astrophotography
astrophotography
hello all. can anyone enlighten me regarding manual guiding for prime focus astrophotography and how is off-axis guiding similar to it ?
Hi,
- Manual guiding refers to your eye looking through a "finderscope" or piggyback mounted scope, and your fingers playing with the control buttons to move the scope right, left, up or down.
- Off axis guiding refers to you having a CCD camera/computer doing automatically what your eye/finger does above.
Difference is :
- Case #1, you get tired
- Case #2, you relax, enjoy a drink and the company (if any) while your computer works.
Cheers
Jean-Yves
- Manual guiding refers to your eye looking through a "finderscope" or piggyback mounted scope, and your fingers playing with the control buttons to move the scope right, left, up or down.
- Off axis guiding refers to you having a CCD camera/computer doing automatically what your eye/finger does above.
Difference is :
- Case #1, you get tired
- Case #2, you relax, enjoy a drink and the company (if any) while your computer works.
Cheers
Jean-Yves
Hi,JY wrote:Hi,
- Manual guiding refers to your eye looking through a "finderscope" or piggyback mounted scope, and your fingers playing with the control buttons to move the scope right, left, up or down.
- Off axis guiding refers to you having a CCD camera/computer doing automatically what your eye/finger does above.
Difference is :
- Case #1, you get tired
- Case #2, you relax, enjoy a drink and the company (if any) while your computer works.
Cheers
Jean-Yves
I beg to differ.
IMHO, they are two different things altogether.
Manual guiding: Your hand controls the the fine tuning of RA and Dec to keep the guide star in the centre of the guiding eyepiece.
Autoguiding: The computer controls the RA and Dec for you and is less tiring.
Off-axis guiding: The guide star used is selected thru the main scope itself and not thru another guidescope. The pro is that you will not be prone to flexure in the mounting system, seeing that the guide star and target is seen thru the same scope. The con is that it is sometimes difficult to locate a star thru the same imaging scope. You can use manual or autoguiding with off-axis guiding.
Take a look at:
http://www.gushie.demon.co.uk/guiding_equipment.htm
http://www.imvo-roure.com/accesorios/re ... _focal.htm
A diagram of the off-axis guider is shown in the 2nd link.
Cheers.
Kay Heem
-
weixing
- Super Moderator
- Posts: 4708
- Joined: Wed Oct 01, 2003 12:22 am
- Favourite scope: Vixen R200SS & Celestron 6" F5 Achro Refractor
- Location: (Tampines) Earth of Solar System in Orion Arm of Milky Way Galaxy in Local Group Galaxies Cluster
Hi,
Long exposure prime focus astrophotography can be guided in two main method - using a guide scope or using an off-axis guider. Both can be done manually or automatically using a auto-guider/computer.
The guide scope method is actually using another scope, normally a long focal length refractor, that is either Piggyback on the main scope or mount beside the main scope(both main scope and guide scope must be on the same mounting plate). You will need a reticle eyepiece on the guide scope. First, you need to find a guide star near the target that you want to image. Your main scope will aim at your target and the guide scope will aim at the guide star. Then keep the guide star on the center of the crosshair using the slow motion control during the exposure.
The Off-axis guider method need an off-axis guider to connect your scope to your camera and the reticle eyepiece. An off-axis guider(eg. Celestron Radial Guider) is a special adapter that mount on to the scope visual back and allow the camera to be mount on the other end. The guider will have a small prism in the guider that will reflect the image to another opening where you place your reticle eyepiece. You need to find a guide star in the field of view(basically the guide star need to be in the same field of view as your target) and keep the guide star on the center of the crosshair using the slow motion control during the exposure.
As I mention above, you can use an auto-guider to guide automatically. Basically, an auto-guider contain a CCD camera to replace your eye and a computer that interface to your motor drive to replace your brain and hand. It is the easiest and most accurate way to do long astrophotography provided you got the MONEY!!!
Hope the information is useful. Have a nice day.
Long exposure prime focus astrophotography can be guided in two main method - using a guide scope or using an off-axis guider. Both can be done manually or automatically using a auto-guider/computer.
The guide scope method is actually using another scope, normally a long focal length refractor, that is either Piggyback on the main scope or mount beside the main scope(both main scope and guide scope must be on the same mounting plate). You will need a reticle eyepiece on the guide scope. First, you need to find a guide star near the target that you want to image. Your main scope will aim at your target and the guide scope will aim at the guide star. Then keep the guide star on the center of the crosshair using the slow motion control during the exposure.
The Off-axis guider method need an off-axis guider to connect your scope to your camera and the reticle eyepiece. An off-axis guider(eg. Celestron Radial Guider) is a special adapter that mount on to the scope visual back and allow the camera to be mount on the other end. The guider will have a small prism in the guider that will reflect the image to another opening where you place your reticle eyepiece. You need to find a guide star in the field of view(basically the guide star need to be in the same field of view as your target) and keep the guide star on the center of the crosshair using the slow motion control during the exposure.
