Please check For Guiding Error Or Backfocus distance Error.

[ollypenrice]

There are always going to be places where the ground moves. The most famous was Herstmonceux which seemed like a geat place for a professional observatory - until they discovered that the incoming and outgoing tide screwed up their PA twice a day!

Olly

[strutsinaction]

Wow. Probably your altitude and freeze-thaw effects creating ground swell. A bit of poetry for a change... Ah, Robert Frost. Too good!

Something there is that doesn't love a wall, 

That sends the frozen-ground-swell under it, 

And spills the upper boulders in the sun, 

Gosh, that take me back. 'Mending Wall', English Literature O'Level, 1980. Haven't read those lines for over 30 years. Suddenly I feel very old. Thanks for the memories!

Regards

John

[ollypenrice]

Gosh, that take me back. 'Mending Wall', English Literature O'Level, 1980. Haven't read those lines for over 30 years. Suddenly I feel very old. Thanks for the memories!

Regards

John

YOU feel old? I was teaching it in 1980!

lly

Sorry Simon, we digress.

[sunka]

Hi guys!

I hope you don't mind me borrowing this topic since I also have problems with star shapes and can't figure it out. First my setup:

-Mount: HEQ5 Pro

-Telescope: 1000mm f/5 newton reflector

-Camera: Canon EOS 50D (BA BCF mod)

-KomakorrF4 (http://www.teleskop-express.de/shop/product_info.php/info/p5836_GPU-Designed-Aplanatic-Newtonian-Coma-Corrector-4-element.html)

-Guide scope: 205mm focal length

-Guide camera: QHY5-II Mono (pixel size 5.2um)

This is tube with DSLR and comma corrector attached (in focus) during flats:

This is example of 4min M101 exposure, no calibration (tiff version: https://dl.dropboxusercontent.com/u/6013601/m101_240s%40ISO1250.tif):

Here is my guiding graph for this particular photo (blue is RA error in arcseconds, red is DEC error in arcseconds):

From errors, I calculated that maximum error in pixels for final image is 2.77px on RA and 1.36px on DEC. Also I always collimate telescope with laser before session so it can't be that bad? I don't know what else to check. Is it possible that there is some flexure in focuser/coma corrector/dslr? 

Thanks

[Singlin]

I have now given up on an oag solution to guiding .

I bought a Moravian 0-300 guide camera which is great and gives me loads of guide stars to chose from.

It has a 22mm backfocus which is too much for my guiding setuo with mz Atik 383 and Filter wheel and coma corrector.

I put the morovian on mz St 80 and came up with the below image and guide graph.

The sub is 15minutes long.

The stars are not perfect but I think I will leave it at that and start imaging again.

Dropbox link to mz sub:

https://www.dropbox.com/s/avoaunz49nu7rrb/Capture_120_102t.fit?dl=0

guide graph:

[Singlin]

I have 42 people in the Hotel at the moment, Local speciality dinner tonight 8 antipasti first, second course (wild Chamois).

I also have 38 degree temperature and an appointment at 23:00 at the observatory to see the Beehive,M37,M44,Jupiter,M81,M3 and M51.

I have just taken a pill to get my temp down but you know what I can't wait to take them up.

Another week of full house and then things start to slow down Hurrah!!!   :grin:        

[Tinker1947]

Don't knock the customers there the next scope ect, hope your temp drops......

[Singlin]

Funny how all my scopes are camouflage black   :grin:          

[Xplode]

guide graph:

PHD 2 with Morovian 0-300.jpg

that's a weird guide graph, most corrections are in RA and always the same way, a few corrections in DEC in either way and very few of them.

It's like the mount is running either too fast or too slow

[Singlin]

Can't do any tests I have been in bed for 2 days with 39 temp.

Feel pretty Cr-- actually.

chest flu and high temp and as soon as I get up I almost pass out.

I get a temp about once in every 10 years but when I do I make up for lost time     :grin:    

As soon as I shake this off I will do more tests with my guiding.

[Singlin]

I have finally managed to get some clear skies tonight and have had another attempt at refining mz guiding.

I updated my mounts clock and did an accurate drift alignment too.

Attached is my PHD2 log file and graph.

My Guide camera is a Morovian G-0 300 it has a resolution of 656 x 494 and pixel siye of 7.4 x 7.4 I attached this camera to my ST 80 guide scope which has a focal legnth of 400mm.

My imaging camera has a resolution of 3326 x 2504 and the pixel size is 5.4 x  5.4 I attached this to my 1000 mm imaging scope.

PHD2_GuideLog_2015-05-09_222202.txt

I would appreciate any comments.

Regards, Simon

PS,

On Wednesday I am having a hip replacement.    

[Thalestris24]

Hi

Looks pretty good to me. You might like to get the latest version of PHD2 v2.5.0

RA osc might be a bit low - maybe increase aggression. The inbuilt guiding assistant tool will advise. Min motion could be lower though PHD2 seems to ignore it! At the end of the day if your stars are nice and round and tight then that's what matters.

Good luck with your hip replacement - I wish you a speedy recovery

Louise

[Singlin]

Thanks Louise.

[ollypenrice]

Hope it clears up, SImon. No joke being ill and running a business. As for the hip, blimey, you're in the wars.

The trace is improving but our Mesu does maybe a tad better. Using an ST80 and lodestar, binned 2x2, we get an RMS around 0.06 which I guess you'd have to double to compare with guiding unbinned. But you're getting there. Do you know what brought the improvement?

Olly

[Singlin]

The only thing I have done is to update the Mesu Clock and Done a very thorougher Drift Alignment.

Maybe my lack of accuracy compared to yours is the fact that I  have more flexure with my newtonian and guide scope compared to your Refractor?

I am in pretty good Shape and had a bad week with my Bronchitis which is cured. I am looking forward to my Hip op as it has been quite uncomfortable for two years now.

Regards,

Simon

[kens]

Just a few thoughts coming off the top of my head when looking at the trace.

First up - not sure if you realise your graph is in pixel units. You can get arc-seconds under Settings which gives a better idea of how well you are guiding

Nearly all you RA corrections are in one direction and pretty frequent which suggests something not quite right

The calibration has your RA and Dec axes at 83 degrees which seems a long way off. I wonder if the RA "drift" is contributing to this

The dodgy calibration could affect your guiding

Polar alignment looks spot on

[Singlin]

I did an experiment and centered a star in the bullseye of my ccd capture sofware with no guiding.

The star started to drift in RA.

Is this normal?

Their was no drift in Dec after a couple of minutes but it started to drift in Ra .

[kens]

Not normal for a mount that costs as much as a small car

But as expected from the PHD log. By the way, in PHD you can click the Brain and on the Mount tab and untick "Enable Guide Output" to get an unguided graph and log

[Singlin]

The star drifted 78 Arcseconds in a Westerly direction in 10 minutes.

What could be causing this?

Regards,

Simon

[Thalestris24]

The star drifted 78 Arcseconds in a Westerly direction in 10 minutes.

What could be causing this?

Regards,

Simon

Hi

Most probably PA error + periodic error, I'd have thought (someone correct me if I'm wrong).

Do you drift align with PHD2? The drift align tool seems quite good. However, near perfect PA isn't required for guided imaging.

Louise

[kens]

The Mesu 200 is supposed to have a PE of just 4 arc seconds peak to peak without autoguiding. And all the drift is in RA rather than Dec so should not be due to PA. The Dec drift was almost zero on the log so the PA appears to be spot on.

Even if it was a PA error, 78 arc seconds in 10 minutes corresponds to being over 20 degrees out on PA

I suspect an incorrect setting in the controller causing the motor to run fast