In short, you can use the visual version of the filter (AstroSolar® Safety OD 5.0)without any problems for prime-focus photography with a DSLR. You need the photographic version (AstroSolar® PHOTO OD 3.8) only for higher magnifications, e.g. if you use eyepiece projection to achieve high magnifications and to capture details on the sun with video cameras.
Single Images, Images of the complete Sun an Focal Photography: AstroSolar® Safety Film (OD 5.0)
If you use a camera which is attached directly to the telescope (in the prime focus), without eyepiece or camera lens, then AstroSolar® Safety Film (OD 5.0) is perfect for you. Then, you also don’t need to worry about looking into the sun through the camera’s viewfinder, and a modern digital camera will achieve exposure times which are so short that they will freeze the seeing. As a general rule, you should always use the display / live view of your camera and never the optical viewfinder, if you are working with the OD 3.8 film – with Safety Film OD 5.0 you can also use the viewfinder.
The solar granulation can be captured even with 600mm of focal length, although a good location (clear, transparent sky) and some image manipulation for enhancing the contrast are really helpfull. The aperture is as important as the focal length, because it defines the resolution of the telescope. A good lens telescope with 80-100 mm aperture is enough. But to see these structures clearly, you should use focals lengths of 1500-2000mm and at least an aperture of 125-150mm – then you have a focal ratio of about f/10, which allows for sufficently short exposure times with a DSLR and Safety Film OD 5.0. But don’t forget that these are only aproximate values, which also depend on the resolution of your camera – that is, the pixel size. The focal length which is necessary to project the whole sun onto the sensor depends on the sensor size – as a rule of thumb, the sun appears ca. 1 cm large for each meter of focal length.
Eyepiece Projection (Afocal Photography) and Lucky Imaging with video cameras: Photographic Film (OD 3.8)
You can reach higher magnifications with eyepiece projection. For this, you need either slim 1¼”-eyepieces and an adapter for projection, or – better – eyepieces with a thread close to the eye-lens like our Hyperion 68° or Morpheus 76° eyepieces. You can find many possible ways for attaching a camera in the Hyperion PDF. Formulas for calculating the resulting focal lengths (sorry, so far only in German) can be found on the description of our OPFA – Ocular Projection and Focal Adapter.
You can reach extreme focal lengths easily with eyepiece projection – thus, the image will get too dark, and you need the photographic film to achieve short exposure times. The seeing will be more prominent, too, so it is better to take many images instead of single shots. For this, you need a video module, so that you can select and process only the best images – this is called “Lucky Imaging”.
So, you can usually take the Visual Safety Film (ND5.0) also for photography, als long as you don’t take solar photography to the extreme.