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Importance of collimation


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I keep my 8" Dob on a trolley in the barn, then wheel it out - sometimes at very short notice - whenever the skies are clear.

The yard outside is smooth enough for cars and shoes but a 5" solid rubber-tyred trolley wheel feels every bump.  Four of them each feels a different bump so the 'scope gets a bit of a jolting before it reaches prime position.  Then it goes through a different pattern of jolting on  the way back.  The other morning I was trying to view the four planets in the east before dawn and was finding it difficult to focus, especially on Jupiter which is usually pretty clear.  As the sun was rising I gave it up but made a mental note to check the collimation.  I had checked it a month before to demonstrate to a friend who had just bought a 'scope and it was OK then but now it was way out.  Viewing the moon tonight I was astonished at the clarity.  I must have gradually got used to a degradation that only became apparent the other morning.

When I bought the 'scope earlier this year, my first ever, I was told it would not need collimating that often.  Well, maybe the dealer didn't put his products through the same treatment as me but I shall be checking my collimation as a matter of routine from now on.  I wonder how many new observers risk, like me, failing to obtain the optimum benefit of good eyepieces from inaccurate collimation.  For me  a valuable lesson learned.

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Under the circumstances you describe, your Dobsonian is having a veritable workout?

I would either cushion the scope against the vibrations, by using cot mattresses or duvets, or change the mode of transport, to something with a little more spring / suspension.

My scope can be separated, the OTA being lighter than the base, makes for two journeys, but no vibration when carrying the lighter optical tube assembly (OTA), but my journey into the garden is not far and I can carry the Skyliner as a complete unit.

I only collimate my scope these days for the fun of it?  something to do when its cloudy! as it seems to hold collimation quite well, otherwise it just gets a quick visual with a Barlowed laser before observing,  I don't expect to use any tools! I have not yet had to collimate my scope away from home or upon reaching the end of my small garden!

The primary mirror itself,  should be no more than just held in place by the mirror clips, NOT held tight! so any movement is inevitable if it feels every bump on its short journey to its final location, and your requirement to re-collimate after every move?

Some folk will collimate for every occasion, part of their routine but the golden rule should be, like everything else, just check first, and if it don't need it, don't try to fix it!  Treat like Glass - Handle with care,  less to worry about.

Edited by Charic
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I check the collimation of my dob each time I use it. Most often it just needs a little fine adjustment but it's part of my setting up process and only takes a few seconds. Like a guitar player adjusting tuning the guitar before playing I guess.

The think the dealers advice was possibly a little mistaken.

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As mine is the flex tube variant I collimate mine everytime it is used. Usually the secondary has drifted by up to an inch, the primary needs very little tweaking. Due no doubt to the secondary being fitterd in the top section on the flextube.

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It is important to keep good collimation. Once you get used to doing it it takes hardly any time at all. Your poor views of the planets may also have been due to poor seeing conditions. Jupiter is low in the morning sky and the atmosphere is liable to be turbulent.

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Under the circumstances you describe, your Dobsonian is having a veritable workout?

I would either cushion the scope against the vibrations, by using cot mattresses or duvets, or change the mode of transport, to something with a little more spring / suspension.

My scope can be separated, the OTA being lighter than the base, makes for two journeys, but no vibration when carrying the lighter optical tube assembly (OTA), but my journey into the garden is not far and I can carry the Skyliner as a complete unit.

I only collimate my scope these days for the fun of it?  something to do when its cloudy! as it seems to hold collimation quite well, otherwise it just gets a quick visual with a Barlowed laser before observing,  I don't expect to use any tools! I have not yet had to collimate my scope away from home or upon reaching the end of my small garden!

The primary mirror itself,  should be no more than just held in place by the mirror clips, NOT held tight! so any movement is inevitable if it feels every bump on its short journey to its final location, and your requirement to re-collimate after every move?

Some folk will collimate for every occasion, part of their routine but the golden rule should be, like everything else, just check first, and if it don't need it, don't try to fix it!  Treat like Glass - Handle with care,  less to worry about.

Either I need to relay the yard with fresh tarmac or invest in pneumatic tyres on bigger wheels.  Bit too old and grey to carry and fit the OTA and base separately at 4.30 in the morning, two of my sessions recently.  But thanks.

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It is important to keep good collimation. Once you get used to doing it it takes hardly any time at all. Your poor views of the planets may also have been due to poor seeing conditions. Jupiter is low in the morning sky and the atmosphere is liable to be turbulent.

