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First steps in MWIR!


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SI rules, but temperature in Kelvin is not that practical for daily usage use.

The °C scale is more practical for that with its strong relation to the common behaviour of Water.

That's true, I too use and think in Celsius.

 

I cannot find any bad consequence caused by the error except that it is not the correct way to write.

Can you?

No, it isn't that important. Still better than writing "nanometers" "NM", "Nm" or all sort of ways, but here it seems everyone knows the right spelling. But anyone can learn, we all make mistakes, myself included.
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Ulf I am surprised you don't know what the Fahrenheit scale is based on.

I grew up in Canada, so learned both systems of metric and imperial.

The problem with setting the Fahrenheit system up was that the water sample used back in 1700 or 1800s was salt water and not fresh water. But this becomes useful for us to know where salt water freezes and boils. Thus why salting the roads in winter is good, as it depresses the freezing point. But if the nighttime temperatures drop below. Then don't salt.

This should help you rationalize it and use it in the future.

 

The one that always made the least sense to me was Newton's temperature scale. With ice melting at 0 and boiling at 33.

 

 

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Andy Perrin

SIMMER DOWN, everyone! I sense this thread is boiling over. Sadly, I have to put the deep freeze on David's notion that Fahrenheit is based directly on salt water samples. The truth is a lot more rational.

 

Fahrenheit based his scale on Rømer's scale. We know that because he said so:

According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[17] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).[18][19]

 

Rømer's scale, not Fahrenheit's, is the one based on brine. As the above makes clear, Farenheit only riffed on that idea, because he was after convenience in marking off his apparatus.

 

But this becomes useful for us to know where salt water freezes and boils. Thus why salting the roads in winter is good, as it depresses the freezing point. But if the nighttime temperatures drop below. Then don't salt.

David, the freezing point of salt water depends on the mole fraction of salt, it's not a fixed temperature value.

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Ulf I am surprised you don't know what the Fahrenheit scale is based on.

I grew up in Canada, so learned both systems of metric and imperial.

The problem with setting the Fahrenheit system up was that the water sample used back in 1700 or 1800s was salt water and not fresh water. But this becomes useful for us to know where salt water freezes and boils. Thus why salting the roads in winter is good, as it depresses the freezing point. But if the nighttime temperatures drop below. Then don't salt.

This should help you rationalize it and use it in the future.

 

The one that always made the least sense to me was Newton's temperature scale. With ice melting at 0 and boiling at 33.

I know more or less, but it appears so strange compared to °Kelvin and °Celsius. Actually originally Celsius had the scale reversed in the beginning, but that was soon corrected.

 

Also using salted water is not that good because the freezing point differ for different salts and how much salt is added

 

This is useful if you want to cool something:

https://en.wikipedia.org/wiki/List_of_cooling_baths

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Andy Perrin

Also using salted water is not that good because the freezing point differ for different salts and how much salt is added

Ulf, Fahrenheit's scale is arbitrary. See my post above. Rømer's scale was based on the eutectic point of water and ammonium chloride salt (not sodium chloride!) and the reason is that it it's an easy temperature to find so it's very reproducible.

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Bill De Jager
And what about the psi? I just can't use it. I am ok with "atmospheres", bars and so on. But "pound-force per square inch" is just no.

 

This really comes down to familiarity. While I learned SI at a young age, on a daily basis I used the American version of the Imperial System because those units were (and still are for the most part) what surround me in daily life. It doesn't matter how logical SI is, or how easy it is to do unit conversions in it, when another system is first implanted as the default and natural system. It's like growing up with a particular language, then being exposed to another language and learning its rules but not yet becoming fluent in it. The language you grew up with will seem natural and easy while the other one will seem unnatural, awkward, and wrong.

 

When I was doing the field research for my thesis I used SI units because I was in an academic environment. That was a pleasure because calculations and unit conversions were so easy, and it didn't take long to get accustomed to working in that system when I used it daily. Once that work ended I was back into the world of feet, miles, pounds, and gallons for decades after.

 

I find estimating measurements, or understanding the magnitude of measurements, in terms of inches, feet, miles, pounds, and degrees F easy and natural. I can't do those things directly in SI; I have to do them in Imperial and convert in my head to get the SI equivalent. Pounds per square inch, and inches of mercury for atmospheric pressure, are familiar while other units of pressure (except for atmospheres) are so unfamiliar that they make no intuitive sense to me. If I'd spent my life in a different environment then these perceptions could have been entirely reversed.

 

In the end, whatever intrinsic advantages and disadvantages any system of measures may have, on a psychological level sheer familiarity over a lifetime exerts a strong influence on perceptions. For me personally this leads to a bit of cognitive dissonance, where on a rational level I support SI yet it still feels wrong intuitively. Such are the complications of being a human being.

