28 July, 2017

Reset Facebook Cache

Problem: Facebook won't show the correct social media tile.

Solution: You can reset the FB cache here:


Related: http://ogp.me/

Error: App Id Missing

developers.facebook.com is a valuable tool. I got the error, that the app id was missing. The solution is to create an app in the Facebook Developer. Use the id from the app in the markup, e.g.

 <meta property="fb:app_id" content="123456789012345">

16 July, 2017

Lens Sweet Spot

Aaarhus seen from my kitchen window today.

During the hollidays I'd like my DSLR pictures to be sharp from the foreground to infinity. Most lenses has a sweet spot, where pictures are better. When you've found that it's a matter of point and shoot.

Some rules of thumb if you want a sharp picture from foreground to infinity. 

When in doubt, try F8 - else try:
  • 24mm ~ >= f11 <= f16.
  • 35mm ~ f16 (street photo, 2m -> infinity sharp).
  • 50mm ~ >= f22 (2m -> infinity sharp).
  • > 80mm (no sharp foreground) f5.6 (from 100 m. -> infinity).
For most lenses the general rule is low f-stop + 2. 
  • e.g. 1.8/50 ~ f4.
If you want to find the real sweet spot for a lens, try settings as above. Shoot several pictures, and compare the sharpness on the PC. For every new picture add an f-stop. 

Source, see this article.

A nice calculator is found here. Here is the result of the hyperfocal calculator:

From: http://www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm 

Hyperfocal Distance

On Wikipedia you can see the formula for hyperfocal distance:

"In optics and photography, hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus." (from: Wikipedia)
In theory we could create an app for the calculations, but ... in the field you just need something that works. I guess the rules of thumb will do the trick.

Sony a58
Change the autofocus area to 1/3 (probably it's in the center). Then you  should have the correct focus, provided that the f-stop is on the sweet spot. Set aperture between >= 8 and <= 11, and set ISO to auto. Then it's a matter of "point-and-shoot". That would be a good street or landscape setting.

Tamron B018S
Look at this site for specifications.

There's a video with a german photographer using apertures ranging from 5 - 11, but more than often 5 or 8. 


  • Try manual focus.
  • Use A on your camera's settings ring. 

14 July, 2017

High CPU speed reduced via BIOS

Low CPU usage after new BIOS settings (htop).

On Ubuntu the average CPU speed was around 30%, which seemed a bit over the top. After some research I found a thread, arguing that the reason might be the power management. In the BIOS I set the low power management to off.

Ubuntu's system monitor. Browser open, listening to Spotify.

01 July, 2017


Swappiness: note that swap = 0 (htop).

Noted that the swap disk often was active. But the system had sufficient RAM. Research suggested, that the swappiness should change to 10. Tried it, and now the system seems to behave as I want i to.

Swappiness values:

  • 0 => only use swap if all RAM is used.
  • 10 => use swap if needed if around 80 - 90% of the RAM is used.
  • 100 => swap is on always.
100 may be a solution on old systems, if you cannot upgrade RAM the swap can save the day. Whether this is heathy for the harddisk, I don't know.