Reciprocal rule for medium format

[Alan Johnson]

For 35mm it is often recommended to use a shutter speed which is the reciprocal of the lens focal length in mm.
However this only applies to a negative which is 36mm wide.
For a 67 camera, which has a negative nearly twice as wide, the shutter speed should be higher by twice the reciprocal of the lens focal length in mm?
All approximate of course.

 

[BobBill]

Interesting. I been blindly going along using a phone app as meter...and it seems to work, though I do bracket often.

 

[E. von Hoegh]

For 35mm it is often recommended to use a shutter speed which is the reciprocal of the lens focal length in mm.
However this only applies to a negative which is 36mm wide.
For a 67 camera, which has a negative nearly twice as wide, the shutter speed should be higher by twice the reciprocal of the lens focal length in mm?
All approximate of course.

No, because the lens is typically longer in focal length. That is, typically 75mm to 105mm for "normal" lenses which I round to 1/100 or 1/125.

HOWEVER. I use a tripod or monopod whenever practicable. Prove this to yourself - make a handheld exposure of something with lots of fine detail, handheld with 35mm, 50mm lens, 1/60 second. Then put the camera on a solid tripod, same exposure. You'll find it is sharper than the handheld photo. I try to use the fastest shutter speed practicable when I must use the camera handheld, 4x5 and 8x10 are exclusively tripod cameras.

 

[Alan Johnson]

I am referring to the same focal length lenses for both formats, since it is the 35mm format to which the reciprocal rule is generally applied.
Say the shake blur on 35mm is equivalent to the width of one distant person. Then on 67 at the same shutter speed it will be equivalent to the width of two distant people.
Hence on 67 to get the shake blur equal to that on 35mm, one distant person, it is necessary to use twice as fast shutter speed ?

 

[480sparky]

You wouldn't need to increase your shutter speed, you could actually slow it down. As the image format gets larger (assuming the focal length remains the same), the FOV increases. And as the FOV increases, slower shutter speeds can be used.

 

[Huub]

I would also suspect that it depends on the camera design. A Pentax 6x7 is very much like a 35mm SLR camera on steroids, with a large focal plane shutter and a big morror moving. A camera like a TLR Rolleiflex is a very different beast, with a small leaf shutter and no moving mirror.
I have no experience with the first camera, but with my Rollei a 30th sec is no problem when being careful. But of course that will depend on how sharp the pictures should be too... And I have no doubt that using a tripod in that situation would still add some sharpness.

 

[E. von Hoegh]

I am referring to the same focal length lenses for both formats, since it is the 35mm format to which the reciprocal rule is generally applied.
Say the shake blur on 35mm is equivalent to the width of one distant person. Then on 67 at the same shutter speed it will be equivalent to the width of two distant people.
Hence on 67 to get the shake blur equal to that on 35mm, one distant person, it is necessary to use twice as fast shutter speed ?

No it will not! Objects will be the same size at the same distance for the same focal length, regardless of the format and field of view the lens actually covers.

 

[Alan Johnson]

A 67 camera shaking at the same angular rate in degrees as a 35mm camera will swing through two distant people in the same time it takes a 35mm camera to swing through one person because its field of view is double.Hence to keep the 67 camera degree of blur at one distant person it appears needed to use a 2x higher shutter speed?
Both having the same focal length lens.

 

[Ian Grant]

I am referring to the same focal length lenses for both formats, since it is the 35mm format to which the reciprocal rule is generally applied.
Say the shake blur on 35mm is equivalent to the width of one distant person. Then on 67 at the same shutter speed it will be equivalent to the width of two distant people.
Hence on 67 to get the shake blur equal to that on 35mm, one distant person, it is necessary to use twice as fast shutter speed ?

I think you've a muddled arguement going on here because the blur/shake is also relative to the degree of enlargement as well as the negative size and focal length.

