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This needs collimation, right?

szymon

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Charic

Charic

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As Martin points out, your just s liitle off with the secondary. But keep at it. Once the secondary is sorted ( alligned and locked in place) you will rarely touch the secondary again !

pm your house telephone and I'll call you back now, if it wont disturb snyone sleeping, I'll talk you throgh the seconday! Fine if you dont want to send number.

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Martin Meredith

Martin Meredith

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I have to agree that secondary adjustment is a weak point with many/most scopes... The bolts tend to dig into the plate they make contact with and then make jerky movements. All I can say is to keep at it (and you will probably need to loosen them off slightly in pairs to allow for the movement in the direction you need).

In the longer term there is a useful mod you can find on AstronomyShed's youtube videos that will make the movement smoother.

Martin

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szymon

szymon

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Ok, sorry, she does mention it, she says:

"Now move the mirror up or down the tube using the central adjusting screw on the mirror holder until you have the secondary mirror centred."

I didn't get that the first, second, third or forty-fifth time I read it, so my fault :-P

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wookie1965

wookie1965

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The middle screw moves the primary in and out of the tube the three other screws effect the tilt these screws are the ones that send you crazy at first, right first thing you have to loosen two to tighten one and vice versa take your time it will come.

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Paul73

Paul73

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Just want to say a huge thanks to Charic who spent about an hour on the phone with me talking this through :-) -simon

What a star!

Could you post a picture of the final view to finish off the thread? That will make it a great "have a read of this one" thread for others who will get close, but not quite 100% there with Astro Baby's seminal article.

I thought that my collimating was pretty slick, but I learned some things from this one.

Paul

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Owmuchonomy

Owmuchonomy

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Ok, sorry, she does mention it, she says:

"Now move the mirror up or down the tube using the central adjusting screw on the mirror holder until you have the secondary mirror centred."

I didn't get that the first, second, third or forty-fifth time I read it, so my fault :-P

Aha!  The thing AB doesn't explicitly mention on the secondary is that the screw in the middle isn't for tightening the mirror, it's for longitudinal adjustment - moving it in and out!

....and for rotating it to enable the user to arrive at a circular, rather than elliptical reflection view, through the peep hole.

Off to pour a drink and try again ;-)

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szymon

szymon

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What a star!

Could you post a picture of the final view to finish off the thread? That will make it a great "have a read of this one" thread for others who will get close, but not quite 100% there with Astro Baby's seminal article.

I thought that my collimating was pretty slick, but I learned some things from this one.

Paul

I shall do...when I get it finished! I got it close last night, but it got very late...

Sent from my iPhone using Tapatalk

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greglloyd

greglloyd

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Good job szymon. Sounds like you a very nearly there. It's a great feeling once you get it all to click in place. It will become easier and faster to do every time. And remember, it's usually only the primary you will have to adjust most times in the future. Like riding a bike, it will become second nature. I have to perform a very quick and slight collimation almost every other observing session with the 12" F/5 because of the weight of the mirror (I have it sitting lose in the mirror cell to prevent pinched optics) and because it is a faster scope. The 8" F/6 rarely needs any adjustment at all.

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wookie1965

wookie1965

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Needs to be somewhere about where yellow line is that circle needs to be the same all the way round. You have the primary presenting a circle and the tilt is spot on the primary is easy to do once you have got this right, once done you wont have to touch your secondary again unless you drop or bang your scope.

post-20428-0-79089400-1410043537_thumb.j

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Charic

Charic

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Hows it going szymon...... 10:52pm image looks close enough, In the areas I've numbered 3, there seems to be a gap (marked in red) between the blackness of the focuser/cheshire tube, and the secondary mirror marked as 4,  but I can't see an equal gap at the 3a marks?  This could just be the lighting angle, but this may also indicate the secondary mirror is further down the tube, and you should withdraw slightly with clockwise turns of the centre screw. Try to avoid rotating the secondary mirror as discussed. But it does look very close to an offset mirror, in which case things are looking good! as per the AB guide. Its very close! Try the Laser-Barlow shadow alignment, then a Star test, defocusing to see the airy disk. A pinpoint of light from a Star (Polaris wont move in the sky, so will give you some time to focus) can be imaged as a series of concentric rings when de-focused through the telescope. If the rings are concentric, you may have it spot on. If the rings are non-concentric, a little more adjustment required maybe.
What else can we see in this image that may help others to understand the reflections?  (1) is the centre hole in the cheshire target faceplate, (2) is the surface of the target/angled faceplate on the Cheshire itself. (3)is the darkness of the focuser tube. Take the Cheshire out and you should see your own eye reflected in-place of 1 & 2. (4) is the secondary mirror and that greyness is the reflection of the primary mirror, showing the spider arms  at (5) as a blurred images of the arms. The areas marked 'T' (tube) shows the inside of whatever your looking through, ie 35mm cap, Cheshire, focuser tube? Some folk may have to click the image to enlarge it somewhat to see my edits on syzmons image.
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Moonshane

Moonshane

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it looks to me like your secondary needs to be moved up the tube, possible be rotated a very little and then adjusted with the three secondary bolts. the main points are :

ensure the secondary is round and central in the drawtube (sometimes this requires an adjustment to the spider vanes)

ensure the reflected primary donut is centralised on the (fuzzy in the photos) Cheshire crosshairs

ensure the eye hole on the Cheshire (the black dot) is centralised in the donut

check each point again after you do all three. if you do this you will be close enough to not matter.

clips are a red herring to some extent.

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Charic

Charic

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Moonshane......syzmon points out, the astro baby guide he's using, notes that some scopes require the secondary to be offset from the centre of the tube. And astro baby is setting up the same telescope. However, we agree,  it still looks like there is some correction required to centre the 'circle' of the secondary mirror under the focuser tube, by carefull adjustment, and rotation. There is an article here by Nils Carlin   http://www.skyandtelescope.com/astronomy-equipment/offsetting-your-secondary-mirror/      explaining what offsetting means if it helps  you syzmon, but you may get to the stage that your offsetting both the secondary and the primary in the last example. I would settle for exact centring of the secondary adjuster in the OTA.

There is no real hard-fast and accurate measure for collimating that I have found, and each person will  have their telescopes, collimated only to a standard that they can see and feel from the final result. Its an art, but pinpoint accuracy is hard to achieve, mainly down to minor discrepencies in the manufactured  tools, the telescopes build quality ie. sloppy focuser tubes, and finally what our own eyes/brain percieves as being  accurate. Get those starlight rings concentric, and thats the best you'll achieve from your telescope.

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