When imaging deep-sky objects with my long exposure modified cameras I often have to discard frames because the stars are not nicely round, but have become streaks.
This is caused by the Periodic Error of my TAL-2M mount.
The problem is that I can only assess the quality of an (i.e. no streaks but nice round stars) AFTER the whole exposure time has elapsed and then I am too late :-\

The solution for this is AUTOGUIDING, whereby TWO webcams are used and automatically guiding corrections are made 'on the fly' during the long exposure imaging by the imaging webcam.
So: one webcam does the actual long exposure IMAGING, while the second GUIDING webcam is aimed at a bright star with shorter exposure times [but it is very nice if this Guiding webcam is also modified for long exposure, so that you can use e.g. exposure times of 1 second which makes it MUCH easier to find a good guide star]. For this you need a Splitter Box and by doing so the computer software can determine the shift in pixels and give a message to the (in my case RA only) motor(s) of the telescope in terms of "a little faster/slower please".
This all happens while the long exposure imaging is going on.

Here are my own experiences with my TAL-2M; whereby I image via my modest TAL-2M telescope and guide with a piggybacked 400mm SLR Photolens with 2x Teleconverter.
Of course the other way around is also possible: please browse further down.

One more thing: on my TAL-2M only the RA is motorized and the DEC is NOT motorized, so I can only autoguide on the RA: therefore to 'manage' the DEC it is mandatory for me that the Polar Alignment is just perfect.

On July 14, 2005 I started the experiments to use my piggy-backed 400mm SLR Photolens and 2x Teleconverter for Autoguiding (Note: the 2x Teleconverter is not on this photo)

1. Prerequisites
For Autoguiding I use the following:

• ASUS laptop with 2 USB ports, a parallel port and a serial port:
• One USB port for the Imaging Webcam
• One USB port for the Guiding webcam
• The parallel port for Long Exposure control
• The serial port to communicate with the APM motor corrector
• Two webcams; one for imaging and one for guiding
• The APM motor corrector [with special modification made by Peter Katreniak]
• Piggy back platform for the guiding SLR Photolens
• Splitter Box enabling me to run 2 long exposure webcams on ONE parallel port.
• SLR Photolens which in this tutorial I use as Guide Scope
  
  • Ideally the Guide Scope should have a focal length equal to or larger than the Imaging Scope. If you cannot manage that try for the next best and Guide with the longest focal length available.
    In my case this is the 400mm SLR Photolens with 2x Teleconverter.
  • I noticed that a dew shield is a highly desirable item: on a humid night my SLR Photolens frequently dewed over, so I am going to buy a camping mat and make dew shields for all my SLR Photolenses.
• K3CCDTools with TAL driver

2. Preparing for Autoguiding
Note: I assume you already know how to image without guiding; should you not know this then first go to my Tutorials page, e.g. Beginners or DSO Tutorial

• Connect all the hardware, including both webcams.
  [On this website you can read how to launch 2 instances of K3CCDTools, each with its own webcam]

• Now I launch WcCtrl and the two instances of K3CCDTools.
  I do this by invoking the wcctrl_k3_k3.bat file - which I made with Notepad and which I stored in the root of my C: drive - with the following contents:
  C:
  cd Program Files
  cd TWIRG
  cd WcCtrl
  start WcCtrl.exe
  cd "C:\Program Files\K3Soft & Hard\K3CCDTools2.4"
  start K3CCDTools.exe
  start K3CCDTools.exe
  
• Make sure your scope is well balanced
• Open the first instance and select the Guiding Webcam (the Brightness Meter should show changing values)
  
• Now open the second instance and activate the Imaging instance
  

3. Setting up the Guiding instance

• Select the Guiding instance
• Via "Settings" and the "Guide" tab define your main environment

Here are the settings I use:



• Enter the details of your guiding scope and camera via Options|Telescope and CCD camera

My settings for my 400mm SLR Photolens with 2x teleconverter and SC3 a b/w RAW camera are:



• Make sure you have set the frame rate at 5 frames per second:

  

• Make sure that the APM motor corrector is switched into position 'Variable' with the adjustment knob right in the middle [I have made a mark at exactly 50Hz, because that is the output I want for my 12V AC 50Hz motor for the RA]
• Aim the Guiding scope (so in this Tutorial: the SLR Photolens) at a bright star, focus very carefully and tweak the camera settings till it is nice and bright on your preview screen.
  This step is required so that later you will be able to find a - probably much weaker - guide star.
  
