Tomservo

9 hours ago, Paul M said:

I've read that the only important numerical value for RC optics is the secondary to primary distance. It it is too far from optimum then good collimation will be difficult.

How to find the correct distance? There are diverging views. One view is to adjust the inter-mirror distance so that the Scopes f/l, as given by plates solving an image, is that given in the scope spec. I.E if the scope spec says it's 1600 f/l then adjust the mirror distance until this is true. Then complete the rest of the collimation process.

Other views are that the design spec is just approximate and that the distance should be adjusted to perfect the star image seen through the scope + a lot of extremely technical stuff:

Just to cheer you along: https://www.cloudynights.com/topic/702687-rc-mirror-distances/

I've never measure the inter-mirror distance on y RC10. I just point the laser collimator down the focuser, hit the center spot on the secondary and return through to the target on the laser collimator. I have a fancy collimator thingy for the rest of the process but after getting it right, still found it needed a tweak on a real star!! So I could have saved myself a bit of cash

 

Thanks Paul, and thanks for that link, it does seem that it's been an issue for a few people. 

It's a bit 'Chicken and the egg' with this, and it doesn't seem to be spoken about too much in comparison to collimation which seems to be the priority.

If it turns out my mirror distances are miles out, then what iv'e done so far has been a waste of time, although I've learn't quite a bit!.

Thanks again.

9 hours ago, Mandy D said:

@Tomservo I have the same scope and from what I understand, it is unusual for the focal length to match the specification. Because this is a two mirror system with hyperbolic mirrors, it is not like a Newtonian with only one active mirror. Both mirrors in an RC play a part in the magnification and effective focal length of the telescope. I understand that the mirrors are produced in volume and paired by selection after production to get a good match. This results in some significant differences in final focal length. What matters is adjusting the scope to it's best performance, not aiming for precisely 1370 mm. So, do not bother trying to achieve precisely 1370 mm. I have no practical experience of any of this, as I have, so far, had noneed to collimate my RC.

Hi Mandy, thanks for replying, it's reassuring to know that you're happy with the scope, and I'm sure I will be soon!

I understand what you say about the hyperbolic mirrors and it makes a lot of sense, although I will feel better about it when I get to know if it's 'in the ball park' of not when I do the plate solving (now I've got it focusing)

The collimation on my RC6 was miles out (maybe had a rough ride with the courier?), and I just thought while I'm at it, I'll check the distance, but I wasn't sure just how important it was.

Thank you.

Hi everyone!
My previous question about my Ioptron RC6 focus issue, provided me with some great advice, thank you all for that.

It has enabled me to get quite familiar with the mechanics of the scope and also overcome some trepidation about removing mirrors and making adjustments etc.

I believe my focussing problems are over, (although I can't comfim that just yet, until the weather changes)

It has left me with another question: What are the repercussions of NOT having the Focal Length matching the specifications?; the spec shows the focal length for the RC6 as being 1370mm. If, after plate solving, this turns out to be different, should I make adjustments to correct this? does it affect the quality of the image?

I note that there is an eyepiece called Ronchi that will show up incorrect spacing, but if the spacing doesn't matter, I don't see the point of it.

Thanks

Clear skies and a bacon sandwich

I have another question!!

Following instructions for Collimating, that I got from the Ioptron RC6 user guide; I did it without any extensions on, basically not setup for use. I used the Cheshire eyepiece and adjust the mirrors to get a good result.

I took the telescope out and attempted a Star Collimation which showed concentric rings in a circular position but seemed to have a glare coming from it at the 6 oclock position.

Today I put the Cheshire in, in place of the camera, (so the scope is now setup as it were for use) and the collimation is out.

Now I know that a Tilt adjusting ring maybe required (more money!) but it made me wonder if the collimating should be done under normal use conditions? i.e. all extensions etc. attached?

waddya think?

