Focusing on stars in AltairCapture, manually.

This is about manual focusing using those opposable thumbs and is aimed at the beginner.

To focus manually, you need a reasonably fast frame rate so you can see the effect of turning the focuser knob on the screen. The problem is that stars can become quite faint at less than a second exposure, making it more difficult to see what’s going on. Here are some tips to get a better star-image to work with.

Start off with a relatively long exposure duration. An out-of focus star will appear as a large “blobby” thing which can be rather faint. You can start off with 3-5 secs exposure to find the blobs against the background sky, and then try turning the focuser knob one way or the other so that the blobs decrease in size. Now you know what direction to turn the focuser knob.

As your focus gets better and the blobs condense to points, you can decrease the exposure time. Eventually you’ll have small star points.

Sometimes it helps to increase the gain and change the histogram settings:

Gain. Increase the gain in the gain menu to amplify the signal. (Equivalent to ISO on a DSLR camera). Go on – dial it up to full to see what happens!

gain-menu

Histogram stretch. Open the histogram menu on the left. A graph appears, which will “react” in real time as the camera picks up light. Colour cameras display separate peaks on the graph for each colour, mono cameras just show a grey graph. The graph represents intensity levels of the camera pixels against their volume. Intensity runs along the horizontal axis from left to right, right being the most intense. Height shows the relative number of pixels with this value. Where there’s a peak, you have a lot of pixels with high intensity. You may not see anything on the graph if the image is very dark, so try it in daytime or shine a light into the lens just to see the graph move, and to get a feel for the interface.

histogram-unstretch

You can set the portion of the histogram which is displayed by moving your mouse on the edge of the graph, and then clicking and dragging the little line from the righthand edge towards the left. This will “stretch” the histogram (or compress it depending on your point of view), and it will dramatically brighten the image in real-time. The same effect can be achieved by typing a lower value, say “30” in the “Right” box. Clicking “Defaults” will reset the histogram:

histogram-stretch

The effect on the image is quite dramatic, and faint objects (including stars) will appear very intense. Noise will appear too – this is perfectly normal.

If you have a mouse-wheel you can use the hand icon at the top of the screen to centre a bright star and use the mouse wheel to zoom in.

zoom-hand

Cameras have very small pixels, so you will always see a “blob”, even at hig magnification when the star looks focused at normal preview scale. In fact, at around 400x the star may look very big and “blobby”, and it may jump around a bit due to air currents (seeing) and your mount’s tracking errors (periodic error), so take your time. The trick is to get the blob as small as possible, but it will never be perfect, and it will always change a little due to to changes in air density above the telescope. One often ends up focusing on an “average” position they feel is best. Every time you touch the scope, you’ll cause vibration which will need to settle a bit before you can make the next adjustment. You may develop a rhythm where you tweak the focuser knob, then wait to see the effect, and so-on. Some imagers can take around 15 minutes to focus, some even more. You’ll get a feel for it. When you’re focused, lock your focuser if it has a locking thumbscrew (which most Altair scopes do) and then you can apply more appropriate settings for long exposures. Focus points can change as the scope cools or warms up too so you may need to re-focus at some point during the night.

A Bahtinov mask makes the whole process easier by creating a special star pattern.

Creating Mosaics & Stitching Images with AltairCapture

Creating Mosaics & Image Stitching in AltairCapture (shortcut = Shift+T)

Stitching or “Mosaicking” combines multiple photographic images with overlapping fields of view to produce a single high-resolution image. Nearly exact overlaps between images and identical exposures are required to produce seamless results. Using AltairCapture it is possible to create digital maps, enhanced microscopy or medical images, or multiple image super-resolution astronomy images. Resulting images can be projected onto Plane, Cylindrical, Spherical, Fisheye, Stereographic, Mercator or Transverse Mercator map surfaces. The Default is Cylindrical.
AltairCapture has 3 stitching methods Video Stitch, Image Stitch and Browse File Stitch.

