6" and 8" Classical Cassegrains for small DSOs

[Commanderfish]

Hi there, has anyone been using the above 6" or 8" Classical Cassegrains (StellaLyra, GSO, TS Optics, Orion CC) for visual on small DSOs, like the Orion Nebula, Globs and Planetaries?  I'm pretty sure it would be good on globs and PNs but I do like Orion and similar nebs.

Also has anyone used a focal reducer for visual?  I could get a 1.5 degree TFOV out of the 8 inch with FLO's x0.75 reducer using a Panoptic 41mm, or a 1.15 degree TFOV using an Ethos 21mm.  Not sure if the focal reducer would create any significant aberration for visual purposes though?

I like the compactness and quick cool down of the scope for a quick set up at home.  I guess the 8" could be a little heavy though. Was thinking about on using this on an Ercole mini next to a 115ED F7 frac, but if the mini can't take it I'd use a full sized Giro Ercole.  The mini happily takes an ST150 with upgraded focuser, Ethos lenses and a big finder alongside the 115 ED.

Edited February 9, 2021 by Commanderfish

[vlaiv]

10 minutes ago, Commanderfish said:

I could get a 1.5 degree TFOV out of the 8 inch with FLO's x0.75 reducer using a Panoptic 41mm

No, that would not work.

Pan 41mm has field stop diameter of 46mm.

With x0.75 reducer, you would be asking telescope to deliver 61mm of illuminated and corrected circle. 

Telescope itself illuminates only 45mm - so Pan 41mm natively without any reduction is pretty much all the scope can deliver - about 1°.

Other than exit pupil being small (at F/12) and narrower field of view - I would expect 8" CC to perform as any other 8" on deep sky - very good.

[johninderby]

I have both the 6” and 8” versions. Don’t really use them for DSOs though it does a great job if the dso fits within the fov.

Haven’t used a focal reducer so can’t help on that. 

The 6” is a bit back heavy so a counterweight that fits on the front of the dovetail could be usefull. I use the 6” on a modified Manfrotto 405 geared head and a Berlebach Report tripod as a grab’n’go setup. Can be carried outside single handed

The 8” is a few kg heavier and would sit nicely on a Skytee II mount although I use a Rowan AZ100.

Edited February 9, 2021 by johninderby

[Chris]

Conversely I've found the Stella lyra 8rc ok for Lunar planetary.

[johninderby]

Dovetail counterweight for the CC 6”

 

[Commanderfish]

28 minutes ago, vlaiv said:

No, that would not work.

Pan 41mm has field stop diameter of 46mm.

With x0.75 reducer, you would be asking telescope to deliver 61mm of illuminated and corrected circle. 

Telescope itself illuminates only 45mm - so Pan 41mm natively without any reduction is pretty much all the scope can deliver - about 1°.

Other than exit pupil being small (at F/12) and narrower field of view - I would expect 8" CC to perform as any other 8" on deep sky - very good.

Thanks that's very helpful - sounds like the pan 41 would vignette with a reducer if that's the right term?

[vlaiv]

1 minute ago, Commanderfish said:

Thanks that's very helpful - sounds like the pan 41 would vignette with a reducer if that's the right term?

yes - same fov will be visible - only "squeezed" in the center with dark ring around it - vignetting.

[Commanderfish]

10 minutes ago, johninderby said:

Dovetail counterweight for the CC 6”

 

 Ah that's clever John.  I also have a Manfrotto 405 which is great for grab and go! I also have a similar dovetail counterweight kicking about.   Is the 6" any good at DSOs like globs/Orion nebula though?  Have a feeling the 8" is going to be better with it's light gathering?  

[Commanderfish]

17 minutes ago, johninderby said:

Dovetail counterweight for the CC 6”

 

John, what exactly is that vixen-looking clamp that you've used to attach the scope to the Manfrotto head, and how did you attach the clamp to the head?  I've still got the original quick release plates on my head which I screw to the bottom of telescope dovetails.  My solution isn't as solid looking as yours.

Edited February 9, 2021 by Commanderfish

[johninderby]

I just bolted a small dovetail saddle to the QR plate. Some saddles have a photo type thread in them that makes it easier.

I modded the 405 by removing the centre section to make it  a proper alt-az head. It’s a simple mod.

The 6” gets used a lot more as it is grab’n’go but the 8” would indeed be better on fainter targets.

[Commanderfish]

9 minutes ago, johninderby said:

I just bolted a small dovetail saddle to the QR plate. Some saddles have a photo type thread in them that makes it easier.

I modded the 405 by removing the centre section to make it  a proper alt-az head. It’s a simple mod.

The 6” gets used a lot more as it is grab’n’go but the 8” would indeed be better on fainter targets.

Excellent, thats useful.  I think I'm going to get hold of one of those clamps for starters.  Do you reckon the 6" is going to be better on DSOs than an ST 150?  The CC 6" should have better contrast and cooldown but maybe not as much lightgathering?

[Tiny Clanger]

25 minutes ago, Commanderfish said:

John, what exactly is that vixen-looking clamp that you've used to attach the scope to the Manfrotto head, and how did you attach the clamp to the head?  I've still got the original quick release plates on my head which I screw to the bottom of telescope dovetails.  My solution isn't as solid looking as yours.

Excuse me butting in , but I got one of these https://www.firstlightoptics.com/dovetails-saddles-clamps/baader-vixen-style-dovetail-clamp.html

which sits nicely on my old hex plate manfrotto 029 and is reassuringly hefty.

