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Not Happy tonight

CELESCOPE

By CELESCOPE
in Imaging - Deep Sky

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CELESCOPE

CELESCOPE

Posted
Posted

Well here we go on the first disappointing result using the C11 for imaging , using the 6.3 reducer, which in truth is bringing it down to about F7 gave me a lot of problems , now it is all new to me this guiding ,i understand that such hi mag ,it will be difficult, wide field with the ED80 was easy going and guiding worked a treat , but seems a different ball game now , gave this just 3 Min's subs , first couple seemed fine ,then the next sub the stars elongated slightly , then the next sub split the stars , , dropped it to 2 min subs , OK for a while ,then started the same again, not as bad ,then over came the clouds to finish the test , managed to save just 3x 3 min subs, now do i increase the aggression on the RA or what, not sure never had the chance to even try , so not a happy bunny , anyway here is the image ,

1625_normal.png

(click to enlarge)

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jcm

jcm

Posted
Posted

Looks brilliant to me , with all that light gathering power of an 11" you will get some great images.

As for guiding , my F6 APO will guide OK in F12 mode ( using 2X barlow) but thats with the 350D. I suppose with a smaller field CCD camera guiding might be more difficult.I will let you know when I get the Atik 16HR next week :D

John

PS thick cloud here - looks like no imaging tonight :lol:

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CELESCOPE

CELESCOPE

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well i,m not sure how good PHD is really yet John , there are advanced setting to do especially for long focal length stuff , i may turn up the aggressive points and try that ,but dont get time with these darn clouds need a couple of clear nights to do testing really.

Rog

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steppenwolf

steppenwolf

Posted
Posted

Roger, what you are describing sounds like classic PE, hence some frames are OK. The increased focal length is, of course, exacerbating the problem over what you are used to. What guide 'speed' are you using (x 0.25, x 0.5, x 0.75)? I find x 0.75 works best for me. Also worth playing with aggression to fine tune.

That said, your M27 is still a nice image!

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centroid

centroid

Posted
Posted

Rog

3 mins is a very short period in terms of exposure, when the imaging scope is guided, so I guess that there's something that not set correctly.

Which way are the stars elongated, vertically or horizontally?

Are you guiding in both DEC and RA?

What software are you guiding with?

How have you set the aggressiveness?

Are you 100% positive that the guide cam is correctly orientated, in keeping with what the software expects to see?

What's the Periodic Error of the mount?

Do you have Periodic Error Correction enabled, and if so, on what data is it running?

There's probably a lot more questions, but we can chat about it tomorrow.

Dave

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moondog

moondog

Posted
Posted

Rog

I'm going through the same learning curve you are with guiding my C8. Last night was my first go with guiding the C8 with the 6.3 reducer.

Like you I use PHD and the QHY5 guide camera. I got very similar results to yours last night, with some good subs, as well as some elongated and split stars.

To say you had all that trouble you got a pretty good M27.

PHD seemed to track the faint star I chose pretty well and didn't lose it. Next time I'll try Steppenwolf's suggestions. It does seem, as I'd been warned, that long FL guiding is not as easy as with the ED80.

You'll soon be up to speed with the new set up, and then I'm sure we'll see some dramatic images !

8)

MD

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Kaptain Klevtsov

Kaptain Klevtsov

Posted
Posted

OK so some stuff that could be messing you up.

guiding on a binary or double star is supposed to be bad.

we had high clouds so if some of those flew over, you could lose the guide star.

atmospheric effect such as seeing could mess you up.

too short a FL on the guide 'scope could mess you up.

too much guiding speed on the EQ6 could mess you up. (setup menu, several guiding speeds available)

wind on the scope could mess it up.

Have another go, it'll work fine.

Kaptain klevtsov

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CELESCOPE

CELESCOPE

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Hi KK no wind probs , in the Dome , have set the guide speed to 0.75 as Steve suggested ,, altered a few setting in PHD as per instructions , will try again hopefully sunday as away now for pure relaxation at holiday home AND DAVE CENTROIDS FOR A TUTORIAL

Rog

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SteveL

SteveL

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Inmy PHD, I run at 100% agressiveness in RA all the time (not sure if I ever changed this, I dont think so).... one other thing I did have to change was the "Callibration Step (ms)" setting when I moved to the piggyback guide scope. I found for longer focal lengths, you need shorter times during calibration (500ms), and on the WO66 with a short FL, I needed longer times (1000ms). The PHD self calibration will try to move the mount to about 5% of the chip area on the guider, and if it cant do that in 50-60 small steps, it will fail. Just a thought....

Also, how often is PHD "taking" an image to use as a guide image? I try to get down to 1 second (1.5-2 on bad nights and the subs show it!).

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MartinB

MartinB

Posted
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I feel for you with this Rog having been through some horrible guiding traumas. It is always going to be a bit of a struggle at this focal length. Make sure you have a reasonable guide star, this shouldn't be a problem for M27, there are plenty there that will give you good brightness off a 1 sec unbinned exposure. Also make sure is is well away from other bright stars especially when calibrating.

The fact that the guiding is working sometimes and not others suggests to me that either the guide star isn't very bright and the guiding is struggling to pick it up or it is either over or under correcting. SteveL runs PhD at 100% aggressiveness which is pretty amazing. For most people this will cause oscillations which get progressively greater as the guiding chases it's tail. This is especially likely the poorer the seeing. 60% aggressiveness is a good starting point. If the errors start to get progressively bigger and oscillate then reduce the aggresiveness.

If you are getting a sinusoidal type oscillation across the worm cycle then the guiding isn't keeping pace with PE and you need to increase aggressiveness

In maxim you can also limit the maximum move which can help stop the guiding from over reacting to big guide star shifts produced by wind or very bad seeing.

The trouble is there are so many variables that you just need to work on one thing at a time.

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