Mix different length subs?

[RogerTheDodger]

Are there and pros/cons of doing this?

[steppenwolf]

With careful blending, this can be very effective, especially on objects like M42 which have a wide dynamic range.

Here's a really good tutorial from a master!

[RogerTheDodger]

Thanks Steve, I'll have a read through that

[ollypenrice]

The tutorial is excellent and the technique the best I've tried. However, it is usually not necessary to use different sub lengths, M42 being the classic example of when it is. One sees lots of beginners mixing arbitrary collections of sub length with no coherent plan in mind and this is pointless. Make your subs as long as the guiding, the LP, the camera thermal noise and the point of saturation will allow. DSLR users might find short subs for star colour a help though.

Lodigruss's technique can also be used on different stretches of the same data, something I do often for galaxy cores, for example. Sometimes I'm lazy and just put the short 'core' stretch under the main stretch and use a feathered, low opacity eraser to remove the saturated parts.

Olly

[RogerTheDodger]

As a thought, is it ever an advantage to stack subs of differing lengths? or does it muck up the averaging?

[ollypenrice]

As a thought, is it ever an advantage to stack subs of differing lengths? or does it muck up the averaging?

I certainly wouldn't do it. I'd make different stacks of different sub length - and then only rarely. This image of the Pleiades had shortest exposures of ten minutes at F3.9 with a sensitive Atik 4000 camera. While the bright cores are over exposed, you have to look at other images of the cluster and wonder if it is really possible to get much greater control;

http://ollypenrice.smugmug.com/Photography/Widefield-images-including/i-DPrc68n/0/X3/M45-COMPOSITE-FIN-sRGB-X3.jpg

Olly

[Psychobilly]

If you using DSS have a look at Entropy Weighted Average Stacking...

You still need a decent number if sub at each exposure length...

Peter...

[RogerTheDodger]

Thanks Both, much to think on during the cloudy nights...