Metric and Imperial mix and match.

Steve

Steve

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I've never understood why we mix and match metric and imperial measures in photography.

I have an Elmar 50mm lens with the depth of field range in feet.

Small film sizes are metric eg 35mm
Medium are metric eg 6x6 cm
Large are imperial eg 5x4 inches

I guess it's just what came first, just seems odd that they have not been standardised.
 
Medium format used to measured with imperial.

e.g. 6x6 used to be known as 2 1/4" square.


Steve.
 
Steve said:
I've never understood why we mix and match metric and imperial measures in photography.

I have an Elmar 50mm lens with the depth of field range in feet.

Small film sizes are metric eg 35mm
Medium are metric eg 6x6 cm
Large are imperial eg 5x4 inches

I guess it's just what came first, just seems odd that they have not been standardised.
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I thought 6x6 was 2 1/4" square? :thinking:
 
Quite a lot of metric sizes and weights are simply conversions from imperial, in countries where this was used.

I'm still wondering why petrol is sold in litres, but fuel consumption is measured in miles/gallon and distances in miles?
 
Phil V said:
I thought 6x6 was 2 1/4" square? :thinking:
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Yes, but we always refer to it in the metric 6x6, whereas we refer to 5x4 in the imperial.
 
Many standard 50 mm lenses were shown as 2" in this country. which, as it is rare for a 50mm lens to actually have a 50 mm focal length, is near enough.
large format lenses were often marked in Inches especially British and American made ones. In the 50's and 60's it was common to own a mixture.

Distance scales for any lens tended to be marked to suit the market involved.
Equally most off camera rangefinders were marked either metric or imperial.
 
My Nikon film gear is in another country, but I seem to remember that the distance scales on the lenses were marked in metres and feet, in different colours? I haven't thought about this for years, so I'm not quite sure though.
 
It's like tyres - unless you have a Princess, M84-90 Metro or an early Saab 900 Turbo fitted with Dunlop Denovo or Michelin TRX respectively....

width of tyre is expressed in mm
diameter and width of rim in inches
 
welshwizard645 said:
It's like tyres - unless you have a Princess, M84-90 Metro or an early Saab 900 Turbo fitted with Dunlop Denovo or Michelin TRX respectively....

width of tyre is expressed in mm
diameter and width of rim in inches
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Almost, the diameter of the wheel is inches, width in mm and the other bit is an aspect ratio in % ie on a 205/50 R17 the wheel diameter is 17" the tyre is 205mm across and 50% of that width is the side wall giving 51mm side wall height.

But there are a few random cars with metric wheels, where it is cheaper to replace all 4 wheels and tyres than buy 1 metric tyre.
 
It's just as bad in in met/aviation. Vertical distances measured in feet (unless you're in Russia) and horizontal distances i metres or Km.

Alan
 
MartynK said:
I'm still wondering why petrol is sold in litres, but fuel consumption is measured in miles/gallon and distances in miles?
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That's simple, the cost of converting petrol pumps had to be paid for by the fuel companies, the cost of changing all roads signs would have to be paid by the goverment, and no goverment wants to spend that sort on money.
 
acetone said:
That's simple, the cost of converting petrol pumps had to be paid for by the fuel companies, the cost of changing all roads signs would have to be paid by the goverment, and no goverment wants to spend that sort on money.
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For many years fuel pumps showed the Gallon equivalent, first with some showing dual scales and later with Tables showing equivalents.

Whilst the minister of Transport can authorise non standard metric signs, he has not done so.
Ony the UK, the USA and Burma use imperil distances on their signs. However the Imperial Gallon and the USA gallon are different. The imperil Gallon is 4.546L while the American is much smaller at 3.79L
 
acetone said:
That's simple, the cost of converting petrol pumps had to be paid for by the fuel companies, the cost of changing all roads signs would have to be paid by the goverment, and no goverment wants to spend that sort on money.
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That's fine, I just wondered about this. I left the UK when they were still using gallons, and found this combination of metric and imperial units when I returned, about 30 years later. I still 'think' in metric units though.
 
maninsuitcase said:
Almost, the diameter of the wheel is inches, width in mm and the other bit is an aspect ratio in % ie on a 205/50 R17 the wheel diameter is 17" the tyre is 205mm across and 50% of that width is the side wall giving 51mm side wall height.

But there are a few random cars with metric wheels, where it is cheaper to replace all 4 wheels and tyres than buy 1 metric tyre.
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:geek: correction, the diameter and width of the wheel is in inches, the wheels of my car are quoted as 17" x 7.5" the tyres are 235/45 R17 W.
The only parameter on the wheel rim measured in metric is the offset:geek:
 
Terrywoodenpic said:
For many years fuel pumps showed the Gallon equivalent, first with some showing dual scales and later with Tables showing equivalents.

Whilst the minister of Transport can authorise non standard metric signs, he has not done so.
Ony the UK, the USA and Burma use imperil distances on their signs. However the Imperial Gallon and the USA gallon are different. The imperil Gallon is 4.546L while the American is much smaller at 3.79L
Click to expand...

Actually IIRC, metric is not the legal standard measurement in the UK...

There isn't a legal standard, though the govt pushed us towards metric to fall into line w most of europe.

