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Collimation of my AT10RC

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#1 Roy Salisbury

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Posted 20 May 2013 - 11:18 AM

Can someone point my in the proper direction. I am trying to find the correct tools (eyepiece, laser, whatever) to collimate my AT10RC. That along with some good directions on using said equipment.

I read that people were using the Hotech SCA laser collimator, so I got that one, but honestly, I am finding that thing is impossible to use on an AT10RC so not sure how people use it on that scope.

LInks to the necessary equipment with instructions would be appreciated (a video would be a plus).

Roy

#2 AstroGabe

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Posted 20 May 2013 - 11:37 AM

I had the same collimator, but it was giving inconsistent results. I had doubts the laser was itself properly collimated. I've since used my glatter laser and haven't looked back. It's more $, but worth it in the end, especially on an RC, where collimation is key.

Gabe

#3 pfile

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Posted 20 May 2013 - 11:44 AM

if it's not badly out of collimation, you might try the RC systems method of collimation simply using defocused stars and your CCD camera.

4th from the bottom on this page:

http://www.aicccd.co...on_archive.html

there are a number of threads here dealing with this topic, you can probably search using google with "site:cloudynights.com at10rc" or "rc collimation", etc.

#4 Roy Salisbury

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Posted 20 May 2013 - 12:19 PM

if it's not badly out of collimation, you might try the RC systems method of collimation simply using defocused stars and your CCD camera.


I did this bit over the weekend. It got me close, but still needs some work.

Roy

#5 Roy Salisbury

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Posted 20 May 2013 - 12:39 PM

I had the same collimator, but it was giving inconsistent results. I had doubts the laser was itself properly collimated. I've since used my glatter laser and haven't looked back. It's more $, but worth it in the end, especially on an RC, where collimation is key.

Gabe


It looks like the "collimator of choice" seems to be the Tak Collimation Scope. How would that compare to the Glatter laser?

Roy

#6 jrcrilly

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Posted 20 May 2013 - 02:02 PM

It looks like the "collimator of choice" seems to be the Tak Collimation Scope.


That's a nice device. I don't currently have one, but I used one with my old Tak CN-212. It's basically a magnified Cheshire/sight tube. The instructions that come with the AT RC models describe using a Cheshire/sight tube and that should suffice, so long as the mirrors are centered with respect to each other. If not, you'll need a bullseye pattern laser to get it all centered up first.

#7 Roy Salisbury

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Posted 20 May 2013 - 03:14 PM

That's a nice device. I don't currently have one, but I used one with my old Tak CN-212. It's basically a magnified Cheshire/sight tube. The instructions that come with the AT RC models describe using a Cheshire/sight tube and that should suffice, so long as the mirrors are centered with respect to each other. If not, you'll need a bullseye pattern laser to get it all centered up first.


First, how can I tell if the mirrors are centered as you suggest. And then, where might I get such a device with a bullseye pattern laser to center them all up?

Roy

#8 jrcrilly

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Posted 20 May 2013 - 06:20 PM

First, how can I tell if the mirrors are centered as you suggest. And then, where might I get such a device with a bullseye pattern laser to center them all up?

Roy


If it looks right in the Cheshire but not in the star test you probably have a centering problem. I'm trying to remember who sold the bullseye laser I have. Glatter also sells one. I'm trying to talk Hotech into introducing one with his self-centering feature (no use trying to align mirrors with an off-center or non-collinear laser).

#9 shiner

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Posted 21 May 2013 - 05:02 AM

Have a look at my blog and videos at:
stevesastro.blogspot.co.uk
...here I discuss a collimation method with a Glatter that is very useful and will get you 95% there if not better.

#10 Roy Salisbury

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Posted 21 May 2013 - 11:55 AM

Have a look at my blog and videos at:
stevesastro.blogspot.co.uk
...here I discuss a collimation method with a Glatter that is very useful and will get you 95% there if not better.


Thanks. I'll take a look.

Roy

#11 Jared

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Posted 21 May 2013 - 12:39 PM

Here is a brief description of a method I use to collimate my AT10RCF. It requires very little equipment, and gets me extremely close to perfectly collimated.

One thing to keep in mind... The AT10RCF does not have the ability to center the secondary over the primary, so instead you need to tilt both mirrors which can then introduce tilt into the focuser. As a result, for best results you may need a tip/tilt plate for the focuser (available from TS in Germany).

