Crosshairs on cheshire?

[Wick]

Hi guys,

I'm in the market for a cheshire, it seems to be the preferred route over a laser on here, does more, more accurate and doesn't need batteries.

I think collimation is ok at the mo, but want to check, and I'll need one at some point.

Have read Astro baby notes and others, I think I understand but won't really know until I get my grubby mits on one!

*** What is the benefit of having the 45 degree 'silver' cut out on it? I think it allows the light in easier but not 100%?

*** And, some have the cross hair etched into it, what does that do?

Was looking at the AC656 from astro engineering but none of their stockists have one? And they have not responded to my email.

Cheers

[Wick]

I've got a skyliner 200p dobsonian by the way. Will be nice when I can edit my signature, only 3 posts to go!

[Moonshane]

I just have and use the cheaper one from FLO. It's black and about £25 maybe new? They come up used for about £15.

[RikM]

The reflective 45° bit makes a nice bright reflection inside with a black dot in the centre. This makes it easier to see where you need to make adjustments. I am not sure why the reflective surface has crossharis etched into it. Perhaps it makes it easier to align with the actual cross-wires in the sight tube?

Mine has a smooth surface http://www.firstlightoptics.com/other-collimation-tools/cheshire-collimating-eyepiece.html

[buzzlightyear]

Hi mate I got one last week and found easy to use on my 200p dob. It showed my new scope was out and was easy to adjust back on target with the crosshairs.

You can google for the instructions and follow them.

[Charic]

Wick........Hi,  I'm interested too, in getting a cross-hair sight tube, instead of the basic 35mm film cap that I presently use. It could help me get a more accurate set-up of the secondary mirror due to the position of the cross-hair at the end of the tube, being closer to the secondary mirror ( a tighter crop should ensure greater accuracy) than just a 35mm peep-hole!. I do use a Barlowed laser to tweak/adjust the primary mirror.

That said, I'm learning that a sight tube should be of a length suitable for the situation (the telescope) that is the result of the inner diameter of the tool and the telescopes focal ratio? This is still being studied, although I have seen a fully adjustable tool. So on a 200P should it be a short tube, long tube, or tailor made? 

My interest lies at present with one available from Sky's the limit, because if you look close enough, the cross-hair seems to be incorporated into a screw in cap. My thought is that if the copper/brass wire is ever damaged, it would appear that you could unscrew the insert, and re-wire a new cross-hair.

Lets see what  develops from this thread.

[buzzlightyear]

Got mine from sky the limit Charic and is good quality.

I don't know how you can collimate the secondary mirror tho but I'm interested to know if you can so I can check mine.

[Moonshane]

I used the same tool on my 6" f5, 6" f11, 12" f4 and 16" f4. you can do everything with a cheshire, including adjustment of the secondary mirror.

[AlexB67]

I use a shorty combination tool,

http://www.ebay.co.uk/itm/Skys-Limit-Cheshire-Collimator-Newtonian-Telescopes-short-/380873311843?pt=LH_DefaultDomain_3&hash=item58add18663

The standard length  black model linked by Rik  and a cap.

I find myself using all three, to cross check, since the cap and shorty are much less susceptible to tilt errors, depending how good and snug your focuser is at holding the tube, it depends how I tighten it in my focuser with the long one a bit more. The cap and shorty are a good reference crosscheck the various bits and do not suffer from this in my setups.   For me I find the cross hairs very hard to see clearly with the short tool, but they appear very clear in the long one.  Each one has its  pros and cons, one shows some things more comfortably over another in my case, since my short range sight is not that good, I need glasses to look through them, but I find with the cap it is a bit easier to visualise the primary. For centring the secondary I use the long tube, and so on.  I am not happy till all three tools tell me the same thing. 

For the small day to day tweaks I do not go that far, but when starting afresh and the secondary needs adjusting I go for collimation OCD i.e .overkill probably, but hey, it is one way to have fun when the clouds are out 

In the end of the day one combination tool  should do all well enough, as long as it sits well in the focuser and gives consistent results when you take it out and put it back in again, it should  tell you the same thing every time.

[Charic]

Got mine from sky the limit Charic and is good quality.

