Deep Sky exposures

snnfly

Can anyone please explain to me how I can image a deep sky object with the necessary long exposure like you can with a DSLR with the ZWO 224 in say Firecapture. Can only see single frames or AVI,

Thanks

riklaunim

One option is to shoot many few-sec exposed frames, and the other it to use bit longer exposures if noise/target allows it.

snnfly

Thank you

draconis

For near real time viewing on your monitor , you can also post process (stack) a handful ( maybe 10 -20 ) short exposure frames .

snnfly

This is what I don't understand. I thought to obtain a deep sky image you had to have a long exposure in order to capture a favourable image. Can this be done in Firecapture?

space cowboy

You can set exposures as long as you like, just as you would a DSLR but this cam is so sensitive its possible to obtain lots of detail from very short exposures ie 5 secs. If you want to stack the captured frames in Deepsky stacker then fit files are best but there are ser, TIFF, avi or BMP as options though BMP is only 8 bit and 16 bit is best option. All these files can also be stacked in as!2 if you prefer.

Hope this helps.

draconis

Yes . Fire capture has a pre process stack function . How you would set it for 'near real time' viewing would depend on the magnitude of the object .There are several dso's that are at or near naked eye viewing magnitudes under optimum conditions that can be viewed on screen with a pp stack of say 3 one second exposures so your screen refreshes its self every 3 seconds .On fainter objects you would increase these parameters (exposure times and #of stack frames) until you get the desired results .These parameters are easy to adjust on the fly .

It should also be noted that the way you set pre processing to view on your screen does not have to be the same as how you set up your image capture .The gain values will be the same , but the exposure times can be different .

firstc8

Hello everyone, I am new to the user group. Just ordered the 120MC-S mostly try to image Saturn.

My backyard is actually more suitable for imaging several close DSOs, consider the time of the night and the environment I am in. So I read a great deal of how to go about getting the best DSO images out of this planetary imaging camera.

I have come to some uneducated summary of what experienced imagers are doing, please correct me where I am wrong.

Since this ccd is not cooled, the exposures should be kept short, mostly under 10s. To compensate, take a dark frame using Firecapture at the start of each session, then take as many subframes while monitoring the chip temperature. Once the temp swing reaches certain level, stop the session, take another dark and start another session, until there is a satisfactory (large) number of subframes taken.

Am I close so far?

Thanks in advance.

ndb

Hello firstC8,

you are perfectly right about the procedure.

But the previously mentionned, short exposures are for a camera such the ASI224MC. The ASI120MM/C has almost the same sensitivity but much more noise, although quite low for a CMOS sensor. Here is my page about the ASI120MM for DSO:

http://nicolas.dupontbloch.free.fr/camera-asi120mm.htm

and the 120MS has a lesser sensitivity due to its bayer matrix, not to speak of the necessary interpolation of pixels.

Here is an image with 15-s exposures, no cooling; stacked and processed.

http://nicolas.dupontbloch.free.fr/dsk-galaxie/m51_2015-05-20_newton254_asi120mm_205x15s.htm

The ASI224MC has almost no noise; a high gain is possible with short exposures but since raw images are very clean, exposures of minutes are possible (I successfully tried 120s). You can see test images on my page:

http://nicolas.dupontbloch.free.fr/camera-asi224mc.htm

One cannot compare the perfomances of the two cameras. I totally neglect my ASI120MM since I tried the 224.

All modern cooled cameras are regulated to avoid taking numerous series of darks per night and multiple-session stacking for every DSO, as you perfectly guessed. In addition the sensor chamber must be insulated in some way to avoid dew and frost; I experienced it with my DIY cooled ASI120MM. That's why I gave up DIY cooling and I'm currently waiting for the regulated, cooled ASI to come.

In all cases, autoguiding gives better images even for 10-second exposures unless you have a excellent mount with a very reasonable load.

Regards,

Nicolas

firstc8

Amazing test comparisons and results Nicolas!

Is the soon to be released ZWO cooled CCD a 224 chip?

From your tests my guess is the current uncooled 224 is sufficient to image close and bright DSOs, so am I correct the benefit of the new cooled 224 will be for more distant and faint DSOs?

riklaunim

ASI224 has a CMOS sensors, not a CCD - which is something new/shocking for DS imaging ;)

Cooling will allow using longer exposures for DS imaging or higher gain for high resolution short exposures DS imaging (like small planetary nebulae). The drawback is small sensor size.

ndb

After the testing sessions the 224 proved to be able to shoot contrasted DSO with 0.5 - 5 seconds exposures only and cooling is not necessary as long as the gain is under 150-200(/600).

