Partial Solar Eclipse 2015

Europe’s biggest solar eclipse since 1999 occurred this month – and 67 per cent of sunlight could be blocked out over Munich. A total eclipse of the sun will occur in Northern Norway and Faroe Islands with two minutes and two seconds of totality. Besides going to be the biggest event of its kind since 11 August 1999, Astronomers said there will not be another total eclipse until 2026. Since the Moon is smaller than the Earth, and very far away, the properly dark shadow it casts will only be about 100 miles wide.

The Eurocrates in the European Crisis Union (EU) feared, that the March solar eclipse may cause power supply glitches across Europe. Green Solar power is now 10.5% of renewable sources in the EU, up from 0.1% in 1999. Well, this article wants only to summarize only the astronomy aspects, how to watch or photograph that spectacle.

I remember 1999, we were at an old monastery building, rented out for education purpose on the country side in Bavaria. We had organized a meeting there that very day and stepped out in the garden, 5 minutes before the event. Fortunately, the clouds had just opened up a bit. It was a total Eclipse, but this time, lower than 80% (67% in the South) you will not notice in significant change in the daylight.

Don’t damage your eyes with the sun

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A stern warning upfront. Dont mess with the sun. These rare, but spectacular events should be observed with precautions (use eclipse viewers and filters)! Otherwise you may damage your eyes. We have a nurse in our astronomy club, which was on duty 1999. Quite a few people were diagnosed with permanent eye damage, caused by even looking only with naked eye in the sun. The danger is even higher (i.e. complete blindness), if one uses optical instruments, like binocular and telescopes without the proper filter. Every time there is a solar eclipse you will find astronomers warning you to never look directly at the Sun. Even more importantly, you should not look at the Sun through a telescope unless you have a professional solar filter that covers the front of the telescope. Why?
The Sun is very bright and by focussing the light onto the back of your eye (the retina) with or without a telescope, you are putting a lot of energy (both optical light and infra-red) onto a tiny area. Even more scary is the fact that the retina of your eye does not have pain receptors, so you will not even feel the damage being done. It may not even become apparent until later. With reading the article, the viewer accepts, that he alone bears the responsibility for correct security measures during his observation. Do not think you will be safe if you just take a ‘quick look’. The filter must be in front of the optical system. with the exception of a Herschel System not discussed here.

Where and when?

Solar-eclipse-2015

The event is taking place on the morning of 20 March, and a partial eclipse will be visible across Europe, North Africa and Russia. In Munich, the partial eclipse – when the moon starts touching the sun’s edge – will start at 9.30am. The maximum eclipse will hit at 10.39 am and this will be the point when the moon is closest to the centre of the sun. By 11.50am the moon will leave the sun’s edge and the partial eclipse will end.


Time 24h	Object	Event
9h30m33.7s	Solar Eclipse	`Partial Solar Eclipse begins Position angle=262.7°, Position angle vertex=294.1°, Altitude=29.1°, Azimuth=129.0° SE`
10h39m04.7s	Solar Eclipse →graphical chart	`Maximum eclipse: Partial Solar Eclipse, Saros-Number: 120 Magnitude=73.783%, Obscuration=68.009% Separation=554.21", Position angle=335.7°, Position angle vertex=356.9°, Altitude=36.8°, Azimuth=147.3° SSE, Duration of eclipse=2h20m, Mean cloud cover=41.5%, ET-UT=67.7sec →Load path of the Total Solar Eclipse into Google Map/Earth`
11h50m56.1s	Solar Eclipse	`Partial Solar Eclipse ends Position angle=48.9°, Position angle vertex=55.8°, Altitude=41.2°, Azimuth=169.8° S`

What’s more, lunar perigee – the time in the Lunar month when the Earth and Moon are closest together – will occur the evening before the eclipse. This makes the 2015 Spring Equinox eclipse a ‘supermoon’ eclipse – sur the press will call that a supereclipse. ‘Nevertheless, it’s nice to have a supermoon, equinox and eclipse all falling on the same day.