In reality the speed you can hand hold at is related to equivavent focal lengths for each format. So in my case that's a 1/30th for 35mm with a standard 50mm lens, a 75/80mm lens on a 6x4.5/6x6 camera and a 135mm ir 150mm on my Speed/crown or Super Graphic although I'd prefer to use a minimum of 1/50, that is the reciprocal of the FL for 35mm and 1/3 the reciprocal for %x4.

Longer FL the rule is about right as well.

Ian

 

[RalphLambrecht]

For 35mm it is often recommended to use a shutter speed which is the reciprocal of the lens focal length in mm.
However this only applies to a negative which is 36mm wide.
For a 67 camera, which has a negative nearly twice as wide, the shutter speed should be higher by twice the reciprocal of the lens focal length in mm?
All approximate of course.

sounds reasonable;However, I 'be never changed the rule for format and it worked anyway.

 

[wiltw]

The original Rule of Thumb for shutter speed=1/FL was actually developed in the days of Medium Format, and that when the 'subminiature' format came along (135) the photographic world largely failed to adapt the Rule to the smaller format! And it was not until the digital format APS-C came along that someone remembered to factor in the 'crop size'. As a result we have today:

• 135 format: = 1/FL
• APS-C format: = 1/(FL*1.6)
• Medium Format: = 1/FL

...so any 'safety margin' that was in the original Rule of Thumb for Medium Format vanished in the 135 format Rule!


In reality, the actual Rules should have been:

• Medium Format = 1/FL
• 135 format = 1/(FL* 2.3)
• APS-C format = 1/(FL* (2.3 * 1.6))

So we should have had as our Rules of Thumb:

• 80mm FL 'normal' = 1/80 min.safe handheld speed ...for medium format (i.e., the 56mm tall frames of 6x6 and 6x7), where 'normal FL' = 1.43x the smaller frame dimension (1.43 * 56mm)
• 34mm FL 'normal' = 1/80 min.safe handheld speed ...for 135 format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 24mm)
• 21mm FL 'normal' = 1/80 min.safe handheld speed ...for APS-C format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 15mm)

as all frames would then have captured the identical linear distance along the short dimension of the frame, and the camera motion induced blur is the same fraction of the same final size prints from each.

If we consider the fact that 135 format uses an OVERLY-LONG FL as its 'normal' -- which was a convenience for the SLR to clear the reflex mirror swing -- when using 50mm FL we ought to be shooting at 1/125 (1 / (50 * 2.3)

 

[jim10219]

I would suggest avoiding overly simplistic "rules" such as this. You'll find they cause more problems than they solve. Different people, different ways of holding the camera, and different cameras will create different results. There's a lot more to consider than just focal length. Good technique will go a long way to improving shake. Learning to balance your body, support the camera with minimal effort, and shooting in between breaths (like a rifle marksman) can greatly extend your range. I've shot 400mm lenses at 1/60 on 35mm cameras tracking planes darting overhead at an air show with Razor sharp results. I can't do it every time, but I can do it about a third of the time, which to me is pretty good.

A better rule would be to use the fastest shutter speed you can get away with if shake might be an issue. The more experience you gain with your camera, the better you'll get at judging what you can get away with.

 

[Alan Johnson]

Yes it is only an approximation, there are articles showing that the degree of blur from the same photographer at the same shutter speed varies round some average.
Also it probably only applies to medium format cameras that are used in an SLR like fashion at eye level and which are light enough to shake like an SLR.
This is the type of camera I am using for landscapes, thanks for the comments.

 

[Ian Grant]

The original Rule of Thumb for shutter speed=1/FL was actually developed in the days of Medium Format, and that when the 'subminiature' format came along (135) the photographic world largely failed to adapt the Rule to the smaller format! And it was not until the digital format APS-C came along that someone remembered to factor in the 'crop size'. As a result we have today:

• 135 format: = 1/FL
• APS-C format: = 1/(FL*1.6)
• Medium Format: = 1/FL

...so any 'safety margin' that was in the original Rule of Thumb for Medium Format vanished in the 135 format Rule!