Heather

[Commanderfish]

28 minutes ago, Tiny Clanger said:

Excuse me butting in , but I got one of these https://www.firstlightoptics.com/dovetails-saddles-clamps/baader-vixen-style-dovetail-clamp.html

which sits nicely on my old hex plate manfrotto 029 and is reassuringly hefty.

Heather

Not at al!  Excellent, thank you.  That's the kind of thing I'm after but I will try and track down a non-marring one - edit: just found an Svbony non-marring clamp on ebay for £20.  Ordered.

Edited February 9, 2021 by Commanderfish

[johninderby]

The CC6” has very sharp optics that will be superior to the ST150 but of course the narrower fov. The CC can do high power lunar / planetary which is the ST150s greatest weakness but OK low power use though.

Don’t think there would be much noticeable difference in light gathering ability and the total lack of CA will help.

This clamp is a best buy and good quality.

https://www.ebay.co.uk/itm/Telescope-Accessories-Aluminums-Alloy-High-Load-Dovetail-Clamp-For-PhotographyUK/163898426577?epid=27028681810&hash=item26291b84d1:g:hyMAAOSwZi5dnYG8

Edited February 9, 2021 by johninderby

[Commanderfish]

3 minutes ago, johninderby said:

The CC6” has very sharp optics that will be superior to the ST150 but of course the narrower fov. The CC can do high power lunar / planetary which is the ST150s greatest weakness but OK low power use though.

Don’t think there would be much noticeable difference in light gathering ability and the total lack of CA will help.

This clamp is a best buy and good quality.

https://www.ebay.co.uk/itm/Telescope-Accessories-Aluminums-Alloy-High-Load-Dovetail-Clamp-For-PhotographyUK/163898426577?epid=27028681810&hash=item26291b84d1:g:hyMAAOSwZi5dnYG8

Ha!  Just bought that exact one about two minutes ago!

[Commanderfish]

8 minutes ago, johninderby said:

The CC6” has very sharp optics that will be superior to the ST150 but of course the narrower fov. The CC can do high power lunar / planetary which is the ST150s greatest weakness but OK low power use though.

Don’t think there would be much noticeable difference in light gathering ability and the total lack of CA will help.

This clamp is a best buy and good quality.

https://www.ebay.co.uk/itm/Telescope-Accessories-Aluminums-Alloy-High-Load-Dovetail-Clamp-For-PhotographyUK/163898426577?epid=27028681810&hash=item26291b84d1:g:hyMAAOSwZi5dnYG8

Thanks this is really helpful.    The FOV is not too worrying as I'll likely mount it side by side with a widefield frac.  Just a case of tossing up the 6" or the 8". 

Seems like the 8" is a bit heavy for a grab and go set up but I bet it really pulls a lot of detail out of DSOs and planets - is it quite a significant jump up from the 6"?

[johninderby]

The 6” does give great lunar and planetary views but yes the 8” would have better resolution and brightness. I find the 8” will take very high magnification. The 8” and 115 combo would suit a Skytee II mount but more grunt’n’go that grab’n’go. 😁

6” is about 6kg and the 8” about 10kg.

Cool down on the 6” would be similar to your 115 ED I would think if it is a doublet..The 8” cools down pretty quick though.

Edited February 9, 2021 by johninderby

[Commanderfish]

Sorry my 115 is actually a triplet apo, I don't know why I called it an ED!  Cool down is really not bad on that one.  Cool down is a concern but the 8" might be similar to the 115 triplet.

Although the 8" is fairly heavy, the size and shape should make it reasonably easy to handle, especially compared to my Starwave 152 which is 11Kg and about a metre long all in.  I wouldn't add tube rings to a CC and I'd probably remove the Losmandy too.  I'd likely stay with the stock focuser.

I imagine that the short CC tubes probably don't have the same issues as longer fracs when you tilt to a certain angle and the EP ends up low down and the angular weight starts to pivot the scope down despite locking the mount...

Out of interest have you ever tried putting the 8" on your Manfrotto 405 and if so what happened?! 😁

Edited February 9, 2021 by Commanderfish

[johninderby]

Yes I think cool down between the 8” would be similar.

I have a carry handle fitted which makes handling the scope a lot easier as it leaves a hand free to tighten the saddle clamp.I also added tube rings to mine. GSO is the only one that makes the right 230mm size.

Did try an 8” SCT and just too wobbly.

[Commanderfish]

2 hours ago, johninderby said:

I just bolted a small dovetail saddle to the QR plate. Some saddles have a photo type thread in them that makes it easier.

I modded the 405 by removing the centre section to make it  a proper alt-az head. It’s a simple mod.

The 6” gets used a lot more as it is grab’n’go but the 8” would indeed be better on fainter targets.

 By the way, how did you take the centre section (tilt axis I believe) off the 405?  I can't see any screws or other fixings and I'm not sure where to attack it.

[johninderby]

You have to remove the plastic disks to get at the screws that hold the parts together. Slide a scalpel blade under the edges to work the disk loose. You can get replacement ones from Manfrotto though if you ruin them.I put the disks back with two sided carpet tape.

There is a small tab sticking out of the bottom section that stops the upper axis from rotating very far that you will see when you have removed the other sections and will need removing with a Dremel.

Edited February 9, 2021 by johninderby

[Commanderfish]

Awesome, thanks.  Probably going to get the 8" CC tomorrow.

[johninderby]

Good stuff 👍🏻

 

This is the handle I fitted.

https://www.wdscomponents.com/en-gb/tubed-handle-front-mounted-black-wds-8517/c-404/p-920

WDS Ltd has loads of useful bits so can be dangerous to look around the site as you can spend more than intended.