last night the weather here improved so dramatically that I had clear skies until almost 3am.
Everything worked perfect after I hooked the whole shebang to the laptop, so I could sit back, relax and enjoy a nice bottle of shiraz.
I chose the sculptor galaxy and decided to push the limits and expose for 10min. To my suprise I found today that after I stacked them all in Deepskystacker the resulting image was completely white and featureless. Tweaking around in Photoshop helped the situation but I am sure that I have totally overexposed the images (vigetting was awefull too). See below the best I could do so far.
So what is the key for correct exposures and how do you determine the amount of shots to be stacked?
Shot details:
150mm f5 newton
Canon 450D no filters
8x10min
no darks, no flats, no bias (was so excited that I forgot about it)
Median Combined in Deepskystacker
PS CS2: levels, curves, crop, downsample (for posting here)
I get the same thing in DSS where my resultant stack is "whitish". I remember seeing a thread about that somewhere but can't find it. Maybe someone else can give you, and me, a hand.
However, I do like your image and the thought of doing the imaging with a bottle of Shiraz is making me thirsty!!! (No, nott the pretzels...)
thanks for the link and the flowers regarding the picture. I will study the intro to DSS and see what I can improve. To be quite honest I sometimes struggle with all the options that one can choose from and it happens that I choose one that damages the result. But I suppose in a few years I know exactly what "convolutive gaussian debayerization with separate channel interpolation offset value anticipation" - or so - is good for... gosh, Kants critique of pure reason is a good night story compared to all these methods.
But one thing is for sure: the more I learn about the difficulties, the more I admire great pictures of others.
10 Min exp's are the goal for DSLR's you will capture the most amount of anything without the noise ruining the party. With that said you need dark skies to do this, if you have light pollution.. GAME OVER 10 min photos might not be available to you.
Keep up the good work things get easier over time!
if 10 Min is the call, what is the maximum? And do I get it right: there is no such thing as too many images in a stack?
thinking about dark skies: Auckers is really an improvement to Melbourne but still pested with street lights and the like. Next time I will try using a CLS filter with custom WB and see how that goes.
Sure, perfect dark skies arenīt too far away. Its more like Perth then Melbourne. But its the lack of a proper location and the convenience factor that keeps me home.
Hey Mario,
donīt take it from the far side but there is nothing wrong with being gentle to a man.
if 10 Min is the call, what is the maximum? And do I get it right: there is no such thing as too many images in a stack
Thanks guys!
Maximum exposure is when it's burned out on your camera, load it into your cannon program and have a close look, it also depends on your iso setting too.
Never too many images in a stack
A lot of deepskystacker problems are the result of applying the stretch that comes as a default in the program, it's helpful for ccd users given the well depth but for dslr users turn it off and make sure it's not applied when transferred into your tif export image. That's all the white problem is... Easy to rectify.
...... thinking about dark skies: Auckers is really an improvement to Melbourne but still pested with street lights and the like ....
Hey Max, where abouts in Auckland are you ? There a few dark sites not far from the city ( 30 -40 mins ). I've got one I want to use up in the Waitakeres by the TV transmitter mast. Gives awesome Sth to West horizon view and some Northern sky with a hill behind to kill most of the city glow in the east. There is also a group that meet up Kumeu way which I'll find the contact for if you want. I keep meaning to get in touch with them.
My back yard in Mt Albert has a 4 meter square concrete slab with a fence around. Blocks most of the low level glow and gives me quite good views high SW to West and some NWest. I'm lucky in that we're up a long right of way with no close neighbours. So away from the local street lights and late at night everyone has gone to bed so very little local glare. On a nice night I get quite good views from my 4.5" newt. Can't wait to see what my 10" build will see. And then get it to the Waitakere site.
By default i believe that DSS doesn't apply these settings to the saved Tiff, if you bring it into PS you should almost have a black image. This is where you start applying a iterative Levels and followed by curves to bring your data to the full 16 bit gamut well as much as you can in any case.
As for blowing out or Too much exposure Stars generally blow out on DSLR sensors that is the pixel well depth has been filled. You can see the effect on the stars of this happening where the center of the star is White and then as you move away from the centroid you get color back. You can move to a HDR method of stacking different length exposures (avandonk does these extremely well.) or alternatively buy a camera with huge pixel wells allowing more data to land in there before saturating.
I am living in Bucklands Beach near Howick. I am having no clue where that place with the Radio tower could be but from the map I reckon it isnīt more than one or two hours drive. Lets go there when the clouds eventually move away. How can I contact you?
my last stack arived almost white in PS too but I havenīt done anything in DSS. But the initial overexposure came as you mentioned earlier from skyglow that was probably amplified by the stacking so either I use filters or move to a dark site. - hopefully soon.
Oh well, for now I have to stick to theory as there is no thinking about going out with a telescope. I hope at least the farmers are happy with the weather.
Interesting it should arrive almost black. because your shooting with a camera that has i think 12bit color range, where as 16 bit has more space in the histogram. Ide reset everything to defaults and see if that helps you out at all.
sounds good but I have trouble finding the check box for this feature. Where is that one buried?
Should be to lower left of stacked image, bunch of sliders, I think you slide all upper to the right and lower to the left.... Play with it and it will become obvious, then save the settings.
Hi Max, I get same thing 10 minutes is most I can get and get similar effect in Maxim wish there was a way to calculate exposure.
peter
In maxim when the screen is displayed, use the screen stretch window... Ctrl H, and set the value to ( max Val) this will display it without any stretch applied.
I am living in Bucklands Beach near Howick. I am having no clue where that place with the Radio tower could be but from the map I reckon it isnīt more than one or two hours drive. Lets go there when the clouds eventually move away. How can I contact you?
Transmitter Tower is up in the Waitakere Ranges, West Auckland on the scenic drive. Google Earth plot is 36.55.44 Sth 174.34.05 West. It's a public viewing spot on a corner on the side of the road. Maybe park about 8 cars there. Very little traffic. About 1.5 hours across Auckland for you I guess, probably less.
Have you thought about going out along Music Point which is down the road from you. Not sure if they allow night access but you can get away from the local street lights and probably have a protected eastern view away from the city lights. Even if you can only get up to the caretakers house before the golf course entrance where I think the put a barrier across at night at least you will be elevated and should be able to find some wind/light protection.
Another option for you is out along the Whitford Road towards Beachlands/ Maraetai. Just get out into the countryside a bit. Omana Beach carpark, Duders Beach toward Clevedon. All close to you ( 20 mins ) on good road. You could almost have horizon skies to the east and north.
Just have to wait for some clear skies. Keep in touch.
Just out of curiosity Max are you using the Autosave file that DSS automatically created in PS or are you working on the final image that you save as a Tiff in DSS as your working document.?
thanks for the insider tips, Iīll certainly check that out.
Hi Paul,
yes I am using the Autosave.tif-file. So I guess I am doing something wrong, am I? what is the difference between the autosave and the final saved tiff?
After quite a number of adjustment layers I got the below, which actually looks better than the picture in the "ABC Universe" but still suffers from chromatic noise and a bit miscollimation (or maybe field curvature?) on the left.
Keep up the good work things get easier over time!
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