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My dob never needs collimation?

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#1 pepit

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Posted 14 August 2014 - 01:18 PM

Hello!

 

So my 10 inch dob has seen some quite long trips, but since I got it in December last year I have never needed to collimate it. It's just always ready to observe. I am surprised at this, considering I have heard people say they collimate their reflectors every time they observe.

 

Any similar experiences?

 


Edited by pepit, 14 August 2014 - 01:19 PM.


#2 Doug Culbertson

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Posted 14 August 2014 - 01:33 PM

I used to have a 10" Z Scope, a dobsonian from a short lived company called Z-Optical. I owned that telescope for four years, and only had to collimate it once; the day that I brought it home after buying it from the previous owner. I checked collimation every time that I took it out, and back then I drove to a remote site at least four times a month, and it always threw up some amazing images.  A telescope like that will spoil you.


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#3 beatlejuice

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Posted 14 August 2014 - 03:27 PM

Mine holds collimation quite well to a certain degree, but it still needs a tiny amount of tweaking every time out to get it exactly where I want it.  It on!y takes a couple of minutes with the Glatter tools. Not sure if I could notice the required tweaking if I was using a sight tube or combo tool and it would probably be OK on many targets without the tweaking but when it comes to planets I just feel better knowing that I am as close as I can get with the tools I have

 

Eric



#4 Jon Isaacs

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Posted 14 August 2014 - 03:37 PM

I am curious how you are collimating your scopes?  How critical are you concerning the alignment of the primary?  

 

:question:

 

Jon



#5 pepit

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Posted 14 August 2014 - 03:57 PM

I am curious how you are collimating your scopes?  How critical are you concerning the alignment of the primary?  

 

:question:

 

Jon

I am not very critical - if stars look relatively round, I consider that good enough. I very rarely check the mirrors, but when I do, they look spot on, at least to me.


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#6 pga7602

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Posted 14 August 2014 - 04:04 PM

 

I am curious how you are collimating your scopes?  How critical are you concerning the alignment of the primary?  

 

:question:

 

Jon

I am not very critical - if stars look relatively round, I consider that good enough. I very rarely check the mirrors, but when I do, they look spot on, at least to me.

 

 

When you do check them, what tools are you using?



#7 LDW47

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Posted 14 August 2014 - 04:08 PM

Hello!

 

So my 10 inch dob has seen some quite long trips, but since I got it in December last year I have never needed to collimate it. It's just always ready to observe. I am surprised at this, considering I have heard people say they collimate their reflectors every time they observe.

 

Any similar experiences?

I have mentioned the same several times on here but the people with a lot more technical knowledge / experience on here never seem to believe it, they seem to think it is impossible. Especially when many of them check / have to adjust the collimation in their scopes each and every time they use them even if they have hardly been moved around over any great distances. I really don't know what people like us or other similar are doing right / wrong but I like it ! The few times I have checked my two Dobs with my Cheshire they seem to be OK and give great views.


Edited by LDW47, 14 August 2014 - 04:09 PM.

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#8 LDW47

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Posted 14 August 2014 - 04:10 PM

 

I am curious how you are collimating your scopes?  How critical are you concerning the alignment of the primary?  

 

:question:

 

Jon

I am not very critical - if stars look relatively round, I consider that good enough. I very rarely check the mirrors, but when I do, they look spot on, at least to me.

 

I have mentioned the same, see my post !  As a matter of fact I transported my 6" Dob 13.5 miles by boat to my remote camp this spring and it still gives great views, go figure, I am sure not blind ?


Edited by LDW47, 14 August 2014 - 04:20 PM.

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#9 LDW47

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Posted 14 August 2014 - 04:11 PM

Mine holds collimation quite well to a certain degree, but it still needs a tiny amount of tweaking every time out to get it exactly where I want it.  It on!y takes a couple of minutes with the Glatter tools. Not sure if I could notice the required tweaking if I was using a sight tube or combo tool and it would probably be OK on many targets without the tweaking but when it comes to planets I just feel better knowing that I am as close as I can get with the tools I have

 

Eric

Have you ever asked yourself how good the tweaking was if the seeing conditions aren't close to perfect on any given night ? Do you think maybe it was all for not sometimes if that is the case ? Unless you are a perfectionist, which many of us are not, tweaking doesn't mean much but I do realize that this erks the perfectionist mind and I apologize !  I was one myself at one time and still am on certain issues but not this one.


