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IC1396 - First Ha image check


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Hi all - A very frustrating night last night... :) The clouds seemed to depart and it got dark enough for me to have a 2nd go at the 314L+, this time using the Equinox 80. I wanted to have a go with the Ha filter, so went for some 15 min subs - I was hoping to get 4 hours worth (at a push), but ended up with only 1 hour as rogue clouds got into a sequence of scudding over at the rate of one every 5 minutes or so :). I eventually conceded defeat at 2am...

Still, I found the FWHM focus box and also utilised all the options I could find to get a looping image that I could see on the screen so that I could frame it :hello2:.

I ended up with this - I know I'd need a LOT more subs before thinking of doing anything with it, but that aside, am I heading in the right direction here, or is it looking a bit "soft"? It's 4x900s Ha with 20 darks subtracted (still no flats... can anyone advise how I can get to see ADU values on screen when trying to work out exposure / flat exposures?)

post-18819-133877611126_thumb.jpg

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did you mean soft as in low contrast or soft as in out of focus?

To me it looks a bit soft as in out of focus, boosting the contrast will not help, if it is soft that's it. It may be down to the long exposure, 15m is a fair while considering guiding issues, seeing variations and possible soft focus. It is a bit noisy, much more so than I would have thought typical from a 15m exposure. Four of those I would expect to be much cleaner but it could easily be cloud, even the stuff you cannot really see because it is so thin.

Ten minute exposures might well tighten it up quite a bit, you just need more of them to smooth out the noise.

Dennis

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Cheers both (sorry - been out of internet reach!). To be frank, I wasn't too sure what might have (or if anything had) gone slightly awry... I thought it looked a little soft / out of focus, but wasn't too sure as when I focused (on Alderamin), I managed to get the FWHM down to c. 1.7 using Artemis Capture, but when I loaded them into DSS and registered them, I noticed that they all ended up around the 5 mark...

However, maybe that could be explained by what I considered dubious guiding - Almost invariably usually any guiding adjustments made are only +/- 1 pixel, whereas I noticed that on Monday night it was +/- 2 (@ 1s guiding exposure). Might this account for it (and also the increased FWHM value?)

I'm not sure about the noise element though - As you know, this is all a bit new to me :), so I'd just put that down to not enough subs, although again, there may have been some of those high thin clouds about (which as you say are not easy to see at night!)

This was also only the second time I've taken 15min subs (the first time was with the 40D and the noise/banding got on top of me - The reason why I decided I ought to buy a CCD!). The reason I used 15 mins here, was simply because I thought I'd need that sort of level of exposure using the Ha filter to get enough signal in the subs, but if I can get away with 10 mins, that would be great... I'm REALLY missing the liveview histogram I had on the 40D though, as that way I could easily see what saturation I was getting, but with the Atik / Artemis capture, it seems to be all guesswork(?) which I'm sure shouldn't be the case - Is there anywhere (or any software I can use) that will enable me to access the ADU value on screen...? I'm currently trialling MaximDL5 for aligning/combining etc - Is there an option on there somewhere to view this info?

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There is nothing that MaxIm will not do! Focus subs will always show a sharper FWHM simply because the exposure is shorter. Virtually no problems with the mount stability, seeing or guiding.

The screen grab shows the picture info I typically have on screen during exposures. Set the Info palette to Aperture and the values shown are for the cursor which is over a bright star. Beware the screen stretch mode which does not show you anything like the quality you can get from the same picture properly processed in PS.

I believe I still have Artemis capture somewhere, I'll have a look at it.

The picture is a single 15m sub from the TMB 152 and STL 11000M.

Dennis

post-15519-133877611805_thumb.jpg

Edited by roundycat
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Andy

The ADU values can be seen bottom right, in the status bar, of the Artemis capture window. Place the cursor over a star, or any part of the image, and it will show you the x & y coords + the ADU value.

HTH

Steve

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For checking your flats exposure depth in Artemis Capture just read the 'white' value in the 'display' window. I go for about half way, around 30,000. Dead easy.

When using FWHM go for longish subs, three seconds or more, unbinned, to allow the seeing to settle. Take time. I always advise newcomers to think in terms of 10 minutes and if you get there quicker, fine. If not it is time well spent.

Olly

Edited by ollypenrice
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Thanks Dennis for info on how to find the ADU in Maxim (I knew it had to be there somewhere - As you said, it seems to do everything else!) and thanks also Steve for pointing out that it IS visible in Artemis (I must have totally missed it - I even looked in the "full" manual to see if it mentioned anything there, but there was nothing mentioned)... and also obviously thanks to Olly for pointing out where the value is to check the white saturation when taking flats in the display window (Again, I feel a right idiot for missing the obvious... sorry :))

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