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Old 12-02-2015, 03:39 PM
GeeM (Graeme)
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First images from my SW 200mm GOTO Dob

Hi everyone,
I took a few shots through my new 8" GOTO Dobsonian to get an idea of what's possible with a Canon 6D. I understand I'll never come close to most of the images I see on here but I had fun just the same. Pics taken from a light polluted backyard so I'm keen to try under a dark sky. Very interested to here your thoughts.

Cheers,
Graeme
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Old 12-02-2015, 04:33 PM
raymo
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It is always a good idea to list details of image acquisition, such as ISO,
exposure, number and duration of exposures in the case of stacked images, and any other pertinent info. It is much easier for members
to offer help, advice, etc:
Anyway, good first effort. In case you weren't aware of it, Dobs are not the best for serious astro work, because of field rotation, but are
capable of nice basic images.
raymo
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  #3  
Old 12-02-2015, 05:12 PM
Akwestland (Andrew and Kim)
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Graeme,

I like the photos.

I am new into Astronomy and one day would like to head down this path I feel. I did take a single image exposure with my mobile phone holding it against the eyepiece of my telescope. It took several attempts but I was suprised at the result. Maybe one day I will put it on here.

Cheers
Andrew
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Old 12-02-2015, 05:13 PM
GeeM (Graeme)
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Thanks Raymo,
Yes I understand the Dobs limitations, its nice to have a few photos to be able to share with friends and family.

They are all single exposures taken with a Canon 6d prime focus.

Orion Nebula - ISO 6400 2 sec
Tarantula - ISO 6400 10sec
Leo Triplet - ISO 12800 20 sec
Mimosa & DY Crucis - ISO 25600 4 sec

Post processed in Lightroom 5.

I am intrigued with Tarantula. I would like to get a better image of that. Darker skies will help I'm sure.

Last edited by GeeM; 12-02-2015 at 05:14 PM. Reason: Additional context
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Old 12-02-2015, 06:06 PM
GeeM (Graeme)
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Thanks Andrew,
This is my first telescope so I'm a newbie too. I looked into more suitable equipment for astrophotography when I was buying my scope but decided against it. I went for simplicity so that I could learn about astronomy. It became obvious that astrophotography is a very deep Pandora's box and it was overwhelming. I'm happy for now to get what I can from my Dob.
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Old 12-02-2015, 07:46 PM
raymo
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Thanks for the details. My thoughts, for what they're worth. Very few
imagers routinely venture above 6400 ISO, [especially in summer, when
high ambient temps. make the images very noisy]. Many imagers stick
around 800-1600. In very low ambient temps. you can go higher.
I'm curious as to why you used the vastly different exposures and ISOs,
unless you were just experimenting.
A good first step is to take exposures close to 0* Declination [ Orion's
belt, for example], and at high Declination [ Crux, for example], and see how long your exposures in those two places can be before the stars in your images start to elongate.
raymo
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Old 13-02-2015, 02:42 AM
GeeM (Graeme)
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Thanks for your reply Raymo,
Just experimenting with ISO mate to see what I could get. I will work out the maximum exposure time as you suggest and go from there.
Cheers
Graeme
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Old 13-02-2015, 09:50 AM
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rustigsmed (Russell)
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nice work Graeme,

its possible to push the SW goto dobs out to 25-30 seconds. I used to image using iso 3200 and 20 second exposures with my 12" goto. you should be able to get similar results with your setup.

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

cheers

Rusty
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Old 13-02-2015, 10:11 AM
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1kmodem (Will)
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Quote:
Originally Posted by rustigsmed View Post
nice work Graeme,

its possible to push the SW goto dobs out to 25-30 seconds. I used to image using iso 3200 and 20 second exposures with my 12" goto. you should be able to get similar results with your setup.

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

https://www.flickr.com/photos/803366...ream/lightbox/

cheers

Rusty
wow nice photos with the dob
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Old 13-02-2015, 10:30 AM
GeeM (Graeme)
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Thanks Rusty,
Thanks for sharing your images, that gives me something to aim for.
I need to add a counterweight to the mirror end to offset the weight of the camera. I had to remove the finder scope as the front end of the scope kept creeping down under the weight.
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Old 13-02-2015, 10:43 AM
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Quote:
Originally Posted by 1kmodem View Post
wow nice photos with the dob
Thanks Will it is amazing what is achievable with 20 seconds subs on the brighter DSOs.

