Andrew's Collimating Ep.

Astroman (Andrew Wall) · #1 16-08-2005, 06:35 PM

Hi,

Just as a matter of interest, and possible purchase, how would you rate the Cheshire Collimating EP sold by Andrews? Is it worth the $29 or whatever it is now?

davidpretorius · #2 16-08-2005, 08:14 PM

As a newbie who may be doing it all wrong, i found the investment of $29 worth it to get the secondary mirror spot on. the primary, i am fiddling with and will be asking for help at snake valley

Darkplague · #3 16-08-2005, 08:50 PM

I found the adjustment of the secondary to be easily the hardest part of collimation. Adjusting the primary is a piece of cake compared to this.

The only problem with the Andrews collimation piece is that it has a lot of slop in it when you put it in the 1.25" adapter. So for example if you collimate it spot on, then undo the set screw and turn the collimation piece 90 degrees, do the screw back up, I found that it looked out again. I overcame this by machining up my own adaptor that fits the collimation piece spot on. It doesnt even need a set screw because the fit is very snug. (1 thou)

stringscope (Ian) · #4 16-08-2005, 08:53 PM

Andrew,

I recently had the opportunity to use an Andrews (BC's) and Orion (mine) collimating eyepieces side by side. The Orion is a classic Cheshire assembly plus sight tube with crosshairs (1mm wire)mounted in the bottom of the tube 120mm from the peep hole. The Andrews is similar except it is only half the length (or even a bit less) and the crosshair wire is thinner. With my 48yo eyes I could not "see" the crosshairs in the Andrews unit. In the Orion unit the crosshairs are still inside my focal range but they are still sufficiently focused to be useable. If I use reading glasses, I can see the crosshairs OK but then the mirror centre marking becomes very blurred...........sigh!! Even with reading glasses I still found the Andrews unit almost unusable for me.

BC might have some additional comments on this.

Cheers,

Darkplague · #5 16-08-2005, 09:03 PM

Quote:

Originally Posted by stringscope

Andrew,

I recently had the opportunity to use an Andrews (BC's) and Orion (mine) collimating eyepieces side by side. The Orion is a classic Cheshire assembly plus sight tube with crosshairs (1mm wire)mounted in the bottom of the tube 120mm from the peep hole. The Andrews is similar except it is only half the length (or even a bit less) and the crosshair wire is thinner. With my 48yo eyes I could not "see" the crosshairs in the Andrews unit. In the Orion unit the crosshairs are still inside my focal range but they are still sufficiently focused to be useable. If I use reading glasses, I can see the crosshairs OK but then the mirror centre marking becomes very blurred...........sigh!! Even with reading glasses I still found the Andrews unit almost unusable for me.

BC might have some additional comments on this.

Cheers,

Yes I also found them very blurry.
You really have to squint hard to see them properly. I never really bothered witht them tbh, I just sight the 3 clips of the primary and roughly centre them in the secondary as best I can.

The thing I found the most benefit to do when collimating is make sure you are looking parallel down the focuser with your eyes. As soon as you change the viewing angle, your collimation changes with it so you think you need to readjust it.!!!!

RAJAH235 · #6 16-08-2005, 09:45 PM

FWIW, A sheet of white paper, bluetacked on the tube, behind the 2ndary will help keep you centred. Adjust your position to see the smallest outline of the paper around the secondary . Try collimating with the tube resting on the table or a bed etc. Get a helper.

L.

elusiver · #7 16-08-2005, 10:09 PM

i'd have to agee with what's been said about the andrews cheshire. the wires are fairly difficult to see, even more so if you're collimating indoors. I found when i collimated outside in the sunshine it was alot easier. But i find myself doing wired things wiht a torch to get them to show up indoors. But.. it should be easier than it is. but it does the job. Collimating the primary is dead easy with the cheshire though(or maybe i'm not doing it right

) casue u just line up the centre spot and the reflection of the cheshire... but yeah.. just need to make up a sight tube for the secondary.

el

elusiver · #8 16-08-2005, 10:12 PM

we'll probably hear from asimov in this thread soon

el

Miaplacidus (Brian) · #9 16-08-2005, 10:12 PM

I'm a bit of a collimation heretic. Never found the burning need to collimate the 8" F6 very often at all. Maybe I'm just lucky, or just not as fussy as some. (Admittedly, I never transport it very far.) Anyway, since I'm temporarily babysitting an 8" F4 I thought I'd better invest in the Andrews Cheshire (I was ordering some other stuff anyway). Well, it does a reasonable job, but frankly I don't find it any better than the old dismembered film canister with a 2 mm hole in the lid that I was using previously. I guess it depends on what $29 means to some people, but it costs nothing to try the film canister first (most camera stores give them away)...

