Monday, May 1, 2017

Eclipse Imaging #1 Individual images

I was reading a lot about how to take individual real-color images of a solar eclipse. But the outlook of constantly adjusting exposure time, changing filters.. wasn't too great. I want to enjoy the eclipse as much as possible and pay as little as possible attention to my gear.

So, I was delighted to learn about Eclipse Orchestrator. It does create a whole script and executes it along a very tight timeline (needs exact location and time). The only thing that it needs is to remove the filter just before the second contact and put it back on after the third. I can do that!!!

Initially, I was thinking of using my 300mm lens for my Nikon camera (I can only use the D7000 as the D750 is not supported) and mount it on top of the TOA-130 scope and use the Mach1 mount to track. But then I realized that I could also use the TOA-130 scope itself with the Super Reducer to take images. The field of view should be perfect and the non-flat image shouldn't be too bad for these images (especially considering that the D7000 isn't a full frame camera!)

So, the equipment that I want to use is:
  1. TOA-130 scope with Super Reducer
  2. Nikon D7000 (connected with DSUSB from shoestring astronomy to short the time between exposures)
  3. Mach1 mount
  4. Eclipse Orchestrator
There are a number of things to figure out:
  • I have an adapter from PreciseParts that should work (might be a few millimeters too short). Need to try it out and measure the distortion in the corners.
  • Need to spend a lot of time trying out the script that Eclipse Orchestrator generates - maybe adding some frames as possible (this turned out to be very involved and I decided to write an extra blog post about it)
  • How can the Mach1 mount track the sun over 2.5 hours?
    • The AP driver has a "sun tracking" speed. Need to try that out and how accurately it keeps the sun centered.
    • I could use APCC Horizons to accurately track the sun
    • "proper" sun guiding solutions (like LuSol) might not work as the sun will be distorted.
  • Need a new Serial-USB adapter (my old ones don't work with Windows 10)
Things I would have to do to set this up onsite:
  • Good polar alignment (not a problem as I will use the TOA scope the nights before for astro imaging)
  • Focus the sun extremely well
  • Enter exact coordinates from GPS (unfortunately Eclipse Orchestrator can't read from my GPS - have to enter them manually)
  • Keep NMEATime running while imaging to make sure that time is as accurate as possible (and disable Dimension4 - it shouldn't do anything as it won't find any internet. but better be on the safe side)
  • Exchange my normal imaging train (flattener, filter wheel, CCD camera) in the morning with the Super Reducer and Nikon camera WITHOUT affecting polar alignment or such.

Update 05/01:
Received the new Serial-USB adapter - works. Yei!!!

Update 05/28:
1. Camera Setting
Tried to figure out what exposure time / ISO to use. Full sun with the Baader filter is best at:
  • ISO 100
  • Exposure 1/400 sec
I need to use that as the basis for Eclipse Orchestrator.

2. Adapter
The adapter that I had, was too short (to match the backfocus of the super reducer). I ordered one with the proper length - but that one brought the camera so far out that I couldn't focus ...
So, I went with the shorter one. Need to measure the aberration in the corners - hopefully it's not too bad...

3. Focusing
Focusing is surprisingly difficult. What I ended up doing:
  1. Focus on a distant object without the filter.
  2. Put on filter and slew to sun.
  3. Use Live View (Nikon Control Pro 2) to focus the sun well (zoom into outer areas or spots and focus on it).
I will have to do this early enough - hopefully the temperature difference before/during/after the eclipse won't change focus too much.

Update 6/4:

1. Centering the sun
Last night, I polar aligned my scope really well. I thought that would making centering the sun a piece of cake ... Not so much. Took me some time to get the sun into the center. The easiest way I found was using the hand control and semi-systematically moving the scope around ... Need to think if I should get a simple solar centering device like my Lunt has ...