Quote:
Originally Posted by GeeM View Post
Thanks Rusty,
Thanks for sharing your images, that gives me something to aim for.
I need to add a counterweight to the mirror end to offset the weight of the camera. I had to remove the finder scope as the front end of the scope kept creeping down under the weight.
Yes I guess the 6d is heavier than my 600d and the scope would be a lot lighter. Might be worth looking into those magnetic counterweights for the dob
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Old 13-02-2015, 11:24 AM
GeeM (Graeme)
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Russell would I be correct in thinking that the unwanted effects of field rotation could be reduced when imaging objects perpendicular to the axis of the earths rotation? I'm guessing I might be able to take longer exposures when the scope is tracking using primarily one axis. Is this what Raymo was eluding too in his previous post?
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Old 13-02-2015, 11:29 AM
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1kmodem (Will)
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With the Prime Focus on the dob, are you guys using any extender/Barlows/powermates?
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Old 13-02-2015, 11:45 AM
GeeM (Graeme)
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Quote:
Originally Posted by 1kmodem View Post
With the Prime Focus on the dob, are you guys using any extender/Barlows/powermates?
Will, my images were prime focus - no Barlow. The field of view seemed spot on for large nebula type objects. For planets I'd need a lot more magnification.
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Old 13-02-2015, 11:46 AM
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Quote:
Originally Posted by GeeM View Post
Russell would I be correct in thinking that the unwanted effects of field rotation could be reduced when imaging objects perpendicular to the axis of the earths rotation? I'm guessing I might be able to take longer exposures when the scope is tracking using primarily one axis. Is this what Raymo was eluding too in his previous post?
you are indeed correct in your thinking. there is even a formula for it:

The formula (not quite the whole story but pretty accurate) is:
Time (sec) = amount of rotation (degrees)*cos(Alt)/(0.004167*cos(Lat)*cos(Az))using the normal definitions of Latitude, Azimuth and Altitude.

0.1 degree as a rule of thumb for acceptable field rotation.

it is a balancing act however, shooting near the zenith (straight up) the dobs struggle to track accurately (and it rotates more quickly). shooting too close to the horizon you are going through too much atmospheric muck.


Quote:
Originally Posted by 1kmodem View Post
With the Prime Focus on the dob, are you guys using any extender/Barlows/powermates?
I just used a coma corrector for deep space objects. when doing planetary however I use a powermate and sometimes a powermate and a barlow.
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Old 14-02-2015, 10:30 PM
GeeM (Graeme)
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Quote:
Originally Posted by rustigsmed View Post
you are indeed correct in your thinking. there is even a formula for it:

The formula (not quite the whole story but pretty accurate) is:
Time (sec) = amount of rotation (degrees)*cos(Alt)/(0.004167*cos(Lat)*cos(Az))using the normal definitions of Latitude, Azimuth and Altitude.

0.1 degree as a rule of thumb for acceptable field rotation
Ok Russell, what am I missing.... I've tried to work out that formulae but to no avail. What do I enter in the first part of the formulae - amount of rotation deg?

Cheers
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Old 18-02-2015, 11:51 PM
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Ok Russell, what am I missing.... I've tried to work out that formulae but to no avail. What do I enter in the first part of the formulae - amount of rotation deg?

Cheers
Sorry mate, i haven't checked this for a while - im fairly sure it is correct. - i don't have the reference in front of me and yes, 0.1 but now you've confused me, but I did have a crack around when i posted my last one, i got 18 seconds for 45 degrees altitude from your profile location looking due east or west.
the best spot is near east or the west and under 45 degrees alt. you are closer to the equator which makes it not as good for you (if you were at the pole it would pretty much make it equatorial!). But saying that my photos were 20 seconds, and its the outer part of the frame that gets the field rotation first. you can stack and crop out the perimeter.

keen to see how you go

rusty
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