The Owl and the surfboard

[gonzostar]

Hi

This image was taken on Wednesday 

96 mins worth of 4* lights.(including flats, bias and darks)

Used Canon 450d DSLR (un-mod)

With the 102 ES APO refractor with a AVX mount.Stacked with DSS and then "processed" in PS

Any tips with processing gratefully accepted.

Cheers for looking

Dean

 

[wimvb]

Nice!. A bit noisy, but if you have the opportunity to revisit this target and get more subs, you can get the noise down.

[gonzostar]

thanks Wim. 96mins worth of subs! how much more do i need  I know some people do 2 hours +.  I s there a relationship between the amount of subs against noise? I guess i am just impatient and think new night new object 

 

Cheers

Dean

[wimvb]

There is a relationship: noise decreases with increased number of subs, specifically with the square root of the number. 4 times as many subs halves the noise.

But also: 4 times longer exposure halves the noise. (Well, about; noise introduced by the camera, read noise, isn't decreased)

That's why you'd want to go for long subs and lots of them.

To make it easier to image the same target on different nights, you can align the camera with the RA axes. Just take a 20 s exposure of a bright star while you slowly slew the mount in RA only. Check if the star trail is parallell to the edge of the image. Rotate the camera and take new exposures until it does. If you image on several nights, subs may be shifted, but not rotated. Depending on how accurately you can point your mount, the amount of shift will be more or less.

[gonzostar]

that makes sense. Also because i have to use a CLS filter for 4 min exposures I'm i right in thinking the more subs aldo the better chance of brinigng out some colour?

[wimvb]

The CLS filter shouldn't cut too much colour, it depends on the characteristics. Most mainly cut the light from sodium and mercury lamps.

More subs will bring the noise down and allow for more aggressive processing, including colour saturation.

With my setup I find that if I don't expose long enough, I can see the read pattern of the camera (thin vertical lines in the background). This is, for me, a telltale sign to increase exposure. Getting the right exposure is a balancing act. Too little will reveal noise. Too much can give bloated stars or star trails.

[ollypenrice]

On 31/05/2017 at 00:44, gonzostar said:

thanks Wim. 96mins worth of subs! how much more do i need  I know some people do 2 hours +.  I s there a relationship between the amount of subs against noise? I guess i am just impatient and think new night new object 

 

Cheers

Dean

It's quite common to see single panel images with over 20 hours of data. AP is like that, but not all targets (thank goodness) need that much!

Olly

[gonzostar]

Thanks Olly I am thinking of doing mono images eventually. Now that guiding is slowly improving. However i am concerened about light pollution in my area. Thats why i have stuck to my DSLR and LP filter for so long, and  20 hrs of imaging would take all year here!  

[wimvb]

On 2017-05-31 at 00:44, gonzostar said:

thanks Wim. 96mins worth of subs! how much more do i need  I know some people do 2 hours +.  I s there a relationship between the amount of subs against noise? I guess i am just impatient and think new night new object 

 

Cheers

Dean

Don't think of imaging multiple targets per night, but rather multiple nights per target. If you can have twelve good images in one year, that will be a good year.

[AKB]

5 minutes ago, wimvb said:

Don't think of imaging multiple targets per night, but rather multiple nights per target.

Unless, of course, you are into EAA, when it's all about just that. 

[gonzostar]

Yep your right Wim and Olly Its about quality not quantity. Lots of data it is then  Isnt there a graph to show number of frames against noise background?

 Sorry no idea what this EAA is?

 

Cheers

Dean