Why can't they make a dob that doesn't need collimating?

[jgroub]

Obviously, refractors almost never need collimating.  The objectives are factory aligned, and cemented in place.  My understanding is that basically, Maks almost never need collimating, or at least, it's very infrequently.  And, of course, I understand that a Mak is a different setup than a garden-variety Newtonian.  

But why can't the mirror cells and the secondaries be perfectly collimated at the factory, and then essentially locked into place?  Why do newts have to be collimated every time you breathe on them, or look at them funny, or even talk about them in another room?  How hard would it be to build them of sturdier stuff so that collimation would eventually be something only grandparents would talk about with their grandkids?  

The reason I ask is because collimation is yet another barrier to people entering into and enjoying this hobby.  It's the same thing as department store refractors advertising their wares by saying "600X!!!"  So, instead of buying the department store refractor, they take some advice from their friend who's into astronomy, and they buy a little reflector, a StarBlast, a FirstScope, a PowerSeeker, something small.  And lo and behold, either when the telescope arrives, or after a couple of uses, the scope is out of collimation, and the views are terrible.  The end user, who is not an expert in astronomy, doesn't know what they're doing and they can't fix it .  And they get frustrated and the scope sits in a closet collecting dust.  And that does no good for anyone.  

That's ridiculous.  We all rail about the department store telescopes.  I don't see anyone railing against this.  

Having reflectors that never need to be collimated would be a boon to the entire hobby.  To take an example from the computer world, the Altair 8800 was never going to take the consumer computer world by storm, because it was too hard to work worth.  It took the Apple and other easy-to-use computers to change that.  Not having to collimate cheap dobs would take our wonderful hobby out from the "you have to do everything yourself" niche and into the mainstream.  This would result in better equipment for everyone, at lower prices.  More people in the hobby would help enormously with light pollution mitigation efforts.  

Are there any technical explanations on how this could be done, or alternatively, why it can't be done?  It seems to me that it would be much easier to manage than in a refractor, because in a refractor, you've got two - or three - heavy objective lenses that are supported only around the edge, yet they are able to be factory-aligned and glued into place, then shipped over seas, handled roughly by longshoremen and delivery men, and yet arrive at your doorstep perfectly collimated.  

On a reflector, you have not only the edges of the mirror, but also the entire back of the mirror that can be used as support to get the collimation right.  How can this be done?  

[Moonshane]

Have you ever used a newtonian scope? Mine only need a full collimation if taken apart and usually need no adjustment or very little which takes seconds to do.

It is possible to create the support system you describe but at a prohibitive cost.

Would you say tuning a guitar prohibits new players who are keen to learn? Neither is hard to do or learn especially when shown by someone competent

[ronin]

To lock onto place the mirror would deform - glass is a strange material - also the weight would go up significantly, to keep something in place means a good solid infrastructure so the OTA tube material would need to be more substantial and so would the spider (bigger diffraction spikes).

I would guess that the weight would go up 4x or more.

If everything were locked then how do you clean a mirror that has problems - you cannot remove it as it would be fixed, yif taken apart then reassembly is a problem, the glass blank and the parabolic centre will not be the same so how do you get the parabolic centre at the right location if no adjustment.

The other side is what really does not need "checking".

Your car cost a lot more and that has a planned service annually.

[orions-knight]

Got a point about smaller reflectors though. 4" or less say. Probably a lot harder to collimate especially for a novice. 

[Beulah]

Excellent analogy Shane...

Quite happy to collimate - knowing that I can hone my collimating skills to ensure great images, can be satisfying and part of the whole experience - even with frostbitten fingers... 

Once mastered, it's like riding a bike.

[Dave_D]

read about this mirror when i was searching for diy serrurier truss designs... looks like a winner for simplifying the mounting of newt mirrors. i'm just wondering why other manufacturers haven't implemented something similar...

http://stargazerslounge.com/topic/206589-carbon-serrurier-truss-newtonian-10-f4-build/?hl=%2Bserrurier#entry2224689

http://www.rfroyce.com/conical/

although it doesn't remove the need for collimation, it should at least simplify the mounting requirements.

[ollypenrice]

Unfortunately the beginners don't want to pay much for their scopes, either. Good lens cells are better than bad ones...

Olly

[laser_jock99]

With the right tools and a small amount of experience collimation should be a breeze and not the barrier some people make it to be.

