Laboratory of Cold Atoms Near Surfaces

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Sunspots

Welcome on the page devoted to the observation of sunspots. Information about solar activity and the official sunspots numbering are regulary updated on spaceweather.com.

Below you can find hints on how to take pictures of sunspots. Some of the pictures are collected on a separate page here. All pictures shown on this page were taken in Cracow, Poland with Panasonic DMC-FZ45 zoom camera (max focal length  108 mm, equivalent for 35 mm – 624 mm).

Remember – SAFETY FIRST! Never look directly at the Sun with bare eye or through binoculars or a telescope! The observations are possible only using a proper filter or performing so called ocular projection, when the Sun image is formed on a screen by  binoculars or a telescope!

There are two main ways of sunspot observations:

  1. directlyusing a filter and looking at the Sun with bare eye, through binoculars or a telescope with a filter or taking a photo with a filter on a camera objective. Sometimes, under proper circumstances we may use a natural filter formed by Earth atmosphere. Globally – at sunset or locally, especially in the morning, when there is a layer of low-laying fog. However, this method is not safe and never look at the Sun through a fog using binoculars! The best way is to take a photo without a filter, as shown here.
  2. indirectly – looking at the Sun image on a screen (may be just a piece of paper) formed by binoculars or a telescope mounted on a tripod.at Camera obscura is also one of the useful (and oldest) methods. Ocular projection seems to be the safest method and allows observation by many people at the same time.

1. What is the best filter for direct observations?

Below you can find a few values of the transmission of three different filters for three wavelengths:


35 mm film
floppy disc 3.5 inch
Baader ND5 filter
532 nm
2.2%
1.2%
0.01%
650 nm
2.4%
0.3%
0.001%
780 nm
0.5%
1.3%
0.01%

As you can see the safest filter is a cheap neutral density (ND) filter from Baader with optical density of 5 (there is also a ND3 option for photography only). Anyway, please remember that in the above table UV and IR are not covered, so filters other than the one from e.g. Baader (for which the protection is guaranteed) might not be safe!

The cheapest dedicated filter is made out of foil. The only thing to do is to mount it on the binoculars, telescope or camera objective. Never mount it on the ocular – for several reasons! The left picture shows the filter mounted with a tape on a cardboard ring.  The ring fits tightly the objective of small binoculars as shown below. In the right picture you can see the filter glued to the inner part of the lens hood.

filter for binoculars


filter for the camera objective


binoculars with filter

8x30 binoculars with a filter on one of the objectives (you have to block the other objective or to add a second filter)


Before each use you have to check if the filter is not damaged and if it is fixed properly.

As with pictures of Jupiter, Saturn and Moon, image-stacking method (with RegiStax software) greatly reduces noise:

sunspots - image stacking

click to enlarge

FNumber 8.0, exposure time 1/320 s, ISO80, 24x zoom (focal length 108 mm). 10 pictures were used for image-stacking (11.11.2011)


Amateur picture of the Sun (left) combined with a professional image taken from spaceweather.com (right):

sunspots - comparison with spaceweather.com


Przetestowano również filtr foliowy Baader 3.8 (nominalna transmisja to 0.016%). Filtr ten może być używany jedynie do fotografowania. Dla aparatu Panasonic DMC-FZ45 i powiększenia optycznego 24x trzeba było użyć maksymalnej przesłony, minimalnego czasu naświetlania (1/2000 s) i minimalnego ISO (80). Ze względu na dużą jasność zdjęcia, plamy są dobrze widoczne dopiero po zwiększeniu kontrastu i zmniejszeniu jaskrawości zdjęcia.


sunspots - Baader 3.8

click to enlarge

  Picture stacked from 18 images taken with the camera on a tripod. FNumber 8.0, exposure time 1/2000 s, ISO80, zoom 24x (focal length 108 mm) 09.08.2012


A 35 mm unprocessed photographic film was also used as a filter when taking pictures of sunspots and partial solar eclipse. A piece of film was mounted on a piece of cardboard with a small hole in the middle:

filter made from 35 mm film


Picture taken with the filter shown above (06.11.2011):

sunspots through a 35 mm film

FNumber: 5.2, exposure time 1/125 s, ISO80, 24x zoom (focal length 108 mm).


One can also get interesting pictures through a morning fog. But be very careful!

sunspots through a morning fog

sunspots through a morning fog

click to enlarge

07.11.2011

click to enlarge

03.11.2011


2. For the indirect Sun observation we just need common binoculars without any filter. The 8 times magnification is enough, but the higher the magnification the more spectacular images we get. For best results we should mount binoculars on a tripod:

binoculars on a tripod for ocular projection

If this is not possible, we may fix it with some effort even to a chair. We point the binoculars objective towards the Sun. Initially we may find the correct position of binoculars by looking at the shadow of binoculars on a piece of paper – it should be the smallest. When we see a bright spot on a piece of paper, we may adjust the focus to get a sharp image. Then we may increase the distance between binoculars and the screen, adjusting the focus at the same time. For 8 times magnification the diameter of the Sun image is about 30 cm at about 4.5 m of distance between binoculars and the screen and 80 cm at about 12 m. The main point is that the Sun, binoculars and the screen should lie on one line and the screen has to be perpendicular to this line. Otherwise the image will be distorted. A simple opaque cover should be also used to reduce the amount of light which shines directly on the screen – without going through binoculars. You may see such a cover made from a black paper in the picture above.

Here we show two pictures of the Sun taken in ocular projection using 8x30 binoculars (left) and 15x70 (right).

sunspots - ocular projection

sunspots - ocular projection

Picture of the Sun on a wall, about 4.5 m behind 8x30 binoculars. Sunspots are seen in the black circle (06.11.2011)

click to enlarge

Image of the Sun on a piece of paper a few tens of centimeters behind 15x70 binoculars. The diameter of the Sun image is about 8 cm (21.01.2012)


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(c) 2011, 2012 Tomasz Kawalec