Mirrors issue?

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flord.lord
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Mirrors issue?

#1

Post by flord.lord »

Hi,

Today I attempted to collimate my new telescope. The result can be seen in the photo.

The primary mirror is perfectly within the FOV (all the adjusting clips are visible, and the secondary and vanes are bang on in the middle of the primary..

However, this whole "reflection" is not centered ON the actual mirror. (The photo doesn't do it justice, it's not that bad).

Is this an issue?

Thanks.
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IMG_20200730_204859.jpg
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5.1" SkyWatcher Explorer 130M EQ-2
4" SkyWatcher Heritage 100P Mini Dob

Greater London - Bortle 8
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goldstar
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Re: Mirrors issue?

#2

Post by goldstar »

Looks like the secondary is too far up the tube and needs to be moved closer to the primary.
It may be missing some of the light cone otherwise.
Loosen the secondary central screw and wind in the three adjustment screws to bring it down further.
Scopes: 200mm f6 DOB:CR 6 150 mm f 7.5 refractor, SW ED 80 mm f 7.5. 2 X 80 mm f7.5 guides.
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flord.lord
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Re: Mirrors issue?

#3

Post by flord.lord »

goldstar wrote:
Thu Jul 30, 2020 9:20 pm
Looks like the secondary is too far up the tube and needs to be moved closer to the primary.
It may be missing some of the light cone otherwise.
Loosen the secondary central screw and wind in the three adjustment screws to bring it down further.
@goldstar Great, I see now. Is it a necessary fix though? I tested last night on the moon, which was nice and sharp, and Vega, which came to a point.

I just don't want to mess if I don't have to.
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4" SkyWatcher Heritage 100P Mini Dob

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SkyHiker
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Re: Mirrors issue?

#4

Post by SkyHiker »

... Henk. :D Telescopes: 6" Mak-Newt (Comet Hunter), ES ED127CF, ES ED80, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S, AVX, LXD55, Tiltall, Cameras: Fuji X-a1, Canon SX40, Xt, XSi, T6, ELPH 100HS, DIY: Dob and camera barndoor trackers, afocal adapter, Dob with foldable base and Az/Alt setting circles, Accessories: SSAG, Plossls, Barlows, Telrad, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK
flord.lord
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Re: Mirrors issue?

#5

Post by flord.lord »

SkyHiker wrote:
Fri Jul 31, 2020 12:06 pm
No it's normal, see https://www.catseyecollimation.com/pensack.pdf
@SkyHiker
Reassuring...but what about the fact that I can see the optical tube through the collimation cap...I have a feeling this isn't natural?
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OzEclipse
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Re: Mirrors issue?

#6

Post by OzEclipse »

If you can see the whole mirror, and more, from the centre of field, it means 100% illumination of the field at the centre. if there is an offset, you may get some asymmetric vignetting towards the field edge. If you're getting good results, use it for a while, look for vignetting and decide if you need to 'fix' it.
Amateur astronomer since 1978
Astronomical interests : astrophotography, visual observing, nightscape photography, solar eclipse chasing
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