C11 over C9.25 for planetary... any advantages?

Robert_T · #1 20-12-2006, 03:12 PM

Hi All,

I've been toying with the idea of upgrading (?) my C9.25 OTA to a C11 (C14 just ridiculously out of the question expensive) for my planetary pursuits. I've seen some good work come out of C11's in recent times and think there might be an edge in resolution and light gathering (= faster exposures = more frames etc). Don't expect there to be much in it, but perhaps enough to warrant.

Any thoughts out there on the C11 vs C9.25 for this?

Another driver for me is differentiating my scopes a bit better - the Mwelon 180 and C9.25 are a little too similar in size. This way I'd have one big scope and one littler one

cheers,

matt · #2 20-12-2006, 03:19 PM

I dunno Rob

I've compared C9.25 and C11 Jupiter and Saturn images produced by Damian Peach and I don't think there's a huge amount in it IMO

I guess if you were able to sell the 9.25 for a good price and have most of the cost of a good second hand C11 covered the switch could be justified.

I guess any increase in aperture and the associated light gathering and increased resolution has to be a good thing.

Any bigger though and cooling and seeing start to play a bigger role

swannies1983 (Dan) · #3 20-12-2006, 03:41 PM

While not specifically talking about differences in visual aspects, this short review talks about a few other differences between the C8, C9.25 and C11

http://www.cloudynights.com/item.php?item_id=1585

Rigel003 (Graeme) · #4 20-12-2006, 04:56 PM

Hi Rob
I have a C11 and while I've been pretty pleased with it's potential for planetary photography, I've also seen equally good, or better, results from 9.25s. I'm sure a large part of it comes down to the expertise of the operator in capturing and processing. The 11 can take a very long time to cool down - up to 1 1/2 hours sometimes, and I've just bought one of the Lymax coolers which should help a lot.

I think you'd appreciate the extra aperture more on deepsky objects.

Dennis · #5 20-12-2006, 05:39 PM

Hi Robert

If you are going to specialise in hi-res Lunar and Planetary imaging, it might be worth considering a more specialised OTA, such as the Mewlon's from Takahashi? Reviews do tend to indicate "refractor like" performance?

I was eyeballing the other night with the C9.25 and the Vixen 4" and the stars just looked fantastic in the Vixen 4", with beautifully formed diffraction rings, whereas the C9.25 looked a little ragged at the edges. The Trapezium looked gorgeous, with diamond point like stars in the Vixen, whereas in the C9.25, they were a little softer and not as distinct.

Cheers

Dennis

EDIT - I mean the larger Mewlon's as I know you have the 180.

swannies1983 (Dan) · #6 20-12-2006, 05:46 PM

Or you could get a Tal 200K like me

. I havent had a chance to look at Saturn yet but the reviews of this scope have been pretty good when it comes to planetary viewing. I have only used the scope to look at the Orion Nebula, the Tarantula Nebula and also Tucan globular cluster. The Tal has easily outperformed my 8" dob in terms of contrast and viewing experience on these objects so far.

matt · #7 20-12-2006, 05:48 PM

Where'd you get the TAL .... and what $$$ are we talking about?

swannies1983 (Dan) · #8 20-12-2006, 06:33 PM

I paid $900US (secondhand 6months old) for an OTA from a guy from the US off Astromart. He delivered it to Utah where I had a conference. Brought it back with me on the plane.

Matthew, who runs "telescope and astronomy" here in Adelaide sells the Tal series. Here's the web address

http://www.telescopes-astronomy.com....telescopes.htm

If you're serious about astrophotography, I would just buy the OTA and get an EQ6 (like me) or a G11. The HEQ5 isn't too bad...ask Bert on here as he has the setup and has taken some wonderful pics using the Tal 200K

There are some reviews on Cloudynights about the scope and also there's a Tal Yahoo group.

anthony2302749 · #9 20-12-2006, 07:49 PM

Hi

We have been down this path before in regards to which SCT is the best for planetary imaging. The truth is, it is all to do with technique just look at Mikes work with a 10" Dob and I have seen some very good work done with an 8" LX90 (serach forum). When it come to planetary imaging, apature is important, but technique is the key. It real does not matter whether you use a 8" , 9.25" 10" SCT etc what you need is excellent collimation, telescope cooled to apparent temperture, good quality zero-shift focuser, excellent quality barlow, excellent quality UV/IR filter, excellent quality industrial web cam, a good mid range PC with 7400rpm HHD, 1.6 Ghz processor or high and above all excellent see conditions. If you can do all this an practice, parctice, parctice then your current 9.25" SCT will work equally as well as any scope used for planetary imaging.

