#1  
Old 05-05-2007, 08:45 AM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
300 D Question

Hi All

I have a 300D and am trying to shoot at prime focus on a celestron C11, not into eyepiece projection yet, for a bit more mag i have a 2 by powermate.

Just looking to start on mooon, planets and open clusters.

(Q1) The moon is too bright so i was going to get a moon filter to put behind the T-ring. Then i thought why not get a sky glow filter rather than this. More expensive but maybe more uses. Is a sky glow filter good for sydney skies and a 300D. I have a UHC filter but this would be too dark and would change colour balance?
(Q2) At prime focus i cant set the aperture (no lens) but can vary the shutter speed. What else should i be setting. At the moment i leave the white balance on auto and select raw quality.
(Q3) On 30 second exposures on say the Jewel Box, i see lots of stuck pixels (red and green dots), maybe 30 or more. Is this hopeless or can they be processed out using dark frames?
(Q4) I dont have a polar wedge, but am hoping i can at least get up to 1 minute on my Nexstar 11 alt az mount, is this too ambitious what would be the limit before i get star trails?

Phew lots of questions

Thanks Paul
Reply With Quote
  #2  
Old 05-05-2007, 09:08 AM
JohnG's Avatar
JohnG (John)
Looking Down From Above

JohnG is offline
 
Join Date: Dec 2005
Location: Cootamundra, NSW
Posts: 1,709
Hi Paul

You might want to have a look at this page, may answer some of your questions:

http://www.covingtoninnovations.com/...300Dastro.html

You also might want to download the Astrophotography Exposure Calculator from here:

http://www.covingtoninnovations.com/...astrosoft.html

Cheers

JohnG
Reply With Quote
  #3  
Old 07-05-2007, 04:44 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Took the advice

Hi John,

Thanks for the advice. The dark frame subtracter mentioned in Covingtons was very easy to use.

This is basically my first picture of a star cluster (the jewel box), not very good but I hope to improve. This is 5 stacked 1 minute images on an EOS 300D with no guiding and dark frame subtraction.

I have another question . If i got say a Lumicon Giant Easy Guider but used it on my alt az mount. Would i still get field rotation if i kept the guide star centered?

I took some other pictures but anything much over a minute i get pretty circles so am looking for a way to do astrophotography without polar alignment, but dont know if this is possible.

Thanks Paul
Attached Thumbnails
Click for full-size image (web1.jpg)
118.0 KB40 views
Reply With Quote
  #4  
Old 07-05-2007, 05:02 PM
JohnG's Avatar
JohnG (John)
Looking Down From Above

JohnG is offline
 
Join Date: Dec 2005
Location: Cootamundra, NSW
Posts: 1,709
Hi Paul

Your effort was pretty good for a first try. As you have already found out, you are going to be limited because of your Alt/Az setup. I have no experience using Alt/Az to photograph, I use a GEM. Unfortunately, using a guidestar in that mode will still cause field rotation.

If you have a look at each corner of your shot (blown up) you will see what is known as Field Curvature, unfortunately a problem when using an SCT, you may be able to get away with slighly longer exposures using a Focal Reducer, this will make the image size smaller but you may be able to crop the image to get rid of the curvature.

Someone with a bit more experience with SCT's may chime in and give some advice, I use a refractor to image.

Cheers

JohnG

Last edited by JohnG; 07-05-2007 at 06:06 PM.
Reply With Quote
  #5  
Old 07-05-2007, 07:35 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Yep even with an OAG you will get field rotation. It is the nature of the alt/az beast. You have two choices, a field derotator (which I wouldn't recommend with a 300D unless you like hearing the sound of crunching camera as it tries to pass through the forks.) or an equatorial wedge.

I'd go for a wedge, or better yet, get an equatorial mount.
Reply With Quote
  #6  
Old 07-05-2007, 07:51 PM
74tuc
Registered User

74tuc is offline
 
Join Date: Sep 2006
Location: Sandy Creek(Sth.Aust.)
Posts: 153
Hi Paul,

RE:" If i got say a Lumicon Giant Easy Guider but used it on my alt az mount. Would i still get field rotation if i kept the guide star centered?"

1. Yes! You will get field rotation in the image whether or not you used a guider and this does not apply to your 'scope only the type of tracking - Alt-Az tracking.

2. The guider you mentioned is also called a "Off Axis Guider" and can be quite frustrating to use. Best steer clear of these for the time being.