In reality, the actual Rules should have been:

• Medium Format = 1/FL
• 135 format = 1/(FL* 2.3)
• APS-C format = 1/(FL* (2.3 * 1.6))

So we should have had as our Rules of Thumb:

• 80mm FL 'normal' = 1/80 min.safe handheld speed ...for medium format (i.e., the 56mm tall frames of 6x6 and 6x7), where 'normal FL' = 1.43x the smaller frame dimension (1.43 * 56mm)
• 34mm FL 'normal' = 1/80 min.safe handheld speed ...for 135 format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 24mm)
• 21mm FL 'normal' = 1/80 min.safe handheld speed ...for APS-C format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 15mm)

as all frames would then have captured the identical linear distance along the short dimension of the frame, and the camera motion induced blur is the same fraction of the same final size prints from each.

If we consider the fact that 135 format uses an OVERLY-LONG FL as its 'normal' -- which was a convenience for the SLR to clear the reflex mirror swing -- when using 50mm FL we ought to be shooting at 1/125 (1 / (50 * 2.3)

Why so anal and complicated, it's a very quick 35mm rule of thumb, nothing more. And what you state fails in practice I should know as I regularly shoot 5x4 hand held, at a recent lecture I asked the audience to pick out the hand held LF work and they couldn't, I shoot 1/25th upwards depending on the light.

Ian

 

[Poisson Du Jour]

I have never applied any such reciprocal rule (f/L) when working wih my P67. I don't think there is any difference between the smaller format and medium format.

 

[Sirius Glass]

The original Rule of Thumb for shutter speed=1/FL was actually developed in the days of Medium Format, and that when the 'subminiature' format came along (135) the photographic world largely failed to adapt the Rule to the smaller format! And it was not until the digital format APS-C came along that someone remembered to factor in the 'crop size'. As a result we have today:

• 135 format: = 1/FL
• APS-C format: = 1/(FL*1.6)
• Medium Format: = 1/FL

...so any 'safety margin' that was in the original Rule of Thumb for Medium Format vanished in the 135 format Rule!


In reality, the actual Rules should have been:

• Medium Format = 1/FL
• 135 format = 1/(FL* 2.3)
• APS-C format = 1/(FL* (2.3 * 1.6))

So we should have had as our Rules of Thumb:

• 80mm FL 'normal' = 1/80 min.safe handheld speed ...for medium format (i.e., the 56mm tall frames of 6x6 and 6x7), where 'normal FL' = 1.43x the smaller frame dimension (1.43 * 56mm)
• 34mm FL 'normal' = 1/80 min.safe handheld speed ...for 135 format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 24mm)
• 21mm FL 'normal' = 1/80 min.safe handheld speed ...for APS-C format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 15mm)

as all frames would then have captured the identical linear distance along the short dimension of the frame, and the camera motion induced blur is the same fraction of the same final size prints from each.

If we consider the fact that 135 format uses an OVERLY-LONG FL as its 'normal' -- which was a convenience for the SLR to clear the reflex mirror swing -- when using 50mm FL we ought to be shooting at 1/125 (1 / (50 * 2.3)

I use the reciprocal rule for 35mm and MF. I have never had a problem with it.

 

[Andrew O'Neill]

First time I've heard of this rule.

 

[wiltw]

Why so anal and complicated, it's a very quick 35mm rule of thumb, nothing more. And what you state fails in practice I should know as I regularly shoot 5x4 hand held, at a recent lecture I asked the audience to pick out the hand held LF work and they couldn't, I shoot 1/25th upwards depending on the light.

Ian

Not anal, simply explaining the historical derivation of the Rule of Thumb -- let me emphasize Rule of Thumb - which is a guideline and nothing more. Some folks are steadier than a rock, and others have Parkinsons' tremble, so the Rule does necessarily apply to all.
But the discussion started with the question of the proper speed for Medium Format (vs. using 135 format) did it not?! And APS-C users have their own version of the Rule as well, so discussion was simply ON TOPIC.

