I just assembled my 12" dob

#1 20-10-2005, 11:33 PM

Can you believe that? I ordered it from Andrews yesterday morning and exactly 24 hours later it arrives! Cant complain about their delivery. I now have what looks like a silver hot water service sitting in the middle of my lounge.

Hey Ken, I'll take you up on your offer to answer some questions.

1. How do you move it around on your own?
2. I fiddled with the two screws under the focuser but dont quite understand them. (crayford)
3. Alt pans smoothly but Az is tight, can you use some silicon spray or something on the nylon pads?
4. Collimation, it was WAY out when I got it, I have centred the mirror by setting all 3 scews to same depth, but was then forced to adjust the three in the secondary to get the centre dot to come close to the middle of the eyepiece, I have now what I presume is a rough collimation but wont know how good until first light.
5. What mistakes did you make?

Dennis.

davidpretorius · #2 21-10-2005, 06:25 AM

Exciting!!!!

1. How do you move it around on your own?
- do you have a garage and concrete etc so if you had wheels on the bottom, you could roll it or do you have stairs, fences etc here you have to carry it. $50 got me a 44 gallon drum trolley that i iattached to the bottom disc and i wheel it round my driveway. If you have to carry, move the base first and then i ipick up the tube by the black discs in the middle and carry it over.
2. I fiddled with the two screws under the focuser but dont quite understand them. (crayford).
-They will lock or unlock the focusser.
3. Alt pans smoothly but Az is tight, can you use some silicon spray or something on the nylon pads?
- armourall is good apparently. once you are viewing, you may even take one spring off or both depending on the angle you are looking at?
4. Collimation, it was WAY out when I got it, I have centred the mirror by setting all 3 scews to same depth, but was then forced to adjust the three in the secondary to get the centre dot to come close to the middle of the eyepiece, I have now what I presume is a rough collimation but wont know how good until first light.
- tricky one, how did you know it was out. usually, you set the secondary first to make sure it and a nice circle is lined up with the focusser and then you adjust the primary. I am new to this and need lots of help. I have centre spotted my primary - there are threads on this
5. What mistakes did you make?

hogly52 (Graeme) · #3 22-10-2005, 02:33 PM

Yup, mine arrived Tuesday, was assembled that night and in a reasonable short time I had my room filled with something resembling one huge mortar tube. Wednesday, slight delay but then got into the collimation, starting at the secondary. Somewhere between secondary and primary I thought I'm never going to get this right, but eventually there appeared to be some sought of alignment. Thursday, again the scope had to take a number while I cleared some higher priority activities, however it did see light later on, albeit limited. Friday, off to the dark site, go through all the finderscope alignments and eventually get three viewers all pointing at the same thing (Yup, fitted a Telrad too). Then settled into a quiet night, exploring here and there, trying out the different lenses

. Of things that need to be corrected, my main concern was the balance issue, at both low and high elevations. In between it seemed OK, but only after cable-tying the battery pack to the lower end of the OTA. The addition of a maglite (red lense) and leatherman, under the cable tie also helped. Still it doesn't solve the problem, particularly with a 2" lense fitted. Definitely more friction required. Everything moved OK, but I do agree, something needs to be done to improve the base mechanism beyond the three supplied teflon pads. The suggestions to be found on this site will be closely looked at! My only other problem for the night, apart from clouds and smoke, was the surprising amount of dust and crud the primary managed to attract in such a short time. I was hoping there would be more enjoyment time before I had to tackle mirror cleaning, so soon after learning collimation

. Anyway, I'll be back there tonight, making the most of the opportunity and whatever the skies can offer!!

rumples riot · #4 22-10-2005, 02:46 PM

Yeah they are a monster of a scope. Well it looks like it is gonna rain for a while. plenty of time just to get collimation right with a laser collimator.

ballaratdragons (Ken) · #5 22-10-2005, 03:10 PM

Dennis & Hogly, Congrats on joining the 12" Dobbie Club!!!!

How do you move it around on your own?
I take the OTA off the base and place it to the side. Then I carry the base outside. Then take the OTA out and put it back on the base. The OTA is not too heavy, just awkward due to size.

I fiddled with the two screws under the focuser but dont quite understand them. (crayford)
The bottom screw locks the focuser in place when you acheive best Focus. It stops the focuser moving when using heavy EP's or your eye pushing the focus tube in.
The top screw is like a clutch. Screwed in it will grip tight and you can carerully focus heavy EP's (I do this when using 2" Barlow & 2" EP together). Screw it out and it lightens the focus (I use this most times). The more you use it screwed in the more it will gradually waer tracks into the focus tube. Only use it 'screwed in' if necessary.

