CPC1100 Collimation/Bob's Knobs

[euphony]

Hi guys,

I am yet to collimate my scope, but I suspect that it might be nearing the time (especially after tripping over it a few weeks ago and knocking it about a foot away from where it started )

Anyway, I notice everyone goes on about Bob's knobs, so I decided to have a look at the instructions and compare them to the instructions in my CPC manual.

When I read the two, it looks like the method explained in the Celestron manual requires less messing around than the method described with Bob's knobs. Yet quite a lot of people swear by Bob's knobs, so I'm a bit confused as to why.

Am I missing something quite crucial and simple?

Chris

[faulksy]

i would be interested in this. its strange my job as a maintenance enginer which means stripping machines down setting them up and fault finding e.t.c. and i am scared to colomate my sct very strange

[Merlin66]

The same collimating method is used. With the Bob's knobs you just use your fingers to tighten/ loosen the screws rather than an Allen key.

[euphony]

Ahh!

So I was missing something quite simple! Many thanks

[Northern Soul man]

http://www.astromart.com/articles/article.asp?article_id=548

Hi Chris - I used this technique after installing Bobs Knobs - had to read it several times and just took it a step at a time - really easy when going through it - only 2 movements are requires and so long as you align the ep and diagonal with your "top screw" - so looking from the back of the scope towards the front your diagonal and ep should show the same position angle as the top screw on your secondary - if the top screw is pointing in the 11 o'clock position - match this with the ep by pointing it to the 11 o'clock position - hope that helps Chris - if your using the scope visually then don't get really hung up on perfect collimation - remember - the seeing conditions, the dirt in the atmosphere and heat rising from the ground will degrade the views a lot more than a slightly out of collimation mirror/lens system - check it with a bright star nice and high - even try polaris - easier to re focus on the pole star - doesn't move that much.

Just be careful if your using the allen wrench on the secondary so as you don't hit the corrector. regards Paul.

[euphony]

Thanks for your help Paul, that is really good to know.

In theory I could just be tweaking the collimation for the sake of it I guess. The next time I get a decent clear night (and I'm around to see it!) then i'll double check on Polaris

Many thanks again,

Chris

[pilkinn]

With Bobs knobs the idea is that you could be looking through the eyepiece and tweaking the collimation knobs at the same time. I reality I don't because I always have the dew shield on as those SCTs dew up very quickly most nights. Bobs knobs are still a good idea as you get a better feel than using an Allen key or screwdriver.

I would recommend checking the collimation regularly - even every session as all it requires is to de-focus on a bright star.

Sent from my HTC Desire S using Tapatalk 2

[Northern Soul man]

Nice 1 Chris, wonder how your getting on with your scope - really impressed with it, was out only last night and had a little run round Cygnus looking at the nebulae - dropped the f ratio to 6.3 - always seem to go back to the favourites though - M57, 27, 71 - the Veil was easily visible - even under light polluted skies, but the Cocoon and North America - i know - really faint and impossible from here. I've found that the planetary nebulae are really nice, the snowball and "Blinking" planetary can stand a lot more mag to really show the outer regions of them and with the reference stars nearby they really stand out, been experimenting with O III and UHC - S and must say they really do make a difference and find the accuracy of the GOTO amazing - wonder how your finding yours mate - I'm really impressed with mine and find that the increase in contrast due to the larger aperture really nice on the brighter Messier's - not really had a good look at Jupiter yet, but its looking good for a month or two when she resides in the early evening and so high up - can't wait. Paul.

[kirkster501]

I was in the same position as you and installed my Bob's Knobs last week. It took me a few hours of playing about to get it right. A but like riding a bike is collimation: takes a while to suss it out but once you have done so it is easy. I know people who tweak the collimation several times per night !

Let me give you a very, very, very big tip. When you install the knobs, do so one at a time. Install the first one then get the collimation right ( i.e with one knob and the other two screws). Then do the next knob. Then finally the third. That saves you from ever being miles out of collimation (like I was).

[Northern Soul man]

When I installed my knobs (oooooh errrrr), i'd only had the scope for a day and when I loosened the first bolt, the whole assembly (mine has the fastar secondary) felt very loose - frightened me to death !!! thought that I'd never be able to get the secondary tight. Put the first Bobs in and began to tighten - to my amazement I felt it bite and after a few turns, the whole assembly tightened, moved to the next screw - same procedure and the last. Checked the scope visually on a distant chimney - must say it looked ok, waited to do a star test on the night - way out on a de - focused star, followed Ed's collimation guide (linked above) and within five mins collimation looked pretty close - not had to adjust since holds collimation well. The only point is that the Fastar secondary is contoured on the outside - so a little tricky to adjust, the knurled bolt heads sort of sit below the moulding - so really can't be turned with gloves on, but I can just get at them with bare fingers. Paul.

[Merlin66]

I had similar "short knob" problems...

Bob has actually made a special set for fastar celestrons which allow the knurled knob to be above the fastar plate......

[euphony]

Hey guys,

Thanks for your replies.

@ Kirkster501: you don't fancy popping round mine and sorting mine out for me do you, and showing me the ropes! (I'm not far probably from youI Over in Shipley/Ilkeston just over the Derbyshire border).

I'm still terrified of it, and don't want to make a hash of it!

