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Old 31-05-2010, 02:10 PM
pjphilli (Peter)
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Meade DSI Camera and Drizzle

Hi - I have been using a Meade DSI2 camera for some time and I really like the ease of use and facilities provided by the accompanying Envisage software. However, it is suggested that the use of the additional Drizzle technology will produce better images. I have tried using Drizzle but I have found that it appears to make no difference to the final image. Has anyone had any success using Drizzle?
Cheers Peter
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Old 01-06-2010, 08:57 PM
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floyd_2 (Dean)
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Hi Peter,
I thought that I might chip in as a DSI II owner, but I'm pretty far from being a guru and as always am happy to be corrected.

I know that drizzle processing is touted as being able to add detail to a shot, but I think that you need to drizzle with the right settings for it to have a chance (which you may already be doing). Drizzle processing won't have much effect if you don't use it to enlarge your images. It can be used to de-rotate your images in simple mode, but it won't actually have an effect on image resolution.

The rule of thumb is to reduce your pixel fraction by the number of frames that you're stacking, up to a minimum of about 0.7. If you're not doing a mosaic, in which cause you'll need a guide camera with the same resolution as the imaging camera, you'll only need to use the Drizzle Resolution and Pixel Fraction settings. The Extended View setting is only for mosaics, where Envisage will issue guide commands to your scope to move it in such a way that your images can be combined to form a larger image from a mosaic of smaller images.

Another thing to note is that the historgram setting is applied to the output image as the drizzle process is taking place, so it's worth making sure that it's set the way you like it.

Are you saving your files in FITS format and keeping all of your individual frames. It's the best thing to do rather than using lossy jpeg and combining in real time as you shoot. You can drizzle your FITS files in offline mode, and spend more time imaging during the evening.

No doubt you already know all of this stuff, but I thought that it might be worth a mention just in case there were one or two things that were of interest.

Dean
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Old 02-06-2010, 03:10 PM
pjphilli (Peter)
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Hi Dean
Thanks for your useful comments. I usually save my DSI2 files as .tif. Yesterday I found a stack of 40x2min images taken when I was trying to image the Keyhole using a O3 filter. The composite image did not turn out much good but I post combined the images using Drizzle with a resolution factor of 2 and pixel fraction of 0.7. I was pleasantly surprised to see that pixelation of the stars was considerably reduced and the DSI2's tendency to produce false colour of the very small stars was eliminated.
I have come to the conclusion that to use Drizzle it is necessary to have a large number of images to stack. Previously I have not had much success in Drizzle with up to about 10 images. I do not know what the lower limit of images is satisfactory but I will persevere with experimenting!
Cheers Peter
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