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First steps in MWIR!

Camera Infrared Lighting MWIR Video
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#21 Stefano

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Posted 04 April 2021 - 00:56

View PostAndy Perrin, on 04 April 2021 - 00:44, said:

Honestly, I am thinking that it might be better to stick things I want to image in the freezer first, though. Look how much the Planck spectrum changes between 70F (21.1C) and 20F (-6.66C):Attachment Screen Shot 2021-04-03 at 8.42.39 PM.png

If we regard the thermal radiation as the "noise" then that's like doubling the signal-to-noise ratio if the incoming MWIR is kept constant.
Also look at the huge difference between 3 μm and 4/5 μm (in both lines). I bet if you put a 3 μm shortpass filter as I thought you will cut down like 99% of the blackbody radiation.

This also means that getting a purely reflected image becomes much more difficult very quickly as you increase the wavelength.

#22 Stefano

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Posted 04 April 2021 - 03:18

Some Schott glass filters you may be interested into (go here to see the full spectrums yourself at various thicknesses, I will report the approximate eyeballed values at a thickness of 2 mm):

Cut-off at ~2900 nm:
S8612, BG39;

Cut-off at ~2850 nm:
BG40, BG42, BG55, UG5;

Cut-off at ~2800 nm:
BG18 (1400-2800 nm), BG38, BG50;

Others:

BG36 (peaky spectrum, cuts below ~3450 nm);

BG60 (up to ~4100 nm, attenuates above ~2800 nm);

BG61 (same as BG60, but with stronger attenuation in the longer wavelengths);

BG62 (similar to BG60);

BG63 (similar to BG60, up to ~4050 nm);

BG64 (similar to BG63);

BG67 (up to ~4100 nm, but with less attenuation);

WG, GG, OG and RG glass (Schott longpass filters) cut in the high 4000s, at ~4500 nm or a bit above;

KG1 and KG2 cut at ~2800 and ~2900 nm respectively, but with low transmissions, KG3 and KG5 have little bumps in the 2000s;

NG filters have a peak at ~2700 and ~3300 nm;

UG1 transmits between ~2150 and ~4650 nm, but the transmission is low; UG11 is practically useless;

VG9 cuts at ~4600 nm;

VG20 cuts at ~4150 nm.

#23 UlfW

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Posted 04 April 2021 - 08:12

View Postdabateman, on 03 April 2021 - 21:28, said:

Andy flowers at 500 might be hard but entertaining.
I woke up today feeling a bit mean and could not resist.
Apologies in advance.

They say that water is a key factor for life and our bodies contain a lot of it. That is logical.
Water changes from solid to liquid and to gas (at a rather normal pressure) at two distinct temperatures.
You can use those temperatures as references and combine them with two decades of our decimal system.

Then you get a logical temperature scale:
Freezing : 0 (°C) and boiling 100 (°C)
Compare with
Freezing : 32 (°F) and boiling 212 (°F)

I guess that the 500 above is temperature in °F. => 260°C

Can someone point out the logics behind the °F :smile: :wink:

No offence, just teasing.

If looking for more strange American units take a look at
AWG where AWG-number goes higher when diameters decrease
https://en.wikipedia...ican_wire_gauge
and
NPT where the NTP-values are much smaller that the actual diameters of the threads
https://en.wikipedia...nal_pipe_thread

Strange and confusing units can sometimes be expensive.
Remember this:
http://edition.cnn.c...c/#:~:text=(CNN)%20%2D%2D%20NASA%20lost%20a,a%20review%20finding%20released%20Thursday.
Ulf Wilhelmson
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#24 Stefano

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Posted 04 April 2021 - 12:06

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.

As of temperature, the SI unit is Kelvin. It is "perfect" as 0 K is 0. It doesn't go negative.

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

#25 UlfW

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Posted 04 April 2021 - 12:17

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.
I have negative numbers in my rational number range. They are quite useful. I cannot imagine being without them or the number 0. :wink:

Thanks for the notice about the space by nm. I am sure I made that mistake many times, even if it is rather harmless. :smile:
I cannot find any bad consequence caused by the error except that it is not the correct way to write.
Can you?

Edited by UlfW, 04 April 2021 - 12:21.

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#26 Stefano

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Posted 04 April 2021 - 14:03

View PostUlfW, on 04 April 2021 - 12:17, said:

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.

View PostUlfW, on 04 April 2021 - 12:17, said:

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.

Edited by Stefano, 04 April 2021 - 14:04.


#27 dabateman

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Posted 04 April 2021 - 14:16

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.


Edited by dabateman, 04 April 2021 - 14:35.


#28 Andy Perrin

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Posted 04 April 2021 - 15:47

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:

Quote

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.

Quote

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.

Edited by Andy Perrin, 04 April 2021 - 15:53.


#29 UlfW

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Posted 04 April 2021 - 15:54

View Postdabateman, on 04 April 2021 - 14:16, said:

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...f_cooling_baths
Ulf Wilhelmson
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#30 Andy Perrin

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Posted 04 April 2021 - 16:02

View PostUlfW, on 04 April 2021 - 15:54, said:

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.

#31 Bill De Jager

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Posted 05 April 2021 - 19:08

View PostStefano, on 04 April 2021 - 12:06, said:

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:

Edited by Bill De Jager, 05 April 2021 - 19:10.

Studying the botany and plant geography of California and western North America for almost 50 years.

#32 dabateman

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Posted 05 April 2021 - 22:45

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.

Edited by dabateman, 05 April 2021 - 22:51.


#33 Stefano

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Posted 05 April 2021 - 23:48

500 °C is almost at the Draper point, where you start seeing things glowing with the naked eye.

#34 Andy Perrin

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Posted 06 April 2021 - 00:13

I definitely didn’t promise any images at 500, F or C. We have enough problems with smoke alarms in my building.

#35 UlfW

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Posted 06 April 2021 - 06:02

View PostStefano, on 04 April 2021 - 12:06, said:

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:
Attached Image: IMG_2532.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".

Edited by UlfW, 06 April 2021 - 06:08.

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#36 Andy Perrin

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Posted 06 April 2021 - 06:13

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.

#37 Stefano

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Posted 06 April 2021 - 10:31

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.

#38 Andy Perrin

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Posted 06 April 2021 - 16:04

Yeah, this thread has gotten seriously off-topic.

#39 Stefano

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Posted 06 April 2021 - 19:27

Andy, if you want to get back on track, can you give the filters above a try? You should have S8612.

#40 Andrea B.

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Posted 09 April 2021 - 18:23

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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