Jupiter is back in the late summer sky…
I tried out some new planetary imaging techniques compared to RGB imaging I did so far: LRGB and Infrared imaging of Jupiter. The pictures were taken at approximatively f/d 25 and I found this is a f/d ratio working pretty well in average condition, optimizing the balance between exposure time, and magnification (1 pixel = 0.25 second of arc) for a planet like Jupiter.
I worked also hard on my Photoshop skills – and try to do less aggressive sharpening in order to produce planetary images with a more “natural” aspect and a better color balance. I found the overall aesthetic aspect of the picture is improved when doing so.
I’ll post other pictures but here are two I took this week,
First – LRGB imaging:
Since Jupiter’s rotation is very fast, the LRGB pictures have to be taken in a short period of time, definitely less than 4 minutes. I took more frames at high speed for the luminance with an IR/UV filter. The fast exposure time (about 1/30 sec) allows to take many pictures but also to find the right window where the turbulence is minimal. Visually, seeing was at 4/10 which is far from ideal – but by taking many frames, the signal/noise ratio is improved. Then I took less exposures for RGB frames – to make sure all the frames are taken in a window of 3/4 minutes. But since RGB frames are used for color – the slight time delay of 2/3 minutes they have with the Luminance layer is not that critical and not really visible on the final picture.
As a summary – I think the LRGB technique I have been using provides superior results compared to my previous RGB technique. I don’t know if it is a valid / general statement – but at least in my case it seems to work better. I think it is because of the advantage of taking many frames at high speed for the luminance layer.
– Luminance exposure: 635 frames at 1/30 sec
– Red exposure: 203 frames at 1/5 sec
– Green exposure: 177 frames at 1/11 sec
– Blue exposure: 202 frames at 1/11 sec
The result is pretty good for a mass-produced telescope at a price tag of less than $1300 in average seeing condition … What do you think?
Second, Infrared imaging:
The camera I use has no IR filter. It allows infrared imaging with the right blocking filter…
For infrared imaging I used the Astronomik IR 742 pro filter – it lets the light pass above 742nm and blocks the light below 742nm.
I was able to verify, as explained on the astronomik site, that the seeing is much better in the infrared – even if the turbulence is quite high – and Jupiter is low on the horizon.
However two factors are reducing the overall resolution
a) At + 742nm the resolution of the instrument is lower than at 500nm …by +50% – given the longer wavelength… The aperture I used is pretty small so it really affects the resolution I can get in imaging.
b) Worse, the integration time has to be raised at +1/4 sec. so the longer exposure time does not allow to take shots so easily in a “low turbulence” window.
The IR Pro planet is not a miracle filter. Still, I found this technique quite interesting – as it certainly provides better quality pictures in a bad seeing environment, and highlights different features compared to the visible wavelength.