Should I keep my SW BD 100 Refractor?

mldee (Mike) · #1 04-03-2010, 08:11 PM

As my knowledge has slowly grown over the last couple of years, I've been slowly setting up a "family" of scopes for my RO obs here in Brisbane, in time for the coming dry season, all for imaging via my QHY8 and DSI III OSC cameras. Not into visual, as I'm 67 and my eyes are lousy. Indeed, the whole thing is just a "computer geek" hobby for me. Not trying to win the Hubble award.

My concept, as a modest amateur setup to perch on my LAN'd EQ6 EQdir'd ADM all-Losmandy S by S pier mount is:

1 - C8 SCT + 3.3 + 6.3 FR's, eventually with Hyperstar, for planetary and (HS) Nebula/DSO

2 - SW BD f5 8"/1000mm Newt + MPCC for Gen Purp astro use.

3 - WO Megrez 80mm f7 triplet apo + FFIII for guidescope and some widefield, etc

I'm getting ready to sell a lot of the scopes and other items I've collected over the last two years of learning. One of these is a virtually unused Skywatcher Black Diamond 100x900mm f9 refractor . I also have an EQ5 goto on which it would sit well.

My question is: since I have an 8" f5 1000mm Black Diamond Newt with MPCC, do I achieve anything in imaging by keeping this refractor? I can't see any reason, but don't want to sell it then regret it.

Any guidance would be appreciated.

duncan · #2 04-03-2010, 08:16 PM

Hi,
I honestly think you would regret selling it in the long run.Would be a great scope on the moon and planets.
Just my humble opinion.
Cheers,
Duncan

citivolus (Ric) · #3 04-03-2010, 08:58 PM

Hmm, I don't know what the quality of that newt is, but given their similar focal length and one having about 12x the light gathering of the other, I know which way I would lean, if image quality was similar that is.

mldee (Mike) · #4 04-03-2010, 09:18 PM

Quote:

Originally Posted by duncan

Hi,
I honestly think you would regret selling it in the long run.Would be a great scope on the moon and planets.
Just my humble opinion.
Cheers,
Duncan

If it was a bigger job, sort of like your 150 x 1200, I would certainly agree. It's just that it's so similar to the f5 Newt and really not that far above the Megrez. I have a couple of good TV Barlows for Megrez/Newt use. I'm also not that much into planetary photography, apart from Saturn and Jupiter, and for those, the C8 should do well.

Overall, I like the textures and pretty colours of the deep space stuff much more. 'Not that there's anything wrong with planetary...'

Sounds like I should add it to the for sale list when I get around to it. It would more than fund the cost of the Hyperstar for the C8.

AlexN · #5 04-03-2010, 09:31 PM

I would sell it... The 8" F/5 newt will stomp all over it for DSO work, and for planetary work, the APO might afford you more contrast, but aperture is king for planetary work 8" vs 4" -- 8" wins.

RobF (Rob) · #6 04-03-2010, 09:43 PM

Wise to consult for advice Mike, but face it, you're not going to realise why you wished you hadn't sold it until you have. Its just the way it always seems to work out....

On a more serious note, I can vouch for the usefullness of an 8" SW + MPCC for everything except medium to widefield astrophotography. Not qualified to pass any judgement on the refractor in question though.

AlexN · #7 04-03-2010, 09:55 PM

Mike - the Newt can do Medium widefield work with the right corrector... a 0.73x Keller Corrector will bring it back to F/3.65 and 730mm F/L..

Being someone who's owned every common optical system on the planet, from my perspective I see no reason to keep two scopes that have the same (within 100mm) focal length, when one has double the aperture... 8" F/5 vs 4" F/9 for visual or photographic work, I would chose the 8" in every situation for any task.

duncan · #8 04-03-2010, 10:11 PM

Yep your right Mike. I got a bit carried away and jumped in to quick without weighing up all the facts. For that i do apologise.
It's been a very long hot day up here. And as you like the DSO over planetary work i do definately agree with your decision.
All the best to you.
Cheers,
Duncan

LOL!

mldee (Mike) · #9 04-03-2010, 11:27 PM

Quote:

Originally Posted by RobF

Wise to consult for advice Mike, but face it, you're not going to realise why you wished you hadn't sold it until you have. Its just the way it always seems to work out....

On a more serious note, I can vouch for the usefullness of an 8" SW + MPCC for everything except medium to widefield astrophotography. Not qualified to pass any judgement on the refractor in question though.

Rob, yep, there's been a lot of positive comment about a newt with an mpcc as being a very cost effective approach.

Cost is one of my main considerations, as I'm not that good a photographer, so seems silly to spend a lot just so I can make poorly-framed, out of focus shots of M42.....If I find my skills markedly improve, I can still then sell the newt and upgrade.

mldee (Mike) · #10 04-03-2010, 11:32 PM

Quote:

Originally Posted by duncan

Yep your right Mike. I got a bit carried away and jumped in to quick without weighing up all the facts. For that i do apologise.
It's been a very long hot day up here. And as you like the DSO over planetary work i do definately agree with your decision.
All the best to you.
Cheers,
Duncan

LOL!

No sweat Duncan

Actually, I specifically bought the Megrez triplet so I would have a small reasonably-performing refractor that I could also use as a guide scope, keeping in mind total weight on the EQ6. Perhaps with a barlow, it and the C8 will be good for Moon and Saturn, etc. I have a SP900NC webcam, and will keep it for the planetary work when the urge gets to me.

Thanks again for your comments.

mldee (Mike) · #11 04-03-2010, 11:38 PM

Quote:

Originally Posted by AlexN

Mike - the Newt can do Medium widefield work with the right corrector... a 0.73x Keller Corrector will bring it back to F/3.65 and 730mm F/L..

Being someone who's owned every common optical system on the planet, from my perspective I see no reason to keep two scopes that have the same (within 100mm) focal length, when one has double the aperture... 8" F/5 vs 4" F/9 for visual or photographic work, I would chose the 8" in every situation for any task.

Hi Alex, you've got me talked into it

I'll put the BD100 in the classifieds along with your ex-8" 1200mm dob soon. I picked up Nettie's 1000mm BD newt, that's the one I'm going to use with the mpcc+QHY8 if the rain ever stops.

Interested in the Keller approach, I'll have to do some research into it. How do you think it would compare to the C8 + Hyperstar, both performance and cost wise? Hyperstar is about US$850 all in + freight for my C8.

AlexN · #12 04-03-2010, 11:59 PM

The 2" 0.73x Keller corrector is 760 Euros... around $1080AU before postage and import taxes last time I did the conversion..

As far as quality is concerned, it would not be as fast as the C8 + Hyperstar. The field of view would not be as wide, however the overall sharpness would probably be better. it would be easier to setup, less fragile,The field would be very flat provided you adhered to the correct back focus distance of the keller corrector..

You would have a much more uniform diffraction pattern from the newt, with an SCT and hyperstar, you have an oddly shaped camera and cables in the optical path creating very strange diffraction patterns.

Contrast in the newt would be better as well, being that the central obstruction would be incredibly low in comparison.

I would want to put a bigger secondary in the newt with that corrector, to make sure it gets the most illumination as possible.

Cost wise, the C8+HS3 is the better option... Overall image quality, I think the newt is the better option of the two...

I myself am considering getting an 8" F/4 OTA and a keller corrector to make it 8" F/2.95.. Extremely fast, narrowband imaging scope..