Jumping Jupiter

Grandpa Ron · Jun 8, 2019

For several nights I have been trying to take a picture of Jupiter. The shots were always blurry (jumpy) no matter how fast the shutter speed. I was blaming this on the thick atmosphere from the low horizon position and poor "Seeing" conditions.

Last night the sky was particularly clear and viewing through the telescope was unusually good. I finally realized the problem was the mirror bounce as the shot was taken.

The setup is a follows,

A home made Dobson telescope with a 1220 mm (48") reflector mirror focal length.
A 2x Barlow lens attached to camera telescope mount for proper focal distance.
Camera mirror locked into shooting position to eliminate mirror bounce.
Camera shutter delay 10 seconds, to allow the scope to settle.
ISO 6400 for a quick shutter time.
Shutter speed 1/8 to 1/20 second to capture planet and moons.

I can only guess at the level of magnification but it appears to 80 to 100 X. These photos are all "as shot", no post processing.

The first figure is a picture of my telescope; a tube with a 6 inch diameter 48 inch focal length mirror, a second mirror to bend the beam 90 degrees, an lens mount to hold the camera. Nothing exotic.

The second figure is the blurred Jupiter image due to camera mirror bounce.

The third figure is Jupiter and all four moons at 1/8th second.

The fourth figure is shot at 1/20th and the forth moon is just visible if you know when to look.

Next will be trying color filters and changing the ISO to try to improve the brightness latitude.

I hope this information encourages others to experiment and expand their photographic horizons.

tirediron · Jun 8, 2019

Nice. Looks like some great woodwork on the telescope.

Designer · Jun 9, 2019

I've never done this, but I'm wondering why you want such a short shutter opening? Does the rotation of the earth dictate such a fast shutter? I understand your mount does not track the planet, but what shutter speed is optimum?

Original katomi · Jun 9, 2019

Are you using a remote trigger and is scope on firm ground I found just walking on the decking would cause vibration

photoflyer · Jun 9, 2019

You are very ambitious. I am excited as last week I ordered my first: Celestron Evolution 6. I also plan to use the piggyback mount to get landscapes with the night sky. Unlike yours,mine is not an aesthetically pleasing addition to the house.

OldManJim · Jun 9, 2019

nice work on the telescope & great shots. astrophotography is a lot harder than it looks!

Grandpa Ron · Jun 10, 2019

Thanks for the compliments.

The telescope is a bit of old school, no digital readouts etc. just star charts and constellation maps. I built it about 25 years ago when DIY was about the third of the cost of new. The plans came from The San Francisco Sidewalk Astronomers group. I just made an octagon wooden tube, instead a thick cardboard cement form tube.

When you decide to do photos, here are some handy recommendations,

You do not need a fancy telescope to photograph the moon, and the larger star clusters.
A camera adapter connected the eye piece holder of my 60mm department store scope, gave me about a 650mm prime focus lens. This is in the neighborhood of 20 to 25 x.
The full moon is surprisingly bright so an ISO of 100 and 1/8th sec. shutter with a remote release is a good starting point.

When you start to chase planets things get a bit more difficult. A magnification of 75 to 100x becomes necessary and another set of problems evolve.

The smaller 0bjects like planets require more magnification, which means additional lens.
Magnification also required more light so a larger telescope is needed.
Stability becomes an issue as does the transit time across the view finder.
Stability and transit time limited my shutter speed choices
Finally the need for clear skies (Good Seeing) cannot be overstated.

My next object is to try to pull out Jupiter's surface feature with color filters and varying the ISO.

Heck, half the fun was discovering what this old gear can do when coupled to a digital camera.

TCampbell · Jun 17, 2019

Go for even shorter exposures. You should be able to see the cloud belts. I went out to image Jupiter last Tuesday ... but the sky wasn't having it (jet-stream directly overhead) -- all the stars were twinkling hard. I'll have to re-try if and when it ever stops raining and being overcast.

Anyway... the typical trick is to grab about 30 seconds worth of video frames and then stack them using AutoStakkert and then do wavelet processing in something like Registax (Registax can also do the stacking but most people seem to find the stacking works better in AutoStakkert than Registax.)

I use a ZWO ASI174MM-Cool camera. This is a CMOS astrophotography imaging camera that has a cooling system builtin (but that's not really needed for planets because they don't use long-exposures). This particular camera has a 'global' shutter and is able to capture at a frame rate of 160 frames per second at full resolution (if the computer can keep up ... the computer needs to have USB 3 and fast SSD storage.)

One of the most popular cameras at an entry-price range for this is the ZWO ASI120MC-S (about $150 USD). Those with deeper pockets go for the ZWO ASI290MC (much faster and less noise and slightly better dynamic range ... but about double the price tag at around $300 USD).

The last time I did this, I managed to get this image. This was shot through a 14" Celestron C14 SCT (f/11). I shoot about 30 seconds worth of frames with a 'red' filter on the camera, repeat with a 'green' filter, and repeat with a 'blue' filter. Each set of frames are stacked and then brought in to Photoshop and assigned to the correct color channel, and this merges them into an RGB color image.

Which isn't great (there are local guys who shoot images of Jupiter that blow this away). They gave me some tips (which I have yet to apply). The main tip (besides needing a night of good seeing) is that the guys that get much better results are heavily barlowing-up the focal ratio to around f/25 or so. This is based on something called Nyquist-Shannon sampling theorem which says that the camera needs to have double the resolution of the thing being sampled (to avoid loss of data). They calculate the resolving power of the scope (using Dawes' Limit) and a bit of math gets you to the ideal focal ratio (with the typical pixel sizes of most modern cameras ... it's usually somewhere between f/20 and f/30.

Anyway... the masters for this type of photography are Damien Peach and Christopher Go.

Here's a YouTube video Damien Peach's work from the 2018 opposition of Jupiter. Keep in mind ... he is imaging this with an amateur telescope (this is not done with some massive scientific grade observatory) ... absolutely mind-blowing how much detail he can capture (that's why he's the master):