Solar photography – Venus transit dry run

[Dennis]

Hello,

With the upcoming Venus Transit (6th June 2012, 8:15am to 2:44pm approx) I reckoned I should set up and re-quaint myself with equipment that had been gathering dust due to some ordinary SE Qld weather these past 12 months or so.

The seeing on Saturday was reasonable up to around 11:00am although I only managed to grab 1 avi that was worth processing in AVIStack.

When the seeing went down hill, I fitted the Canon 7D to try some ½ disc shots (Solar disc won’t fit in FOV) and I made a mosaic (from x2 single shot frames) in CS5.

• Tak Mewlon 180 F12, DMK31 at prime focus for hi res shot (123 frames from 2500).
• Canon 7D with Tak x0.8 Reducer/Flattener for disc shot. (1/3200 sec, ISO100)
• Full aperture Baader astro solar film (ND38 photo)

Cheers

Dennis

[Rigel003 (Graeme)]

Well you don't seem to have lost your touch. Terrific detail and the granulation in the first one is great. Now pray for a cloud free day on June 6

[iceman (Mike)]

Very nice Dennis! Thanks for the reminder!

[sheeny (Al)]

Excellent as always Dennis.

I think you have your black point a little high for my liking in the full disc shot though. I see a pretty ugly halo of artifacts around the sun on my puter.

Al.

[Dennis]

Thanks Graeme, Mike and Al, I appreciate your comments.

@Al, thanks also for the feedback. The full disc Sun was generated from 2 frames in CS5 and I used the auto blend mode so it may have done something to the blacks (the effect is not visible on my screen). The solar disc blend line was quite difficult to suppress due to some quite pronounced vignetting with the Mewlon/7D combo.

Hmm, wonder if I should upgrade to a full frame DSLR, like the Canon 5D Mk III, just so I can fit the whole of the solar disc into the one frame…LOL!

Cheers

Dennis

[peter_4059 (Peter)]

Great details and processing Dennis. I'm on the steep learning curve trying to get ready for next month. I'm fortunate with the FOV of the Newt I get a full disc in a single frame so just need to work on how to focus better now.

Peter

[Dennis]

Hi Peter

Thanks – there is a lot to learn indeed!

The task of establishing the “perfect” system configuration (‘scope/camera) and the ideal exposure is made more difficult when you shoot at different times of the day and under varying seeing conditions. The event will span 8:15am to 2:44pm (ish), approximately a 6 ½ hour period.

Today, I had the Vixen 4” f9 refractor and the Canon 7D at prime focus even at that focal length, 918mm, there were significant variations between frames depending on the state of the seeing at the time of the exposure. I was using a full aperture Baader astro solar filter (ND38) which saw me shooting at 1/5000 sec, ISO100 and I think the blue channel might have been clipped, so I’ll experiment with 1/6400 or maybe 1/8000.

I then fitted the Canon Extender x1.4 but got an Err message – I think that I need to tape some pins on the extender as it is trying to report on a non-existent lens.

I then tried the Tak x1.6 extender but had to remove the JMI motor focus to obtain sufficient in-focus. At the end of all that, it seems that the way to go for full disc shots for me could be the Vixen ED102S, JMI motor focus, Canon extender x1.4 and Canon 7D with the Baader ND38 full aperture solar filter. There is significant light fall off at the limb.

I ran a 30 sec Canon movie and have yet to convert it to an AVI for processing in AVIStack, although it seems too much work to grab small movie segments from which to produce single stills to then combine into an overall movie.

I’ll probably just stick to taking single shots at timed intervals and try to make a movie from these and just tolerate the frame to frame variations arising from the variable seeing conditions.

I think a motorised focuser will be very useful over the long session so that focus can be periodically checked without having to touch the ‘scope. Remote Live View on the PC at x10 mag is really helpful here.

However, all this presupposes decent weather and the Sun clearing the tree tops from my back garden set up location, before 8:15am on Wed 6th June!

Cheers

Dennis

[Matt Wastell (Matt)]

Well done Dennis - I hope we see Venus close to a sun spot - image one would looks sweet with Venus in it!

[Dennis]

Thanks Matt – a clear sunny day with minimal jest stream activity would be just fine!

Cheers

Dennis