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PHD odd setting

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#1 RenaudVL

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Posted 19 September 2013 - 07:41 AM

Not sure if this is the right section for this question.

I have had many many mount ( CGM, CGEM, Sphynx, GM-8, G11(never should have sold that one)), always manage to get PHD to guide adequately.

Now with my IEQ45 mounted with a C9.25 Hedge at f10 it has been really difficult to get it to do 300 sec exposure. Last night I was able to get it to do 600 sec with these setting. The set is bear bone to minimize the weight, finder, Orion 70mm finder, Orion Starshoot guider and Canon T3i

Posted Image

Posted Image

What I find odd is that I had to reduce my exposure to 0.5 second, every anther combination failed...

Any thought on what is going on. With my previous mount I was exposing at 1.5 or 2 sec.

Thanks

Renaud

#2 Madratter

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Posted 19 September 2013 - 09:01 AM

No offense meant but that graph is horrible in RA even considering the fact that the finder is f/3.9 instead of 3.2 for the 50mm and that it is 70mm instead of 50mm.

One thing I notice right off the bat is that your minimum motion is at .25 That means the things have to get off quite considerably before it will even attempt to correct it. The RA hys value is also much higher than normal.

You don't say what the rate of corrections is on your mount but that also matters. Is it .5, 1., .1, or whatever. That will affect how much that max RA value actually does. Make sure it is at least .5 sidereal given what you are seeing here.

One possibility for why it is requiring such short exposure times is that otherwise, it just doesn't have enough motion per exposure to actually manage to correct things.

That RMS with proper settings and such should probably be down at .2 or less.

#3 Raginar

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Posted 19 September 2013 - 11:09 AM

My guess is your polar alignment is off. Set everything back to defaults... try 80 RA hys of like 10-15 (remember this is the 'extra' it applies to try to minimize another correction) and a Min Motion of like... .15 or so. Like MR said, it's already got a small star to look at since you're using a finder guider so you need to engage the corrections early. Next, go to a long exposure like 2-3 seconds so that your local 'seeing' due to atmospherics isn't affecting your guiding. Finally, My guess is that your MxRA/Dec need to be significantly higher. Try setting them to like 1000 or 1500...

Other things to check are the .5x autoguide rate on whichever mount you're using. If your mount is using backlash compensation, turn it off. Also, make sure it's balanced both in RA and declination (starizona has a great guide on that) and then make sure you have it slightly heavy to the W (weight pulls down to the W) to remove any backlash from your iEQ45.

Beyond that, lower the weight on your mount by switching to a refractor. Lower your image scale by getting a shorter focal length (a reducer would help immensely with your setup now, or go with a ED80 or something like that to learn with).

Set your 'South' to AUTO. There isn't a reason not to unless you have some issues with declination guiding. Use the autoguider cable... I find I have better success than with ASCOM through the real cable. Make sure you have it set to 2x2 noise reduction. Make sure your calibration steps are significantly high (finder guiders do that, like 3-5000) and that you're getting around 6-20 steps for each direction. Too many is just wasting your time and too few isn't enough data points.

Otherwise, my guess is your settings are just wrong. Reset to default and try again.

#4 Madratter

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Posted 19 September 2013 - 11:41 AM

To put things in perspective, with my setup (50mm finder f/3.2 finder, Atlas mount, SBIG ST-i color guider), I consider anything over .08 RMS quite bad.

My guiders focal length is 162 mm. Yours (assuming I have the right one) is 279mm.

Your guider has a pitch of 5.2 microns. Mine has a pitch of 7.4 microns.

Both those things will make my numbers smaller than yours.

To convert to what I would expect with your equipment for equal guiding:

.08 RMS * (279 * 7.4) / (162 * 5.4) =

an equivalent RMS of 2.36 * .08 = .19 RMS

The other night I was running at .02 to .03 RMS. More usually, I'll be around .05.

Anyway, the point isn't my great equipment. It isn't. The point is I really doubt your equipment is more than twice as bad as mine. Something odd is going on here.

The settings above are definitely bad ones, even though they may be the best you have found so far.

As I said above, you really need to be making corrections earlier (smaller minimum motion). You need to get your exposure time out to something like 2 seconds or else you'll constantly chase seeing. The Hysteris value is way off what it should be.

Make sure your mount is balanced properly. I find that makes a BIG difference in how well my mount tracks.

#5 Footbag

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Posted 19 September 2013 - 11:43 AM

I agree about checking your polar alignment. PHD has so many settings that we tend to look there first when we are troubleshooting. Frequently, it has nothing to do with the PHD settings.

In your case, I'd start back at the defaults. That and a new alignment may just clear it up for you.

#6 Madratter

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Posted 19 September 2013 - 12:00 PM

I absolutely agree about going back to the defaults. The only number I would change from the defaults to start with is the calibration step size. I would probably have that up at more like 1000, but if you want to leave that at default, that is fine too. It will just take longer to calibrate than needed.

#7 RenaudVL

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Posted 19 September 2013 - 05:53 PM

Thanks every one for your advice, clear sky tonight...
Back at it...

I'll keep you posted

#8 Madratter

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Posted 19 September 2013 - 06:03 PM

Thanks every one for your advice, clear sky tonight...
Back at it...

I'll keep you posted


Please do. We might be able to help as you go.

#9 proteus5

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Posted 19 September 2013 - 06:35 PM

Very good info in this thread, a few things I also need to adjust. One question how do I go about resetting to the defaults?

#10 nodalpoint

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Posted 19 September 2013 - 07:35 PM

I think once you go to the brain icon there's a reset option in that list.

#11 Wembley2000

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Posted 19 September 2013 - 08:13 PM

One of the problems I had with my ieq45 was the planetary gearbox made high frequency periodic error (about every 6 sec if I remember correctly) . The only way I could get good stars with mine was very short guide exposures with PhD or use metaguide for guiding. Just not a very well designed gearbox IMO.

Wem

#12 proteus5

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Posted 19 September 2013 - 11:31 PM

I think once you go to the brain icon there's a reset option in that list.


Thanks, I'll have to check again, I must have missed it.

#13 RenaudVL

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Posted 20 September 2013 - 06:53 AM

I think once you go to the brain icon there's a reset option in that list.


Thanks, I'll have to check again, I must have missed it.


Was looking for that also yesterday evening. I manage to find the default setting by doing a search in the help menu. I found them under The Advanced Panel.

Unfortunately, by the time I could confirm that my polar alignment IS off it got real cloudy and had to roll up the observatory roof.

Thanks again every one, you have been most helpful.

Renaud






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