17 replies to this topic

[A Star Geezer]

This is a photo through the culmination cap. Any thoughts first time. The brown color is from my log walls

[Vic Menard]

Hard to tell. Try taking another image, but this time, place a white sheet of copy paper behind the secondary mirror against the inside of the tube wall opposite the focuser. That should make the bottom edge of the focuser and the actual edge of the secondary mirror easier to see. It's also helpful to include aperture, focal ratio, make and model, if possible.

 

I've attached an annotated view--all circles are concentric.

 

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[Keith Rivich]

BTW its "collimation", not "culmination". These words have different meanings but we know what you meant. I'll let Vic handle this but to me the collimation is more then close enough to produce a good image. 

[ChristianG]

This is the culmination of his collimation efforts! Looks good to me, BTW...

 

--Christian

[DeepSky Di]

Title changed. Hope this works for everyone.

[A Star Geezer]

Deep Sky thanks for the correction. Keith Thanks for the correction( but I did have most of the letters correct.) Vic here is another image of my collimation ( the white haired guy can learn ) attempt . Its a Apertura ad10 10 inch dobsonian focal length 1250mm which works out to F4.9. I'm using an Apertura collimation  cap with  the white paper.  

 

 

 

One looking down focuser no cap The red and 3 dots are cell phone case and cameras

Edited by A Star Geezer, 01 February 2025 - 03:02 PM.

[Vic Menard]

OK--here's what I see:

1.) The secondary mirror placement is slightly off--the green circle is optimal. I would leave it "as is".

2.) The secondary mirror tilt adjustment is also slightly off (blue cross hairs relative to the primary mirror center marker). If you don't have a laser or a sight tube with cross hairs, you should leave it "as is" (the allowable error (for high magnification performance) for a 10-inch aperture without coma correction is about 1/3-inch--your current error is about 1/2 the diameter of the primary mirror center marker which appears to be about 1/2-inch diameter, so you're inside the allowable error.

3.) Looking at your collimation cap alignment, your primary mirror tilt read error is probably less than 0.02-inch, and the allowable read error at f/4.9 is 0.05-inch.

 

So... your current alignment is "good enough" to use "as is", and considering you arrived at this alignment with a collimation cap, I have to say, "Nice work!" 

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Edited by Vic Menard, 01 February 2025 - 04:27 PM.

[A Star Geezer]

Vic 

I will leave it alone thank you for your critique of my collimation, did a lot of reading and lots of mental practice before attempting it. Just a few questions if you don't mind.

1: The secondary mirror placement is slightly off--the green circle is optimal. Would this be corrected by the center adjustment bolt on the secondary mirror, or the three bolts, and bring the circle down.

2:The secondary mirror tilt adjustment is also slightly off. Which bolts would correct this? 

3:Looking at your collimation cap alignment, your primary mirror tilt read error is probably less than 0.02-inch, and the allowable read error at f/4.9 is 0.05-inch. The primary mirror adjustment would bring the would bring the doughnut up and to the left to correct it, and center it.

  I'm asking these questions just for general knowledge and this is the kind of curious guy (my name is not George) I am thank you for all your help. Now if I can just have some clear sky. 

[A Star Geezer]

This might be a strange question but how do you keep finger prints off your scope. My black and shinny apertura shows finger prints very easy. will a light coat of car wax help our will the wax dust be a problem 

[Spile]

Vic 

I will leave it alone thank you for your critique of my collimation, did a lot of reading and lots of mental practice before attempting it. Just a few questions if you don't mind.

1: The secondary mirror placement is slightly off--the green circle is optimal. Would this be corrected by the center adjustment bolt on the secondary mirror, or the three bolts, and bring the circle down.

2:The secondary mirror tilt adjustment is also slightly off. Which bolts would correct this? 

3:Looking at your collimation cap alignment, your primary mirror tilt read error is probably less than 0.02-inch, and the allowable read error at f/4.9 is 0.05-inch. The primary mirror adjustment would bring the would bring the doughnut up and to the left to correct it, and center it.

  I'm asking these questions just for general knowledge and this is the kind of curious guy (my name is not George) I am thank you for all your help. Now if I can just have some clear sky. 

