Making a post about some of the different sorts of mosaic/panorama’s that I do.
TAKING THE FRAMES
For the majority of my astrophotography panorama’s – I’ve just been using a sturdy tripod and ball head. First up then I level the tripod (mine has a spirit level) by adjusting the legs. The foreground hasn’t been too close that I’ve worried about having a nodal point, however having said that, one of the panoramas I did recently (not shown) would have benefited from it and next time I might use my improvised version of a panorama head (using a flash bracket).
The nodal point is basically so that the camera/lens is set back enough so that the image is effectively taken from the same position. If you’ve just got the camera on a tripod and swivel it around, then the point of view will shift slightly in each image. Ideally I would use a levelling panorama head – that makes it easier to set the level plane rather than adjusting the legs of the tripod to make sure that when the tripod head swivels that the camera remains level. But I don’t have one yet.
Taking the images I do one layer and then the next – not really fussed whether I do the top layer (focused on the sky) or the lower layer (focused on the land). However if the sky is too high (sufficient space for the milky way core and have some horizon that matches), then it’s an idea to change focal length to something wider or go look for a hill so that you can angle up and have the foreground. I have done a 3 layer panorama once and it didn’t really add anything additional for me. I do however have some thoughts about using much more than 3 layers.
Have to ensure that there is some form of overlay which is normal for panorama’s so that the software has common points to connect the images to each other. When I do single layer panoramas it’s easy – I overlay around 1/3 from image to image. However when I’m shooting in the dark, it’s a bit harder. I tend to just shift the angle by 15-30 degrees each time (measured on the tripod head). Just a note about this though – it depends on what your lens parameters are (I don’t do 15 degrees when I’m using a 200mm for the pano).
I make sure I leave plenty of space to each side of where the milky way hits the horizon as the potential stitching distortion. For me – the important frames are the sky frames – I do a test where the arch is expected to be the highest to make sure that there is sufficient horizon and space above the milky way before proceeding too much. I could probably have a little less margin here, but much more and it gets more painful to put it together. Also – the edges for my wide angle will result in more lens distortion, so the centre/mid area is preferred to contain as much of the information as possible. The bottom level doesn’t matter too much – I tend to go mid way or having a third for the sky.
If the software can’t match up the corresponding common points – then using control points takes a long time – manually matching frames to adjoining frames – so I tend to like as much overlay as possible to avoid this.
I also make sure that the sides of the panorama have around 2/3 or more buffer before the milky way – expecting the final stitch to cause distortion and will lose parts.
A few different software options are available. Some examples (but not limited to):
- Photoshop – for the easy panorama’s – single tier
- PTGui (http://www.ptgui.com/) what I prefer for the larger mosaic/panorama of 2+ layers. I like this software because if the panorama doesn’t work automatically, there are plenty of options to fix it – such as determining the common points, moving the panorama around and also for masking in/out things you want to keep/exclude from the final stitch.
- Hugin (http://hugin.sourceforge.net/) – I haven’t used it, but it’s free and apparently is pretty close to PTGui.
Single level panorama is fairly straight forward and photoshop shouldn’t have any problems stitching this together. I may consider this for images where the milky way is low to the horizon.
Two sorts that I use for the 2 tiers using PTGui tend to be Full Frame and Transverse Mercator. The advantage of using 2 or more tiers is gives you more space to move. However will have more challenges too with the wide angle lens.
Full Frame mode – is more for your “traditional arch” milkyway.
This is what the stitching pattern for this sort of image looks like (I’ve removed the image files to show) – note that this is not specifically the above image.
Tranverse Mercator mode tends to start off with an effect that I like – it warps the sides to bring into the middle. So the effect is to straighten the milky way and frame it with what is almost the horizon.
This is what the stitching pattern looks like for the above panorama/mosaic
also seen here:
I expect to do some additional variations in due course. This is just what I’ve been doing so far.