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Secondary adjustment needed?

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#1 Blueox4

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Posted 04 August 2020 - 11:24 AM

This view is my secondary through a Catseye Teletube set at f/4 with the focuser racked out a bit. The primary mirror cover is in place. If I rack the focuser all the way in The view seems to clip off some of the top of the image of the secondary. Do I need to make any adjustment? It looks to me like the secondary has to go down a bit towards the primary but I want to ask if that is correct before I adjust it? 

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#2 KBHornblower

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Posted 04 August 2020 - 12:38 PM

This view is my secondary through a Catseye Teletube set at f/4 with the focuser racked out a bit. The primary mirror cover is in place. If I rack the focuser all the way in The view seems to clip off some of the top of the image of the secondary. Do I need to make any adjustment? It looks to me like the secondary has to go down a bit towards the primary but I want to ask if that is correct before I adjust it? 

I would not change that adjustment.  When you have the peephole at the focal point the secondary will appear to be a bit too far from the primary because of a perspective effect.  When you rack out to the apex, where the secondary and the reflection of the primary appear to have the same diameter, the secondary will appear centered if everything is right.  Your first step here needs to be tilt adjustments to put the center of the primary on the crosshairs.  Try that, post a photo, and we can take it from there.



#3 Vic Menard

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Posted 04 August 2020 - 02:53 PM

This view is my secondary through a Catseye Teletube set at f/4 with the focuser racked out a bit. The primary mirror cover is in place. If I rack the focuser all the way in The view seems to clip off some of the top of the image of the secondary. Do I need to make any adjustment?

I can't tell. It will be more obvious if you put a white piece of paper behind the secondary mirror (opposite the focuser against the inside of the tube wall). You also may need to shorten your Teletube another half inch or so. When you post the next picture, remove the primary mirror cover so I can see the primary mirror center marker.


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#4 Blueox4

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Posted 16 August 2020 - 05:57 PM

Here’s a couple pics. I’m at the stage I’m trying to use my CATSEYE Autocollimator. Any critique on how this looks is appreciated. I had to lower my secondary mirror a bit as it was not initially centered in the sight tube. Does the secondary and primary appear to be aligned correctly? 

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#5 SteveG

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Posted 16 August 2020 - 06:27 PM

Here’s a couple pics. I’m at the stage I’m trying to use my CATSEYE Autocollimator. Any critique on how this looks is appreciated. I had to lower my secondary mirror a bit as it was not initially centered in the sight tube. Does the secondary and primary appear to be aligned correctly? 

At f4, I would expect the secondary silhouette to be offset further to the right. See what Vic says.

 

I need to order that clip on light!



#6 Vic Menard

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Posted 16 August 2020 - 07:28 PM

...Any critique on how this looks is appreciated...

Better (but you forgot the white paper).

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#7 Blueox4

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Posted 16 August 2020 - 07:42 PM

I’ll post a better pic with the white paper tomorrow Vic. Appreciate the insight as I learn how to collimate this. 



#8 Blueox4

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Posted 17 August 2020 - 03:18 PM

The first two taken with the Telecat sight tube set to f/4 length but pulled out a bit of the focuser. The last one with the Telecat all the way in the focuser set to f/4... with the white paper this time:)

 

I’m hoping this looks good so far?

 

I am learning how to use the Autocollimator. I put it in the focuser with no set screws and if I touch it the reflections move. I’ll just put it in one way and be consistent in how. I want to be able to collimate to the best I can using a Paracorr at f/4 probably doesn’t leave much wiggle room for best views. 

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#9 Vic Menard

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Posted 17 August 2020 - 04:44 PM

I'm having some difficulty matching the HotSpot to the primary mirror edge. Is it possible that the HotSpot is slightly off center?

 

 

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#10 Vic Menard

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Posted 17 August 2020 - 04:45 PM

TeleCat (secondary mirror alignment) is pretty close.

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Edited by Vic Menard, 17 August 2020 - 04:45 PM.


#11 Vic Menard

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Posted 17 August 2020 - 04:58 PM

If you leave your secondary mirror "as is", this looks like your "best fit" after primary mirror alignment:

 

 

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#12 Blueox4

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Posted 18 August 2020 - 12:12 PM

I'm having some difficulty matching the HotSpot to the primary mirror edge. Is it possible that the HotSpot is slightly off center?

