HEQ5 very large RA drift

[cuivenion]

Hi, I'm getting very large drift in RA with my HEQ5. I think it might be responsible for my bad guiding (double stars in some cases). It seems to happen when the scope is pointed west of the meridian it behaves a lot better pointing east:

I disabled the guiding output to try and provide an example. A star will move visably from my crosshairs over the course of a minute or so and PHD2 has to make constant large RA corrections. Do I have a mechanical problem that can be fixed? Is this fairly normal and will pec training help? I have the mount balanced as well as I can with a slight east heavy and camera end imbalance. There doesn't seem to be a lot of backlash. Goto's are good until I cross the meridian which I assume is down to cone error.

Any help much appreciated.

[SteveA]

Quite possibly a large periodic error. May be worth capturing a longer data set and running it through PecPrep, you will be able to to see fairly easily if it is PE.

Steve

[michael8554]

Dec line is flat so PA is good.

If it's PE then if left unguided for long enough the RA line would come back to the zero line and probably head on up to +20 before returning to the zero line again.

I understand that the Belt mods improve PE because these mounts have a non-repeating PE that can't be dialled out with PEC ?

Michael

[cuivenion]

Thanks for the replies, the mount already has the belt mod. I did try to take a longer graph but the clouds rolled in:

Seems to bear out whats being being said about periodic error. I'll have to see if I can take to long graphs either side of the meridian and convert them to pec files.

[SteveA]

As you are running EQMOD you could try the built in AUTOPEC feature.,This allows you to capture the PEC data whilst guiding and basically automates the the whole process. Interesting that you are having this issue as I am having a very similar problem with an EQ6 and poor guiding. I only discovered the AUTOPEC after reading around and discovered that as I hadn't been keeping up with the updates that my version of EQMOD didn't have it. I installed the latest version last week and started playing with this. Not really had a chance to assess the results although things do look more promising.

Steve

 

 

 

[cuivenion]

8 minutes ago, SteveA said:

As you are running EQMOD you could try the built in AUTOPEC feature.,This allows you to capture the PEC data whilst guiding and basically automates the the whole process. Interesting that you are having this issue as I am having a very similar problem with an EQ6 and poor guiding. I only discovered the AUTOPEC after reading around and discovered that as I hadn't been keeping up with the updates that my version of EQMOD didn't have it. I installed the latest version last week and started playing with this. Not really had a chance to assess the results although things do look more promising.

Steve

 

 

 

So you don't need the guiding output disabled, you just guide as normal and set autopec recording?

[SteveA]

Yes that's correct...

As I mentioned this had all passed me by until I started looking into it and found a thread on the EQMOD user group

From the documentation then....

• First select the number of cycles that you wish capture PE over. The longer the better the results will be.
• With you mount being guided by your auto-guiding software (either via ST-4 control or ASCOM PulseGuide) hit the record button.
• The PE will be measured and plotted on the capture graph which displays a single cycles worth of data. Each tim a new cycle is started the colour of the capture graph will toggle between Red/Green. The progress of the capture is displayed in the Status Area.
• Once capture is complete the periodic error data is written out to a text file with the suffix _EQMOD. This can then be further analysed using PECPrep. A PEC file is automatically produced using the PE data and saved to disk.
• If the AutoApply PEC oprtion has been selected the PEC file will be automatically loaded into EQASCOM.

AutoPEC can be preformed whilst guiding+PEC is being applied.

Steve
 

[cuivenion]

Thanks, does the difference in focal length between guide and imaging scope not matter as far as pec is concerned?

[SteveA]

There's always going to be a difference in the image scale between the imaging camera and guide camera even when using an OAG and this doesn't normally present any particular issues when guiding. Clearly there are general guidelines regarding the ratio of these two, I seem to remember a ratio of 4:1 being mentioned somewhere. If you are happy there being a difference when guiding I don't see why recording PEC should be contentious. I dare say if you recorded PEC data through your main camera there would possibly be small differences with that recorded through the guide camera. The PEC data is massaged by a whole set of filters and transformations in order to extract a mathematical model that can then be applied to the tracking, I assume that after this the two models would be pretty similar....but I'm no expert here, maybe someone else has a better handle on this?

Steve

[cuivenion]

That's true. I have one or two guide logs that are long enough. I'll put them through pec prep and see how well they work.

[dph1nm]

The period of the Periodic error should be about 10 mins on the HEQ5, so that looks about right.

NigelM