hi. just like to know some deep sky astrophotography mystery that cloud me quite abit. seem that no books on astrophotography explain clearly. 1) In astrophotography, there is prime scope n a guide scope. how do u guys actually align your guide scope to your prime scope. as in when u guide through your guide scope, how to u know your prime scope is photographing the object u wanna take. could it be taking something else??? 2) how do u guys choose your guide star??? i mean there is thousands of stars near a deep sky object. so which do u guys choose?? d brightest??? 3) what happen while u guiding the guide star, a big patch of cloud comes in. how do u find your guide star back>???
4) do u guys took totally unacceptable AP pics?? i mean can't be perfect pic all the time.
Uncovering deep sky astrophotography mystery
Here is the answer to your questions as far as I know.
1. There is no need to properly align the main scope and the guide scope. Normally, both scope will point to roughly the same area of the sky. The main scope will be pointed to the object of interest, while the guide scope is align to a reasonable bright star that is used for guiding.
2. Normally the guide star will be chosen base on these criteria
a) close proximity to the object of interest.
b) bright enough to be seen in your recticle eyepiece
3. Don't wait till the patch of cloud comes in. I will stop the exposure (even if not reach the requires exposure) when a patch of cloud cross the object of interest. Do let this happen, as the cloud will interfere with the image.
4. Unacceptable image? Sure...tons of them. Bad guiding, not enough exposure, clouds, nearby people bumps into your scope, nearby people shine torchlight into your scope! and others.....
Hope you can understand my explanation.
1. There is no need to properly align the main scope and the guide scope. Normally, both scope will point to roughly the same area of the sky. The main scope will be pointed to the object of interest, while the guide scope is align to a reasonable bright star that is used for guiding.
2. Normally the guide star will be chosen base on these criteria
a) close proximity to the object of interest.
b) bright enough to be seen in your recticle eyepiece
3. Don't wait till the patch of cloud comes in. I will stop the exposure (even if not reach the requires exposure) when a patch of cloud cross the object of interest. Do let this happen, as the cloud will interfere with the image.
4. Unacceptable image? Sure...tons of them. Bad guiding, not enough exposure, clouds, nearby people bumps into your scope, nearby people shine torchlight into your scope! and others.....
Hope you can understand my explanation.
hi jermng,
have you read robert reeves astrophotography book? he covers this ground well. good read. otherwise, guiding is pretty much straight forward, as in the technique. but try to choose a guidestar as close to the image center in the main scope or lens as much as possible. this can be faciliated by the use of three-point-screw-type tube rings. we normally guide around 300X with the Vixen GA4 or GA3 illuminated device. however there are exceptions to this, such as when one takes a nebula in a sparse starfield or M31 for example, where a guidestar is chosen moderately far away from image center, but so far had no problems with this. only when you choose a guidestar perhaps as far away as three degrees of or more, that you will start to see effects of field rotation on your film or DSLR frame.
have you read robert reeves astrophotography book? he covers this ground well. good read. otherwise, guiding is pretty much straight forward, as in the technique. but try to choose a guidestar as close to the image center in the main scope or lens as much as possible. this can be faciliated by the use of three-point-screw-type tube rings. we normally guide around 300X with the Vixen GA4 or GA3 illuminated device. however there are exceptions to this, such as when one takes a nebula in a sparse starfield or M31 for example, where a guidestar is chosen moderately far away from image center, but so far had no problems with this. only when you choose a guidestar perhaps as far away as three degrees of or more, that you will start to see effects of field rotation on your film or DSLR frame.
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universe24
- Posts: 227
- Joined: Thu Oct 02, 2003 12:26 am
Came across this excellent article that summarises the recent trends in webcam autoguiding. If you are inclined to go the automated route, I suppose this might answer some of your questions on guiding for long exposures. http://astro.neutral.org/articles/autog ... iding.html