Maybe I should have titled the thread another ... another colimation thread
Anyway not that I can quickly find it (the thread) but someone else had posted a photo of how their colimation looked so I thought I would do the same and invite comment
Quick shot down the focuser with the A70 point and shoot.
To be honest I have never been completely satisfaied that I have the secondary right (thus the question) but basically my procedure is:-
1.) Using laser check that the laser is centered on the primary. OK (rotate it in focuser etc. appears colimated itself and I have checked over a few meters)
2.) Using barlowed laser check I hold up a peice of paper with a small hole over the bottom of the focuser (inside the tube) to see if the shadow of the centre spot centers on the hole - OK
Thats it.
Now visually, as per attached it sort of looks ok but I am worried about the area marked 3. As I see it the secondary appears centered in the FOV as does the primary (all clips shown etc.). Its the rings and centre spot at 3 that has me worried. The outer ring is at the top and the centre spot is off to the right. But as per above those two checks reckon its good but as i said my secondary has me worried (mostly cause I have really buggered around with it )
Anyway anyone care to comment?
Thanks
Took the scope out at about 7 after checking scolimation etc. and did a quick look at the moon (which looked good). Sat down the watch mythbusters to let it cool etc. and then the cloud rolls in and now its raining - Takes the scope back in
To be honest I have never been completely satisfaied that I have the secondary right (thus the question) but basically my procedure is:-
Hi Scooter - as Starkler and Rajah note, it is almost there. I've only bothered to respond because of your comment re the secondary; I encountered similar probs when re-coming to grips with collimating.
My solution, when I got to your final photo situation, was to go back to the secondary and re-centre and re-circularize it (for want of a better description) within the focusser tube. Basically, re-adjusting the sec to make sure it was as concentric/centred as possible in within the focusser tube. Then I went back to the primary adjustments - and then did the whole lot again for a third time!
It is my belief that re-iterating these procedures fixed the problem that you have stated you aren't quite happy about in the photo - I did this because no amnount of tweaking the primary from the position your example illustrates would sort that out. Incidentally, I use an Orion sight tube/chesire tool: don't own a laser job but my problem was exactly the same as yours'. My star tests are now producing superb diffraction rings (on good seeing nights!)
I've made similar posts a couple of times in IIS since I sorted my problem out inviting "wiser heads" to comment on my methodology and my assumptions; but so far no-one has responded - though I'm starting to form the opinion, based on other observations, that there are many people out there who really don't know a whole lot about collimation - or at least the finer points. Those that do could well take the attitude that it's much easier to demonstrate rather than articulate in a post: it is very hard to put it in words! (which means probably that no-one could understand my garble, that's why they didn't respond!)
It all depends on where the secondary mirror is attached to it's vanes - there are two different arrangements normally used, and you'll see different results for each one.
The two styles are called "offset" and "non-offset" (or "partially offset"). Before you can tell if you're seeing the right things you need to know which of these applies to you :-)
Most commercial scopes will go with "non-offset" secondary attachment, in which case your original image shows very good collimation. The small reflection of the secondary mirror should appear off-centre, that's normal.
There are many good resources on the net for help with collimation, google is your friend :-)
Hi Bird - partial offset (I think you meant by this "partial offset" not "non-offset") has been around for a very long time, as is "classical collimation" (again I think you transposed your terms): I believe that it is still the same mantra as when I stopped collimating when I packed away my scopes for an extended mothballing, way back around 1973 - ie "for partial off-set collimation the image of the primary mirror should be displaced slightly down the tube, in other words deliberately off-centre towards the primary for f5 (and particularly) below f5 newt scopes.
This practice was employed without any regard to the secondary mirror's mechanical "set" in the spider assembly, (in fact, I am unaware that any of them ever had anything but a centrally located secondary mirror.)
As to your assertion that they can have an "off-set" mechanical system I'll just have to take your word. However, with Scooter's "hazy" photo and my even hazier recollections of partial off-set collimation demonstrations I am in no position to comment re whether the image in his scope is tending to a partial off-set alignment or not.
I again ask/put out the request for "wiser heads" to give some input on this and my previous post re my own assumptions!