1) Adjust the primary using a site tube (pinhole site) in the focuser so that the secondary appears centered in the primary baffle. I use a 2" site tube from Farpoint. Just choose any good quality site tube/cheshire.
2) Look through the front of the telescope from a distance of about 1 meter and line up your eye so it is slightly offset from the center and so you can see one of the secondary spiders lined up with its reflection in the primary and also the reflection of your eye. There will be a hall of mirrors effect here, so you may see several reflections of your eye. You want to adjust the secondary so that your pupil, the spider, and the reflection of the spider are all in the same plane. This adjustment is surprisingly subtle--you can easily see changes of as little as 1/32 of a turn in the secondary set screws.
3) Repeat the process with a second spider (90 degrees from the first). This may throw off the first spider, so go back and forth between them a bit till you have made this adjustment for all angles.
4) The adjustment to the secondary will have thrown off your initial adjustment to the primary. Go back to step one above and repeat through step three. You should quickly converge on a solution.
5) This will get the mirrors lined up with respect to each other and ensure that the optical axis goes through the middle of the focuser, but it will NOT ensure that the focuser is orthogonal to the optical axis. So there is still one step to go. Put a 2" laser in the focuser (I wouldn't trust any of the 1.25" lasers just because the 2"/1.25" adapters usually have enough slop to mess this up). The 2" laser should point to the secondary spot, and the return beam should be straight back to the point of origin. Adjust the tip/tilt of the focuser until the return beam is back to point of origin. Note, the source MAY not perfectly hit the center spot, since the physical center and optical center of the secondary may not exactly coincide. The trick is to ensure the return beam is centered.

That should do it. Equipment required: a good site tube or cheshire, a good 2" laser (something collimatable like Howie's lasers or the ones from Farpoint), and the tip/tilt plate from TS. If you have a Moonlite focuser, I believe tip/tilt adjustments are built in, so you won't need the TS plate.

Once you get good at this technique, it should only take you 15 minutes or so. After using this technique, you will want to confirm your results using a star test. The best way to do this photographically is to use an out-of-focus star field. Tweak the primary mirror so that no on-axis coma is visible (perfectly concentric rings). Tweak the SECONDARY mirror so that astigmatism in all four corners is oriented the exact same way--if you have slightly football shaped stars (which you will), then you want the points of the football pointed exactly towards the middle, or exactly 90 degrees from the middle (inside vs. outside focus) in all corners. Finally, you can tweak the tip/tilt on the focuser so that out of focus stars are the same size in all four corners.

You shouldn't have to make more than very minor tweaks using your camera. If you do the daytime routine correctly, anything more than 1/32 of a rotation of a set screw should make you suspicious.

I know this routine sounds a little strange (especially step two above), but it is surprisingly sensitive once you get used to it, extremely easy to perform, and, most importantly, WORKS. Using this technique and a well matched flattener, on nights of good seeing I am able to get 2" FWHM stars all the way to the corners of a 35mm imaging plane.

#12 Roy Salisbury

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Posted 22 May 2013 - 11:06 AM

Have a look at my blog and videos at:
stevesastro.blogspot.co.uk
...here I discuss a collimation method with a Glatter that is very useful and will get you 95% there if not better.


OK.. I watched all the videos, and this is really helpful. Since the Tak scope that I was going to get is back ordered, I am going to get the Howie Glatter collimator. That and a Cheshire eyepiece should be here tomorrow so I can try it out this weekend.

Thanks

Roy

#13 shiner

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Posted 22 May 2013 - 11:53 AM

A proper, accurate collimator like Howie's is so incredibly useful irrespective of your RC scope. Very useful on refractors and reflectors as well. It will repay itself over the years many times over. A sound and wise investment.

Don't dismiss the Cheshire technique though. That's all that many use with great success. I have not tried Jared's method. I may give that a go too.

#14 rainycityastro

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Posted 22 May 2013 - 01:30 PM

Hi Jared,
Thanks for the comprehensive set of steps. This is really beneficial for those of us trying to be absolutely sure that the instrument is perfectly collimated. I am trying to reason about them in my head prior to implementing your method.
I have a question regarding step 1.

"1) Adjust the primary using a site tube (pinhole site) in the focuser so that the secondary appears centered in the primary baffle "

Lets take the case where the primary is perfectly centered and aligned with the tube. The secondary is also aligned and centered in the tube. But there happens to be a misalignment in the focuser tube, i.e. The focuser alignment adjustment has been misaligned. (either on the moonlite focuser or the TS alignment ring)
When looking through the pinhole, would the secondary still appear centered in the primary? It seems to me that it will not. In this case, won't you be adjusting the primary when you should be adjusting the focuser?

Hard to visualize how the optics would look in all these cases :)

Regards,
--Ram

#15 Jared

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Posted 23 May 2013 - 12:12 AM

If the two mirrors were perfectly aligned but the focuser was not, then the pinhole in the focuser WOULD show the secondary concentric with the primary baffle. You wouldn't be throwing anything off with this first step. In fact, if you have good eyesight you can prove this to yourself without ANY Cheshire or pinhole under good light... Get your eye at the same distance as it would be if you were using the pinhole (almost right up against the focuser) and move your head around till the reflection of your pupil appears centered in the secondary spot (assuming your secondary has a spot "ring" like mine does). Again the primary baffle and secondary should appear concentric, and you never even used the focuser! This is exactly what the pinhole site is doing.

#16 Nicola

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Posted 23 May 2013 - 05:15 AM

Apologies for popping into the topic, but this is actually kind of related:
Is there anyone having a good instruction manual for the Takahashi Collimating Scope? I've got one but the instructions inside are in Jap-English and leave me with many questions.

