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Full spectrum camera vs h-a filter on scope

vertigo262

By vertigo262
in Getting Started With Imaging

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vertigo262

vertigo262

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I'm not disagreeing with you aside from creating an image. I'm talking about the ability to see what comes out the camera. When I take a picture, you can't see much correct?

so in preview, I want to be able to see what I have as well as possible to figure out what I have. then, once I have this image that I'm trying to see faint objects, I want to be able to do things like, brighten, more gamma, stretch, etc.

This way I can take an image that does not show much, and start to preview more details. But the image that came out of the camera. I don't want a noisy low res image, because that doesn't resemble what I have. 

That is what I mean. I think we all agree that taking your image after you know you have what you want and processing is very important. But I think we are discussing two different things.

But I think this conversation wasn't that I have bad previews, but that ADT's preview is low res and noisy compared to what I see when I manually load the file in basic image viewers like Acdsee. and BYE and I'm guessing other programs don't have this problem.

It is a problem I can live with. It just struck me as odd, when I was out at night and taking some test shots, and I had to load the cr2's in Acdsee to see what I had, and that solved the problem, and I never had that problem in BYE. 

So I think we veered off topic somehow :)

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Thalestris24

Thalestris24

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Hi

The image preview (1:1) and (1:1) scroll settings let you see the preview at full resolution. Obviously, it's tricky to show a dslr full-res image on a screen anyway but the scroll setting is one way. I've put in a request to Ivo to include a histogram stretch facility for EOS so it will be more like the ccd version. I think that will be quite useful sometimes though I don't make a great deal of use of image previews generally. Once you get used to your setup, you'll have a good idea what are ok settings for your camera and you'll just make sure your target is centred, guiding is running smoothly and you'll just run a suitable exposure plan :)

Louise

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Thalestris24

Thalestris24

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Here are a couple of screen captures of preview images I got from my qhy8l. Cooled ccd's are inherently less noisy compared to dslr's :). Fewer pixels, but still.

This is a 120s exposure showing the full image in the window:

post-33532-0-60721700-1424465136_thumb.p

Same image but stretched a bit using the histogram tool and displayed using (1:1) scroll

post-33532-0-46602300-1424465172_thumb.p

Of course, you'd normally stack at least 10 such subs with calibration frames later so the final result, hopefully, doesn't bear much resemblance to the single sub previews. They just give a rough idea. I use them mostly to make sure my stars aren't too eggy ;)

Louise

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kalasinman

kalasinman

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why not? my other generic image programs open up all my raw no problem? and quickly too

They do not allow you to view a RAW/NEF directly. What they do is open a jpg written into the file when the picture was taken as an aide to preview. The "why not" is that it's not possible to directly view a data file as a picture.

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lensman57

lensman57

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They do not allow you to view a RAW/NEF directly. What they do is open a jpg written into the file when the picture was taken as an aide to preview. The "why not" is that it's not possible to directly view a data file as a picture.

It is possible but the RAW conversion must first be done by an application that does use  dcdraw ( in case of Canon ) first to convert the data and then a temporary stretch is applied as in Pixinsight or Nebulosity and Maxim, I am not sure if StarTools does it or not as I work in Fits not CR2 nor NEF but I will have a look. The images displayed in the capture software are mostly from a Jpeg conversion with different degrees of compression. The OP has a valid point in asking the question why the Jpegs do not closely resemble what the raw file contains? The answer however is obvious, a JPEG conversion gets rid od most of the data 14bits to 8 bits for DSLR and 16bits to 8bits for CCDs and anyhow as we are talking AP and not daytime point and shoot the resulting stack has a much wider dynamic range than a single sub so it would be irrelevant even if the jpeg had by some means managed to retain much of the original data.

A.G

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Thalestris24

Thalestris24

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Yeah, interestingly, DSS uses dcraw but previews of cr2 files seem poorer quality compared to a jpg saved from raw+jpg - presumably it's still displaying the embedded jpg and uses this for speed? APT does give the option of storing acquired image files as tiff format instead of cr2. I've never tried this - I've always assumed the tiff files would be rather large compared to cr2... I might give the save as tiff a try one day, just to see :) I've noticed that if you save as raw+jpg in APT then it only displays the jpg as thumbnails from which to select a preview image. If the jpgs are removed then it shows the cr2 file and you can preview that - though presumably still as (embedded) jpeg :) Startools won't open cr2 files.

Louise

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vertigo262

vertigo262

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anyone know of any real-time stacking software. Not for photo quality, but for previewing. For example, something to aim your scope at, and expose quickly into stacks, to view objects in semi realtime. it would just keep collecting exposures and stacking per exposure time so you can see what is out there.

Would think that would be cool, just to cruz around and view things

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Thalestris24

Thalestris24

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I have no clue? isn't Mallincams a ccd or is it something different?

I'm going to try it out, if I can get it to not crash. will be interesting

I think it only supports video cameras and ascom compatible ccd's. Deepskystacker Live would seem a way to do it with a dslr. I think if you've downloaded DSS then the Live version is already included but I've never tried it myself. I think, though, that such stacked images will likely be noisy and have pronounced vignetting but could be worth a try.

Louise

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vertigo262

vertigo262

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I know, I keep cleaning my cmos, but they keep coming back. rosetta I did some darks, but these were just tests to see the difference. I also, have some dirt on my inner telescope lens as of last time I went out, I'm guessing from dew. I have no clue how I'm going to clean that out, unless I take apart the scope which I am not that daring.

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vertigo262

vertigo262

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ya, that is what I've been doing. When I go out for a serious shoot with something in mind. although, to get the dirt out of my scope looks like I have to take off the front lens. EEEEEEEEEEEEK!!!!!!!!!!

that is really sucks. 

So, this is what I've been wondering. Let's say I go out to shoot a nebula, and it takes several days to shoot the same nebula.  I'm assuming I have to do my calibration frames for each day. and then put them all togethor in DSS. 

because the darks flats and bias are going to be a little different each time. especially the flats. At least that is how I guess you would do it

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Thalestris24

Thalestris24

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Hi

If you do the flats properly they should compensate for things like dust on the sensor as well as for vignetting. The marks you have aren't in sharp focus so not on your sensor. They won't be from your scope objective either - best leave well alone! Most likely they are on the lp filter. Ideally you should take flats just after imaging. If you don't move the camera or change the focus you should be ok to do them later. You can create libraries of darks and bias frames. It's helpful to always image at the same iso if possible - 400 or 800. That reduces the number of calibration frames you need to take. Temperature of darks and lights should be within 10 deg (centigrade) of each other.

DSS allows you to stack across sessions with different exposures etc.

Louise

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Thalestris24

Thalestris24

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Louise, I didn't realize there is such a large latitude in the difference in temps between darks and lights. Thanks! That means if I take darks at 20c that will cover almost all year,

Um, it's something I read somewhere... I figure there must be some way of establishing noise levels vs temperature empirically... I've also read that the apparent sensor temperature may not be accurately reflected in the measured temperature which I suppose is that stored in the exif.

Perhaps the most important thing is to leave a long enough gap between lights and between darks for the sensor to cool to ambient. Clearly if you take lots of short exposures one after the other without a reasonable wait time then the sensor temperature will keep increasing creating lots of noise. So it would seem logical to wait a certain time between exposures, whether light or dark. How long exactly? Hmm... I'm not sure... Maybe the same as the light exposure. So a 30s light might need a 30s cool down. Ambient temperatures will vary and can't be changed and sensor temps will tend to be higher than ambient. I think noise doubles with every increase of ~10 deg. Cooled cameras are much simpler!

I'm sure someone else can confirm :)

Louise

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