Admittedly I faffed around to begin with- but now it's a 30 second tweak. 

[pete_l]

...  they buy a little reflector, a StarBlast, a FirstScope, a PowerSeeker, something small.  And lo and behold, either when the telescope arrives, or after a couple of uses, the scope is out of collimation, and the views are terrible. 

It's my understanding that on the Orion Starblast 114mm Autotracker (AKA Skywatcher Virtuoso Heritage 1145p outside the USA) the rear mirror of this 4½ inch reflector is fixed so the only collimation that is possible is to the secondary mirror. Whether that's a step forward or not I'll leave up to others.

[Peter Drew]

It's not difficult or expensive to make smallish Newtonians that need little or no collimation over long time periods. At AstroSystems in the '70s and '80s, Newtonians from 4.5" to 8.5" aperture had their primaries and secondaries bonded into position, the "secret" was to bond a piece of 2mm thick felt to the mounting plate and then the optics to the felt. This method held the optics firmly in place without optical strain, ask any 6" FG1 owner.     

[nightfisher]

I have to admit to being a collimation numpty, however i was shown "how to" by Moonshane, and seeing as the secondary near as never goes out, i can now tweak my primary in about 5 seconds, so it really is no big deal

[John]

I've found that most of the refractors that I've owned did need some collimation attention. Once set they do hold collimation for long periods though. On quite a few refractors the focuser optical axis was not aligned with that of the objective lens and focusers rarely have the facility to alter that easily.

As has been said though, newtonian collimation is not really difficult or time consuming. Like most things a little learning and practice is needed but that goes for many other aspects of the hobby too. 

[RichM63]

Why can't they make a dob that doesn't need collimating?

How can a few bits of wood or bars of metal even be collimated?

[Ptarmigan]

Would you say tuning a guitar prohibits new players who are keen to learn? Neither is hard to do or learn especially when shown by someone competent

I tried to learn to play a guitar once,

everyone was pleased when I gave it to my Sis-in-law and returned to collimating my scope, which, I agree, is a doddle

[bomberbaz]

The Skywatcher 100p has a fixed primary mirror and you collimate with the secondary only. I did this once with the very smallest of twaeks when I got it 5 months since. This little scope has been treated rather roughly in comparison to my main scope, its been in and out of the car, back garden, front garden, you get my drift and it is still perfectly collimated. Its needs to be at F4 so if a begginer asked me wat to buy for a £100 to start up I would give them this as an option amongst any others.

[jamespels]

1. Collimating a scope isn't that hard, especially if you have Shane around to do it for you

2. Unless you are able to close and seal the tube at both ends, the mirror is going to need a clean at some point. Fracs manage this because the objective and focuser essentially form two ends of a sealed tube; a newt is necessarily open at the end so the same does not apply.

3. Some scopes really do not take much collimating. My beloved (sadly now sold, which I still regret) Tal 2 could go through most of a season of car trips, being knocked by the kids and so on and stay perfectly aligned. My SW250P, on the other hand, goes out every few moves.

The options for learning collimation...

1. See Shane

2. See somebody who Shane taught

3. Read Astro Baby's guide to collimation (just Google it)

(no offence to anybody who didn't learn from Shane, btw!!!)

[Moonshane]

Lol

I'm not that good!

[LeeB]

It's not difficult or expensive to make smallish Newtonians that need little or no collimation over long time periods. At AstroSystems in the '70s and '80s, Newtonians from 4.5" to 8.5" aperture had their primaries and secondaries bonded into position, the "secret" was to bond a piece of 2mm thick felt to the mounting plate and then the optics to the felt. This method held the optics firmly in place without optical strain, ask any 6" FG1 owner.     

Great point about astro systems, from my sig. you can see i have afew newts but the astro systems 150fg  holds colli very well, example drove to lucksall last weekend , scope 100miles there and back on parcel shelf after the bumps and a stop start return journey, checked it and it was still dead on. not close but dead on, a little more fiddly to do originally but I honestly think you could drop it and it would'nt budge. Mine wasnt bonded though it uses nylon locks on all axis.

The tal also hold colimation but does it because its built like a tank.

As for the other scopes, the faster they are the tighter the tolerance, but as moonshane states its not difficult and most only need a minor tweak unless disassembled.