Although in the USA it is metric, even though no-one uses it. :shrug:
 
I think of measurements in a mixture! Small measures are in "thou", until they're big enough to be mm then inches, feet until metres. After that, miles kick in. I try to stick to SI units but keep slipping back to Imperial measurements for some things. (Oh, and 6x6 will always be 2 1/4" square to me but 6x4.5, 6x7 etc are all metric...) I'm 6'1 1/2" tall and weigh about 17 stone - never got the hang of measuring myself in metric.
 
If I'm correct, new road signs have both imperial and metric systems in use, purely because although the government would prefer to use the metric system, but people are old... And are so used to the imperial system, you can't just change everything to metric, after all, I never got taught imperial AT ALL, in my educated life (I'm 25) but if anyone asks me how heavy or tall I am?!? "13 stone and 5ft 9in"....
And of corse, from an engineering perspective... Every piece of metrology equipment I've used, is accurate to 1 micron ( 0.001mm) or half a thousandth of an inch (0.0005in) which is 0.00127 of a millimetre, meaning metric is a more accurate system.
 
Stevenjay5 said:
If I'm correct, new road signs have both imperial and metric systems in use
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I think they all have to be imperial.

I recall a few years ago, a council put up some direction signs for pedestrians with the distances in metres and they had to change them all to yards.


Steve.
 
Steve Smith said:
I think they all have to be imperial.

I recall a few years ago, a council put up some direction signs for pedestrians with the distances in metres and they had to change them all to yards.

Steve.
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Your right sorry Steve, only road signs in use that use metric measurement are bridges, to stop foreign drivers from destroying them... Haha....
 
Stevenjay5 said:
If I'm correct, new road signs have both imperial and metric systems in use, purely because although the government would prefer to use the metric system, but people are old... And are so used to the imperial system, you can't just change everything to metric, after all, I never got taught imperial AT ALL, in my educated life (I'm 25) but if anyone asks me how heavy or tall I am?!? "13 stone and 5ft 9in"....
And of corse, from an engineering perspective... Every piece of metrology equipment I've used, is accurate to 1 micron ( 0.001mm) or half a thousandth of an inch (0.0005in) which is 0.00127 of a millimetre, meaning metric is a more accurate system.
Click to expand...

As an apprentice in the late 60s a standard 0 to 1in measured to 0,0001in
 
welshwizard645 said:
:geek: correction, the diameter and width of the wheel is in inches, the wheels of my car are quoted as 17" x 7.5" the tyres are 235/45 R17 W.
The only parameter on the wheel rim measured in metric is the offset:geek:
Click to expand...
I meant the width of the tyre, but yes the wheel width is also measured in inches and the off set is mm.
 
I've got a lovely reprint of a railway Engineering company's catalogue from 1924 where all locomotives are specified in metric and imperial, with some of the designs being designed in metric.

I was once told by someone that there is a discrepency in the size of a modern inch due to the fact that modern measuring implements have been manufactured and marked by metric equipment, IE 25.4000000mm to the inch, instaead of whatever the correct figures after the decimal place are. I assume it's possible there are some pieces of equipment were this may be true but I'm danged if I could prove it!
 
EDIT: My Zeus book gives me 25.4mm as being 1.0000488 inches. Interesting.
 
paulminus273 said:
As an apprentice in the late 60s a standard 0 to 1in measured to 0,0001in
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Sorry my bad again! I missed out a zero! I agree a analog micrometer will measure in thousandth of an inch, I meant to write 0.00005in! ( Half a thousandth) Which is what my digital mic will now measure, compared to a metric measurement of 0.0001, basically there is a discrepancy in accuracy between the two! :)
 
Stevenjay5 said:
Every piece of metrology equipment I've used, is accurate to 1 micron ( 0.001mm) or half a thousandth of an inch (0.0005in) which is 0.00127 of a millimetre, meaning metric is a more accurate system.
Click to expand...

Stevenjay5 said:
Sorry my bad again! I missed out a zero! I agree a analog micrometer will measure in thousandth of an inch, I meant to write 0.00005in! ( Half a thousandth) Which is what my digital mic will now measure, compared to a metric measurement of 0.0001, basically there is a discrepancy in accuracy between the two! :)
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I hope you have someone checking your calculations!

A thousandth of an inch is 0.001in, so half a thousandth is 0.0005in.

An inch is 25.4mm, so half an inch is 12.7mm, so half a thousandth is 0.0127mm. You had one extra zero the first time and two extra zeroes the second time.

One micron is 0.001mm which is roughly half a ten-thousandth of an inch.

But of course none of this means that metric is more accurate. It just means that your equipment is more accurate with metric than imperial measurements, assuming of course that it is capable of 0.0005in or 0.01mm (or even 0.001mm) . But it could easily be otherwise: I have a ruler which is marked in millimetres but also in 1/32in, which means it measures more accurately in imperial.
 
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e902717 said:
228mm sounds bigger than 9" ;-)
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But measuring accurately to the nearest millimetre requires a bit more time and attention than measuring to the nearest inch, which may not always be practical or appropriate...
 
Sorry for my imperial calculations as I said, never taught them, and ever used them, and your terminology is far better than mine yes there both as accurate as each other, but metric is more accurate on metrology equipment.
 
In wood working and joinery, Rules are rarely as accurate/consistent as using a layout rod. If you want an accurate fit you mark one piece from another.(or master template)
 
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In the offshore oil industry we use a mixture of UK Imperial US Imperial and Metric. For example, studbolts are specified as 5/8" x 90mm.
 
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