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Equipment Discussions >> Cats & Casses

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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Need help collimating Explore Scientific Mak-Newt
      #5311874 - 07/10/12 07:37 PM Attachment (85 downloads)

Trying to collimate the explore scientific 152 f/4.8 mak-newt that I just received today from Astronomics.

I'm certainly not pleased that it was not collimated better out of the box.

At first I assumed the secondary was properly positioned in the factory so I threw in my Orion laser collimator and went to check the tilt of the secondary, but I found that I didn't have enough freedom to tilt it enough to get the laser into the primary mirror's center spot.

I called ES and he said I need to use a sight tube on it, after the phone call I realized my collimation cap should do just fine for now.

I took out the laser and replaced it with one of Orion's collimation caps, and you can see what it looks like in the attached picture taken by my camera phone looking down the focuser tube.

Is this a case of the secondary being improperly vertically positioned? I'm surprised it's so far off. I tried to adjust it but no luck so far since the online pdf instructions are different from how the actual scope is built. They may have been written for an ealier model or protoype.


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TG
Pooh-Bah


Reged: 11/02/06

Loc: Latitude 47
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5311958 - 07/10/12 08:39 PM

You still need the laser. The sight tube is step #1. Rotate and adjust the secondary till it shows a centered profile in the "field" of the sight tube. Normally, the MNs don't have a vertical adjustment for the secondary but if you tighten/loosen the three screws by the same amount, it will move up or down and usually only a small amount is needed. Rotation for my Intes M-N is harder to achieve and requires loosening the retaining ring of the secondary (which itself has a tiny hex set-screw in it). If the Chinese ES scope is a clone of the Intes ones, you should have something similar. At this point, it may still look elliptical but it should be symmetric in the sight tube. After this, you insert the laser and adjust tilt till you hit the center but before you proceed, iterate on the secondary-in-sight-tube again till both are perfect. When this is done, the secondary should look circular in the sight tube and equidistant from the tube walls. Only then start adjusting the primary.

IOW, this is just like adjusting a Newt except in ONE crucial detail: in a Newt, the aperture stop is at the MIRROR. In a Mak-Newt, it is at the CORRECTOR. This means that the Newt can tolerate misalignment between tube and optics (usually requiring an adjustment of focuser tilt) but in a Mak-Newt, the corrector, tube and focuser better be square from the beginning or you will start blubbering from frustration soon

If you have Suiter's Star Testing book, he's got a good explanation for the principles and method of collimating Newts as well as a method for making sure your focuser is square to the tube.

Finally I should say that for your short focal ratio, the secondary offset may become important for even illumination of the field. However, I've never understood this properly as it's not critical for my needs (my scope's an f/6 and has a small secondary anyway). If you have a concern here, talk to the reflector guys especially starman1.

Regards,

Tanveer.


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: TG]
      #5312014 - 07/10/12 09:15 PM

It seems there is nowhere near enough movement possible to center the secondary in the focus tube... as if there is only 1 or 2 mm of play in the vertical position?

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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5312186 - 07/10/12 10:50 PM

Two things tell me the secondary mirror is too far from the corrector plate:
1) that's how it looks through the collimation cap.
2) if the secondary was too far from the corrector, it should pull the laser spot on the primary toward the focuser, which is exactly what I see. There is not enough freedom in the secondary tilt to get the laser spot to the center of the primary.

I will have to consult with ES and maybe send it back.


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spencerj
Pooh-Bah
*****

Reged: 11/17/04

Loc: Londonderry, NH
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5312641 - 07/11/12 10:30 AM

On my MN66, I can slide the mounting plate for the focuser forward or back to center the secondary. Does the focuser or mounting plate on the ES allow for any adjustment?

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bykhed
scholastic sledgehammer
*****

Reged: 10/22/07

Loc: Westminster, CO
Re: Need help collimating Explore Scientific Mak-Newt new [Re: spencerj]
      #5312913 - 07/11/12 04:18 PM

Google "barlowed laser collimation" and also find some of the great docs for mak-newt collimation on the web. I found that barlowed laser collimation gave me the best results with a mak-newt.

-Matt


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: bykhed]
      #5312957 - 07/11/12 04:48 PM

I will use a barlow with the laser when adjusting the primary, but I don't think it can help with the tilt and position of the secondary.

Something I don't understand is why the laser spot on the primary cannot get within 1 cm of the center spot, when the vertical position of the secondary may only be off by a few mm. A ray trace sketch suggests to me that the 45degree angle of the 2ndary would result in Xmm offset of the laser on the primary whenever the 2ndary vertical position is offset by Xmm.


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TG
Pooh-Bah


Reged: 11/02/06

Loc: Latitude 47
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5313113 - 07/11/12 06:01 PM

Quote:

I will use a barlow with the laser when adjusting the primary, but I don't think it can help with the tilt and position of the secondary.

Something I don't understand is why the laser spot on the primary cannot get within 1 cm of the center spot, when the vertical position of the secondary may only be off by a few mm. A ray trace sketch suggests to me that the 45degree angle of the 2ndary would result in Xmm offset of the laser on the primary whenever the 2ndary vertical position is offset by Xmm.




You're correct, a barlowed laser will help only in collimation of the primary. However, I never had success with it on my Mak-Newt due to (1) my mirror having a central plug, and (2) the return of the laser not being visible from the front. Due to the corrector there's no way to use a small hand-mirror do view the return as you would do for an ordinary Newt. However, doing the usual collimation with the sight tube resulted in perfect collimation.

