Chesire v Cap?

[ghostdance]

Really dumb & noobie question I guess, but...is it worth buying a Cheshire if you already have a collimation cap?

I have a cap - dead easy to use & centre the dot. Through the cap everything looks pretty much spot-on going by Astro Baby's great advice & pics.

What would I gain in terms of improved collimation by using a Chesire?

I don't really want to incur expense if the cap pretty much fits the bill...(call me Scrooge...but the money could go on other - cough, TeleVue - objects of desire )

Thanks for any advice from all you Professor Collimators!

[Owmuchonomy]

I'm new to collimating for my 12" Dob. I sold the laser that came with it, made a cap and bought a Cheshire for £20. I use the cap for the 2ndry and the Cheshire for the Primary. As you can tell I am now the world's expert on collimation. ;-)

[Charic]

I started with the 35mm film cap, then laser, then Cheshire in that order. Everything can be done just with the cap as you so rightly stated. I bought the Cheshire to see if there was any further accuracy I could achieve over the 35mm cap. I think it is better, so if I need to collimate, i'll use the Cheshire to align the secondary and the primary. I'll use the laser with a Barlow when in the  field/garden/dark site to check collimation.

Because the Cheshire I use is a 'long tube' version the  field of view  is narrower, ensuring for me a little more accuracy. My Cheshire came from Skys_the_limit.

[steppenwolf]

The collimation cap is probably the best tool for secondary alignment as it is so easy to see what is going on. It really does make good sense to use a Cheshire for the primary alignment though. Not that my opinion can be trusted on this as I like calibrated lasers too !!

[Charic]

..........use what you feel most confident with. Like the rest of us, you'll only find out by buying into whatever is available.  If you trust a calibrated laser like  Steve and I do, then thats fine. My Laser is as accurate as is possible for my needs, however the Skywatcher focuser  is not the tightest fit, so error can creep in. If you know how to compensate, then things will be accurate every time. The best compensation for my needs is using a Barlowed Laser to check the primary. But I can collimate just by using the 35mm cap. then to treble check, the laser and Cheshire agrees. But when do you stop. If there was another method, maybe I would invest in that too, but now that's overkill.  The 35mm cap helps to align the eye on axis. The Cheshire aligns better due to its construction, and the laser works best for me Barlowed.  I don't regret having all three, my money was not  wasted! 

[Jason D]

Collimation cap is not the best tool for the secondary mirror alignment. It is a good tool for the primary mirror alignment -- assuming it fits well in the focuser and its central pupil is small and well-centered.

The main issue with the secondary mirror is aligning the eye-axis with the focuser axis. Check the attached animation. It is hard to tell if the primary spot reflection is centered without cross-hairs.

The sight-tube/cheshire piece is a good tool for both secondary and primary mirrors alignments.

Whether the additional accuracy provided by the sight-tube/cheshire over the collimation cap is worth its cost or not, it is a subjective question. 

Jason

[ghostdance]

Thanks Charic, Steppenwolf ( I wonder - the book, the band? Or both?) & Owmuch - I appreciate your advice 

Going by your advice Charic, I am intrigued that the Chesire may offer a greater degree of alignment so I agree, my best course of action is to pony up for a basic Chesire (or used, if they ever get sold) just to see what level of precision is possible. I don't think I'll go the laser route as yet (mainly because of outlay - I am a cheapskate after all!) but you never know. I'll bet it sure looks purty if nothing else

Cheers fellas.

One last thought, just a throwaway - does the cap ever show apparent good collimation, and then the Cheshire shows not?

[ghostdance]

Collimation cap is not the best tool for the secondary mirror alignment. It is a good tool for the primary mirror alignment -- assuming it fits well in the focuser and its central pupil is small and well-centered.

The main issue with the secondary mirror is aligning the eye-axis with the focuser axis. Check the attached animation. It is hard to tell if the primary spot reflection is centered without cross-hairs.

The sight-tube/cheshire piece is a good tool for both secondary and primary mirrors alignments.

Whether the additional accuracy provided by the sight-tube/cheshire over the collimation cap is worth its cost or not, it is a subjective question. 

Jason

Thanks Jason! Ah, I begin to see what a Chesire can do then - I've assumed the spider vanes would be accurate for centreing....dammit, where'd my wallet run off to....?

[Charic]

.........don't use the spider vanes for centring  a Newtonian!

Mine are not symmetrical  and factory built?

[Charic]

.......secondary mirror adjustment for me is achieved initially by just looking down the focuser, no tools,  centralise the mirror, and   three  visible primary clips.

 Its ok so far,  the cap or Cheshire just  assists me with my  eye alignment to the eyepiece axis. 

The 35mm or dust cap with a 1mm hole at one end,  can allow you too offset your eye/EP axis, due to the size/length of the focuser tube.  You move your eye around, you will see more?

