Just above the image you see a scrollbar. This is the zoom-control, you can zoom the current image from 61 to nearly 5000x magnification. This is done by a zooming algorithm and does not take much time. Try changing it to about 200x (hold the control and read the magnifications). Now go to the telescope-bar and change the FFT-space to 128, you hardly notice the change probably because 128x128 FFT is very fast. Increase the magnification to about 1500x, you will now notice that the first diffraction ring clearly shows signs (brighter parts) of undersampling. Now again change the FFT-space, first to 256 and then to 512 and notice the differences.
The step from 128 -> 256 clearly removed most of the undersampling. Creating another Scope
Leave the previous image as it is. Go to the telescope-bar and press the ADD button on the bottom. You will see the telescope-control changed from Scope 1 to Scope 2. Notice that the previous image shows Scope1 in its caption bar. Most of the images show this. Set the Lower Spherical function of Scope 2 to 0.5 wave and again press the Star-image button. This will create another starimage. If your screen allows it will be next to the previous image else it will be below the image. The new image is made active and the telescope-bar shows the aberrations. If you activate the first image again (click anywhere on the image) the telescope bar will show Scope 1 and all its settings. You can also change image 1 to show the aberrations of scope 2. First select image 1 (caption= scope1...), than select scope 2 in the telescopebar and than press the Update button on Image1 (red V). Now image1 and 2 show the same images at different magnifications. Change another aberration in the telescopebar (for instance coma) and this time press the calculate all button in the telescope-bar. This button will recalculate and update all images that are connected to scope2. Lets change image 1 back to scope 1. First activate image1, than select scope1 from the telescope-bar and then press the update button on image 1. Close Image2 by pressing the closebutton on the image2-window. Creating a double star
Our active scope is still scope 1. Press the Double Star button. To the right of image1 (active image) a double star window appears with a special toolwindow below. Also the Double Star Table button on the left of the image is activated. You will see a list of double stars that is loaded from a comma-separated-value file called (doubles.csv). You can also load other double star-files (and make your own) with the load button. The files are comma separated: Name, magnitude A, Magnitude B, Separation in arcseconds and Angle in degrees. Due to the comma-separated values you need to use "." as a decimalseparator in these files. The default double star is put at 2" arcseconds and with angle 0 and equal magnitude. If you want to choose one from the list simply click on the grey-column with numbers at the row you want to see (right-arrow appears) and the image will change to this double-star.The lists are sortable in many ways. If you click on the column-name Magn A, it will sort the list on Magn A. Shift-Click will reverse the sort-direction, if you shift-click on another column you get a multi-field sort operation.
You can also enter the separation/angle in the field on top of the tool-window. You need to press update in this toolwindow to
show that setting. The current list is a list of very close doubles at equal magnitude, click on load and select doubles1.csv for a
the Astronomical League's list of doubles (except multiples). The tool window can be closed by its close button. To reopen it again press the Double Star Table button on the double-star image. For the next step please close the double-star image. Modulation Transfer Function
Assuming we only have a starimage from Scope1 active. First select scope2 (0.5 wave LSA) and create a starimage for this telescope. Then press the MTF-button, you will see the large effect of 0.5wave LSA on the MTF. Select image1 and ... no MTF values. This image was calculated before the MTF-function became active and therefore does not show these values. To get them simply press the Update button on image 1. If you now activate image2 again you will see the caption of the MTFwindow changing and the MTF also. Close the MTF window. Remember that the MTF-values are only calculated if the MTF-window is visible or when you call the MTF-window by pressing the MTF-button. Wavefront or PupilPhaseScreen Images
Pressing the Wavefront button will show a menu with 3 choices:
-Wavefront; shows a coloured image of the wavefront-values
-3dwavefront; a 3d freely rotatable image of the wavefront-values
-interferometric: the wavefront aberrations as seen during interferometric testing Wavefront:
This image will show the PV and RMS in waves for the active telescope. Like with the star-image you can change
the active telescope by selecting another telescope from the telescope-bar and using update in the wavefront image. You can have as many wavefront images as you want (memory allowing).
3Dwavefront:
This control is very new and does not attach completely to the images yet. Activate the control (select menufunction) and then select a telescope from the telescope bar and press the calculate-all button. If you do this with scope2 you will get a nicely curved image resembling the 0.5 wave LSA. The three sliders above the image allow you to freely turn the wavefront around. Be aware that at small apertures (same applies to other wavefront images) only a few cells are containing wavefront information.
Interferometric:
The numerical value above the image controls the amount of bars visible in the image. All other functionality comparable to
standard-images.
Close all windows. Intra- Extra Focal images
Press the Intra-Extra Focal button. This will create (for the active telescope) an image of +/-2 waves of defocus (default). You can change the amount of focus with the slider on top of the image. Remember that large amount of defocus will lead to undersampling very easy. You can decrease the resolution or increase the FFT or increase the aperture to surpass this effect.
