View source for Suggestions for comparing resolution qualitatively between surveys

=Create a three-color image using bands of your choice. =

Within IRSA tools, IRSA Viewer is the best way do this. On the main screen where you search for objects, you have a 3-color option, including loading from disk (as opposed to, say, IRSA holdings). However, the final resolution of the 3-color image is set by whatever you load into the red plane, so even though your lowest spatial resolution observations are probably also the reddest, in this context, don't load them into the red plane.  Finder Chart will make 3-color images for you if you click a single button in the image toolbar, but you don't have control over which images it uses for the color planes.

ds9 also allows you to make 3-color images. For ds9, you need to tell it, "Ok, I want to make a 3-color image now" (Frame/rgb) and then you can load in each plane separately (in the pop-up, pick the color plane, then do File/open. Change the color plane and go back to file/open, etc.). Regardless of tool, whichever image has the lowest spatial resolution should be super obvious, because, say, the sources will appear to have blue blobby rings if you load the lowest resolution image into the blue plane. 

=Align or align & blink images. =

You can flip through images in any of these tools; ds9 will do it for you if you want. For ds9, do file/open and find the first image; do frame/new then file/open and load the second image, etc. If you used the command line trick (ds9 *.fits), you will load all the images into individual tiles, in alphabetical order (which is most likely not wavelength order!). If you did them one-by-one, you will have them virtually in a stack, in the order you loaded them. To see all of them at once, click on 'frame' then 'tile.' To get it back to one at a time (in a virtual stack), pick 'single.' To line them up on the sky, pick from the top "frame" menu/match/frame/wcs to match them in terms of area on the sky. (That command means, "align all the images I have loaded in ds9 to be North up, all on the same spatial scale as the image I have selected when I initiate this command." WCS stands for world coordinate system, meaning that there is information about the ra, dec, and mapping of pixels to ra and dec in the FITS header.) To scroll through the whole stack, pick 'next' or 'previous', or go ahead and blink them. You can configure the length of time spent on each frame. You can change the ordering - explore the menu options on the top "Frame" menu. In the 'single' frame case, the image you are looking at is the active one; in the 'tile' view, the one with the blue outline is the active one. Click on the tile to make it the active one. The commands are similar in the IRSA tools; there is a "match WCS" tickbox and you can view images one at a time or tiled in the tool.