• Now make sure your guiding camera is perfectly East/West orientated: see my Polar Alignment tutorial how to do this.
  [I know that K3CCDTools can determine the camera angle and use it when controlling the DEC, but as my DEC is not motorized I have to see to it myself that the camera is perfectly East/West orientated.]
• Start the K3CCDTools Drift Explorer
  Here is the icon:
• Currently I use these settings of the Drift Explorer (as my DEC is not motorized 'DEC Control' is unchecked)


• Please allow me to explain the parameters in my own words here (but you should read the K3CCDTools manual too of course!)
  Incorrect values might cause your guiding to become too 'nervous' and thus overcorrect or too 'lazy' causing incorrect tracking
• Dead zone parameter
  Because of the turbulence the guide star might more or less 'dance' on your screen. Now, you would not want to do the guiding based on a dancing star, would you?
  The Dead Zone parameter takes care of that and ignores the turbulence. More turbulence = increase dead zone value.
  You have to experiment to select the best value for your setup and actual turbulence.
  Hint (from Tom How): defocusing the guide star VERY SLIGHTLY can often help in hiding the effects of seeing from the guide camera.
• K parameter
  If you notice a lot of drift with your mount then - in case of manual guiding with a hand controller - you would press the appropriate button longer than when you experience less drift.
  This is exactly what the K parameter does: it amplifies the normal adjustment.
  Again you have to experiment
• Q parameter
  Q is the time you would 'normally' press the button when doing the guiding manually.
  Experiment!

  For your convenience I have copied the following text from the K3CCDTools manual:
  The length of the autoguide pulse (in milliseconds) is calculated according to an equation:
  t = K * delta + Q
  - where delta is the measured drift
  - K & Q are the coefficients
  This means, that Q defines the minimal pulse length when the autoguiding intervention is made, while K defines the amplification of the measured drift.

• Interval parameter
  Here you specify how frequently the system should 'look' at the guide star.
  The value depends on your imaging exposure time: for example it would be silly to 'look' at the guide star only every 15 seconds when you are doing a 60 second imaging exposure, as you might be too late and the streaks/elongated stars are already there. But also: when the frequency is too high your guiding will be nervous.
  Experience will tell you (and me) what value to use, but take it easy.


• Now click on the top left button of the Drift Explorer panel and select the bright guide star on the preview screen
• Presto: in my (RA guiding only) case the Left Arrow and Right Arrow buttons start to blink, indicating that the setup is ready for autoguiding, so let us proceed with the next step.

4. Setting up the Imaging instance

• Select the imaging instance
• Make sure you have set the frame rate at 5 frames per second:

  

• Aim the scope at a bright star, focus very carefully and tweak the camera settings till it is nice and bright on your preview screen: now you will be able to find your DSO, because your setup is perfectly focused.
• Next make sure your imaging camera is perfectly East/West orientated: see my Polar Alignment tutorial how to do this.
• Now find the DSO you wanted to image (I do not have a GOTO mount, so I have to use my setting circles) and tweak the imaging camera settings just as you would do when imaging without guiding
• Alas: your nice bright guide star is no more in the Guiding instance, so you have to adjust the guide scope to a bright enough star which you can use as guide star.
  To manually move the piggy-backed SLR Photolens around in a controlled fashion I use my slow motion Witty on top of which is my Piggy back platform with the SLR Photolens and Guiding webcam
  Hint: to find a guide star I crank up the camera settings of the Guiding webcam to maximum brightness/gain etc.
  And if your Guiding webcam is a Philips Vesta Pro you might want to do the 1/5 second exposure time trick
  Of course you should not loose your DSO while searching for the guide star!
  Note: I tried hard but could not find a guide star with my SC3a colour camera [at 1/5 second exposure] when mounted on my 2x400mm SLR Photolens. With the more sensitive SC3a b/w camera I had not problems in finding a guide star ... so far.
  When imaging the Veil Nebula with a 50mm SLR Photolens and autoguiding via the TAL-2M in prime focus with the SC3a colour camera I immediately found a guide star, but maybe I was just lucky this time.
• When you have found a nice guide star - which is easiest when your guiding camera is very sensitive [or even a long exposure camera itself] - use the Drift Explorer again: the 2nd button on the top resets and then select the guide star via the top left button

Here is an example:.
You see the screen print of a 30 second exposure; I imaged with my TAL-2M and focal reducer - focal length ~ 690mm - and autoguided with 400mm SLR Photolens and 2x teleconverter: focal length 800mm.

Example of a 60 second exposure:
TAL-2M in prime focus - focal length 1200mm - and autoguided with 400mm SLR Photolens and 2x teleconverter: focal length 800mm.

5. Guiding with the main (1200mm) scope and imaging with piggy-backed 135mm SLR Photolens

I wanted to image NGC6960 (part of the Veil Nebula) and used (for imaging) my 135mm SLR Photolens with SC3a b/w RAW camera and H-Alpha filter; guiding would be done with my TAL-2M in prime focus and SC3a colour camera.
I found it very hard to find NGC6960 with the 135mm SLR Photolens, because I had not yet lined up my TAL-2M with the piggy backed 135mm SLR Photolens, so they were 'out of sync' with each other.
I aimed my TAL-2M at a bright star (Altair) and put it in the centre of the K3CCDTools 'circles'; after which I tried to find Altair with the piggy backed 135mm SLR Photolens by making adjustments with my Witty.
This took a long time, mainly because of the light absorption of the H-Alpha filter which requires long exposure times and I did not want to remove the H-Alpha filter because that too takes time and I had already focused the 135mm SLR Photolens.
When I finally was ready to image ... the clouds came :-{

I learned my lesson and the next time I have used the sun to synchronize TAL-2M and 135mm SLR Photolens: much easier!
(Of course I used my Solar filters).

This indeed helped a lot: when I aimed my 1200mm focal length scope at Altair, my 135mm SLR Photolens also had Altair on the preview screen.
Then it occurred to me that I could both instances simultaneously with the live video feed on my screen and after having done so I adjusted the 135mm instance, while keeping an eye at the 1200mm instance at the same time.
I tweaked the 135mm instance with my Witty till I was happy: here you see a screen print of what I mean:

My TAL-2M 1200mm focal length and my 135mm SLR Photolens are now in perfect sync with each other.
At this moment the clouds came so I leave it here for when I have clear skies again.

While waiting for clear skies I made an (as yet experimental) Filter Drawer which wil hopefully enable me to remove/insert the H-Alpha filter without disassembling my setup.

I am aware of the fact that there is a difference in focus with/without the H-Alpha Filter, but re-focusing surely will be a lot easier than re-finding the object.

I am experimenting with the following two scenarios, in both of which the Filter Drawer and the Witty play an important role.

