How to take long exposures of DSOs with Skywatcher 150PL

[PhoenixRising]

Hi all,

Well, my dual axis motors arrived and have now been fitted to my eq3/2 mount. Im using a 150pl Scope and a Canon 350d in prime focus and will also dwant to do some experimenting with a focal reducer and nebular filter with eyepieces.

My question is, how do I use the afore-mentioned motors to maintain the stars in position on screen whilst I have the shutter open to avoid star trailing? If the cameras connected I cant see what Im doing. So how do I get get the 1-5 minute exposures I want? I realise I have to Polar align accurately but does anyone have any other tips?

My first targets will be Plaedies and Nebula in Orion, possibly Andromeda galaxy depending on seeing over the next week or two.

Thanks all for any help

[Hawklord]

Ideally you need a guider. Either another cheaper refractor attached to your main scope or mount and using a high magnification eyepiece or an illuminated guiding eyepiece. An alternative is to use an off-axis guider, but it might rob you of inward focus travel.

[PhoenixRising]

So I get a cheapish refractor and mount it to my newt so I can see more accurately what I'm looking at through the refractor whilst the shutter is open, manually adjusting the motors with the hand unit, keeping one of the stars in the centre of my fov to prevent streaking, starting at say 20-30sec subs, then moving up as I get more skilled, is that right?

[Beyond_Vision]

Ideally you need a guider. Either another cheaper refractor attached to your main scope or mount and using a high magnification eyepiece or an illuminated guiding eyepiece. An alternative is to use an off-axis guider, but it might rob you of inward focus travel.

Not something you can do with a eq3/2 mount as it does not have the ability to be autoguided.

Phoenix what you need to do is get the mount as accurately polar aligned as you can. Then spend some time getting the scope focused as properly as you can. You will need to point the scope at a bright star like Vega, Deneb, Cappella whatever is visible from your location. You will need to adjust the focus slowly whilst looking through the camera view finder. Get the best adjustment you can then take a short 10-15s image. Check the focus on screen and if need be adjust the focus a small amount noting the direction you have rotated the focus knob. Take another picture if it's worse rotate focus the other way a small amount. This can be a bit time consuming but gets quicker with practice.

A right angle view finder that clips onto the DSLR viewfinder can help a lot. These are available on Ebay etc for around £20-30.

I would take short exposures to start with and increase the time until you see the stars elongated. Then reduce the exposure time to maintain round stars. You will probably find that you will only manage no better than 1-2 minutes with your current mount.

Regards

Kevin

[Hawklord]

Yep, though it can be quite tiresome to begin with. Long focal lengths on the refractor with accurate polar alignment helps. It also needs to be well fixed to avoid flexure and pointed roughly in the same part of the sky. With good alignment and practice you may only need to use the RA adjustments.

[jgs001]

Once you've got the maximum exposure time you can, take a very large number of frames.

[PhoenixRising]

So its a tossup between a guider scope, or a right angled viewfinder for the 350d? I find the 350d has a very small viewfinder, and although Id prefer to use the camera to guide, I think the view finders too small. The 350d has no live veiw (I think). So which guider scope do people recommend?

[jgs001]

I thik it was said that you can't guide the eq3-2. So aim for 30s to 1 minute and take over 100frames. You should get some reasonable results like that.

[PhoenixRising]

sorry, I meant to say finderscope, Im trying to work out whether to get a right angled viewfinder for the camera, get a better finder scope, or whether to attach a small skywatcher travel refractor to my Telescope?

[Beyond_Vision]

You cant autoguide with your current set up. The right angle view finder I mentioned is just to help you focus it attaches to the DSLRs viewfinder. Like the one in the following link

1-2.5X Angle Finder for Canon 5D 20D 40D 30D 350D A1D - eBay (item 260417891718 end time Nov-22-09 17:47:34 PST)

[PhoenixRising]

Well, after 5 hours of pain tonight I worked it out. I thought you had to hold a button in on the remote to make the motors move, you dont! So, after 7 weeks of waiting, I set up tonight in a quite misty night to try to get mt first DSO pic. I realised that using a camera with eyepieces is really only for planets. I tried various 1.25 inch eyepieces in an Antares camera adapter also occasionally using an Antares focalk reducer. Waste of time, FOV was so small there was no point. Anyone got any ideas how I can increase my FOV on a Skywatcher 150PL for imaging DSOs? Anyway, I finally figured out how to use the motors and just stuck my camera into the telescope for some prime focus pics. I went for Paeides. Some of it is missing because, as explained, I just couldnt get set up using eyepieces and am not sure where to go from here. So, quite misty and light polluted night. First proper attempt, 22 30 second subs, 7 dark files, iso 800. (I think thats how to say it all anyway!) Go easy on me, this is the hardest thing Ive ever tried to learn. Any tips? Also, any ideas how I can increase my FOV on this scope for pics? Thanks for any feedback

[jgs001]

You're off to a very good start there, now you're working out some of the kinks. There's a lot of experimentation needed to work it out, then just wait till you change something ...

Anyway, the stars look good, they've stacked well. There's some vignetting showing, that'll be caused by using the 1.25" ep fittings. I wouldn't worry about that at the moment though.

I can't help on increasing the FOV though sorry.

[PhoenixRising]

Right.

Having had no joy with the Antares Eyepiece Adapter and various eyepieces and methods of connecting, problems with light gathering and vignetting etc, I was sure there had to be another solution to my problem. Prime Focus is nice but very little FOV, prob only 15-20 deg.

Having done some research online, I found some people were using the Baader Hyperions which connect straigt to the camera. So I bought this:

Baader Hyperion Clickstop Zoom 8-24mmTelescope Accessories | Rother Valley Optics

8-24mm, tried it in the shop, connects beautifully to my Canon 350D, no vignetting, 2" compatible, and no faffing with eyepieces etc, also suitable for planetary. Ive seen some of the DSO work this device can produce and am impressed. I also have a 0.5 focal reducer to use with it just in case! Surely now I've cracked my humble beginnings in this hobby. Ill repost after a clear night to let you know of progress, there have to be other newbs like myself having these problems and although Ill be eating beans on toast till Chrismas, It'll be worth it to get a good Stack of the Pleaides.

[Hawklord]

Really nice and pretty impressive for first attempt. You've even got some nebulosity. Fingers crossed for clear skies!

[PhoenixRising]

Heres another go from tonight, 2 1/2 hours dodging wind and cloud to get 22 shots of which DeepSkyStacker only used 5!! Dammitt, I cant feel my fingers now! I think its ok. would have uploaded as a tif but the file was too big (10mb), as Id really like to see what this could look like if someone processed it, I think theres alot more can be pulled from pics with a bit of CS knowledge. Anyway, here it is: 5 subs, stacked in 6 dark frames. Iso 800, exp 30 secs each, prime focus no filters, blumming cold and windy!

[PhoenixRising]

Sorry Guys, just posting the same pic after floundering around in photshop for a bit, still learning and all. Any tips on post prcessing from anyone?

[iamjulian]

I'm no expert, but there seems to be some extra data in the blue channel.

Image below only to display this blue light, not intended as a finished photo

I don't know the Pleiades well enough, but could this be nebulosity, or not?

Hope you don't mind me playing with your excellent image!

[jgs001]

I think you're making nice progress... You appear to have clipped the black quite badly in the editing, and this has caused a loss in the nebula. I think there is probably a lot more you can pull out... Have a look at MartinB's processing tutorial (section 3 in tips and tricks) on stretching the histogram. Be careful not to cut into the main curve of the data though.