collimation.)

Maybe the fact that you can see the dual diffraction pattern is a better demonstration of optical quality than viewing a single star. Or maybe it's a good demonstration of seeing stability. With poor optics and/or poor seeing, you wouldn't be able to view such things. Maybe we should identify a series of relatively close, high-contrast doubles and compare optics/conditions to find out if "diffracted doubles" could be a valuable optic/condition measuring technique. (It should be relatively easy to take digital images of the view.)

What do you think? Has anyone looked at Antares defocused before?

Chris

Post by **weixing** » Fri Aug 13, 2004 11:25 am

Hi,
I have look at Antares defocus pattern before and it seem normal to me. Anyway, I think my newtonian do show a similar defocus pattern when I do a star test, but I can't remember whether it is inside focus or outside focus... my inside focus or outside focus is not the same

By the way, I think this may be cause by lower spherical aberrations. I'll check on the Antares and my star test on other star when the sky is clear.

Have a nice day.

chris shaw · Post by **chris shaw** » Fri Aug 13, 2004 11:34 am

Do you mean you also see a smaller diffraction pattern INSIDE the larger Antares diffraction pattern with your Newtonian??

Chris

Post by **weixing** » Fri Aug 13, 2004 11:47 am

Hi,
If I remember correctly, one of my defocus pattern do have a smaller diffraction pattern in a larger diffraction pattern on any star, not just Antares. I'll draw the pattern down next time I do a star test and check out what is the aberrations... I think it should be lower spherical aberrations.

Anyway, does the smaller diffraction pattern at the centre of the larger diffraction pattern??

Have a nice day.

chris shaw · Post by **chris shaw** » Fri Aug 13, 2004 12:21 pm

I will attach it to my gallery for your viewing. It says 'No Thumbnail' but if you click on the picture you can see it. What is lower spherical aberration and must I return my Maksutov to the manufacturer?

Chris

Post by **weixing** » Fri Aug 13, 2004 12:43 pm

Hi,
Base on your image, that doesn't look like any of the aberrations I had seen before. I think it is highly possible that the smaller diffraction pattern is the Antares's companion. The seeing must be super good in order to have that type of diffraction pattern. I must try that next time on good seeing night.

Anyway, if seeing is that good, you shouldn't have any problem seeing the Antares's companion when focus. Unlike my newtonian, which the diffraction spikes of my secondary spider on Antares will cause problem when I try to see it companion... Since your MCT don't have secondary spider, you shouldn't have this problem. May be you should try to move the Antares just outside the FOV and check whether can see the companion or not (I haven't try this method myself yet, but I think it should work).

Have a nice day.

chris shaw · Post by **chris shaw** » Fri Aug 13, 2004 12:47 pm

Antares' companion was washed out by the primary star's brightness so I couldn't see it. I will try to move it outside FOV. My observation is near Newton area and the seeing was not that good. However, Antares was close to overhead and it was a relatively clear night for the city center.

Chris