Don Pensack's excellent article in IIS seems to support my assumption re re-iterating the secondary-primary adjusting to arrive at a correct secondary alignment (ref approx para 16), and his alignment images (the first one, then the next RH side one) lead me to believe that these are partial off-set alignment diagrams, but I dunno!
Hi Bird - partial offset (I think you meant by this "partial offset" not "non-offset") has been around for a very long time, as is "classical collimation" (again I think you transposed your terms):
Cheers, Darryl.
Darrly, sorry I wasn't more clear - I didn't mean the terms to be read like that, I added the third option (partial offset) as an afterthought, not meaning to attach it to "non offset" :-(
I probably should have said there are *three* attachment schemes - non-offset, partial offset and full offset, that might have been clearer :-)
And they all look different when you're collimating so it's useful to know which one you've got.
Collimation is just a tad out on this old pic.
Slight adjustment of Primary was all it needed to get all concentric.
It 'doesn't look right' if viewed through focuser tube but star test is 'spot on'.
OK sort of makes sense (thanks for the link RAJ). So non offset = Bad and a Partial offset or full offset = Good. I am also of the opinion that any of these could be acheived (i.e spider sits secondary in the middle of the tube but it can go up or down the tube slightly as well as tilt).
No idea how I have mine set up up of course but will try to find some pics of how it should look online.
Just did another quick photo of the inner rings for ya K Man (hazy - I was working with a size limit ).
.....then of course in another thread I read someone had the center spot marked incorrectly now wouldn't that throw a spanner in the works
Scooter's picture shows a slight miscollimation, but everyone is correct to note the outline of the reflection of the secondary will not appear concentric in the collimated scope. AND, the reflection of the spider vanes will not be coincident with the wires in a sight tube, either.
It's difficult to get a good photo through the focuser or peep hole of a tool. It's so easy to be ever so slightly off angle, which results in parallax and the appearance of miscollimation even if the scope is properly collimated.
The laser/barlowed laser technique earlier described works fine to collimate a scope, but it does not set the original position of the secondary in regards to rotation or position under the focuser. It may be hard to realize this, but the secondary can be successfully collimated even if it is not centered under the focuser and even if it is improperly rotated. All this results in is uneven illumination around the periphery of the field and a slight tilt to the field (which is often ignored).
If this were not so, lasers would be useless in collimation, because only the axial (center) is collimated by a single beam laser. Off axis rays are not.
Which is why a sight tube is useful to use even if you primarily collimate with a laser.
A sight tube allows you to make the outline of the secondary concentric with the focuser (for even field illumination) and to make it appear round (for proper tilt of the focal plane and even edge illumination). So it's quite useful to at least start out with a sight tube, though crosshairs aren't necessary for those two operations. Then, a laser or sight tube will perform the same function for correcting the tilt of the secondary. Actually, when we adjust the tilt of the secondary, we are aligning it with the axis of the focuser, which is why it doesn't matter if the focuser is perfectly perpendicular to the tube.
Then, the laser techniques describe (single beam out, barlowed return) will do the mirrors just fine.
For f/6 or longer. For f/5 and shorter, better alignment is still possible and tolerances for miscollimation grow less as the f/ratio shortens. And if you use a Paracorr, tolerances near zero below f/4.5.
For the shorter f/ratios, an autocollimator (like the Catseye Infinity XL) becomes nearly essential, and can collimate the telescope equal to or better than a star collimation (it's actually easier than a star collimation). I have been very cautious when using a sight tube and cheshire (same ideas as laser and barlowed laser) yet still found residual errors with an autocollimator. Indeed, the autocollimator is SO sensitive one can see collimation changes with tube contraction in falling temperatures, or changes in collimation with the altitude of pointing if the mechanicals aren't solid enough (that's an entire thread worth there).
Careful use of an autocollimator will show you the best star images your instrument is capable of. I've said that I was surprised at how much the seeing improved when I learned to use an autocollimator and I meant it.
The overall key to doing collimation is to repeat the process beack and forth between the tools a couple times. Each movement as seen in one tool has an effect on what's seen in the other. By repeating and going back and forth you arrive at a condition where the tools and procedures all agree.
Hi everyone!!..
It's also a good idea to ensure that your focuser is correctly collimated and the focusing movement is smooth without any slack in or out..this has caused me a few headaches in the past!!!
Cheers!
)
but will try to find some pics of how it should look online. 
