Collimation with Cheshire, self centering vs. HG Parallizer

[Guest MichaelDurban]

Not so long ago I was still having repeatability issues with my Cheshire.

 

It seemed whenever I collimated either my secondary or primary mirror the collimation would

always be off when inserting -or taking out- the cheshire..

 

I even made alignment marks on the drawtube, the 2"-1.25" adapter and the Cheshire..

(I have a SW 250p)

 

I also thought a self centering adapter would solve these problems...I was too cheap to order a

HoTech laser collimator.

 

and so the troubles..irritations began..

 

My Cheshire/Twist Lock setup..the best of both worlds..or so I thought.

 

After using this setup for a few months things didn't improve.

I inserted my cheshire in exactly the same way as I had taken out only a minute ago.

Collimation was off...

The same happened to my laser colli..

 

I know that fastening the cheshire, with the twistlock will throw it off, I didn't know it was this bad.

(I'm a OCD collimator..so, ...it's even worse!)

 

Then the self centering thing just broke down, so I unscrewed it to determine what the cause was...

 

 

 

The twist lock simply revolves -and tightens- around an inner PLASTIC collar.

No wonder...my cheap makeshift idea turned out to be just that...cheap..

 

Broken....What you see is what you get..

 

Finally I decided enough was enough, and after reading posts regarding the Howie Glatter Parallizer I thought that

things couldn't get any worse...so I ordered the HG-P

 

Well...what a difference...

 

 

The HG-P fits snuggly in the adapter, no play at all...there's only one brass screw..that's all..

Simply slide in you Cheshire, or laser...and off you go...

 

 

Even after taking the scope outside, taking out the cheshire, then reinserting it...the collimation is always dead on.

No shift, no play...

 

I couldn't be happier...

If you feel yourself drawn towards buying a (cheap) self centering -or twist lock- device...don't

For US$ 40,- you have a parallel centering device, made solidly and durable..

 

 

(I have no affiliation with HG products, nor do I actively endorse the distribution of these products, this is just

my view, and experience..)

[BAZ]

I have to agree with you, collimation can take over your life. Have you ever seen the Barlowed laser method? I find this a quick and reliable way of collimating when out in the field.

 

>http://www.youtube.com/watch?v=ZCAy0kYnk9g

[Guest MichaelDurban]

yes..I used the barlowed method a while back..but I like the Cheshire.

 

For me there's only one way to collimate your secondary since I

don't use a colli cap.

 

Cheshire is just so accurate..

 

(is that old Dion in the video?..with his famous line :" lasers lie...and I'm going to show it to you..")

 

haha

[BAZ]

Yeah, that's Dion. A top bloke to boot as well.

 

He has done loads of great tutorials, and is a real asset to the astro community.

[andyboy1970]

I have a revelation self centering adapter and use a deluxe cheshire (FLO) with great success, removal and reinsertion of the cheshire with no change in collimation so i'm happy with the self centering adapter.

I don't like laser collimaters.

Also very worthwhile checking that your focuser assembly is square. (another Dion video)

Edited September 14, 2014 by andyboy1970

[Guest MichaelDurban]

Yes...

 

well I had no success with the self centering adapter..

Too many inconsistencies...

 

I normally follow Nils Olof Carlin's advice..not sure why but

he was the first one I came across when searching for collimation.

He mentions that squaring the focuser doesn't really matter, as long as

it's in certain limits of course..

[andyboy1970]

I replaced the focuser on my little Skywatcher 150p and had to insert 3mm of shims under one side of the focuser square it to the tube/secondary.

My 200p has the same issue but I haven't sorted that yet.

I think it is a lot more critical for imaging than visual.

[Daz Type-R]

This is one of 2 reasons why I upgraded my stock S/W focuser for a Moonlite (the Televue ep's weight a lot and to aid with collimation).  The self centering adapter on the Moonlite is awesome, I use both a Cheshire and a laser (my laser is very well collimated itself) and since switching to the Moonlite collimation is never an issue, you can take the laser in and out all day and it is always in the same place!

 

But I did have to collimate the focuser itself, it was not sitting squarely to the OTA but luckily Moonlites come with collimation screws to help with adjustments like this.

 

I do not see an issue with using lasers as long as they are very well collimated them selves, I just look as them as another tool in the box, I use both a laser and a Cheshire when collimation my 200P.

[Guest MichaelDurban]

I just forgot to mention..

 

The SW 250 does not take 2"

It first has a whatever size - 2" adapter, and then you can use another 2"-1.25" adapter.

 

So there's double the trouble..and double the screws...which shouldn't matter that much if you

leave the adapters in the same place and don't unscrew them once you fasten them (which I did...)

 

In any case, it's all solved with the Parallizer...so that may be a heads-up for SW dob/newton owners.

[Guest MichaelDurban]

Daz..

 

Am I correct in saying that one of the more conventional method for

squaring the focuser is using the laser..

 

Is there a way to do it without a laser?

(Don't want to hijack my own thread..eh...a link maybe?)

 

thank you

[Guest MichaelDurban]

You guys got me worried now...and my OCD is setting in...

 

[Daz Type-R]

No you do not need a laser but I think it makes it easier if you have one.

 

I took the secondary off and then when I took the stock focuser off I measured the distance from the edge of the OTA to the start of the hole in the OTA for the focuser, I then measured from that to the other side of the hole and then worked out the where the centre would be (by dividing the width by 2).  I then marked that on the OTA with a dot.  For me, the holes where the secondary spider vein are attached to the OTA are aligned right in the middle of the hole for the focuser, so it was easy to work out where the exact centre of the hole is for the focuser on the opposite side of the OTA.  I then marked this with a small white dot.  So the next time I remove the spider of the focuser, I just put the laser in and align it to the dot, simples.

 

And I do think it is important to align the focuser to the OTA, other wise, you will have a kink in your light train, the further out you withdraw the focuser, the bigger the angle.

[Daz Type-R]

Also, IMO, I think any focuser with grub screws in it is just asking for inaccuracies, each time you put an ep in and out, in and out, every time one grub screw will be adjusted differently than last time.  How can you be expected to get accurate collimation when your tools are in different positions. I think the only true way to get accurate collimation is to use a 2" focuser with a 2" to 1.25" self centring adapter, but even that could be prone to errors unless the grub screws holding the 2" adapter are equal.

 

But then I am just being paranoid, for visual, I doubt a slight inaccuracy will even be noticed.