Newtonian collimation. Overdone?

[Carbon Brush]

There are many posts on SGL covering collimation issues. I get the impression that some regard collimation as something to be done every time out.

Based on my experiecence, I disagree. There, a controversial statement to get you all reading and reaching for the reply button!

Many years ago when people started to get into 'hifi' rather than just listening to their record players, someone made an interesting statement to me. Something along the lines of....These hifi enthusiasts are so busy listening for the scratches and distortion, they forget to listen to the music.

Are we perhaps doing the same with collimation? Looking for the defects instead of enjoying the view?

A bit of history. My first newt was an Orion optics 8" F4. Collimation was **** at first. But that was because OO didn't build it properly. 3 very experienced people scratched their heads on this one before declaring 'send it back'. The second attempt by OO worked somewhat better and I learned how to collimate. But despite regularly carrying it on a car journey between houses, it did not need much attention.

Later I bought used OO 10" F4.8 scope to supplement the 8". The idea was to avoid the risk of damage from regularly transporting the scope. The biggest problem collimating the 10" was that my arms weren't long enough to wave a spanner on the primary nuts and look down the eyepiece. But once again, it required little attention in the collimation area.

Time passed and the OO scopes were sold on. Then I got a used SW 200P. More by accident than intent. It was a scope + mount package and I wanted the goto mount, planning to sell on the scope. A quick look at and through made me decide it was a nice scope and one to keep. This had been a first astro scope to the previous owner who had little knowledge in this area. So he would probably have relied on a 'grown up' to collimate for him. I then took it on an 80 mile car ride home. Collimation was basically OK on my first light. Since then I have made only minor adjustments at infrequent intervals.

My measure on collimation basically goes....When sideways pressure on the focusser, or a different 2/1.25" adapter makes the collimation look right or wrong, you know you are on the limit of what the scope mechanics will give you. Any adjustments are just going to have you running in circles.

The 200P has shown me detail on Mars at up to x285 when the sky allowed. Stars are not comets or blobs. They are points that often move and wobble due to unstable air. Usually the sky (not the scope) limits what I see.

If a newt needs attention every (or almost every) time out, there is something else mechanically wrong. Maybe the primary is moving side to side and needs the screws tightening. Maybe the heavy focus assembly is distorting the thin scope body. Maybe the spider is loose.

So a somewhat controversial view on collimation of newtonians.

I will now put on my hard hat, goggles, etc and awiat the replies!

[Peter Drew]

Controversial?, not really. It depends on what you expect of your telescope, a reasonably collimated Newtonian will give "satisfying" results specially on the Moon or DSO's but for planetary performance the best collimation is better. It's a bit like runnng a car, without much maintenance it will get you from A to B reasonably reliably, but if you want performance, economy and reliability a little attention is worthwhile. I do feel that the "difficulty" of collimating is overemphasised, once the procedure is understood and with a bit of practice it is straightforward. It is the mechanical design of the collimatable components that makes things difficult.

[DarkerSky]

A great post there David. Should be a sticky post IMO.

Its funny actually. I saw the post title and part of me was expecting to read another post about someone trying to collimate their scope to within a nanometer of its life again. I think the subject of your post David is long overdue.

In the late 80s when I bought my first newtonian I remember a vague discussion with Astro Systems about collimation. The general consensus of opinion in those days was that small newtonians (under 8") would rarely need collimation attention. based on that I bought a 6" from them, and later a 8.5", which I still have. In fact I bought the 8.5" in August 1990 - 22 years ago this month - and have NEVER collimated it. Sure, iv'e checked it with a cheshire and lasers, but nothing needs doing. Last February I took it to an outreach event. Granted I had a nice widefield baader hyperion ep in it for the event, but what was interesting was that 3 people remarked that it gave the best view of the M35 open cluster that they'd seen in any of the scopes that were out there (7 of various types and models IIRC)

I also now have a 12" OO solid tube and a 16" lightbridge. The 12" OO needs only slight attention. My 16" needs collimation checking every time I use it. That's mainly because I dismantle and reassemble each session. Its truss mounted so you're always going to get a bit of play anyway. But even that, now I have it sussed, requires no more than a minute's worth of tweaking.

