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poltabs

By poltabs
in Imaging - Discussion

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poltabs

poltabs

Posted
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OK I have decided to wait until either the funds build up enough or a second hand CCD comes onto the market before buying I thought I would jump into the auto-guiding now.

Firstly how long can you expect to capture for before auto-guiding becomes essential? I know it will depend on the mount and accurate polar alignment but roughly what could I expect with the Nexstar 8 GPS?

OK so onto auto-guiding, havent got any of the hardware so what would you recommend as a scope and camera to start auto-guiding succesfully? Bearing in mind I am trying to keep the spend down as am saving for the CCD? I dont want to use a Toucam as they dont appear to be sensitive enough so anyone any thoughts and ideas?

Many thanks

Kevin

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narrowbandpaul

narrowbandpaul

Posted
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the orion starshoot autoguider is the one we use. It is fantastic. We have used it on a variety of scopes from 60mm-78mm apertures, and it always picks up a star...well more than one. it is more than sensitive enough to pick up 8th mag stars, but your field of view is dictated by the focal length of your guidescope.

If you can, to get the most accurate guiding, I would recommend guiding at a similar resolution as your imaging...to a certain extent. Can you calculate the resolution of a telescope/camera combo?

The Startravel telescopes from SW present good value for money. The 80mm or 100m f/5 might do if your tube is sturdy enough. There are also longer focal ratio options if these scopes are too short focal length wise, also from SW.

i am describing here separate guiding, completely independant of whats in your imaging train. It allows for narrowband imaging, and using guidescope rings allows you to easily find a star if one is not present.

The camera is around £100, the scope is less than £200 (i think)

if you need anymore help just drop me a line.

With regards to your CCD choice, I quite agree with biding your time and saving up. We might be doing the same. Plus you can do some more research, to make sure you get the right camera for you

best wishes

Paul

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SteveL

SteveL

Posted
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One issue not mentioned above, and something as a fellow NS8GPS owner I need to tell you, is that a 80mm or 100m OTA on the NS8GPS will cause problems. Sure, you can get it to balance with some extra counterweights (err... a LOT of extra counterweights!), but even an ED80 will be a problem because it is just too long to fit comfortably on the top of the C8 tube. I will take a picture of that next time I get the NS8 out, it just looks top-heavy and "wrong". WO66/72 maybe? Do you have a counterweight kit yet? You really will need one before you attach any guide scope to the C8, or you can/will damage the gears and clutches, I would almost put money on you needing more counterweights than you think :D

With accurate sub-pixel guiding,there really is no need to be guiding at the same scale as your imaging. Sure it would be nice to be able to do it, but it gets heavy on the scope and expensive on the wallet to do so.

If you can find yourself a cheap DSI Mk1 (colour or mono), they work great as autoguiding cameras.

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Psychobilly

Psychobilly

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I use a Skywatcher Equinoxe 66-pro with William Optics FF III mounted on my CPC800XLT with 5" guide rings for a guide cam I use either the DSI I C or DSI II C with PHDGUide connected to the mount using a Shoestring Astronomy GPUSB. I have conducted experiments with various combinations of FR and Barlows on the scopes to vary the relative images scale and have found quite acceptable guiding performance with all setups.

At the moment I am going a bit overboard as I use the 8" at f6.3 to guide the "66" and 0.8X FF at f4.8 (approximately) whilst wide-field imaging using a Nikon D200.

Obviously the CPC Mount is a lot more sturdy than the NS8 one so the comments about correctly counterbalancing are very valid... I have seriously "abused" my CPC800 mount and its still happy but have I finally got round to counterbalancing it with about 4.6kg of brass on a rail under the 8" ota...

Billy...

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ngc2403

ngc2403

Posted
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Kevin,

what is you set up at the moment?

if you tel me roughly how long it take before you get trailing in your image or how long your scope can hold a star at a set magnification and FOV then i can give you a rough estimate of the tracking potential of your mount.

i personally get ~ 45seconds to 1minute on a clear still evening. if the seeing is poor then my tracking can be longer. if you think of the trailing as being a star focused to one pixel then trailing is when it moves more to being one and a half long. is you think of the seeing then this becomes see four pixel seeing then trailing starts when you get the stars bigger than 6 pixels. OK?

The stars move at 15arc seconds per second but i have found from a few of the graphs of tracking that i have taken that my mount tracks with ~15.076666 and it is about the average for low end mounts.

I would guess having never seen a Periodic Error graph of our mount type or used one that you would get ~25-60 seconds unguided before trailing at f/6.3. PURE GUESS

ally

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MartinB

MartinB

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Kevin, your unguided tracking time will be dependent on the focal length you are imaging at along with the quality of your polar alignment. It will also depend on the stage you are at in the worm cycle. With my NS8 and a 3.3 reducer along with a very good polar alignment I could manage 3 mins and keep 80% of subs. At F6.3 2 mins is realistic. The NS8 has great tracking, I plotted mine at +/-10arc secs

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poltabs

poltabs

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Oh and what will I need to attach the St80 to the NS8 - guide scope rings & plate? Where do I get those from?

Questions, questions, questions, sorry guys to pester you all

Cheers

Kevin

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