Stacking Photographs.

The how and why of making a composite photograph.

Or... How to use RegiStax.

When the shutter on the camera opens, billions of photons strike the camera's sensor. No matter what type of sensor your camera has, it is not perfect, and cannot capture all the photons that strike it. Every time you open the shutter, a different picture is captured. If you take ten pictures of the same scene, you can be comfortable that your sensor has picked up a lot more information, because it has been exposed ten times, and while each single picture doesn't catch ALL the photons, ten pictures captures most of them.

HDR photography uses a set of three pictures taken at slightly different exposures, and stacked together. This is a feature of many cameras now, and the finished HDR picture is much better than any single picture because the sensor has been exposed to the scene three times, capturing more photons than a single shot.

The weaker the light source, the more there is to be gained from stacking, and therefore stacks of more than three pictures are used to photograph the Moon and stars. Stacks of ten are common, and stacks of 50 are easily worked with, and create a fantastic product. I've heard of professionals stacking 300 photos together, but I've never attempted this! 50 is my maximum stack for now, but a stack of just ten is a vast improvement over even HDR photography - simply because there is more detail captured on the sensor in ten exposures.

Single image:

Stacked image of ten exposures:

I have resized these images differently, but the first image is actually one of the images used in the stack of ten to make the second shot.

You can see that there is a big difference in these two images. The writing on the Tardis is much clearer and more detail stands out. This is very important to get a good pic of the Moon, because of the subtle textures.

The above shot was my very first ever attempt at stacking. I was a little heavy handed on the sliders, but the effect is still pleasing.

Jupiter an moons:

How to do it.

You'll need a bit of kit called 'RegiStax'. It's available for Windows as a free download, no catches. IKR! You can find it here: http://www.astronomie.be/registax/

Scroll down the page to this entry. Click the link and download RegiStax 6.

If you think you'll use this program a lot, then install the update as well since you're here. If you just want to try stacking, forget the update for now.

Follow the instructions to install it. I don't remember any sneaky tricks - it's pretty honest software.

Once installed, you should find an icon on your desktop that looks like this:

You're ready to rock and roll!

Find a still-life study, and take ten identical shots of it. You'll need a tripod; you can't do this hand-held. If you don't have a tripod, use a pillow or beanbag (wheat-packs are great) to rest your camera on. As you'll want perfect captures, use a remote trigger, or the timer release function for your shutter to eliminate any camera shake when you press the shutter-button. Some cameras can be set take ten exposures in a row (lucky buggers).

When you have ten captures uploaded to your computer, smile, and run RegiStax.

When RegiStax opens, you'll have this on your screen. You don't need to adjust anything or check any boxes. It works right out of the box. Click on 'Select' to choose the ten images you have ready for stacking.

Now, you have to select ALL the images you wish to stack. You can either Ctrl-left click your images one by one until they are all selected. Or you can select the first in your set, then hold down Ctrl-Shift-left click the last image, to select all the ten images at once. As long as you have all ten images selected. They should be listed in the 'File name:' box. Hit 'Open' to load your ten images.

You can check all images were loaded by looking down the bottom at your frame count. If you don't have ten images, restart RegiStax and select them again.

That's the hardest part over.

Now, go to the top left, and click on 'Set Alignpoints'.

RegiStax will think for a moment, then cover your image in red dots. The green bar will move to the next icon along.

That green bar always indicates the next process is ready to be completed. Click on 'Align'.

Registax will think for a bit, then the green bar will move across to 'Limit':

Click on 'Limit'. Notice we haven't touched any of the adjustments.

The screen will change to look like the pic above. You can now press 'Stack'. It will take quite some time. Be patient. When the progress bar reaches 100% you're ready for the next step.

There is no need to save your image yet. Click on the 'Wavelet' tab above.

Now your artistic eye is needed.

Adjust the sliders for layers 1 through 6. Each of these is a different part of the wavelength. Watch the preview and just nudge all the sliders up a little bit. You'll notice the change. Fiddle with the sliders until you get a pleasing effect for your eye. I find I need a whisker more on layers 5 and 6 than the other layers.

Once you're happy with your preview, hit the 'Do All' button, which should be underlined with a green bar.

Watch the progress bar slowly climb...

When the bar gets to 100% it will stop, of course. The 'Do All' button will still be underlined, but you're done. Hit the 'Save image' button.

Give your stacked file a distinctive name. I usually add an 's' to the end of my file name - ie, 'IMG_7016s'.

Your stacked image is in full resolution. Use your normal method to resize it.

Congratulations, you just stacked your first ten images, and now have the finished product. You may decide later on that you were too heavy handed on the sliders, as I did when I first started. You get better at it as you go.

If you found this post helpful, please recommend it to others, thanks :)

Best of luck stacking. If you get REALLY stuck - you can contact me on Twitter - @tyabblemons, or leave a comment here - but don't expect miracles, I don't work for RegiStax.

Good luck!

Brad Lemon

6/07/2013