RC 8 Scope Decision

[dave_galera]

Hi All,

I currently use a Tak FSQ85 on a Tak EM-200 mount which I use for imaging, this is my prime imaging setup and I think it always will be.

But, I want to have a go at imaging some smaller objects and this means going up on FL, and I have been considering the Altair Astro RC8 which will cost around 1800 GBP with all the bits and a Feather-touch focuser (Don't do the 'C' word!!!). However, considering the price against higher end RC's, there are no free lunches and as they say 'you only get what you pay for'. After some research on the RC8 I came across some comments from a German guy, forget his name, who understands optics and he basically says this scope, or GSO equivilent, is a load of rubbish (except he used stronger words) and I don't know enough about optics to agree or disagree. Looking at a lot of images taken with this scope I must admit I don't like the stars they look very blobby and like perfect round white discs i.e not natural at all, in fact I have only seen one image with stars I like......now this could be down to bad processing, I don't know.

The only other alternatives I have are the Orion AG 8" or the Orion ODK 10". The AG 8" is very fast but has a reduced FL of 760mm, AG 10" has a FL of 950mm at even more cost. The ODK 10" while having a good FL of 1700mm has a weight of 12Kg which might be pushing the Tak EM-200 mount with all the camera gear and guide scope on it. But both these scopes produce the necessary results. As this setup will not be my prime imaging setup I want to keep costs reasonable but not to a position where I am sacrificing image quality to any large extent.

So you see my problem.....which way to go, would love to hear from someone with experience of the RC8 scope...Altair or GSO
Thanks in advance for any help you can give in deciding which way to go.

Regards,
Dave

[swag72]

Dave, I've pm'd you over on PAIG.

[dave_galera]

Dave, I've pm'd you over on PAIG.

Hi Sara, Sorry got nothing.

Try dave@qdigital-imaging.com

Dave

[dave_galera]

Hi Sara, Sorry got nothing.

Try dave@qdigital-imaging.com

Dave

Aaaah, just got it, thanks.

Dave

[perfrej]

It is the combination of scope focal length and camera that will dictate what you get. If you get a camera with reasonably small pixels, a scope such as the Tak 106 will give you great galaxies. What camera were you thinking of putting behind your long focal length?

/per

[dave_galera]

It is the combination of scope focal length and camera that will dictate what you get. If you get a camera with reasonably small pixels, a scope such as the Tak 106 will give you great galaxies. What camera were you thinking of putting behind your long focal length?

/per

Hi Per

I use the Atik 383L+ with the EFW2 filter wheel on my Tak FSQ85, and I must admit I would prefer to stick with a refractor if possible.

An FSQ106 with this camera would give me FOV of 114' x 87' @ f5 or 76' x 58' @ f7.5 with the extender.

An ODK would give me 35' x 27' @ f6.8

An TOA-130 would give me 63' x 48' @ f7.7

Dave

[perfrej]

Consider the image scale instead. A 1.7m FL with the 383 gives you a ridiculous image scale of 0.65"/px, which means you will have blobs for stars. Binning that and you are at a good image scale but get a low pixel count (2 Mpx instead of 8).

For a 1.7m FL, a good pixel size is around 10u (383 has 5.4 if my memory serves me correctly).

My philosophy is to go with a refractor and the proper image scale. For instance, get a galaxy with the 106... The M33 below was shot with a 8300-based camera and a Tak 106. It kind of proves that galaxies can be done at 530mm FL

/per

[ollypenrice]

Hmmm, I take Per's point but M33 is a huge galaxy. It is one of three, along with M101 and M110. After that they do get radically smaller.

I'm wary of these GSO based RCs. Even the demon tweaked ones like the Ian King re-engineered one have tales told of difficult fettling and lots of time to get them right. You do see some good results but you see an awful lot of bad ones as well.

