Hi Ray, et al,

Just a quick note on the latest version of PEMPro. The Polar ALignment Wizard seems to invert the direction needed to correct for mis-alignment on both Alt and Az.

I'm in Sydney, Australia - had the Southern Hemisphere box checked, have lat and long correct to the arc sec (according to Google Earth). I ran through all nine steps (including moving a star in 5 arc minutes to get compass directions correct (for both Az and Alt seperately) - checked the image scale was correct and ran the wizard again on my permanent peir rig.

My alignment was about 1 arc minute off - got it down to about 0.1 arc minutes on both axes last night. However the correction directions where inverted for both axes. Each time I adjusted the mount in the direction and magnitude shown - the alignment error doubled. I did the same magnitude in the opposite direction describe and the mis-alignment reduced.

Ray, maybe a sign got missed somewhere for us Southern Hemisphere users (and shouldn't this tick boxed be a computed field anyway - from a users Longitude? South should be a dead giveaway).

Anyway please have a look into this - may help less experienced folks use your great software.

Clear skies,

Matt

Matt,

I'm beginning to think you guys down under are playing tricks with me

If I invert the logic again it will be back to the way it was before someone else from Australia posted they thought it was inverted. So, are you SURE that you ran all steps of the wizard and especialy the N/S/E/W step had decent star movement and you selected the same star in all three images?

-Ray

Ray,

Absolutely. I doubled checked everything. I use a Celestron C9.25 SCT - not sure what your other user was using - but surely the star test corrects for any number of folds in the light path?

When I did the star move I was on Sirius and Dipha - centred rig in the middle of my Canon DSLR's finder. Stars that bright on a 3 second shot are impossible to confuse in your image - and they started dead centre. The FOV is about 20 * 30 arc minutes - so the stars where always in view in the frame (and each pixel is 0.454 arc seconds).

Not sure what is going on here - I was wishing for even an invert correction direction button!

I know in the past - the correction directions worked for me, so I wonder what is occuring here? It seems like a more subtle error than I thought.

When I realised directions where inverted for me (and I've been using PEMPRo for a few years now) it was simplicity to fix. Now at a reported +/- 0.1 arc minutes pointing error (six arc seconds) I simply can't move my mount that small an increment easily - its finer than the smallest adjustment I can do with the bolts!

Interested to know what you reckon the solution is - as me knowing to invert the direction is a dead easy fix at the moment.

Cheerio matey,

Matt

Matt,

So was this the step with the graph that was "inverted"? If so exactly what did you do based on what the screen said? (e.g. move the mount East? or West?)

-Ray

Ray,

I ran through to measure the image scale and pointing directions (step 3 or 4 is it) - then I actually jumped to step 7 or 8 - as I wanted to check Alt first. I kept it at a star 20 - 30 degrees above the horizon due East.

The tracking reported raise the mount 1.4 arc minutes - and step 8 is it - took a reference star - change the mount's elevation until the satr was at the tip of the move to arrow. The I re-centred the star (or chose a new one at 20 degrees above the horizon) went to step 7 and measured it again. This time it said raise the mount 2.7 arc minutes! Each time I let it track for 20 minutes.

So I thought oh oh - correction amount correct, correction direction inverted. So I went through step 8 again - then I simple took a reference star and reverse the correction direction but kep the amount.

I re-centred - ran again and this time after 20 minutes it said raise 0.5 arc minutes. One more adjustment (reverseing direction again) and it was down to lower it 0.1 arc minutes.

So I slewed to Dipha (very high near the meridan) and did step 3 again to get directions correct, Then I went to at Az correction step 4 or 5 - ran that - it said move East 1 arc minute. Following the arrows and correcting than re-ran it. This time it said move East 1.8 arc minutes. Inversion again. So I shifted it back again reversing the direction suggested and this time it said move West 0.2 arc minutes. Chose a new star - re-ran and 20 minutes later it said move East 0.1 arc minutes - so I left it there.

Hope that helps. (PS I only reversed the Alt with the Az as its been so long I couldn't remember which you normally do first - and Sirius was in exactly the right direction to be of use.

Matt

Matt,

quote:

I ran through to measure the image scale and pointing directions (step 3 or 4 is it) - then I actually jumped to step 7 or 8 - as I wanted to check Alt first. I kept it at a star 20 - 30 degrees above the horizon due East.

The tracking reported raise the mount 1.4 arc minutes - and step 8 is it - took a reference star - change the mount's elevation until the satr was at the tip of the move to arrow. The I re-centred the star (or chose a new one at 20 degrees above the horizon) went to step 7 and measured it again. This time it said raise the mount 2.7 arc minutes! Each time I let it track for 20 minutes.

That might be the problem - You cannot skip to the Alt measurement if the Az adjustment is not close to 0. If Az is not close to perfect then it will contribute to drift in the altitude step unless you measure 90 degrees from the meridian. That is the reason Az is done first.

