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A few quick Ha images


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They were all guided 3 minute exposures and I used Flats - but swopped the Ha filter out before taking the flats as I think otherwise they would probably all have been black.

M42 stack of 19 images

NGC1499 also stack of 19 images

IC443 stack of 13 images

They should all have been x20 but a few frames were spoilt

I stacked them in DSS and processed them with Photoshop Elements (not Pixinsight on this occasion as I was in a hurry to see what they would come out like !)

The backgrounds could definitely do with some work to smooth them out a bit.


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I think the flats have to be done with the filter in place. It looks to me like you've added the wrong flat to the image and in turn it has now overcompensated and over exposed the corners. Easy on the curves with Orion's Nebula, I think you may have pushed it a little too much around the midsection where you've lost some detail.

Did you use any darks or bias frames ... being a DSLR user, these are always a must ... not sure about CCD users.

One thing I'm learning from this hobby, is that every image is a working progress ... :o). I did my first Ha image last weekend, and I was blown away as well. I just can't wait to get out there and get some more subs to improve on the ones I already have. Many Ha images out there have almost 10 hours worth of data. Just have to keep churning those subs ... build up detail and contrast.

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Thanks Nico

As you say the flats haven't done a very good job. I don't think DSS is able to handle the difference in brightness between the flat and the light frame. I should have spent more time and done them in Pixinsight.

Doing normal imaging I use the flash from a digital camera to provide the illumination but this is of course too bright for narrowband. I then use Pixinsight to adjust the brightness of the flats (as I have no control of the exposure time) and save a series of differently illuminated flats before adding them to the light frames and choosing the best combination.

I didn't use dark or bias frames as they're not usually necessary for my normal imaging.

Yes the amount of detail in narrow band images is mind blowing.


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I've been doing flats using the white t-shirt method, with more or less good results. Double up a white t-shirt and wrap it at around the telescope/lens hood with an elastic band. The open a white window on my laptop and place it up against the hood and shoot away. I check the histogram to make sure that the peak lies in the middle (adjust the exposure time if it doesn't) ... if its for Ha images ... I only check the red channel.

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