Imaging globulars tips

[bomberbaz]

I want to image a few globulars and looking for tips to stop them blowing.

My thoughts are lots of very short exposures but not sure if I should alter gain.

Tips please on this using a 72ed and 183mc pro. 

[michael.h.f.wilkinson]

I used a lot of short exposures on my ASI183MC-Pro to get this on M13, in just 1h 38.5 minutes exposure, I think a mix of 60 s and 30 s exposures, but I was using a bigger scope (6" F/5 Schmidt Newton)

[bomberbaz]

1 hour ago, michael.h.f.wilkinson said:

I used a lot of short exposures on my ASI183MC-Pro to get this on M13, in just 1h 38.5 minutes exposure, I think a mix of 60 s and 30 s exposures, but I was using a bigger scope (6" F/5 Schmidt Newton)

That's very nice michael, controlled the stars very well indeed. 

Did you use unity gain and a UV/IR type filter?

Steve

[michael.h.f.wilkinson]

9 hours ago, bomberbaz said:

That's very nice michael, controlled the stars very well indeed. 

Did you use unity gain and a UV/IR type filter?

Steve

I think I was using a luminance filter. I would have to look up the gain settings

[ollypenrice]

There's no point in using short exposures if you don't need them and it's easy to see if you do. Take a test sub and read off the brightness value of the brightest part. If it's not saturated in linear (unstretched) form there is no need for it to become saturated with careful stretching. Leaving yourself a bit of a margin would be helpful, though.

With globulars, it's all in the stretch if you're not saturated. A handmade Curve with a heavy lift at the bottom and flattening early is what's needed.

Alternatively, you can do two stretches, one gentle to keep the core controlled, the other hard to bring in the outer stars, and blend them using a high dynamic range technique. Just mixing long and short in a single stack won't solve any problems. You do need an HDR blend. Photoshop has one built in, there are proprietory ones available, or you can use layer masking. I use this method in AP: https://www.astropix.com/html/processing/laymask.html

Olly

[michael.h.f.wilkinson]

I should add I was using short exposures mainly because I hadn't got guiding to work properly. I just used exposures that worked just with tracking. It did work