Medium Format - full frame 'equivalent' focal lengths

[grahamc]

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Hello.    I remain confused by determining what medium format focal lengths equate to in full frame terms. Hoping people can help here.

I am aware that this depends on the ratio of your medium format camera 6x6 or 6x7 etc.   

I own a Plaubel Makina (6x7) with 80mm lens.  Based on numerous sources, I had thought the FL in full frame terms is equivalent circa 40mm 

However just reading this on Hasselblad website has confused me :

"....A lens pair of XCD 1,9/80 and XCD 4/45P, respectively, deliver 63mm and 36mm equivalencies"

Can someone please clarify why is the 80mm cited as equivalent 63mm here. ?   I'm quite certain from the view & images that my PB670 80mm delivers is approx 40mm equivalent as expected. 

Thanks in advance

Edited July 27, 2023 by grahamc

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[robbie3]

Hi Graham, the digital Hasselblad's sensor is smaller than the film cameras approx 6x6cm film size

Sensor Dimensions: 43.8mm × 32.9mm  vs  56mm x 56mm film frame size for 6x6.

I think this affects the 35mm equivalent focal length you're seeing quoted.

Nice camera btw, I've been tempted many times but restrained myself.

Wim Wenders used a Plaubel Makina 67 for many of his shots in his book "Written in the West", one of my favourite books.

 

This link might be useful as it's not a straightforward calculation, usually calculated on the diagonal of the frame which will be different on your camera to the Hasselblad 6x6:

http://www.hasselbladhistorical.eu/HW/HWequifoc.aspx

 

Edited July 27, 2023 by robbie3

[grahamc]

8 minutes ago, robbie3 said:

Hi Graham, the digital Hasselblad's sensor is smaller than the film cameras approx 6x6cm film size

Sensor Dimensions: 43.8mm × 32.9mm  vs  56mm x 56mm film frame size for 6x6.

I think this affects the 35mm equivalent focal length you're seeing quoted.

Nice camera btw, I've been tempted many times but restrained myself.

Wim Wenders used a Plaubel Makina 67 for many of his shots in his book "Written in the West", one of my favourite books.

 

This link might be useful as it's not a straightforward calculation, usually calculated on the diagonal of the frame which will be different on your camera to the Hasselblad 6x6:

http://www.hasselbladhistorical.eu/HW/HWequifoc.aspx

 

Thanks a lot Robbie 

Yes I love the 670 , and so considering a medium format digital camera also, as I seem to have caught the MF bug !  But may just buy the W67 as a wider option to accompany the 670

[Guest]

Hi Graham,

I assume your Makina has the same negative format as my Pentax 67II, namely 55x70mm (diagonal is 89mm). Full frame is 24x36mm (diagonal is 43mm). Calculations for 80mm focal length:

• Horizontal full frame equivalent: 80mm x 36mm / 70mm = 41mm
• Vertical full frame equivalent: 80mm x 24mm / 55mm = 35mm
• Diagonal full frame equivalent: 80mm x 43mm / 89mm = 39mm.

As Robbie said, for Hasselblad digital you use their sensor format in these equatioins: 32.9x43.8mm (diagonal is 55mm):

• Horizontal full frame equivalent: 80mm x 36mm / 43.8mm = 66mm
• Vertical full frame equivalent: 80mm x 24mm / 32.9mm = 58mm
• Diagonal full frame equivalent: 80mm x 43mm / 55mm = 63mm.

Most frequently, the diagonal equivalent is mentioned. Hasselblad is doing this in your quote.

Regards,

Joachim  

PS: Next time, we should have a 6x7 outing.

Edited July 27, 2023 by Studienkamera

[250swb]

6 hours ago, grahamc said:

Thanks a lot Robbie 

Yes I love the 670 , and so considering a medium format digital camera also, as I seem to have caught the MF bug !  But may just buy the W67 as a wider option to accompany the 670

Here is a simple calculator

https://fl.danielpietzsch.com/

highlight the format and slide the bar along to your focal length and get the 35mm equivalent

As you will see a 55mm lens (W67) is equivalent to 28mm on a 6x7 camera, and the standard 80mm is the equivalent of a 40mm.

[TomB_tx]

I think the most common "normal" lens for the Pentax 6x7 was 105mm - so a bit longer perspective than 50 on a FF 35. The 105 is a pleasing lens though - I've used it a lot on my 6x7.

[250swb]

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44 minutes ago, TomB_tx said:

I think the most common "normal" lens for the Pentax 6x7 was 105mm - so a bit longer perspective than 50 on a FF 35. The 105 is a pleasing lens though - I've used it a lot on my 6x7.

My ‘Texas Leica’ Fuji GW670 has a 90mm so ‘standard’ does vary far more than 6x6 cameras.

[david strachan]

 

Hi Steve...My GWS690 II has a fixed lens f5.6 65mm lens and gives a negative 56mmx 83mm...it is equivalent to 28mm in 35mm Format photography.