-Ray

Ray,

Thanks - good to know that - but does that explain why both correction directions where inverted? To start with pointing error was about 1 arc minute in Az and Alt - is that enough to cause what I saw?

Many thanks,

Matthew

Matt,

Please try using the graphs instead of the reference images so we can establish a baseline. For Azimuth make sure you follow the direction to rotate the mount either clockwise or counterclockwise as directed (don't use East/West, because thet is ambiguous, depending on which way you are looking, in the front or the back of the mount).

Once you can establish that the graphs are telling you the correct directions (or not) I can address the images. As it stands I don't know if the calculation or the image is wrong, or if this is some other issue.

Thanks,

-Ray

Ray,

Happy to do that - and we'll get more consistent results if I note all that occurs at every step (scientific method).

Having not labelled the four knobs East / West and Up / Down - I was lazy - I simply looked at the picture and followed the direction of the arrow.

I guess I have to work out which knob applies to each direction.

Cheers,

Matt

Matt,

OK, thanks!

-Ray

Ray, Matt

I think I was the guy who initially had reversed curves on a G11 in the Sthn Hemisphere, I never tested it again, so I cant verify if the latest version works, sorry if I caused confusion if I was wrong ;-). But that was in PEC mode. I now have a PME and it works fine, although the recommended corrections in polar align mode seem confused (indeed reversed), could be me, but is this the same problem Matt is having?, could it be just the correction instructions are wrong?.

Edit, I just spoke to a paid setterupper of multiple PMEs in the SH, has found the same prob.

This message has been edited. Last edited by: Fred Vanderhaven,

Hi Fred,

It doesn't matter who, I was just kidding around when I said that. I'll figure out what's going on so we can all be sure PEMPro's directions are not inverted.

-Ray

Hey Fred,

I never did pop in to see your set-up but one evening I'd love to do that - see how you've set up all your gear + watch you process one of your stunning images! Given you live about 2km from me - it shouldn't take a year to set up (blame it on kids and a hectic family life).

Ray - the weather hasn't been too kind to us lately in Sydney lately - see the dust storms that sent the sky red - it was blood red - life on Mars, then the next day we had white dust, today its 60km / hour plus winds.

I ran a MaxPoint 85 star model - said I was 56 arc seconds low in Alt and 2 arc minutes 26 seconds West in Az. I want to see if PEMPro says the same thing. Particularly the Az error in the model. A few arc seconds wouldn't worry me - but 2-3 arc minutes should be discernible and I would expect both sets of software to roughly agree.

Stay tuned for more information once the weather returns to normal!

Matt

Ray et al,

I did another run with PEMPRO Polar Align Wizard, not altering the sequence of any steps this time.

Same thing again. Correction directions were reversed for Az. I didn’t do the Alt steps – as I had a feeling the Alt was not too bad according to MaxPoint’s sky model.

So after setting up the image scale and moving a single bright well centred star to determine compass points I did 4 lots of 10 minute runs in Az - just observing how consistent was its correction advice in East / West adjustments. The first run said move 3.8 arc minutes West. Second run said move 3.3 arc minutes East! Third run said move 3.2 arc minutes East, Fourth run said move 3.6 arc minutes East.

So I took a reference image and moved the mount in the direction indicated. The next run said move 7.4 arc minutes East. So I took another reference image and reversed direction. Then it said move 2.2 arc minutes East. I repeated the Az corrections (moving about 80% of the magnitude recommended, but in the opposite direction) until the recommended corrections where fluctuating +/- 0.2 arc minutes East or West.

I then ended PEMPro and re-calibrated my mount on 3 guide stars (Achernar, Dipha and Nunki) and proceeded to do a 83 star sky model in MaxPoint. Now it told me Az error was 3 arc minutes West, whilst Alt error was 5 arc seconds too low.

Puzzling – changing Az effected MaxPoint’s view of my Alt error – from about 1 arc minute down to 5 arc seconds – but it thinks Az error is no better – if not slightly worse!

After an evening dodging clouds and suffering chilling, highly gusting winds I finally decided to image NGC 2070 for an hour. The pointing was dead on, and guided tracking very fine.

So bottom line - more experimentation required to analyse pointing, tracking and drift. If MaxPoint thinks there is Az error – whilst PEMPro thinks all is good- tracking should show one way or another which is correct! Maybe my mount isn’t perfectly level and one of the two software packages is being confused. Or of course operator error is always a possibility.

Cheers,

Matt

Hi Matt,

You said you adjusted the mount East/West. Did you remember to really use Clockwise/Counterclockwise instead of East/West? For instance, if you adust the scope so it points farther East, the back side of the telescope moves West, which can be confusing depending on which end you think you need to move East. That is why Clockwise/Counterclockwise should be used.

-Ray