diego_alonso Posted February 12, 2006 Share Posted February 12, 2006 Hello everybody, i would like to know if a 6x9cm roll film back willchange the focal lenght of the lenses, i mean a 150mm on a 9x12cm(4x5") is a 43 mm on a 35mm format so using the same lens on a 6x9cmback will be like 65mm on a 35mm????Thank you very much for your help. Link to comment Share on other sites More sharing options...
tito sobrinho Posted February 12, 2006 Share Posted February 12, 2006 Diego: The focal length does not change. A 200mm lens on a 35mm camera has the same focal length on a 6x6, 6x7, and 6x9. What changes, is the format. Link to comment Share on other sites More sharing options...
diego_alonso Posted February 12, 2006 Author Share Posted February 12, 2006 Sure i did not expressed well, i mean the rapport. Link to comment Share on other sites More sharing options...
gary_s. Posted February 12, 2006 Share Posted February 12, 2006 Well as stated, the focal length of the lens does not change, however the apparent length does change. For example a 150m lens on 4x5 is roughly equal to a 40mm lens in 35mm terms. On a 6x9, the same lens is roughly equal 64mm lens, depending upon how you do your calculations. I took these figures from http://www.largeformatphotography.info/lenses/ Hope it helps. Gary Link to comment Share on other sites More sharing options...
dan_fromm1 Posted February 12, 2006 Share Posted February 12, 2006 Aaaargh! Why all these questions about the effect of changing the size of the camera's gate on focal length when what's at issue is cropping and its effect on the angle of view? Think angle of view. For those who are severely challenged by arithmetic and thinking in general, a lens of focal length x on nominal 6x9 sees very nearly the same angles of view, horizontal and vertical, as a lens of focal length 0.43x on 35 mm. .43 * 150 = 64.5. Link to comment Share on other sites More sharing options...
tito sobrinho Posted February 12, 2006 Share Posted February 12, 2006 Yeah! When I use a 300mm on my 8x10 camera and change the back to a 4x5 format, it does not mean I would have a 600mm lens. Link to comment Share on other sites More sharing options...
glen peterson Posted February 13, 2006 Share Posted February 13, 2006 Tito 8x10 is 4 times larger than 4x5. Therefore I think you have a 1200mm lens. Link to comment Share on other sites More sharing options...
diego_alonso Posted February 13, 2006 Author Share Posted February 13, 2006 That�s the point, i am buying my first LF camera, i will travel to Namibia and i think that is easier to devlope or kepp the roll films than sheets, anyway i would like to use both, i have the camera but not lens yet so before buying a lens i would like to consider some things. Do you have the same angle of view with a 90mm on a 9x12 than a 6x9. How do you make the composition and the focus??? Thank you very much for your answers and please forgive my English, i hope you understand my questions. Link to comment Share on other sites More sharing options...
dan_fromm1 Posted February 13, 2006 Share Posted February 13, 2006 Diego wrote "That?s the point, i am buying my first LF camera, i will travel to Namibia and i think that is easier to devlope or kepp the roll films than sheets, anyway i would like to use both, i have the camera but not lens yet so before buying a lens i would like to consider some things. Do you have the same angle of view with a 90mm on a 9x12 than a 6x9. How do you make the composition and the focus??? Thank you very much for your answers and please forgive my English, i hope you understand my questions." Your english is better than good enough. You want to take equipment you've never used before and have no idea how to operate on a trip? This is not a good idea. Buy a good book on using a view camera. NOW. You'll learn more about how to operate a view camera from it than you will here. Steve Simmons wrote one that's been recommended for beginners. IIRC, a lens' angle of view is 2*arctan((.5*length of edge of frame)/(focal length)). If you use Excel, the formula I gave you will return the angle in radians; use the degrees() function to get degrees. If the camera's gate isn't square, there are two angles of view to compare between a pair of formats, horizontal and vertical. Please don't ask the question again. I see that you use a Rollei. If you've been happy with the way it sees the world, your first lens for 4x5 should be 150 mm, for 6x9 should be 100 mm. Link to comment Share on other sites More sharing options...
michael_briggs2 Posted February 13, 2006 Share Posted February 13, 2006 "Do you have the same angle of view with a 90mm on a 9x12 than a 6x9?" Think of it this way. If you use a 150 mm lens on 9x12 cm film, a certain amount of the scene will end up on the film, according to the angle of view equation that Dan gave. Now take that piece of film and cut out a 6x9 cm piece. Obviously less of the scene will be on the 6x9 cm film, so the angle of view will be less. If you want to take photos on 9x12 sheet film and 6x9 roll film, and you want a normal view for both, you need two different lenses: about 150 mm for the 9x12 and about 100 mm for the second. The 150 mm lens will be long for the 6x9 cm roll film and the 100 mm lens will be a moderate wide angle for the 9x12 cm sheet film, assuming that it even projects a large enough image to cover the sheet film. "How do you make the composition and the focus?" Usually a LF cameras use ground glass and a darkcloth. You adjust the focus until the image looks sharp on the ground glass. I second the suggestion to buy a book. There are excellent books by Jim Stone, Steve Simmons, Jack Dykinga and Leslie Strobel. Link to comment Share on other sites More sharing options...
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