Landscape astrophotography with IRIS

13 November 2015. Comments .

Оглавление #

Introduction #

On the web:

This post aims to teach how to apply the power of image stacking and noise reduction to a landscape astrophotography with ordinary DSLR. Wide-field astrophotography has its own features: rotating sky and motionless landscape are present in the frame. Astronomers who shoot the sky do not face this problem, hence usually people don’t talk about it. I’ll do.

The post is for: photographers who is familiar with RAW, who knows how to use masks in GIMP or Photoshop. For those who have already tried night photography, who have been charmed by the night photography and crave more. Probably it is not the best idea to start learning how to shoot night photos with this post; first try something less complicated.

Necessary equipment: camera, shooting in Raw; lens; tripod; computer with Windows OS.

Higly recommended to have: remote control (I use wired PiXeL TC-252 N3 with Canon 6D) or smartphone application for remote control.

What you will do: choose the place with excellent starry sky; shoot 30–50 frames with right parameters; register and stack frames in free software IRIS; complete in photo editor like Photoshop or GIMP.

I decided to write this a post after I got the following picture (click and hit F button for bigger size):

Canon 6D + Canon 24mm f/1.4L II @f/2.5; ISO 16000; 15 frames × 15 sec; darks, offsets.

This image is created using 46 frames. The reason why do people stack images is demonstrated by the following animation. In the animation I compare two frames: one obtained with 15 stacked frames, and the other is just one frame, processed in LightRoom.

Zoom 4:1

15 кадров means 15 frames; 1 кадр means 1 frame. I am sorry but I’m too lazy to redo the animation.

The difference in faint details is just tremendous. It’s not surprising: when you reduce noise for the single frame, computer cannot distinguish between the noise and the faint star. And that is from where the main idea of stacking images stems. Digital noise on your CCD/CMOS basically is a random signal. That means that the certain pixel in one frame is highlighted with the noise and in the other frame it isn’t. On the contrary, any star always stays in the same position (of course, after registering pictures to take the Earth’s rotation into account). That’s why the signal of the star after stacking will increase and the noise will decrease. Single-to-noise enhancement is a fundamental task for astronomers, and similar techniques is being used to process images from all the professional observatories in the world.

Here is a link to all the images which have been used to create the photo «Crimean way». You can download all the files and use them to follow the steps in this manual. Try to make the best of the single image and compare it with the result after stacking the images.

Shooting: theory #

Basic info #

Series of frames to shoot #

The importance of dark and offset series #

I wondered: is it really important to shoot dark and offset frames for our purposes? Without thinking twice I’ve made a comparison (perhaps it is not perfectly correct but still it provides some idea of dark and offset series importance). Animation shows 2 images: 15 stacked frames with subtracted darks and offsets and just 15 stacked light frames.

Zoom 4:1

15 кадров + dark&offset means 15 frames with dark&offset;
15 кадров, без dark&offset means 15 frames without dark&offset. I am sorry but I’m too lazy to redo this animation

It turned out that for 15 frames there is almost no difference. Maybe it will work differently for a lower amount of frames.

Shooting: practice #

Procedure #

What I’ve done to shoot the «Crimean way»:

Shooting tips #

Photo processing #

This part is as short as possible. See tutorial from official website. See all the IRIS commands here or here.

Finally, we came to the most important part — photo processing. In astrophotography I like the fact that during the night you can be relatively relaxed and stargaze lying on the ground next to your shooting camera. The main work starts at home.

IRIS installation & setup #

Load the files #

Create offset, dark and flat maps #

Preprocessing #

Registering images #

Stacking images #

Set the color #

Save the result #

Additional processing in photo editor #

My astrophoto examples #

In these examples you can see that IRIS can be used in very different ways. E.g., If you stack images without registering, you’ll have startrails. If you shoot the thunderstorm, you can stack images and obtain result with lightnings from different frames in one image. Don’t be afraid to experiment! In this post I told you only about 5% of IRIS capabilities. Learn more on the official website.

Originals are available at album.

The end #

Please don’t think that this tutorial covers everything. It is a good idea to have a look on the tutorial at the official website. Check out DeepSkyStacker — a freeware similar to IRIS. It works with the same light, dark, offset series as IRIS. Working with DSS is more intuitive.

I’ll be glad to answer your questions.

Good luck with shooting!