3. Try using a wedge and polar alignment and tracking to start off with then look at guiding.

4. Moon too bright? Stop the scope down with an off centre mask.

5. Good attempt on your pic - may need some practice at focusing

Good luck,

Jerry.
Reply With Quote
  #7  
Old 07-05-2007, 07:59 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
I've got one too.

4. use a faster exposure. Is it still too bright at 1/1000 of a sec? You've still got a few up your sleeve after that. (Or use an aperture mask )
Reply With Quote
  #8  
Old 07-05-2007, 08:12 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by [1ponders] View Post
Yep even with an OAG you will get field rotation. It is the nature of the alt/az beast. You have two choices, a field derotator (which I wouldn't recommend with a 300D unless you like hearing the sound of crunching camera as it tries to pass through the forks.) or an equatorial wedge.

I'd go for a wedge, or better yet, get an equatorial mount.
Hi 1Ponders,

Thanks for your reply, it is very hard to know what to do for a beginner.

(1) I have a Nexstar 11 and just checked it with the camera mounted in the diagonal and i have about 4 inches clearance. So, I like the idea of a field de-rotator but they are expensive and i am not sure of the accuracy of my drive system.

Still i would like to investigate them, can you recomend one for a Nexstar 11?

(2) I can get a wedge, but am not sure if i have the ability to 99.9% polar align it. Especially in sydney where it is hard to get a clear view of the horizon (Inner Sydney). So I have a question. If i nearly Polar align it will i be able to increase the exposure time from a minute, or is 'nearly' polar aligned totally useless and the same as Alt/Az mount?

Thanks Paul
Reply With Quote
  #9  
Old 07-05-2007, 08:26 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Ok..
1. I don't know what the clearance is with a Nexstar 11 but the field derotator juts out the back a fair way. Maybe one of the Meade users can answer this. I do know though the the derotator doesn't work on all areas of the sky. go figure I'll try to dig up the web link for that info.

2. As long as you can see down to about 20 -25 deg either east or west and see straight up then you can polar align using the drift method. You can do it higher east or west but it takes a little bit longer and you have to swing back and forwards from meridian to horizon a few times using smaller adjustments. Nothing that couldn't be gotten used to. Nearly polar aligned will always be better than alt/az. You can still get field rotation in equatorial mountings. It depends on how far from polar alignment you are and how far the star you are trying to guide on is away from the area you are trying to image. The closer the better.

You could also align using the 300D method. Ccheck out Alex's (xelasnave) method here http://www.iceinspace.com.au/forum/s...ad.php?t=11654
Reply With Quote
  #10  
Old 07-05-2007, 08:29 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
http://www.allaboutastro.com/Article...drotation.html
http://www.allaboutastro.com/Article...vsrotator.html

There ya go. Check out Jays site. He surely knows his stuff.

http://www.allaboutastro.com
Reply With Quote
  #11  
Old 07-05-2007, 08:59 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by [1ponders] View Post
I've got one too.

4. use a faster exposure. Is it still too bright at 1/1000 of a sec? You've still got a few up your sleeve after that. (Or use an aperture mask )
Thanks for the link. Also Alex's link looks interesting. As far as the moon is concerned i tried using a moon filter, this is my second nights shot, the first nights was very very very overexposed. Tuc47 is certainly correct, focusing is a pain in the ..., and very difficult through the 300D viewfinder

I may look at connecting up a lappy to help focus. Still its all fun and gives something to do in Sydney where the sky is so bright. Makes one appreciate the simple pleasure of a dark sky site and just looking .

Thanks everyone for all your help.
Attached Thumbnails
Click for full-size image (web2.jpg)
145.7 KB19 views
Reply With Quote
  #12  
Old 07-05-2007, 09:30 PM
DobDobDob's Avatar
DobDobDob (Ron)
Blacktown isn't so black

DobDobDob is offline
 
Join Date: Jan 2007
Location: Prospect, NSW, 2148
Posts: 1,316
Good on you Paul, that moon shot brought a tear to my eye (you know why), keep going at it mate
Reply With Quote
  #13  
Old 07-05-2007, 09:38 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by tailwag View Post
Good on you Paul, that moon shot brought a tear to my eye (you know why), keep going at it mate
Thanks Ron,

Astrophotography is hard work, but i hope it will be interesting. The camera is working out fine, thanks m8, and you were right about the charger .

Good luck finding your BIG dob, hope it comes in soon .

Paul
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 04:54 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement