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The first thing is to get the equipment together. I have been using a Skymax-80 as a guide scope on my 8" Classic, so the first thing is to see how it works on the C14. The focal length of the Skywatcher is 1000mm so is about a quarter of the focal length of the C14 at f11. I could get a larger MAK, but I would probably only increase the focal length to about 1500mm. The advice is usually to have a much longer focal length than this on the guide scope, but I am not sure how practical that is because the increase in weight could become an issue for the CGE1400. The Classic has a focal length of 2000mm at f10, and this set up was OK. We shall see.....

My first attempts were to attach the guide scope to the top of the C14 tube, however, you can not balance the mount with the counter weights supplied. Although in principle I could get an extra counter weight, the advice so far is that I should avoid doing this. As a note, I bought a camera mount for the C14 that attaches to the top of the tube, however, I have not been able to use it with my camera because I can not balance the scope with it attached. At some point I can see that I might have to get another small counter weight.

My current answer to this problem has been to get a Losmandy DCM camera mount that attaches to the rail below the tube. This seems to work very well, the weights are shown in the position required to balance the mount when the Canon 350D camera and guide scope, guide camera etc are attached, so there is still room for increasing the load if required.

The camera shown on the Skywatcher is an Orion SSDSI camera, again, this has worked well for me in the past for guiding on the Classic.

Update: I now also have a 11lb weight which I use with the spectroscopy set up (see other pages). So far this additional weight seems to be OK.

First attempt at guiding at f11, March 2008

With everything set up and a clear night predicted it was time to try guiding the CGE1400 for the first time. The Polar alignment was good as it turned out and only minor adjustments were required with the drift method. I suspect that no adjustment would have been necessary if the front leg of the tripod had not lowered slightly under the weight of the telescope, I am not sure if the leg slipped a little or if the paving slab settled under the weight, but it is something to watch in the future. If it is the leg slipping then it will need some sort of fix, I would not want the telescope to tip over!

With the telescope aligned a test was done to see what sort of drift occurred over 3minutes, shown on the right.

This was rather pleasing, I never had anything as good as this with the Classic.

In the past I have used Astroart 4.0 to guide the LX200 and it worked very well, however, I spent several hours trying to get it to guide the CGE without any success. I really do not know why this is, but I tried everything that I could think of, but it just made the images worse than without any tracking, which rather defeats the object! I plan to figure out why this would not work some time because it does not seem to make any sense to me.

Shot details: Unprocessed, single 183s shot at ISO800, f11, no tracking, Canon 350D
In the end I gave up trying to guide with Astroart and tried PHD Guide. Now in the past I have not been able to get this to guide well on the Classic, but on the CGE it seemed to work well. I set up a series of 10 exposures of M95, but it got progressively more cloudy as the sequence progressed so only 5 of the exposures were usable. I had some problems with the camera settings, they are fairly basic in PHD and I did not have time to sort it out at the time, but I have now found that if I launch other software, such as MaxIm DL essentials that came with the camera, at the same time as running PHD, the CCD parameters can be adjusted though MaxIm DL menus.

My first attempt at guiding at f11 on the CGE with the Orion SSDSI is shown on the right. There was a fairly strong wind and one of the frames that I used was poor, which is why the stars are not quite round.

No flats were taken and there is amplifier glow in the bottom right which I have not removed, but if you compare this to the picture that I took with the Classic ( Classic M95 picture ) you can see the difference. Smaller field of view but more detail, look particularly at the clump of stars just below M95 at about 7 O'clock (they are about 11 O'clock on the classic photo).

At this point I had to pack up for the night due to cloud. I am looking forward to next time now......

Update May 2008

Last night there was a thin layer of cloud which made it poor for imagining, however, Arcturus was clear enough to sort out guiding with the MaxIm DL software. Although PhD guide is working well, there is more functionality in MaxIm and I also felt that if I put some time into this I might be able to guide better with this software in the long run.

I set up the guide camera with the x axis lined up with the RA axis of the telescope and used the graph function within MaxIm to monitor what was happening. Things improved dramatically by increasing the calibration time to 20s in X and 30s in Y. The next improvement was to set the backlash in Y to 1s. The telescope was then tracking approximately +/- 2 pixels. Reducing the aggressiveness factors to X = 5 and Y=6 made the tracking as good as I think it will get, the error was really very small, much better than +/- 1 pixel on the graph, even though it was fairly windy.

Now I need to wait for a clear sky to see how it works in practice!

Second night out guiding at f11

The telescope was set up and polar aligned, but I did not use the drift method to refine the polar alignment tonight. My aim was to test out the tracking and PHD guide software. A 3 minute exposure with no guiding looked OK, a bit extended but not too bad. I then set the PHD guiding up on a reasonably bright star and set 15 x 3min exposures at ISO800 going. I then stacked them without aligning each frame to get the picture shown to the right.

