90 mm Astrograph

Jack Schmidling Productions, Inc.
18016 Church Road ~ Marengo IL 60152
Phone:815 923 0031 ~ Fax:815 923 0032 ~ Email:arf@maxx.mc.net

Astrophotos JSP Homepage

This astrograph was built around a WWII vintage lens offered for sale by an individual on sci.astro.amateur. It was described as a B&L 508mm, F5.6 telephoto lens. After spending a few days in the machine shop and foundry, I ended up with a nice little astrograph that fits the niche between the 4 x 5 press camera and the 10" Newt.

The astrograph has a 4 x 5 film back but the field is restricted to a 2.5" circle of optimum quality, providing a field of about 7 degrees. The lens is useless at F 5.6 as the chromatic aberration is so severe that no reasonable focus is possible. However, at F 8, crisp focus is possible and only very bright stars show a chromatic halo.

The astrograph is mounted in the rings normally used for a guide scope and guiding is done through the 10".

[AG Photo]

90 mm Astrograph

Riding piggyback on the 10" Newt


The Pleiades

Scope: 90 mm Astrograph
EFL: 508 mm
Exposure: 30 min, F 11
Film: Hypered Techpan


This photo was taken at F11 before I realized that it only needed to be stopped down to F 8 to get rid of the chromatic aberration. In spite of this, some nebulosity is visible around Merope, the lower left star in the "dipper". It is hard to see in the scanned version but quite conspicuous on the print.



Scope: 90 mm Astrograph
EFL: 508 mm
Exposure: 60 min, F 8
Film: Hypered Techpan

COMMENTS: This photo was taken at F 8 for an effective aperture of about 2.5". We have all seen better pictures of M31 but after comparing this one with the one taken with my 8" Newt, I removed the latter from my M31 web page.

This object is simply too big for a normally configured Newt to get any detail at all at the edges of the galaxy. They just drop away like they are not there. This fact is nothing new to designers but it came to me as a slow learning process. The only way to get a good photo of M31 with a Newt is to center the edges in two separate photos. For a very dramatic example of how well this works go to the M31 feature on the Astrophoto page.


~ [Return to top of page]

JSP homepage