What Does This Message from PHD Mean After Calibration?

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Jerry Gerber avatar


My guiding numbers are between .1" and .4", mostly around .2".  Should I just ignore this message?  I'd still like to know what it means...

Thanks!
Jerry
Tony Hopkinson avatar
Hi Jerry,
I'm certainly no expert on PHD2 by any means but the comment in the panel "your declination of -0 degrees" would suggest it thinks you're on the Equator? is this the case?
Tony
Mau_Bard avatar
Hi Jerry, I would not ignore the message.
Firstly I would try and repeat the calibration and see if it works well this time. If not, I would suggest you to start from scratch and create a new profile using the wizard and following carefully the instructions. After that run again the calibration. If it not working again probably there is some mechanical problem.
In general, my suggestion is to ask this sort of questions in the PHD2 forum where the SW authors are very active and helpful. And they are great problem solvers!

Hope this helps!

Mau

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Eduardo Oliveira avatar
Provided your mount is pointing to the correct location (that is, your GOTOs are reasonably accurate) at declination close to zero (celestial equator, obviously not terrestrial equator), this message shows that there is a difference between the expected and the measured RA and DEC guide rates. Your mount will only point accurately if you are polar aligned fairly well. I would first check that the mount is polar aligned well and that your GOTOs are accurate. If the error persists this would indicate some mechanical issues as pointed by others.
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jeffreycymmer avatar
You might want to check that your focal length and sensor pixel size settings are correct.  Severe dec backlash could also cause this message.  Another thing to check is if you see 'Star lost' being displayed at the bottom during calibration.
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Makrem Larnaout avatar
You need to adjust the speed rate of your mount
Dave & Telescope avatar
If you are really getting .2-.4" RMS errors I honestly don't know what you're going to do to improve that! That being said if the error message continues to show it's probably worth looking into. Your step count is a little high so as someone else pointed out you might consider increasing your guide speed. Every mount behaves differently so 18 steps might be fine for yours but PHD 'recommends' around 12 or so. Recalibration could also be considered, close to zero dec, near meridian and as high an altitude as possible could also be considered. Other good suggestions as posted earlier

HTH
Dave
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Guillermo (Guy) Yanez avatar
I would try to move the mount to a point near but not exactly con Dec 0. Say around Dec +5 deg in the northern hemisphere or Dec - 5 deg in the southern hemisphere. I would suggest you platesolve the image at that point with whatever capturing software you are using as sometimes PHD2 will have incorrect readings for the exact telescope position. Indeed, the RA rate should be equal to the dec rate on the equator and it claims it is way off at 77%. There is a chance you are not exactly on Dec 0 deg but way off. Again, plate solving should help PHD2 here.
In case the position of the scope is correct, there may be an incorrect rate in RA that you need to adjust from the driver or the mount options (e.g., 0.5 guide rate) . Also check for mechanical issues as cable snag or stiff RA worm gear.

I would not ignore the message as others have pointed out. Regardless of having apparently good RMS numbers, the guiding could be poor due to bad calibration parameters. You will want to inspect the resulting images and see if stars are absolutely round and with expected FWHM or HFD (depending on your seeing and imaging train). If the images look as expected, then you may just go ahead and declare the session a successful one. smile Otherwise , look for the possible issues indicated above.
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Ross Salinger avatar
What mount is being used that can get guiding at .1 arc second? I'd like to buy one if they are for sale.

When asking questions about PHD, it's best to post the entire guide log so that we can see what's going on. The screenshot shows hat the mount is not responding properly, it's drifting. That would indicate perhaps a polar alignment error or something loose in the mount or the guiding system.

Don't judge by guiding RMS. Judge results by measuring your actual images.
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Jerry Gerber avatar
Because my mount (10Micron GM1000) has absolute encoders, Ed Thomas of Deep Space Products told me that guiding is not only unnecessary but gets in the way of the mount's exceptional guiding capabilities.  I think he is probably right, because the first two unguided images, with 5 minute subs, came out great, stars are very round and sharp.   Maybe I should simply not use the guiding if it's over complicating things.   This scope is on a permanent pier at a remote site.
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Dark Matters Astrophotography avatar
Jerry Gerber:
Because my mount (10Micron GM1000) has absolute encoders, Ed Thomas of Deep Space Products told me that guiding is not only unnecessary but gets in the way of the mount's exceptional guiding capabilities.  I think he is probably right, because the first two unguided images, with 5 minute subs) came out great, stars are very round and sharp.   Maybe I should simply not use the guiding if it's over complicating things.   This scope is on a permanent pier at a remote site.



With a refractor I doubt you'll need to guide as your image scale is unlikely to be very aggressive at all. If you can avoid it, I would as the overhead isn't likely worth it.
Arun H avatar
Jerry Gerber:
Because my mount (10Micron GM1000) has absolute encoders, Ed Thomas of Deep Space Products told me that guiding is not only unnecessary but gets in the way of the mount's exceptional guiding capabilities.  I think he is probably right, because the first two unguided images, with 5 minute subs, came out great, stars are very round and sharp.


10 Micron, much like Astro-Physics mounts with absolute encoders, should allow you to build a sky model. That should allow you the ability, especially from a permanent site, to not have to guide particularly with a low focal length refractor.

That said, I think your guiding issue is easily solvable. PHD2 is excellent software with great diagnostic  capabilities. I use a mount with absolute encoders, and I guide. I do occasionally get messages similar to yours. Redoing the calibration and/or assuring the mount is synched should take care of things. You also need to specify, when you build your profile, that the mount you are using has absolute encoders. As others have said - the PHD2 forum is an excellent place to get very good advice.
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Brian Puhl avatar
Chances are your guide rates are different, but if it guides fine, I would ignore it.  I don't see anything concerning on the graph. 

I run completely different guide rates on my RA and Dec and get that message almost every time, yet my guiding is still just fine around 0.2 to 0.5" RMS
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Paul Vinciguerra avatar
Not sure what mount your using but it’s referring to your guide rates in the hand controller being different speeds. For example the DEC may be set at .77 and your RA is 1.0.   I’ve had that error when adjust my guiding rates. If u click on the brain in PHD and under guiding tab it shows your guiding rate. Both your DEC & RA should be both set to the same rates in your hand controller and that should match the same rate in PHD.   Hope that helps.
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Alex Nicholas avatar
I run my RA at 0.45x and my dec at 0.35x, and I have a very smooth average of .3" to .5" guiding… Given you're guiding a mount with absolute encoders, I really wouldn't be to concerned with anything PHD warns you about… as long as its nudging the mount the right amount every few minutes, you should be just fine…
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Aris Pope avatar
Jerry, I've always had the best success sending my guide logs directly to the PhD form. Brian and Bruce are pretty good at getting back to you and they pretty much know the system better than anyone.

https://openphdguiding.org/getting-help/
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Aris Pope avatar
@Jerry Gerber  I also forgot to add that my buddy @Scott A Schneider  who I image with quite a bit has an AP Mach 2 GTO with absolute encoders like your mount. He was having issues and I suggested the same to him. The guys at PhD2 are very helpful and help him get along as well.