Well, that’s a bit concerning. This was spotted by the mirror maker. I have a thread saved on how to use a camera to determine the center. I guess I’ll have to do that to confirm it’s spotted correctly. 
 

Vic,

 

  Can I post a picture of the mirror out of the Mirror Box On a white background and could you Please use whatever software you’re using to Outline it as above and see if it’s centered? It looks like it’s off quite a bit in the photo. That’s concerning and I’d like to confirm that. 



#13 Vic Menard

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Posted 18 August 2020 - 01:45 PM

Well, that’s a bit concerning. This was spotted by the mirror maker. I have a thread saved on how to use a camera to determine the center. I guess I’ll have to do that to confirm it’s spotted correctly. 
 

Vic,

 

  Can I post a picture of the mirror out of the Mirror Box On a white background and could you Please use whatever software you’re using to Outline it as above and see if it’s centered? It looks like it’s off quite a bit in the photo. That’s concerning and I’d like to confirm that. 

The more I look at your images, the more I think there is some kind of baffle either in front of the primary (in the mirror box) or in the upper tube assembly. I don't think I'm seeing the whole reflected edge of the primary...

 

So, before you pull the primary mirror out of the mirror box, maybe some pictures of the mirror box and the upper tube assembly would be useful, along with some measurements of the clear apertures (primary mirror, mirror box, and UTA).


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#14 Blueox4

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Posted 18 August 2020 - 02:21 PM

The more I look at your images, the more I think there is some kind of baffle either in front of the primary (in the mirror box) or in the upper tube assembly. I don't think I'm seeing the whole reflected edge of the primary...

 

So, before you pull the primary mirror out of the mirror box, maybe some pictures of the mirror box and the upper tube assembly would be useful, along with some measurements of the clear apertures (primary mirror, mirror box, and UTA).

It’s a 16” mirror. Aperture of the mirror box opening is 16-7/8”. Aperture of the UTA is 17-1/4” 

 

here’s a few pics. 

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#15 SteveG

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Posted 18 August 2020 - 02:31 PM

Note in post #9 you can’t see the secondary vane holders that are seen in the top two pictures of the mirror box.



#16 Vic Menard

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Posted 18 August 2020 - 03:28 PM

Hmm... you may need to measure it.

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Edited by Vic Menard, 18 August 2020 - 03:29 PM.


#17 Vic Menard

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Posted 18 August 2020 - 03:33 PM

If you have a good 12-inch rule you should be able to measure from the edge of the HotSpot to the edge of the primary mirror at 12 o'clock, 4 o'clock and 8 o'clock (don't try to measure to the center, use the edge of the HotSpot).



#18 Vic Menard

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Posted 18 August 2020 - 03:37 PM

Note in post #9 you can’t see the secondary vane holders that are seen in the top two pictures of the mirror box.

I'm happy to see that you can't see the spider attachments--but I'm curious why I can't see all three of the primary mirror retaining posts. I think something is obstructing the very edge of the primary mirror reflection...

 

Is there a filter slide under the focuser?

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Edited by Vic Menard, 18 August 2020 - 03:42 PM.


#19 jwpkrfan

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Posted 19 August 2020 - 07:31 PM

It looks like at 9:00 position part of the reflection is missing. Looks like a vertical slice was taken out of the mirror.

#20 Blueox4

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Posted 19 August 2020 - 08:57 PM

I’m taking these pics with a handheld cell phone. I’m sure they are not centered perfectly. I have to think that has an impact on whether the image is cut off on the corner. I also believe my hotspot is centered correctly but my picture taking is not. The thread here: 

 

https://www.cloudyni...-a-center-spot/

 

describes a technique for photographing the mirror to check if it’s centered. Part of that is having the camera  certain ways away from the mirror based on its size. That must be critical to accurate measurement. I will be doing this at some point to confirm my hot spot is centered. 