With your skywatcher 150p and 200p's collimation should not really be an issue providing it has been done once properly, either by the retailer or the owner. Of course, careful transportation is always important. If the retailer ships the scope to you using a carrier then it could be possible that the mirror alignment shifts. If you can pick up the scope yourself from the retailer and put it across the backseat of your car, chances are you won't have to re-collimate unless you drop it.

[Mr Flibble]

In my experience any collimation issues or difficulty usually involve the secondary. Once this is set correctly it's pretty much a case of leave it alone and it will hardly ever need touching again. The primary is a doddle and if it needs a tweak its usually very slight and only takes seconds - for this reason I usually check when setting up, mostly for peace of mind because I transport via car to a dark site and its more than likely gonna get a bit of a knock. But yes, I agree with your post David.

[John]

I agree 100% with Peter. Collimation is the means to get the best performance out of the scope. It's less critical with deep sky observing but for planetary / lunar / binary stars, you need the scope to be on top form and that means in accurate collimation.

The faster the scope the more this is critical as the "sweet spot" where you get diffraction limited performance gets smaller rapidly as the focal ratio gets lower (faster). Plus the proportionately larger secondary will have more negative impact on image quality when the collimation is a bit out than the smaller obstruction in slower scopes.

It's not mandatory of course but personally I'd like to think that the £'s I've invested in my gear are delivering the best performance that the conditions allow.

[Capricorn]

I suspect that a truss tube dobsonian will go out of collimation pretty quick, Getting everything back to a repeatable position every time must be impossible.

A solid tube newtonian with good secondary supports will maintain collimation better.

Then is the scope carried outside carefully or put in a car lying horizontally and driven to a darker site then dragged out.

Not exactly the best thing to maintain the collimation that is expected.

I would equally say that if yopu collimated a newtonian then handed it to a different person they would still end up tweeking the collimation that you have just set, to get it right.

Much simpler to bin all the dobsonians and get a refactor.

Problem gone. :evil: :evil:

[NGC 1502]

Hi David, thanks for a breath of fresh air on this subject

There is a collimation article in Sept Sky & Telescope mag by Gary Seronik that takes a similar approach.

I often hear that a credit card should fit between the mirror clips and the mirror surface. I wonder how much expansion folks expect. Of course the mirror must never be clamped,

but not a good idea to have it flopping around all over the place either, especially if being transported in a car. Thickness of a credit card is way too much, just a smidge is enough.

Regards, Ed.

[acey]

An 8" f6 Newtonian rarely needs recollimating - I used to take mine out along bumpy roads regularly and I would collimate a couple of times a year using a punctured film cannister. If Jupiter's Moons looked spikey in steady seeing then I knew it was time to recollimate. Larger, faster scopes may need more regular tweaking, and collapsible ones certainly do - my 12" flextube shows slight miscollimation every time I reach my dark site (checked by Cheshire) so I always spend a minute or two collimating it.

But I totally agree, the subject is over-done, over-discussed, over-agonized. Saddest of all is that some potential scope users even seem to get put off buying a reflector because they read so many threads about collimation woes, and wrongly get the idea that a Newtonian is some kind of high-tech high-maintenance gizmo requiring constant attention and adjustment. It's like never wanting to get a guitar because you think you won't be able to tune it.

[eyepod]

"Saddest of all is that some potential scope users even seem to get put off buying a reflector because they read so many threads about collimation woes, and wrongly get the idea that a Newtonian is some kind of high-tech high-maintenance gizmo requiring constant attention and adjustment."

I was one of those people....!! but after you've done it once its no problem, I have a 8 inch flextube dob and the secondary i've only had to adjust twice, once when i got the scope out the packaging and then when i flocked the tube so had to remove it. Primary needs a very slight tweak after 2-3 observing sessions.

Jason

[ollypenrice]

I only use a Dob (a 20 inch F4.1 truss) for deep sky and I tend to agree with the OP that you can work yourself into a tizzie for no good reason. It gives a good DS view on imperfect collimation. It is never as good on the planets as a good refractor anyway but if you do want to do planetary with a Newt (as well you might) then collimation matters a lot more.

