First images in Ha

[Ric]

Thanks Nick & Dan, I'm glad that this has helped out the both of you as well. It is a testament to the great spirit of this forum.

I managed another imaging run on M16 again last night. This is a combination of 50 images @ 21.2 seconds with the DSI II Pro and the f/3.3 focal reducer. The gain was set to 0 this time and darks were subtracted.

The stars have now sharpened considerably which is very pleasing however I now have noticed that there are what looks like record player grooves appearing, especially to the right of the nebula.

I'm not sure what has caused it as it was not present in the preview when taking the subs only after combining. I have not encountered this before so I'm a bit clueless as to what it is. A few ideas that have sprung to mind is that the image was taken very close to a 98% Moon so that might have had an effect or now that the gain is at 0 should I have adjusted the offset as well which was set to 50.

All thoughts and comments appreciated.

Cheers all

[jase (Jason)]

Hi Ric,
I’ve seen the “record groove” effect before when using MaximDL’s flatten background function. I’m not sure if you used this at all, but its caused by insufficient map points to measure the background.

Are you saying this effect is not in your subs (or at least a few of them). I can’t imagine the problem being related to the moon considering it emits strongly in the blue wavelengths which is being blocked by the Ha filter.

Perhaps try a different combine method. It also looks like you need to stretch your data more as its black clipped.

Just a tip: in MaximDL, open up all your subs in Maxim. Select one of the images and perform a screen stretch to the desired levels (that most details reasonably easily). Then from the menu View | Equalise screen stretch. This will stretch all you images to the same screen stretch value as the reference image. Then select View | Animate. Select all images for animation and play them (blink them). Have a close look at each sub as they pass. The animation will loop. You may find a few offending images that you dont want to include in the combine function. Simply take note of the offending filename and drop it when you do the combine.

[Ric]

Hi Jase, thanks for the tips I shall give that a go. It certainly looks a lot darker on the desktop CRT monitor, this morning it was processed and posted on the laptop with a LCD display which fools me into thinking the images are a lot brighter.

Cheers

[jase (Jason)]

Hi Ric,
This has just “clicked”. If you’re indicating the effect does not occur in any of your subs, it will be the drizzle (field derotation function) causing the problem. The subs may not be successfully derotated as they are stacked or they are successfully being derotated, but there are differences between you subs (other than rotation). I suspect the latter considering the stars are derotated. I would check your subs. I don’t believe there is any correlation between the gain setting and drizzle process.

[Ric]

Hi Jase I did use the "Drizzle" function rather than the "Deep Sky". I find that the Deep Sky mode gives a lot more star trailing that is almost impossible to remove in the Alt/Az mode.

Cheers

[skeltz (Rob)]

Nice images ric pretty good for such short exposures to!!
good job mate...

[Ric]

Thanks Skelty

Cheers