The Antennae - FINAL RESULTS NOW UPLOADED

[rmuhlack]

This is a DSLR "Work-in-Progress", and also an exercise in theory meets practice.

I have been experimenting with different ISO settings on my uncooled 400D in an attempt to find an optimum, and (being the nerdy type that I am) thought the best way to settle it would be to conduct an experiment. Firstly run a series of darks at different temps and plot SNR vs exposure time for different ISOs and temperatures (as per Roger Clark's methods here (http://www.clarkvision.com/astro/canon-10d-signal-to-noise/)). Graphs are relative to the noise of my 400D at 300s ISO800 and 20 degrees C (the plot for 20C is not shown here)

To my surprise ISO1600 came up trumps, so it was time to test with something challenging. I decided NGC4038 - The Antennae.

The data I have so far was taken over two nights using my VC200L with focal reducer - this is a HDR combine in Pixinsight of 67 x 180s ISO1600 subs (ambient temps of about 10-14C) and 53 x 240s ISO1600 subs (ambient temps of about 8-13C). Hi res version here: http://www.astrobin.com/full/40743/?mod=none

Am hoping to add to this over the next few imaging sessions, but I thought the process of determining exposure time might be of interest to some. And of course any advice or comments on my image capture and processing is also very welcome. The balance between the background and extended galaxy arms in particular I found quite challenging. I plan to post some updated images when I have collected some more data.

Thanks for looking :)

[gregbradley]

Great image Richard. Way better than I would normally expect to see from a DSLR.

So you took various images at various image lengths and plotted the resulting SNR (measured at the same spot on each image?).

I wonder if this result would vary with ambient temperature as sensor noise varies with temp.

Great work. I'll have to do the same with my Nikon D800e to see what the ideal ISO is for it.

Greg.

[tilbrook@rbe.ne]

That's impressive Richard!

I tried the Antennae last year, got nothing like your image.
you've inspired me to try again.

Cheers,

Justin.

[rmuhlack]

Thanks Greg/Justin.

Greg - it does vary with temp as you would expect. The graphs show the SNR for two data sets - one for an ambient of 14C (this was basically constant throughout this test) and then another where ambient varied from 5.5 down to 3 C during the test (and this variation should be taken into account when interpreting the results. ideally I should do it again when temps are expected to be more constant). Its done by taking a series of dark frames only, and then measuring the standard deviation of each dark frame (across the entire frame). Roger Clark's website gives the formulae for then calculating relative SNR.

[rmuhlack]

One clear insight from those plots is that my earlier idea of using ISO400 which has a lower gain and therefore greater dynamic range wasn't doing me any favours with respect to noise (even though I did see much better star colour). eg this image of Corona Australis from two weeks ago: http://www.iceinspace.com.au/forum/attachment_browse.php?a=137559

I think these results suggest that a better approach for me to enhance star colour would be to take a separate set of short subs at ISO1600 (say 60s) and then do a HDR combine in Pixinsight.

[graham.hobart]

That's pretty cool Richard.
What do you think about a cooled DSLR?
If this keeps temp relatively constant (my CentralDS modded Canon will stay at 1'c EXIF) then shoot at 1600 but also with some shorter subs for the star colour?
Great thinking!
I like the cut of your jib my man!
PS Antennae are excellent
Keep up the good work
Graham.

[rmuhlack]

Thanks Graham. By cooling the DSLR you're going to get a similar sort of boost to SNR (when compared with an uncooled equivalent). However unless you have a very old CentralDS camera (like a 350D) the ISO you should use may be different as your camera will have different gain settings as its 14bit instead of the 12bits that im using.

But yes, i would imagine the same principle would still apply: Determine what ISO maximises your SNR, and then vary the sub length and use HDR combine to increase the effective dynamic range of your image :cheers:

ps as a side point, i'm curious to know what sort of condensation problems are seen with a cooled DSLR, when the cooling takes the camera below the ambient dew point..?

[RickS]

Very nice work, Richard! Some good research and a nice image.

[Larryp]

Very nice, Richard:thumbsup:

[multiweb]

Impressive. :thumbsup: Great write up. Thanks for the links.

[Ross G]

Great looking photo Richard.

When I was shooting with a Canon 350d and 1000d I also found that 1600asa seemed to be the "sweet" spot.

Good luck.

Ross.

[David Fitz-Henr]

Excellent image Richard!

