This article has been produced based on my practical experiences when taking photographs of the Sun using telephoto lenses and a tripod.
When attempting to take photographs of the Sun great care must be taken. On NO account look at the Sun through any optical device, telescope, binoculars or camera lenses, without the correct filtration. The Sun is very bright and emits a large amount of ultraviolet and infrared radiation, if this is allowed to enter the eye as a focused image, a lot of damage could be caused, even blindness, so take care.
If we are to photograph the Sun we must not only reduce the amount of visible light but also ultraviolet and infra-red radiation to enable the photographs to be taken safely, and to bring the light level down to a level where the film will record a well exposed image.
It is essential that the correct filter is used in order that no damage is done to the eye, or even the equipment. The filter MUST be placed over the front of the objective and not part way along the light path, as some long focal length lenses allow. The reason is, we need to stop the heat from entering the lens, the Sun emits a large amount of infrared which would heat up the elements of the lens, and parts of the camera, possibly damaging them.
The filter that I use, and will describe here is Mylar film. Mylar is an aluminium coated plastic film that is used in the food packaging industry, for sealing products such as crisps, soup etc. It is also use in other industries.
Mylar can be obtained form a number of sources, but the best and safest is from an astronomical supplier, that way you will know it is suitable for the job. The quality of the coating varies tremendously so beware you don't want to use Mylar that has any flaws or more transparent areas on it.
The Mylar I used came from the food packaging industry which was not very dense but by using 2 sheets together produced the correct density.
Mylar film work by reflecting nearly all the light and heat allowing only a small percentage of the light through. It has a drawback as a filter in that it introduces a blue colour to the Suns image, that's something you'll have to live with.
There are two ways of attaching the Mylar over the lens, one is to just use an elastic band to hold it in place, use more than one band just in case it should break while you are looking through it. Or you could mount the Mylar in a holder, and make an attachment to hold this in place in front of the lens. Don't worry about getting all the wrinkles out of the film, it does not degrade the image as the film is very thin. In fact you may cause the coating to crack if the film is pulled to hard.
Photo of 800mm telephoto lens with a Mylar filter on a home made holder. Holder made from sheet of aluminium with an aperture (4" dia) covered with Mylar and taped in place.
Very dense welding glass
No. 14 not any lighter. This produces a green image and the optical quality is very poor as the glass is not optically flatExposed and developed Black & White negative film
This must be completely over exposed and developed to the maximum density, and must be a metal halide film. It's the silver in the film that reflects the light and heat.Note. In all cases the filter you use MUST be placed over the front of the lens. I can't vouch for any of these alternatives as I have only used Mylar film.
If you going to use any filter other than Mylar (purchased from an astronomical supplier) then you must take further advice on it's suitability and how to use it.
I can't be held responsible for any injury caused by the Sun while observing or taking photographs.
In order to demonstrate how large (or small) the Sun appears on a 35mm film I have taken a number of photographs of the Moon with different lenses ranging from a wide angle lens of 24mm focal length right up to an 1600 focal length telephoto (an 800mm lens with a 2x teleconverter). The Sun and Moon are the same angular size in the sky
As you can see you really need a focal length of 800mm or over the best being 1600mm which allows the Sun to fit in the frame easily. The following table shows the size of the moons image on 35mm film when taken with various focal length lenses.
Focal Length Size of Image (mm) (mm) 24 0.22 28 0.25 50 0.45 80 0.73 135 1.23 200 1.82 300 2.73 500 4.55 800 7.27 1000 9.09 1600 14.55You can use the following calculation to determine the image size on 35mm
It is often said that teleconverters degrade the image and should be avoided, and that they also loose a lot of light, typically 2 stops for a 2x converter.
What I have found by experience is...
"An image produced with a teleconverter is FAR SUPERIOR to an image taken with the same lens without the converter and having the image enlarged to the same scale."
Why ? Well it's down to the resolving power of the film, if you enlarge a negative or transparency you enlarge the grain, and the amount that the teleconverter degrades the image is less than you loose by enlarging the film. And you have the added advantage of having a larger image on your slide in the first place. I can not say this of 3x converters as I have only used 2x and I would certainly recommend only using good quality multi-element converters that have all the optical surfaces coated.
You need not stop at one teleconverter, I regularly use two 2x converters together and the results are fantastic, far better than enlarging the image afterwards.
As to the light loss, well, yes please.
I would like to add that a 1000mm lens is likely to produce better images than a 500mm with a 2x converter, so if you have a choice use the longer lens.
Most of my photographs of the Sun were taken with a Practica MTL5B, a 35mm SLR (Single Lens Reflex) manual camera that takes low cost 42mm thread lenses. The camera was also very low cost.
The camera must have a cable shutter release. This is used to reduce any vibrations that may be caused by operating the shutter.
I can't emphasise enough the necessity of a good strong heavy tripod that does not vibrate like a tuning folk every time the shutter is pressed. If you can't keep the camera still during an exposure you will be very disappointed in the results.
A driven mount is not needed, the only advantage in using one is to keep the Sun in the centre of the viewfinder. Only short exposures are needed as there is no problem of the Sun trailing, and so spoiling the image.
Photo of 800mm telephoto lens and Zenit camera on a fixed tripod. Note the Mylar film covering the lens, in this case it was held in place by a rubber band.
The Sun is a very bright object, slow fine grain films can be used, indeed best results will be made with the slowest of the films...
Both these are 25 ISO rated films and are capable of producing very sharp well defined images.
- Kodak Technical Pan 2415 for black and white photographs
- Kodak Kodachrome 25 for colour slides
As you move to faster films, the film grain starts to degrade the image. But you may need to use a slightly faster film to get the correct exposure. As the density of Mylar film will vary depending on where you obtained it, a faster film my be required to maintain the fast shutter speeds that you generally require in order to get moments of good seeing and to try and freeze any camera movement and the movement of the Sun across the film.
This is going to be a matter of experiment, all you can do is run through a roll of film using lots of different exposures, altering the aperture and exposure time. Ideally the exposure time wants to be as short as possible i.e. about 1/1000th sec - 1/2000th sec, this is fast enough to freeze any bad seeing and camera vibrations.
Exposure: 1/1000 f32 (2 sheets Mylar) Film: Ektachome 100HC Date: 89/03/11 08:13 UT
Exposure: 1/1000 f32 (2 sheets Mylar) Film: Ektachome 100HC Date: 89/06/13 11:35 UT
Exposure: 1/1000 f64 (1 sheet Mylar) Film: Kodachome 25 Date: 89/09/06 06:46 UTDriven mount, only used to keep the Sun in the viewfinder. At this scale the Suns disk will not fit in the picture.