(If I were to do it again I might go the whole hog and get the laser version.)

Astroman (Andrew Wall) · #10 17-08-2005, 06:39 AM

Thanks guys,

It was only a passing interest, my mirrors are probably as good as they are going to get. Maybe I am just paranoid. I think they do need a clean though, the moon lastnight was shocking to look at, blurry, grey, yuk....... Not the same moon that I have seen through the scope before.

davidpretorius · #11 17-08-2005, 08:25 AM

is this right?

when i was lining up the veins with the cross hairs, i am aligning the secondary.

once i get up the guts to take out the mirror and centre spot the primary, then aligning the cross hairs with this spot aligns the primary.

hence all collimated????

slice of heaven · #12 17-08-2005, 08:40 AM

Quote:

Originally Posted by davidpretorius

is this right?

when i was lining up the veins with the cross hairs, i am aligning the secondary.

once i get up the guts to take out the mirror and centre spot the primary, then aligning the cross hairs with this spot aligns the primary.

hence all collimated????

Veins???
The secondary mirror needs to be positioned centrally under the focuser using the sight tube then rotated and angled to centralize the reflected view of the primary in the secondary mirror. The primary is then adjusted to line up the centre spot with the crosshairs.
The sooner you take the plunge and centre spot your mirror the easier it'll be. You need to check the clamps as well so it has double benefits in doing it.

BC · #13 17-08-2005, 08:44 AM

I've just seen this thread and thought I'd confirm Ian's comments. I think the Andrew's cheshire appears to work just fine as a cheshire to adjust the primary, but it is useless (IMO) as a sight tube because it is not long enough to focus on the crosshairs. The point made earlier about the amount of slop in the fitment of the tool is also very true, so that may in fact negate its value as a cheshire. I am in the process of making a sight tube, but will undoubtedly end up purchasing one of the Orion units ($75 I think) which simply works well. "Buy an Orion one" is my advice.

davidpretorius · #14 17-08-2005, 08:45 AM

ok i will be very brave and disassemble tonight.

slice of heaven · #15 17-08-2005, 08:47 AM

Youre on the right track Darkplague, understanding the shortfalls and pitfalls of the method and tools you use is vital.

ving (David) · #16 17-08-2005, 09:13 AM

mines fine...

Thiink · #17 17-08-2005, 11:43 AM

There was a similar discussion going on in this thread (it took some searching, but I found it!).

I've been meaning to replace my Cheshire with a longer one as its really hard to get the crosshairs to focus properly in my Andrews one. The Orion unit looks like the go. We need to organise some groups buys.

elusiver · #18 17-08-2005, 12:26 PM

maybe worth a go at trying to mod the andrews. need some 1.25" inside diameter to 1.25" outside diameter plumbing pipe.. which i belive does exist. Remove the crosshairs from the original andrews cheshire.. and re-cross hair the pipe using this template from star ware. That way you can make sure u make the right length cheshire for you scope, using this from Nilfs Olof Carlin.

Quote:

Find a piece of plastic or other suitable tubing that fits your focuser snugly without wobbling easily (I have used PVC tubing for electrical conduits and for drains, and aluminum tubes from old vacuum cleaners). Make a peephole cap from any material that you can make a nice hole in, that can be cemented to the tube end and is reasonably dark. Make a hole about 1 mm, centered as well as you can (if you find it too small, you can make it a little larger later). The length of the tube should be the inner diameter times the focal ratio: I have a tube with 28 mm inner diameter for my f/5.6 telescope, so I cut it to 28*5.6 = 157 mm length.

so with a couple of bucks worth of pipe you could get turn your andrews cheshire into a full working combo sight/cheshire for you scope. Total cost.. under $40 plus i'd say a couple of hours if you really took ur time. A good way to get through a cloudy night.

el

asimov (John) · #19 17-08-2005, 05:00 PM

This is just my opinion, but I don't have any desire to get a cheshire. My 2" sight-tube works a treat for the secondary, even giving you the necessary off-set automatically. As to primary collimation, I rely on the star test.

Starkler (Geoff) · #20 17-08-2005, 07:18 PM

What do you want the crosshairs for in any case? They just seem to get in the way of seeing the centre primary donut in the ring of light from the cheshire