First Widefield shot with Astrotrac

[Specman]

The Astrotrac worked well and tracked for over 90 minutes without star trails. Polar scope was a bit of a faff (magnets that hold it are worse than useless).

It appears I have a lot to learn about taking pictures of a pitch black sky!

Here is my first best attempt of Orion, 12x 30 second exposures @ ISO 800, EF24mm lens Bulb setting wide open. On a positive note, no star trails But that is about all this shot has going for it!

I also soon discovered how rubbish my collection of lenses are and how difficult to focus in the dark it is. Even worse with a EOS clip filter fitted.

Any pointers from an expert would be appreciated. Thanks

[LukeSkywatcher]

Very nice image. Orion doesnt pop out at you like it can do. Maybe try it again but with more exposures.

Betelguese,Rigel and M42 are starting to come alive. More exposures i'm sure will bring them out more.

Nice dark sky there.

p.s.~~~i am no expert. You have taken a better image of Orion then i ever have.

[saturn5]

Well Orion looks nice and sharp so theres not much wrong with your focus on this occassion.With regards to the focusing,if possible focus on the brightest star/planet you can see.You will see it get smaller as you get nearer focus,when you go beyond the focus point it will start getting "fatter " agian,just repeat the process till you think you have the star as small and sharp as is possible.With a bit of practice it becomes quite easy but it is a bit of a pain to start with.You should be pleased with your first shot.

Dont have to through that malarky any more since i got a lens with an infinity mark on it.

You should try much longer exposures.2 or 3 minutes will really show up the gems Orion has to offer.Stack several of those and you'll see a big difference.

Whereabouts in Orkney are you,I'm from Stromness but made the exodus to a Dounreay apprenticeship 35 years ago and stayed here ever since

[Specman]

Dont have to through that malarky any more since i got a lens with an infinity mark on it.

You should try much longer exposures.2 or 3 minutes will really show up the gems Orion has to offer.Stack several of those and you'll see a big difference.

Whereabouts in Orkney are you,I'm from Stromness but made the exodus to a Dounreay apprenticeship 35 years ago and stayed here ever since

Thanks Stewart,

My 24mm lens has infinity marked on it also. A god send once I discovered it!

In your Orion Astroscapes you said you used the following:

Canon 17-40L lens @19mm

30 second exposures

F4.5

ISO 4000.

How come the image isn't washed out at 4000 ISO? I tried 1600 for 3 minutes and the RAW preview seemed rubbish so I binned it. Over exposed and washed out. Picked up loads of light polution.

I'm down in the South Isles, Burray.

Cheers

Mark

[Beyond_Vision]

I would increase the sub time at 24mm focal length you should be able to get 5 minute with reasonable polar alignment. Use the liveview function at 10 x on a bright star to focus. If you can after focusing I would check the image on a laptop to make sure you are focused prior to starting the run off.

[Specman]

I would increase the sub time at 24mm focal length you should be able to get 5 minute with reasonable polar alignment. Use the liveview function at 10 x on a bright star to focus. If you can after focusing I would check the image on a laptop to make sure you are focused prior to starting the run off.

Thankyou for your reply.

I know that you yourself use an Astrotrac and have a couple of questions about the polar scope and arm.

Firstly, if you remove the illuminator and put the scope in from above (which makes more sense) you get a nice positive magnetic 'clic'. When fitted to the arm from below, the magnets barely hold the polar scope in place. It is as if the arm has been assembled upside down. Do you have a similar problem?

Secondly, when polar aligning is it best to do it with the arm at 180 degrees (opposite) the tracking arm or doesn't it matter? Can you just move the arm to a more comfortable position for alignment?

Do you have any tips for a better polar alignment? The instructions were a little confusing.

Thanks

Mark

PS I was running the camera through the laptop to check focus. Quite a long winded procedure.

[Beyond_Vision]

Yes it quite easy to dislodge the polar scope and drop it on the floor this is probably the only flaw in the design. You can secure it with an elastic band. Once the polar alignment is done it's best to remove it so that you dont end up dropping it. I believe a member called Wobbly Bob has come up with a good method of securing it in place although I cant recall how he did it. You could drop him a PM to ask. The polar scope arm can be moved to where ever it is comfortable.

Here's a copy of a post I made on how to polar align it.

Make sure the tripod is level and that the Astrotrac is facing North. A quick tip here is not to fit the polar scope to the polar scope arm at first. With the polar scope arm swung out use the hole where the polar scope fits to roughly sight the mount on polaris. It is much easier to use a geared tripod head to adjust the angle of the mount. Place the polar scope back in and you should still have polaris in the field of view. Rotate the polar scope so that the the Plough and Cassiopeia on the graticule are in the same position as the constellations in the sky.

There are three alignment points on the polar scope graticule you may not be able to see all three stars that are associated with the these marks unless you are in a dark sight. You should be able to see at least one or two of them. You will need to alter the azimuth and altitude of the mount (and possibly a small rotation of the polar scope) so that at least two possibly three of the stars line up with the marks.

With wide angle lenses below 30mm just getting polaris on it's mark would be good enough. The longer the focal length of the camera lens / scope the more accurate this will need to be. At long focal lengths you may then need to drift align.

Regards

Kevin

[saturn5]

Thanks Stewart,

My 24mm lens has infinity marked on it also. A god send once I discovered it!

In your Orion Astroscapes you said you used the following:

Canon 17-40L lens @19mm

30 second exposures

F4.5

ISO 4000.

How come the image isn't washed out at 4000 ISO? I tried 1600 for 3 minutes and the RAW preview seemed rubbish so I binned it. Over exposed and washed out. Picked up loads of light polution.

I'm down in the South Isles, Burray.

Cheers

Mark

The shot was taken from a dark site with very little light pollution,only a few small villages which are miles away and no moon,not quite as dark as it gets but getting near it.Limiting magnitude is about 7 but about 10 miles further to the southwest,in among the hills its supposedly nearer 8.

[Specman]

Thank you for all your replies. I'll have another go and report back.

Clear skies!

Mark

[Zul]

Very nice!