Apart from the flip hour angle for Paramounts, this discussion is also useful for any mount owner, trying to get their head around mount and SGP limits.
A couple of things come to mind. In the video I suggested not to flip early - probably due to hang ups with some of my earlier mounts. The mount limits may not necessarily be symmetrical and in my case, I would not want to do a flip and have the weights that much higher than the telescope. My exposure lengths are all different too and I would not necessarily know which exposures would be in play at the meridian. I made the assumption to set the limit based on the max likely exposure (20 mins) though with CMOS cameras, this is likely to be less.
I re-read the Paramount manual - good for insomnia. The default values for the flip are before the meridian are interesting. - and your third suggestion makes sense, in so much that there is little point starting to image just before the meridian, when you have to flip shortly afterwards and slew/center/focus/guide all over again. I shall move my TCS flip value back to a value that would not try and flip outside the slew limits.
Working through your third case, your example has an exposure duration that is longer than the slew limit - so an early flip is even more useful. Mine is the other way around (35 mins and 20 min). That would mean my meridian flip occurs past the meridian, rather than ahead. So in my case, I could simply uncheck the wait for meridian (flip) in SGP, as it just wastes time and put the unique TCS Paramount flipping point to the meridian (or a lttle before, up to the slew limit, it does not really matter). In doing so, I would not waste any imaging time at all and, in the case of starting a SGP sequence near the meridian, it would flip to the best side on the initial slew?
It does your head in ChrisâŚespecially try to navigate the two Hemispheres on topâŚLol. A beer is definitely in order.
In fact if you use the little equation I mentioned the time required to set the meridian flip âbeforeâ the meridian can always be expressed by Texposure-Tslew limit. In your case T exposure is 20 mins and Tslew limit is 30 mins. So you can set your slew limit before the meridian to -10mins. But -10mins before the meridian is a double negative and is in fact 10 mins after the meridian. So you could set you slew limit to up to 10 mins after the meridian without creating an issue and without losing imaging time.
Yes if you were starting an imaging run and your target is coming up to the meridian you will want to avoid a flip and you would prefer to start off with the OTA on the west side of the pier. However, if the Flip Hour Angle on The SkyX and the âMinutes Past the Meridianâ on SGPRo are set to 0, then you have problem, because when you slew to the object the OTA will be on the east side of the pier and a meridian flip will be required soon. Therefore, if the object you want to start on is coming up to the meridian but is say 15mins short of it, you would set the two flip parameters to say -20mins. That way the object will start off in the red zone and when SGPro asks The SkyX to slew to it, the OTA will move to the west side of the pier and can stay on that side for the rest of the night.
HaâŚthereâs only one problem with that theoryâŚpractise!. I get an error message when I try to enter a negative time to the meridian flip. It says my Mount doesnât support that. It would be interesting to understand why not.
In the ASCOM world of telescopes there are 2 kinds of mounts:
Type 1: Mounts that let you explicitly ask for a meridian flip and then attempt to get you back to where you are pointing, but on the other side of the mount. For this mount, you can ask for a flip anytime you want.
Type 2: Mounts that DO NOT provide functionality to explicitly request a flip. This is TSX. In this case, the best SGPro can do is issue a slew command and hope that the mount thinks it should flip at the time of the slew command. For this reason, we canât support early flips because the mount will almost certainly just ignore the slew command (as in⌠Im already there, stop asking me to do stuff that I already did).
TSX can implement their driver in such a way that they can support early flips, but I canât speak to the difficulty of implementation on their part.
Thanks Ken,
I had missed your response. My apologies.
In my experience, if the Flip Hour Angle on TSX is set to match the Minutes past the Meridian to Flip on SGPro, the flip always works.
In TSX the Flip Hour Angle is a parameter that can be set to determine to which side of the pier the OTA ends up when a slew is initiated. This can only happen within the software slew limits. In my situation that is from -1.5 hours to +1.5 hours from the Meridian. Outside these my telescope will hit the pier.
If for example I set the Flip Hour Angle to -1.0 hours, then as an object tracks across the sky at the sidereal rate, the following occurs:
if the object is more than 1.5 hours from the Meridian say -2.0 hours, the OTA will always end up on the West side of the pier (remember I am in the Southern Hemisphere)
if the object is between 1.0 and 1.5 hours before the Meridian, the OTA will end up on the West side of the pier.
If the object is before the Meridian but within 1.0 hour, it will move to the East side of the pierâŚthe counterweights will be up in the air.
If the object is after the Meridian the OTA will also end on the East side of the pier. Now the counterweights will be down.
There are times when it would be nice to force a flip before the Meridian, but as I said I get the error message which says the Mount doesnât support it. I donât understand why or who is saying the Mount doesnât support it. As far as I know, as long as the astronomer sets the Flip Hour Angle in TSX to match the negative âMinutes past the Meridian to Flipâ, when SGPro tells TSX to slew to the object the OTA will end up on the correct side of the pier and the flip will work. If it works for hours past the Meridian, I can see no logical reason it wonât work for hours before the Meridian.
What do you think?