Alt pans smoothly but Az is tight, can you use some silicon spray or something on the nylon pads?
Best results have been achieved by placing a washer system in the centre. There is a thread in here somewhere about using Plastic Milk bottles to make the washers. The weight of the whole dob box and OTA are pressing down on those 3 teflon pads, so the centre has to be supported, that's what the washer system does.

Collimation, it was WAY out when I got it, I have centred the mirror by setting all 3 scews to same depth, but was then forced to adjust the three in the secondary to get the centre dot to come close to the middle of the eyepiece,
Don't worry about getting the 3 screws in the big mirror the same. It isn't accurate that way.
Firstly: look down the focuser without an EP, and look AT the small 2ndry mirror. You should adjust the 3 screws on the 2ndry until the Big Primary mirror is pefectly centred in it. Then go to the Primary mirror and gently adjust the 3 screws in it until your centre spot it centred.

This will not collimate the scope to it's best but at this point that is as close as you can get. Next step is to do a star test to collimate it perfectly. I use a collimating tool called a Cheshire Eyepiece, then Star test.

What mistakes did you make?
Lots! I was collimating in the wrong order, I tried to change the Azimuth without Teflon pads (mine came with horrible roller bearings), I didn't set my 2ndry mirror in the right place (in the centre of the focuser and with a slight offset), I didn't understand what the 2 screws on the focuser were for and fiddled with them too much and slightly scored the focuser tube, I did not use the 3 Primary mirror screws the correct way, etc, etc.

It was with help from all the great guys and gals in here that I finally started to get things right.

I still have a lot to learn but I can pass on what I have already learnt. I have owned scopes for 20 years but this GS 12" was a new monster to me and I'm sure I will learn even more about it yet.

jjjnettie (Jeanette) · #6 22-10-2005, 07:57 PM

When I first looked through my new scope, I couldn't get it focused and thought it was a collimation problem. But after leaving the scope to cool for 1/2 hour, things cleared up heaps. Personally, I wouldn't dive in and twist those knobs too soon.
Same with the dusty mirror, I think that most people would agree that a lightish coating of dust on the mirror won't affect what you see through the EP too much. Whereas an accidental scratch from cleaning will effect it for ever.

hogly52 (Graeme) · #7 22-10-2005, 11:02 PM

Quote:

Originally Posted by jjjnettie

When I first looked through my new scope, I couldn't get it focused and thought it was a collimation problem. But after leaving the scope to cool for 1/2 hour, things cleared up heaps. Personally, I wouldn't dive in and twist those knobs too soon.
Same with the dusty mirror, I think that most people would agree that a lightish coating of dust on the mirror won't affect what you see through the EP too much. Whereas an accidental scratch from cleaning will effect it for ever.

Thanks for your advice

. However, it did need the collimation, and it was a good time to start to learn how to do it. Cooling is not a big problem where I am, the temperatures don't drop a great deal during the night. I just have to watch taking it from an air-conditioned environment to the outdoors, a sort of reverse situation. The dust, well, I'll keep an eye on it and see how it goes. It's just bad luck that dust is part of the environment in the north, so I'll learn to live with it, a little bit anyway.

I had another good night tonight, picking up a number of the Messier objects around Sagittarius.

Graeme

ballaratdragons (Ken) · #8 22-10-2005, 11:13 PM

Well done Graeme.

Something that will help keep dust out of your scope (but mainly spiders and spider-webs off the mirror) is a Giant shower cap over the mirror end.

Go to a pet shop and buy a Plastic seed catcher for the bottom of a round bird cage. It looks just like an oversized shower cap. Wack that on the end and spidey and dust can't get in!

hogly52 (Graeme) · #9 23-10-2005, 09:21 AM

Thanks for the information. I certainly hadn't thought about spiders and the like creating a new home, but now that you mention it I had better. Because not only would I get the usual range of insects, then they'd be followed by the geckos

. I can do without their sticky feet and droppings on the mirror!

Better still, I'll keep moving and using it, and no-one will want to make a home inside it!

Graeme

ballaratdragons (Ken) · #10 23-10-2005, 11:11 PM

I found a spider-web on the mirror cell half an hour after bringing it in one night!

Here is the link to the product name and size. http://www.iceinspace.com.au/forum/s...ght=shower+cap

Here is a pic of it in action. http://www.iceinspace.com.au/forum/a...&stc=1&thumb=1

hogly52 (Graeme) · #11 24-10-2005, 06:53 AM

Excellent idea, now to find a pet shop. Nhulunbuy doesn't have a demand for such a shop. However, I'll be back in Cairns in a few weeks.

It's a wonder the scope outlets haven't picked up on them as a possible accessory, with a re-tagged label.

