Transit of Venus, One Camera and One Tracker ... Movie or Image Sequence?

astrostu · May 24, 2012

The upcoming transit of Venus will be visible here for about 3 hours from start to just before half-way before it sets in the mountains. I have one Canon 7D, one 400mm lens, one 2x extender, one solar filter equivalent, and one mount that will track the skies. I'm trying now to figure out if I should do HD video of the whole friggin' thing, or if I should do an image sequence, like once a minute.

Here's what I've come up with so far in terms of pros and cons for each:

Pros for Image Sequence:

Roughly 3x the number of pixels to work with for each "frame."
Can take sets of 5 (or 10 or whatever) images for each "frame" to stack.
If sequence is fine enough in temporal resolution can sorta make a continuous-looking movie.

Pros for Movie:

Continuous except for mandatory 7D breaks at the 15-minute mark.
Can't really stack images, so processing time goes WAY down.

Cons for Image Sequence:

See Pros for Movie
Insane amount of processing time. With the recent solar eclipse, I ended up spending about 7 minutes on each frame, and with 75 frames total, that was over 8 hours.

Cons for Movie:

See Pros for Image Sequence
Small drifts over time may result in needing to realign camera, which would make a giant jump in the movie.

Regardless of either, I will be doing a movie once the sun contacts the mountains instead of an image sequence.

Thoughts?

pgriz · May 24, 2012

Well Stewart, the image size, even with a 400mm is still going to be quite small, especially for Venus, so doing it in HD seems like a unfortunate waste of available pixels. As well, I'm not sure watching a small black dot crawl on the face of a bigger circle would be that interesting in itself. Now if you had a filter that would show a narrow-band (H-alpha? OIII? ), then there would be texture on the sun surface and that would make the image "pop" more. I'm going to vote for the individual images with stacking, but then I can do it because I won't be doing the hard work! Seriously, what will give you the best visual record - that's what I would go with.

astrostu · May 24, 2012

I wish I had an H-alpha filter, but unfortunately, they do not make camera-type H-alpha narrow-band filters. I've searched online and posted on the BAUT forum (a year or so ago) and everything I've found points towards folks saying to get a dedicated solar telescope. And they are NOT CHEAP. It would also require (I think) a separate kind of mounting system to the tripod and would require hooking up the camera through T-rings and mounts resulting in vignetting (I think) to the 1.25" eyepiece barrel.

That said, it IS on my list of "I WANTs!" and with two weeks to go, if I sell some coins, may be something perhaps worth getting .... and just my luck it'll be cloudy

.

Oh, and I did photograph the transit of Mercury in 2005 (or 6?). It was pretty uninteresting and I agree that an active sun in H-alpha would be much more interesting. But my 1000mm lens did show it and resolved Mercury. Venus will be at its largest possible size at this time, a full 58 arcseconds, and it should be easily resolvable even from Boulder's skies.