I don't know how you can collimate the secondary mirror tho but I'm interested to know if you can so I can check mine.

buzzlightyear......Collimating a telescope is lining up its optical components. Collimating the secondary is to make sure the mirror is central to the focuser tube and that the tilt of the secondary is aligned to the primary mirror.  (either using a laser or by visually observing the "3" mirror clips!) Its the first step in aligning your mirrors. The secondary doesn't need adjusting too often unless you  drop the scope? Ouch!

I think my system is ok, but the 35mm film cap only aids eye alignment, there's still an amount of error that  can occur. My thinking is  that having the right tool, can only be the best option. So many  folk recommend the sight/combination tool.

Buzz..........does it look like the cross-hair on that tool un-screws, so that you could repair if necessary? Some tools. the wire just fits through the tube walls, and is the end of the wire is visible externally. 

[Charic]

I use a shorty combination tool,

http://www.ebay.co.uk/itm/Skys-Limit-Cheshire-Collimator-Newtonian-Telescopes-short-/380873311843?pt=LH_DefaultDomain_3&hash=item58add18663

The standard length  black model linked by Rik  and a cap.

I find myself using all three, to cross check, since the cap and shorty are much less susceptible to tilt errors, depending how good and snug your focuser is at holding the tube, it depends how I tighten it in my focuser with the long one a bit more. The cap and shorty are a good reference crosscheck the various bits and do not suffer from this in my setups.   For me I find the cross hairs very hard to see clearly with the short tool, but they appear very clear in the long one.  Each one has its  pros and cons, one shows some things more comfortably over another in my case, since my short range sight is not that good, I need glasses to look through them, but I find with the cap it is a bit easier to visualise the primary. For centring the secondary I use the long tube, and so on.  I am not happy till all three tools tell me the same thing.

For the small day to day tweaks I do not go that far, but when starting afresh and the secondary needs adjusting I go for collimation OCD i.e .overkill probably, but hey, it is one way to have fun when the clouds are out 

In the end of the day one combination tool  should do all well enough, as long as it sits well in the focuser and gives consistent results when you take it out and put it back in again, it should  tell you the same thing every time.

With you on that quote, the more options that have the same result will only confirm your setup.

My old eyes can't focus with a Telrad, so that had to go, but I can focus quite well through the telescope. Might have the same problem using a cross-hair. I won't know till I try?

[scarp15]

I tend to do a quick check with a Rigel collimation cap concerning secondary alignment, prior to using the premium Cheshire collimating eyepiece. 

[Charic]

I'm still trying to find in simple terms why the length of the tool is so important. I know the focal ratio affects the light cone, and I suppose therefore the focal point, so a sight tube should be of such a size as to match the focal point to achieve the correct alignment.

Something along those lines, still looking.

We'll always look for something better to almost perfection, and wont stop  fiddling. My collimation setup is basic, done in the right order, and appears to be ok  for  MY EYES ONLY!  I'm sure someone else having a peek may say. Hmmm! not quite right.

[Moonshane]

it's to do with the size of the secondary. faster = bigger for the same aperture. bigger means it's harder to see the whole secondary down the hole in the cheshire if it's longer so a shorter one night be best. personally I just rack the focuser out/use an extension (or pull the cheshire out) if I cannot see all the secondary.

[AlexB67]

I'm still trying to find in simple terms why the length of the tool is so important. I know the focal ratio affects the light cone, and I suppose therefore the focal point, so a sight tube should be of such a size as to match the focal point to achieve the correct alignment.

Something along those lines, still looking.

We'll always look for something better to almost perfection, and wont stop  fiddling. My collimation setup is basic, done in the right order, and appears to be ok  for  MY EYES ONLY!  I'm sure someone else having a peek may say. Hmmm! not quite right.

I wouldn't overly worry, especially in your scope at f/6. The most important part in the setup, as long as the secondary is reasonably aligned is the alignment of the primary with respect to it, and the cap can do this very well.  I can't say having the short combination tool I use on my smaller f/5 scope has actually improved the views over what I could achieve with the coli cap only.  A combination tool will not hurt, it will confirm more accurately what going on. Also the bigger the scope the smaller the collimation tolerance gets.   With the 8 inch Dob you have I doubt when all is set and done after you get such a tool and use it, that you'll see a noticeable change visually, unless it was incorrectly collimated to begin with. 

[Charic]

Cheers AlexB67...........I've been happy with my results so far, but its taken longer to get the result I wanted on Jupiter. Maybe the clarity of the final image could be improved, so any further (accurate) tweaking to get to the limit of my scope would be nice. Its more than likely just my old eye that's at fault, with focusing, or just the seeing conditions, but when it was good, it was really good.