A larger refractor (120 to 140 ballpark) with your small pixels would be giving you tolerably sensible sampling of a little over an arcsecond. (TOA130 would be 1.11, or my TEC140 would give 1.14.). You would also be able to bin the colour and, in some cases, the Ha. Not on glaxies with nice structural Ha like M106 but where the Ha amounts to blobs, as it often does, it would be fine in Bin 2.) 

I'd expect to pay a little under 4000 euros for a used TEC140 and with its flattener it is now proving an absolute delight. I'm using it at 1.8 arcseconds per pixel. You do get spoiled using a Tak refractor. The TEC is right up there in every way. You'd beat these, which was done with the 4000 and pixels just over 7 microns. 

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=1793652809&k=39n8qx9&lb=1&s=O

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=1793683457&k=nTnjCcS&lb=1&s=O

Tim recently said that imaging galaxies at F10 with the Celestron Edge was fine. I was surprized since it seems slow to me but galaxies are funny customers. Having used one for a while I'd worry slightly about open tube reflectors long term and would have an Edge on the shortlist, at least.

Olly

[dave_galera]

Thanks Per and Olly, your comments are valued.

Yes Olly I also take Per's point about image scale, I must admit I never considered this as I think I got caught up with all the other parameters that had to be considered.

You are right Olly about Per's comment on the M33 it is large and there are very few other large galaxies, planetary nebulae etc.

I still have my Celestron C8 (somewhere) so I am going to have a play with that, although I am likely to loose my patience over the coma that it has even with the flatener/reducer and getting the backfocus distance correct. But as I hate defraction spikes maybe the Celestron Edge is a consideration as well as the Takihashi FSQ-106, TSA-120 or TOA-130..........I think the GSO and Orion AG/ODK are out the window so this simplifies things a bit.

Now I am getting really confused, I don't think my old brain will take it like it used to do LOL!!

Thanks again for your valued comments.

Dave

[kirkster501]

You should look at some of the things that johnrt has done with his RC6 - it might change your mind.  I have never truly got going with my RC8 carbon as yet - a combination of rubbish weather, caring duties and playing with my new Tak instead!  But I hope for good things from this scope in due course.  Especially when galaxy season comes round.

Two weeks now with rubbish skies in UK

[ollypenrice]

You should look at some of the things that johnrt has done with his RC6 - it might change your mind.  I have never truly got going with my RC8 carbon as yet - a combination of rubbish weather, caring duties and playing with my new Tak instead!  But I hope for good things from this scope in due course.  Especially when galaxy season comes round.

Two weeks now with rubbish skies in UK

John's results, as you say, are stunning. However, I'd beware of basing a setup choice only on the best of what is out there in terms of images. It's probably best to take the norm. If you didn't do this you could easily convince yourself that DSLRs can match CCDs. They can't.

Olly

[kirkster501]

John's results, as you say, are stunning. However, I'd beware of basing a setup choice only on the best of what is out there in terms of images. It's probably best to take the norm. If you didn't do this you could easily convince yourself that DSLRs can match CCDs. They can't.

Olly

Yes indeed. Fair point.

That said, I will make sure I get good results from mine as well! I am a tinkerer and do not mind getting stuck in.  The longer FL will work  a treat on small objects.  This is my only real effort so far and the scope was slightly out of collimation and it was the height of summer.  Taken with a DSLR (before I got my Atik).  I think it has the potential to be a good scope.

[Gina]

I've found the MN190 (1000mm FL) to be a very good astrograph though we rarely get goot enough skies in the UK to do it justice.  You'd probably want to change the focuser (as many have done) to a decent R&P.  Not too much of a slouch either at f5

[perfrej]

I can second Gina's choice if you want to stay around 1000mm FL. Very good scope for the money. In fact, it is unbeatable if you give some tweaks (there are long threads on this on SGL)!

/per

[ollypenrice]

I agree that a good MN190 can take on the world, just like John's RC6, but it's a big scope for the EM200. I know Dave has a sheltered observatory, though, which would help. It can be done (MartinB does it) but I wouldn't call it 'comfort zone' for the EM200.

Olly