That was my first thought, but there has been little change between daytime and night time temperature locally so no heat haze and no local industrial pollution, Tonight the moon was about on a level where I expect to see Venus in a few hours time. Moon was crystal clear tonight.  If the skies are clear I'll be out at 5 this morning and hope to see an improvement.  If not I'll be happy to blame atmospherics this time but in future will check collimation routinely.  Crikey, I'd better get to bed!

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Either I need to relay the yard with fresh tarmac or invest in pneumatic tyres on bigger wheels.  Bit too old and grey to carry and fit the OTA and base separately at 4.30 in the morning, two of my sessions recently.  But thanks.

You could make a simple sling and carry the tube over your shoulder. Length of rope or fabric knotted to form a complete circle, lay it on the ground, lay the tube on top of it, gather the two opposite loops together, put your arm through them and off you go. Just need to make sure they don't slip on the tube, but there are lots of solutions for that, such as a couple of strips of old bicycle tyre incorporated into the sling. Be a lot cheaper than Tarmac.

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I have to recollimate every time I use the scope as mine is a truss tube obsession style. Takes about 30 seconds and I'm ready to go. No big deal. My scope has 2x 10" pneumatic wheels on wheelbarrow handles. I can move that over anything and it doesn't feel the bumps.

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You could make a simple sling and carry the tube over your shoulder. Length of rope or fabric knotted to form a complete circle, lay it on the ground, lay the tube on top of it, gather the two opposite loops together, put your arm through them and off you go. Just need to make sure they don't slip on the tube, but there are lots of solutions for that, such as a couple of strips of old bicycle tyre incorporated into the sling. Be a lot cheaper than Tarmac.

Thanks KenG,

I keep the Dob in a dry, stone-built barn.  I built the trolley from an old packing case with wheels I bought on line.  The Dob is permanently mounted on this trolley.  The surface to the yard was laid at least 50 years ago, possibly longer, from unevenly shaped stones about the size of a baby's fist and held together by tar.  My viewing  position is no more than ten metres away.  Just lately the evening sky has been mostly cloudy but the sky before dawn has been magnificent.  So, if I wake up early, by accident or design, I slip an old padded coat over my pyjamas, head for the barn and I'm observing in three minutes. 

I'm truly grateful for your suggestion but I was being slightly ironic in response to a previous reply.  Re-laying the drive would cost thousands and I'd rather spend the money - if I had it - on a bigger 'scope but I do love the convenience of just hauling the trolley straight out.  Also I need to move around the yard to get clear views of different objects otherwise obscured by buildings or trees.  Low-pressure tyred wheels will be on the list when I'm next in UK but, again in response to another suggestion, I have devised a scheme to lay tubes of foam insulation across the existing trolley base with a second base installed, on which the Dob will stand, cushioned by the foam to reduce the jolting.  I'll be doing that tomorrow.  But thanks again for the suggestion.

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I have to recollimate every time I use the scope as mine is a truss tube obsession style. Takes about 30 seconds and I'm ready to go. No big deal. My scope has 2x 10" pneumatic wheels on wheelbarrow handles. I can move that over anything and it doesn't feel the bumps.

10" wheels, by George!  Tempting idea.  Thanks, John.

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My 10" Dob is fairly good but I check collimation most times and usually needs a little tweak. However, the primary is a 45 second job but the secondary is a little more time consuming!

Whenever I have collimated I've never had a problem with the primary.  With a laser collimator a quick squint down the tube:bullseye:move on.  The secondary took me a couple of minutes the other day and was clearly time well spent.  I will make it part of my routine from now on.  Thanks for the helpful response.

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I assume mine is way off - I cannot focus on the moon properly and there is a lot of glare. I haven't collimated since I bought it.

What scope is it ?

The collimation would need to be a long way off not to be able to focus at all.

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Focus lock maybe? Does the focuser move backwards/forwards when you rotate the focuser wheels!

Sounds daft, but many folk with new scopes are unable to focus, due to either the friction not set correctly ( a grub screw under my focuser ) , or the focus lock itself is too tight, and yes, the focuser wheels still rotate, giving the impression that its not focusing?

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Focus lock maybe? Does the focuser move backwards/forwards when you rotate the focuser wheels!

Sounds daft, but many folk with new scopes are unable to focus, due to either the friction not set correctly ( a grub screw under my focuser ) , or the focus lock itself is too tight, and yes, the focuser wheels still rotate, giving the impression that its not focusing?

Good point, Charic.  I let a friend handle my scope for the first time - never having used one before.  He complained he couldn't focus.  When I tried neither could I.  Then I discovered he had been turning those grub screws under the focuser.  Consequently the focuser would not move up or down.  He thought he was tightening the eyepiece compression ring at the time.  I hope that's all it is, Gurey, but I've learned my lesson.  Check the collimation regularly.

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