Edited by LDW47, 14 August 2014 - 04:21 PM.


#10 LDW47

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Posted 14 August 2014 - 04:23 PM

I used to have a 10" Z Scope, a dobsonian from a short lived company called Z-Optical. I owned that telescope for four years, and only had to collimate it once; the day that I brought it home after buying it from the previous owner. I checked collimation every time that I took it out, and back then I drove to a remote site at least four times a month, and it always threw up some amazing images.  A telescope like that will spoil you.

Sounds like my experiences !



#11 FrostyThe2nd

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Posted 14 August 2014 - 04:53 PM

I always collimate my scopes every time I set it out to observe.  My bigger scope tends to require more tweaking.  Personally, it's a fun and rewarding game that involves shooting a laser beam to achieve a prized image.  With a Glatter and Bob's Knobs thumb screws, it takes less than 2 minutes.    



#12 Doug Culbertson

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Posted 14 August 2014 - 04:57 PM

I am curious how you are collimating your scopes?  How critical are you concerning the alignment of the primary?  

 

:question:

 

Jon

 

Jon, back in those days I was using the best tools available to me; an Astrosystems laser (remember the big gold one?) and a set of Tectron collimating tools. That old Z-scope just held collimation forever. I did forget that I had to recollimate it after I had the mirror refigured.  :)



#13 beatlejuice

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Posted 14 August 2014 - 05:10 PM

 

Mine holds collimation quite well to a certain degree, but it still needs a tiny amount of tweaking every time out to get it exactly where I want it.  It on!y takes a couple of minutes with the Glatter tools. Not sure if I could notice the required tweaking if I was using a sight tube or combo tool and it would probably be OK on many targets without the tweaking but when it comes to planets I just feel better knowing that I am as close as I can get with the tools I have

 

Eric

Have you ever asked yourself how good the tweaking was if the seeing conditions aren't close to perfect on any given night ? Do you think maybe it was all for not sometimes if that is the case ? Unless you are a perfectionist, which many of us are not, tweaking doesn't mean much but I do realize that this erks the perfectionist mind and I apologize !  I was one myself at one time and still am on certain issues but not this one.

 

 

Well, since it only takes a couple of minutes to do, I never have to ask myself anything.

 

Eric



#14 LDW47

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Posted 14 August 2014 - 05:26 PM

 

 

Mine holds collimation quite well to a certain degree, but it still needs a tiny amount of tweaking every time out to get it exactly where I want it.  It on!y takes a couple of minutes with the Glatter tools. Not sure if I could notice the required tweaking if I was using a sight tube or combo tool and it would probably be OK on many targets without the tweaking but when it comes to planets I just feel better knowing that I am as close as I can get with the tools I have

 

Eric

Have you ever asked yourself how good the tweaking was if the seeing conditions aren't close to perfect on any given night ? Do you think maybe it was all for not sometimes if that is the case ? Unless you are a perfectionist, which many of us are not, tweaking doesn't mean much but I do realize that this erks the perfectionist mind and I apologize !  I was one myself at one time and still am on certain issues but not this one.

 

 

Well, since it only takes a couple of minutes to do, I never have to ask myself anything.

 

Eric

 

There is difference between just checking it as part of the fun / interest in this great hobby and actually having to adjust it because it has gone out of whack for some reason as many claim it does. I'd be a bit worried if it did for no apparent reason other than moving it a bit and was careful not to bump it while moving around, after all they are pretty solidly built and are not that fragile / sensitive. No big deal, to each his own !



#15 Starman1

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Posted 14 August 2014 - 05:31 PM

I have seen 6" and 8" newtonians that pretty much stayed collimated.

I have never, ever, seen a 10" or larger that did.

Now it's conceivable that if the mirror cell is really locked down, and the clips press against the mirror with firmness,

that a 10" might stay collimated after a brief car ride.

I've never seen it, but it's conceivable.

