Sky-watcher Explorer 150PL and EOS550D...what do I need to know?

[Nastyness]

Hello all!

I've just purchased the above and would like to have a go at astrophotography...I also have a Rev Astro 2.5x Barlow lens and all necessary t-adaptors, etc... So what do I do now?! What kind of images can I expect? Deep-space and planetary would be nice, but is that expecting too much from this setup?

Also, what kind of magnification can I expect? I'm not clear on the calculation!

Many thanks.

[brantuk]

Magnification is focal length divided by eye piece size but it's the field of view on the camera chip that's important for photography. Try either 12Dstring or CCDCalc to estimate the field the chip will pick up (both free to d/l) :

http://www.12dstring.me.uk/fov.htm

The New CCD Astronomy Home Page

Do you have an eq mount that's polar aligned and an RA motor at least? And are you guiding or just tracking? I'm not particularly good with dslrs but you'll need raw mode, start with shorter exposures of 30 secs to 1 min, and experiment a bit between ISO 400-1600. Choose a bright object that's high at the moment - I'd suggest M42 as a good start for a first object. Oh - and you won't need the flash but you will need a bhatinov mask to focus.

Others will have better or more specific ideas but I hope that helps to get you on the way

[Parus major]

I'm by no stretch of the imagination any good at imaging nor will I ever be. Just to give you an idea of what the 150PL ota can see I got this with a webcam and a fair quality mount-

A decent camera like yours will do far, far better. I just though I'd post the "size" of image you can expect.

[RikM]

That's a smashing pic. The 150PL with a webcam is great for that sort of thing. Using a DSLR for planetary images is very difficult. The chip is huge compared to the webcam so the planet will just be dot in the middle of the frame. You will need quite short exposures. Take loads and use Registax to compile them.

For deep sky images you need a really solid EQ mount and long exposures. As long as you can without star trailing. Again, take loads and stack them up. For deep sky images, use Deep Sky Stacker.

Both software packages are free to download.

[Nastyness]

Do you have an eq mount that's polar aligned and an RA motor at least?

I have the EQ3-2 mount and have no problem with polar aligning, but I have no RA motor...to be honest, I didn't realise I needed one! Just had a quick look and it looks like I could get a dual axis kit, or just the RA kit? What would you recommend?

[brantuk]

I got the dual axis kit on my 150P when I had one. You'll need an RA motor at least to track the object as it moves across the sky, otherwise long exposures will just elongate or yield star trails.

I think you need to get a good book though to totally familiarise yourself with astro photography - it's quite a steep learning curve - Steve Richard's "Making Every Photon Count" is excellent to guide you through all that's needed.

Here's a review with a link to where you can order it

http://www.astronomynow.com/books/MakingEveryPhotonCount.html

[RikM]

I have the dual axis drives on mine too.

[Nastyness]

I have the dual axis drives on mine too.

It is necessary, though? Will just the RA motor be enough to track and capture images similar to your's?...which by the way, are stunning!

I won't be mod'ing my 550D...so will I be needing an LPS filter? If so, can anyone recommend a good but reasonably inexpensive one?

[Parus major]

For tracking you only need the single axis motor but for the sake of twenty quid the dual motors would be something you'd wish you'd went for. Using the hamdset for one axis and the slow motions for the other I'd find counter intuitive.

[RikM]

Thanks for that

I bought the dual drives because I thought it would be good value. £70 for one or £90 for two??? Actually in hindsight I wish I had got the single RA drive and a 2" SW LPR filter for more or less the same money. But...I do need to qualify that...I am dyslexic and I can't tell which handset button moves the scope in which direction. I have to press a button and see which way it moves, then try again, and again etc. With just RA on the handset and a slowmo for DEC I think it would be easier, certainly faster. But that's just me.

The 150PL is much longer focal length than the 150P that I use. That makes it (probably) a better all round visual scope, but not so suited to deep sky imaging, which is my main interest. At f/8 you will need much longer exposures to gather the same amount of light as I get at f/5. You will also need more accurate polar alignment because star trailing will start to show sooner.

For webcam imaging of planets and the moon though, it is the other way round. The PL has the advantage because the longer focal length gets you upclose and personal and since these are bright objects, long exposure time is not really an issue. Webcams tend to beat DSLR because you can take many hundreds of exposures (1 - 3 min avi at 15 frames per second!) that gives you a better chance of getting sharp captures.

Brantuk's recommendation of Steve's book is spot on BTW. If you want to get into deep sky AP it would be well worth getting a copy.

[Nastyness]

are you guiding or just tracking?

Being new to all this, I'm not completely sure of the difference? Is guiding similar to focal subject tracking in a camera, where you would pinpoint the object you are wanting to capture and the guide system will follow it? Where as a tracking system relies on very accurate polar alignment and possibly some human intervention?