my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Magnacom effect on F number of long focal length lenses?

Author Topic: Magnacom effect on F number of long focal length lenses? George May Film Handler Posts: 60 From: Bath, United Kingdom Registered: Nov 2001 posted 12-18-2006 06:54 AM                        I'm rationalising the set of (long focal length) lenses I carry for a mobile drive-in. One of my options is to use a Magnacom with one main lens to give me a range of focal lengths. In particular, I have an f1.6 105 mm Isco I'd like to use. Using this with a Magnacom I think I can get an effective focal length of over 170 mm. But the diameter of the Magnacom suggests that my f number will rise to well above 2.5. In the past on these forums people have expressed diametrically opposed views on the effects of Magnacoms on light loss. Can anyone supply me with any useful pragamatic quantitative information to help me here? Thanks. A Happy Christmas to you all.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-18-2006 03:11 PM                        There is no question that there is light loss with Mangecoms; this is transmission loss. Whether the gain provided by the lower f stop of the prime lens will offset the transmission loss in the magnecom is the question. My guess is that it is a bit of a wash: light will be about the same. Your advantage will be variable size of picture and the possibility of the center focussing slightly further away, lending some better focus to a curved screen. I used this to great advantage in the days of 70mm. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-18-2006 05:30 PM                     I believe that Dwight Lindsay at Schneider once quoted me 92% transmission for the Schneider Magnacom. There is definitely not much glass in there to create a loss.....! Older "coke bottle" Magnacoms will be worse though, er should we consoder em all coke bottles . The biggest objection that I have with them is loss of contrast and image distortion both of which are more than just negligible. Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-19-2006 10:56 AM                        Glenn Berggren once told me that the new multi coated Magnecom had 20% more light than the old ones. He had previously said that there was no light loss on the old ones. Therefore we have a lens with light GAIN????? Visions of a drive in with a 500 watt bulb and 45 magnecoms are what I still think of when the discussion leads to Margecoms. Louis  |  IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.