I have just read (need to re-read again)  this article ( http://web.telia.com/~u41105032/kolli/kolli.html#simplesight ). it seems to answer many things, but still doesn't say why the length is important, just that if your building the sight tube yourself, its inner diameter times the focal ratio equals the length of the tube? Looks like I will just buy one, but knowing the theory is key. 

[buzzlightyear]

buzzlightyear......Collimating a telescope is lining up its optical components. Collimating the secondary is to make sure the mirror is central to the focuser tube and that the tilt of the secondary is aligned to the primary mirror.  (either using a laser or by visually observing the "3" mirror clips!) Its the first step in aligning your mirrors. The secondary doesn't need adjusting too often unless you  drop the scope? Ouch!

I think my system is ok, but the 35mm film cap only aids eye alignment, there's still an amount of error that  can occur. My thinking is  that having the right tool, can only be the best option. So many  folk recommend the sight/combination tool.

Buzz..........does it look like the cross-hair on that tool un-screws, so that you could repair if necessary? Some tools. the wire just fits through the tube walls, and is the end of the wire is visible externally.

I'll have a look today mate.

[buzzlightyear]

Charic I can't see a problem with renewing the crosshairs

[Charic]

The long Cheshire at Sky's is 16cm long!

I suppose with the the shorty version, there may be a limit to its use, no margin for adjustment, and maybe, no different to what I'm already using with the 35mm cap, but the longer version should allow a tighter crop/view of the secondary, for the initial  adjustment, with respect to using the basic (although it works well enough!) 35mm cap.

I just want to ensure that my secondary is accurately set by using a proper tool, rather than just the 35mm cap. If I need to see the primary at any stage, I could just withdraw the Cheshire slightly?

I'll centralise the secondary mirror alone with the Cheshire, Maybe tilt with the Laser( as I believe my laser is fairly accurate!) and Barlow the Laser for the Primary mirror.

Decisions?

[Moonshane]

personally I do everything with the cheshire but your system will work assuming your laser is straight.

[buzzlightyear]

I did notice it is possible to tell if secondary mirror is out by just looking into focus tube on its own.

When I did it I thought it looked out so put the cheshire in and it was. Adjusted secondary to cheshire centre then took it out, put my eye in the empty focus and the secondary circle was bang on my eye pupil!

[AlexB67]

I did notice it is possible to tell if secondary mirror is out by just looking into focus tube on its own.

Yes you can do that for a rough estimate, the thing with that is you need to make sure you are looking down the centre and it will be hard to be very precise. The small peep hole in the tool forces you to look down centrally to avoid any errors like that, but like you said as a first rough check it can do the job. When I got my first scope and had no tools at all, for the first couple of days I did just that to check and rough it in while I was waiting for the coli cap to arrive in the post, since mine was badly out. 

[buzzlightyear]

Yeah like I said it just accured to me while doing collimation on my scope. I was not on about being accurate but just noticed it is visable to the eye of somewhat

[Myopicus]

Just looking at my cheshire now (it's the red one from FLO) ;

The wires don't appear to be easily replaceable -the holes are tiny, on close inspection one of the wires wasn't totally straight, so looking the 'wrong way' up the cheshire i sighted agains the crosshairs on the 45 and gave the bent wire a bit of a nudge until it was aligned exactly.

Bought some allen keys yesterday, and am going to have my first pop at collimation tonight (secondary is definitely out). Want to get it spot on, as it looks like there's going to be clear skies on Tuesday, when I've got a bunch of friends round for my birthday - the scope was a present from my (incredibly lovely and generous) wife so I want to impress all and sundry with some decent views!

[Charic]

Well I was going to buy a Cheshire this Week , but then I spied  the new (for me anyway ) "Starguider" lens bag from Sky's!

I needed something  better to keep my optics and tools in( presently using two plastic biscuit tubs ?)  and about £95 cheaper than a TeleVue version, it seems great value, and should be here next Week.

ps. Just ordered  the Cheshire 'Long Version' from  Sky's (had to be done)  I'll completely loosen the spider and align, because it appears to be 1.5mm offset? Then once all collimated, I`ll let you know, if at all, it was any easier using the tool over the 35mm cannister? Another extension to the bad weather no doubt!