Date: 6 August 2005
Camera: Canon 300D
Telescope: Meade LXD55 SN10
Details: 114x30sec exposures at ISO1600, prime focus, unguided
Processing: ImagesPlus- Dark, Flat and Bias calibration, DD. Photoshop CS- levels, curves. Noiseware.
Hi Itchy,
That's a great image of the Eagle Nebula. I really like the wide field. That's a lot of images to take, over 100 ! wow... and unguided too. Could I ask how the image would look if you did not subtract dark frames and did not flat or bias calibration ?
Hi all
Here is a shot I took some months back.
Its 2 x 15 mins ISO 1600, Baader UHCS, 10 inch F5.6 scope, EOS 300D.
Scott
[IMG]http://www.iceinspace.com.au/forum/attachment.php?attachmentid=5268&st c=1
Nice image Scott, that red nebula is really red and the sky black.
That's a great image of the Eagle Nebula. I really like the wide field. That's a lot of images to take, over 100 ! wow... and unguided too. Could I ask how the image would look if you did not subtract dark frames and did not flat or bias calibration ?
Paul
Ok Paul, you got me intrigued, so I stacked the converted RAWS without calibration. I was rather suprised with the result. There is a little vignetting but it is not overpowering. The biggest difference was in how much faint detail I was able to extract. It was much harder to get anything out of the uncalibrated stack, and even the fine detail in the brighter parts of the nebula is missing.
Conclusion: Calibration is definitely worth it. What's your (and others) opinion?
Tony, the one on the right looks a lot better but I don't know If I'm seeing It that way because of better contrast . As I go over It I can find the same detail I think but Its probably my inexsperiance again .
Ok Paul, you got me intrigued, so I stacked the converted RAWS without calibration. I was rather suprised with the result. There is a little vignetting but it is not overpowering. The biggest difference was in how much faint detail I was able to extract. It was much harder to get anything out of the uncalibrated stack, and even the fine detail in the brighter parts of the nebula is missing.
Conclusion: Calibration is definitely worth it. What's your (and others) opinion?
The Uncalibrated image is on the left
Cheers
Yeah, I'd have to say the calibrated image certainly looks better for a number of reasons. I guess the only reason I asked was to see what type of difference there would be in the resulting image. Now I can see for myself, thanks.
Some time ago I made my own CCD camera (the Cookbook 245 with LDC) and of course dark and bias frames were always part of the process. I guess since getting my Canon EOS I had fallen in to the trap of thinking darks, bias frames etc really don't make that much difference with the digital slr. However I can see now that I should be doing darks etc.
Can you subtract darks etc with photoshop ? or do you need to purchase software ?
someone will correct me if i'm wrong, no doubt, but you can subtract darks easily with photoshop but dividing flats..that's another matter. Plug ins are available and artificial flats can be constructed but IRIS-free (!!!) or Imagesplus seem to be the answer.
also Maxim DSLR- a stripped down version of Maxim has I believe been recently announced that will do the job
IRIS - is great but you have a big learning curve as its not all that intuitive
Can you subtract darks etc with photoshop ? or do you need to purchase software ?
Thanks.
Hi Paul
You can subtract darks in Photoshop, but you need to do it one frame at a time. If you have a full version you can use apply image --> subtract. If you only have elements or a light version of PS, you can do it by pasting the dark on the light and use the difference blending mode. Difference is not a true subtraction, but because your dark should be less than your light, it should do the job.
Flats are another story. There is no operation in Photoshop that perfroms a correct flat division. There are various methods for removing vignetting in photoshop after stacking but I'm not convinced that they do the same job as a good flat.
If you want to go with freeware, there is IRIS (very good but command driven and originally french), or you can try PixInsight (more sofisticated but not intuitive).
I have purchased ImagesPlus and I would reccomend it highly. Using it improved my images immediately. I now use ImagesPlus for RAW conversion, calibration, aligning and combining. All of these processes are automated and easy to learn with the help of training videos that come with the package.
someone will correct me if i'm wrong, no doubt, but you can subtract darks easily with photoshop but dividing flats..that's another matter. Plug ins are available and artificial flats can be constructed but IRIS-free (!!!) or Imagesplus seem to be the answer.
also Maxim DSLR- a stripped down version of Maxim has I believe been recently announced that will do the job
IRIS - is great but you have a big learning curve as its not all that intuitive
Howdy all
I find that I have to be careful subtracting darks with Photoshop, I do use Photoshop but often have to reduce the opacity of the dark otherwise I will get dark coloured spots on nebulosity areas. I find the lazy way out is to do the dark subtraction with reduced opacity (a partial subtraction one could call it), then use the Gradient Exterminator plugin for photoshop to remove most of the vignetting and amp glow. I had a look at IRIS but it looks like it does have a steep learning curve.
Scott
You can subtract darks in Photoshop, but you need to do it one frame at a time. If you have a full version you can use apply image --> subtract. If you only have elements or a light version of PS, you can do it by pasting the dark on the light and use the difference blending mode. Difference is not a true subtraction, but because your dark should be less than your light, it should do the job.
If you want to go with freeware, there is IRIS (very good but command driven and originally french), or you can try PixInsight (more sofisticated but not intuitive).
I have purchased ImagesPlus and I would reccomend it highly. Using it improved my images immediately. I now use ImagesPlus for RAW conversion, calibration, aligning and combining. All of these processes are automated and easy to learn with the help of training videos that come with the package.
Hope this helps
Cheers
Hello Itchy,
I have PS full version but I find that the method of subtracting darks does not appear to work quite correctly.
I've downloaded IRIS and am working through that for the time being.
Howdy all
I find that I have to be careful subtracting darks with Photoshop, I do use Photoshop but often have to reduce the opacity of the dark otherwise I will get dark coloured spots on nebulosity areas. I find the lazy way out is to do the dark subtraction with reduced opacity (a partial subtraction one could call it), then use the Gradient Exterminator plugin for photoshop to remove most of the vignetting and amp glow. I had a look at IRIS but it looks like it does have a steep learning curve.
Scott
Geeday Scott,
yes that's it ! When I attempted to manage darks in photoshop, i found no problem making an averaged master dark frame. In wide field imaging the dark subtracting is okay but in subtracting dark frames from an image filled with nebulosity, dark holes usually appear in the dark subtracted image.
Possibly the dark holes are where "hot" or "extra noisy" ccd sensor pixels appear on the dark frames, then when you substract these bright pixel values from the image, you end up with black pixel areas in the dark subtracted image.
you can but the result is not as good as an averaged master dark. In built camera noise reduction will subtract the noise it sees in that particular exposure. If you get a cosmic ray strike during that partcular dark you end up with a messed up exposure.Taking several and avergaing gives a better and msoother view of the cameras dark noise.
Using in built darks subtraction also mean you waist valuable imaging time for each exposure while camera does noise reduction.
Awsome shots
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