[Guest]

10 hours ago, 250swb said:

My ‘Texas Leica’ Fuji GW670 has a 90mm so ‘standard’ does vary far more than 6x6 cameras.

Pentax had two standard lenses for the 67 system, 2.4/105mm and 2.8/90mm. I use the latter.

[grahamc]

21 hours ago, Studienkamera said:

Hi Graham,

I assume your Makina has the same negative format as my Pentax 67II, namely 55x70mm (diagonal is 89mm). Full frame is 24x36mm (diagonal is 43mm). Calculations for 80mm focal length:

• Horizontal full frame equivalent: 80mm x 36mm / 70mm = 41mm
• Vertical full frame equivalent: 80mm x 24mm / 55mm = 35mm
• Diagonal full frame equivalent: 80mm x 43mm / 89mm = 39mm.

As Robbie said, for Hasselblad digital you use their sensor format in these equatioins: 32.9x43.8mm (diagonal is 55mm):

• Horizontal full frame equivalent: 80mm x 36mm / 43.8mm = 66mm
• Vertical full frame equivalent: 80mm x 24mm / 32.9mm = 58mm
• Diagonal full frame equivalent: 80mm x 43mm / 55mm = 63mm.

Most frequently, the diagonal equivalent is mentioned. Hasselblad is doing this in your quote.

Regards,

Joachim  

PS: Next time, we should have a 6x7 outing.

Thanks Joachim , and definitely keen to do that next time !

[grahamc]

15 hours ago, 250swb said:

Here is a simple calculator

https://fl.danielpietzsch.com/

highlight the format and slide the bar along to your focal length and get the 35mm equivalent

As you will see a 55mm lens (W67) is equivalent to 28mm on a 6x7 camera, and the standard 80mm is the equivalent of a 40mm.

Great stuff. Thanks Steve 

[adan]

Basic equation: the width of an image across the film from side to side is:

35mm film: 24mm image width (plus room for sprocket holes)
120 film: 54-56mm image width with a thin border or rebate ("6x6," implying 60mm x 60mm negatives, is a bit of marketing exaggeration  ). Hasselblads tend to produce a very slightly smaller neg than Rolleis/Yashicas/Mamiyas etc.

If the overall image format/shape/proportions are the same - e.g. Barnack format 2:3 to MF 6:9 - then the math is easy. 56/24= 2.333. The 50mm equivalent on a 6x9 medium format camera is a 117mm lens. But as we know, Leica M "50mm" lenses are actually about 52mm lenses, so correcting for that gets us to a 121mm lens on the 6x9 camera.

35mm = 82mm
21mm = 50mm
...and so on.

However, once the shapes become different, then the whole character of the picture is going to change anyway - Diane Arbus or Vivian Maier square pictures won't ever "look like" Cartier-Bresson or Elliott Erwitt or Ralph Gibson 2x3 photos, no matter how equivalent the focal lengths.

But if one must, that is where the proportions of the diagonals must be taken. That's the only way roughly compensate for the different shapes and get an idea of how much of the world can be squeezed into a specific frame.

And using our handy-dandy Pythagorian equation:

The classic 35mm film frame has a diagonal of 43.3mm
A square MF picture 55mm on a side has a diagonal of 77.78 mm...divided by 43.3 gives a "focal length equivalent factor" of 1.8
An "ideal format 6x7" picture has a diagonal of 85mm....divided by 43.3 gives an "FLEF" of 1.97
A 645 micro-medium format neg (actually 56mm x 41.5mm) has a diagonal of ~70mm....divided by 43.3 gives an "FLEF" of 1.62

Checking our work... a 38mm Zeiss Biogon Superwide for the Hasselblad = "21.111" on a 35mm camera. And I can testify that is how "wide" the Biogon appears.

....and a 50mm Zeiss for Hassy comes out as "27.7" (call it 28mm) on 35mm

..... and an 80mm on Rollei/Hassy/Mamiya/Yashica/etc. comes out 44.4mm (a "wide-ish normal" - except that some say that the focal length that equals the diagonal is the real "normal" lens for any camera, which would make it simply a "normal normal")

...... while Hassy's 100mm Planar = 55.55, and the 90mm used on some Eastern Europe "6x6" cameras comes out "50mm" on the button.

And the favorite "long normal" of many using the Hasselblad film cameras - 120 macro - equals about a 67mm (not too far off an Elmarit-R/Nikkor 60mm Macro, or the 65 Elmar Macro for the Visoflex).

[LocalHero1953]

A commonly advised rule of thumb for 5x4 is a factor of 3: so the equivalent of a 50mm lens for 5x4 is said to be 150. Whereas if you take @adan's logical formula, the factor should be 3.5 for the long side of the negative (125mm/36mm) or 3.7 for the diagonal (160/43). This has always puzzled me. But then I stopped worrying about it and just got used to the look from my 90, 125 and 240 large format lenses.

Edited July 28, 2023 by LocalHero1953