Star test, Arcturus, Celestron NexStar 5SE XLT

A simple Star Test is done by focusing and defocusing a bright star in both directions: IN focus & OUT focus. This way you may check your telescope optics as well as collimation. Concentric rings should be obtained when focusing and defocusing on perfect lenses and mirrors.

This video is a star test of a very bright star, Arcturus at around a magnification of 200x. A 6 mm eyepiece on a 1250mm focal length telescope yields that power.

The telescope used here is a 125mm telescope, a Celestron NexStar 5SE XLT and the camera for recording was a Canon EOS 450d (Rebel XSi) DSLR.

The focuser is moved back and forth during the recording of this video.

This video is not about Ufo Sightings nor Nasa Imagery, nor Nibiru, Aliens, etc. It is just a visual aid to check optics quality and collimation on a telescope.

Star test, Optics, Collimation, in focus, out focus, focusing, Telescope, Celestron NexStar 5SE XLT, Astronomy, Astrophotography, Astrophoto, Backyard, 2011, Canon EOS 450d, Rebel XSi, video, DSLR, Live video, Reflector, Refractor, SCT

Category:

Science & Technology

Tags:

• Star test
• Optics
• Collimation
• in focus
• out focus
• focusing
• Telescope
• Celestron NexStar 5SE XLT
• Astronomy
• Astrophotography
• Astrophoto
• Backyard
• 2011
• Canon EOS 450d
• Rebel XSi
• video
• DSLR
• Live video
• Reflector
• Refractor
• SCT

[ahlberto]

The scope is astigmatic and is very descolimated

[CumputerPhysiscsLab]

@ahlberto How could you see that?

[krisDM3000]

Looking good! But the NexStar has a tracking mount right? When you don't have a tracking mount it's easier to do that test on Polaris.

[CumputerPhysiscsLab]

@krisDM3000 Yes, it has a mount. Thanks!

[J122BO55]

@CumputerPhysiscsLab how much would i have to pay for an telescope like this one?

[CumputerPhysiscsLab]

@J122BO55 Celestron C5 costs around 500 US$

[pseudorandomly]

Regarding the astigmatism discussion here: jkt8012 is correct; astigmatism manifests itself as a 90 degree flip, not a 180 degree flip. The central hole does appear slightly oval, but you have to be careful about judging that from a processed video image; software might have stretched the image to conform to a particular aspect ratio. I'd tweak the collimation more precisely before trying to judge that, so it's easy to tell if the bright rings are oval by the same amount as the dark hole.

[mateuszlee]

aren't they a bit of egg shape ?

[ahlberto]

@jkt8012 No,youre wrong.The image flips 180º (not 90º...) as you can see in the video.Its a bad C5 sample and the optics are faulty and completely astigmatic.Its a pitty but the SCTs are usualy very good.

[jkt8012]

ahlberto is not correct about the astigmatism. Although the pattern is oval it does not flip 90 degrees on either side of focus which is the characteristic of astigmatism. This oval pattern could be due to unequal air density in the tube. However , he is correct about the scope needing collimation. The shadow of the secondary is not centered. .

[buija1]

super

[ahlberto]

@CumputerPhysiscsLab Hi.The descolimation is obvious and the oval shape of the dougnout denounces a optic with astigmatism