Equivalent length for medium format 6X7 90mm to full frame Nikon

[peterB1966]

Hi, as I understand it the 35mm film equivalent of a 6x7 MF 90mm is 45mm (or in some instances people have said 47), but to get the equivalent of my full frame I need to do another conversion, i.e. if 35mm is equivalent of 50mm, then the 45 becomes 65mm.

Is this correct, or am I on the right track?

 

[Huub]

It depends a bit what you measure as the aspect ratios of full frame 35mm differ from 6x7 MF. A lot of people take the diagonal and then 45mm equals more or less to 90mm, but to match the negative sizes of full frame 35 mm and MF you will have to step up to 6x9.

 

[peterB1966]

It depends a bit what you measure as the aspect ratios of full frame 35mm differ from 6x7 MF. A lot of people take the diagonal and then 45mm equals more or less to 90mm, but to match the negative sizes of full frame 35 mm and MF you will have to step up to 6x9.

Hi, not too sure if you are confusing the issue (and therefore, me ) by talking about the negative sizes - what I am trying to work out is, what is the equivalent focal length of my 90mm (on MF6x7) compared to my full frame digital. Or perhaps I am missing something?

 

[koraks]

Or perhaps I am missing something?

Yes, aspect ratio. That's what @Huub pointed out; I think he understood your question perfectly. The problem is that the answer depends on what you compare on both formats: image diagonal or some other metric? Note that the aspect ratio (6x7 for 6x7cm, 2:3 for 35mm) has impact on the image diagonal, which in turn is often used as a starting point for focal length comparisons.

 

[peterB1966]

Yes, aspect ratio. That's what @Huub pointed out; I think he understood your question perfectly. The problem is that the answer depends on what you compare on both formats: image diagonal or some other metric? Note that the aspect ratio (6x7 for 6x7cm, 2:3 for 35mm) has impact on the image diagonal, which in turn is often used as a starting point for focal length comparisons.

Drat - I was hoping for a simple ratio / formula so I could establish the equivalent focal length once and for all. I have discovered a long time ago that the answers on Photrio are never as simple as one may have hoped

 

[peterB1966]

UPDATE: I did an empirical test, lining the back of my D610 up with the film back on my RB67 and, interestingly enough, the 90mm seems to be the equivalent of 50mm on my full frame, which implies the second conversion step was not neccessary!

 

[koraks]

the second conversion step

If you meant that a conversion from 35mm to 'full frame digital' would have been necessary, then obviously not, because full frame digital (as used by most people) is the same as 35mm...
The caveat is that full frame digital in a medium format context would mean something different, of course...

the answers on Photrio are never as simple as one may have hoped

That's because they usually include the various nuances, caveats etc. that the real world has to offer
As with many things, there's a truthful, nuanced/complicated answer, and there's a wrong answer. Some people like the latter for its potential brevity.

 

[peterB1966]

If you meant that a conversion from 35mm to 'full frame digital' would have been necessary, then obviously not, because full frame digital (as used by most people) is the same as 35mm...
The caveat is that full frame digital in a medium format context would mean something different, of course...

Yes, I see it now - I think misunderstood when people said that 35mm film is equivalent of 50mm full frame ... they were talking of sensor / film size, and not focal length equivalents, am I right?

 

[koraks]

people said that 35mm film is equivalent of 50mm full frame

That's an odd formulation. I suspect they said something like "a 50mm lens on a 35mm camera is the equivalent of a 90mm lens on a 6x7cm camera." In that case they're talking about focal length equivalents for different sensor/film sizes.

 

[peterB1966]

Thanks.

That's an odd formulation. I suspect they said something like "a 50mm lens on a 35mm camera is the equivalent of a 90mm lens on a 6x7cm camera." In that case they're talking about focal length equivalents for different sensor/film sizes.

Thanks.

 

[wiltw]

Since aspect ratios are different, I suggest that one take the short dimension of the frame, and use that to calculate a ratio to the FL of the lens

• 6x7 frame is about 56mm on the short direction of the frame, 135 format is 24mm on the short direction of the frame
• MF: 90mm FL / 56mm = 1.6
• 135: 1.6 x 24mm = 38.6mm FL

Both 6x7 and 135 format frames would have the SAME AOV/same FOV in the short dimension of their frames when those FL

Remember...if you make an 8x10 or 16x20 print from both formats, the long direction of the 135 negative DOES NOT MATTER because it gets trimmed off to fit the standard print size!!!

 

[Steve Goldstein]

I use the same approach as wiltw but have slightly simplified the math so I can do it quickly in my head.

To go from 6x7 to 35mm: multiply 6x7 focal length by 3/7.

To go from 35mm to 6x7: multiply 35mm focal length by 7/3.

To go from 4x5 to 6x7: multiply 4x5 focal length by 7/12.

To go from 6x7 to 4x5: multiply 6x7 focal length by 12/7.

 

[Ian Grant]

People get too hung up on the equivalents, the reality is we or should I really only want a rough rule of thumb.

What happens for instance if you shoot 6x17, which I do, what is a standard lens compared to say my Rolleiflex/MPP TLR's 75mm lenses. I guess I look at it a different way, I shoot 6x6, 6x9, 6x17, and 5x4 (and 10x8). I think of the vertical aspect first, and then the horizontal, and regardless of the format it's finding the right balance. It is very rare I crop negatives, and when I do it has been apparent from the shooting stage.

