chunky Posted December 18, 2011 Share Posted December 18, 2011 alright guys ive had my scope since july and i have used it a fair few times. ive tried collimating once but i still cant get my head around it. i went right out of focuser and the star looked like this shapei dont think it is rightis this just a primary mirror adjustment?i have the cheshire collimator do i need to put it into a 2inch fitting inside the focuser? and do i need to put it right in the focuser? also does the focuser need to be zoomed right out or right in.any links for this will be great i have tried astro babys but no luck with me. if there is anyone in the maidstone area who could come and show me id pay Link to comment Share on other sites More sharing options...
John Posted December 18, 2011 Share Posted December 18, 2011 Difficult to say for sure but if thats an out of focus star image then the "bite" out of it could be due to a tube current (warm air) that has not yet dissipated. The tend to stick to the tube walls you see.Was there not also a black circular shadow somewhere on the out of focus star disk ? Link to comment Share on other sites More sharing options...
chunky Posted December 18, 2011 Author Share Posted December 18, 2011 i cant remember now i just no it had that shap to it. im sure it was only there when i zoomed out of focus (so the focusers out as far as it would go).but when i zoomed right in (focusers right close to the tube) there circle was more completethe scope was out side for a good couple of hours so i dont think it was a cool down issue.( also while i have a thread going just want to ask) is it ok to keep my tube on its mount when storing as i read a post the other day about keeping it off its mount. Link to comment Share on other sites More sharing options...
twotter Posted December 18, 2011 Share Posted December 18, 2011 I store my 200p dob on it's mount and it's fine. As for collimating, I found Andy's shot glass video to be very helpful: Collimating a NewtonianOnly needed to do it the once and it took about 15 minutes with only a slight adjustment to the primary required. It's been fine for the last 9 months (not had much use to be honest). Link to comment Share on other sites More sharing options...
chunky Posted December 19, 2011 Author Share Posted December 19, 2011 ill have a look around and try over christmas Link to comment Share on other sites More sharing options...
umadog Posted December 19, 2011 Share Posted December 19, 2011 Andy's shot glass is helpful except that the rendering of what you should see down the eyepiece is wrong, so it may confuse you. Be wary of that: the reflections should not be concentric. Try these links: Rob Campbell's Home Page All the information is in there. If it doesn't make sense still then either ask here or find a local club. You are likely to want to tweak the collimation on each observing session since the tolerance for high-power viewing is of the order of 1 to 2 mm for the primary mirror (much more for the secondary). > is this just a primary mirror adjustment? It's likely to be both.>i have the cheshire collimator do i need to put it into a 2inch fitting inside the focuser? If you mean a 2"->1.25" adapter then, yes.>and do i need to put it right in the focuser?It sounds like you have a Cheshire/sight-tube combination tool. The Cheshire portion does the same things as a collimation cap with a shiny inside surface. For this tool it doesn't matter how far in you place the tool. The reason the tool is long and has cross-hairs is because that is the sight-tube portion of the tool which is used for framing the secondary in the focuser an adjusting the secondary. To centre the secondary you place the tool in such a position that it frames it tightly as viewed through the pupil of the tool. See the links. > also does the focuser need to be zoomed right out or right in.We don't say "zoom", since the focuser doesn't alter magnification. It alters focus. I recommend you rack the focuser to about where it would be when you're in focus with your eyepieces. Use that position for adjusting the primary. Otherwise, it doesn't matter a whole lot I don't think. Link to comment Share on other sites More sharing options...
kniclander Posted December 19, 2011 Share Posted December 19, 2011 isn't that "bite" likely to be one of the mirror clips being within the secondary and the others not (so you need to start by adjusting the sceodnary so you can see all the mirror clips)? Link to comment Share on other sites More sharing options...
Jason D Posted December 19, 2011 Share Posted December 19, 2011 When you defocus the star and see the "bite", look down the OTA and see if the focuser drawtube is intruding into the OTA. If yes, then that is the cause.Jason Link to comment Share on other sites More sharing options...
chunky Posted December 19, 2011 Author Share Posted December 19, 2011 ota? sorry still learning from here Link to comment Share on other sites More sharing options...
chunky Posted December 19, 2011 Author Share Posted December 19, 2011 is this the tube of the scope. Link to comment Share on other sites More sharing options...
Per167 Posted December 20, 2011 Share Posted December 20, 2011 Yes! OTA = Optical Tube Assembly. Took me quite a while to figure that out.. I see in you signature that you have a Skyline 200P. It's not a FlexTube, is it? I used to see something similar to your picture when looking at a defocussed star before just to find out that it was the light shroud (piece of cloth wrapped around the open part of the extended flex tube) hanging into the tube a couple of cm. Link to comment Share on other sites More sharing options...
chunky Posted December 20, 2011 Author Share Posted December 20, 2011 No i have the soild tube verison. and i dont think it is the focusers, but i will check. as it is when its defocused the way from the ota (see using it already) Link to comment Share on other sites More sharing options...
todd8137 Posted December 20, 2011 Share Posted December 20, 2011 hi there sounds like you have in a great time,theres a zillion ways to do it and every one as there way of do in it.as a trule i check mine every session,it becomes second nature,if you can get a lid of a film canister make a hole in the center and put it in to the focuser whenyou then look threw ,you should see the 3 clips that hold the mirror in place .if you do not see then the secondary might need a fiddleits not some thing i can explain but when you have done it once you will never forget ,is there no one local to you ? Link to comment Share on other sites More sharing options...
chunky Posted December 20, 2011 Author Share Posted December 20, 2011 im in maidstone no1 hs come forward yet Link to comment Share on other sites More sharing options...
