June 2015

Business part of meeting was limited (so as to spend most of the time on the main topic) but we have 2 new members who joined over the last month. Had about half a dozen visitors tonight; some came after seeing our booth at Sunfest. 24 people total at this meeting.

Next month’s meeting: Telescopes, basic to advanced, by Evan Zorn, with several “samples”

Night viewing this month:

Conjunction of Jupiter and Venus, peak date June 30 (within 3 degrees of each other on that date)

June 1 and 29, moon within a few degrees of Saturn. Saturn in opposition with rings tilted if can photograph.

Summer triangle—Altair, Deneb, Vega (Summer Triangle used for navigational purposes before GPS!)

Globular clusters—Sagittarius beehive cluster

Astrophotography 101 Part 2—Basic Image Processing by Rick Bryant

Overall: This is a learned skill and reflects your own philosophy on astrophotography.

Using just a few tools will take care of 80-90% of your processing needs. Rick uses Photoshop.

Gray scale and color scale:

From gray/black at one end to the colors on the other—red/green/blue channels, each with some level of intensity

Linear (raw sensor, scale from 0-200) vs. non-linear (scale 0-800)

Cameras are non-linear

Your eyes, JPEGSs, TIFFs and Photoshop files are non-linear

Destructive vs. non-destructive processing, both on scale from 0-800

Clipping shadows or highlights—you can make image more black or white by clipping shadows or white highlights around stars or comet tails

Stretching the mid-tones

Bit depth: how many bits in each of the blue/green/red channels. Your camera uses 8; software will use 12 or 16.

Basic workflow elements:

Combine (stack) images

Linear to non-linear conversion

Scientific image editing (optional)

Artistic image editing (optional)

Most images will benefit from artistic editing using the Photoshop that may come with your camera.

Basic Artistic Transforms and Clipping

Bit depth

Histograms

Curves

Exposure

Color saturation

Rick demonstrated basic image editing and transforms with JPEG images and stacked raw images.

Histograms show relative pixels in each color intensity.

Stretching the mid-tones; use mid-tone slider to stretch colors.

With curves, you can use an S curve to bump up the mid-tones.

You can make blacks darker but not cropped; whites whiter but not clipped

With exposure, you can increase or decrease to make blacks blacker and increase star glow

Fine-tune colors—cyan/magenta/yellow; red/green/blue. Can work with hues; big gross control. Saturation is vividness of colors, ranging from no saturation (black and white) to 100% saturation, which would be the effect of a 1960’s or 1970’s disco. Too much saturation may give your images too much pop.

Brightness and contrast denotes sharpness of edges between intensities.

Example of JPEG image of moon, comet and trees, taken in Sooner Park:

Assume 8 bits; go to 16

Use histogram to pull highlights over some; want to keep trees black. Stretch the mid-tones. Take out some of the green.

Work with curves

Work with saturation

Cropping

Example #2: Stacking, with nebula picture taken years ago

With Photoshop could stack 7-10 images; more than that, use Deep Sky Stacker

Do as much correcting as can in raw converter.

Change exposure to bring out more of the mid-tones

Then match to first image. Match in color and exposure in the raw as much as you can.

Let the raw converter take each image and put into into one

Two basic techniques: linear and working in layers.

Highlight, copy, go to the first image, and paste. Any layer will affect the image underneath it. You can use an opacity tool and move it to align the images. If you do opacity 50% and transparency 50% you can see half of both. Then continue doing this for each layer up to the final background; you can’t change that . With (say) 4 images, you will end up with 100% of the background layer, 50% of the one above it, 33% of the next layer and 25% of the top layer.

Then take the composite image, make it 16 bit, stretch the mid-tones and get rid of some of the darks.

Then look at curves; perhaps do an S curve.

Deep Sky Stacker works in linear mode. Have to manually do a linear to non-linear conversion.

For his last example, he did a composite of 3 pictures of a solar eclipse. He created a new file to do this.