Venus trying to eclipse the Sun
These photographs were made at about 6:30 am local time by a half-awake Andrew Davidhazy from a cow pasture located in the picturesque suburb of Rochester, NY known as Honeoye Falls. To see enlarged views of the above photographs simply "click" on them and they will show up in a new window. Return here by simply closing that new window.
The photograph showing the full disk of the Sun was taken with a Questar telescope of 1500 mm focal length with a solar filter fitted onto the front of the scope. At EI of 100 with a Canon Digital Rebel the exposure time was about 1/4 second.
The photograph of the Sun with Venus and some tree leaves, as well as the one where Venus seems to be reaching out for the edge of the Sun (an optical phenomenon I believe) were taken with a 300 mm Canon f/5.6 FD lens projecting an aerial image in front of a 28 mm Schneider Componon enlarging lens set to f/16 and projecting an enlarged view of the primary image formed by the 300 mm lens onto the sensor of the Canon Digital Rebel.
Lenses and cameras were joind with all the extension tubes and bellows I had at hand as shown in the illustration below. I am sure there could have been a "neater" arrangement buy one needs plenty of projection distance to multiply the prime lens' focal length by projection ... or a short intermediate lens. The exposure time was 1/4000 second because I did not have a filter for the lens.
The equivalent focal length of this combo was something like 3000 mm or 3 meters!
This is because the enlarging lens placed behind the 300 mm Canon lens enlarged the aerial image by a factor of about 10 times. Of course the relative aperture of the combination is very small so this method lends itself as a solution when photographing subjects that are very luminous - such as eclipses. However, it is an approach that should be remembered in cases of "emergency".
Note that not only does the light level drop at the image plane but resolution is also affected. This is because the primary image, which for all intents and purposes has good and useful resolution when projecting an image onto a piece of film or a sensor now is enlarged and the resolution of the projected image is as many times poorer than that of the prime lens as the starting resolution divided by the degree of image enlargement provided by the enlarging lens. Actually a bit worse because the enlarging lens itself degrades the image slightly.
You might think that it would be better to simply enlarge the primary image formed by the 300 mm lens on film or a digital camera's sensor but the problem with that is that film or a sensor has its its own limits on resolution and this is at least partially avoided by projecting the aerial image formed by the prime (300 mmm in this case) lens.
Finally, consider that when there is plenty of light available making an extreme telephoto lens from a shorter prime lens is something that can save the day for the long distance photographer.
To wrap up I must confess that I did do some local color and saturation plus sharpening adjustments to the basic digital image files.
Feel free to drop me an email about this technique if you have any questions or constructive comments! You can reach me at firstname.lastname@example.org.
Choose School of Photographic Arts and Sciences for information on Rochester Institute of Technology's photography related programs or Imaging and Photographic Technology to visit the website of this unique BS imaging program.