It depends on the resolution of the tools, for one thing.

If the scope is collimated with a combination sight tube/cheshire, it's possible.

If the scope is collimated with the 3 Catseye tools?

Heck, most scopes don't even hold collimation merely by moving them up and down in the resolution of an autocollimator.

Let alone after travel in the back of a car.

I would argue that if the mirror clips hold the mirror that tightly, they are too tightly pressed against the mirror.

I'm dubious.


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#16 LDW47

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Posted 14 August 2014 - 05:42 PM

I have seen 6" and 8" newtonians that pretty much stayed collimated.

I have never, ever, seen a 10" or larger that did.

Now it's conceivable that if the mirror cell is really locked down, and the clips press against the mirror with firmness,

that a 10" might stay collimated after a brief car ride.

I've never seen it, but it's conceivable.

It depends on the resolution of the tools, for one thing.

If the scope is collimated with a combination sight tube/cheshire, it's possible.

If the scope is collimated with the 3 Catseye tools?

Heck, most scopes don't even hold collimation merely by moving them up and down in the resolution of an autocollimator.

Let alone after travel in the back of a car.

I would argue that if the mirror clips hold the mirror that tightly, they are too tightly pressed against the mirror.

I'm dubious.

I have 6 & 8" Dobs so I can't speak for anything larger, I am just glad I get such great views with out having to adjust ! Nothing can bounce around more than a 13.5 mi.boat ride but my scope is well stored in a solid wood case, foam lined and it came through with out problems.



#17 Kipper-Feet

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Posted 14 August 2014 - 05:46 PM

This thread reminds me of the dear old bag lady living on the street who was asked why it was that she carried a thermometer in her shopping cart.

 

"Well," she answered with a snarly smile, "when sleeping on the streets at night, how would I know how cold to get if I did not have a thermometer?"

 

My collimation tools are all home made. Using a sight-tube, a Cheshire Eyepiece and a Cheshire/sight-tube combo tool, I have purposely put my primary mirror out of collimation to see what effect it would have on the image in the FOV.

 

I have since determined that, under my skies, with my gear and as viewed through my eyes, there is a remarkably large 'collimation' tolerance zone in which the quality of the image does NOT change at all.  

 

To quantify this.  With my Cheshire type tools I'm adjusting the tilt of the primary mirror to move the reflection of the peep-hole into the center of the doughnut. This is more like what a user would see in a well illuminated collimation cap rather than a typical Cheshire/sight-tube with a well illuminated inclined plate.  

 

The doughnut decal is white but appears to be black in the reflections.  The peep-hole is blocked by my eye and so appears to be black against the grey colour of the Cheshire's cap.  Ergo, a black doughnut and a black peep-hole seen against a well illuminated light grey background.

 

The peep-hole on all my tools is 1.6mm in diameter.  My doughnut has an inner dimension of 3.7mm.  I am finding that if the reflection of the peep-hole is moved anywhere inside the inner circle of the doughnut, there is no additional advantage in tweaking the primary.

 

It matters not if I move it middle-for-diddle.  The image does not improve.

 

If, after setting up and cooling, the reflection of the peep-hole is seen to already be somewhere, anywhere, inside the doughnut, then I do nothing else.  If the peep-hole appears to be somewhere behind, or away from the doughnut, I quickly tweak it to somewhere inside and that's enough.  Genuine!

 

Likewise when it came to checking the centring of my doughnut decal on the primary.  I figured that if it's centre was within 2.4mm of the actual optical centre of the cheap, mass produced Synta mirror, it was within tolerance and good enough.  It was and I left it alone.


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#18 coutleef

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Posted 14 August 2014 - 06:37 PM

I am surprised at this

 

my 12 inch requires collimation each time because of temperature swings between nights!



#19 Dennis_S253

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Posted 14 August 2014 - 07:10 PM

I haven't had a problem with my Z12. Of course I only take it from my room to outside on a dolly. Views seem to always be good. No big bumps or anything. I don't know.


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#20 Brian Carter

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Posted 14 August 2014 - 07:36 PM

I would argue that if the mirror clips hold the mirror that tightly, they are too tightly pressed against the mirror.
I'm dubious.