Planning the Shot

Observation site

This time we went to an open field araound a little church in upper bavaria. Watching and photographing an eclipse really isn’t very difficult. It doesn’t take a lot of fancy or expensive equipment, but a safe solar filter or solar viewer. The first step in eclipse photography is to decide what kind of pictures you want and select site and lens accordingly. Are you after scenes with people and trees in the foreground and a small but distinct eclipsed Suns, which you can stack in a trail. An 28 mm lens will do and cover the path of the sun without a need to readjust,

Every shot has its lens. Canon 60Da and 28mm Lens vs. 600 mm APO telescope Note APS Chip size

Additional you want a close-up, then you dont need a photogenic foreground but good accessibility and a telescope. An 80 mm Apo with focal length of 600 mm will do (f 7.5). Of course the sky during expansion of darkness and end should be blocked. Plan, prepare and test your equipment long before. First consider where it is that you want to go, what ways on photographing the eclipse you prefer (plural in cameras), and the specific mood or close-up you want to create with your shots. Next visit the site at the time of the eclipse a few days day before and make trial shots. Knowing the location before hand is one of the best things you can do when planning your eclipse trip. The best thing is, if you have already been there before. Use Google Maps Satellite view to spot new locations for getting a nice background and foreground in the right direction. Next. You have planned everything down to details. You know exactly where and how you want to take photos at a specific location. Wouldn’t it be sad, if you arrived half an hour late?

Lens and focal length

A standard 50mm lens on a Canon 5D camera yields a minuscule 0.5mm image, while a 200mm telephoto or zoom produces a 1.9mm image (see table below). A better choice would be one of the small telescope and APS chip. I use a focal length of 600 mm, which is most common among small APO’s and yields a solar image of 4.6mm.

Focal length		Size Sun		Vollformat	APS 2/3
14	mm	0,13	mm	98×147	65×98
20	mm	0,18	mm	69×103	46×69
28	mm	0,26	mm	49×74	33×49
35	mm	0,32	mm	39×59	26×39
50	mm	0,46	mm	27×40	18×26
70	mm	0,64	mm
105	mm	0,96	mm	13×19	9×13
200	mm	1,83	mm	7×10	5×7
300	mm	2,75	mm
400	mm	3,67	mm	3,4×5,1	2,3×3,4
500	mm	4,59	mm	2,7×4,1	1,8×2,8
600	mm	5,50	mm
1000	mm	9,17	mm	1,4×2,1	0,9×1,4
1500	mm	13,76	mm	0,9×14	0,6×0,9
2000	mm	18,35	mm	0,7×1,0	0,5×0,7

Image sizes of the Sun in mm is focal length in mm / 110 for full size chip.

Camera and Chip Size

The imaging chip in most DSLRs is only about 2/3 the area of a full size chip. This means that the relative size of the Sun’s image appears 1.5 times larger in a DSLR and a shorter focal length lens can be used to achieve the same angular coverage compared to a SLR. See here some CCD and DSLR examples of my cameras. Note the MX716 and Lodestar ist not used for sun pictures.

Used Camera	MX716	LS	5D	60D	10D
CCD w (mm)	6,47	6,45	36,8	22,3	22,7
CCD h(mm)	4,83	4,75	23,9	14,9	15,1
CCD hor. (Pixel)	752	752	5616	5184	3152
CCD vert. (Pixel)	582	580	3744	3546	2068
Pixel	8,3	8,2	6,4	4,3	7,4
Pixel	8,6	8,4	6,4	4,3	7,4

For example, a 500mm lens on a DSLR Canon 5D full size produces the same relative image size as a 750mm lens on a DSLR Canon 60D. Another issue to consider is the lag time between digital frames required to write images to a DSLR’s memory card, adequate battery power, and speed as well as space on the memory card. Think if you want plain overview shots or, time lapse over full darkness period.

Exposure times for various combinations of ISO speeds, apertures (f/number) and solar features (chromosphere, prominences, inner, middle, and outer corona) are summarized above. This guide was developed from eclipse photographs made by the author, as well as from photographs published in Sky and Telescope. To use the guide, first select the ISO speed in the upper left column. Next, move to the right to the desired aperture or f/number for the chosen ISO. The shutter speeds in that column may be used as starting points for photographing various features and phenomena tabulated in the ‘Subject’ column at the far left. For example, to photograph prominences using ISO 400 at f/16, the table recommends an exposure of 1/1000. Alternatively, the recommended shutter speed can be calculated using the ‘Q’ factors tabulated along with the exposure formula at the bottom of the table. Keep in mind that these exposures are based on a clear sky and a corona of average brightness. The exposures should be bracketed one or more stops to take into account the actual sky conditions and the variable nature of these phenomena.

