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Why settle with reflector scopes when refractors have no collimation?


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Collimation seems to be one of the most annoying things I've encountered in this hobby, after buying a 8" RCT I often wondered why did I do that when I could have just bought a bigger refractor scope and not have to worry about that? I see people in my astronomy club get just as good pictures if not better than mine. Why are those scopes designed like that in the first place? and why can't they design them so they can already be permanently and accurately collimated, it just makes no sense to me!

Edited by Quetzalcoatl72
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Sounds like you need a mak or a Classical Cassegrain. The mak should never need collimating and the Classical Cassegrain almost never needs collimating. Never had to colimate my Classical Cassegrain since I got it over a year ago.

 

Edited by johninderby
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5 minutes ago, johninderby said:

Sounds like you need a mak or a Classical Cassegrain. The mak should never need collimating and the Classical Cassegrain almost never needs collimating. Never had to colimate my Classical Cassegrain since I got it over a year ago.

 

i was going to get the RCT CC but i thought the f/l was too long

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I have collimation experience only on a newtonian and to be honest it's not really that hard to do...  Sort of have become part of the routine for me at the beginning of each session. RCT might be more time consuming though...

Oh and refractors can be out of whack too...

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5 hours ago, Quetzalcoatl72 said:

you end up spending 400+ on a collimation kit though

Collimation kit for a reflector can be as low as 2 sheets of differently coloured cardboard and a Cheshire Collimator.

No need to spend £400+.

Edited by iapa
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I use a £10 laser collimator and it takes about 1 minute or less to do. I tweak it maybe once a month if that. I genuinely spend more time walking up and down the garden putting the Bahinov mask on

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1 minute ago, JSeaman said:

I use a £10 laser collimator and it takes about 1 minute or less to do.

Same.

In my case was price what drove my decision to Newt.

Edited by barbulo
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Reflectors are centuries old, pre-dating lasers by some time, ergo collimation processes without a laser must have been determined, e.g. collimation caps.

I do have a cheap laser, took me many hours to collimate the laser reasonably.

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6 hours ago, Quetzalcoatl72 said:

you end up spending 400+ on a collimation kit though

I got a Cheshire collimator for £25 and it seems to do the job! I do have a background level of dread that I'm doing it wrong but I'm happy enough with the images I take.

It appears from my experience that keeping a reasonably  well collimated scope collimated by moving the primary is pretty straightforward - I'd expect it's much harder when you need to move the secondary mirror.

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People are emotive about collimation and approach it with fear.  Why?  You can't break anything and it is a mickey mouse job to do once you get the hang of it.  If you are into reflectors, you need to get into collimation.  Commit to yourself that, one night, you are going to master this, come what may.  It's like repairing a puncture if you are a road cyclist; something you have to know how to do as part of the activity.

To answer the original question, people want reflectors in one of their various guises for their aperture.  Big, quality refractors are megabucks and become enormous when you get past the 7 inch aperture - assuming you have the funds for such an aperture which will be tens of thousands whereas a 8" reflector is a couple of hundred.

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10 hours ago, Quetzalcoatl72 said:

why can't they design them so they can already be permanently and accurately collimated,

This isn't as easy as you think. Even if the mirrors are fixed there is always flex/movement in the OTA itself, especially after the odd drop or knock. 

A truly fixed collimation reflector would probably weigh an awful lot considering the extra strength of the OTA necessary. 

Besides, refractors are supposed to not require collimation yet I've owned three fracs and the first one was out of collimation in the lens cell and not adjustable. The second had misaligned objective and focuser which wasn't adjustable either but was bodged with shims to line up. The third was perfect. 

Edited by CraigT82
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I’ve found where many beginners get themselves into difficulties with collimation is when they make massive adjustments to the primary and secondary and get so far from being collimated that they just get hopelessly lost. Just minor tweeks is usually all that is needed and of course with experience it becomes a simple process.

I now use a Concemtre to set up the secondary. Far more accurate than any other method. 

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10 hours ago, Quetzalcoatl72 said:

Collimation seems to be one of the most annoying things I've encountered in this hobby, after buying a 8" RCT I often wondered why did I do that when I could have just bought a bigger refractor scope and not have to worry about that? I see people in my astronomy club get just as good pictures if not better than mine. Why are those scopes designed like that in the first place? and why can't they design them so they can already be permanently and accurately collimated, it just makes no sense to me!

Hi, I think you've chosen an ambitious starting point in the world of reflectors, so I can understand way you're frustrated. RC's are very fiddly to collimate, the pay off being you get that lovely flat aberration free field of view. They are not impossible to collimate, but when for example I had mine, the only method that worked for me was to defocus a star in the centre of a good eyepiece, then make very minor adjustments until the defocused star became more symmetrical. It was trial and error as to which collimation screws to turn. Once done it's was done unless travelling anywhere in which case collimation could, or should I say would get knocked out of alignment.   

When it comes to reflecting telescopes I would always always recommend that someone starts with either an f/5 or above Newtonian or an SCT. These are way more collimation friendly :) Many entry level Newtonian telescopes now days even have factory fixed primary mirror. 

I think the precision of RC's requires them to be adjustable really. If you tried to fix an RC's collimation in place, not only would it add great cost to the purchase price with all the bench testing and skill required to do that, if it ever had a hard knock and moved a millimetre the telescope would quite possibly be unfixable by anyone other than the manufacturer. The factory fixed Newtonians I mentioned would still be adjustable via the secondary mirror, and I think they can get away with fixing the primary because the tolerances are typically much larger than an RC.

EDIT: Oh, and as others have said, Reflectors are much more practical and affordable at larger apertures which is why most modern professional observatories use them.       

Edited by Lockie
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Just now, johninderby said:

I’ve found where many beginners get themselves into difficulties with collimation is when they make massive adjustments to the primary and secondary and ……………

Me, me, me !!!!

I stripped my Quattro 10CF to it’s component parts and spent some time putting it all back, but checking everything was spot on as I went.

Never needed doing since

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Yeah, collimation is a pain but well worth learning to do. I do prefer a ‘frac though that you can pretty much buy, use and never worry about collimation unless you have a major drop or knock on it. Was out last night collimating 2 scopes; 1st one C8 SCT. Took around 20 mins to do to get it pretty much spot on via a star test on Polaris. The next scope took much longer, my Stellalyra 6 RC. Took ages to do, but finally with very small incremental adjustments back and forth on the 3 screws on the secondary did finally fall right. In all I think I spent an hour doing that which was 3 times longer than the collimation my SCT took.

Edited by Knighty2112
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learning to undertake a collimation procedure regarding a reflector, I think assists to get to understand the optical light path alignment a bit better and appreciate the instrument you are using. On most occasions it is just a slight routine chore, not unlike if you were to go out cycling, you would check your tyre inflation, brake cable tensioning etc. I think that there is certainly plenty to be learned concerning gaining accurate collimation. I use a simple Rigel collimation cap and may combine a Cheshire eyepiece, investment in other tools would perhaps gain yet more accuracy. 

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10 hours ago, Quetzalcoatl72 said:

you end up spending 400+ on a collimation kit though

I made my first one for free. The one I have now was less than £20.

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I can't speak on behalf of everybody but I feel that there is a general 'fear of collimating. I know I certainly was at first but once you do it a few times it becomes a second nature.

I would go as far as saying that I actually find it quite therapeutic now......🤔

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