A PHOTOGRAPHIC STAR SURVEY WITH A 5.5 INCH SCHMIDT CAMERA
Foreword:
The following is a translation done in 2007 of a text written many years earlier. This was revised in December 2015 as an answer to Randall Rosenfeld, RASCís Archivist, who wished a copy for the Society archives.
1- Original project
I began the sky survey in 1977 after I acquired a 5.5 inch Schmidt camera from Celestron. This has been a long term project, which occupied much of my effort in astronomy during eight years. It had a precipitated ending in March 1985, when my career brought me to Ottawa for a three years term (I came back to Rimouski during Summer 1988).
Out of a total of 916, there are about 75-100 pictures I hoped to improve by taking new exposures, but this was never done. Nonetheless, the existing set of pictures has some merit and thanks to computer technology, now it is possible to reproduce it at very low cost.
Since I acquired my first CCD Camera (an ST6 from SBIG in 1993), my Schmidt is in a locker likely never to see light again. This is because digital cameras have made photographic emulsions obsolete. But, I find some consolation thinking that my Schmidt is one which has been used the most.
2- An electronic version in 1996
The idea for an electronic version of my survey came to mind in Spring 1996 after I realized I had all the required equipment at hands, i.e. a suitable scanner and a CD-ROM burner. I did some evaluation about the time required to do all the work and concluded that it could be done before the next Fall annual convention of the Fédération des Astronomes Amateurs du Québec https://faaq.org/wp/
I discussed the project with a friend, Luc Bellavance, who showed immediate enthusiasm. In particular, he wrote the code for the guide in html format (html was then pretty new), which you can open by clicking the file ìindex.htmî in the root of the DVD. This guide, in French, describes how the picture where taken, darkroom processed and filed. Luc also provided his expertise regarding image processing. Finally, Gaétan Laflamme has been of great assistance too, checking and correcting the orientation for a number of the scanned pictures (aiming the north at the top) and providing his expertise with the machine capable of writing CDs (DVD did not exist yet at that time). In 1996 a scanner and CD burner cost many thousands of dollars, we were fortunate to have access to the newly acquired one at the office where we worked (Québec Tel, which today is part of Telus). Each picture is contained in a BMP file which is a little less than 1.44Mbytes in order to fit on a 3.25" diskette. Today they make us smile, but diskettes were a popular medium at that time.
In order to help find your way amongst the multitude of pictures, I invite you to look at section 4 of the html guide or simply open the files TABLEAU1.GIF and TABLEAU2.GIF, the latter two being in the root of the DVD. They show, respectively, the numbering of the pictures from 0 to 12 and 12 to 24 hours of Right Ascension.
The unique hard copy of the survey (on 8 x 10 inch photographic paper and weighting 35 pounds) covers from 30∞ south up to the North Pole, for a total of 916 pictures. But, on the scanned version I omitted the band between 20∞ and 30∞ south because that area is quite close to the horizon from my 48.5∞ north latitude and the quality suffers from atmospheric extinction. In all, 820 pictures made their way into the electronic version.
The majority of the objects in the directory "Objets_particuliers" come directly from the original pictures of the survey, but there are exceptions. Some (Rosette, Veil, Horsehead, ..) have been taken after 1988 with the then high-tech hypered 2415 film, but still with the same Schmidt Camera.
3- Remarks about the pictures and their quality
The 916 pictures were printed on 8x10 inch, glossy paper. To me at least, glossy seems to enhance resolution. The limiting magnitude is around 13-14 and each frame cover an area approximately 8.6∞ x 5.9∞.They are not all of the same quality and there are many reasons for this.
When I began the project, I made test with the black and white films then readily available and decided to go with Kodak Plus-X, which showed smaller grains capable of resolving close stars better than other films. But, in retrospective that was not a good choice, because its sensitivity is too different compared to human eyes and also very poor in the red, thus inefficient with nebulas emitting the important H-alpha.
My main instrument at that time was a Dynamax-8 (Schmidt Cassegrain with optics similar to the Celestron 8, but poorer mechanics) with the Schmidt Camera mounted piggy-back. Of course that was not GOTO and aiming was done manually. Because of the shaky set up and various mistakes, many pictures are not well centered on the targeted field.
Such Schmidt is prone to generate scratches because of the way the film is loaded and unloaded from the camera, so there are many. Also, some stars are actually the mark of specs of dust, and accidental warping of the negative generated what looks like crescents. The guide in html format explains and illustrates these defects well.
If I were to do the scanning again, I would use higher resolution. Nonetheless, as is, on a computer screen it is easier to see fine details than on the original prints.
4- Content of the electronic version
In all, this electronic version of the survey contains some files in the root plus the following directories
- 01PICTURES_BMP_format (820 scanned pictures of the survey)
- guide_htm (a guide in html format)
- Objects_particuliers (photos of particular objects from my atlas)
- Observatoire_photos (photos of my observatory of the time)
Except for this readme file, all other written documents on this DVD are in French.
Damien Lemay, 2015-12-21