The design of my Cheshire is different. the hole is much longer in length along the barrel until it exits the angled mirror face,  allowing a tighter and greater chance of more accuracy for me ( my observation) Some folk complain that a longer Cheshire reuduces their image area, so the clue is to withdraw the Cheshire slightly to improve the size of the visible area.

I have the 'Longer' Cheshire which at only 13cm still looks short when inserted into the focuser tube. On this Cheshire there is also a cross hair, which according to my observation, can be replaced if damaged? we all love to poke around!.

But as Jason D states, its all subjective, and personal choices.

The Cheshire I use is this one, Its cheap but effective and only £23 if you're watching a budget. http://www.ebay.co.uk/itm/Skys-Limit-Cheshire-Collimator-Newtonian-Telescopes-long-/380801248654?pt=LH_DefaultDomain_3&hash=item58a985ed8e

[ghostdance]

Charic, thank you again....I've obviously been barking up the wrong wossit with regard to the spider vanes....I feel like a clod....heh, but even a clod can look at the stars (somebody shoot me)

Thanks for link - I'd seen one of StL Cheshires (at least I think it was them) but with the angled cut out nr the top (sorry, I'm hopeless with technical descriptions), a 'sight tube'?

I'm now realising I know nuttin about Cheshires the more I get into this, so I'm pretty glad I asked! My wallet & I will have a conflab. I will attempt bribery of the worst kind i.e. "let me have this & I promise not spend a bean for the next month..."

Fingers x'd behind back of course!  

[Charic]

...........the link doesn't show the cut out and the angled face in their pictures.......trust me, it does have it.

I`ll image mine now......standby!

A slight trick in the visual, it appears there's a hole right through the face plate , and your looking through  to the back. The hole is vertical from the eyepiece, this is the 'length' that I mention, which keeps alignment tighter.

I used a mirror just to show the logo is the same?

[ghostdance]

I am indebted*, Charic, my thanks!

*Heh, at least I will be, according to my bank manager

[steppenwolf]

The collimation cap is probably the best tool for secondary alignment as it is so easy to see what is going on. It really does make good sense to use a Cheshire for the primary alignment though. Not that my opinion can be trusted on this as I like calibrated lasers too !!

Please note that my comment here applies to ensuring that the secondary is aligned and centred with regard to the focus tube - I mask off the primary completely and the area behind the secondary for that matter.

[Moonshane]

Cheshire / sight tube combo is all you need

[jetstream]

My vote is for a separate sight tube and Cheshire. Very easy and accurate.

[Charic]

The Cheshire I use is both a 'Shorty' and  'Long' version ? Unscrew the sight tube and its a 'shorty'

The shorter version alone is £21.10

The difference is the extension sight tube as described by jetstream, although it would be awkward to just use this sight tube alone, as it will fall through and strike one of the mirrors as it falls? You can only use this site tube attached to the Cheshire, but you have the option to go long or short otherwise, but losing the crosshair sight.

[Daniel-K]

Cheshire / sight tube combo is all you need

AMEN! 

as shane says!!

ive had alot of fast scopes down to F3.6 and even then i found a cheshire & a sight tube gave far better results than a £300 collimation kit. £26 from flo= money well spent!

[jetstream]

From reading some posts on the site it seems like some members can get confused with a combo tool. Presenting options to get the job done is a good thing, no matter what tools are chosen. I use the Catseye tools, which are excellent and it may be surprising how many people own them or have owned them....   Unbarlowed lasers can also give people fits when collimating.

[Charic]

$3  film cap or  $300   Catseye pro-tool. Still gets the job done?

Will always be a personal and subjective topic, no matter what the choice.

EDIT: (  Catseye available for less @  £90+  uk )  

[jetstream]

Totally agree, except the Catseye tube/Cheshire cost 90 pounds.

[Charic]

.....cheers Gerry, I should have double checked , I just quoted from the first page  I  googled ?

The thread has been edit corrected. But figuratively speaking , either or, you make  your choice with the tools.

[ghostdance]

Thanks all for your advice and discussion. I'll get a Cheshire imminently. To illustrate my complete ignorance & numptyness tho

- what exactly is the difference between a sight tube and Chesire? The only (non-cap or laser) collimating aids I've seen ( FLO et al) are called Chesires & have the crosswires and cutout with the angled plate. So what is a sight tube? Or, what part of the Chesires I've seen comprises one? They appear to be separate devices gong by some posts.....or have I - not unusally for me - got this all completely skewed?

[jetstream]

I think the separate tools were more common years ago, easier to use, more expensive to make. Not many brands left out there that I can tell, Jim Fly's Catseye brand tools are the among the best there is. The sight tube aligns the secondary, under the focuser, round and accurately toward the primary. MUCH less visual info going on in there compared to a combo too. It takes the "witchcraft" out of collimation and provides true offset collimation by using it. A collimation cap with crosshairs so to speak.

This one is built and designed by experts in collimation

[ghostdance]

Thanks jetstream

So, your pic is a sight tube... The Cheshire part is? I'll have a look at the Catseye kwipment, see if I can get a visual.