Walking the Dogs, Regents Park

 

He's walking them into Regent's Park. Those aren't his dogs, he's a pro. The back-pack tells you that, and the short leads. People walking their own dogs use those variable-length leads, or even none at all. How much do they make? In that postcode, according to Google, it could be £22 per dog per hour. That's £110 he's got on those leashes. Nice work if you can put in the probably substantial effort to get a steady stream of clients lined up.

Caffe Nero, Covent Garden

I'm a big Caffe Nero fan. It was founded by two Australians (because Australians are really modest about their coffee-making abilities) and the got three things right: the coffee; the branding / decor; and before 2020, hiring and training staff. I suspect that Pret kept its stores open for longer in the Great Madness and held onto a core of its staff - the outlet on London Wall was open in mid-Mat 2020 when almost no-one was in the City. But even so, I prefer the vibe of a Nero to the other chains. And anything is better than the pram-Mummy magnet that is Starbucks. 

The Head Office is on a side-street in Covent Garden. 

The blur on the bike turns out to make the shot, I think.

American Kandy, Covent Garden

This location used to be a Swatch shop. A long time ago. It was empty for a while and then a clothes shop took the site. Whatever the brand was, it clearly made no impression on me. The lockdowns put an end to it. Then this appeared. They are all over the place: the cheap end of Oxford Street, there's even one near the British Museum. There are a few YT videos on them, like this....



The clue is in the ridiculous prices of the candy bars. You can clean a lot of cash at £10 a bar of some junk that costs nothing at a bankruptcy sale, or is time-expired stock bought from a manufacturer. They won't be paying the rent, because they got a deal to occupy the premises from a landlord, and only mugs pay business rates, amirite? Go out of business when the bailiffs come, right?

None of it would work if whichever bank it is did proper KYC (Know Your Customer) checks on these businesses. But I'll bet they don't bank with one of the UK clearers.

Anyway, what you should be looking at are the sparkling colours, the way the camera handles the range of sunlight and shade effortlessly, and the depth of detail (though I haven't posted the full version). This is the kind of photograph I always knew the X-E4 could take. I'm getting there.

Life on Hold Because Pollen and Heat

Pollen is not good for my brain, and there's been a lot of it for the past couple of weeks.

I'm waking up like someone has been spraying pollen into my bedroom all night.

Temperatures over 70F are too much.

It is a miracle that I even found the laptop to write this.

In the meantime, grab a cup of coffee and settle in to watch this...



Hither Green is directly south of Greenwich. The equivalent distance west is Putney. The route is direct and sensible until it gets to Clapham, and then... I won't spoil it.

What struck me was how many junctions and lines going everywhere there are in south London. Then you get to Clapham and you have four choices: main lines through Richmond (for Reading), Wimbledon (for Woking, Porstmouth and Weymouth), Croydon (for Gatwick and Brighton), and the Overground south and north. Those lines are incredibly simple: there aren't any junctions on the Reading line until Virginia Water and then there's only one more at Ascot. None of which stops this train taking the most complicated route to Woking.

Yes. I had nothing better to do. It was hot. I did scrub through the final section of the journey from Ascot.

Camera Maths, or Why The Crop Ratio Works

I still think there's something odd about APS-C cameras. 'Odd' means 'It doesn't quite do what my old full-frame film camera did with the same settings'.

Time for some maths.

We will work all these examples with a full-frame (35.8 x 23.8 mm) sensor with a 50 mm lens at f8, and an APS-C (23.6 mm x 15.6 mm) with a 35mm lens at f8. Shutter speed is on Auto.

Let's look at how much light is getting in.

The f-number is the ratio of focal length to diameter of the shutter pupil. So the diameter of the full-frame shutter pupil diameter is 50/8 = 6.25mm giving an area of 3.142*3.125^2 / 2 = 15.34 sq mm. Which is a proxy for how much light is getting in. The APS-C will have a shutter pupil diameter of 35/8 = 4.375 mm, giving an area of 3.142*(2.19)^2 / 2 = 7.53 sq mm. The APS-C has 7.53 sq mm of light falling on 365.8 sq mm of sensor, or 2.06%. For the full-frame, it's 15.34 / 853 = 1.8%.

Slightly more light per sq mm falls on the APS-C sensor. If we want the same, we will need 7.53*1.8/2.06 = 6.6's worth of light, which means a pupil radius of sqrt(6.6/3.142) = 1.45 mm, a diameter of 2.9 mm and an f-number of 35/2.9 = 12. Or I could increase the shutter speed by 14%. Shutter speeds don't do that. ISO's don't either.

Let's look at depth of focus.

According to Wikipedia, depth of focus is roughly

2u^2 Nc / f^2

for a given circle of confusion (c), focal length (f), f-number (N), and distance to subject (u). The circle of confusion is conventionally 0.05 mm. For the full-frame lens and a subject 5 metres away, the depth of field is 2*(5000)^2 * 8 * 0.05 / 50^2 = 8000 mm, which is from 4m in front of the subject to 4m behind them.