See measures of noise here (Chinese):

http://sbrngm.tistory.com/?page=7

and here (Chinese):

http://sbrngm.tistory.com/287

and here (French):

http://www.webastro.net/forum/showthread.php?t=129196

I'm waiting for a cooled version to go on with in HAlpha imaging because some thermal noise appear at a corner of the frames with two-minute exposures, hot pixels and other noise also increase with time and vary during the imaging session (although pretty good results considering the CMOS sensor!).

With regulated TEC and on-the-fly dark subtraction by FireCapture, acquisition and pre-processing should turn out to be as effective and simple as with a real regulated-TEC CCD camera; in addition I expect super clean raw frames.

Planetary nebulae and star clusters only need very short exposures up to 4 seconds (Newtonian at F/4.7), hence I don't think that cooling can bring a conspicious improvement for such contrasted objects to start DSO imaging, but in my opinion the cooled versions should offer the widest range of applications of all astronomical cameras at a fair price.

Nicolas

purdyd

I haven't used the 224 sensor but with the imx174, cooling definitely makes a difference even as short as one second.

I do have to agree that externally cooling does have some problems and is a hassle.

From the French site linked, with the 10 second exposures, there was a noticeable difference in noise in the imx224 simply cooling from 33c to 14c

My guess is that will translate well to shorter exposures

In my testing 10msec cooling makes no difference.

So in my opinion, the cooled cmos cameras will be better for guiding and much better for dso imaging at anything 1 second and above

firstc8

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draconis

I agree I use fit files for dso's and deep sky stacker

wargrafix

I can't wait to try dso with this camera. I finally got started with the camera and i am impressed!

xs_man

Hi all,

As Nicolas says ASI 224 a really a wonderfull 'toy' for imaging bright deepsky objects as

planetary nebulas or globular clusters with the 'short exposures technique' (Lucky Imaging).

And I agree, under 5 seconds no need of cooling. Cooling is usefull only for medium

and long exposures necessary for faint DSOs.

Here are exemples of pictures I've made with Uncooled ASI 224 (with Ir cut filter) and a 16" Newtonian F/D 4.5 on equatorial mount. Exposures are between 250 to 1000 milliseconds. Some are taken directly at F/D 4.7, other with 1.5x or even with a 2x Barlow.

For NGC 2022, I used the ASI 185 which have a greater FOV a nearly the same sensitivity as ASI 224.

Sorry guys, in French only ! ;)

http://www.webastro.net/forum/showthread.php?t=135332&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=135055&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=134065&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=134472&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=133969&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=133613&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=133097&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=132823&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=132980&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=131958&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=131582&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=131324&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=131000&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=130517&highlight=ASI+224

http://www.webastro.net/forum/showthread.php?t=130189&highlight=ASI+224

BR.

Albéric

wagner trindade

Hi Albéric

Very impressive images, congrats.

Just let me ask you some questions:

- Did you use darks, bias?

- Did you guide or in such small exposure was it not necessary?

- Which software did you use for capture, stacking and post-processing?

Regards

Wagner

firstc8

Wow, I replied in this thread back last October when I just started astro imaging, looking back I think I have come a fair (not long enough) way.

The 224mc is a great camera for lucky one shot color imaging. The other benefit is, because of its high sensitivity, it can be a guide cam even in very demanding setup.

I have been using it as a guide cam on my Celestron off axis guider, using C8 at F10 (FL=2030mm) and working with the low budget Celestron AVX mount. By all accounts, this setup would have been near impossible.

The AVX mount bad periodic error (PE) alone would have killed it. But my 224mc is sensitive enough to pick out guide stars when PHD guide frame interval was set at 0.5s--fast enough to handle the bad PE.

224mc uncooled however would not be good for very long exposures, such as narrowband imaging. Even cooled CMOS chips have limitation for very long exposures because of amp glow and random hot pixels. They can be treated but sometimes difficult to remove completely.

Sam@ZWO

we always recommend control our camera through ASCOM driver to do long exposure

there are lots of other software suitable for DSO imaging