Method 1, Video Stitch:
When the video window is active, choosing the “Process > Stitch” command will invoke the video Stitch dialog as below:

altaircapture-stitching-1

Snap: Click to capture image from camera. One should try to move the slide to a position to capture the desired images. As you move the sliders, the next image should have some overlaid areas with the previous image.
Reset: When an image or images are captured, the Reset button is enabled, clicking Reset will remove all images from memory. It will be disabled when there is no captured image in memory.
Snap: Snaps a single image from the camera.
Cancel: Clicking cancel stops the stitching process.
Next>: Clicking Next> go to next step in the process.
Finish: Clicking Finish will begin to stitch the captured images according to the settings you’ve just made.

Stitching Methods:

stitch-method-selection

Panorama Straighten: Controls the image stitching direction. It can be Horizontal, Vertical or None. Default is Horizontal.

Projection Type: For image segments captured from the same point in space, stitched images can be arranged using one of various map projections. AltairCapture includes Plane, Cylindrical, Spherical, Fisheye, Stereographic, Mercator or Transverse Mercator map projections. The Default is Cylindrical which can be useful for planetary imaging.

Seam Finder: Controls the seam matching and finding method, AltairCapture includes None, Voronoi Diagram, Graph Cut Color or Graph Cut Color Grad. Default is Graph Cut Color.

Exposure Compensation: Exposure Compensation is required between images to minimize exposure differences. AltairCapture includes None, Gain or Blocks Gain Exposure Compensation methods. Default is Blocks Gain.

Bundle Adjust: Bundle Adjustment is an algorithm which attempts to solve the problem of simultaneously refining the 3D coordinates describing the scene geometry, as well as the parameters of the relative motion and the optical characteristics of the camera(s) employed to acquire the images, according to an optimality criterion involving the corresponding image projections of all points. AltairCapture can use Ray adjust or Reprojection error bundle adjustment methods. Default is Ray adjust.

Stitching Parameters:

stitch-parameter-selection

Match Confidence: 1~100, Default = 65.
Panorama Confidence: 1~100, Default = 100.
Match Strength: 0~100, Default = 25.
Blend Strength: 0~100, Defaults = 5.
Defaults: Clicking Defaults will set all parameters to Default.
< Back: Clicking <Back will return to the previous step.
Finish: Clicking Finish will begin to stitch images according to the above setup. After the Finish button is clicked, AltairCapture will start to stitch, and a progress dialog pops up.
Cancel: Click to cancel the stitching process.

The final stitched image will be created in a new image window which can be saved.

final-stitched-image-tiled-junctions

In the stitched image, there are can some junctions visible between areas; these are caused by realtime changes among the  image edges in either direction, caused by air-motion, for example. Increasing the amount of overlap can help reduce this. In most situations this isn’t visible, but some touchup might be required in Photoshop or another imaging application. 

Method 2, Image Stitch
If a set of images are opened in AltairCapture, for example stitch001.jpg, stitch002.jpg, stitch003.jpg, and stitch004.jpg are opened as shown below:

image-stitch-4-panel-mosaic

Then choosing the Process > Stitch command will invoke the Image Stitch dialog boxes as follows:

The Available Images box: After you click Snap, the images opened in AltairCapture in new dialogue boxes, and are held in memory. Here, 4x images are listed in the list box. Click the image file name to select the files to be added to the Selected Images for stitching:

image-stitch-select-images2

The Selected Images box: The images selected for stitching. Use Add>> to add the Available Images to the list.

image-stitch-select-images1

Add>>: When single or multiple images are selected and highlighted in the Available Images window, the Add>> button will be enabled. Clicking Add>> will add it or them into the Selected Images list for processing.
Add All>>: Clicking Add All>> will add all of the Available Images into the Selected Images list for processing.
Remove: When an image or images is or are selected and highlighted in the Selected Images list box, the Remove button will be enabled, click Remove will remove it or them from the Selected Images list box.
Clear: Used to clear all images in the Selected Images list box.
Cancel: Cancels the stitching process.
Finish: Clicking Finish will start to stitch the captured images according to your chosen settings.
Next>: Clicking Next> will go to the next step.
(The remaining steps are the same as the Video Stitch process with the final stitched image being shown in a new window when complete).

