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Guiding trouble


Sammyb

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A few months ago I had my first ever attempt at guiding and managed 5 minute subs no problem at my first attempt. I thought excellent! Away I go! There's no stopping me now!

Ever since then its all gone to pot and is constant grief.

My equipment is an SPC900NC (un modded) on a 50mm finderscope. Guiding an 200P Explorer on an EQ5 Synscan mount via EQMOD. All balanced fine (I think).

Last night it would not calibrate in Dec - gave me an error. When it finally calibrated the guiding was simply ineffective - I could barely get 1 min subs.

Calibration always seems to take an age.

On Phd I could see the guide star (which was a good star) shifting slightly away from the cross-hair and hear the mount motor sounding like it was trying to correct it which it eventually did but there was a lag. This looked to be in the N/S orientation - which corresponds to where I had difficulties with the calibration.

I was trying to image M42 and as with other nights I seem to struggle with targets lower down where the scope is more horizontal. My best results have been with m27 when it was high in the sky last year and a more vertical scope.

Is it a weight/balance problem?I think the scope is balanced.

Any advice you could give would be appreciated. I am going mad with this.

I have attached my PHD settings.

Thanks,

Sam

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Welcome to my world :icon_scratch:

This seems to be a subject that crops up all the time. I too have had a session where everything was working fine and I was getting the best graphs, yet having parked the scope and then tried again the next session it was all over the place....

No real answer as to why....

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Its difficult to get 200P Explorer on an EQ5 Synscan guiding well due to fact that mount is not strong enough and if there is any backlash in DEC axis, it will be sometimes difficult for PHD to clear it.

Try guide in RA only and make sure your polar alignment is as perfect as possible. You can also decrease Minimum motion to 0.06 in order in increase guiding accuracy.

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Thanks for respondng. I will have a look at those settings.

I am suspecting it might generally be a weight issue with the 200P on the EQ5. I have a plan to save up some cash and put the 200P OTA up for sale and get an ED80 for the EQ5.

In the meantime I must focus on targets that are straight up!

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Hi Sam, You may have seen my recent thread on here, guiding EQ3-2..? Well although our setups are a bit different I may be able to help. I was experiencing the same N/S correction problem as you, my star would drift south and I could here the DEC motor click into action to save the day, but by the time any backlash ect had been taken up it was to late and the sub was ruined. I think I have solved this now. Bare in mind I have already got a lot of the basics covered i.e Drift aligned + pier mounted, Balanced so its slightly heavy on the east side, mount serviced and tuned as much as poss etc etc, so this is what I have done to solve the DEC problem. First I found out which way the star drifted. It was drifting south. I then immediately set PHD to only guide DEC in south mode. Remember that DEC is only adjusting for polar alignment error NOT errors in the mounts drive, so in "theory" it should only need to adjust DEC in one direction to correct for this. After this I used the fast slew mode on my hand controller to get the star back to centre screen MAKING SURE THAT THE LAST DEC MOVMENT WAS SOUTHWARD so the any backlash was pre taken up so when the DEC motor is commanded by PHD do make the south drift adjustment it would be straight on the case with no messing about taking up BL if that makes sense. I'm not sure if the EQ5 synscans suffer much from backlash...? anyway after this my setup seems to be working OK.......

I may be talking squit, Guiding is still very new to me, just though id share my findings.....

HTH

Stan, :icon_scratch:

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Stan - thanks. It sounds like you were experiencing the same problem. It took a while for PHD to clear the BL during the calibration the first time around.

I will try this next time around for definite.

If it works I will offer to come round your house and cook you a roast beef dinner and pour you a nice bottle of guiness (although Suffolk is quite a distance).

Cheers,

Sam

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Stan! Looks like I owe you a roast beef dinner and a bottle of Guiness!

Vast improvement! I'm really pleased!

I used the graph output in PHD and I think I've got some other issues I need to deal with - that will be the subject of another post when I get round to sorting out the screen grabs.

Thanks very much for your help.

Sam

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Hi Sam.

Re. having DEC guiding turned off.

Unless you have a perfect mount and perfect polar alignment, you will need to have DEC guiding enabled.

As your alignment is unlikely to be perfect, even with a scope in a permanent observatory, you'll find that on one side of the meridian, the vast majority of guide corrections in DEC are always one way...either north or south, and the other side of the meridian, they will be the opposite way.

Switch your DEC guide mode to whichever of these, either N or S, that you find to be the way your DEC corrections are occuring. This will then mean that, when a DEC correction is issued, there will be no backlash to be taken up, and you'll avoid any yo-yo'ing back and forth on the DEC axis.

If, as sometimes happens, you need a correction in the opposite direction, just leave it and wait...the mount will soon settle back down again without any external help.

Cheers

Rob

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I think something that may have helped me is that use the synscan handset in standalone mode to give me the clock position of polaris for my polar alignment.

The previous night I inputted the date in dd/mm format instead of mm/dd so my polar alignment will have been a bit more out and there may have needed to be excessive dec correction.

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