Pempro Question

[scagman (John)]

Hello,

I've been using the ccd drift method to get my PA pretty good. I can do a 10min exp moving the scope 5min each way and I end up with a single line. Its not a perfect single star width but wouldn't be twice the width of the star.
I can get pretty round stars with a 5min unguided exp.

I have got pemproV2 and tried to use the PA routine to check my PA.

I have run the wizard to set image scale etc but when I use pempro to measure PA its reporting I need to adjust my mount 600+ arce minutes to the west.

This sounds way to much error for the amount of trailing I'm seeing in my images. So I was wondering if any one could give some suggestions or settings I may have missed or set wrong.

Thanks

[alistairsam]

Hi John,

I'd suggest using another method to re-confirm PA, like Alignmaster.
Don't go by what one software says when you are pretty sure your PA is close.

I did that mistake at snake valley, where I was pretty closely aligned, but then ran Polealignmax which uses plate solving, and ended up with an error of 5 degrees. took me 3 hours to get back on track.

so before adjusting as per pempro, try monitoring drift in phd using the main scope at the meridian and e/w and also measure using alignmaster.

have you checked the location settings in pempro as well as timezone settings? not sure if they'd affect, but its possible.

Cheers
Alistair

[scagman (John)]

Hi alistair,

I'll give alignmaster a go next clear night.
I run PHD turned dec guiding off and the graph looked reasonable after 3-4 minutes (image 1 below) so I was going to use pempro to verify PHD and give me a measurement on how far out I was.

I have checked the setting, they all seem fine, I actually get them from the mount.

I was using the meridian to measure.

I am pretty happy with my PA at the moment(see below 5min unguided image) and running Pempro was more of a verification more than anything.
But now its thrown 600+ arceminutes at me I want to try and find out why/what is wrong as I also want to use pempro to do a pec curve. So if I have a setting wrong it may affect the pec curve??

cheers

[White Rabbit]

Are sure that pempro isn't reporting 600 arc seconds? 600 arc mins is huge, 600 arc seconds isn't small either and you can't be that far off if your sub looks like that after 5 mins. I'd say it has to be a setting you have wrong somewhere.

My mount is permanently set up outside and the slab I have it on moves all the time so I realign every full moon using pem pro. I align to about 30 arc seconds each axis. Pem pro has been the most hassle free consistent polar alignment method I've used, and I'm pretty sure I own or have tried them all.

One mistake I made early on was I was using my guider to measure PA rather than the main scope.

Thanks
Sandy

[stevous67 (Steve M)]

Hello John,

I'm a pretty heavy PEM2 user, and a 600 arc min error is a reporting error if you truly think you are close to alignment. Sandy may be right over the translation being in seconds instead. Correctly stated too, 600 sec out is still huge.

I've often seen PEMPRO blamed when in fact the user made a simple setup error. When you don't know, it's not easy to see the error made. So try reading again the manual set up steps per your mount type. Depending on your focal length, you definitely could try alignmaster, but alignmaster will never provide the same alignment accuracy as PEM. Longer focal lengths will benefit from a good understanding of PEMPRO2.

I use PEM for remote and observatory setups, and I can achieve a 0.1 arc min error result in about 15-25mins max. An AP mount certainly helps, but with a G11, I can do it in the same time frame.

Two recommendations, leave out the black screen/ move star routine in PEM for both RA and DEC. Just use the graph/ plot screens; these are all you need to complete to achieve an excellent alignment. I also recommend at least two iterations to get reasonable accuracy (0.1 arc min error). Lastly, make a cheat sheet per adjustment that helps you work out the amount of revolutions of your mounts knobs per arc minute of error, and the direction of rotation needed to fix the east, west, up, download error corrections.

Good luck!

Steve

[alistairsam]

hi John
I presume you diabled ra and dec guiding and not just dec?

[scagman (John)]

Hi Guys

Yes definitley 600+ arceminutes.

I'm sure its operator error/wrong settings but I cant seem to find the error.

The mount settings look right and pempro seems to goto where its thinks its pointing.
Its like pempro stops tracking when its starts its measuring routine as the star just flys of the image by the time the 2nd exp comes up.

I'm using the main scope/ccd (ed127/QHY8L) combo to do measurements.

I'll try skipping the move star routine next clear night.

The guides I was reading to use PHD to adjust PA, said to turn dec guiding off, didn't mention RA so I left it on. I'll try with both trned off next night I'm out.

I'll try resetting everything and start again.

Cheers

[g__day (Matthew)]

I have been using PEMPro for a few years now - on a permanently mounted rig. Often it is good, sometimes it reports bizarre misalignment.

I align using an SCT - so I wonder how much mirror shift / flop is altering the PEMPro advice.

I note that PEMPro for me in the Southern hemisphere seems to inflect the movement corrects required.

I have had great success using PHD with DEC guiding disabled to drift align.

Finally I note there always seems to be great disagreement between all of:
1. PEMro using multiple 30 minute runs
2. Tpoint using say 130 stars well placed
3. PHD using drift alignment
4. Astrotortilla using plate solves

You would think a majority agree! I would guess my polar alignment to the Refracted South Celestial Pole is between 30 - 120 arc seconds - I can just never get all or even most of the above software to agree and the mirror shift in my SCT makes further improving my polar alignment challenging!

[scagman (John)]

Hi Matthew,

I'm glad I dont have to worry about mirror flop I have enough other little issues to overcome.

Yes you would think that you would end up with similar results each time even with differant software.

I was checking settings and things last night and noticed I had the unbarlowed focal length set in maxim. 957 instead of 1860. I dont know if that would affect pempro thou. I will have to wait till this crappy weather improves somewhat before I can test it.

Cheers

[alistairsam]

Hi John,

I tried Polar aligning with pempro for the first time tonight and I was able to get my PA very close, within a few seconds.
But I did not use the star exposure step, I used the measurement step before that where it selects a star and plots the graph in realtime asking you to turn either ways.. I did not read that number either, the points would be very close to the line and it would suddenly jump to "adjust 400 odd arc secs" or so.
so I just ignored that but kept an eye on the drift, made small adjustments and watched the graph steady in realtime and kept it as flat as I could. This got my very close and I could go unguided for a few minutes.

Cheers
Alistair

[scagman (John)]

Hi Alistair,

I'm surprised you were able to see anything last night, Very foggy up here.

I must be doing something totally wrong as my star just disappears off the image after the 1st exposure and the plots on the graph just goes straight down off the graph.

Next clear night I'll give it another go, skipping the calibration screen and see what happens.

Cheers

[alistairsam]

Originally Posted by scagman

Hi Alistair,

I'm surprised you were able to see anything last night, Very foggy up here.

I must be doing something totally wrong as my star just disappears off the image after the 1st exposure and the plots on the graph just goes straight down off the graph.

Next clear night I'll give it another go, skipping the calibration screen and see what happens.

Cheers

Does it do the same with Phd as well. you just need tracking on. no guiding. click disable guide output in phd and watch the graph. it should be the same as pempro which would mean your PA is off.
but then your unguided subs tell a different story. strange.
does it do the same in both axes?
was clear all night.

Alistair

[scagman (John)]

No the graph in PHD looks as expected. See above attachment. Thats with dec only turned off as per guides. I will try with guiding disabled next time. Yes it was clear all night.

I only tried Pempro pointing north and at the meridian. PHD looked similar if not better when I tried it pointing to the east. didnt bother trying east with pempro after it reproted 600arceminutes when pointing north.

Cheers