I usually image from my backyard, but when I'm not imaging I put my telescope back into my garage. Depending on the target location, each night I may place the telescope in a different location to avoid some obstructions, and since I'm forced to stay on a (flat but somewhat irregular) grass surface, every time I need to re-level my mount. Honestly, I don't spend too much effort in levelling, I just use the bubble level built-in to my mount and call it a day. I mostly keep the same PHD2 calibration for every session, and get variable results on my guiding. Do you think I'm better off recalibrating my guiding every night?

PHD2 recalibration when moving mount
#1
Posted 24 January 2025 - 06:34 AM
#2
Posted 24 January 2025 - 07:07 AM
I am in the same situation. I don't get too hung up with leveling, but I do recalibrate before every imaging session. Only takes a minute.
- Dynan likes this
#3
Posted 24 January 2025 - 07:17 AM
I am in the same situation. I don't get too hung up with leveling, but I do recalibrate before every imaging session. Only takes a minute.
I see! Thanks
#4
Posted 24 January 2025 - 07:33 AM
The argument for re-using the calibration is: you are polar aligned; the mount must be in the same orientation in space (even if not in the same place).
The argument for re-calibrating is: it doesn't take long.
- Dynan and gsaramet like this
#5
Posted 24 January 2025 - 07:39 AM
If you callibrate home, then you travel far North or South (say 50 miles or more), you should recallibrate. If you travel East or West and stay at the same altitude, not needed; however, as others said, at least it is quick to callibrate.
But within a reasonably sized home, I don't think it is needed.
Edited by fmendes, 24 January 2025 - 07:40 AM.
#6
Posted 24 January 2025 - 10:26 AM
RAM
So. Oregon
#7
Posted 24 January 2025 - 11:13 AM
#8
Posted 24 January 2025 - 11:18 AM
Thank you all guys, I will try to recalibrate each time to see if my guiding improves
#9
Posted 24 January 2025 - 12:09 PM
The argument for re-using the calibration is: you are polar aligned; the mount must be in the same orientation in space (even if not in the same place).
The argument for re-calibrating is: it doesn't take long.
This. I don't recalibrate unless I (remember that I did) change things. The thing between parentheses is important
Can get funny. I am shooting with a duo sensor cam, and I forgot I rotated the camera 90 degrees. That's the result
#10
Posted 24 January 2025 - 12:49 PM
There is no good reason not to recalibrate. But, in all honesty, it should not be necessary unless you moved the guider relative to the mount.
PHD needs to know the relationship between the movement of stars in the guider and the movement of the mount. So if anything between the RA/Dec axes and the guider has changed, then recalibration is necessary. Rotating the OTA in the rings, rotating the guide scope in its mount, detaching the guider from the OTA, removing the guide camera would all require recalibration. If you did none of those things, and took care not to let any of them happen by accident, then recalibration should not be necessary.
But, like I said, there is no good reason not to do it.
- Spaceman 56 likes this
#11
Posted 24 January 2025 - 01:08 PM
There is no good reason not to recalibrate. But, in all honesty, it should not be necessary unless you moved the guider relative to the mount.
PHD needs to know the relationship between the movement of stars in the guider and the movement of the mount. So if anything between the RA/Dec axes and the guider has changed, then recalibration is necessary. Rotating the OTA in the rings, rotating the guide scope in its mount, detaching the guider from the OTA, removing the guide camera would all require recalibration. If you did none of those things, and took care not to let any of them happen by accident, then recalibration should not be necessary.
But, like I said, there is no good reason not to do it.
That is not always true. If the mount has large periodic error and you happen to be calibrating the dec axis at a part of the cycle where the RA has a substantial slope, the star will be moving in RA along with dec (probably giving an orthoganility error, but I'm not sure if that is always true). If you happen to be calibrating the RA axis when there is "extra" PE movement, the RA rate can be inaccurate. With mounts like that (like my old CEM25), some calibrations are better than others. If you get a good one, it can pay to keep it if you can.
The proof is in the guiding, though.
#12
Posted 25 January 2025 - 01:17 AM
If you callibrate home, then you travel far North or South (say 50 miles or more), you should recallibrate. If you travel East or West and stay at the same altitude, not needed; however, as others said, at least it is quick to callibrate.
But within a reasonably sized home, I don't think it is needed.
This doesn't make sense. Calibration establishes the relationship between the guide camera and mount, nothing more. The odds of this changing with a physical move of the gear is high, microns are important, so a recal is usually warranted
#13
Posted 25 January 2025 - 06:30 AM
If the levelling of the mount changes then I may be wrong, that may cause the same errors as the guidecam being rotated.
Whatever, for a non-permanent setup it's good practice to Cal every night.
#14
Posted 25 January 2025 - 10:30 AM
Yes sorry that is not correct. When you calibrate, it defines the trajectories/angles on the sensor that correspond to mount movements in RA and DEC, and also pixels per second for a guide pulse. This depends on your chosen guide rate. With some simple math this can be converted to units of arcseconds/s. Leveling has no effect
#15
Posted 25 January 2025 - 10:37 AM
I almost never recalibrate unless I rotate the guidescope or rotate the camera and am using off axis guiding. Calibration simply determines what direction and rate of movement of the scope and unless this changes there is no reason to recalibrate. This might vary with mount types but I doubt it unless the performance of a mount is different from night to night.
Form my AM3 and AM5 mounts which I set up in the driveway, feet aligned to driveway seams, I can setup in generally the same spot, check level to make sure nothing crazy happened, and go with some polar alignment errors and no recalibration. Guiding consistently below .7 and sometimes as low as .4 if seeing is good. That's below what I need.
Your mileage may vary, might be fun to experiment rather than reading advice from someone with different equipment.
#16
Posted 26 January 2025 - 09:16 AM
This doesn't make sense. Calibration establishes the relationship between the guide camera and mount, nothing more. The odds of this changing with a physical move of the gear is high, microns are important, so a recal is usually warranted
It depends on a few factors. If I image with OAG, I usually recalibrate every time I rig up (and every rotation as I haven't learned how to use the manual rotation plugin in NINA). But when I use my guide scope connected to the saddle, it simply does not move significantly to warrant a recalibration, even if I rig down the equipment and drive 60 miles West. Yes, it may move microns between sessions, but it may move within the same session, due to temperature variations. In any case, PHD2 is smart enough to compensate for these small variations.