So for DS, don't get steamed up. For planetary, get your head round good collimation. As it goes dark I can be running around like a fly with a blue posterior and tickling up the Dob for observing at 80X is not time well spent.

Olly

[russ.will]

To extend the OPs metaphor; Sure, you shouldn't be tweaking the hi-fi rather than listeing to music, but there's no harm in checking for fluff on the stylus before you start.

I generally check collimation every time I observe, if only because a small tweak of the primary is so quick, why let the errors build up into a an extended session of fiddling? Thus far, I've never needed to adjust the secondary on either my 300p FlexTube, nor the 200p Explorer that preceded it, since the initial, careful setup. I would also note that the big FlexTube holds collimation extremely well, whereas the 200p seemed to wander off on a regular basis. Go figure...

It must be said that both were in a risable state out of the box, be it because of manufacturers tollerances, or courier abuse. Picking the scope up from the dealer may save one courier journey, but it was probably a courier that delivered it to the dealer, a haulier that brought it from the docks and another that brought it to the docks, prior to six weeks alternately cooking and freezing, on the high seas.

You may as well learn to collimate well, because you will have to, but do it right where the secondary is concerned first time and you'll seldom need to pay it much attention in the future.

Russell

[umadog]

I agree: for planetary observing with a fast Newt it's super critical. On a truss Dob the collimation needs tweaking much more often than a solid tube. Larger scopes with sling-based cells will tend not hold precise collimation if you transport them (that's been my experience, anyway). The tolerances for collimating a fast scope are tight, but modern gear makes it possible to hold everything rigid to within a fraction of a millimetre. It must do, or these sub f/4 beasts wouldn't work well (which they do when made right).

[squeaky]

I had a lot of "fun" collimating my 300P Flex recently.

The two main things I discovered about it, fresh from the box, was that the upper end of my OTA was slightly oval due to different tensions on the N-S and E-W spider arms, and that the clips on the primary were so loose that they rattled when I transported the scope in my car. I HAD thought that the rattle was the tommy bars for tightening the flex trusses but, as it turned out, it was those clips. My collimation at this stage was miles out every time I checked.

Having dealt with all those issues I now only have to do a quick check and a minor tweak before each session.

I made up my own "Bob's Knobs" 4mm x 40mm screws with 4mm wing nuts glued and screwed tight, so thirty seconds to centre my laser dot on the primary IF it needs it, and another thirty to nudge the primary.

Even so, most times (after packing it all in the car, setting up after a drive, repacking, driving home, unpacking to the shed....) the most "movement" I see now is that the laser dot will be on the edge of the donut instead of smack in the middle. Not going to cause a viewing problem if left alone but, as I say, it's now a piece of cake to get spot on.

[cotterless45]

I've never had to re collimate my 150p, it just stays true.The Lightbridge is a pain, but a stiff AE shroud keeps the truss tight and it's just a matter of tweaking.

Afraid I'm a hyper tweaker and use a Barlow with a laser in the end to tweak after a Cheshire check. This does pay off for planets, the detail, especially on Mars has been amazing.

When travelling with a solid ota, I semi inflate one of those awful red and blue camping mattresses and roll it around the ota, then bungie the lot to the headrest supports. A 1000 mile round trip and the collimation stayed true.

I've found that once the 2ndry is set, it is the primary that needs a tweak,

Nick.

[John]

Afraid I'm a hyper tweaker and use a Barlow with a laser in the end to tweak after a Cheshire check.....

The barlowed laser method is well worth looking into

http://www.smartavtweaks.com/RVBL.html

[LeeB]

I agree an f6 or higher has a good size sweetspot but I still like it dead on , my 10"00" rewards spot on set up. As to "refractors are best", they do have an edge on planets but most of the bad name/rap they recieve is from , I have never collimated brigade. An 8inch F7 plus well collimated scope is a pleasure on planets and will give any 5 or 6 inch fract a run for its money. I can't see the point of owning a 10 inch plus quality scope if it performs like a 6 inch seben.

[Black Knight]

This is an interesting thread, really useful.

