When trying to compare 6x7 lens to 35mm lens what is the multiplication factor to find the equivalent?
For example a 50mm 6x7 lens for my RB67 is equivalent to what length lens in a 35mm format and what was the factor to calculate?
A good rule of thumb is to take the ratio of the normal lenses.
On my Pentax 67-II, the normal lens is a 105 mm. On my Nikons it's a 50. So your ratio is 105/50. (I don't have a calculator handy to calculate it, but it's a hair more than 2x.) You can multiply this ratio by the 35mm focal length to get the 6x7 focal length. Or take the inverse of that ratio (calculate 50/105 or divide 1 by the ratio you just calculated) and multiply that ratio by the 6x7 focal length to get a 35mm focal length.
Bear in mind that 35mm is a 2x3 ratio and 6x7 is, well, 6x7. Apples to apples this is 14x21 compared to 18x21. 35mm is slightly wider, relatively speaking. Therefore, comparing focal lengths is not quite apples to apples.
Another way of thinking about is is angle of view along the long side.
6x7 image size is actually about 56 x 66 so a 50mm lens on an RB67 gives you an angle of view of about 67 degrees (no maths here, just drew it on CAD at work and measured it).
On 35mm, this angle equates to a lens of 27.27mm focal length so you can consider it similar to a 28mm lens on 35mm .
Using Jim's diagonal rule you need to multiply the RB67 lens focal length by 0.48 to get the 35mm equivalent. Using the long side angle of view the figure is 0.56. Just divide the RB67 focal length by two and you will be close enough.
That's what I needed! I have a 28-105 zoom on my Nikon F-100 that stays on the camera. I use the shorter end quite a bit So if I got a 50mm or 65mm RB67 lens to go with my 127mm I would have the normal to shorter end covered.
What would you folks recommend for the longer end? I don't really have much choice do I? I guess a 180mm?
When I had an RB years ago, I went with a 65, a 127, and a 250. I found that I rarely used the longer lens, but your style of shooting may vary. Basically I went with doubling the focal length each time.
A good rule is if you're migrating to 6x7 from 35mm, what's the lens you use most on 35mm, then double it and it will be good for you on 6x7. On my F-100 I find I tend to use a 35mm lens most often, so for me, 65mm on my RB67 is what I use most.
24mm. focal length x.48 for 6X7....X.55 for 6x6..... x.62 for 6x45 these figures were obtained from a source that I cannot remember at the moment since it was a very long time ago, but they seem pretty accurate.
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