Solar Filters

You definitely need good eclipse eyeglasses and a Baader AstroSolar Safety Film (visually and/or photographically) or filters and optional ND and Solar Continuum filter.There are three types:

ASSF – Baader Solar Filter

AstroSolar™ Safety Film (OD 5.0) – visual and photographic solar observation with telescopes or binocular
AstroSolar™ Silber Foil (OD 5.0)
AstroSolar™ Foto Film (OD 3.8) advanced photographic solar observation with telescopes or binocular; This material is not intended to serve for protection during visual solar observation and not necessary for imaging the sun with camera or tele-lenses.

AstroSolar Safety Film OD 5.0 is used in all three prefabricated filters:

ASBF – Baader Solar Filter for binoculars and camera lenses
ASSF – Baader Solar Filter for spotting scopes, amateur telescopes and camera-lenses
ASTF – Baader Solar Filter for high-end telescope

A standard ND table brings them in context. ND stands for neutral density, which simply means that the filter is able to reduce the light that reaches your camera sensor (or film). The ‘neutral’ part means that the filter (should) do so without any color shift. The ‘density’ values are given both logarithmic (extension of the shutter time = 10 ^ ND) as well as in linear dimension (the extension of the shutter time).

neutral density ND log	light passing	attenuation (extension shutter time) ND lin	difference f-stops
0,0	100 %	1	0,0
0,3	50 %	2	1,0
0,45	35 %	3	1,5
0,6	25 %	4	2,0
0,9	12,6 %	8	3,0
1,0	10,0 %	10	3,3
1,2	6,3 %	16	4,0
1,8	1,6 %	64	6
2,0	1,0 %	100	6,6
3,0	0,1 %	1.000	10
3,8 **)	0,0063 % photographic AstroSolarFilm	6.310	13
5,0 **)	0,001 % visual AstroSolarFilm	100.000	17
6,0	0,0001 %	1.000.000	20
7,0	0,00001 %	10.000.000	23
8,0	0,000001 %	100.000.000	27

*) photographic AstroSolar Safety Film OD 3.8 is dangerous for visual without adding an ND 1.8

**) visual AstroSolar Safety Film OD 5.0 is usable for photographic purpose for advanced use, use OD 3.8

Unfortunately, the information ND are specified differently, i.e. most commercially offered ND8 filters are actually 0.9 ND filter. Look through or read the complete item description. Looking at the table above, you can see that, in fact, a filter factor of 8x is equal to ‘only’ 3 f-stops of light reduction (Standard ND8 filter with linear 8x elongation factor). This corresponds to a ND0,9 filter according to a logarithmic measure (e.g. Baader # 245 8322). The attenuation factor is 8 in any case. A ND1.8 filter factor has 64 attenuation.

Calculating exposure times

Say you are out shooting city in full sunlight and instead of a ‘regular’ shutter speed of 1/250 (without the use of any filters) you want to blur out the (hopefully walking) tourist your composition using a long exposure. Using the table above, you want to calculate how your exposure changes using a 10 stop ND filter.

ND Filter	3 stops	6 stops	9 stops	10 stops	13 stops	16 stops	20 stops
1/1000	1/125	1/15	1/2	1s	8s	1m	16m
1/500	1/60	1/8	1s	2s	16s	2m	32m
1/250	1/30	1/4	2s	4s	32s	4m	1h
1/125	1/15	1/2	4s	8s	1m	8m	2h
1/60	1/8	1s	8s	16s	2m	16m	3h
1/30	1/4	2s	16s	32s	4m	32m	8h
1/15	1/2	4s	32s	1m	8m	1h	16h
1/8	1s	8s	1m	2m	16m	2h	32h
1/4	2s	16s	2m	4m	32m	3h	64h
1/2	4s	32s	4m	8m	1h	8h	128h
1s	8s	1m	8m	16m	2h	16h	256h

Exposure SoFi - from the ultimate ressource - Totality Eclipses of the Sun THIRD EDITION by Mark Littmann, Fred Espenak Ken Willcox

Exposure SoFi – from the ultimate resource – Totality Eclipses of the Sun THIRD EDITION by Mark Littmann, Fred Espenak Ken Willcox

These exposure tables below are given as guidelines only. The brightness of prominences and the corona can vary considerably. You should bracket your exposures to be safe. For my 7.5 APO and selected ISO 200: 1/1000 – 1/250 – 1/60 bracketing is suitable for partial or annual sun.

