PHD2 Dec in on axis and dithering

[Datalord]

After battling my mount a bit, I finally got some hysteria under control by guiding in Dec only in one direction. However, since turning that on, PHD will now only dither in one direction, and now I fear for my data.

Is there a way to force PHD to dither using both axis, even if I turned Dec into only South? Oddly enough, there is an option to "Only dither RA", but it seems to me it just does that.

[michael8554]

Guiding Dec in one direction is usually arranged with a small PA error and balancing Dec heavy in the same direction as the drift, to take up the Dec backlash.

But there's no reason you can't  leave Dec guiding on Auto, it will still only guide in one direction if you have a suitable MinMo setting, and Dither on both axis will work. 

There's a Fast Recentre After Dither tickbox in the Guiding tab, but gaps between exposures may still need to be lengthened because of the Dec backlash.

Michael 

[alacant]

8 hours ago, Datalord said:

Is there a way to force PHD to dither using both axis, even if I turned Dec into only South?

AFAIK, later versions do so anyway. If you have an older version, you could use the phd2 dither app to effect the same. To avoid disturbing DEC guiding, you may want to dither RA only but that -for us at least with dslrs- introduces more streaking noise.

HTH

[Datalord]

17 hours ago, michael8554 said:

Guiding Dec in one direction is usually arranged with a small PA error and balancing Dec heavy in the same direction as the drift, to take up the Dec backlash.

But there's no reason you can't  leave Dec guiding on Auto, it will still only guide in one direction if you have a suitable MinMo setting, and Dither on both axis will work. 

There's a Fast Recentre After Dither tickbox in the Guiding tab, but gaps between exposures may still need to be lengthened because of the Dec backlash.

Michael 

Well, bitter experience tells me I need to only do it in one direction. It calmed down both axes considerably, so my dec RMS was 0.54" yesterday. Down from 0.8-0.9.

9 hours ago, alacant said:

AFAIK, later versions do so anyway. If you have an older version, you could use the phd2 dither app to effect the same. To avoid disturbing DEC guiding, you may want to dither RA only but that -for us at least with dslrs- introduces more streaking noise.

HTH

Hmm, I have a pretty up to date version. How recent is this change? 

I'll look into the dither app if I can't solve this, thanks! 

[alacant]

17 minutes ago, Datalord said:

Hmm, I have a pretty up to date version. How recent is this change

Hi. Upgrade to the latest anyway?

From the PHD2 manual:

'If your mount has a substantial amount of declination backlash in the mount, you may be guiding in only the north or south Dec direction.  If PHD2 receives a command to dither in declination while you're operating in this mode, it will temporarily allow guiding in both Dec directions until the dither and settling are completed.  It will then revert to the original north/south-only guiding mode.  If you don't want this behavior, you should restrict dithering to 'RA-only' ('Global tab of the Brain dialog).'

HTH.

[Datalord]

14 minutes ago, alacant said:

Hi. Upgrade to the latest anyway?

From the PHD2 manual:

'If your mount has a substantial amount of declination backlash in the mount, you may be guiding in only the north or south Dec direction.  If PHD2 receives a command to dither in declination while you're operating in this mode, it will temporarily allow guiding in both Dec directions until the dither and settling are completed.  It will then revert to the original north/south-only guiding mode.  If you don't want this behavior, you should restrict dithering to 'RA-only' ('Global tab of the Brain dialog).'

HTH.

Yeah, I read that and have exactly that option in the settings. I tried clicking it on, save, click off, save. Just leave it on, then turn it off. No avail, it only dithered in ra. 

It's very odd, I think it only started yesterday where I was playing around with the algorithms. I ended with PPEC in RA (magic!) and hysteresis in Dec. Neither of these is affect dithering. 

[alacant]

4 minutes ago, Datalord said:

it only dithered in ra

Do you have the latest development release?

[Datalord]

19 minutes ago, alacant said:

Do you have the latest development release?

Definitely not. I'll update it tonight when I get home. 

[michael8554]

1 hour ago, Datalord said:

Well, bitter experience tells me I need to only do it in one direction. 

I think you're not understanding my post.

I understand your need to guide Dec in one direction only, I'm in the same situation. 

If you've set PA with a slight drift,  and balanced so that Dec is heavy in that direction, PHD2 will only need to correct in one direction, even with Dec guiding set to Auto.

But I too must try that revelation that 2 way guiding is enabled for Dither.

Michael 

[Datalord]

3 minutes ago, michael8554 said:

I think you're not understanding my post.

I understand your need to guide Dec in one direction only, I'm in the same situation. 

If you've set PA with a slight drift,  and balanced so that Dec is heavy in that direction, PHD2 will only need to correct in one direction, even with Dec guiding set to Auto.

But I too must try that revelation that 2 way guiding is enabled for Dither.

Michael 

Ah, right, but somehow the algorithm starts oscillating in Dec if I do auto. Perhaps I gave up too early, but I'm very, very pleased with 0.53" and as such I don't want to go back just because phd is having a fit. 

Btw, I can't balance the scope heavy anywhere as it is remote and must work at all places. 

[michael8554]

If it oscillates then too much Aggresion, but I appreciate how difficult it must be getting a good setup for Remote op.

With one direction Dec, what happens when your mount reaches a position where Dec flops the other way ?

Michael 

[alacant]

1 hour ago, michael8554 said:

what happens when your mount reaches a position where Dec flops the other way

?

[michael8554]

Datalord is dec guiding in one direction only.

At some point in the mount's traverse across the sky it's going to become heavy in the other direction, so the one direction dec guiding will be in the wrong direction. ..........

Michael 

[Datalord]

2 hours ago, michael8554 said:

Datalord is dec guiding in one direction only.

At some point in the mount's traverse across the sky it's going to become heavy in the other direction, so the one direction dec guiding will be in the wrong direction. ..........

Michael 

It will? Seems to me only ra will do that? 

[alacant]

7 hours ago, michael8554 said:

guiding will be in the wrong direction. ..........

Hi. It seems a lot but this may help. Cheers.

[alacant]

5 hours ago, Datalord said:

Seems to me only ra will do that? 

Hi. No. RA is always in the same direction. HTH.