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First attempts at Deep Sky Imaging.


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18 minutes ago, Bill Maxwell said:

These stars dont look right - are they out of focus or is it something else?

Orion nebula taken last night.

Grateful for any advice!

Bill

Orion Nebula.tif 28.41 MB · 1 download

@Bill Maxwell Please upload the image in either jpg or png format so that it can be viewed within the browser.

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It would be useful to know a little bit more about the equipment you used and how you processed this image. 

From the nebulosity, the focus does not look too bad, albeit it is not completely sharp. 

The blue rings around the brighter stars look to me like processing artefacts.  Depending on the type of telescope you have, the brighter stars will tend to develop blue/violet halos around them that can be exacerbated during processing, particularly if the image is stretched hard to bring out the nebulosity.  There are also ways to reduce the blue / violet halos during the processing stage.

It also looks to me like you might have an issue with your back focus (the distance from the camera's chip to the first piece of glass in your optical train).  If you zoom in on your stars towards the four edges of the frame, they are elongated in a manner that suggests the camera's chip might be too far from the first piece of glass in your optical system after the camera:

How to adjust sensor reducer flattener spacing for better ...

There will be information online about the correct back focus for your camera / telescope combination.

The picture is a good start.  Very nice composition. 🙂

 

 

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AMcD,

Thanks for your comments.

Image taken with Sony a58 through Starwatcher Startravel 120. Exposure was 30 seconds at ISO1200 and there were about 20 images. Scope mounted on AZI GTI.

Completely new to processing but stacked with Sequator and processed with GIMP based on a few You Tubes I had viewed.

Will look online as suggested for back focus information.

JPEG uploaded as requested.

Bill

Orion Nebula.jpg

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4 hours ago, Bill Maxwell said:

Scope mounted on AZI GTI.

Not saying this is the issue, but AZ mounts are not really "ideal" for imaging.  The reason being is that you get field rotation.  Now at 30 second exposures with 20 subs the rotation won't be a lot, and most stacking applications can process the rotation out to align the stars correctly, but when you start taking longer exposures of fainter objects then the rotation can be an issue as longer subs have the rotation in them which causes odd shaped stars.

Is the JPEG just a single sub ? - the aircraft light trails suggest it is unless they appear on every sub ?? 

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6 hours ago, Bill Maxwell said:

Scope mounted on AZI GTI

In circumstances where you are using an AZ mount it may be field rotation, as mentioned by Malcolm, rather than a difficulty with the back spacing, that is causing the elongated stars in the pattern seen in the photo.  I think if your back spacing turns out to be per the measurement given online, then the odd shaped stars in the corners are more likely to be field rotation, especially if you were using longer exposures.

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Malcolm,

The JPEG is produced from the TIFF file that Sequator produced. The light trails were on only one of the light frames and I did expect that the stacking would have eliminated  them.

Sounds like I should be using shorter exposures with my setup? And more care with focussing?

Bill

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Nice to get an image to build on it's a good start. If using in altaz mode then east and west keeping under 60° helps minimize rotation effects and a crop on the final stacked image where the frames don't overlap. The blue is chromatic aberration, some find a wattern #8 yellow filter can help quieten the CA. I personally find sequator stacking creates strong purple bleeding, I prefer deep sky stacker. For plane trails kappa sigma clipping with at least 20 frames can help loose those.

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Hi Bill

The Orion Nebula is an easy target for imaging, but difficult to process.

Because the central area is so bright compared to the rest.

Requires a combination of short exposures that don't overexpose the central region and brighter background stars.

With longer exposures that tease out the nebulosity.

Michael

 

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Thanks all.

Advice all taken on board.

I have re stacked original lights in Deep Sky Stacker and the Tiff looked completely different. I have had another go at processing and I think this looks better (with a crop) and has resolved stars in the core!1398223406_OrionJPEGCrop.thumb.jpg.21437befa82e23163269efa2d45b9d59.jpg

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Hi Bill

Much better.

R, G, B Black Levels need adjusting to remove the overall red caste.

The bloated stars may be due to the "Sony Star Eater" problem I've heard of.

Or lack of an IR Filter.

Image1.jpg.65385a9a0bf256b86aaccf79c1724193.jpg

Black level is correct but displays too bright here

Michael

Edited by michael8554
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Bill, some good advice from the other members, and the stack processed in DSS looks a lot better.  There are still some artefacts that are giving purple rings round the bright stars, but that may be down to how the Sony DSLR records the image, and could be removed with more processing.

You don't mention any darks or flats being used in the processing.  If you are simply stacking 20x 30sec exposures at a high ISO then you are compounding any noise in the images caused by the sensor.  I would suggest dropping the ISO down to around 800, and stick with 30s to start.  Take 50 or 60 images, and then cover the objective lens with the cap and take 40x 30s images.  This will form a start, and I'm sure others will chip in with how best to shoot the flats etc.   Look at the images and if you see any light trails or satellite trails, discard them.  Stack both the remaining lights, and the 40 darks and then see what results you get.  I would suspect you'll still get some distortion at the edges of the result, but hopefully the result will be better. 

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