Hey All, So I'm getting a Rollex 6x9 back for my Linhof, so I can use 120/220 film on the 4x5. I'm just trying to figure out what angle of view I'd be getting in 35mm terms, if I put on say a 90mm lens? On the 4x5 that's a good wide angle, on a 645 it's like a 50mm equivalent, but what does it translate on a 6x9 frame? Likewise I have a 180mm and wondering how I should calculate that as well.

The "normal" lens on 6x9 is in the 100mm-110mm range. Because of the 6x9 format, you capture a lot of a scene within that frame. I guess the best way would be to compare photos taken with a 35mm, 6x6 and 6x9. I feel comfortable saying that 6x9 provides a much wider view than 35mm. The field of view feels like 28mm but without getting that wide-angle "feel" from your photos.

Nominal 6x9's (2.25" x 3.25", 6x9 is a lousy metric approximation) normal focal length (diagonal of the frame) is 100 mm. 24x36's normal focal length is 43 mm. A 90 mm lens on 2x3 (short way of referring to 2 1/4 x 3 1/4) sees what a 39 mm lens would see on 24x36. Shortish normal lens, really. Do the arithmetic yourself for y'r 180 (hint, 180 = 2 * 90).

Wow, thanks for the great info guys, it's exactly what I was looking for! That lens chart is gold, thanks Dan!

Calculating "normal" FL (traditional) formula: square root of image length squared plus image width squared... (6x9cm) 56^2 + 84^2 = 10192 sqrt of 10192 = 101mm (normal for 6x9cm according this old formula) 90(your lens' FL) / 101(normal lens' FL) = .89 normal FL for 135 format is 43mm .89 x 43 = 38mm equivalent on a 135 format camera... just shy of normal Many consider the old traditional formula flawed preferring to use the long edge of the image area for calculation but I don't know a formula for that. I'd "guess" multiplying the long edge by 1.2x is pretty close.

Um, er, ah, 2x3 and 24x36 have the same aspect ratio so comparing the formats' long, or for that matter their short, side as a basis of comparison is equivalent to using the diagonal. The diagonal is the conventional basis but as we've seen some people don't follow the convention. O-N-F, all dimensions of 2x3 are approximately 2 1/3 times the equivalent dimensions of 24x36. I don't know where you got your 1.2 times.

Ascertaining the aspect ratio and the 35mm equivalent in lens is all fine and dandy, but you need to bear in mind when you compose on that large 4x5 ground glass that you are not using the entire image. You are already cropping down to 6x9cm, and it makes zero difference what ever lens you decide on for standard, the image you capture is pre-cropped. to fit the back. I hope you have some guide lines to figure where the 6x9 is going to be when you trip the shutter. Honestly, I seriously considered a 6x9 back for my 4x5, but came to the realization that is was a waste of time and film. If you really want that size negative, get a dedicated camera for it. Now, if you were talking 6x12, that might be another story.

Of course that's true, Dan. You're correct as usual. I just added that tidbit of information in case the OP ever decided to shoot 6x6cm, 6x7cm or 6x12cm. I "guessed" at the 1.2x factor for choosing a normal lens based on long edge... 6x6cm..... 56 x 1.2 = 67mm 6x7cm..... 70 x 1.2 = 84mm 6x9cm..... 84 x 1.2 = 101mm 6x12cm... 112 x 1.2 = 134mm I'd "guess" that's fairly close although 1.22x or 1.25x might be closer. However, I'm sure there are better calculations. I just don't know of any. Using 1.25x instead... 6x6cm..... 70mm 6x7cm..... 88mm 6x9cm..... 105mm 6x12cm... 140mm Yeah, those seem more reasonable. So my NEW "guess" is 1.25x to calculate normal FL based on the long edge of the image.

O-N-F, what does your 1.2 or 1.22 or 1.25 have to do with the OP's question? You've lost me completely. Rick, I use a 4x5 standard and focusing panel to shoot 6x12, have reluctantly decided to park my 2x3 gear and use my 6x12 rig for that format with, of course, a 2x3 roll holder that fits it. By an odd coincidence the 4x5 focusing panel is marked for smaller formats so framing for them with it isn't much of a problem. I just have to pay attention to the frame lines. As it happens, the 2x3 roll holder I got to use with my 6x12 rig has a gate that's offset from the camera's optical axis. Putting additional marks for framing with it wasn't hard.

Dan... where did you miss the OP's reference to 6x4.5cm? That's closer to 4x5" or 6x7cm ratio than 6x9cm. What does 1.2, 1.22 or 1.25 have to do with the OP's question? Plenty, because many people prefer to select normal FL base on the longest image side vs. the diagonal and there's some merit in that.

Forget 'normal' on 35mm...the 50mm usual number is longer that the diagonal of 24x36mm frame dimension. 'Normal' is much too variable, as I have seen manufacturers of 135 format cameras with 45mm, 50mm. 52mm, 55mm and 58mm lens FL, all called 'normal'! Forget that the "normal" lens on 6x9 is in the 100mm-110mm, too. Instead, relate FL to the frame short dimension, for a precise geometric equivalence! With 55mm (or 56mm) frame height limited by film width of 120/220, the 90mm lens is 1.64x the 6x9 format frame height. 1.64x the 24mm frame height of 135 format yields 39mm, so 90mm on 6x9 format would be about the same Angle of View as using 39mm lens on 135 format camera in terms of Angle of View captured within the frame. Using 180mm on 6x9 (3.27x the frame height) would be like using 79mm on 135 format. Using the short dimension of the frame completely allows you to compare any format, in spite of the fact that the aspect ratio is 1:1, 1:1.2, 1:1.25, 1:3, 1:5 depending upon the camera model you pick up!

somebody put this comparison shot of nearly wall formats known to man up on flickr. https://www.flickr.com/photos/31007239@N06/6818977997/

While this shows what using 75mm FL sees in the increasingly larger frames of the different formats, it does not address the OP question about "equivalent AOV comes with what FL?"

Yeah the ground glass on my Linhof has 4x5 and 6x9 frame lines. I wanted the option to use movements like swing, tilt, rise/fall etc. along with the option of not having to shoot on 4x5 sheet film.

I'm not sure what a 'crop factor' is but Chapter 14 of the Horseman VHR manual (available on the Butkus site) lists the angle view of a number of popular focal lengths for both 6x9 and 6x7 format Horseman rollfilm backs.

I like ONF's multiplying the long dimension X 1.25. Simple for the likes of me. It's just an approximation and there's no life threatening consequences involved.