#21 Bree

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Posted 19 August 2020 - 09:40 PM

The one thing on my mind here is that it looks like you are pointed at the cling.  I dig that one is supposed to use a white surface, but, if you accidentally drop your adjustment tool you could scratch, or worse yet, break your primary mirror.

"Important safety tip, thanks Egon"  (Dr. Peter Venkman, Ghostbusters)


Edited by Bree, 19 August 2020 - 09:40 PM.

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#22 Vic Menard

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Posted 20 August 2020 - 07:53 AM

...The thread here: 

 

https://www.cloudyni...-a-center-spot/

 

describes a technique for photographing the mirror to check if it’s centered. Part of that is having the camera  certain ways away from the mirror based on its size. That must be critical to accurate measurement. I will be doing this at some point to confirm my hot spot is centered. 

I'm aware of the potential centering and parallax issues. But your image in post #9 is taken from near the focal plane and "close to" the focal point. I still think you should check your HotSpot centering.

 

I'd still like to know if you have a filter slide installed. And I'd like to see a picture through the focuser that clearly shows all three of the primary mirror retention posts, preferably through a collimation cap or Cheshire, or perhaps a fully shortened TeleCat combination tool. (White paper background behind the secondary mirror and no shroud covering the trusses.)

 

(Edit: With the shroud removed you shouldn't need to use the LED clip-on flashlight to illuminate the HotSpot, and if you need to illuminate the bright Cheshire ring, you can do that from outside of the field of view so you can eliminate the LED scatter in your image.)


Edited by Vic Menard, 20 August 2020 - 07:57 AM.

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#23 Vic Menard

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Posted 20 August 2020 - 08:11 AM

A few more questions:

 

Do the two large blue rings coincide with a retaining lip on your secondary mirror holder?

Are there more than two screws (small red circles) around the periphery of the secondary mirror?

What is the attachment to your focuser (green arrow)?

Is the flat spot in the violet circle your focuser intruding into the light path, or a filter slide, or something else?

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Edited by Vic Menard, 20 August 2020 - 08:17 AM.


#24 Blueox4

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Posted 21 August 2020 - 08:30 AM

A few more questions:

 

Do the two large blue rings coincide with a retaining lip on your secondary mirror holder?

Are there more than two screws (small red circles) around the periphery of the secondary mirror?

What is the attachment to your focuser (green arrow)?

Is the flat spot in the violet circle your focuser intruding into the light path, or a filter slide, or something else?

Thanks for your help Vic!
 

yes, the blue rings are concentric with the lip of my Protostar secondary holder. 
There are 3 screws on the shroud of the secondary holder not 2.

The end of the focuser you see is the end of the rack of the Feathertouch focuser.(see pic)

That flat spot appears to me to be the visible part of the rack in the focuser.

 

no filter slide. 
 

I’ll post additional pics you requested in the previous post later today also.

 

Thanks Vic! 

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#25 Vic Menard

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Posted 21 August 2020 - 09:03 AM

1.) yes, the blue rings are concentric with the lip of my Protostar secondary holder. 

2.) There are 3 screws on the shroud of the secondary holder not 2.

3.) The end of the focuser you see is the end of the rack of the Feathertouch focuser.(see pic)

4.) That flat spot appears to me to be the visible part of the rack in the focuser.

1.) When I checked New Moon's website, I found that they use AstroSystems secondary mirror holders. Looking at your holder's retaining lip, I don't see the expansion gap (usually with two paired screws seen in the silhouette reflection). And now I wonder if the secondary mirror surface is flush to the retaining lip?

 

2.) I'm guessing the third screw is located at the 6 o'clock position (opposite the one on top at 12 o'clock in post #23--I think I can almost see it). 

 

3.) I pulled my UTA and checked my FeatherTouch, mine has the flat pressure plate. Is yours a R&P? (Edit: I think the reflection of the bottom of the focuser in post #23 is the light playing tricks--looks like the "standard" FeatherTouch Crayford.)

 

4.) I think you need to rack your focuser almost all of the way in to get the primary mirror reflection small enough to fit "inside" your secondary mirror (so we can see the full primary mirror and the three retaining posts). What's your secondary mirror minor axis dimension?


Edited by Vic Menard, 21 August 2020 - 09:12 AM.

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