Hi All,
Just like to share my first attempt at colour, no laughing, well not to much anyway.
I been experimenting and learning since I bought my new scope and equipment a few months back and its now starting to come together.
The image was taken with a LX200R 12" and a DSI II camera with a f3.3 focal reducer. The images are a combination of 20 each of Red, Green and Blue at 20 seconds each and processed on a trial version of Maxim DL.
As I said I've only been playing this game for about 3 months and still have a lot to learn but I'm pretty happy with this.
All comments appreciated.
Nice one Ric. You're off to a great start. You'll notice a fair bit of vignetting around the edges and corners. That is the only thing that really detracts from the image. A couple of flats will help fix that next time
Hi Paul,
Thanks for the advice,
I was actually just reading a chapter on flats in the "New CCD Astronomy" book the other day. I have mainly been concentrating on getting the focussing right, but I will now move along the learning curve and work on other areas as well.
Nice sharp well guided stars there.
Vignetting is the fall off in brightness around the edges of an image. Not normally noticable in daytime photography, but in astro imaging because we stack images and stretch the levels, the increase in contrast makes it noticable. A flat field will cancel it out, by making the image brighter in the corners by the same amount that it is dimmer in the corners. A 100% accurate flat field will give a perfectly even image.
A flat field has to be of an evenly lit area, such as a white wall, or card held in front of the end of the scope a few feet away. Professional scopes take "dome flats" that is images of the white illuminated interior of the telescope dome, or "sky flats", an image of the blue sky overhead before dark. If the camera is rotated, or focus altered, or filters changed, new flats should be taken for best results.
Scott
Hi Matt,
I was just looking up vignetting and I quote from "The New CCD Astronomy" book "This refers to having a brighter centre area in the field of view, and can range from a very slight difference to an extreme difference".
The way I read it, the flat field would even this difference out and produce a more uniform image.
I,m sure other member with more experience could elaborate on this.
Yes Ric that is about the gist of it. In addition to vignetting, a flat frame will counteract the effect of dust on various optical surfaces within the image train. That is why it is best to take a series of flats for each filter combo and if you change reducers , barlows or powermates. Be awaye though as you move into the area of flat fields that if your illumination source is too axis critical, dust motes will look like 3d donuts instead of being completely removed. That is why sky flats or dome flats (sometimes)in partnership with a white tee shirt over the OTA end is to be preferred over a light box.
Having said all that is said, I'm not too certain that vignetting is a real issue with your image. It seems that there is a significant frame shift due to stacking and maybe a gradient issue. Try cropping the vacant area from the top, and crop the left to get rid of those two uranus coloured stars. I believe it will look much better.
HTH,
Doug
Hi Doug,
Thanks for the help and advice, it is appreciated.
I shall do some cropping as you suggested and have another read up on taking flats and make sure I get it right, nothing worse than rushing in and then having to do it all again afterwards.
Hi Ric I was going to add to the last post but you beat me to it.
here is a version of your image cropped and adjusted both with levels and curves. I noticed your black point was clipped, but see what you think of the redo.
A flat field would be good though just the same.,
cheers,
Doug
Hi all,
Both reworked versions look great, I dont mind at all if anyone wants to rework an image. It shows me what else can be done and keeps me keen to do and learn more.
Your right Tony I do love my scope and look forward to the day when I can set it up permanently on a pier in a observatory but thats a little while away so its alt/az for the moment, still saving for a wedge and image processing software at the moment. I still cant make up my mind on the software.
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