GPS or non-GPS telescope?

[vivid]

Hi guys,

I'm a noob deciding between stuff like CPC 1100 or C11 is better.

Just wanna ask if I were to enter the coordinates/time on the C11 it would be just as good here in SG. I'd be basically orbbing most of time at the rooftop (163m AMSL). I have receeded, there are 3 different locations which would enable me to cover a 360 deg view, and 25 deg from zenith is pretty ok.
The $$$ saved would be useful for accessories, eyepieces etc.
I guess with a CG-5 mount it'd be more flexible for astrophotography next time as well. Don't wanna end up with something limiting, I mean the conditions here in SG is already limiting. ie, see clear skies, I can set it up by 10 mins up there, no sweat. I want it "fast".

Home -> Lift which is 3m away -> rooftop garden. Nearest point @ garden is a 20m walk. The other 2 points are about 200m walk, so it could be as much as 400m walk.

Question : OTA can use a bag, i'd carry it to protect from vibrations else end up collimating every time I use it. LOL. The tripod's the big issue, how does one carry it? Those free trolleys they include with printer purchases @ PC show ok?

I'm a amateur photographer turned pro-photographer, last time during hobby time I was the siao type who trekked several clicks with tripod/cam, camo etc just to get nature shots, birds etc. But this time is 42kg, no joke.

Cheers!

[orly_andico]

Fork mounts set up faster because you don't have to polar align. Trouble is you cannot separate the tube and the fork, so the total weight is quite high.

I think the CG-5 is marginal visually for a C11, and is way underweight if you wish to do DSO astrophotography with the C11. I think a C9.25 or smaller is the upper limit for a CG-5.

[Gary]

Wa! Duxton Rooftop Garden access.

10 min a little too long. With more practice, try to aim for 5 - 6 min. Was obing a couple of days ago, by the time I change my eyepiece to a higher mag (a few seconds) the clouds blocked the view already. lol.

Dont mind paying 5 bucks to ob there someday. Much better than paying 20 bucks at Sands Sky Park .

[vivid]

Orly, seriously I would not mind a C9.25, just that its way more ex than the C8 and the C11 is a better value. Anyway if jump from C8 to C9.25 not much diff in terms of aperture.

What would be the issue with very very long exposures with the CG-5GT if i were to slap on a dSLR? Lets say just a D90. (700g body)



One question, would just entering the coordinates found on google earth be sufficiently accurate as compared to the GPS found in the CPC for accurate Goto? Or not so impt after a while, so that I can skip the CPC.
It would be a really big object to squeeze into the drybox as well. (And I already have a pretty big drybox).

Gary, if you interested I bring you up there lah.

Anyway I am also interested in the magnification, coz got good view to do terrestrial....wanna peek at Batam as well....ships, Shenton Way offices etc. There were instances where there were excellent atmospheric stability, distant lights do not twinkle much or at all. Batam absolutely no issue, we are talking about seeing Tg Balai/Pulau Tebbingtinggi. (I need something to convince my wife/FIL that it is worth it, coz they Indo... LOL!). "Got use".

[orly_andico]

Long-exposure imaging with DSLR is a very big challenge with SCT.

I started a thread about this on CN Forum some weeks back (I'm using a C9.25) and the consensus is that Atlas/HEQ6 is minimum, and you should go larger (e.g. Losmandy G11, AP Mach1 GTO) class if you're serious about DSO imaging with a C9.25.

Here is that thread..
http://www.cloudynights.com/ubbthreads/ ... ll/fpart/1

The same advice would apply to the C11 as it's both heavier and longer focal length.

The advice I took was.. give up the thought of DSO imaging with an SCT.

[weixing]

Hi,
IMHO, GPS are not importance for GOTO telescope in Singapore. A single set of Singapore coordinate can use anywhere in Singapore. Also, some of our handphone got GPS ma.

By the way, if you want to take very very long exposure, you need to do guiding... Basically, IMHO, you need to do guiding for scope with focal length greater than 1500mm even for shorter exposure.

Have a nice day.

[vivid]

Hi,
IMHO, GPS are not importance for GOTO telescope in Singapore. A single set of Singapore coordinate can use anywhere in Singapore. Also, some of our handphone got GPS ma.

Bro, tio lah.... our mobiles got GPS coordinates. Though resolution is often in the 50-100m range, I think it will do nicely.

