johnrt

Steve, I have left you a comment on your thread with my thoughts on the issues in your images.

THe next plan for this scope is a feather touch focuser, this is going to cost almost as much as the OTA itself, but I see it as an investment I can move on to perhaps an 8 or 10" RC at some point down the road.

Don't worry Olly, I'm a strong believer in taking on board ways and means to improve my images, I'd be lightyears behind where I am now if I hadn't listened to what people had to say about the images I'd taken!

The dark halos are easy to explain, slap dash sharpening on my behalf, more careful and thorough masking of stars, simple.

I believe the slightly misshapen stars are a guiding or balance issue. The PHD graph is as flat as a pancake but yet I still get a little drift in the DEC axis. I'm still only running the 6"RC & ST80 on an HEQ5, at a focal length of 900mm I think it is doing pretty well, but perhaps an EQ6 would serve me better.

That is stunning John. Many congrats. I aspire to being able to do these sorts of shots on my RC8 when i get a CCD one day. I bow to your expert eye Olly but what distorted stars? Very interested in the eye of an expert....

John, what mount you using and what guiding setup have you got. I got eggy stars as well on my one and thus far only outing with my RC8 so far. Appreciate you two experts views on my efforts?

Steve

Well I certainly don't consider myself an expert! Are you guiding on your set-up Steve?

The galaxy there is truly outstanding, John. Hat's off, it really is something special and shows what this small scope can do. Now when you look at an image as good as this your pickiness goes up a notch (or several notches) and the stars are not perfect. They show slight distortion. Is this from the optics, do you think, or from the guiding?

In any event you have your money's worth with this instrument.

Olly

Thank you for the very kind words Olly, they really are appreciated! Are you talking about a slight elongation towards the top of the image in the stars?

The weather has not been kind, but we all know that. I've recently bought a 2" IDAS LP2 which screws in to the CCDT67 inside the focuser. I managed to capture the RGB data for this image with the IDAS in place, the luminance was shot without. My first impressions are that the IDAS makes a significant difference.

I will be either adding further exposure time to, or replacing the lum data with the IDAS in place. But in the meantime here is what I have so far on M101 using the Altair 6" RC.

Never heard of them, but it looks like a fairly recent set-up, so could be fine or maybe not? A site with a trusted good reputation is astronomiser who I have had personal experience with and can recommend.

http://www.astronomiser.co.uk/

You all make me laugh. If ever there was a stereotypical bunch of astronomers fretting over collimating a scope - I wonder if there is an astronomy version of the Betty Ford Clinic for us to check in to when it all gets too much!

Chris, I found the collimation screws tight on my OTA too, little tricky to get very fine adjustments at first, but the upside is it goes nowhere once you're happy.

Collimation on these RC type scopes is not difficult at all - you just need to go slowly and make very, very small tweaks on the adjustment screws as the mirrors will shift more than you expect. Once you are collimated, they tend not to need any adjustment - I last adjusted mine in November and it hasn't needing tweaking again since. The Cheshire eyepiece alone is good enough to get "very good" collimation, I'm sure the holographic laser will achieve "excellent" collimation but spending the value of the scope again, just to collimate that extra 5-10% extra, in my opinion isn't justified.

I'd love to trade up to an 8" RC as I'm really loving the little 6" now I have sorted the issues I had with it, but I think I might be pushing my HEQ5 a little too far with the bigger scope.

You've really got me thinking of one for the smaller stuff instead of the MN190 or Quattro I was considering. Seems to work well with the 314. How do you find it holds focus throughout the night? I'd be looking at hanging a 314/EFW2 & maybe an OAG off it (if the st80/qhy5 wasn't good enough). I also see you are tempted by a feathertouch for it.

It holds the focus fine once it is dialled in, but to be honest the focuser supplied isn't great but will do for now. I'll definitely be adding a feather touch from FLO when I can sneak one in past the lady who holds the purse strings.

Continuing my experiences with this scope here is an image I have put together with it over the last few days. The 3.5 hours of luminance was shot under great conditions, no moon and decent seeing. The RGB however was taken with at least a 50% illuminated moon and at least One night had lots of moisture and very high thin cloud about. But still, you take what you can get in the UK!!

It adds up to about 8.5 hours - 3.5 in Lum, 2 in Red & Blue and just an hour in green. Same kit as before APCCDT67 tele compressor, Atik 314l+ & Pixinsight / CS5 for the calibration, integration and processing.

Hopefully I'm starting to build up a good idea of the possibilities with this scope for anyone who is considering one.

Having owned a 6" RC for almost a year I would certainly not recommend one as a first purchase for astrophotography. They are, as Olly says, tricky to collimate and their long focal length and slow f/ratio require very long exposures which means good tracking and guiding. You will be right at the limit of an HEQ5 with the 8" RC, unless you are thinking of the carbon fibre tube version. Mine also came with a set of mechanical issues to iron out and took me the best part of my first year of ownership to get it suitable for imaging.

So what would I recommend? For the budget you would spend on the 8" RC you could get yourself a smallish (80mm?) fast ratio triplet refractor and matched flattener. This type of scope is the workhorse of most DSO imagers and will cover a range of targets all year round, they are lighter and the shorter focal length and faster f/ ratio much more forgiving. You can then always work up to an RC type scope once you have found your feet in AP.

Thank you for the comments guys, you are making me blush!

Seriously though what would the equivalent 900mm focal length f/6 triplet refractor set you back?

