Dumbbell Neb

[Stu Wilson]

My first go at Dumbbell Nebula trying out my new guide cam setup.

The image is only 6 x 5min subs and 5 darks but as far as I can work out the guiding seems to be working.

[Stu Wilson]

Last nights attempt with 21 x 5min subs

[wimvb]

Nice result. What hardware and software do you use?

Btw, darks add noise to the image. To keep the added noise down, increase the number of dark subs that make up the master dark.

[Stu Wilson]

200p skywatcher with NEQ6pro mount orion starshoot as guide and canon 650d dslr. Use DSS and Photoshop.

[newbie alert]

1 hour ago, wimvb said:

Nice result. What hardware and software do you use?

Btw, darks add noise to the image. To keep the added noise down, increase the number of dark subs that make up the master dark.

Thought that the darks subtracted the noise from the image

[Starwiz]

9 minutes ago, newbie alert said:

Thought that the darks subtracted the noise from the image

Only if you have enough of them stacked to cancel out the random noise in each dark frame itself.  Hence, the master dark.

[Starwiz]

BTW, some advocate not using dark frames with a DSLR due to the wide range of temperature differences in the lights and darks.

[wimvb]

Noise, being random, can't be reduced by subtraction. Rather, if two noisy images are subtracted, the noise actually increases. But if you stack images, noise averages out. What a dark master does is eliminate hot pixels (which are not random) and amp glow. Bias frames eliminate the read pattern of the sensor. This is sometimes referred to by the misnomer "fpn", fixed pattern noise.

Noise can only be reduced in the final image by averaging (calibrated) sub frames.

Because hot pixels and amp glow are very temperature dependent, and dslrs don't have a temperature control, dark frames may not completely eliminate these defects. Some find it therefore easier to not use darks, but remove hot pixels through processing.

For cooled cmos/ccd, the situation is entirely different.

[gorann]

3 hours ago, wimvb said:

Noise, being random, can't be reduced by subtraction. Rather, if two noisy images are subtracted, the noise actually increases. But if you stack images, noise averages out. What a dark master does is eliminate hot pixels (which are not random) and amp glow. Bias frames eliminate the read pattern of the sensor. This is sometimes referred to by the misnomer "fpn", fixed pattern noise.

Noise can only be reduced in the final image by averaging (calibrated) sub frames.

Because hot pixels and amp glow are very temperature dependent, and dslrs don't have a temperature control, dark frames may not completely eliminate these defects. Some find it therefore easier to not use darks, but remove hot pixels through processing.

For cooled cmos/ccd, the situation is entirely different.

Or suppress hot pixels by dithering

[wimvb]

1 hour ago, gorann said:

Or suppress hot pixels by dithering

Of course. If hot pixels always turn up at the exact location, they can't be completely removed in processing. (Wish I had a mount with that good stability and repeatability.)

[Stu Wilson]

Interesting comments from all and cheers.

Im just starting out down this guided and imaging route so bare with me.........

[gorann]

15 hours ago, wimvb said:

Of course. If hot pixels always turn up at the exact location, they can't be completely removed in processing. (Wish I had a mount with that good stability and repeatability.)

 

7 hours ago, Stu Wilson said:

Interesting comments from all and cheers.

Im just starting out down this guided and imaging route so bare with me.........

Forgot: If you are using PS, then the "dust and scratches" filter can be very effective in removing hot pixels - just have to play with the settings so you do not mess up the stars.

[Stu Wilson]

Cheers ill try it