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davesparx

My first rosette!

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Hi there,

This is my first attempt at the Rosette. I did 5 *200secs lights and 5 * 200s darks with a canon 1100d with filter removed and a CLS-CCD clip filter in.

I used an ED-80 without the focal reducer on an NEQ6.

I'm really pleased with this but wish that I'd fitted the focal reducer before the guiding went bad!

This is processed and slightly enhanced, as you can see.

David

post-19599-0-92649500-1388485585_thumb.j

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Very nice! Can anyone (or your good self!!) explain what this idea of multiple lights and darks is about? I usually take 2-3-4 min bulb exposures through the scope. Why do you do multiple "lights" and "darks"?

Cheers

Frank

Btw happy new year all!!!

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That's a nice rosette! Very envious. I can't see it because of trees. I don't think you need the focal reducer. I think it's a matter of framing and it'll be spot on. Great first effort.

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Frank  - buy a copy of the book Making every Photon Count. It explains everything. Worth it's weight in gold.

Cheers

Ian

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alittle shame about the framing, but that`s one thing you`ll not forget next time, looking at this again i think that there is more detail to be had from this image with alittle more processing in photoshop.

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Darks are images of the fixed pattern noise in your camera. They won't be dark, they'll be spattered with pixels of varying degrees of brightness. Say one pixel on your dark, which should read zero brightness, actually records a brightness of 1,732. When the dark is subtracted from the light (the image of the Rosette) that value of 1,732 will be subtracted from whatever was recorded in the image, so giving the image the correct value. Clever!

Now not all the noise in your camera is fixed. Some is random. A pixel which should record 42,765 on the Rosette will sometimes randomly record a higher value and sometimes a lower one. If you average the values recorded in multiple images these random mistakes will average out to almost nothing and you'll get a cleaner and more accurate picture. The need to take multiple images applies to every image you take in your camera. Lights, darks, bias (if you need them) and flats should all be multiples, stacked and averaged.

Your Rosette (a very good debut) needs colour balancing. Red is too high. We know this because the background itself is magenta/red.

If you have Photoshop or similar you can look at the histogram in each channel. The top left of the peaks should be roughly aligned.

levels%20aligning-L.jpg

You can also use the colour sampler tool to sample the background sky well away from the nebula. I like to have a value of 23/23/23 in RG and B for pure background sky. Some like the blue a bit higher, even to around 28.

Olly

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Hi there, chaps

Many thanks for all the advice. You are right, Olly. There is way too much red. I just saw a lot of the rosette nebulas and how red they were and shifted the red way too far over. I didn't realise that injecting a bit more colour wouldn't make up for a desperate lack of exposure time :)

I'll have another go on the next clear night and see if I can improve. I have a modded 1100d and, with the CLS-CCD filter I haven't ever bothered to do flats before (or biases). Are the darks and lights alone, enough to make a decent photo?

This one was really to see the difference between a modded DSLR and a stock one. I won't forget the framing error, either :) I suppose that it's just about doing a sub and then moving the mount direction a little and then getting PHD back into guide mode?

I'd just like to say thank you, once again for all the help, advice and thanks from you all.

Let's see what the next one looks like! :)

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