Guiding better after the Meridian Flip...?

[kirkster501]

Hi all, any thoughts as to why my guiding is better after the flip because after numerous observations, it most assuredly is.  Mount is MESU 200 and using PHD2 and using a guide scope.  Everything is balanced as far as I can tell - not the easiest of mounts to balance is the MESU.  I do not appear to have any flexture either and in any event, this also applies when I am using OAG as well.

What tinkering do you guys do with PHD2 settings such as min move, Hysteresis and aggressiveness?

[tomato]

Unfortunately with my current set up location, I have little need to meridian flip as one hemisphere of the sky is almost completely inaccessible. Guiding performance with the Mesu can vary a lot from session to session even though I polar align with Sharpcap to <30” every time (still having movement on the final tighten down).

Last night imaging M106 I was getting total RMS of 0.6”, with very few corrections in Dec but RA needing regular corrections in both directions. I reduced the RA aggressiveness setting in PHD (currently at 65%) and this helped a bit as there was an element of over correction happening. But... on nearly every session I get periods of around 60 secs or so with near perfect tracking, with no corrections on either axis. This has to be due to seeing conditions I presume, but my guiding exposure time is 3.5-4.0 secs which should be enough to smooth these out?

[mihaighita]

13 hours ago, kirkster501 said:

Hi all, any thoughts as to why my guiding is better after the flip because after numerous observations, it most assuredly is.  Mount is MESU 200 and using PHD2 and using a guide scope.  Everything is balanced as far as I can tell - not the easiest of mounts to balance is the MESU.  I do not appear to have any flexture either and in any event, this also applies when I am using OAG as well.

What tinkering do you guys do with PHD2 settings such as min move, Hysteresis and aggressiveness?

Very odd to have better guiding after the flip... Most probably you have some imbalance there.

I always have my MESU on very low aggression and relatively high hysteresis. As of lately, I am using aggression of 45% in RA and 30% in DEC and 32 hysteresis. I found that these values with a 5-second exposure will give me the best results in average seeing conditions at long focal length (I have a 2000 mm FL GSO 10 inch RC on top of the mount now). At low FL should not matter too much on this mount it will make round stars in any configuration of PHD2.

Balance can be tricky to do on the MESU but I use a hand scale with an attached strap held by a "contraption" I made to help me with the positioning and raising the scale perfectly perpendicular to the end of the OTA and end of the counterweight bar. The only pain with the balance has been shifting the 25+ kgs of OTA in the saddleplate. 

 

Edited February 11, 2019 by mihaighita

[Tomatobro]

I like Mihaighita's method of checking balance as it would also highlight any change in the rotation drag of the mount itself. I used to check compressors by wrapping cord round the drive pulley and using a spring balance to measure the start and rotation pull as part of routine checks.

[Astroblue17]

Yeah I thought this was weird! I had it happen to me recently, went from .8-1.0 to .15 to .30 I was shocked. Took a 10min exp for giggles and to see if guide results were correct.…was picture perfect. Normally I get a way with 5min exposures. I thought my balance was pretty good but could of been off or cable drag a little 

Edited December 15, 2023 by Astroblue17

[ollypenrice]

The only mechanical variable I can think of is balance.

On the other hand, your flips will be performed later in the night, by which time the seeing is very likely to have improved. Have you tried taking a short-term RMS just before the flip to compare with one of the same duration just after it? Your pre-flip RMS may have a lot of earlier-evening bad seeing built into it.

On 12/02/2019 at 00:23, mihaighita said:

At low FL should not matter too much on this mount it will make round stars in any configuration of PHD2.

Just a pointer to the fact that round stars, of themselves, say nothing about guiding precision other than that errors in RA and Dec are equivalent. If they are both large and equivalent you will get round stars and lost detail. We actually had this while setting up our first Mesu.

Olly

[tomato]

A couple of nights ago my guiding was 33% better after the flip but I was imaging a target only ~30 degrees above the horizon and the guiding was improving prior to the flip, so seeing was playing a big part, I think.

[Clarkey]

As said by a few people, looks like a combination of balance and seeing.

Just think yourself lucky that you have a Mesu. You should try a SkyWatcher mount. Random movements everywhere!

[Scott Badger]

Maybe the improvement is because the the mount is slightly unbalanced in RA and after the flip it’s east-side heavy? Depending on the mount, that can sometimes result in better guiding than perfect balance.

Cheers,

Scott

[tomato]

In the absence of other variables, the atmosphere can play a significant part. Imaging a target at 75 degrees elevation guiding was at 0.4 arc secs total RMS cf. 0.5 with a target at 30 degrees elevation.