To complicated? Here the minimalistic approach using the following equipment: a comfortable chair, a sturdy tripod, a cable release, a right angle finder, and a solar filter for the telescope or telephoto lens.

ISO		f/Number
100		2,8	4	5,6	8	11	16	22	32	44
200		4	5,6	8	11	16	22	32	44
400		5,6	8	11	16	22	32	44
800		8	11	16	22	32	44
1600		11	16	22	32	44

Feature	Brightness	Exposure time
Partial 4.0 ND	11			1/8000	1/4000	1/2000	1/1000	1/500	1/250	1/125
Partial 5.0 ND	8	1/4000	1/2000	1/1000	1/500	1/250	1/125	1/60	1/30	1/15
Bailys Beads	11			1/8000	1/4000	1/2000	1/1000	1/500	1/250	1/125
Diamond Ring	11			1/8000	1/4000	1/2000	1/1000	1/500	1/250	1/125
Chromosphere	10		1/8000	1/4000	1/2000	1/1000	1/500	1/250	1/125	1/15
Prominences	9	1/8000	1/4000	1/2000	1/1000	1/500	1/250	1/125	1/60	1/30
Corona 0,1 Rs	7	1/2000	1/1000	1/500	1/250	1/125	1/60	1/30	1/15	1/8
Corona 0,2 Rs	5	1/500	1/250	1/125	1/60	1/30	1/15	1/8	1/4	1/2
Corona 0,5 Rs	2	1/125	1/60	1/30	1/15	1/8	1/4	1/2	1	2
Corona 1 Rs	1	1/30	1/15	1/8	1/4	1/2	1	2	4	8
Corona 2 Rs	0	1/15	1/8	1/4	1/2	1	2	4	8	15
Corona 4 Rs	-1	1/8	1/4	1/2	1	2	4	8	15	30
Corona 8 Rs	-3	1/2	1	2	4	8	15	30	60	120
Annual Sun with OD 5.0	8			1/250	1/500
		1. Choose ISO
		2. Select lens focal ratio
		3. Straight down to feature column – approximate values

For ISOs or f-numbers not listed, use formula S = f power²/(I × B) to determine your exposure. S = exposure or shutter speed (seconds),f = focal ratio, I = ISO, B = brightness, for example partial an anular phases B= 500. Safety factor for overexposure 2. (Source: Totality Eclipses of the Sun THIRD EDITION by Mark Littmann, Fred Espenak Ken Willcox).

Example S = 7.5 ^ 2 / 2(200*256) = 0.0022 (1/500)

EV 0 corresponds to an exposure time of 1 s and a relative aperture of f/1.0. If the EV is known, it can be used to select combinations of exposure time.

I use an Italian Manfrotto (190) tripod with a compact geared head. The geared head has three large knobs that allow me to make small, precise adjustments in altitude and azimuth every minute or so to easily track the Sun. With the viewing display of my Canon (a ND 3.8 is photographic OD 3.8 is not safe for using the finder, except you use an additional glass ND1.8 log), I check the position of the image and then quickly lean back to view the eclipse. I focus manually on a sunspot and the focus ring is then taped down to secure it. After setting the camera in program mode and matrix metering, I’m ready to go. I just sit back with the cable release in one hand and my eclipse glasses in the other.

In case of a total eclipse, thirty seconds before totality begins, the Sun should be centered again and the solar filter removed. A dozen or more shots are quickly taken in the seconds before second contact and again after third contact. This results in nice diamond ring sequences.

Recording intervals for overview and Time lapse

tbd

Focus control over the time

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Don’t damage your eyes with the sun

Where and when?