Graeme

#12 24-10-2005, 12:58 PM

Thanks for all the good feedback, I am going out to Ron's this weekend coming and hope to do some beter collimation with him (oh by the way Ron, if your reading this, can you help me please?) as he has years of dobby experience and must be an old hand at it by now. One thing to consider for dust is, when using it on or near ground level, lay down a poly tarp first, that way the fan wont blow the dust all over your mirror. I have put in about 6 hours observing time so far and am blown away by the aperture, imagine how good it will be when correctly aligned. Even my wife said (while viewing tuc47) "Wow, now that is pretty, I understand why you wanted it now." And for her, this comment is impressive, she just doesnt get much from Astronomy.

ving (David) · #13 24-10-2005, 01:11 PM

Quote:

3. Alt pans smoothly but Az is tight, can you use some silicon spray or something on the nylon pads?

try ez-sliders (or other furniture slider) from your local bunnings or other hardware store... they work wonders

Rastis · #14 24-10-2005, 02:07 PM

Hi Chaps,

(4. Collimation, it was WAY out when I got it, I have centred the mirror by setting all 3 scews to same depth, but was then forced to adjust the three in the secondary to get the centre dot to come close to the middle of the eyepiece, I have now what I presume is a rough collimation but wont know how good until first light.)

Is this a common problem with the Andrews dobs, or a once off.
Rastis.

ballaratdragons (Ken) · #15 24-10-2005, 02:12 PM

Rastis, purely by the effect of delivery practically every dob will need collimation when unpacked after delivery.

Bintel goes thet extra bit and collimates every dob leaving their shop, but by the time the truck has delivered it, it will probably be out again. I was fortunate in that when mine arrived (from Andrews) it wasn't far out.

ving (David) · #16 24-10-2005, 02:15 PM

at andrews you get basically what comes from the manufacturer. while bintel collimate before you get it... but the fact remains that you are going to have to colimate at some stage regardless. you need to get a cheshire (or other collimation tool) and learn how to do it

it inescapable.

ving (David) · #17 24-10-2005, 02:17 PM

if you want links on how to collimate, just ask and thou shalt receive

hogly52 (Graeme) · #18 24-10-2005, 03:08 PM

Even as a very new newbie, I can only endorse the requirement to learn how to collimate, with a tool. Sooner or later you'll need to do it, if you transport it, you'll need to do it, if you clean the mirror, you'll need to do it - the picture is clear, one day, you'll need to do it. The sooner you learn, the sooner the fears are conquered!

As for the dust, dust for me enters through the sky pointed end when in use

. An unfortunate location of the dark nite site. Thus far I've not used the fan because night time temperatures don't vary a great deal, or very quickly, from day time temperatures

(for my location). However, as stated previously I do like the idea of the showercap on the earth pointed end, to prevent dust from below or unwanted creepy crawlies establishing a new home.

The scope and the lifestyle are great, and can only wish I started this earlier in life

.

Graeme

RAJAH235 · #19 24-10-2005, 09:48 PM

Graeme. Hi

. Congrats on your 12". Don't worry too much about a little bit of dust. It accumulates all the time. Just take the nec. steps already stated & keep the ends covered in plastic when not used. Here's a guide to collimating.
http://skyandtelescope.com/printable...rticle_790.asp
In place of the 'Cheshire' (until you get 1), use a film canister. Put a 1~2 mm hole in the centre of the cap, assemble & place in the focuser. You may need to rotate it just to make sure the hole is in the centre of the cap............ Check in diff. locations as to how your collimation is going.
HTH.

L.

hogly52 (Graeme) · #20 25-10-2005, 06:58 AM

Hi Raj, Last night I did exactly that, went out and made my lowest cost purchase yet, a roll of film. I then placed the film in a sealed bag in the fridge (might use it some other time) and went to work on the canister. It's very kind of Kodak to centre-mark the lid for drilling. Anyway, in no time at at all I had my first collimating tool, and in even less time the optics aligned according to my new tool. Of course, in accordance with Murphy's Rules, the sky was nothing but clouds

.

From my local mentor, Ian of GAA, I'd been tutored closely on collimation and techniques not involving tools to bring my own initial efforts pretty close, but the canister did take it a huge step further and was so much easier and repeatable. I'd also scoured the collimation resources on this site and others, so the reading was behind me. I've also ordered a collimating tool from Bintel.

In the meantime, Ian had also given me a laser collimator to try. All I can say about it is, if we could get it collimated, then it might be useful. But the efforts of the two of us have proved fruitless, and it just does not appear as if it will ever produce anything apart from offset circles of varying diameters when rotated. Efforts to collimate it only appear to change the diameter of the circle, and maybe the offset. We'd be very interested to hear of the experience of others in using this tool. Using a v-block to support the tool while rotating has not helped.

Must say, I'm thoroughly enjoying the support and friendship provided by the IIS society!

Cheers,

Graeme