deepsky intro

wargrafix

Hi all, i have a celestron 9.25 and focal reducer and recently purchased the asi224 camera. How do i begin deep sky imaging? I use firecapture

riklaunim

You have a planetary telescope and a planetary camera. Starting DS imaging with such setup will be quite hard.

1. What mount you have? Guiding is required usually

2. If you guide with ASI224 then you will have to have main imaging camera

3. What focal reducer do you have?

wargrafix

Thank you for your prompt advice. :-)

I am using the asgt cg5

I have the celestron 6.3 reducer

I have 2 ota. 9.25 and a 102mm refractor. I have taken long 2 mins exposure over 2 hours with the 9.25. Thinking of doing planetary nebula. How do i get started using this camera to do that?

wargrafix

I probably didn't clarify my experience. I have used the ota with my dslr. Now that i have this camera, i wished to know what is done for deepsky using this 224mc camera

ndb

Hello,

the C9.25 at f6.3 with the ASI224MC has a sampling rate of 0.5 arc sec / photosite, this is very small and seriously resembles a typical sampling rate for planetary imaging at high resolution. To fully exploit such a resolution, exposures have to very short to avoid turbulence blurring, e.g. 0.5 second up to 5 seconds, as long as the deep-sky objects are contrasted (M51, M13, M57...).

I've shot this way at f/4.7 (see my early posts with the ASI224MC and others with the ASI120MM which has nearly the same sensitivity but 8x more noise).The ASI224MC should work at f/6.3 too, for contrasted objects.

riklaunim

As NDB pointed out you have a very very hard setup for any DS imaging. For a test you can try M42 Orion Nebula core. It's very very bright and if that doesn't capture clearly and nicely you will know that this setup isn't for DS imaging.

And you don't have guiding?

wargrafix

Eventually i will use the 224 for guiding but i would like to see how it perfoms for dsos. I got so used to unguided that my expectations are to that level. Besides i could image with the 102mm refractor of its too difficult.

I think i was a little unclear. With the setup, whats the capture procedures? With my dslr i just had to point to target, set iso and using an involometer and shoot. But how is it done with a webcam?

~~3 hours 47 mins unguided with the 102mm refractor~~

riklaunim

It's not a webcam, but still - you point it, set the exposure time, gain to some extent and you start imaging.

wargrafix

Thank you. I guess that is what i was meaning to ask, like what sort of gain and exposure settings to use. Like firecapture, can, it export stack-able frames? Literature on this is not very widespread

riklaunim

You can use any ASCOM compatible capture software like Nebulosity or FireCapture too - it can save frames as FITS.

wargrafix

Thank you. Whats a typical gain setting? Exposure time in firecapture can be changed?

firstc8

NDB wrote:
Hello,

the C9.25 at f6.3 with the ASI224MC has a sampling rate of 0.5 arc sec / photosite, this is very small and seriously resembles a typical sampling rate for planetary imaging at high resolution. To fully exploit such a resolution, exposures have to very short to avoid turbulence blurring, e.g. 0.5 second up to 5 seconds, as long as the deep-sky objects are contrasted (M51, M13, M57...).

I've shot this way at f/4.7 (see my early posts with the ASI224MC and others with the ASI120MM which has nearly the same sensitivity but 8x more noise).The ASI224MC should work at f/6.3 too, for contrasted objects.

Will a dark site at high elevation allow much longer exposures? How much can the dark site improve image quality, if atmospheric interference is the limiting factor?

wargrafix

Seeing in Trinidad is less than 1 arc second seeing. A dark site lets more light through because the sky has more contrast and not lost in the LP. 2 mins at a black zone is worth 16 mins from a yello zone

firstc8

wargrafix wrote:
Seeing in Trinidad is less than 1 arc second seeing. A dark site lets more light through because the sky has more contrast and not lost in the LP. 2 mins at a black zone is worth 16 mins from a yello zone

That is substantial. But I suspect narrowband imaging will not have as much exposure time difference between black and yellow zones?

Another popular imaging software is Sharpcap, I found it very user friendly for DSOs.

224mc uncooled will be limited to bright and high contrast DSOs like NDB said. There are some incredible DSO images by 224mc in this very forum, you can read the imagers' camera settings, light train specs...and try them yourself.

wargrafix

I know!!!! Amazing shots have been taken. I phrased the thread wrong. I should have said what settings are used for dsos in capture software when using these cameras for dsos.

riklaunim

firstC8 wrote:

Will a dark site at high elevation allow much longer exposures? How much can the dark site improve image quality, if atmospheric interference is the limiting factor?

You don't need "longer". Just a much darker site will have lower sky noise so the same average exposure will actually show more, you would be able to catch even lower magnitude detail.

Seeing can affect a DS image if you have a long focal length -> resolution. Not to mention that at such high resolution OTA air currents will be the key problem to avoid (not much of a problem for 8" SCT, but for bigger with no active cooling it will be a problem).

firstc8

Well if I can make shorter exposures that can help too.

wargrafix

So last night i gave it a shot. I tried 2 globular clusters and m51. The ability to change exposure length was a mystery in fire capture but sharp cap was easy. I tried it and could see the object slowly appearing on the screen. I am guessing it livestacks. I did 15 seconds each on m51. I shot maybe 300 but when dss saw the shots it only wanted to stack 1. Now there would be considerable noise so when i lowered the star detection rate it began to think noise was stars. Of course the thing came out like a mess but its an interesting start. I live in a yellow zone ish

riklaunim

firstC8 wrote:
Well if I can make shorter exposures that can help too.

It doesn't actually. If the sky background is at like 10 mag then everything at 10 and lower mag will never be captured by the camera no matter what exposure time will be used. If the sky background is like 20 mag then you will be able to capture for example 19mag detail if the exposure will be long enough to put 19 mag signal above shot/read noise. In both cases the exposure time have to as long as needed, not as long as you can get. Whenever sky background signal starts to be higher than noise - that's the longest meaningful exposure.

riklaunim

wargrafix wrote:
I did 15 seconds each on m51. I shot maybe 300 but when dss saw the shots it only wanted to stack 1...

That's why implicit applications can fail easily. Try Autostakkert2 or Nebulosity. In Nebulosity you can pick stars so it won't have to "detect" them.

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