[LargeFormat] A really big lens

[Jim Hemenway]

Hi Michael:

I thought of that when I first saw the lens, (150 .75) but was too lazy 
to do any researching.

Hmm, an f.75 150mm long-portrait lens for a 35mm camera?

Jim


Michael Briggs wrote:
> On 10-Oct-2004 Jim Hemenway wrote:
> 
>>If only I had a 16x20 field camera for this!
>>
>>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3842947706&category=30076
>>
>>Well... that and the required $9,750
> 
> 
> 
> If you had a 16x20 camera and this lens, I think you would get only a small
> spot in the center of the film illuminated.
> 
>>From the auction description: "De Oude Delft (The Old Delft),   LARGE LENS G
> 11377 E150/0.75 RAYXAR".   "RAYXAR" suggests a lens related to X-rays, probably
> imaging a phosphor screen.  150/0.75 suggests 150 mm f0.75.  This would fit
> with imaging x-ray screens because, at least in medicine, one wants to reduce
> the x-ray exposure as much as possible.
> 
> Searching the web, I find pages on similar lenses:
> 
> http://home.intekom.com/franlet/astronomyPAGE69.htm
> http://home.intekom.com/franlet/astronomyPAGE68.htm
> http://www.macrolenses.de/ml_detail.php?ObjektiveNr=158
> 
> The Dutch name of the lens is because they were used on old Philips x-ray
> machines.
> 
>>From the optical diagram for a 65 mm lens on the first link, the film is placed
> only 0.8 mm behind the rear element.  The auction photos show the rear cell to
> have a much smaller diameter than the front cell, perhaps 3 or 4 inches
> diameter.   So the image can't be larger than about 4 inches in diameter.
> 
> This is not a large format lens -- it is a super-fast lens.  f0.75 is close to
> the theoretical limit for a lens in air: f0.5.   This is why the front element
> is so huge.
> 
> Auctions purporting to sell satellite optics should be considered sceptically. 
> Would a space agency sell a spare lens?  More likely they would keep it for
> future use or for display in a museum.  It more likely that the seller is
> misinformed or a fraud.
> 
> --Michael
> 
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