Does certain SD card have much affect on the quality of photos?
Thats exactly the point of digital: all data is either a 0 or a 1.
So if the card has the (analog) values 0.8, 0.3, 0.9, 0.7, 0.9, 0.1, 0.2 stored the data will still be retrieved as 1, 0, 1, 1, 1, 0, 0, making any data degredation much less significant than with analog recording.
Thus, either you still have the data - or its completely gone.
Thus all the SD card can do is
(a) provide data security - dont lose the data, possibly even under hardened conditions (long storage time, radiation, cold, heat, water, corrosion, ...)
(b) provide writing speed - well also reading speed, but writing speed influences how fast photos can be stored on the card during actually shooting, while reading speed only helps with reviewing photos afterwards.
That argument is very old and very misleading IMO. Yes, digital recording/playback is an on/off affair within the digital circuits. On/off is represented by a 1 and a 0 code. Signal/no signal. Works great on paper as theorized back in the 1930's when circuits couldn't process data fast enough to test the on paper theory. Real world conditions though suggest digital is not perfect and, in fact, can never be "perfect". Nor is analog perfect. What's very much not perfect is the conversion process which takes an analog waveform and converts it to a digital set of data points and then the digital process which returns the data to a usable analog signal.
Sample the same analog "write" signal five times and you'll find five different results of the A to D conversion. Sample five D to A conversions and you'll find five different "read" versions of the same data. Read/write errors, error correction, buffers, filters, aliasing, phase shifts, etc all place their stamp on "digital".
One aspect of digital which has always bothered me is the focus on one single piece of the digital pie. You cannot divorce the storage media from the write/read processing system. In general, I'd agree with the idea you typically get what you pay for, both in equipment and supporting devices. Paying more typically gains you tighter control over the processes which create the device. Fewer errors and more consistent performance over time are to gain.
However, any one device (a SD card) is simply a part of a system and it is the performance of the whole which is of concern to the end user. Since on paper specs are often misleading and incomplete, relying on the system's designer to suggest which individual components are best for their system is about the only way to begin. Canon suggests you use cards they have tested and approved for their cameras. Buy those cards and you'll likely have the best system performance from your camera. Buy something other than those cards and you have placed your money down and you've said you're willing to take your chances.
The idea "a file is a file" is not quite the truth either. As I have said in other such threads, a digital file is similar to a CD sitting on a shelf. What do you get from a CD sitting on a shelf? Nothing. It isn't until you place the CD into a processing system that you have anything tangible to speak of. For example, until Fuji began to produce cameras which didn't rely on a "conventional" sensor construction, the typical digital image file was constructed and deconstructed using an aliasing filter - a low pass filter - through which the data had to pass. Filters are known to cause phase shifts which in turn cause errors in the implementation of the data. Yet filters are also used to correct errors within the digital processing system itself. It's a classic Catch 22 when it comes to digital systems. Either you use a filter to correct the errors inherent in the system or you forgo the filter and allow those errors to pass unchecked to the successive circuits where those errors might even be compounded.
The debate over whether aliasing artifacts are more bothersome than the effects of the anti-aliasing filter will continue since many digital adherents believe digital was created as the perfect storage system and, therefore, what digital is on paper must be what digital is to the human perception systems. Yet the results of digital 1 and 0 data processed with the filter and without the filter yield quite different results;
Non-low-pass filters explained Goodbye to anti-aliasing TechRadar
I would think the data as interpreted by such diverse systems would lead us to see that a file is not just "a file". It is the processing of the file by a system - both in read and write functions - which makes a significant difference in the end result. For the purposes of this thread, staying with the designer/manufacturer's suggested parts of that system is your best advice unless you have the actual test gear and knowledge to say otherwise IMO.
If you use a Canon system, buy the SD cards Canon has tested and approved. Buying a "faster" card simply means the system can buffer the data at a faster rate of speed. How fast do you require your camera to process data? If you are the rather typical photographer who shoots, reviews and then shoots again, you do not need a fast buffering action. If, however, you shoot in continuous frames and that buffering speed is important to your results, then spend the money for the faster card. For most of us, "fast" just isn't a requirement.
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