 

[RalphLambrecht]

The original Rule of Thumb for shutter speed=1/FL was actually developed in the days of Medium Format, and that when the 'subminiature' format came along (135) the photographic world largely failed to adapt the Rule to the smaller format! And it was not until the digital format APS-C came along that someone remembered to factor in the 'crop size'. As a result we have today:

• 135 format: = 1/FL
• APS-C format: = 1/(FL*1.6)
• Medium Format: = 1/FL

...so any 'safety margin' that was in the original Rule of Thumb for Medium Format vanished in the 135 format Rule!


In reality, the actual Rules should have been:

• Medium Format = 1/FL
• 135 format = 1/(FL* 2.3)
• APS-C format = 1/(FL* (2.3 * 1.6))

So we should have had as our Rules of Thumb:

• 80mm FL 'normal' = 1/80 min.safe handheld speed ...for medium format (i.e., the 56mm tall frames of 6x6 and 6x7), where 'normal FL' = 1.43x the smaller frame dimension (1.43 * 56mm)
• 34mm FL 'normal' = 1/80 min.safe handheld speed ...for 135 format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 24mm)
• 21mm FL 'normal' = 1/80 min.safe handheld speed ...for APS-C format, where 'normal FL' also = 1.43x the smaller frame dimension (1.43 * 15mm)

as all frames would then have captured the identical linear distance along the short dimension of the frame, and the camera motion induced blur is the same fraction of the same final size prints from each.

If we consider the fact that 135 format uses an OVERLY-LONG FL as its 'normal' -- which was a convenience for the SLR to clear the reflex mirror swing -- when using 50mm FL we ought to be shooting at 1/125 (1 / (50 * 2.3)

hardly a rule of thumb anymore

 

[Alan Johnson]

Ian C has kindly sent details of the theory, which I have never seen before, and agreed they be posted for anyone interested.

 

[Ian C]

This version of post #20 is probably easier to read. I removed a few typos and did some revision.


The common rule is a simplification that works fine for small formats, but becomes increasingly inaccurate with increasing format size. More correctly, the rule should depend on magnification, which is where the focal length comes into play. It is, of course, the angular sweep of the lens axis during the time in which the shutter is open that must be limited to some practical value that is the same for all formats and lenses.

The general magnification in terms of focal length and format dimensions is easily reckoned. The format dimension chosen can be: minor dimension, major dimension, or the diagonal, as you choose. In the following, I’ll use the format diagonal as it is most naturally compared to the focal length of the lens.

This will yield the denominator n of the reciprocal representation of the shutter speed 1/n seconds as handheld speeds are most often used.

The magnification is m = f/d where d = format diagonal and f = focal length of the lens.

In general, the required shutter time is

(1) t = k*(d/f)

where k is some constant empirically determined long ago that gave rise to the generic “rule.” The value of k should remain constant for all formats and lens choices to limit the lens to the same angle swept by the lens axis during the shutter-open period. Note that k can be altered so that the results are satisfactory for a particular user.

Using the common situation of a 50mm lens on the 35mm format (24mm x 36mm), the diagonal of the format is 43.3mm. The rule has the minimum safe handheld shutter speed as 1/60 second (actually 1/64 second).

Solving equation (1) for k we get

(2) k = t*f/d

Using the values in the above situation

k = (1/64 second)*50mm/43.3mm = 0.01804

Of course, if we’d used a different format dimension we’d obtain a different constant. That would work fine, so long as we did so consistently for each format considered.

Substituting this value for k in equation (1), we get

(3) t = 0.01804*d/f

Does this work?

For the 50mm lens on the 35mm format (d = 43.3mm) we get

t = 0.01804*43.3mm/50mm = 0.015625 seconds

But we want the denominator n in order to easily select an appropriate shutter speed, so, using the reciprocal key on a calculator,

n = 1/0.015626 = 64

i.e. we want 1/64 second shutter speed which is conventionally marked “1/60” second on the shutter-speed dial..

We can simplify the calculation by reciprocating equation (3) to get the final form of the equation for n.

