A project for collaboration with other comet imagers
Ever since Dr Brian May’s presentation at Astrofest in February 2015, I have been wrestling with the idea of genuine 3D imaging of comets for viewing with one of Dr May’s stereoscopes. Having presented my “proof of concept” to the Comet Section of the BAA last Saturday, it is now time to share this more widely and encourage others to join in.
These two images of 41/P were assembled from LRGB stacks of 22 subframes of 120-seconds each. The first 120-sec subframe of the right image started 29 seconds after the first 120-sec subframe of the left image. That’s a 75% overlap – which I count as simultaneous!
For the purposes of this project, there are three types of stereoscopic image:
Type 1: Simultaneous imaging
This is surely the holy grail of 3D comet imaging, taking two images simultaneously from different locations.
The “simultaneous” constraint could be relaxed, as long as there is full disclosure of the time interval, but if relaxed too far then the image becomes effectively a Type 2(b).
Type 2: Delayed imaging
2(a) Two images taken from the same location, but with a substantial interval between them. For example, a comet rising in the east at dusk will be setting in the west at dawn – if that’s eight hours later then the Earth will have rotated by one third (and also moved one third of one day in its orbit around the Sun). A 24-hour interval could be contemplated, using images from successive nights’ captures.
2(b) Two images from different locations and taken at different times. A brief search among the images posted online suggests that there might already be many candidate images available.
Both 2(a) and 2(b) carry the risk that a fast-moving comet will not occupy the same field of view in both images. The tail could also change substantially, reducing the impact of the 3D effect.
Type 3: Synthetic 3D images
These are achieved by simply moving the comet from one image to the next in post-processing, creating an entirely synthetic 3D effect. The comet will appear as a 2D image in front of the stars, and the tail will have no depth. I’m not interested in these images.
Colour or monochrome?
Colour images will need the specialised viewer (stereoscope) or they can be revealed by using a “cross-eyed” technique. Not everyone is comfortable with the latter, and the left-right layout has to be reversed!
Monochrome images can be rendered in red and cyan for left and right channels, then viewed using red and cyan 3D glasses which are readily available. I have tried this and it’s not very good, but I am open to suggestions.
How should contributors collaborate?
The easiest collaboration method is going to be a buddy system, where two imagers agree a target and an imaging time. You will have to consider the comet’s visibility and elevation above the horizon, the hours of full darkness, and the start time of the first exposure.
In the northern hemisphere, an imager in the USA paired with one anywhere else would be ideal. South of the equator, I guess any two of Australia, Africa and South America would be the choices.
How to contribute images
I’m happy to collect, rescale, align, crop and present your individual images in the correct format for viewing through the stereoscope, or you are welcome to do that yourselves. If you do it yourselves, please add your name(s) to the “Left eye” / “Right eye” text at the foot of the image.
If you publish independently, please acknowledge that the idea came from here and let me have a copy of your completed image to add to the gallery that I will set up. All image pairs will be shared in Neil Norman’s “Comet Watch” on Facebook.
I would like the entire project to be open and free from non-commercial copyright, so that anyone can download the images, view them and/or modify them as necessary for viewing and sharing with other enthusiasts. There should be no commercial use except by whoever took the photos, so I’ll be adding this Creative Commons licence stamp to each image:
I hope I’ve got that right, but if you have any other preference for copyright, please do let me know.