What is the point of a guide camera if you have an automated system?

[Trippelforge]

I have been wondering this lately as someone suggested to me that it would be a good upgrade. However I am not sure what it does when you have an automated tracking system. For instance I am looking up at buying this today as a XMAS present for my son. And assumed it had the capability to align and track. So I was hoping someone could explain to me why guide camera's are used.

Thanks

[Dr_Ju_ju]

If configured properly, then what you linked to, would hopefully drive the mount to point the scope to the right part of the sky.... 

BUT, if you want to truly ensure, that it is indeed pointing at what you want it to point to, and ensure that it keeps pointing at that target, then you need a system that will look at the sky, take an image of what it's supposedly looking at, compare it with a reference image of the target, and then adjust the mount position to correspond to that image.

You could use the main scope to do that, but it's usually better to use a separate guide camera, to perform that function, which can also be used by separate dedicated software to keep things aligned, e.g. PHD2 etc.

      

[fwm891]

Do you take photographs through your telescope?

If you only do visual only observing and your mount will track the sky a guide camera is a useless addition.

If however you do or intend to take photographs through your telscope then a guide scope/camera combination will enable you to take long exposures of night sky objects.

There is a difference between tracking and guided. Tracking is regulated by the mount to simply reverse the Earth's rotation and keep and object within the field of view. Guidance however locks onto a star within the field of view and sends pulses to the mount to adjust it's speed to precisely follow  that star, essential when taking images of more than a few seconds duration.

Edited November 21, 2022 by fwm891

[Owmuchonomy]

Looks like you have the EQ3 mount, if you wish to take up Astrophotography then a better mount such as the HEQ5 or better is required. Even that will require guiding with a guide camera for exposure lengths over 30 seconds or so. Tracking objects in the night sky for visual enjoyment is done much more easily as some error can be tolerated.

[DaveS]

Unless your mount has encoder guiding, then you *will* need some form of guide camera, either with an off-axis pick off, or else a separate guide 'scope.

Encoder guiding means 10 Micron *minimum* and 4-5 figures.

[allworlds]

Wasn't there a thread on these forums for people imaging with the EQ3-2 or CG-4 ? It's not the best mount but IIRC it's doable with a small scope (OP has an 80 mm apo).

Anyway. With just tracking the telescope follows the movement of the sky but there are inevitably errors. It's motors and gears and polar alignment and nothing is ever perfect. If you try too long of a sub unguided you'll see stars becoming oval instead of staying points. A guide camera creates a feedback loop to correct those errors, driving the motors a little more or a little less to make sure that the stars stay in the same place (to within the system's precision) in the camera view.

Does your mount currently have a motor drive on both axes? If yes, is there a guiding port or similar for those motor drives? If yes to both then the benefits of this kit by itself will be miminal.

[Rallemikken]

36 minutes ago, Trippelforge said:

So I was hoping someone could explain to me why guide camera's are used.

As pointed out by others; guide cameras is used to take REAL LONG exposures with long scopes. BUT: With this upgrade together with a good polar alignment you can take exposures up to one minute with a DSLR, maybe more without a guiding system. The focal lenght of the scope must not be to long, and you will need an adapter between the camera/phone and scope. 

For pure visual it isn't many advantages with tracking as long as you find what you seek in the first place. But if more than one use the scope, or you bring it around at parties and birtdays, it's VERY handy!  If this kit supports select-and-point and it can be controlled by a laptop or phone, that will also be a big upgrade. Problem with most beginners is where to look!

[Trippelforge]

41 minutes ago, allworlds said:

Wasn't there a thread on these forums for people imaging with the EQ3-2 or CG-4 ? It's not the best mount but IIRC it's doable with a small scope (OP has an 80 mm apo).

Anyway. With just tracking the telescope follows the movement of the sky but there are inevitably errors. It's motors and gears and polar alignment and nothing is ever perfect. If you try too long of a sub unguided you'll see stars becoming oval instead of staying points. A guide camera creates a feedback loop to correct those errors, driving the motors a little more or a little less to make sure that the stars stay in the same place (to within the system's precision) in the camera view.

Does your mount currently have a motor drive on both axes? If yes, is there a guiding port or similar for those motor drives? If yes to both then the benefits of this kit by itself will be miminal.

Ya that was probably one of mine and I do have a CG-4. And you are also right I my scope is an 80mm and is pretty light. I think between the scope and camera I am sitting around 9lbs maybe?

OK so I think I get it now, it gives the capability of the tracking system to adjust and fine tune itself. You can get a fairly low cost guiding camera can't you, something from ZWO listed as planetary? 

Currently I have the Celestron branded dual motor drive setup. It does not however have a guiding port or any type of external connection capability. Just a simple hand controller. That is one of the reasons I was looking at purchasing the drive system. That and the fact that it also will allow me to go-to and is compatible with the asiar (if I got that route eventually). It just seemed like a nice add-on from a convenience standpoint. 

Anyhow so getting a guidescope for long exposure imaging is going to be a huge plus due to improving my scopes tracking capabilities?

 

[carastro]

Not all add on motor drive systems are capable of adding guiding, so be careful what you buy.

I am presuming from your response that you will be wanting to image and therefore getting a mount that is capable of guiding is essential if you want to keep nice rouind stars on long exposure.

Carole 

[AstroMuni]

2 hours ago, Trippelforge said:

Anyhow so getting a guidescope for long exposure imaging is going to be a huge plus due to improving my scopes tracking capabilities?

Most good mounts can hold their tracking quite well between 30-60s. For long exposures (over 60s), a guidescope is essential. Think of it this way - when the shutter of the main camera is open it cant see the small movements that are causing the object to move away from the centre. But the guidescope would be taking much shorter exposures and can notice these and send correction signals to the mount.

There is a workaround of working without a guidescope for exposures that cause a small drift but you can live with.... You could get the mount to realign every couple of exposures using platesolving so the drift will be corrected once every so often.

[ollypenrice]

We should not really think of tracking and guiding in terms either of exposure time or focal length. These give a very crude estimation of what goes on.

We should think of the tracking-guiding accuracy as the extent to which a point of light on the sky is held in the same place on the camera chip.  During one rotation of its driven worm wheel a good, budget mount will allow that point of light to drift by maybe 30 seconds of arc and back.  Once autoguided, that may come down to O.5 seconds of arc, or to 1 second at worst.  That means you have improved your tracking accuracy from between 30x and 60x. In other words, it is transformed.

When we get into the detail we find that the guiding error should broadly be no worse than half the image scale. A short refractor might be imaging at 3 arcseconds per pixel, so it needs to guide with an error of half that, 1.5 seconds, When your  guiding is any worse than that you are beginning to move your camera relative to the sky and you are blurring the image.

Although it isn't free, an autoguider performs a near-miraculous task. You'd probably need to spend an extra £5000 to go from a mount with a 30 second error to one with a 3 second error, a 10x improvement. An autoguider can give you a 30 to 60x improvement for a couple of hundred.

Olly