I read somewhere that someone had a problem after using Bob's knobs in that they tended to have to collimate it all the time after installing them?!?

@ Paul: i've been getting on quite well with it, but I'm really not sure how light polluted my skies are. I generally tend to think that they're not too bad as I can occassionally make out some mag 12 NGC galaxies, and have seen some very basic detail with M51, but then on the other hand i have sometimes tried to increase the mag to get more detail out of planetary nebulas for instance and I get no more detail than looking at it with my largest eyepiece, they're just slightly bigger with no more clarity. Not sure if it's collimation issue, atmospheric issue, that I'm not waiting until it's quite dark enough, I'm just being impatient and not experimenting enough or not giving myself enough time before I am itching to see something else.

I've been very impressed with the scope overall though, some lovely views of globulars and M57 clearly. Andromeda is clearly visible, but couldn't make out dust lanes, but it was quite low in the sky then and now it has disappeared behind the house. When it appears higher and in the back garden I hope to tease more detail out if it.

i can't see the veil nebula without my OIII filter (I find the OIII filter very odd in that it makes everything so dark and smudgy, but I can just make out the nebulosity, is it supposed to be like that?).

Dumbell Nebula etc easy enough, owl nebula (once, not seen it since!) I have never been able to view the North American nebula, cocoon nebula or the Heart and soul nebulas, I just can't make out a thing

I thought I saw the eagle nebula once, but it was very low in the sky, so i think it was just a twig from a bush playing tricks with my mind

I have viewed Jupiter a few weeks back with it, but it was very low in the sky (It was 11:30pm, it had just come over the rooftop across the road and the cloud was starting to roll in). I could make out all the 4 big moons, but struggled to get any detail on the planet itself, but that would the the atmospheric conditions I would guess). When it gets higher it's too late and/or hiding behind the front of the house, so i need to wait a month or two for that..

I have managed to check it at 6am in the morning though, but only through binoculars, when I can again make out all 4 moons, but obviously no detail (also saw the bright fuzzy patch of the Orion nebula earlier this week at the time through the bino's which I thought was cool!).

So, yes, overall, very impressed with the CPC, but sometimes frustrated as I expect to be able to make out more detail than I do, but that could be for a number of reasons. Looking forward to dark clear winter nights, and also the addition of a CCD camera to see if I can get a bit more clarity on some objects and hopefully get some imaging done (once I figure out why my pc won't pick up the live video stream!).

A great scope, definitely keeps it's tracking well, bar the odd night.

I babbled a bit there didn't I!

[euphony]

Oh, and how do I know if it's a fastar version? Mine was bought second hand, only used for a year or two apparently and nothing in any documentation mentions fastar.

[Merlin66]

On Bob's site there are illustrations of each type of secondary holder......

[euphony]

Ah, thank you, I will have a look at his site again

[Northern Soul man]

Hi Merlin thanks for the advice but couldn't really comment on the size of my knobs cause I bought them from a UK supplier but they sit slightly below the secondary moulding - not a problem though as I can manage with them.

Hey Chris thanks for the "babble" - nice to know your thoughts on the scope - really I think its an individual thing as regards comments on what you see. I've owned a number of scopes ranging from 5 - 12" apertures and what I found to be the greatest improvement using the cpc is that the increase in contrast over smaller apertures - yes the higher mag due to the larger aperture - but increased mag is not the reason, contrast, for me, always wins over increased mag and prefer the smaller/brighter image as opposed to "drowning the view with more mag.

What I can see is on parr with your comments Chris, when I see the veil, I should have said that I can "detect" it, not that I can see great detail there, but just the relative size and shape of most nebulae as viewed when at the zenith - I find the GOTO here really useful - I had a 12" dob before the cpc and really struggled with "zenith" observing because, trying to turn the dob was a real struggle for me when searching directly overhead.

Dont get me wrong, visually your never going to "see" real detail you get in photos/images, only "hints" of detail. The magnitude scale is a little off - putting because all deep sky varies greatly in size, your doing really well at mag 12 Chris but the relatively small planetaries are way brighter than the larger (diffuse) galaxies and nebulae and because I've seen the objects in smaller apertures previously I can compare the views and have found that the slight increase in aperure over previous SCT's is what I have come to expect to see.

I think the different amount of light pollution we have to put up with will decide on what we can and can't see, but for me, the slight increase in aperture has made invisible objects in an 8" visible in the 11", but as said before the increase in contrast is the greatest improvement for me.

You read reviews of different telescope systems and all have said that the increased size of the secondary obstruction in the SCT's have always been their downfall, but for me not the case, yes, if you put it in a side by side comparison with a similar aperture dob/reflector, but , for me, the SCT is a really capable instrument when taking overall size and performance into consideration - looking at the overall picture - a very good scope and for me the preferred choice - but that's just me.

Chris I think I must be the biggest "babbler"!!!

Great thread guys. Paul.

[Merlin66]

Here's a couple of images of the "extended" Bob's on a fastar C11.

[euphony]

Thanks for the helpful comments Paul, really pleased you're finding this scope as great as I am.

I think from looking at the info mine isn't a fastar, thanks Merlin

I tested whether it was collimated or not last night when I was looking at Vega, and to my amazement is seems to be still perfectly collimated! I wasn't expecting that!

I'll check it regularly though to keep on top of it