SD, microSD and speed rating

[tomczak]

Would anyone know of some congruent summary of SD cards and their ratings? I'm confused:

1) There are Class (e.g. 4,6,10) ratings. There are also UHS class 1 and class 3 ratings. And some cards list transfer rates (maximum? minimum? average? writing? reading?). There is also 'x' ratings. Do those numbers make any sense? Are they translatable somehow?

2) Even if the ratings make sense, how do I know what's good for the camera? i.e. is the SD card writing speed the bottleneck or the cameras are usually slower than cards?

3) Is there any disadvantage to usnig microSD cards inside SD adapter rather than bigger SD cards?

Cheers and thanks.

[Dieter Mayr]

Maciej,

The classes are defined by the minimun speed for reading and writing.
Class 2 is 2 MB/s , Class 10 is 10 MB/s .
UHS 1 is 10 MB/s and UHS 3 is 30 MB/s.
These values are, like almost every rating today, totally optimistic, means a continuous stram of data, fastest possible bus hardware, no fragmentation.
So, in real life these values will be reached in very few cases.
The "x" rating is made obsolete by the classes, 16x equals 2.3 MB/s, so roughly class 2 and so on to 100x = 14 MB/s, roughly calss 10.
The technology of all physical sizes of the SD card is identical, so a adapter is just a mechanical adapter and wires between the contacts, so I would not expect big performance issues with a (physically) smaller card in a adapter.
For what's good for the camera I woudl first of all trust the manufacturer, the make tests and suggest a class of card usually in the manual.
But I would say, a fast card is never wrong, even if the camera has a botleneck somehow, it pays with a sufficient card reader with faster download speeds.
Personally, I am hardly limited by writing speed to the card at my style of photgraphy, I seldom make fast long series shots, but downloading a full card faster is always a welcomed thing.

Hope it helps a bit