(4) n = 1/t = 55.424*f/d (expressed as the denominator n)

On the 35mm format we get the following combinations of focal length and minimum handheld shutter speeds:

35mm, 44.8 (1/44.8 seconds, so use the next faster speed, 1/60 second)

50mm , 64 (1/64 second which is the true value of the speed conventionally marked “1/60” second).

100mm, 128 (1/128 second, conventionally marked “1/125” second.)

200mm, 256 (1/256 second is conventionally marked "1/250" second.)


For the 6 x 7cm format (56mm x 69.5mm, diagonal about 90mm) we get:

50mm lens, 30.79 (indicates about 1/31 second. 1/30 second is probably close enough).

90mm, 55.42 (use 1/60 second)

180mm, 110.8 (use 1/125 second).


For the 4” x 5” format (95mm x 120mm, diagonal = 153mm):

150mm lens, 55.4 (use 1/60 second)

300mm lens, 108.7 (use 1/125 second).

Note: The common version of the “Reciprocal of Focal Length Rule” fails badly with increasing focal length. This is obvious when you examine the 4" x 5" results.

So long as you’re satisfied with the results of using a 50mm lens on a handheld 35mm camera at 1/60 marked shutter speed, this formula translates accurately to any format. You can always tighten or relax the standard by altering the constant k as the results dictate. Increasing k gives faster times, while reducing k recommends slower speeds. As has been pointed out, some folks can get good results handheld at slower shutter speeds than others. Too, some cameras or camera-and-lens combinations are much easier to hold steady than others, which can be exploited as safely using a slower speed than otherwise indicated.

The main idea is to limit the angular sweep of the lens axis during the shutter-open period to the same value for all formats and any lens of known focal length f.

 

[Alan Johnson]

"Image Clarity" by John B Williams ,p191 gives a table including the resolving power of hand held cameras at various shutter speeds for a maximum resolving power of 100 lppm.
Shutter Speed....1/30.....1/60.....1/125..... 1/250.....1/500.....1/1000.....MaxRP
RP............................16.........30.........53..........78...........93............98..........100
He says resolving power is sacrificed at all shutter speeds when high quality systems are hand held, the question is by how much.
From Ian C's post above, the selected speed should translate to all formats.

 

[wiltw]

This version of post #20 is probably easier to read. I removed a few typos and did some revision.


The common rule is a simplification that works fine for small formats, but becomes increasingly inaccurate with increasing format size. More correctly, the rule should depend on magnification, which is where the focal length comes into play. It is, of course, the angular sweep of the lens axis during the time in which the shutter is open that must be limited to some practical value that is the same for all formats and lenses....

The main idea is to limit the angular sweep of the lens axis during the shutter-open period to the same value for all formats and any lens of known focal length f.

Ian's post shows 1/60 for 35-50mm on 135 format and 90mm on 6x7...my own earlier corrected derivation from the historical Rule of Thumb (for medium format) shows about 1/80 for the 'normal' FL of three formats.. only about 1/3 EV difference and well within the bounds of 'rules of thumb' that do not universally apply to all shooters!

 

[Patrick Robert James]

Rules. Boring.

They really mean nothing. What camera are you using? A Pentax 67 is going to be different than a Mamiya 7 but both have the same negative size. I have sharp images with handheld 4x5 at 1/8s. 35mm with a 50 at 1/8 as well. I am sure I am not alone.

Rules are stupid. Maybe this one should be called a "suggestion".

 

[wiltw]

Rules. Boring.

They really mean nothing. What camera are you using? A Pentax 67 is going to be different than a Mamiya 7 but both have the same negative size. I have sharp images with handheld 4x5 at 1/8s. 35mm with a 50 at 1/8 as well. I am sure I am not alone.

Rules are stupid. Maybe this one should be called a "suggestion".

As has already been made clear, "Rule of Thumb - which is a guideline and nothing more."

Rule of thumb
From Wikipedia, the free encyclopedia

A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. It is based not on theory but on practical experience.​