So back to my standard lens for 6x17 it's 75mm same as my TLRs, I want the same vertical perspective but with a wide panoramic format.

Ian

 

[wiltw]

Steve's calculations exactly mimic the process that I suggested..regardless of method used, the same FL results!

...since almost everyone has a smartphone with calculator, you really only need the calculation to be done when figuring out what FL initally to buy, and once you bought the 'equivalent FL' you simply pick up that lens without need for any calculation!

 

[Steve Goldstein]

...since almost everyone has a smartphone with calculator, you really only need the calculation to be done when figuring out what FL initally to buy, and once you bought the 'equivalent FL' you simply pick up that lens without need for any calculation!

True, but...

I work with both 6x7 and 4x5. The 6x7 kit, being more portable and faster to use, is more likely to be what I'm carrying, especially if I'm somewhere with my wife (she's very tolerant of my photography, but I don't want to abuse her good will by taking 20 minutes to set up a LF shot). If it's a place I can get to again with the 4x5 without too much trouble and I feel the image could benefit from the movements afforded by large format, it's nice to be able to quickly ballpark what focal length(s) to bring on my return trip by multiplying the "best" 6x7 focal length by 12/7.

If I'm somewhere without a camera I'll just fire up the Viewfinder app on my phone and take screenshots. Either format will do - it's simple enough to convert one to the other - and that'll tell me which of the lenses I own to bring if I return.

 

[peterB1966]

To go from 6x7 to 35mm: multiply 6x7 focal length by 3/7

Am I correct that that implies, with a 90mm lens that I do the following equation?
(90 x 3) / 7 = 38.6mm

If I'm somewhere without a camera I'll just fire up the Viewfinder app on my phone and take screenshots.

Wow, never realised there was something like this, whihc exactly why I wanted to know my equivalent focal lengths!

Which one do you use, and do you know if it would cater for my Mamiya 6X7

 

[Alan Edward Klein]

I compare the horizontal angles of view because the vertical and diagonal are meaningless for normal viewing.( except if you're doing a portraiture).

Who visualizes a diagonal point of view? We normally want to know the width that we want to capture.

 

[Steve Goldstein]

Am I correct that that implies, with a 90mm lens that I do the following equation?
(90 x 3) / 7 = 38.6mm

Yup. Simple as that.

Wow, never realised there was something like this, whihc exactly why I wanted to know my equivalent focal lengths!

Which one do you use, and do you know if it would cater for my Mamiya 6X7

The one I have is called "Viewfinder Preview", and I've had it for a long time through several generations of iPhone. It supports different formats, and for each format you can add more focal lengths than you'd reasonably need. I use it for 6x7 and 4x5. My version is 1.11.0, no idea how old it is.

 

[Alan Edward Klein]

I compare the horizontal angles of view because the vertical and diagonal are meaningless for normal viewing.( except if you're doing a portraiture).

Who visualizes a diagonal point of view? We normally want to know the width that we want to capture.

Here's an example. a 90mm 6x7 has an angle of view of H= 40.7 v=34.5 D=51.6 degrees.
On a 35mm full frame a 45mm lens H=42.6 V=29.9 D=51.4 which matches the diagonal only of the 90mm 6x7
However, matching horizontal angle of view with a 35mm camera's 49mm len: H=40.3 V=27.5 and D= 47.6

So depending on which dimension you're comparing would get you different equivalents. I find the horizontal width the most important because that;s the way I see the scene.

Here's the link I used to get these angles of view.

DOF and angles of view

 

[peterB1966]

"Viewfinder Preview"

Fantastic! Have purchased it

 

[DREW WILEY]

It would be more realistic to compare a 90mm lens on 6X9 format rather than 6x7, due to the similar proportion to full-frame 35mm, where it would nominally indeed be 45mm, certainly not 65mm.

 

[gone]

Ahem.....smiles, clears throat, etc, etc

Why are photographers so "fussy"?

I've been making images for well over half a century. Before photography, I did etchings, block prints, paintings, all that. Still do. Photographers are different than artists though, no matter what your definition of the word artist may be. Other than the usual categories like print, original...

www.photrio.com

 

[DREW WILEY]

Choosing the right lens for a different camera to photograph a block print according to the same perspective, well, that might be important to someone. It would be to me if the copy stand were involved. Or it might be important to someone photographing a cramped interior space. Or maybe they just want reasonably matched lenses due to familiarity of visualization related to angle of view, or just for the hell of it. It's a legitimate question.

 

[peterB1966]

Ahem.....smiles, clears throat, etc, etc

etc

Choosing the right lens for a different camera to photograph a block print according to the same perspective, well, that might be important to someone. It would be to me if the copy stand were involved. Or it might be important to someone photographing a cramped interior space. Or maybe they just want reasonably matched lenses due to familiarity of visualization related to angle of view, or just for the hell of it. It's a legitimate question.

Totally - I need to scout locations for tableau photos with my RB67, but as it is cumbersome and I already have my DSLR with me wherever I go, I was hoping to use the DSLR to see how different locations would work on the only two Mamiya lenses I have, i.e. can I use this location for a specific shot I had in mind, or will e.g. a third of the scene be cropped out.

Which is why I was so happy to find out about "Viewfinder Preview", which I think will change things up massively for me.

 

[RalphLambrecht]

Drat - I was hoping for a simple ratio / formula so I could establish the equivalent focal length once and for all. I have discovered a long time ago that the answers on Photrio are never as simple as one may have hoped

Often the quality of the question is the foundation for the quality of the answer.