Planning for my next scope...

[codemonkey (Lee)]

Weighing up my options for my next scope, which include the RC8 which I recently sold... lol. Probably be a little way off yet but I'm trying to figure out what I want next. Of course, I want all the things:

1. 200mm + aperture -- well, maybe. Looking for something faster than my 100 ED, 200+ would be nice
2. (Effective) focal length of 900mm
3. Well-corrected colour
4. Holds focus very well -- I don't actually need to adjust my focus during a run at the moment and I'd like to keep it that way
5. No need for collimation, or holds it very well -- it's hard enough to get time for imaging without having to worry about that each time I want to do it
6. Imaging only scope

Does anyone have any experience with the various low-end 0.5x reducers paired with the RC8? I say low-end because I've not seen any "good" ones. This probably speaks to their effectiveness. It'll need to illuminate a sensor 11mm diagonal without introducing distortion.

The RC8 pretty much ticks all the boxes, except for the focal length so if I could simply introducer a reducer that offers more compression than the CCDT67 I have does, that could be a winner...

[AlexN]

I've got an 8" f/5 Newtonian here that might float your boat Lee? 8" f/5 is pretty fast, good aperture and resolution,

I know you aren't keen on collimation but it really takes 5 minutes to get it spot on and cone be done in daylight.

If you want to give it a test run let me know.

[glend (Glen)]

The only cost effective solution above 200mm is going to involve mirrors. How big is you budget? The Planewave CDK 12.5" might suit you but it weighs 20kg on its own and allow $18k just for the ota, but its very nice. You would need a bigger capacity mount as well, maybe a PMX.

[codemonkey (Lee)]

Originally Posted by AlexN

I've got an 8" f/5 Newtonian here that might float your boat Lee? 8" f/5 is pretty fast, good aperture and resolution,

I know you aren't keen on collimation but it really takes 5 minutes to get it spot on and cone be done in daylight.

If you want to give it a test run let me know.

Thanks Alex, appreciate it! :-)

I'm starting to think an 8" newt is pretty much my only serious option. I need to consider whether the extra light gathering power and colour is worth the effort over a smaller, say 120mm triplet refractor.

I think if I go with a mirror-based system I'm restricting my options to ones with a carbon tube. Is your 8" CF or steel?

Originally Posted by glend

The only cost effective solution above 200mm is going to involve mirrors. How big is you budget? The Planewave CDK 12.5" might suit you but it weighs 20kg on its own and allow $18k just for the ota, but its very nice. You would need a bigger capacity mount as well, maybe a PMX.

Cheers Glen. Unfortunately that's way out of the equation. I'm looking to spend no more than 3k (landed) and it needs to sit on my NEQ6.

Possible options include:
* TS ONTC F4.5
* Skywatcher Quattro

[AlexN]

My 8" is steel tubed however I've found focus shift to be minimal. If you were to add the cost of robofocus to the scope that will automatically adjust for any temperature induced focus shift, you are still looking at around $2500 less than a triplet refractor that will still undergo focus shift due to temperature. Mirror based systems are cheaper and provide much more light per dollar than any apo

[AlexN]

I'm using a 5" newt with robofocus at the moment and once it was trained for temp compensation I get ccdsoft to autofocus St the beginning of an imaging session then walk away. It does the rest on its own. For a cheap scope I have 5" of aperture, 0 colour fringing issues, 0 focus shifting between subs.. The downside is 5 to 10 mins of collimation prior to imaging.. Small price to pay.

Diffraction spokes become the only other thing people don't always like. I'm considering a curved spider for the scope to remove spikes. Then I have all the upsides of a top notch apo with none of the drawbacks and 1/7th of the cost.