5.1 Scenario A: first find the object and then a guide star

1. Setup K3CCDTools for guiding (see above 3. Setting up the Guiding instance and 4. Setting up the Imaging instance)
2. Aim main scope (in prime focus) at a bright star and focus to perfection
3. Use the Filter Drawer to remove the H-Alpha filter from the (imaging) SLR Photolens optical train
4. Cover the Filter Drawer (no filter inserted yet)
5. Focus the 135mm SLR Photolens rather well
6. Line up 135mm SLR Photolens at the bright star, so that main (guiding) scope and (imaging) SLR Photolens are in sync
7. Push the whole setup to the desired object (I use my setting circles) and make sure it is on the preview screen of the imaging 135mm SLR Photolens instance
8. Have a good look at the star pattern on the preview screen
9. Put both windows of the guiding and the imaging instance on the computer screen (see above example)
10. Gently push the main scope with piggy backed SLR Photolens left/right/up/down till a nice guide star is on the preview screen. While doing so keep a watchful eye on the preview screen of the imaging instance and use the Witty to keep the object (or star pattern) in the centre of the video feed.
11. When a nice guide star has been found: use the Filter Drawer to insert the H-Alpha filter into the optical train of the SLR Photolens
12. Adjust the exposure time of the imaging instance
13. Focus the 135mm SLR Photolens to perfection
14. Tweak the imaging camera settings to perfection
15. Use the Drift Explorer to start and control the Autoguiding

The above scenario worked out marvellous: I found NGC6960 immediately with the 135mm SLR Photolens and did not loose it while searching for a guide star with my main scope: success!

5.2 Scenario B: first find a guide star and then the object

1. Setup K3CCDTools for guiding (see above 3. Setting up the Guiding instance and 4. Setting up the Imaging instance)
2. Aim main scope (in prime focus) at a bright star and focus to perfection
3. Use the Filter Drawer to remove the H-Alpha filter from the (imaging) SLR Photolens optical train
4. Cover the Filter Drawer (no filter inserted yet)
5. Focus the 135mm SLR Photolens rather well
6. Line up 135mm SLR Photolens at the bright star, so that main (guiding) scope and (imaging) SLR Photolens are in sync
7. Push the whole setup to the desired object (I use my setting circles) and find a guide star in that area
8. Now put both windows of the guiding and the imaging instance on the computer screen (see above example)
9. Next use the fine controls of the Witty to get the object on the Preview screen (it is a great help to have a detailed star chart (such as Cartes du Ciel or Megastar) available with the field-of-view of the imaging camera-with-lens superimposed.
10. When the object has been found: use the Filter Drawer to insert the H-Alpha filter into the optical train of the SLR Photolens
11. Adjust the exposure time of the imaging instance
12. Focus the 135mm SLR Photolens to perfection (hint: use a white marker pen to put marks on the SLR Photolens)
13. Tweak the imaging camera settings to perfection
14. Use the Drift Explorer to start and control the Autoguiding

This scenario worked also very nice, as I departed from a guide star and the star hopped to the object: the fine controls of the Witty made that very easy.

Here are some Filter Drawer and Autoguiding test results.

	August 11, 2005. First test results. The object is NGC6960. Exposure 60 seconds, H-Alpha filter inserted in filter drawer, autoguided. Seeing: fog building up rapidly, but I just wanted to do the tests.
	August 11, 2005. First test results. The object is NGC6960. Exposure 75 seconds, H-Alpha filter inserted in filter drawer, autoguided. Seeing: fog building up rapidly, but I just wanted to do the tests.
	August 11, 2005. First test result of dark frame, to see if any light was leaking. It seems no further action is required. Exposure 75 seconds, H-Alpha filter inserted in filter drawer.
	August 12, 2005. First real result: exposure 240 seconds, H-Alpha filter inserted in filter drawer. Imaging: 135mm SLR Photolens with SC3a b/w RAW camera, Baader Infra Red Blocking Filter and Astronomik H-Alpha filter. Guiding was done via my TAL-2M 15cm f/8 in prime focus with my SC3a colour camera. Settings of the imaging camera: Brightness 50, Gamma 100, White Balance: auto, Gain 100. Seeing: 8/10, urban light pollution.
	August 16, 2005. This animation shows the difference between a guided and an unguided 90 second exposure with my 135mm SLR Photolens with SC3a b/w RAW camera and Astronomik H-Alpha filter. The guiding was done via my TAL-2M 15cm f/8 1200mm focal length with my SC3a colour camera.