2. Keeping the sun centered
I tried using Horizons that comes with  APCC Pro. This worked REALLY well, the whole day, the sun stayed more or less in the center. The only thing is that TSX shows the scope at some point far away from the sun as it probably sees these adjustments but interprets them wrong ...
But overall, the process was simple enough!!!
So, I created the ephemeris file already and can the use it when I'm there. It will be slightly off as I have to use the default GPS coordinates, but they should do.

3. Focusing
Focusing is still tricky. I ended up ordering a combined Hartmann/Bahtinov mask for my scope. Hopefully that will help (will need to figure out how to use that on top of my solar filter!)

4. Eclipse Orchestrator
With everything setup, I worked through the Eclipse Orchestrator script again.
  • Eclipse Orchestrator uses ISO 100 and 1/400 sec exposure time as the initial setting. I know that I didn't set that, so it's good to see that we agree here :-)
  • Need to remember to set the camera to Mirror Up - otherwise it will try take two images every time. The good news is that the camera didn't fall behind - even when taking two images. The fast SD card is great!
So, except focusing, I feel pretty good now about this

Update 6/12:

After trying a lot of things (Bahtinov mask, Hartmann mask, FireCapture...), I think the best way to focus is to do it manually. Use Live View of the camera, zoom into the edge of the sun and then carefully move the focuser into and out of focus until I find the right position.

Update 7/7:

I ran the script over and over again. Unfortunately, it always had delays:
  • using MirrorUp increased the delays by more then 0.5 sec
  • using the D750 vs. the D7000 did not make a difference
The weird thing is that even the first image has already a delay ...

One thing left is a super fast SD card. I am currently using a SanDisk Extreme Plus which has a write rate of 90 Mb/sec. The Extreme Ultra has 300 Mb/sec. I ordered one of these to see if that makes a difference.

I also ran the entire script and it uses:
  • 6GB (240+ images)
  • 60% battery
So, I should be good running it from one battery and the SD capacity isn't an issue at all.

Eclipse Orchestrator is using ISO 200 and 1/1600 sec exposure. I could drop this to ISO 100 and 1/800. But there is no easy way to set this to 1/400 (as I measured). I guess I'll leave it as is.

Update 7/16:

The script will take images as follows:

1/4000 100
1/3200 100
1/1600 100
1/800 100
1/400 100
1/200 100
1/100 100
1/50 100
1/6 100
1/3 100
1.6160, 320

I will need to take dark frames for these (and will probably use the 1/4000 dark frame as a bias frame).

Not sure if and how I want to take flat frames (especially considering that I want to image at night the night before and after). Maybe I'll skip these...

Update 7/17:
I tried the faster SD cards with 300Mb/sec but had exactly the same delays as before. Looks like I have to live with it (though I sent an email to Eclipse Orchestrator support and asked about this).


So, here is the plan for these images:

Before leaving for OSP:
  • Clean Nikon Sensor and Super Reducer
  • Run Eclipse Orchestrator script several times
    • How much memory will I need for all images? (shouldn't be a problem)
    • How much battery will I need for all images?
  • Take bias and dark frames (according to all exposure times from the EO script)
  • Try out focusing routine of EO
At OSP before August 21:
  • Recreate the whole Eclipse Orchestrator script with the exact GPS coordinates from our place using the mobile GPS.
  • Run the whole script (including guiding) the day before
On Monday, August 21:
  1. Assume that from the previous night(s) the scope is very well polar aligned.
  2. In the morning, exchange the CCD camera with the Nikon camera
  3. Start AP Horizons and load Sun ephemeris. Start tracking on Sun (might need to manually center sun)
  4. Focus manually on edge of the sun - take a lot of time for this!
  5. Connect GPS to scope, start NMEATime to constantly correct the time
  6. Make sure that the Nikon is set to:
    • MirrorUp
    • Bulb exposure
  7. Start Eclipse Orchestrator
  8. Before first contact, replace battery for fresh one
  9. Before second contact: check battery (and replace if necessary) plus check focus
  10. During Eclipse, make sure to listen to commands and remove and put back the Baader filter.