+1.

Mirrors should "float" a bit, which means they move.

I'm also dubious to all this. My first 10" held collimation reasonably well because the mirror was glued to a piece of wood in a sonotube. Even the cheapest dobs these days are better than that, which means they aren't going to hold collimation. But of course the views look great, it's a big mirror so you're going to see plenty, even if the mirrors are just barely aligned. Still not getting nearly what you could get if you just spent five minutes with some decent tools before each session. That's the trade off with a dob: you get a big cheap piece of glass that gathers lots of light for almost no money, but you have to turn a couple screws before using it and push it around to see stuff.

These collimation threads are frustrating, it's amazing how so few reflectors need collimation these days. Makes me feel like my scope is junk.

#21 AhBok

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Posted 14 August 2014 - 07:48 PM

If I only used a Cheshire to collimate my AD12, I would think it stayed pretty well collimated for a week or two at a time and maybe more. The autocollimator, though, reveals the small collimation errors that make the difference in great vs. ok views of the planets on nights of good seeing. If I am not looking at the planets, I only check collimation with the Cheshire, but when viewing detail on Mars, Jupiter or Saturn, I find the autocollimator a must and a few small tweaks are always required.



#22 17.5Dob

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Posted 14 August 2014 - 07:49 PM

I guess it all depends on how particular you are with your viewing.

Both of my past two incarnations of my 17.5" were true dobs. I'd remove the mirror from the "back door" and it's porch chair polypropylene webbing sling, sitting on the homemade 9 point flotation adjustment, with just a couple of "security clips", each and every night.

The first thing I'd do on the next session, while waiting for the mirror to equalize, was a quick in and OOF star check. If all I was trying to do was track down a few obscure NGC galaxies or "pleasure viewing" some big WF nebula, as long as my stars were in the ball park, that was close enough. Come on now, at 65X, I'm not planning on splitting sub arc sec double stars, or trying to see as many lanes in Saturn' s rings as possible ! Heck, even the maximum magnification I use, or even have available is only 222x.

I didn't build a 17.5" f4.5 to do planetary observing or AP. It's just a light bucket, "close enough" is just fine.


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#23 LDW47

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Posted 14 August 2014 - 09:37 PM

I am surprised at this

 

my 12 inch requires collimation each time because of temperature swings between nights!

What's that got to do with mirror alignment ? There is no way average temp swings are going to do that !



#24 LDW47

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Posted 14 August 2014 - 09:41 PM

 

I would argue that if the mirror clips hold the mirror that tightly, they are too tightly pressed against the mirror.
I'm dubious.


+1.

Mirrors should "float" a bit, which means they move.

I'm also dubious to all this. My first 10" held collimation reasonably well because the mirror was glued to a piece of wood in a sonotube. Even the cheapest dobs these days are better than that, which means they aren't going to hold collimation. But of course the views look great, it's a big mirror so you're going to see plenty, even if the mirrors are just barely aligned. Still not getting nearly what you could get if you just spent five minutes with some decent tools before each session. That's the trade off with a dob: you get a big cheap piece of glass that gathers lots of light for almost no money, but you have to turn a couple screws before using it and push it around to see stuff.

These collimation threads are frustrating, it's amazing how so few reflectors need collimation these days. Makes me feel like my scope is junk.

 

So basically what are you saying to all us fortunates that don't require constant collimation on our so-so Dobs ? I guess we aren't as lucky as some that own Dobs that require never ending collimation !  Right ! We only call them like we see them, nothing more / nothing less.


Edited by LDW47, 14 August 2014 - 09:42 PM.


#25 LDW47

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Posted 14 August 2014 - 09:44 PM

If I only used a Cheshire to collimate my AD12, I would think it stayed pretty well collimated for a week or two at a time and maybe more. The autocollimator, though, reveals the small collimation errors that make the difference in great vs. ok views of the planets on nights of good seeing. If I am not looking at the planets, I only check collimation with the Cheshire, but when viewing detail on Mars, Jupiter or Saturn, I find the autocollimator a must and a few small tweaks are always required.

Does it overcome all the nights when seeing is only so-so, if not then whats the big deal ?








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