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  #21  
Old 08-09-2012, 01:58 PM
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OzEclipse (Joe Cali)
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Originally Posted by colinmlegg View Post
Hey Joe, yes it's been awhile since that Puno -> Cusco train ride. I see you've done a few eclipses since . I've been back to the altiplano a few times myself ...had a lasting impact on me!

Thanks for the light curve. I need to spend a few hours reading your site. Lots of interesting stuff there.

I'd love to see the eclipse in Cairns, but I've left my run a bit late so my only option now is to drive up and rough it in my troopie. Will decide this month. Like Geoff, my focus is wide angle and video/timelapse. Ideally I'd like to shoot from an elevated spot overlooking the ocean and preferably free of people. I have a fulldome fisheye and multi-camera system that can cover the entire sky. Any thoughts on where I could locate myself?

Colin
After Qosco, I spent another 3.5 months hobbling around the continent in that leg brace. Had a great time. After the knee reconstruction I went back to central and south America for another 4 months in 1998. As you say, easy to get hooked. Anyway - off topic!

Re-eclipse and fish-eye. Most beach sites have trees lining the beach. Because of the incoming tides and equipment type project like yours needs to be high up the beach where the trees will be covering half the sky and your FOV so you need a site off beach where you can see most of the sky. There is a lot of open ground by the road side in the areas 1km around the skyrail base station.

If you want something more secure where your gear won't be disturbed, I am setting up an observing site on a 40 acre farm near Port Douglas. Cost will be $50-60 per person and you can move in to set up anytime in the day or two before.

This site will have a lot of very experienced eclipse chasers, Astro club members and a Sydney Observatory Group and their web cast coming off it.

http://joe-cali.com/eclipses/PLANNIN...glas_Obs_Site/


You can camp there on Tuesday night at no extra charge however there are no facilities except portable toilets. However, while camping out the night of the eclipse or at least being out most of that night is unavoidable, I'd recommend against camping the whole time. It's oppressively hot and humid in November. When I was there mid-Nov 2010 it frequently rained at night and of course lots of insects. Really unpleasant!

I might be able to offer you some various options for better accommodation depending on your budget. Call me on 0429 233 616 if you are interested.

cheers

Joe
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  #22  
Old 08-09-2012, 06:35 PM
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OzEclipse (Joe Cali)
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correction to URL

Sorry, I left out one character in the URL in the previous message.
It's : -
http://joe-cali.com/eclipses/PLANNIN...glas_Obs_Site/

or

http://tinyurl.com/9lzmvqq

And I should say that anybody not just Colin who wants access to this type of field site arrangement is welcome to contact me. So far it's mainly been bigger tour groups and people with more complex equipment set ups who have requested access.

Individuals with just a camera and tripod or a pair of binoculars should easily find somewhere for free (see the site survey articles on my web site) and should probably save their money.

Cheers

Joe
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  #23  
Old 09-09-2012, 08:03 AM
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Hi Colin,

Minimum EV steps are 1/3rd looking through the menus. I have used it attempting a day/night transition and its reasonably good up to a point but then it does not do long enough night shots at high enough ISO to be useable for that.

Perhaps with auto ISO on that may help it as well. As I recall that is what I also had going.

Greg.
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  #24  
Old 17-09-2012, 04:24 PM
geoffsims (Geoff)
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I thought I should add that one interesting possibility is using compact Canon digicams for time lapse. Using the CHDK firmware hack, which runs off your SD card, allows access all sorts of features that are otherwise not available, including intervalometers (via custom scripts). There is the possibility to write some quite intricate scripts, although at least a few already exist that dynamically change the exposure time to get the optimum exposure, while keeping the aperture/ISO constant. I haven't run a test yet, but considering the simplicity, it appears to give good results.

The main benefit I see here is that you don't really have much to lose (since they are presumably not your primary camera[s]). Additionally, you could do things like point them away from the Sun (to capture people operating equipment), or any other interesting angle you can think of, while reserving the primary DSLR camera for the full frame landscape sequence.

Incidentally, I have two quite nice newish compacts from the last two David Mailin competitions, so I think I may as well put them to good use.

I am still thinking about the best way to do the primary sequence, but having multiple angles at least means you can edit and cut in various sequences throughout the partial phases, for example, to make an otherwise "boring" and long ingress/egress sequences, seem more interesting.
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  #25  
Old 16-10-2012, 11:04 PM
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Originally Posted by geoffsims View Post
I thought I should add that one interesting possibility is using compact Canon digicams for time lapse. Using the CHDK firmware hack, which runs off your SD card, allows access all sorts of features that are otherwise not available, including intervalometers (via custom scripts). There is the possibility to write some quite intricate scripts, although at least a few already exist that dynamically change the exposure time to get the optimum exposure, while keeping the aperture/ISO constant. I haven't run a test yet, but considering the simplicity, it appears to give good results.

The main benefit I see here is that you don't really have much to lose (since they are presumably not your primary camera[s]). Additionally, you could do things like point them away from the Sun (to capture people operating equipment), or any other interesting angle you can think of, while reserving the primary DSLR camera for the full frame landscape sequence.

Incidentally, I have two quite nice newish compacts from the last two David Mailin competitions, so I think I may as well put them to good use.

I am still thinking about the best way to do the primary sequence, but having multiple angles at least means you can edit and cut in various sequences throughout the partial phases, for example, to make an otherwise "boring" and long ingress/egress sequences, seem more interesting.
Geoff, re. Canon point & shoots, I believe the minimum exposure step is 1/32 stop, compared with 1/8 for DSLRs. So setting the exposure to auto should produce fairly clean footage with only minimal flicker. Certainly worth a shot.
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  #26  
Old 17-10-2012, 09:50 AM
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OK, I produced a light curve from my data. It's not a conclusive scientific test, but it's not bad considering I had no intention of producing such results. I used the original set of images I posted, plus a similar set from pre-totality (the original set were post-totality). Recall these were fixed exposure so the relative intensities are correct. In this instance they were 1/30s, f/4, ISO 100, 17 mm lens on Canon 400D.