All the aberrations from the telescope except the defocus aberration will affect these images. Planets (1)
Press the Planet-button and select an image from the dialog. You can select JPEG (default), BMP or TIF images as input files. Choose the previous standard image called mars.jpg. It will be loaded into an imagewindow called planetoriginal. On the top of the image you will see the filename and the imagesize in pixels. Above this is the planetary resolution control. Planetary calculations are done at 512x512 FFT and the resolution is set in the original image. In this case the default 10 pix/arcsecond is shown but if you want to accurately show mars we need to know how big the planet would be using 10pix/arcsecond. Double click on the planet-image a cross will appear. Double-click again at the edge of the planet and do another double-click on the other side of the planet to measure the distance.The current resolution of 10pix/arcsecond assumes that mars is about 13-14 arcseconds wide. That's a possible value for mars but suppose we want to know how mars will look in june during the close approach when it is about 20" wide. You can achieve this by reducing the pix/arcsecond setting to 6.6. Now press the updatebutton in the planetoriginal. A new image appears with the aberrated mars-picture. The magnification is rather high, you can see this by activating the LRGB-controls of this image and activating the USE DIMMING checkbox. Mars will loose some light, now reduce the magnification with the zoombar until the L(uminosity) control is in the middle. This is the maximum magnification before the image starts to dim for the current telescope. Now load another planetary image, first close the previous windows. Press the Planet-button and choose JupiShadow6_4.tif, notice that the resolution directly went to 6.4. As a convention you can name your planetary images and add the resolution at the end, the decimalseparator is "_". If you want to know how big the planet is in this image you can measure it with the above methode , it should be around 43 arcseconds. Now press the Update button in this image, you will get an aberrated view of a shadowtransit on Jupiter. Planets (2)
Now we can also add the effects of refractors to planetary images. For this you will need the different wavefronts at different wavelengths. Together with the authors of the telescope design software packages ATMOS/MODAS(Massimo Riccardi/Ivan Krastev) a fileformat (*.OPD) was developed to serve as a exchange basis between design software and Aberrator. The *.OPD files are ASCII and therefere easy to create for other programmers. They start with a header-line that states wavelength(nm) and aperture(mm), after that a series of X,Y,Z values describe the wavefront.X,Y is the position of the measurement in the wavefront-screen and Z is the aberration in waves at the used wavelength. X,Y values should not have fractions and should fill a wavefront screen (for more details contact the author). To select these files you press the OPD-button on the buttonbar. That will open the OPD-dialog, now go to the directory with the set of OPD-files that came with Aberrator and select Doublet1486. You will see the header in the control above the filenames, it states 486.13,100. So this file is for a 100mm doublet generated at 486.13nm. Press the pointing hand button to the left of the BLUEOPD textbox. The filename is now transferred to the BlueOPD and will be used to aberrate the blue-plane of the planetary images. Also the fileindicator has moved 1 step down to Doublet1546, press the pointing hand next to green and do this also for red. You now have Doublet1486/546/656 as wavefront-planes for the planetary aberration. You can inspect the wavefronts by pressing the coloured OPD-button to the right of the text-boxes. Now also select UseChromaticOPD in this control and close it (closebutton). Press UpdateImage on the original planetary image.You will now see the effects of the chromatic aberrations from this design. Be aware that this approach is a simplified way of simulation. Planetary images are not made out of 3 different wavelengths in ordinary life but out of a full spectrum of wavelengths. We can however only use three in simulation. You can experiment (using ATMOS/MODAS output) with different sets of wavelengths. Close all planetary images. Chromatic effects(1)
Since we have just loaded the OPD-files we can also use them to calculate a starimage. To do this press the chroma-button. You will see a rather yellowish disc with a blue halo appearing. Again this is mainly due to oversimplifying the problem. Accurate choosing of wavelengths can be a better approach. You can also add some defocus to the image (change telescope setting to -1 wave and press calculate all). Do the same for +1 wave of defocus and notice the large differences. You can change the defocus with three controls, first the standard edit-box with up/down arrows. Second by entering defocus in mm (waves depending on focal-ratio), and third with a fast and more crude approach below the standard editbox (slider). Re-activate the OPD-window (press OPDbutton) and uncheck the UseChromaticOPD checkbox. Close the OPDwindow and press calculate all. Now again calculate for +1 and -1 wave of defocus, the images are now alike. Chromatic effects(2)
Go to the menu and select from tools the ChromaticControls. You see that only three waves are active (red lines). The graph shows the photopic (daylight) spectral response and below this you can see the colours belonging to the wavelengths. On the left is a scroll-box with all wavelenghts and checkboxes from 400-700nm. You can select as many as you want by hand. But this can be tedious so a special control is available. Change the stepsize control to 24 (nm). Now from 400 to 700nm every 24th wavelength is selected you can press calculate all (or the update on the chromatic image) to see how much that affects the images. On the right are lateral and longitudinal chromatic shifts. These are currently modelled as linear functions around the 555nm wavelength. After this close all windows again. Slice or Side view
Press the Slice button. This is new and will show the side-view of the diffraction effects. Start with the current settings for telescope 1 (set any aberration to zero). Press the updateimage button in the Slice-form.The calculation takes some time and if you have to wait too long you can always press ESC to stop the calculation. The FFT-space is default at 128, that means oversampling can easily pop up. The image size is freely controlable, only the height can not be larger than the FFT-space. You can also set the focus range to larger/smaller focus values. Add some spherical aberration to the active telescope and run the Slice-function again.
This is the end of our fast tour of the Aberrator. I hope you have enjoyed the new possibilities and I am looking forward to bug-reports and ideas as a spin-off from the release. kind regards, Cor Berrevoets
Ritthem, The Netherlands |
