# Did the medium range KTM tracking cameras for the Shuttle really have a “150 inch lens”?

The Curious Droid YouTube video How did NASA get those great film shots of Apollo and the Shuttle? found here and linked-to in this comment contains the following passage starting at 05:26:

This piece of footage here of the shuttle Discovery at T+40 seconds is shot from a medium distance camera about 3.8 kilometers from the launch pad using a 150 inch lens with a 4,000 mm focal length as the shuttle is accelerating through 20,000 feet. As discovery goes through a 145,000 feet at 123 seconds into flight, the boosters separate, which is captured here by another 150 inch, 4,000 mm focal length lens on a KTM. The weight of the lens alone on these was about 115 kilograms, and the tracking to keep the discovery in the frame was done by a human, and not an automated system. After three minutes the job of filming the ascent was transferred to the largest telescope on the site, the permanently mounted 24-inch aperture Recording Optical Tracking Instrument, or ROTI. With a focal length of up to 12,700 mm, ROTI had enough magnification to follow the launch for up to five minutes after liftoff. ROTI used both radar assisted tracking and a joystick for manual adjustment, which had such a fine sensitivity but it could register the heartbeat of the user if held too firmly.

High quality, imaging, achromatic lenses are never 150 inches (~3800 mm) in diameter. The Yerkes Observatory's 40 inch (1,000 mm) refractor is the largest diameter refracting telescope ever built, and that was about f/18.

Even if it were a reflecting 3.8 meter diameter primary, f/1.05 would be an impressive looking instrument.

Question: What are this optical system's actual specs, such as diameter of primary lens or mirror, focal length, and number of reflecting and/or refracting elements? It sounds amazing!

• 4000 mm is just over 150", so the 150" refers to focal length, not diameter. – Hobbes May 5 '18 at 7:29
• @OrganicMarble For want of a "c", the lens was organic. Thanks! – uhoh May 5 '18 at 15:15
• now all you need is an h... – Hobbes May 5 '18 at 15:34
• @Hobbes (blush) I'll get there eventually. At least I spelled Yerkes right. – uhoh May 5 '18 at 15:47
• The Yerkes refractor was not the largest diameter ever build, the Great Paris Exhibition Telescope of 1900 had a lens of 1.25 m (49 inch) diameter. – Uwe May 7 '18 at 16:55

The lens is a Brashear (now L3) SR 150 lens.

Focal length 150" - 3810 mm
Aperture 15.4" - 391 mm

This is a Cassegrain-type lens. The lenses are installed on an L3 Kineto Tracking Mount.

A really good overview of all the photography going on during a Shuttle launch is Ascent, an hour-long video that shows samples from each type of camera. Many of these cameras are high-speed, so you get fantastic slow-motion shots of the Shuttle taking off. The narration has a lot of detail on the cameras used, and all the stuff going on in the first minute after launch.

This PDF has a map of the camera sites around the pad.

• Super-informative and well-sourced answer, thank you! – uhoh May 5 '18 at 8:59
• "Ascent" is indeed a remarkable film. – Organic Marble May 5 '18 at 11:28
• The Cassegrain telescope is not a refracting telescope, it is a reflecting telescope. It may be build without any lenses, only with curved mirrors. – Uwe May 6 '18 at 20:02
• you're right, but the term "lens" is used here as "the optical assembly in front of the film transport" as is common in photography. The manufacturer also calls it a lens. – Hobbes May 6 '18 at 20:18
• So it is, in astronomer terms, a 15-inch f/10, approximately. – hobbs May 7 '18 at 5:58