Neil McRae Posted December 20, 2011 Share Posted December 20, 2011 Go to Astro Babys site and get her collimating guide. It has always worked for meNeil Link to comment Share on other sites More sharing options...
LukeSkywatcher Posted December 20, 2011 Share Posted December 20, 2011 isn't that "bite" likely to be one of the mirror clips being within the secondary and the others not (so you need to start by adjusting the sceodnary so you can see all the mirror clips)?Mirror clip was my first thought also. Link to comment Share on other sites More sharing options...
chunky Posted December 21, 2011 Author Share Posted December 21, 2011 ill give it another try when i get a chance over chrstmas. has anyone used or seen this beforeFirst Light Optics - New Perspectives on Newtonian Collimation - Vic Menard Link to comment Share on other sites More sharing options...
Moonshane Posted December 21, 2011 Share Posted December 21, 2011 hi ChunkyI am too far north to help directly but try the following which will get you close enough for good visual images:always make any adjustments with the scope either horizontal or at 45 degrees or so as this will reduce the risk of damage caused by dropped tools.1) with nothing in the focuser, the main scope cap off and the scope pointed toward something light (the sky away from the sun or a white ceiling) put your eye as close to the centre of the focuser as possible. does the shiny part of the primary look round and central to the focuser tube? yes? - move on to 2) if not then you will need to adjust the position of the secondary up or down the tube and turn it to make it round. Astrobaby's site shows how better than I can explain. it may be necessary to move your head back away from the focuser to check roundness as this makes the silvered part of the secondary stand out more.2) With 1) checked, insert your Cheshire into the focuser with the focuser set to approximately the position where you achieve focus with most of your eyepieces. If in doubt, put it halfway. Check that the donut on the mirror is centered on the cross hair centre (not the spider vane reflections (ignore these)). If yes, move to 3) if no, then you need to adjust the tilt of the secondary using the small grub screws in the secondary holder. adjust by very small amounts and eventually tighten all three (not with a face melting strain though - just over finger tight) gradually and sequentially, checking as you do it that the donut has not moved and that the shape remains round.3) The next stage is to centre the primary mirror with the secondary. With the Cheshire still in, see if the black dot (centre hole of the cheshire) is centred in the donut. If yes, you are lucky and it's already collimated. If not then after backing off the smaller bolts (retention bolts) at the primary end, adjust the larger bolts/screws (you generally need to adjust two only) until the dot is centred. you are now collimated. you can tighten the retention bols to just finger tight (again sequentially and gradually) but I find that often puts the collimation out. If you do it carefully you should be OK.You can do a final check with a star test but I can never get conditions good enough to make this meaningful. In reality whilst you should check 1) and 2), it is generally unusual for these to have moved much. It's 3) which is both the most common adjustment required and also the most important. hope this helps and makes sense. Link to comment Share on other sites More sharing options...
Moonshane Posted December 21, 2011 Share Posted December 21, 2011 ps, I agree that the most likely cause of your 'problem' is the focuser drawtube. It's not a problem though as you would never observe like this. Link to comment Share on other sites More sharing options...
kniclander Posted December 21, 2011 Share Posted December 21, 2011 ill give it another try when i get a chance over chrstmas. has anyone used or seen this beforeFirst Light Optics - New Perspectives on Newtonian Collimation - Vic MenardI'd suggest something a bit simpler - like a degree in astrophysics ...seriously, try Andy's shot glass or astro_baby's guide (google either).anyone want to bet on mirror clip v forcuser drawtube?mirror clip - 13/11drawtube - 11/10inconclusive - 8/5 Link to comment Share on other sites More sharing options...
todd8137 Posted December 21, 2011 Share Posted December 21, 2011 hi there do you have skype,or msn ? to discuss this and try and help you out with this ? Link to comment Share on other sites More sharing options...
Jason D Posted December 22, 2011 Share Posted December 22, 2011 I'd suggest something a bit simpler - like a degree in astrophysics ...I assume you read Vic's book. Just curious, why did you think the book was too complex?Jason Link to comment Share on other sites More sharing options...
chunky Posted December 22, 2011 Author Share Posted December 22, 2011 Cheers guys for the replies. and thanks moon shine made it a bit clearer for me i gave a quick go last night to adjust the primary to my chesire. then i saw your comment so i will check stages 1,2 when i next get a chance Link to comment Share on other sites More sharing options...
Moonshane Posted December 22, 2011 Share Posted December 22, 2011 no worries. I often check 1) and 2) but usually there's no adjustment needed and you may find the same thing. e.g. I tweaked my 6" f11 secondary the other night for the first time in about a year. you may find that Link to comment Share on other sites More sharing options...
kniclander Posted December 22, 2011 Share Posted December 22, 2011 I assume you read Vic's book. Just curious, why did you think the book was too complex?Jasonok, you got me:o, actually not but this is t'internet - do you think anyone actually knows what they're talking about (present company excepted).I will buy the book and see if I can get a cheap copy. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.