[rmuhlack]

Well I now have almost twice the amount of image data on the Antennae that I did before. As far as a practical test of using ISO1600 to maximise SNR, I think the results here speak for themselves. I am very happy with this result :)

The final tally comes in at:

Day 1: 67 x 180s ISO1600 subs (ambient temps of about 10-14C)
Day 2: 53 x 240s ISO1600 subs (ambient temps of about 8-13C)
Day 3: 47 x 180s ISO1600 subs (ambient temps of about 10-13C)
Day 3 continued: 49 x 240s ISO1600 subs (ambient temps of about 7-10C)

I have uploaded a "widefield", a close-in crop, and just for laughs a comparison with Hubble's famous image of this galaxy pair :D

Processed with Pixinsight. Hi res image here: http://www.astrobin.com/full/40910/?mod=none

As always, feedback welcome :thumbsup:

[E_ri_k]

Thats impressive Richard! Well done :)
Erik

[RickS]

Lovely image, Richard!

[LucasB]

Great stuff Richard. That is very impresive and I also love the experimenting and documented results.:thumbsup:

Lucas

[strongmanmike]

The final result is excellent Richard, one to be proud of :thumbsup:

and go the Hubble comparisons, never done it myself :confuse3: but looks like a good idea :whistle: :P

Mike

[rmuhlack]

LOL thanks Mike ;) (hmm...I wonder where I got the idea from...) :P

[strongmanmike]

Oh yeeeeahh (http://www.pbase.com/strongmanmike2002/hubble_comparisons)...thoooose :scared3:

Mike

[Shiraz]

very impressive image Richard. Nice when an experimental investigation pays off. Regards Ray

[spacezebra]

Stunning Richard!

Cheers Petra d.

[spearo]

Great work!
frank

[rmuhlack]

Thanks for the kind words everyone :)

Looking at the image on a different screen I thought the extended arms looked a little too faint. As I am heading interstate this week for work and so away from my image processing PC, I have a quick repro before I finish packing the car for my long drive.

This is just a minor curve adjustment just to show off the extended arms a little better, but without over-doing it.

Hi res: http://www.astrobin.com/full/40910/B/?

[astronobob]

Agree, impressive result Richard, that is very smooth work indeed :thumbsup:
Also very interesting Re: iso 1600 for 240 seconds with Dslr, the prove is in the puddin'mate, Well done ! !
I should delve into this positive excersize, Great Image and post Richard :thumbsup:

[John K]

Bumping this thread back up - possibly belongs in terms of my question in the astro-photography equipment section.

Over the last 12 months have used the S/N ratio graphs that Richard shared here to get the best results with my Canon 400D.

Now my camera is in the process of getting TEC cooled, and I am wondering what the new S/N ratio numbers will be? It will go 15 degrees below ambient so in winter this means well below zero.

So the question becomes, has anyone done some S/N ratio tests with a cooled DSLR that's close to the 400D sensor or an older model perhaps that they can share?

One of the things I am hoping with my modified and cooled to be DSLR, is to have better results with something like 10 minute exposures of faint galaxies where I think the non-cooled DSLR CCD's let things down.

Any info that people can share would be great.

John K.

[Placidus]

Stunning.

[rmuhlack]

I did some testing when I installed active cooling on my 1000D (Digic 3 and live view,m but otherwise almost identical to the 400D). I was able to dig up this result for 0 C.

I had some condensation troubles with my setup when operating it below the dew point, so in the end I went for a setpoint of 10C - still well below the typical operating temp of the camera, but above the dew point on most evenings. My testing did not show the drop in SNR at longer subs that it did with the uncooled camera. rather SNR increased with sub time. Consequently I decided to run with 10min subs with the cooled 1000D, with good results as shown here (http://www.astrobin.com/search/?search_type=0&q=rmuhlack%20lacerta&camera_type=any&camera_type=0&camera_type=1&camera_type=2&camera_type=3&camera_type=4&camera_type=5&telescope_type=any&telescope_type=0&telescope_type=1&telescope_type=2&telescope_type=3&telescope_type=4&telescope_type=5&telescope_type=6&telescope_type=7&telescope_type=8&telescope_type=9&telescope_type=10&telescope_type=11&telescope_type=12&telescope_type=13&telescope_type=14&telescope_type=15&telescope_type=16&telescope_type=17&telescope_type=18&telescope_type=19&telescope_type=20&telescope_type=21&telescope_type=22&license=0&license=1&license=2&license=3&license=4&license=5&license=6&sort=-integration).