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Best Gain for imaging Jupiter?


PhotoGav

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I'm using Firecapture and an ASI120mc to image Jupiter at the moment. Hopefully getting some good captures. I've popped in to warm up for 15 minutes and just wondered... What is the better way to go with gain? I've been trying all sorts of things out and have ranged the gain from 50% to 80%, adjusting the exposure to get the histogram to about 70%. (Sub question - Is that about right, 70% histo?) Which gain value should give the better image - the lower value?

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I think you can be quite aggressive with the histogram with the 120MC, even going up to 80 to 85% if you wish.

My general approach was to set the exposure time to get a frame rate of, say, 30fps, then adjust the gain to get the histogram filled to where I wanted it.  If that meant the gain was getting well over halfway then I'd think about increasing the exposure time.  If the gain was very low on the other hand, I'd probably wind the exposure time down a bit.

James

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Yes, I think so.  It's something of a balancing act in that you don't want excessively long exposures because that means you're more at the mercy of the seeing, but high gain increases the noise and you don't want that either.

James

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Hi,

Just been out on Jupiter with an ASI120MM in a C11 and 2x barlow.  With gain set to 50% I get exposure times of around 18ms for 70% on the histogram, this will give up to 60fps depending on image size.  If I knock the gain down to 40% my exposures go up to around 26ms for 70% on the histogram and gives around 36fps.  I see a lot less noise on 40% and the frame rate is still pretty reasonable.

Of course I am mono so have to do three runs usually of 6,000 frames each.  Each colour takes between 130 to 180 seconds and I have to de-rotate the final RGB to combine without blurring.

I often do a run on 50% gain (7,500 to 10,000 frames) and on 40% gain (6,000 frames) and decide at processing which was best, usually the 40% gain.

Hope that helps.

Robin

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Thank you for your help James & Robin. I look forward to processing tonight's captures and I feel that I may regret the high gain captures. I was getting up to 112fps though - I had to experiment! My poor laptop is groaning from all this data...

Will be interesting to see your images from tonight Robin. I went for the colour version just to make life easier and a bit cheaper. I always wonder if I will regret that decision and end up moving over to the mono before long.

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"A bit" cheaper is something of an understatement, to be honest.

Yes, the colour camera is a few beer vouchers cheaper, but then when you add in a set of decent RGB filters and a filter wheel (especially if you go for a motorised wheel) colour can probably work out hundreds of pounds cheaper.

James

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"A bit" cheaper is something of an understatement, to be honest.

Yes, the colour camera is a few beer vouchers cheaper, but then when you add in a set of decent RGB filters and a filter wheel (especially if you go for a motorised wheel) colour can probably work out hundreds of pounds cheaper.

James

Absolutely. The problem is I was using 'a bit' as a relative term to my Astro spending... A few hundred quid is only 'a bit'... :grin:B)

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Hi Gav,

Re mono or colour, I would say colour first for a couple of seasons before making the move to mono. Mono is a lot harder, you need more kit, it is more to set up and keep working correctly and then you have three times the processing, plus combining the final image.

I nearly went back to colour earlier this year as my mono results weren't too good.

Pics from Thursday night are in this thread.... ...... To be added to.

http://stargazerslounge.com/topic/237850-jupiter-26th-feb-grs-transits-shadows-and-occultations/?p=2577603

Robin

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Personally, I find the mono planetary imaging to be relatively easy. Yes, theres more steps in the processing, but the data that I've captured so far (and I am a noob) is of much higher quality, so you can do more with it.

There's an interesting debate on mono vs colour in planetary imaging.....especially when using stacking tools like AS!2, as it uses a Bayer drizzle algorithm. This uses the normal drift in the avi file to "fill in" the resolution lost to the Bayer mask.  Older programs such as Registax use a "nearest neighbour" algorithm that produces much poorer results if you de-Bayer in stacking.

Alternatively, you can use DeBayer.exe, which comes with Firecapture, to de-Bayer before stacking.

Have a read of this interesting article:

Colour imaging S T_s.pdf

Regarding gain...it's a balance. Higher gain will allow you to use a faster fps, which means that there are many more frames to stack which lowers noise. I tend to push the gain up relatively high on Jupe as there is a limited amount of time to grab the frames. On more static object, then drop the gain (but not so much as you will start to get  onion-ringing)

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Nice image Robin! OSC is certainly 'easier', especially with the time critical Jupiter.

@Zakalwe - thank you, that's a very interesting article. Gives me some faith in the potential of my camera! I'm churning through the data from last night - first quick processes look promising (at least by my current standard of planetary imaging!). I will be trying the Firecapture debayer app, though I have used PIPP for that step so far, which gets a good write up too. So much to learn. The article talks about aiming for only around 30% histogram... That seems very low, but maybe some experimentation is required. Certainly a lower gain seems to be advisable.

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