IMAGING WITH APOs

ASTROPHOTOGRAPHY with APOs
using 4 x 5 FILM

INTRODUCTION
With the introduction of the super-apochromats from Roland Christien and Astro-Physics in the late 1980's we saw the opportunity open for image sizes and fields that we could never obtain using Newtonians. The first A-P APOs that we used extensively for astrophoto work included a 6-inch f/9 and a 4-inch f/8. With these systems, 120 format film produced spectacular images across the entire film plane.

As Roland's line of APOs expanded, their capabilities expanded as well. In 1991 the EDF line offered up a potential for hi-res wide field imaging that was too tempting to pass up. The 6-inch f/7.5 EDF was capable of covering a field of 4-inch diameter with star images of 12 micron diameter over the entire field. At that time, Roland had not built a camera system for the 4x5 film format (the standard EDF is designed to work on a 6x7cm film format and use a PENTAX 6 7 camera body) and so Brad began to build a camera body that would incorporate Roland's field flattener into the design of a film holder for 4x5 film formats. The first exposures were made in 1993 and after these, a final version of this camera was constructed and was shown to Roland at the 1994 WSP. The camera allows for a Nitrogen purge to be used throughout the exposure in order to keep the hypered film at its peak performance level by keeping the film away from the degrading effects of atmospheric moisture.

Over recent years other manufacturers have come out with several APO designs intended to compete with the AstroPhysics systems. We both have inspected a number of these and star tested them in the field. From these experiences we can say that it is quite clear that all APOs are definitely NOT equal !! While several designs have been excellent when star tested ( most notably *some* very expensive flourite designs ) they were not designed with imaging in mind and would only serve our needs if we were solely interested in 35mm or CCD imaging. Other APOs were found to be quite inferior to the AstroPhysics EDFs when star tested. Given this quality dispersion among APO manufacturers we strongly urge anyone interested in moving to an APO system to take the efforts to find one in use and to star test it ( or several ) before buying. You should also be sure that you know that the manufacturer will stand behind his/her product and will allow you a trial period with a full return and refund if you are not 100% satisfied. For details (!!) on star testing scopes we highly recommend Dick Suiter's excellent work on the subject!

IMAGES and the INTERNET
With 4x5 negatives on the 6-inch EDF, the useful field is over 4 degrees in diameter. The negatives can easily be used to produce prints of 40x50 inch proportions. Most of the images you see here on this web page are LOW RES scans (~ 70 DPI ) designed to meet the restrictions of the internet and the CRT monitor. If we posted a high res image here it would occupy many CRTs ( and > 4 MB ! ).

In order to give a flavor of what is recorded in a single neg we would like to show several views that have been obtained from a single negative of the North American Nebula (NGC 7000).

The first image shows the entire 4x5 negative of the area around the North American Nebula.. While this image is nice looking here on the net, it is quite spectacular in a print and magnificent in prints of 16x20 inches and larger.

To present to you some of the details that are present in this image we have scanned two areas of this image at relatively high resolution.

The first is the area of the Pelican Nebula to the east of the North American. This high res scan shows details that are basically lost when one tries to present the entire image in a format that is convenient for internet consumption. Not that while this portion of the 4x5 neg is over 1 inch off axis that the star images are still perfect showing no degradation when compared to star images at the center of the negative.

Another high res scan of the area of the 'Gulf of Mexico' is also shown to illustrate the capabilities of the 6-inch EDF when 4x5 film is used.

A further advantage of using a camera that can use 4x5 film, and 4x5 film holders is that Roll Film backs can also be employed to allow one to use 120 films and film formats of 6x7 or 6x9 cm. For color films this allows the user to have a much wider selection of films for use. Of the roll film holders on the market, the TOYO roll film back seems to offer decided advantages over some of its less expensive competitors.
PROCESSING PROBLEMS with 4x5 Tech Pan
The first photo runs with this camera and 4x5 Tech Pan produced disastrous results. The film was very non-uniform in appearance and was unprintable. Several months of work went into perfecting the process of this film so as to obtain extremely uniform film processing. George Greaney and Jerry Lodriguss both offered up their experiences with processing systems to help find a commercial system that could produce the uniformity required for the high contrast Technical Pan emulsion. The end result was the use of a JOBO rotary processor system and the adoption of an elaborate pre-wash system.

The move to 4x5 sheet film showed us both that some of our previous 120 film shots which showed 'mysterious fogging' were really the result of non uniform processing of the 120 Tech Pan. The cause of these mysterious fog patches could never be tracked down due to its haphazard appearance and lack of traceability. The 4x5 films clearly showed that the problem was a processing problem. The testing of virtually every processing system known led to the adoption of the rotary system to solve this problem. The details of this will be presented in our new book on astro-imaging (Film and CCDs !!) that will be published by Willmann-Bell and which is now in editing stages.

Enjoy !!!

Brad Wallis
If you have comments on this HINTS piece or on any of our other HINTS pieces, please send e-mail to Robert at: robert.provin@csun.edu

If you have suggestions for additional HINTS pieces, please send us e-mail also !!

The material in this note may be used for personal use only any reproduction without written consent of the authors will be prosecuted. Copyright 1997 Brad D Wallis

See "A MANUAL OF ADVANCED CELESTIAL PHOTOGRAPHY"
for more comprehensive information on many other topics of interest for astrophotography.
-- THIS MATERIAL IS FOR PERSONAL USE ONLY --

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