Anthony

jase (Jason) · #10 20-12-2006, 08:08 PM

If you're after a specialised instrument such as a dall-kirkham optical design, you may wish to check out - http://www.unitronitalia.it/gladio.htm
With a native focal ratio of F/25, it has planetary telescope written all over it.

Robert_T · #11 21-12-2006, 10:22 AM

Thanks Guys,

Jase I've seen those Lazarroti? optics on the web before and have been intrigued - I wonder if anyone has used them on the forum. They look ideal from pov of F ratio and cool-down properties... dew might be a problem though!

Anthony, I certainly agree on all the factors you list needed for top planetary photography. I have them all from Lymax coolers to Hutech mirror locks and zero shift moto focusser, the DMK industrial grade firewire mono cam and motorised filter wheel and take great care with collimation etc using bob's knobs etc, the latest processing software etc. I can always use more practice on technique of course and am constantly learning tips from the guys here and the getting the best seeing is all about putting in the time to score those sweet moments. With these in hand though it must be said that aperture (optical quality being equal, and that's perhaps debatable between C9.25 and C11) should deliver finer detail due to improved resolution capability... when the seeing conditions allow. Guess I'm seeking a little leg-up for that bity of extra motivation

cheers,

davidpretorius · #12 21-12-2006, 11:24 AM

i am reserving my right to a reply once paul haese starts smacking around his 18" SDM.

In my mind (with no real hard evidence) c14 and c9.25 were always the picks for planetary, but the CHris Go in cebu is producing fantastic stuff.

Paul once explained the difference between c9.25 and c11.

My gut feel is that if we can sort cooling issues out with big mirrors, then 16" and 18" dobs or SDM's may be the go????

Robert_T · #13 21-12-2006, 11:33 AM

Quote:

Originally Posted by davidpretorius

i am reserving my right to a reply once paul haese starts smacking around his 18" SDM.

In my mind (with no real hard evidence) c14 and c9.25 were always the picks for planetary, but the CHris Go in cebu is producing fantastic stuff.

Paul once explained the difference between c9.25 and c11.

My gut feel is that if we can sort cooling issues out with big mirrors, then 16" and 18" dobs or SDM's may be the go????

Thanks Davo - scuse my ignorance but what's a what's an SDM

davidpretorius · #14 21-12-2006, 11:42 AM

SDM are like the obsessions I think

http://www.sdmtelescopes.com.au/

g__day (Matthew) · #15 21-12-2006, 03:09 PM

If you are really serious about astro-imaging isn't it the mount you should be seriously considering upgrading rather than the OTA, from one fine model to another?

Robert_T · #16 21-12-2006, 06:00 PM

Quote:

Originally Posted by g__day

If you are really serious about astro-imaging isn't it the mount you should be seriously considering upgrading rather than the OTA, from one fine model to another?

g_day, this is for planetary imaging only (is there any other kind?

)... far less demanding on mount precision etc, as the driven dob pics on this site attest. No for me it's all about the optics!

cheers,

g__day (Matthew) · #17 21-12-2006, 10:13 PM

Then yes going by maximum magnification in perfect seeing for a SCT is amout 50x per inch of aperature, you are going from 475x to 550x magnification. So if seeing is good enough I'd guess you'd be pleased, but why not go to a evening viewing and compare these scopes yourself before you part with $$$?

Also definitely read http://www.cloudynights.com/item.php?item_id=1585 a review from an owner of a C8, C9.25 and C11, particluarily on back focus and image shift. For visual the C11 gets best praise, with the C9.25 as best all rounder and best price performance.

John K · #18 22-12-2006, 09:35 AM

Hi Robert,

just to add to the multitude of options that people have provided you with might also like to consider a 14.5" or 16" Conical Mirror in a Dobsonian with Truss and an equatorial platform. Likely to cost you around the same as a C11 but with far better optics and more aperture.

http://www.rfroyce.com/conical/

jase (Jason) · #19 22-12-2006, 10:20 AM

The R F Royce mirrors are nice. I've looked through a 10" and was very impressed with the views. Would highly recommend them. Though at native focal ratios between F/4 and F/8, they're quite fast for a planetary scope. Sure a barlow or powermate can resolve this, but why add more glass to your imaging train when you can get a scope with a higher native focal ratio such as F/25 found in some classical cassegrains or dall-kirkham optical designs.

Depends on how much of a purist you want to be.