Method 1, Stitch from browsed files:
Click the Folders Sidebar to activate the file browsing menu. Double-click the right directory to show the images under the directory in the Browse window. Choosing the image files to be stitched and then clicking the right mouse button will display the context menu. Choose the Stitch sub-menu to start the image stitch operation (One can also choose using Process>Stitch, after the files are selected in the Browse window)

browse-window-stitch

After the Stitch command is selected, the usual Stitch dialogue will pop up, and the rest of the process is the same as the other stitching methods.

Altair Planet Killer 685nm IR Pass Filter – test with GPCAM camera

Ever looked through a telescope with a high power eyepiece? You’ll notice the air shimmer, kind of like a “heat haze”. What’s happening? Well, your telescope is magnifying air currents, as well as the distant object you’re trying to view. Heat causes convection currents in the air, changing the air density and that causes distortion by bending light passing through it.

By using your GPCAM in video mode you can “freeze” this apparent motion and capture a video file in either .SER or .AVI format. Once you have that you can process the file to discard the bad images and then stack and align the good ones into a much sharper image which averages out the distortion.

Of course if you start of with sharper images in the first place, you’re going to get an even sharper end result!

That’s where the Altair “Planet Killer” 685nm IR Pass Filter comes in handy, which is best used with a monochrome camera.

IRP-685-450w

It allows infra-red light beyond 685 nanometre wavelength to pass through the filter and it blocks the shorter wavelengths.

Altair FILTER INSERT IR-PASS-685NM

Shorter wavelengths are the most affected by these air currents (often referred to as “seeing”), but the longer deep red and infra-red wavelengths aren’t as affected.

So your video appears noticeably sharper and more contrasty, making it easier to focus. And of course if you stack these images you get a much better end-result. Use AltairCapture or SharpCap to capture the video and Registax or AutoStakkert to stack and process this into sharp images.

What’s more, you can get better results that you otherwise would when the object is low on the horizon (you’re looking through more air after all). You can also get a darker background when imaging during the daytime.

We send an Altair Planet Killer filter to Robin Glover (author of the GPCAM-compatible SharpCap image processing software) to try out on his Altair GPCAM Mono camera. Robin used his Altair 10″ F5 Reflector without any Barlow lens to capture some video of the moon in the early morning.

According to Robin “Conditions were windy and I had to have the side of observatory folded down, so the scope was catching the wind quite a bit. The moon was fairly low by this time and the sky somewhat hazy at that altitude, so not perfect conditions by any means. The filter definitely has an impact on the moon – more contrast and easier to obtain a good focus and be sure that it is in focus.”

Lunar image without Altair Planet Killer filter:

without_09_27_53_g3_ap68

Lunar image with Altair Planet Killer filter:

with_09_24_28_g3_ap66

Both images were processed through AutoStakkert – best 100 frames selected from 1000, same settings used in both. No sharpening or other post-processing applied. The original 16 bit .PNG files were converted to .JPEG, with same compression to save space. Exposures 1.2-10ms.

Attaching the Planet Killer filter to your Altair camera couldn’t be simpler, just screw it on to the nosepiece. Mono cameras with lenses ship with two CS-Lens adapters with built in filters. Make sure you have the “clear” CS Adapter/Optical Window attached and not the UV/IR Blocking one (pinkish hue). Otherwise you will block out the IR light your’e trying to pass! Here’s a diagram:

GPCAM-PLANET-KILLER-FILTER-DSC_5194-600w

Want to experiment? How about L-RGB planetary imaging with two cameras and one filter! 

You could use your Planet Killer filter as the Luminance filter when doing L-RGB imaging with a mono camera, filter wheel and Altair Premium Dichroic LRGB CCD filter set.

Or, instead of using a filter wheel, you could even combine the data from your mono GPCAM and Planet Killer filter with colour data from a colour GPCAM!

The possibilities are endless…