[codemonkey (Lee)]

Originally Posted by AlexN

My 8" is steel tubed however I've found focus shift to be minimal. If you were to add the cost of robofocus to the scope that will automatically adjust for any temperature induced focus shift, you are still looking at around $2500 less than a triplet refractor that will still undergo focus shift due to temperature. Mirror based systems are cheaper and provide much more light per dollar than any apo

Originally Posted by AlexN

I'm using a 5" newt with robofocus at the moment and once it was trained for temp compensation I get ccdsoft to autofocus St the beginning of an imaging session then walk away. It does the rest on its own. For a cheap scope I have 5" of aperture, 0 colour fringing issues, 0 focus shifting between subs.. The downside is 5 to 10 mins of collimation prior to imaging.. Small price to pay.

Diffraction spokes become the only other thing people don't always like. I'm considering a curved spider for the scope to remove spikes. Then I have all the upsides of a top notch apo with none of the drawbacks and 1/7th of the cost.

Cheers Alex :-)

I've actually found with all of the APOs that I've owned that I get no focus shift in my imaging runs, in fact I can even go back the next day and as long as I'm shooting with the same filter, I can often leave it as-is. I've been spoilt with 'fracs :-)

Interesting that you don't have much of an issue with focus shift on a steel tube newt!

I think I'm pretty well sold on the TS ONTC 8" at the moment so I may pull the pin soon... sooner rather than later actually, since the wife was surprisingly agreeable... makes me suspicious!

[AlexN]

Lol. What does she want?? The only time my wife is agreeable on me buying new astro gear is. No, wait, never.

[codemonkey (Lee)]

lol. I know, right? I have the feeling I'll be paying more than I bargained for this deal.

[Somnium (Aidan)]

not sure if what you are after is sold there but Andrews communications is having a 10% off sale on all scopes and mounts at the moment. given that they are already considerably cheaper than the competition it is tempting me to pick up a GSO RC 14 and an EQ8. not sure if the shipping makes it not worth it though.

[codemonkey (Lee)]

Thanks Aidan! I've gone ahead with a semi-custom build from TS in Germany, so unfortunately Andrew's Comms great deals won't help me out this time, but a good reminder for everyone else.

14" RC and an EQ8... that's some serious kit. I sold my EQ8, actually not long after getting it, but only because it was total overkill for what I was planning on putting on it and I realised I'd be better off putting the extra money into other pieces of kit. Almost regret it... almost. Nice mount.

I hope your typical seeing can support the whopping 2.8m of focal length on that... I'm jealous!

[glend (Glen)]

Lee which focuser and secondary did you choose for that TS custom? It looks great in the link and should sit nicely on the NEQ6.

[codemonkey (Lee)]

I went with the Moonlite 2.5" focuser... I've had two Moonlite's before and loved them and I wanted the extra options a 2.5" offers over the 2".... I really did want to try and Feathertouch though, I've never used one before.

As for the secondary I was fairly ignorant in this area so I went with their recommendation which was the standard 70mm one; hopefully that was a good choice.

I was planning on going with a white tube because I got the impression that there's problems with the other colours wearing easily, but after placing the order they encouraged me to go with the natural carbon fibre look, even though I don't like it that much, because apparently the white finish suffers from wear issues like the other colours.

I also ended up going with the F5 over the F4.5. It's weird, the F4 and F5 variants are both 200eur cheaper than the F4.5. I plan to use the SW coma corrector which acts as a 0.9x reducer anyway, bringing the F5 down to F4.5 so it's a win-win.

[glend (Glen)]

I am a fan of f5 s as I have two of them, and the big dob is a f4.5. The f5 I, imho, easier to collimate. Re the secondary, what is your primary use, visual or imaging?

[codemonkey (Lee)]

Purely imaging... I've never really done any visual. I keep telling myself I'll do some soon, but there's too few clear nights (without crazy wind!) so they always get a camera attached instead of an eyepiece.

[codemonkey (Lee)]

Also, I've gotten myself confused in all this. They recommended the 63mm secondary for my purposes, which is what I went with.

[glend (Glen)]

Lee that makes more sense, the 63mm, 70mm seemed to big. Thanks