Thanks Paul, that fancy collimator IS a nice piece of kit though! I often wonder why some kind of software can't be written to use Asiair for collimation? (I haven't wondered too much though)

I was outside last night getting it to focus on Polaris, (now I have an awful neck ache) It was recommended I think on the Sky at night site that I use a med - to high magnification eyepiece, so I bought a 4mm, but I couldn't even find it with that; so I put a 23mm in and found it with that. Now...because it was terribly out of focus, the first thing I saw was the doughnut, which was large; I focused it up and changed to the 4mm; I focused on that, which was a relief! and took it past it to get a doughnut but it was quite small and difficult to make out the rings; what I think I saw was some reasonably concentric rings with a small glare of light at the bottom (like a diamond ring) does that sound like a big issue? 

Using Polaris is an obvious choice if you can't use a tracker yet, but it definitely ain't practical for making adjustments, and its hard on the knees!

Is there a solid reason why I shouldn't us the 23mm eyepiece for this? 

I'm wondering now if I mixed the eyepieces up! but I'm pretty sure I didn't.

It's reassuring to learn that a tilt adapter isn't necessarily needed; my setup seems very solid, I guess I'll find out.

I plan on setting it up again tonight with all the gear back on it and see if I am indeed getting a proper focus now, if I am I'll use a star a bit lower down to check the collimation.

Thanks again

Thank you both for your information and suggestions and I do appreciate  the time spent here. It is quite a learning curve but it's very interesting and I tend to be persistent with things like this so i'll keep at it. I will be taking your advice on board.

I find a lot of the videos online showing how to collimate using the stars, assume that you can already focus on them, which I've not been able to do, however........

I did a collimation  today with a Cheshire eyepiece, and it was quite an eye opener (if you'll forgive that); what I thought I had achieved with the Laser collimator before was probably making it worse!

I did manage to get the required result according to the pictures in the instructions.

I will be testing it out on the stars, as soon as I've found a way to see through the clouds.

Thanks again

Tom

Thank you everybody for replying to my questions: 

Paul, I'll check out that link, the collimator I used was a laser one....that went back today and I'm waiting for a Cheshire to turn up tomorrow. I do tend to jump in at the deep ends, but I tend to enjoy the task. Thanks.

Carbon Brush, Yes it was new, but the problem is they are about 200 miles away from me, we seem to be starved of Telescope dealers these days where I am (Essex), But....If push comes to shove! Thanks.

Bosun21, I may ask him the question after I get a result tomorrow, thank you for that, I'm assuming I just leave @Chris a 'Public message'? (not sure how it works) Thanks

Anne S, Thats interesting stuff, I worked my way up to using all the extensions and found I still needed another 10mm; I achieved that by pulling the camera out by 10mm at which time I managed to take a few images of the moon. Although they were 'ok' I had to stack a lot of them to get it anywhere near reasonable. I was at that stage I contacted RVO, and I was less than impressed with their answers. Then Moon was almost in focus but then its a lot closer and bigger than the stars. I'm beginning to get concerns about the mirror distances now but I don't know enough about that aspect yet, (it may explain why I needed to use all the extensions) after I collimate it again tomorrow I'll do some research on that. Thank you

Hi there! I am a beginner, and I realise thie could be 'Cockpit Trouble' but I've been struggling with this ever since I bought it.

I've never managed to get it in proper focus from brand new. The RC6 has 3 extension rings to adjust the 'Back Focus' but it never seemed to be quite enough.

I had it very roughly focussed on the moon by holding the Eye piece out from the mount by about 10mm.

I contacted Ioptron through RVO and they more or less said there was nothing wrong with the one they had there, and that was it!

I bought loads of stuff for it and managed to extend the back focussing a bit more.

I've now got the ASIAir Plus and ZWO ASI224MC Camera, and the  ZWO EAF (focusser) for it.

I bought a Laser Collimator and adjusted the Primary mirror and then the Secondary mirror, and as they were both considerably out of alignment I thought I'd cracked it....But No!

I'll do my best to attached some pictures I took on my IPad this evening of the focussing attempts; they will show by the position readout numbers on the focusser that it reaches best focussing position and then goes out of focus further on. The 'Best' focussing position (1831) is total rubbish.

I'd really appreciate some suggestions!! (aside from taking up knitting!)

Thanks.