[John]

I agree an f6 or higher has a good size sweetspot but I still like it dead on , my 10"00" rewards spot on set up. As to "refractors are best", they do have an edge on planets but most of the bad name/rap they recieve is from , I have never collimated brigade. An 8inch F7 plus well collimated scope is a pleasure on planets and will give any 5 or 6 inch fract a run for its money. I can't see the point of owning a 10 inch plus quality scope if it performs like a 6 inch seben.

All good points

Often it's only when you get a chance to try another scope similar to yours, that is in good collimation, that you realise the difference it can make.

[earth titan]

At last! Someone who agrees with my view of collimation.

I have an f4 and an f5 newt and the limitations are not in my opinion, due to the collimation of the optics.

My f4 suffers from focuser flex when I fit the camera, I live in a light polluted area and all the houses around me give of thermals. I get my collimation the best I can with a barlowed laser and check every few days.

My f5 is a truss tube and needs doing every time, but never seems to suffer too much.

I have floaters which get in the way, which make viewing a little problematic but okay.

You do the best you can but spending the same sum of cash on collimation tools as you would on a scope, seems to me to be the law of diminishing returns.

Typed by me, using fumms...

[Jason D]

An interesting thread....

But wouldn't the same argument be made for similar questions such as:

1. Why spend on a premium 10” scope for a reputable builder when you can buy at least 4 new mass produced 10” scope for about the same price? The cheaper mass produced scopes do give pleasant views of targets such as Saturn.
   
2. Why buy a premium eyepiece when you can get a stock eyepiece with similar specification for 1/5^th the price?
   
3. I can keep going with similar questions.
   

It all comes down to personal preference. Some are willing to pay more for what might be considered as small gains by others. This is a hobby. Everyone is free to spend their money whichever way they please.

With respect to collimation tools, the premium tools cost as much as a single premium eyepiece. There are a large number of amateur astronomers out there who own several premium eyepieces so the cost of premium collimation tools is a small subset of their investment. For those who think the price of premium collimation tools is not worth it then they should not buy them and there is nothing wrong with that.

Personally, I own premium optics, premium eyepieces, and premium collimation tools. In addition, I am someone who believes in having a perfectly collimated scope. I would check and fine-tune collimation several times during one session. Attending to collimation does take away little from my observation time but who is counting?

Jason

[LeeB]

Jason D , making perfect sence..

[Moonshane]

I'm in the middle. I check my secondary far less stringently than my primary. Each time I observe I adjust the primary, usually a minor tweak, takes a few seconds. My secondary etc I check every now and again, depending on the time I have. I recently used my 16" f4 dob masked to 170mm (f11) to view Zeta Herculis at 600x, obtaining a good split (obviously in excellent seeing) and 'perfect' diffraction/airy rings. My 6" f11 newt can be used at 400-500x to view lunar/doubles and rarely needs collimation adjustments other than the primary.

My 6" truss / travel dob does need a bit more work but once set up, again it's just primary adjustments.

[TheThing]

Is this turning back into one of collemation threads that the OP was against, quite rightly so.

If your collemation is out everytime you use a scope then you really need to look at the mechanics of the scope itself rather than keep collimating.

To use the car analogy from above, you wouldn't keep a car if every time you took it out you had to fill the oil, tune it up and put air back in the tyres. Likewise, you'd think twice about buying said car if the dealer told you you had to buy premium oil for it at 5 times the price of standard oil when it does the same thing!

Yes some scope will need collimating more than others, 16"+ or truss/collapsable. If you are collimating every few mins or hours though, no matter how quickly you can do it, you're wasting time and effort and you should be more concerned that you have problems with the scope.

My f5 6" was collimated for the first time in 3 years last week, only because it was slightly soft when imaging the moon. Visually, even on the planets at high mag, it wasn't problematic.

If it ain't broke...

TheThing

[NGC 1502]

Post #23 - If your collimation is out everytime you use a scope then you really need to look at the mechanics of the scope itself rather than keep collimating.

This is very definitely true. Like I mentioned earlier, it's often said a credit card should fit between the primary mirror surface and the mirror clips. That's way too much, and can let the mirror move around. Don't clamp it down, but just leave a tad clearance. Check for loose spider vanes as well, mirror collimation springs that are not stiff enough, focuser slack, flexible truss tubes or not a secure fitting each end etc.........lots of stuff to check, but well worth it.

Regards, Ed.