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thomasv

Fornax Lightrack II experiments

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I've picked up a second hand Lightrack II recently, so was keen to test it. My plan was to use the guiding assistant in PHD to get a graph of the tracking performance, but initially the mount wouldn't move. After a search, I had to modify the guiding cable that came with the mount, as it was wired up 'the other way' to the one required for QHY5L. After that it calibrated fine and could run the test. Below is a 22min graph of the unguided performance, while it's not within the 2" peak-to-peak quoted, it's still pretty good. 

Next I've tried it with a canon 300mm lens (unguided again), the picture is a crop of a 10min exposure, slightly eggy, but again pretty happy with that. 

log1a.thumb.PNG.04b61079e93ea9b3c1d3f5dc3cbb632b.PNG 

10min_col_50p_crop2.jpg.4deb3617db5af6cc561815d116ea9046.jpg

setup.jpg.9f987168c073c083645dee2335f0763f.jpg

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Interesting.

I was wondering how I can guide my Lightrack II

I own an Orion StarShoot autoguiding pro (I believe the camera is a QHY5L-II).

- How to set up PHD2 (since you can only guide in RA, special setup is required?)

- what modifications do I have to make to the cable?

Also, I just returned my Fornax wedge and ordered the skywatcher wedge, how do you like it? I am a bit worried it could be a bit light. What is the total weight of your gear mounted on the lightrack?

Can you make fine ajustments in ALT with little efforts?

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Hi, sorry for the delayed reaction, I'm away on holiday.

There are two options for the ST-4 cable wiring and the cable supplied by Fornax is configured as per SBIGs convention. Basically you need to reverse the connections, what was pin 1 becomes pin 6, etc. Of course this is easiest done at the headphone type connector end, make a note of the original colours of wires going to the 3 pins, and reconnect as described. Normally you can see what order the coloured wires are at the st4 end.

Sorry I don't have my pc with me, so can't tell you exactly where, but you do have to tick the RA guide only option, I think it's on the main screen.

The skywatcher wedge is ok with the lightrack, i'm sure the fornax wedge is better, I just didn't want to remorgage the house for one. With a bit of practice you can make fine adjustments, the trick is not to loosen the locking screw completely, just enought to be able to move with the adjustment screw. I think my setup is about 4kg.

 

post-33644-0-32286000-1517100710_thumb.jpg

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Thank you for your reply. I just got my autoguider camera ORION SAGPRO (which I understand is a QHY camera)

I have connected the camera St-4 to the lightrack with the provided RJ12-3.5mm jack, in PHD selected "on camera" mount and set DEC guiding to "off" in advanced settings.

Upon opening the 3.5mm jack I see the following three cables:

image.png.d6051580a950f286502a8537d8df0853.png

According to the SBIG scheme  they are :

- blue: +DEC 

- yellow : -DEC

- black: No connection

And therefore to make it compatible with QHY wiring they must become:

 

- blue --> purple

- yellow --> green

- black --> red

 

Now, the doubt I have is why would they control DEC if the Lightrack only moves in RA and DEC is disabled in PHD????

 

image.png.5aef587186a848a2190d4e56712f61d2.png

 

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Hi,

I wonder if the colours are assigned in the reverse order to the pin numbers. I'm not actually sure what the picture represent, is it the connector on the cable, or the socket, and looking from which direction.

I've checked, I did what you describe:

- blue --> purple

- yellow --> green

- black --> red

You can test if the PHD commands get through to the mount by using the manual guide option and listening to the sound of the mount. The high pitched whistle doesn't change, but there is a lower frequency noise (murmur) that changes frequency slightly if you issue left/right commands.

 

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Modification done

- blue --> purple

- yellow --> green

- black --> red

I can hear the "murmur" changing frequancy when I hit East/West in Manual Mode (you have to push your ear to the Lightrack case to hear the murmur)

I will try guiding as soon as the sky clears up a bit

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Sounds promising, great. Would be interested in seeing a graph of the tracking performance with PHD's guiding assistant like I posted above to compare against the performance of my 2nd hand unit.

 

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How did you get the above graph for unguided performance? I am new to PHD and want to make sure we compare apples to apples

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You start guiding as normal, which will first calibrate the system. Then tools --> guiding assistant will open a new window, disable 'dec backlash' measurement and start. This will then disable the guiding and uses the guide camera to measure the accuracy of tracking, leave it running for about 20mins. Make sure that the camera type (pixel size) and guide scope focal length are set correctly under PHD general settings, so that the results in arcsec are correct.

You will need to download a separate piece of SW called PHD log viewer to then analyze and display the guiding performance. This takes the PHD guide log file as input, which is normally in your Documents folder /PHD. 

 

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I did a test tonight. The test is done with a 350mm imaging scope, which is balanced. Polar alignment with Polemaster

guiding camera pixel size and scope focal length are set in PHD2, DEC guiding is set to OFF in advanced settings

Below the logs

Guided: it seems that guiding is working properly, since the trend-line is responding to guiding pulses. I can get nice round stars at 4min subs exposure

image.thumb.png.f1de04805ef712417f9c9539c8f7aa0a.png

 

However, after starting Guiding assistant, I get this weird graph below:

image.png.0d7f04a182ca133ebe10752da92139da.png

 

I don't think the lightack has such bad behavior as I can take nice 2 min subs  unguided, so, what is going on?

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I wonder if something has moved at 22:17, the trace is nice and horizontal before, then there is a jump and then iit starts to diverge, indicating probably that polar alignment has shifted? Don't know what it could be, tripod or wedge, would you mind posting a picture of the setup?

 

 

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The first part with horizontal Trace is the guided part, as soon as I start guiding assistant and guiding is stopped, there you get the jump and the Trace starts to diverge.

 

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OK, sorry. Can you tick the DEC box near the bottom to display the DEC trace. If both are drifting away in a straight line, I would have thought it's ought to be a polar alignment problem. I thought that guiding assistant gave an estimate of the polar alignment error, but I now can't find it anywhere in the log viewer, so I think it may only display it while it's running live.

 

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