I found Explore Scientific customer service excellent. What have they to say about it?

Tanveer.


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: TG]
      #5313400 - 07/11/12 09:19 PM

ES said that they want this to be confirmed with a sight tube and basically the collimation cap is not good enough to confirm anything. I ordered the celestron Cheshire Collimating Eyepiece which will be here Friday with a little luck.

He mentioned the focusing draw tube can be adjusted. There are a couple of hex screws I loosened which allow me to move the draw tube to center the secondary, and get the laser into the primary center doughnut, but so far can't figure out how to lock it down.


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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5313427 - 07/11/12 09:43 PM

Hi Neutrino,

I have the ES Comet Hunter also. You basically collimate it the same way you would a standard Newtonian. I wouldn't be too surprised if the scope arrived out of collimation simply because of the shipping and rough handling it may have gone through to get to you. It's not something that Explore Scientific has any control over.



Quote:

Is this a case of the secondary being improperly vertically positioned?




You should be able to eyeball the vertical position but sometimes it's difficult to get the light just right so you can actually see the edges of the secondary mirror. From you picture it looks like the secondary is not centered in the draw tube. To move the secondary towards the corrector plate, loosen the three adjustment screws "a little" and tighten the large center screw. Keep doing this until the secondary is centered in the drawtube. It may not take as much as you think. Then work with the laser to adjust the tilt of the secondary, and then thirdly, the tilt of the primary.

I reworked my collimation tonight just to see how much travel I have within the secondary itself. In order for me to get the tilt correct I had to loosen two of the thumbscrews completely and tighten one of them pretty tightly. I eventually got the laser (I'm using a Hotech 2" laser) in the center of the donut and snugged up the other two screws lightly. After that I centered the primary with the laser.

Patrick


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: Patrick]
      #5313486 - 07/11/12 10:23 PM

Hi Patrick,

Thanks a lot for your description and inspiration. I got the thing collimated.

The secondary has a big center screw which I believe is just the 'rotation lock screw' which puts the 3 plastic rotation locking pins in place. However, my 2ndary seems to be able to rotate whether or not those are locked unfortunately ... At some point the design of this system changed so yours might be different.

Anyway, behind the big center screw (which can be removed) is a small hex screw, and on mine, I turned it counter-clockwise all the way until it hits a hard stop, this allows rotation of the 3 thumbscrews adjustment screws to bring the 2ndary as close to the corrector plate as possible. In previous attempts I may not have gotten the center hex rotated all the way due to the 3 screws preventing that?

Then, like yours, two of the thumb screws had to be loose and the 3rd pretty tight to get the laser in the donut.

Then I could collimate the primary as usual.

If only I could make some small adjustments to the draw tube direction, I could probably make it so my 2ndary adjustments are not so maxxed out.

It is cloudy last night and tonight, a very unusual situation for these last few months here in socal... so first light will have to wait.


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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Need help collimating Explore Scientific Mak-Newt new [Re: sneutrino]
      #5313561 - 07/11/12 11:12 PM

Quote:

behind the big center screw (which can be removed) is a small hex screw




I was not aware of the small hex screw behind the big center screw...so I suspect our scopes are the same. I was trying to be careful not to drop the secondary mirror onto the primary...something that can happen with a typical Newtonian secondary, so I didn't think of removing the center screw.

Glad you got the scope collimated though! I hope you like it! I've enjoyed mine.

Patrick


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rtanton
Vendor (Explorer Scientific)
*****

Reged: 02/06/07

Loc: Mission Viejo, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: Patrick]
      #5314315 - 07/12/12 01:25 PM Attachment (75 downloads)

This image may help:

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rtanton
Vendor (Explorer Scientific)
*****

Reged: 02/06/07

Loc: Mission Viejo, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: Patrick]
      #5314317 - 07/12/12 01:28 PM Attachment (55 downloads)

Images of a collimated Comet Hunter:

Edited by rtanton (07/12/12 01:38 PM)


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rtanton
Vendor (Explorer Scientific)
*****

Reged: 02/06/07

Loc: Mission Viejo, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: rtanton]
      #5314343 - 07/12/12 01:39 PM Attachment (48 downloads)

more images:

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rtanton
Vendor (Explorer Scientific)
*****

Reged: 02/06/07

Loc: Mission Viejo, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: rtanton]
      #5314350 - 07/12/12 01:42 PM Attachment (58 downloads)

another image:

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Patrick
Postmaster
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: Need help collimating Explore Scientific Mak-Newt new [Re: rtanton]
      #5314360 - 07/12/12 01:48 PM

Good information Russ...thanks for posting.

Question:

I don't understand about the 'recent update' statement. What is the secondary center pivot point? Does it refer to being able to adjust the secondary mirror so it's perpendicular with the focuser draw tube?

Apparently I've been collimating the secondary backwards because I've been loosening the center screw to collimate, and then tightening it when done.

Patrick


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rtanton
Vendor (Explorer Scientific)
*****

Reged: 02/06/07

Loc: Mission Viejo, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: rtanton]
      #5314372 - 07/12/12 01:52 PM Attachment (61 downloads)

collimation procedure:

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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Need help collimating Explore Scientific Mak-Newt new [Re: rtanton]
      #5314699 - 07/12/12 04:38 PM

Russ,

These descriptions need to ship with every Comet Hunter! The manual I have is out of date.

Patrick


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Need help collimating Explore Scientific Mak-Newt new [Re: Patrick]
      #5315100 - 07/12/12 09:37 PM

Is the draw tube direction adjustable?

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