 

Now what we really need to do is convert everything to base 12. That would be very logical and much more convenient when working with quantities in real life. Imagine if "10" could be divided by 3, 4, and 6! Of course, SI would need to be revised, and familiar SI quantities (including temperatures) would change to numbers that just feel wrong. Any takers? :wink:

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But we are still all forgetting the important image Andy promised us.

I want to see that flower in your oven at 500!

What the hold up, just get the fire extinguisher ready.

 

Bonus points if your oven goes up to 500 C. About 932F. Some of the really older ones with self cleaning mode do.

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Andy Perrin
I definitely didn’t promise any images at 500, F or C. We have enough problems with smoke alarms in my building.
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And also, you have to put a space between the number and the unit. 365 nm must be written with the space, not "365nm". I am saying this as a lot of people make that mistake here. I too make mistakes of course, but this is a rule I know and always follow.

 

See here: https://en.wikipedia...s#General_rules

Interestingly such "errors" with no space between number and unit are very common, not only on this forum, but everywhere.

 

Could it be that that rule is needed mainly for strict scientific documents like when writing a thesis or an official standard?

 

It is true that standards are written that way.

The main reason for the space is to avoid any confusion or possibility to have several interpretations.

 

It appears to be more relaxed in less strict texts.

When that is not the case the space is just a waste of space making texts longer and could be omitted. (pun intended)

 

Here is one example without spaces, between number and units:

post-150-0-45507600-1617688871.jpg

Any extra space here would add confusion as the different information-parts are divided by spaces already.

 

There are writing rules in different languages to guide how to write things.

For me it is quite normal to omit spaces as in the Swedish language there are rules to join some words in a way not used in English.

If I remember correctly there are similar rules in German.

When you separate words that should be joined, using English rules, texts look really funny and wrong.

They can even cause confusion, losing the strict intended meaning.

 

I will fallback to writing in a way that looks OK and will continue doing those "mistakes".

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Andy Perrin
Yeah, I agree, unless there is a real need for a style guide and consistency to avoid confusion, it’s probably better to leave people’s spelling and grammar choices alone. Even American English style guides differ.
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I will keep writing following SI rules, as I have always done. I am Ok if other people choose to do otherwise, as long as the meaning is kept.

 

I think that Canon lens has that spelling as part of its name, so I would write it the "wrong" way, since this is how Canon decided to name it.

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Andy, let me know if you want me to split off any side topics.

***

 

As a further off topic comment: Grammar, punctuation and spacing rules are by consensus. However the consensus is somewhat situational and location dependent. Also, over time consensus changes. Most all of us here are well educated enough to recognize and properly interpret any differences in grammar, punctuation and spacing.

 

For example, I do not think that anyone will ever become confused by "400mm" versus "400 mm". (I don't even know why there is a rule for that! Perhaps the space adds clarity?) Or, for example in spelling, nobody will ever confuse "color" versus "colour". (I learned both ways to spell words like that, so I myself am very inconsistent in some spellings.)

 

Anyway, I do not enforce any particular set of rules here. When *I* am the one writing or editing, however, I likely will use the set of rules with which I am familiar. Occasionally in Stickies or Pins, I might enforce a certain way of writing simply for consistency throughout the article or document. I do also try to clean up certain awkward phrasings for those for whom English is a second language, but only after asking their permission first.

 

The occasional spelling and typos we all make, those I "fix for free" if I spot them. And I want to be told of my own errors because nobody can properly edit themselves.

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Andy Perrin
It's okay, we can leave it, but I do think we'll all be happier if we don't spend time correcting other people's grammatical errors or telling each other to tag things. Factual errors are a different story.
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So do you have those flowers in the oven yet for some dinner time photos?

 

You can actually buy an electric 500 C oven to cook your pizzas in 90 seconds. Crazy times but might be fun for other imaging. If you buy a cast iron pan, you can image melting metals.

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I had the idea of seeing molten metal hot enough (>~300 °C) to glow in the NIR region but too cold (<~525 °C, the Draper point) to be red-hot to the naked eye. There are several metals which would work. I don't know if I will ever try, but I certainly won't melt lead again. Tin is better.
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You only need a 660 C to melt Aluminum foil. Best to do so in cast iron, as it can handle twice as much heat.

You can burn some magnesium if your pizza oven doesn't go up there. Road flares get quite hot and melt some metals.

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Andy Perrin

Hah. Guys, I’m not planning on burning flowers or melting anything. Honestly there would not be anything new to see from that whicht can’t be done in LWIR closer to room temperature. Water glows just fine in LWIR for example, so why melt metals? It wouldn’t look any different. Black body radiation is all the same, regardless of where the peak emission is.

 

No, I’m interested in MWIR reflectography and that will be the focus, because that’s where we will see differences from other areas of the spectrum.

 

What I need now is time, honestly. I’m way too busy with work to play with cameras.

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