Thanks a lot
Nicola

#17 dawziecat

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Posted 23 May 2013 - 05:52 AM

I've got one but the instructions inside are in Jap-English and leave me with many questions.
Nicola


I recently got the Tak collimating scope and confirm Nicola's findings. The Instructions are a comically bad translation!

Example:

"Some Mewlons have a little amount of the spider adjustment. The perfect collimation for these will be so difficult. Then, do it at the utmost condition."


If this is typical of a Tak instruction sheet, Takahashi really should address the issue. Back in the 50s this was common. It is crazy for a major corporation to fall into this kind of thing in this day and age.

#18 MikeCatfin

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Posted 23 May 2013 - 07:31 AM

Apologies for popping into the topic, but this is actually kind of related:
Is there anyone having a good instruction manual for the Takahashi Collimating Scope? I've got one but the instructions inside are in Jap-English and leave me with many questions.

Thanks a lot
Nicola


The ken Crawford video (5th from the bottom) shows how to use it to collimate an RC scope.

RC Collimation

#19 Roy Salisbury

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Posted 23 May 2013 - 09:34 PM

So, i went ahead and got the Howie Glatter laser with the holographic attachment. However, its not a circular pattern as expected, but a grid pattern. Im sure i can still make it work, but just not what I was expecting after watching the videos.

Roy

#20 nemo129

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Posted 24 May 2013 - 06:53 AM

You need this one if you want the Concentric Circle Pattern.

#21 shiner

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Posted 24 May 2013 - 10:51 AM

I like Jared's method too of looking for the hall of mirrors. I messed my collimation up deliberately and I tried it and I have got it back I think. Only issue is weather is absolutely 100% pants in UK; star test out of the question at the minute and that is the ultimate test. The HG laser is very useful for aligning the focuser.

An issue I have found is that racking in and out of the focuser moves the laser very slightly and does not reflect the laser back to the origin for all focuser postions. Whats your thoughts on that Jared? The laser is 100% accurate. This slight uncertainty is a fly in the ointment so to speak... The only difference between Jared's method and the concentric circles method is the holographic attachment.

#22 rainycityastro

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Posted 24 May 2013 - 12:35 PM

Jared, this is a great explanation and makes sense. Thanks.

--Ram

#23 Roy Salisbury

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Posted 24 May 2013 - 02:55 PM

You need this one if you want the Concentric Circle Pattern.


Thanks. I have placed the order. I'll use the other one this weekend and see how good I can get it, and then double check with the other one when it arrives.

Roy

#24 Jared

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Posted 24 May 2013 - 03:36 PM

An issue I have found is that racking in and out of the focuser moves the laser very slightly and does not reflect the laser back to the origin for all focuser postions. Whats your thoughts on that Jared? The laser is 100% accurate. This slight uncertainty is a fly in the ointment so to speak... The only difference between Jared's method and the concentric circles method is the holographic attachment.


I have had this happen before with less expensive focusers, and with a Feathertouch 3545 when it was slightly out of adjustment. It is possible for the focuser to cause a small amount of image shift--moving the laser slightly off the optical axis. Frankly, it is very unlikely it is enough to matter, but the only way to tell for certain is with a star test. Best solution if your focuser is adjusted properly (mating of the rack and pinion and tightness of the teflon pads or roller bearings that apply tension to the draw tube) is to make sure you always approach focus from the same direction--just as the SCT user community has learned to do. As I mentioned, though, I'd be surprised if there is enough of a shift to matter at focus since it is unlikely that you are introducing tilt.

One thing I will mention, though, is that even with high quality focusers I have found that the rotation feature introduces tilt. I would recommend you NOT USE IT if you have a larger CCD chip. Instead, just lock it down and find another way to rotate your camera for proper framing and guide star selection. I have seen tilt in Feathertouch 3" and 3.5" focusers as well as the top-of-the-line William Optics focuser and also in a bunch of less expensive focusers. I've never owned a Moonlite so can't speak to that brand. I still love my Feathertouch focusers and would recommend them to anyone, but I think the teflon sleeve between the rotating portion and the body of the focuser is not a good way to guarantee a secure fit. Use the camera's dovetail attachment or a lock ring on whatever threaded adapters you have instead. If you are using a 2" nosepiece connection, you can probably ignore this recommendation since you are sacrificing orthogonality in your focuser anyway.

#25 Roy Salisbury

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Posted 25 May 2013 - 01:50 PM

OK.. Since I won't get my focuser collimating ring until next month (back ordered), I have two choices and I am not sure which one is correct.

1. Adjust the primary mirror that the focus tube is on to get it "centered" on the whole mirror. That throws off the center spot. I can then adjust the secondary to get the laser return centered.

2. Adjust the primary mirror so the center spot dead on, and then adjust the secondary to get the laser return centered. This will throw off the focuser and not be centered.

What is the correct way to go? I'm thinking #2 is the right way, but then my star images will not be round.

???

Roy






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