Technical photography issues explained

I recently came across the channel of Gerald Undone who has very succinct but detailed explanations of complex technical issues in photography. If you don't understand them after watching his videos, you are probably beyond salvation.

I have selected some, and there are probably more in his channel.

I was particularly intrigued by the depth of field explanation, which says that it is the same regardless of focal length, but the bokeh looks more pleasing in high focal length lenses because they also magnify the out of focus area in the photo, along with the subject.

The one about crop lenses was also enlightening, and it explains how speed boosters work.

And finally here is one on white balance. It allows you to detect the photographers who really care about it, because they wear something grey on their wrists.


Glitter bomb

Just in time for xmas, here is a video that went quite viral. An engineer who had his packages stolen made a special package for the thief, that, among other things, shoots glitter and video that eventually makes it to youtube. The action starts at 5:45.


Electric hurdy gurdy

I recently had the pleasure of hearing Guilhem Desq perform live.

Here is an example of the amazing sounds he can produce.

And here is a much softer song, about a dragonfly falling in love with a tree.

What is nice about the videos is that they show the complexity of the instrument, which has a dragon on one side.

You can listen to more of his songs from the soundcloud addon on his website.


Fitbit heart data

You probably know someone using a fitness tracker. Recent models track daily heart rate and sleep. With just a few years of such models in the market, the companies collecting these data anonymously can provide insights that we simply did not have the data for just 5 years ago.

Here is such a summary from fitbit data.

Among the highlights are that 7 and a bit hours of sleep seem optimal for having a low standing heart rate, that Italians have a very low resting heart rate after controlling for daily activity while Indians have a very high, and life events (like surgeries or family gatherings) can be identified by looking at resting heart rate variation throughout the year.


Allele surfing simulation

You may have heard of the idea of a genetic bottleneck. It is when genetic variation is lost by sampling a very small subset of a population. Just by chance, the frequencies of alleles on the subset of the population will be different to those in the whole population, and overall genetic variation is likely to be lost by population sampling.

This is why small population sizes are not good, and species on conservation lists are required to not drop to too small population sizes. The limited genetic variation remaining in a small population poses a risk because it makes the species susceptible to whatever relies on genetic variation for adaptation, such as environmental changes or diseases.

Here is a visualisation of a bottleneck.

A more recent way to think about bottlenecks is that you don't need a catastrophic reduction in population size to achieve them. Population expansion can have the same result, because expansion is usually from a subset of the population, for example the individuals in the edge of the species range.

Furthermore, if the expanded individuals establish a population locally, it is difficult for genetic variation to be reintroduced at the expanded range, by more individuals migrating from the original population centre, because there is no space for them by the time they arrive. That is why, in terms of genetic variation, there is “Southern richness and Northern purity” in European species (see Hewitt 2000).

It is quite obvious once you think about it.

But you don't need to think anymore! You can now run a simulation illustrating this on your browser. Head here and press the play button and see for yourself that the multicoloured centre of a disk, representing ancestral genetic variation, quickly turns into random sized unicolour pizza slices, i.e. genetic variation is lost by population growth as the disk grows.

The authors have a more formal explanation...


The origins of non-Eucledean geometry

Here](https://youtu.be/nkvVR-sKJT8) is an essential video that distils a lot about geometry, that anyone finishing school should know.

A bit of history, a bit of philoophy, a bit of math, from ancient Greece all the way to our modern understanding of spacetime and the universe.

Well worth the time of watching the whole series.

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