M20 Trifid Nebula

[Carole]

I was somewhat surprised to have got this as I always thought the Trifid was too low, but with Blacklands nice southern horizon I decided to give it a bash.  Although I had been guiding happily earlier in another part of the sky, for some reason it was not happy in this area (despite recalibrating) so had to reduce to 2min subs.  

I am quite pleased with this for only 10 x 2min subs, just annoyed I couldn't have done longer subs.  Was going to try 3mins but can't remember now why I packed up, probably because it was early hours.

10 x 120secs 800 ISO + D,F,B
WO Megrez 72 APO (would have been better with the ED120, but already had this scope on for previous image)
Modified Canon 450D, no CLS filter
YES  Duncan/Fay, this is the same data that I showed you with the weird stacking/processing on my laptop

[JohnP]

Although I had been guiding happily earlier in another part of the sky, for some reason it was not happy in this area (despite recalibrating)

might be to do with balance of scope?

Nice capture though - I think it's always a good opportunity to try & get objects you can't get from home at DSC's. Like you I have no chance of ever getting this from my garden...

John

[Carole]

might be to do with balance of scope?

Well I did balance the scopes and made it very slightly East heavy.  Previous image was in the west and by the time I imaged M20 it was in the South/South West, never quite sure what balance is needed for directly South (properly balanced?)

Carole

[Mike]

Do you set the DEC in the calibration routine?

[Carole]

Do you set the DEC in the calibration routine?

Do you mean the PHD calibration routine Mike?  Not quite sure what you mean. 

Carole

[Fay]

Oh so it stacked 0k again on the desktop?

[RobertM]

might be to do with balance of scope?

Well I did balance the scopes and made it very slightly East heavy.  Previous image was in the west and by the time I imaged M20 it was in the South/South West, never quite sure what balance is needed for directly South (properly balanced?)

Carole

The main criteria is that the RA axis is driving against a very very slight weight ie. east heavy; where your scope is pointed has no bearing on that.  It's only a rule of thumb as some mounts work perfectly balanced, which is what they all should do.

That's a very good image with those subs, especially considering the skies were the most light polluted I've seen at a DSC (not including the toilet block lamps).

Robert

[Carole]

Thanks Robert,

The main criteria is that the RA axis is driving against a very very slight weight ie. east heavy; where your scope is pointed has no bearing on that.

Hmmmm, that's slightly different to what I have been told.  I was told if I am pointing East then the weights should be slightly heavier, if I am pointing West, then the weights should be slightly lighter (so East is still heavy), thus if I change my position from imaging East to imaging West I need to move the weights.

Or have I misunderstood them or you?

Carole

[Carole]

Oh so it stacked 0k again on the desktop?

Yes Fay, it's really weird isn't it?
I'm going to take a look at the stacked image (i.e. before Photoshop and see whether it is DSS or Photoshop which is causing the problem.

Carole

[JohnP]

Carole - Its should be slightly heavier on East - So if the weights are on the east side of the scope (i.e. you are imaging in east) then lower them down the shaft slightly (say 1/2 inch or so) & if scope is on East side (i.e. you are imaging in  West) then move weights 1/2 inch up shaft (from balance) so scope side is slightly heavier.

John

[RobertM]

Thanks Robert,

The main criteria is that the RA axis is driving against a very very slight weight ie. east heavy; where your scope is pointed has no bearing on that.

Hmmmm, that's slightly different to what I have been told.  I was told it I am pointing East then the weights should be slightly heavier, if I am pointing West, then the weights should be slightly lighter (so East is still heavy), thus if I change my position from imaging East to imaging West I need to move the weights.

Or have I misunderstood them or you?

Carole

Well, I am telling you what you're trying to achieve and 'they' are trying to tell you how to achieve it.  Take the situation where your scope tracks from one hour before the meridian to one hour after - it starts pointing east then finishes west.  Does that change the balance? No absolutely not !  it is the position of the counterweights that determine balance.  In fact if you can track all the way from eastern to western horizons then no change on counterweight position is necessary.

If the counterweighs are on the east then you want them slightly heavier (driving against the counterweights) and if on the west then slightly lighter (driving against the scope).  That's basically what John said but I've removed where the scope points from the equation as I think it confuses the issue.

Does that make sense ?

Robert

[Carole]

I am doing what John says above.

I have had another go at processing this.  Think I've messed up the brighter stars though. 



Carole

[JohnP]

Carole have you got Noels Action Tools for Pshop? - There is an action called 'Make stars smaller' which always seems to work well for me if I need it.....

John

[Carole]

have you got Noels Action Tools for Pshop? There is an action called 'Make stars smaller'

Oh yes I have, I had fogotten about that, thanks John.

Carole

[RobertM]

But PLEASE DON'T ADD SPIKES ...