Each star here is actually 4 dots, the number of frames for each dot is 4, so the period for each dot is 12 minutes, a quick check of the raw images shows that this is the case, each consecutive 4 frames stack fine, then there is a jump.

Looking at this against a star map, the jumps seem to be in DEC, not sure why they have a period of 12 minutes. Perhaps it is to do with the guiding software, clearly requires further investigation. I hope that with a precise polar alignment this effect will be removed. Altering the backlash settings in DEC might also help a little, it is not very responsive visually with the hand set in DEC at the moment and does tend to jump suddenly when you try to make alterations.

25 May 2008. It is cloudy and the weather looks set for being poor for the next week. It is a good time to think about what I might try next to improve the autoguiding. Thinking about the graphs that I obtained from MaxIm, it looks very much like when I use longer exposures, that an oscillation sets up. The process of autoguiding is a feed back loop, which has a complex set of parameters which can be considered. Thinking about this, it is probably one reason why changing the aggressiveness was such an improvement previously. Taking this one step further, perhaps if I reduce the maximum possible movement for each correction, and perhaps increase the minimum movement, below which value no correction will take place, then this might reduce the oscillations when I use longer exposures on the SSDSI. It would be a great help if I could use longer exposures on the guide camera, from tests with no guiding the mount should be able to track for 30s without much error, which confirms in my mind that the errors that I get with the guider on are created by the guiding system. Next time I get out with the telescope I am going to test this, looks like it might be a while though from the weather predictions.

Test Exposures

I have now run a series of test exposures with MaxIm DL set up as described above. Shown to the right is a star from a 300s single exposure on the main camera, which was obtained at f11, and 5s exposures on the guide camera. The shorter the exposures on the guide camera, the better the result. At f11, 10s exposures on the guide camera allow 180s exposures on the main camera and still get a good star shape. The issue is finding bright enough guide stars to allow very short guide camera exposures and more accurate guiding. I plan to try the Wantec out as a guide camera, I think this is likely to be more sensitive. For spectroscopy the level of accuracy with 10s guide exposures for 300s imaging frames is fine, it does not matter if the star moves slightly of the spectroscope slit and then back again.

The small errors that I am getting are still in DEC, the tracking in RA as very good. I have not checked the alignment of the telescope for a while and this could be refined I am sure, and would probably reduce what DEC error there is.

23 Nov 2008. After a very long break due to building work and tree cutting which all required the telescope to be packed away I have got the CGE out again. Extensive tests could not get MaxIm guiding as well as PhD Guide, so it looks like PhD Guide is the winner so far. Tried using a focal reducer on the guide scope and this seems to be ok, guided last night just as well with the advantage that it was easier to find a guide star.
21 March 2009. Last night I tried out PemPro. This is software for correcting periodic error in the mount, but it also has a polar aligment function as well. The polar alignment software uses the drift method and this worked very well. The software has instructions on each new page on how to use the functions on that page which made it very easy to follow. After Polar Alignment I then ran the PEC functions and these also worked very well. I am very impressed with this software and will use it from now on to set the mount up. It really made polar alignment fast and easy.

To the left is a star taken at f6.55 with an exposure time of 5 minutes. The polar alignment was done in a fraction of the time that it usually takes me to get tracking this good.

Below this is the full frame exposure that this star was taken from. 300s exposure at F6.55 of M109. CGE1400. PhD guide used with 4s exposures on guide camera

Test of the Watec camera: I replace the Orion SSDSI with the Watec camera to see if I would be able to guide on fainter stars. Although I could indeed see fainter stars when I had the camera set for maximum sensitivity, the noise created problems for the calibration routine. I also had the feeling that the down loads were not synchronised with what the Watec was doing either, The problem was resolved by decreasing the number of summed frames by the Watec camera, but this then degraded the sensitivity so that it was no better or even worse than the SSDSI. It looks like, certainly for the moment, that I am going to stick with the SSDSI. An alternative approach would be to get a larger guide scope, but I am not ready to do this yet!
This picture was 5 x 183s shots at ISO 800, f11, with dark frame subtraction
Here is a processed image (to the right) from the photograph above of M95. The blue and green channels have been used to enhance the picture, the red channel contained little useful data due to light pollution.
After a rather long break, I eventually got a chance to identify why the guiding was jumping in DEC. By removing the backlash settings completely on the CGE mount, the problem was resolved and PHD now guides very well at f11.

A week on and it is still cloudy and raining so I tried reprocessing the image again, shown to the right. Amazing what can be done with some mathematics!
If you take the images from the above and align and stack them you get the image shown to the right. No flats taken.

This is another image of M95, I rather like this as a test object (if you had not already guessed that!). The image is 15 x 183s, at ISO 800 and f11. The stars are not round yet, but more detail is coming out.

Time to pack up again, storms with high winds are on the way...also there is now a thin layer of cloud which is making it hard to get a guide star.