As I mention above, you can use an auto-guider to guide automatically. Basically, an auto-guider contain a CCD camera to replace your eye and a computer that interface to your motor drive to replace your brain and hand. It is the easiest and most accurate way to do long astrophotography provided you got the MONEY!!!
Hope the information is useful. Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance." -
weixing
- Super Moderator
- Posts: 4708
- Joined: Wed Oct 01, 2003 12:22 am
- Favourite scope: Vixen R200SS & Celestron 6" F5 Achro Refractor
- Location: (Tampines) Earth of Solar System in Orion Arm of Milky Way Galaxy in Local Group Galaxies Cluster
Hi,
No, there is no semi-auto guiding
. As long as you correct the guiding error yourself, it is still consider manual guiding even you use a motor drive.
Remember, when doing Auto-guiding you only need to point the main scope at your target, select the guide star (either through the guide scope or the off-axis guider) and the computer will do all the error correction.
Have a nice day.
No, there is no semi-auto guiding
. As long as you correct the guiding error yourself, it is still consider manual guiding even you use a motor drive. Remember, when doing Auto-guiding you only need to point the main scope at your target, select the guide star (either through the guide scope or the off-axis guider) and the computer will do all the error correction.
Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance." 
If you are just starting out, go for off-axis guiding. Cheapest way to go. All you need is an off axis guider plus a reticle eyepiece. Easy.gwenyi wrote:oh alright. what about motor drives that u have to attach to the mount for astrophotography ? is it in between manual guiding and auto guiding ?
Guidescope would require you to buy a scope and all the mounting stuff. Can your mount take the weight in the first place? Lots of things to consider.
Autoguider? Does your mount have an autoguiding port?
As with almost all astro equipment, stuff can be expensive. I suggest taking a look at different setups people are using before deciding. Some points to note:VinSnr wrote:
If you are just starting out, go for off-axis guiding. Cheapest way to go. All you need is an off axis guider plus a reticle eyepiece. Easy.
Guidescope would require you to buy a scope and all the mounting stuff. Can your mount take the weight in the first place? Lots of things to consider.
Autoguider? Does your mount have an autoguiding port?
1. Some scopes do not have focusers with enough in-travel to accomodate an off-axis guider (OAG). You have to actually try it out on your own setup. The meade and celestron ones only attach via a SCT thread. For newts, take a look atL
http://www.lumicon.com/egnewt1.htm
2. Much tougher to find guide stars thru an OAG.
3. Separate guide scopes make it easy to find guide stars, but the whole setup takes a greater strain on your mount.
SCT users like OAGs as SCTs have more than enough back focus and the OAG will eliminate any mirror flop.
Kay Heem
That's right. The above was spot-on.kayheem wrote:As with almost all astro equipment, stuff can be expensive. I suggest taking a look at different setups people are using before deciding. Some points to note:VinSnr wrote:
If you are just starting out, go for off-axis guiding. Cheapest way to go. All you need is an off axis guider plus a reticle eyepiece. Easy.
Guidescope would require you to buy a scope and all the mounting stuff. Can your mount take the weight in the first place? Lots of things to consider.
Autoguider? Does your mount have an autoguiding port?
1. Some scopes do not have focusers with enough in-travel to accomodate an off-axis guider (OAG). You have to actually try it out on your own setup. The meade and celestron ones only attach via a SCT thread. For newts, take a look atL
http://www.lumicon.com/egnewt1.htm
2. Much tougher to find guide stars thru an OAG.
3. Separate guide scopes make it easy to find guide stars, but the whole setup takes a greater strain on your mount.
SCT users like OAGs as SCTs have more than enough back focus and the OAG will eliminate any mirror flop.
Kay Heem
OAG are mainly used by SCT users. For refractors, you might not have enough focus travel.
And of course, it's not easy to find guide stars using OAG but well, have to compromise if wanna save money from buying a guide scope.
Hi Wenyi,
Here is yet another perspective:
You could consider going into wide-field astrophotography first. The tolerance requirements are not as stringent as prime focus imaging. You can start off with a mount, and a cheap but functional guidescope together with piggybacked camera-lenses. Rather than jumping straight on into prime focus imaging (assuming that is what you might be considering). You would also need a guiding reticle and preferably be guiding at powers 200-300X. I think you already have a camera and refractor at hand? Can't remember if you have a GEM already, but you could consider investing in a guiding reticle next to bring you on into this next level of imaging.
Good luck,
rcj
Here is yet another perspective:
You could consider going into wide-field astrophotography first. The tolerance requirements are not as stringent as prime focus imaging. You can start off with a mount, and a cheap but functional guidescope together with piggybacked camera-lenses. Rather than jumping straight on into prime focus imaging (assuming that is what you might be considering). You would also need a guiding reticle and preferably be guiding at powers 200-300X. I think you already have a camera and refractor at hand? Can't remember if you have a GEM already, but you could consider investing in a guiding reticle next to bring you on into this next level of imaging.
Good luck,
rcj