In both case 1 and 2, given the minimal tilt/rotation error I would ignore it. If it really bugs you, then you would only need to adjust the outer bolts to correct it (raising the secondary at 5 o’clock very slightly) but I would leave it alone.

[Bill Weir]

This might be a strange question but how do you keep finger prints off your scope. My black and shinny apertura shows finger prints very easy. will a light coat of car wax help our will the wax dust be a problem 

Do you mean the outside of the actual tube? If so then just get over it. The more fingerprints the more you love it. If you can’t deal with that then might I suggest stickers. Fingerprints don’t show. 90% of mine are fully astro related and most of those are swag from conventions and such. This scope now has even more than in the shown image.

 

Bill

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[A Star Geezer]

Spile  I plan to leave it alone I believe in leaving a sleeping dog sleep. 

Bill   Good point about more finger prints the more you love it. I do like the stickers adds character to it. I'm new to this so I might be asking some weird questions  

[Vic Menard]

1: The secondary mirror placement is slightly off--the green circle is optimal. Would this be corrected by the center adjustment bolt on the secondary mirror, or the three bolts, and bring the circle down.

2: The secondary mirror tilt adjustment is also slightly off. Which bolts would correct this? 

3:...The primary mirror adjustment would bring the doughnut up and to the left to correct it, and center it.

1.) It's hard to tell with the secondary mirror tilt error, but the error appears to be a small rotation error, which would require loosening the center mounting screw to allow rotation.

2.) The secondary mirror tilt error is corrected by adjusting the secondary mirror tilt adjustment screws (the 3 screws surrounding the center mounting screw).

 

Note that the error is corrected by centering the reflection of the primary mirror (or the primary mirror center marker) relative to the bottom edge of the focuser (or the bottom edge of a sight tube, or better yet, the sight tube's cross hairs). You should not be tempted to use the actual edge of the secondary mirror as the reference unless you're absolutely sure that the edge of the secondary mirror is correctly centered relative to the bottom edge of the focuser.

 

Your secondary mirror placement is close, but adjusting rotation and secondary mirror tilt may/will change the secondary mirror centering. This is expected, which explains why the process is iterative, and also why you should always end secondary mirror alignment by referencing the bottom edge of the focuser, (or, if you're using a simple thin beam laser, by aligning the outgoing laser beam to the primary mirror center marker).

 

3.) No. Adjusting the primary mirror tilt has no affect on the primary mirror center marker centering--adjusting the secondary mirror tilt centers the primary mirror center marker. Adjusting the primary mirror tilt centers the reflection of the underside of the focuser (seen inside the reflection of the secondary mirror) relative to the primary mirror center marker, which is essentially stationary while adjusting the primary mirror tilt

[A Star Geezer]

Thanks Vic you increased my knowledge of how things work. I guess one of the 2 rules I learned in the Marines as a radio repairman applies here " If it ain't broke don't fix it "

[gnowellsct]

This might be a strange question but how do you keep finger prints off your scope. My black and shinny apertura shows finger prints very easy. will a light coat of car wax help our will the wax dust be a problem 

I just handle the scope a lot from all sides and make sure my prints are all over.  Then I don't worry about it.  --Greg N

[Bucket-o-Light]

My Apertura AD8 came with the Apertura laser collimation tool, and it works great. That might be an upgrade to consider.

 

It makes collimation a snap. Just put it in the eyepiece socket, lower the focuser fully, adjust the secondary mirror so the laser beam hits the center dot on the primary mirror, then adjust the primary mirror collimation bolts until the laser hits the center of the bullseye on the tool. Takes less than five minutes usually for me, and I’m still a newbie myself.

 

Collimation is something you’ll be doing quite often on a reflector, so making it as easy on yourself as possible would be my advice. You can even collimate in the dark with the laser tool, which is convenient after having moved your scope to a dark site.

Edited by Bucket-o-Light, 06 February 2025 - 11:23 PM.

[RichA]

BTW its "collimation", not "culmination". These words have different meanings but we know what you meant. I'll let Vic handle this but to me the collimation is more then close enough to produce a good image. 

You mean the culmination of the collimation was successful?

[WISDOC]

 If there are no fingerprints you are not using it. Shame on you for neglecting my scope's brother! Finger prints on the scope are a sure sign of an active astronomical observer. Be proud of them.

  Clear skies and keep looking up. Doc