[Konvas] Mirror lenses...

[colcam at aim.com]

 Mirror lenses "flip" the image exactly like other lenses-- try your SLR camera lens without the prism-- the image is upside down.  You flip the negative when you print in both still cameras and movie cameras. 

Mirror lenses don't have the same method of restriction of light, so ND is used instead of an iris, but that means DOF is not as adjustable.  

The 270 degree take off view from a telescope is the optical path-- internal mirrors, not the lenses. 

The only mirror I have use to shoot movie work was a 500mm  f4 with a 3x on it-- an effective T11 lens 1500mm in focal length hung on the rods on front of an Arri 2b at 48fps.  The reason I used it was we needed LONG and FAST, and that was as long as we could get and wind up with enough light on the film for the gag.

Good mirror lenses are expensive, good straight optical path lenses are expensive--  a straight 400mm f6.3 may be sharp and cheap, a straight 500mm f8 may be sharp and cheap-- but swinging one around as you work means one is easier to use than the other one.  If the lens is of good quality the image is not warped, if it is of poor quality, it is warped-- straight or mirror.  This has little to do with cost, but higher speed and better quality always cost more than junk.

This has been a recording.

 

 

-----Original Message-----
From: Adam Frey <thefirstrule at chainsawlinux.com>
To: Konvas Discussion List <cinema at konvas.org>
Sent: Sun, Nov 8, 2009 7:40 pm
Subject: [Konvas] Mirror lenses...









Let's talk about mirror lenses. I've never owned one; well at least for 
any of my cameras. But I do own a telescope that uses a mirror lens. 
That said, I see them on Amazon and ebay quite often. Usually 500mm and 
up. Given, they don't seem like they are able to adjust the f-stop, but 
most of them are at least f6.3 to f8 like this one: 

http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Dphoto&field-keywords=mirror+lens 
 

Now, in my telescope, it flips the image 180 degrees. In other 
telescopes I've used, it flips the image something like 270 degrees or 
something (can't remember exactly). 
 

So, my question is: 

1) Anyone used them for Motion Picture work? 

2) is the image warped in any way? 

3) is the image flipped? 

4) is getting a mirror lens worth it, or are they cheaply constructed? 

5) did the LOMO factory build any mirror lenses? 
 

With the last one, I don't remember seeing any LOMO mirror lenses, but 
has anyone else seen one? 
 


Cheers, 
 

Adam Frey 

Director/Cinematographer