The ST80 will be fine - PHD is capable of sub pixel guiding so will handle it. You could even go shorter with a finder guider and guide the RC successfully.

Uh, dunno where my image has gone from in my post above, but here it is again!

I spent a little more time looking at my collimation today using a cheshire and a 1.25 centering gadget. I think my collimation is good enough. I have the dot bang in the middle and concentric circles. I think it is OK.

With collimation there is always a monkey on my back saying "tweak it a bit more, go on you might make it a bit better still" !!! I think sometimes you have to know when enough enough. This is not the space telescope after all..... Speaking of which how the heck do the collimate the HST ?!!!!

Yep, you could be there for hours, I get mine as close as possible, but I'm not going to get hung up about it!

I know a couple of people who do exactly that, they use the IDAS in front of all their LRGB filters with a mono camera and with great success too. I also plan to add one to my set-up to do exactly the same.

Also John meant to say did you notice that the mount alignment is much more critical on such a long FL scope compared to the ED80? Very much more so! I was missing targets last night all the time.

I also don't have a FR as yet so need to image at the native F8 which means long exposures- slow compared to the ED80 which is my only other encouter with Astro Photography.

My reason to get the RC8 is to get bigger scale on galaxies and GC's.

Steve

My HEQ5 handles the 6" & ST80 guidescope pretty well, I needed the longer counterweight bar to balance but it points accurately and tracks away at up to 15 minute exposures with just a polar align via the polar scope (no drift aligning here!!).

I strongly suggest you make sure you align the finder scope in daylight and you will be fine. I forgot once and what a waste of about 2 hours that was trying to even put Jupiter on the chip without a finder was a nightmare!!

A last update on my M82 image, this time with Ha added to the red to highlight the emission jets being blown out by the galaxy. I shot 18 x 15 minute Ha subs (remember I couldn't manage 5 minutes before I sorted the primary mirror out) and blended them to the red channel in Pixinsight.

This image takes the total imaging time up to 11 hours - 4.5 hours Ha and 6.5 hours LRGB.

Hi John, I will weigh it and let you know.

I had a small fiddle with one of the screws at the back of the scope whilst looking through the cheshire and could see the reflctions slightly change so immediately put it back to what it was! Not touched the secondary yet. It looks pretty good TBH but the centre "spot " and the immediate adjacnet ring is not perfectly central. Very near to it but not perfect. So a little worj to do on it at some point!

Rgds, Steve

I used this guide to help me get to grips with collimating mine 6" RC. It might be of help if you haven't already seen it.

http://www.astronomics.com/documents/astro%20tech/astro-tech%20at6rc%20collimation%20sheet.pdf

Hi John,

I have bought the CF 8" version and have got the upgraded Feathertouch focuser as well. I bought it as a job lot on ABS for half the price new. I think the collimation is very slightly out on mine - does it make that much of a difference in your experience? You said you used the Cheshire EP method. Is that all you did? From your encouters taking it apart do the screws on the rear cell adjust the mirror or the focuser plane?

Thanks, Steve

Hi Steve,

Congrats on your new scope! It sounds like you got a bargain!!

The collimation of the secondary (front set of screws on spider) on my scope needs a regular check to keep it in good collimation.

The rear set of screws adjust the optical axis (primary mirror and baffle tube assembly) this shouldn't need adjusting often. If the primary is out that will make a huge difference, not so much the secondary. All I use to collimate is a cheshire eye piece. The trick is to make very small adjustments, you'll be surprised how much a small tweak on a screw will shift the mirror.

Just out of interest how much does your 8" CF weigh?

John

Just a quick update with a work in progress image - still to capture on this is the Ha and another dose of luminance.

Maybe it's just because I used to my ED80 triplet imaging at f/4.8 but I found f/9 on the RC almost unusable - I don't have the patience for that!!!

I agree Olly it's a real shame there isn't just a little more thought and planning in to these scopes - they do have the potential to be great, but that potential should be realised by the manufacturer not the tinkering end user!!

A recent (very) rare glimpse of space yielded this result with the (primary mirror fixed) 6" RC - 8 x 10 minutes exposures in Ha. This length of sub was impossible before the primary mirror fix.

I've been thinking of getting one of these, will probably have a look at them at AstroFest.

Can you say what mount you used for it? I'm thinking of hanging it on an AS-GT class mount. I'm currently using two 80mm scopes successfully and was thinking of something that will give a narrower FOV.

Chris

I use it with a HEQ5, which I was blaming for the poor performance. Since the fix I have found if handles the 6" RC & ST80 with ease.

Nice review, sorry you had a few problems. I use mine only for visual and I find it very good. I don't know where all this rubbish comes from about it only being for astro photograpy. I had mine now for about 2 years and I use it a great deal, I still have not found the need to colimate it.

Alan.

I really have no idea about visual stuff so really can't state anything for certain, but I get the impression this scope is dismissed as not suitable for observers off the back of the specs on paper rather than actual practical experience.

can you be a bit more specific about fixing the issue of your primary colimation? didi you use this guide? http://deepspaceplac...8rcpointing.php

Yes the process was similar, but I didn't need to go as far as in that guide.

1. remove top and bottom rails (philips head screws)

2. remove remaining screws holding rear section of the scope & remove - at this point the mirror was obviously rocking about in the cell and I could even spin it round!!

3. unscrew and remove primary baffle tube.

4. loosen x2 hex screws in primary compression ring

5. tighten compression ring to stop movement of mirror.

It was simply a case of re-tracing my steps backwards. The collimation was off afterwards, but not by a huge amount.

John