I used DCRAW to convert the raw images with no white balance, scaling or Bayer matrix interpolation (essentially outputting the raw data points in ADU at each pixel position). I then converted the images to FITS format, and collapsed them into the various colour channels (R, G, G, B) using Python routines (NB: there are two green channels as a result of the Bayer structure). I collapsed the colours because the response from each colour filter will be different. Then, I picked a few regions of interest and examined them.

Results are attached, I used only the green filter and units are in raw ADU. Some explanation:

- Whole image (median) is just a global median pixel value of the entire image.
- Sky (median) is a median of a 50x50 pixel region of sky, approximate 50 degrees from the Sun
- Land (median) is a median of 50x50 pixel region of the landscape.
- Around Sun (mean) is the mean value of a 60x60 pixel region centered on the Sun

As evident from the initial set of images, they are extremely underexposed near totality. From the ADU counts, you can see it flattens out just above 250 ADU which is probably an indication of the bias level of the camera. So data here is not really valid. It is also worth pointing out that the "Around Sun" curve data is probably skewed too as many of the included pixels would have been fully saturated, particularly a few minutes before/after totality.


Now to spend a bit of time examining this data, along with Joe's data, and the implications for how to tackle this project!
Geoff, would you mind converting those charts to EV? I'd like to compare with Joe's curve. As you say, with a month to go I better get cracking on this!
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  #27  
Old 18-10-2012, 01:12 PM
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For those interested in Eclipse light curves, there's another from Fred Bruenjes, Eclipse Orchestrator author. Scroll 2/3 down the page.

http://www.moonglow.net/eclipse/2005apr08/index.shtml
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  #28  
Old 20-10-2012, 02:10 PM
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Attached - I just took the log2 of the ADU values. By the looks of things, in Joe's plots, there is about 5-6 EV drop in light within 5 minutes of totality. Mine do not show as great a change. I'm not sure why - possibly because my exposures were too short and is below the noise level of the camera.
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  #29  
Old 20-10-2012, 03:41 PM
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Thanks Geoff. I've asked Fred for a higher time resolution version of his curve for comparison. Just eyeballing it though, it looks similar to Joe's.

I've gone back and forth on the bracketing question during totality. Leaning towards no atm, based on your images and using a 1/4s,iso 100,f/4 exposure. At iso 100 RAW (5D2), I should be able to pull 2 stops (or more) out of the shadows, which gets me to your recommended 1 sec for landscape. My concern is the highlights + horizon. Any chance I'll get blowouts along the horizon (where the sun still shines?). Should I pull back to f/5.6 to be safe, and live with darker shadows?

If I can avoid bracketing or complicated multi-cam hdr setups, I reckon 20 sec (24fps) of smooth(*ish) footage is feasible via bulb ramping. Assuming the light drops 3 stops in the last 3 minutes and totality is captured at 1/4 s shutter, 1fps.

1. Ingress Partial phase 3 mins -> C2. 1/30 -> 1/4 sec (bulb ramp). 180 frames

2. Totality. 1/4 sec (constant shutter). 120 frames

3. Egress Partial phase C3 -> 3 mins. 1/4 -> 1/30 sec (bulb ramp). 180 frames

* It's likely the bulb ramp will suffer some flicker near the start and end. Need to test this in the next day or so.

I'll run the full test soon and report back.
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  #30  
Old 20-10-2012, 05:47 PM
geoffsims (Geoff)
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Colin, some good ideas! Linear or logarithmic bulp ramp?

Post or PM me your email and I will send a link (tomorrow) so you can have a play with my raw images from 2 eclipses (2008, 2010), and see which exposures give the best results. Keep in mind they were taken with a 400D. I will do the same.

From memory I could not squeeze out enough landscape light from 1/4s, but dynamic range on the 5DII is obviously better.

BTW, will serial port bulb control through EO be accurate enough for bulb ramp?
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  #31  
Old 20-10-2012, 09:02 PM
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Thanks Geoff. Email colinleggphotography @ gmail.blah

Unfortunately, PC timing is an issue for bulb ramping below 0.6 s. You need 0.001 accuracy between frames to smoothly follow the ramp and the best you can get from a PC is ~0.01. When I said earlier that bulb is only good for >= 0.1 sec, it's because +-0.01 is 10% inaccuracy. Just good enough for a single shot. 10% variation would still be noticeable as flicker though, if you strung a few of those together.

So, the way out is a microcontroller that does the timing. You can go 2 ways. 99% automatic with something like Little Bramper, or 100% auto with a custom controller like I have.

If you don't have Little Bramper or equiv, I have 2 spares from the first batch that I can lend out. It'll mean 2-3 seconds manually de-activating and re-activating the ramp within 10 sec of C2 and C3 and your ramp will be linear. I can send one over before I head off if you're interested.

The 3rd alternative is Promote Controller. It has bramping in the latest firmware. Unsure how sophisticated it is compared with LB?

And having said all that, it's likely you'll still see some flicker between 1/15 and 1/30 s. This is where even 0.001 is not fine enough. Better than the 1/3 stop alternative with AV or 1/8 in Full Auto though.
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  #32  
Old 20-10-2012, 09:35 PM
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I've been thinking about this too. The best ones I've seen on youtube are the ones that show the crowd.
James
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