Stacking advise required

As a total beginner in this area, trust me when I say I know nothing!

I took a number of moon shots a week or two ago using my 30D with a 100-400L and Kenko 1.4X Pro300 converter, 15 of them from memory, just taking shot after shot with everything set on manual. Just sat next to the tripod continually pressing the shutter release cable.

Surprisingly, considering that there was a perfectly clear sky and the exposures were identical, there is quite a lot of difference between the best and the worst which I don't understand. However thats not really what I need advise on. When you start stacking images, what amount of opacity do you give each layer? I assume there is some kind of formula to calculate this? I tried using the deep sky star stacking software, but it rejects all but one of the images, I assume because it is designed to be used for star fields it will not work on anything else?

So assuming a totally empty brain (stop that sniggering in the back row), I'd really appreciate some general guidance.

I forgot to mention I use Photoshop v7. It has virtually everything that CS4 offers, but lacks anything labelled "smart" and only offers 8 bit layers.

I've been stacking Moon pictures for quite some time, so I think I can offer some advice.

First, think about why you stack moon images. It's not for the same reason the deep sky photographers stack. They want to bring out dim objects and that's not an issue on the moon. It's either bright or black. You stack moon shots to reduce noise of two types: sensor noise at the pixel level and smearing due to atmospheric turbulence. The scale of this smear is also very small, only a few arc seconds or a few km at the distance of the moon.

Stacking reduces the noise and the smear, but only when you're at high focal lengths. Under 1000 mm, you won't see any benefit. If you keep your ISO low, like 100, you won't have enough noise to matter and, with these short focal lengths, you won't notice any image smear from turbulence.

Above about 1000 mm, you'll start to see some benefit. 2000 mm is the longest FL I use, and that requires a Barlow lens on a 4 inch refractor. At that image scale (the moon would be about 3800 pixels across!) you do see some subtle benefits of stacking. A photographer will notice the decreased noise, but it's pretty slight.

Just a note, above about 1600 mm the entire full moon disk won't fit in an APS-C frame. But you can always stitch.

Now, how to stack for the moon. In Photoshop it's easy, go to File:Scripts:Statistic​s. Set stack mode to "mean" and check the box "attempt to automatically align sources" or you'll get modern art instead of a nicely-aligned picture.

So stacking is very easy in Photoshop, but you won't see any improvement unless you're using a telescope.

If you stack, use only your best images. I suspect your differing images might be due to autofocus?

I don't think you will find the script Rick refers to in Photoshop 7.

The correct opacity setting in Photoshop for stacking with layers is 1/N, where N is the position of the layer, with the background layer having N=1. So the second layer is 1/2 (50%), the third is 1/3 (33%), etc. After five or six layers you can merge them into a single layer and start adding again. This results in an averaged stack, not a median stack, but it works well for most images.

I'm not sure which deep sky stacking software you tried, but if you tried DeepSkyStacker, it definitely won't do the job well for the moon. DSS needs to find stars in order to perform the alignment. There is another free software application called Registax that works well for the moon. It allows you to select a feature (crater, mountain, etc) to align on, and optionally allows you to select multiple features to correct for scaling and rotational alignment variations. And it allows you to set the Quality value for image rejection, which means you can keep all of the frames with a low enough Quality value or reject the poorer ones with a higher value. Google "registax" to find it.

Don

Follow and read the links provided here in the "Astronomy Discussion" section . Baz has a great way for stacking with examples .

https://photography-on-the.net/forum/showthre​ad.php?t=766644

Thanks fellas, thats given me something to think about.

By the way, I had everything in manual, even the focusing, so AF was not causing a problem.

Hi there,

Stacking photos aims for better signal to noise ratio. When twitching "wavelets" to reveal detail noise appears quite fast. the more you stack, the more you can abuse the wavelets.

I suggest you try "registax" and one if the (many) excellent tutorials available in several languages. Aligning the pictures can be a pain, even a very basic tracking device will immensly help. I will gladly help should you have more specific questions - I've spent many a night doing this...

ecce_lex,

Sorry, shows how little I know, but what do you mean "wavelets"?

I've downloaded a copy of registax and just one of seemingly millions of tutorials. Have not given it a try yet.

Hello,

Registax breaks the photo in six layers each corresponding to a level of detail - from large (this will alter the shape of the moon) to very small (twitching this will influence very small features of craters, such as irregular rims). Registax calls these 6 buttons "wavelets". It's basically a sharpening tool.

In short, the process goes like this:

Your photos of the moon will be registered by registax. It creates a list of some sort for itself.
Then the program will attempt to align them - you choose one / several points of alignement, better in the more contrasted zones.
Registax then stacks them according to the method you specified (check tutorial for extensive description, or even the help file).
Then you will sharpen using the 6 "wavelets" - results ARE dramatic if the frames were stacked properly. Do not abuse it, noise is ugly if you do, a good sign of immoderate use is a white rim around the moon.
You can rotate, set contrast etc., but Lightroom does that better.

Ask away, happy to help out.
Good luck

[for large files / video, your PC needs to be of the "gamer" kind]