The only thing that changes in this calculation when we switch to the APS-C sensor is the focal length, from 50 to 35. It changes to 16.3 m (!), 8 metres in from to 8 metres behind. That's a whole lot of extra depth of focus.

Why does the APS-C have a shorter focal length and why that one? Everybody does this, but we should understand why.

The 35 mm sensor has an area of 35.8 * 23.8 = 852 sq mm. The Fuji APS-C has an area of 23.6 * 15.6 = 365.8 sq mm. So the APS-C sensor is 43% of the full-frame area. Or the 35 mm is 2.33 times larger than the APS-C.

The APS-C sensor is showing you a smaller part of the full-frame image for a given focal length. To get the same image with an APS-C lens, we have to have a shorter focal length (shorter focal length = wider and higher picture). How much shorter?

The answer involves some school geometry. (Graphics are not my strong point.)

The focal point of the lens is behind the sensor. (I know, I learned it at school, and I'm still nodding along. Optics is magic, not physics.) The distance behind the focal point and the sensor is the focal length. (Which has nothing to do with the length of the lens. It's the length of the path the light takes between the front lens and the sensor: lenses with huge focal lengths are obtained by using mirrors. Lots of mirrors.) But I digress.

The key bit of camera geometry is the angle in red, called the field of vision. (Wrong notation in the picture.) School geometry says the it is the angle $\theta$ such that

$\tan(\theta) = \frac{\text{sensor width}}{2* \text{focal length}}$

The magic maths is this: for a given distance $D$ away, the width of the picture that the sensor will capture is $2 D \tan(\theta)$. This is why you move forwards to get nearby things you don't want in the frame, or backwards to include more of them.

Since we want the same field of vision with the APS-C as the full frame, the angle stays the same, and we can set

$\frac{\text{sensor width}}{2*\text{focal length}}$ (full-frame) = $\frac{\text{sensor width}}{2*\text{focal length}}$ (APS-C)

or 35.3/100 = 23.6/2*(APS-C focal length), 

giving APS-C length = (23.6*100)/(2*35.3) = 33 mm. 

Which is 2mm shorter than the industry-standard equivalent of 35mm.

(Now you know why nobody explains why you use the crop ratio.)

So using the same f-stop and the industry-rule of thumb equivalent lens sizes, the APS-C gives us - for the same shutter speed - a slightly brighter, ever so slightly narrower picture with way more depth of focus, than a full-frame. The difference in brightness is not enough at sensible ISOs to affect the shutter speed, even if you have shutter speed or ISO on auto, so it will be slightly brighter.

The ISO / shutter speed is way too coarse to adjust for the small change in brightness. But that depth of field can be adjusted, by halving the f-stop you would use on a full-frame, and letting the camera make the shutter speed adjustment.

Taking Pictures With the X-E4: Some Default Settings and Habits

(I had a series of posts about how I took a bunch of under-exposed pictures. Re-reading them recently, every one was close to gibberish. I've done the right thing, and removed all but the last two. The one about crop ratios and camera maths stays, as does this one about my default settings, which has been edited to make sense.)

Nobody writes detailed instruction manuals anymore. I used to like those. Now one has to experiment. Which is easy to do on a technology one already knows, but learning a new technology by experiment is very messy.

So the result of learning what I could about digital camera technology as implemented in the X-E4 is this:

My default settings are 0 for the exposure compensation; f4 for the aperture; A = aperture priority for shutter speed, and an ISO bracket between 160 and 800. There's a post that explains the f4 setting choice.

I assigned the Quick Menu to the Q button, and reduced the number of options to eight. One is always the Custom settings. The others are: ISO, Film Simulation, sensor format, Clarity, Grain Effect, Colour Chrome and screen brightness.

I created two custom settings: one for colour film (Provia) and the other for black-and-white (Acron). I turned the Autosave Custom Settings to OFF, so I could see that I had to Save the changes. When you save a Custom Setting, all the other settings are saved with it as well as the ones you consciously changed. Aspect ratio, file size, sharpness, the works. This is actually a Good Thing, because there are many other things you may want to tweak along with the film type.

I bought a BlackRapid RS-4 Camera Sling. This wonderful gadget lets you slide the camera along the strap up to your face. Ordinary straps make you move the strap. Watch a YT video about the BlackRapid.

I am also bedding-in two habits: checking the dial settings before I take the first shot, in case anything got jogged; and looking at the first shot I take to make sure it is in the mode I want. So the photos I took on the next river ride were a lot better than the horrible ones I took going down to Barking.

Also, here's a video. It's not great, and the wind noise is terrible, but it's one of the first videos I shot with this camera.

Which Of These Boats Is Not Like The Others? (Chelsea Embankment)