Lagoon Nebula
actually BOTH Meng Lee and Vincent is right! gee. haha
there is a compromise (as always isn't it?) between going deep and getting sky-limited exposures. Expose too long for a given capturing medium (whether DSLR or CCD), and you will have washed out sub exposures. The exposure duration threshold here is really up to the discretion of the imager, the imaging scope and setup,
and the light pollution characteristics of the site at which the session was conducted. For my location in the balcony, I am limited 10 minutes colour channel exposures. Any longer and the exposures are washed out. Washed out means the histogram profile of the exposure is all cringed up to the right, and stars are equal brightness with the sky background. No amount of vigorous processing can correct this. When the full moon is up, this is limited to 5 minutes. For narrowband, i have tried up to 30 minutes of exposure in HA, and it is still not washed out. For darker sites, these numbers would be bigger. I have not personally evaluated the sky-limited exposures for my DSLR, but I think it cannot go more than 5 minutes according to a specific ISO setting. So how to go deep? Deep would be as long as you can obtain sky-limited exposures, which one would need to evaluate for your particular system. If it is within a few minutes, then perhaps, with good drift alignment and stable conditions (no wind, etc), autoguiding may not be needed. It is important to have good gears too, then even with autoguiding, the software do not need to have a high frequency rate of monitoring for the guide star.
Another factor comes into mind as well -> imaging focal length
As one embark into higher f.l., you could have an increment in general sky-limited exposures, but at the same time, one would need to take greater care in ensuring autoguiding is done properly.
Popular autoguiders in the market can be had from Yankee Robotics (Nugget), CCD-Labs (QHY), and very soon, SBIG (again).
there is a compromise (as always isn't it?) between going deep and getting sky-limited exposures. Expose too long for a given capturing medium (whether DSLR or CCD), and you will have washed out sub exposures. The exposure duration threshold here is really up to the discretion of the imager, the imaging scope and setup,
and the light pollution characteristics of the site at which the session was conducted. For my location in the balcony, I am limited 10 minutes colour channel exposures. Any longer and the exposures are washed out. Washed out means the histogram profile of the exposure is all cringed up to the right, and stars are equal brightness with the sky background. No amount of vigorous processing can correct this. When the full moon is up, this is limited to 5 minutes. For narrowband, i have tried up to 30 minutes of exposure in HA, and it is still not washed out. For darker sites, these numbers would be bigger. I have not personally evaluated the sky-limited exposures for my DSLR, but I think it cannot go more than 5 minutes according to a specific ISO setting. So how to go deep? Deep would be as long as you can obtain sky-limited exposures, which one would need to evaluate for your particular system. If it is within a few minutes, then perhaps, with good drift alignment and stable conditions (no wind, etc), autoguiding may not be needed. It is important to have good gears too, then even with autoguiding, the software do not need to have a high frequency rate of monitoring for the guide star.
Another factor comes into mind as well -> imaging focal length
As one embark into higher f.l., you could have an increment in general sky-limited exposures, but at the same time, one would need to take greater care in ensuring autoguiding is done properly.
Popular autoguiders in the market can be had from Yankee Robotics (Nugget), CCD-Labs (QHY), and very soon, SBIG (again).
ST-4 is pretty good. And it's quite inexpensive thesedays.rcj wrote:actually BOTH Meng Lee and Vincent is right! gee. haha
there is a compromise (as always isn't it?) between going deep and getting sky-limited exposures. Expose too long for a given capturing medium (whether DSLR or CCD), and you will have washed out sub exposures. The exposure duration threshold here is really up to the discretion of the imager, the imaging scope and setup,
and the light pollution characteristics of the site at which the session was conducted. For my location in the balcony, I am limited 10 minutes colour channel exposures. Any longer and the exposures are washed out. Washed out means the histogram profile of the exposure is all cringed up to the right, and stars are equal brightness with the sky background. No amount of vigorous processing can correct this. When the full moon is up, this is limited to 5 minutes. For narrowband, i have tried up to 30 minutes of exposure in HA, and it is still not washed out. For darker sites, these numbers would be bigger. I have not personally evaluated the sky-limited exposures for my DSLR, but I think it cannot go more than 5 minutes according to a specific ISO setting. So how to go deep? Deep would be as long as you can obtain sky-limited exposures, which one would need to evaluate for your particular system. If it is within a few minutes, then perhaps, with good drift alignment and stable conditions (no wind, etc), autoguiding may not be needed. It is important to have good gears too, then even with autoguiding, the software do not need to have a high frequency rate of monitoring for the guide star.
Another factor comes into mind as well -> imaging focal length
As one embark into higher f.l., you could have an increment in general sky-limited exposures, but at the same time, one would need to take greater care in ensuring autoguiding is done properly.
Popular autoguiders in the market can be had from Yankee Robotics (Nugget), CCD-Labs (QHY), and very soon, SBIG (again).