If that's the case with HP GPS I guess also can bring it to my wife's hometown in Pulau Tebbingtingi, which is about 60km from Tg. Balai (nearest source of light pollution). Pure black skies at night on the rooftop which blocks off all direct lights from the street level (not tha they are bright in the first place). The air is darn clean too, coz Straits of Sumatra mah. I was absolutely mesmerised even with just the naked eye.
But if some neighbour begins to clear the land or burn rubbish then siao liao lor.....

Orly, thanks for the info!

[orly_andico]

add on to Weixing's post...

I used to think that with a very good mount, you could avoid guiding. I was wrong.

Even an 800mm FL telescope, with a 5-micron pixel pitch (14MP DSLR, the D90 is 12MP so maybe 5.5micron, pretty close) would have a per-pixel resolution of about 1.2 arc-seconds.

The best mounts out there (e.g. Astro-Physics) have +/- 3 arc-seconds periodic error. The CG-5 has about +/- 20 arc-seconds (!!!) or 40 arc-seconds peak-to-peak.

edit: the ASA DDM85 claims sub-1 arc-second resolution, it uses a harmonic drive instead of worm gears.. but at a large cost and weight.

Now a C11 has a focal length of 2800mm, for a per-pixel resolution of 0.3 arc-seconds! so the mount error will completely swamp any resolution you get from the C11.

Also consider that urban seeing causes disruptions in the order of +/- 5 arc-seconds (it's much, much worse in the day.. so forget any ideas of reading street signs in Batam.. with my C9.25 during the day I can see heat shimmering over <1 km distance at the eyepiece).

The bottom-line is, everybody starts imaging with a fast, short refractor. I have a Zenithstar 70ED but I think the Megrez 72 is better (also buy the field flattener when you can no longer tolerate oblong/comatic stars at the corners of your image). This will serve well for DSO imaging for a long long time even on a CG-5 class mount. Wait! you say, a measly 70mm telescope has poor resolution. And yes, it does.. around 2.5 arc-seconds or so. But when you consider mount error, seeing error... the 2.5 arc-seconds ain't so bad, it will not be your limiting factor.

If you want to go up against Rob Gendler and do multi-hour exposure of small DSO's (e.g. planetary nebulae or Hickson galaxies) then prepare to cough up huge $$$ for a capable mount.. kind of defeats the portability clause..

On the other hand, if planets is all you want, I believe a CG-5 can marginally carry a C9.25 or maybe even a C11 if you reinforce the tripod. That's my plan (when my Great Polaris gets here... stuck with VPOST reorganization)

[timatworksg]

Prob with mounts are that the payload specs shown are never correct..or near correct. An SCT coupled with a DSLR already subtracts the payload max by a pretty fair chunk. Then finder or guidescope, a CCD guider if attached, extension tube if needed,..etc etc, will pretty much bring the overall payload close or slightly exceed the shown max. Sometimes you get lucky,...but with DSO's it's tricky and even with guiding software it'll be frustrating when tracking seems off! As Orly mentioned, the diff in arc-seconds causes error, coupled with gear ratio, counterweights, payload, wind, thermal, etc etc. I tried DSLR to C8 but still fell back to my 80ED! using my Meade DSI would significantly lighten the payload, but it needs a laptop! Where else a DSLR+drift alignment makes set up easier.
Kinda agree with orly that SCT imaging will need a sturdy expensive mount...Paramount SE??...lol! And switching back to my 80ED is kinda testament to that.

Probably why it's mostly home Observatories can pack all the accessories for great DSO pics! For outings/camp outs, a good mount (heavy), counterweights, DSLR, scope, EP's, accessories, CCD, laptop, battery....my back can take it!,,.,lol

Personally, if you can find a niche and don't crave luxurious imagery, simple set ups with a DSLR suffice and I like the wide view of an 80ED. Importantly,...it's all in the fun of trying! If you do a web search, some pretty decent images have come from an IOptron Mini tower!! And they are DSO's,..though not as intense as those 7hr comps! Find an avenue and stick with it, learn, try and then as you progress, improve and upgrade. I'm still stumbling, but it's a hobby and whatever is done is always fun...no matter how weird!

[orly_andico]

My friend Kevin in the Philippines uses a Kenko Sky Memo with a 100-400mm L IS lens. That's his grab-and-go astrophotography setup.

I'm planning to retain my Z70 for astrophotography, and an Orion 100mm ED as my visual grab-and-go.

The C9.25 is just too darn large to be a convenient carry scope.

(don't get me started on my 10" dobsonian....)