photoshop..mrngbss wrote:nice and sharp! Which software did you use to stack the 4 frames?
Omega Centuari
When exposure gets longer, tracking errors and field rotation sets in. That's where polar alignment and autoguiding setup is needed. it will get really messy. A tracking mount is not really enough for long exposure astrophotography.
Photo Album:
http://www.flickr.com/photos/14113965@N03/
http://www.flickr.com/photos/14113965@N03/
but why do we still need long exposure astrophotography thesedays?Meng Lee wrote:When exposure gets longer, tracking errors and field rotation sets in. That's where polar alignment and autoguiding setup is needed. it will get really messy. A tracking mount is not really enough for long exposure astrophotography.
A DSLR with decent exposure + stacking + magic of image processing still gives pretty good photos.
think Meng Lee is referring to minutes long exposure. Nowadays much can be done with 10 minutes subs alone...and then stacking. You don't need to expose single subs of 1 hour like in film days. nevertheless there are still ccd imagers who are engaging longer duration subs to obtain deeper images. this is still the only way to extract faint data. What is not there on the initial sub exposure can never be 'magically' conjured up even with stacking. stacking in this case is useful only because it suppresses the noise and increases the dynamic range in contrast values between (for example) the very faint parts of a nebula and the resultant noise floor of the image.
Let me supply an example. Suppose there is a tiny galaxy in the FOV and the individual subs is too short such that there is not even have 1 electron in the pixel well where the galaxy is, then no amount of stacking will bring that galaxy into the pic. I hope this is a suitable example to illustrate why long sub exposures get you deeper.
In light polluted places the subs are mostly controlled by skyglow saturating the sensor.
In light polluted places the subs are mostly controlled by skyglow saturating the sensor.
Photo Album:
http://www.flickr.com/photos/14113965@N03/
http://www.flickr.com/photos/14113965@N03/
ok...this type is for you to handle. For us, we are not going that direction. Don't have the $$$ for it also.rcj wrote:think Meng Lee is referring to minutes long exposure. Nowadays much can be done with 10 minutes subs alone...and then stacking. You don't need to expose single subs of 1 hour like in film days. nevertheless there are still ccd imagers who are engaging longer duration subs to obtain deeper images. this is still the only way to extract faint data. What is not there on the initial sub exposure can never be 'magically' conjured up even with stacking. stacking in this case is useful only because it suppresses the noise and increases the dynamic range in contrast values between (for example) the very faint parts of a nebula and the resultant noise floor of the image.