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this is not actually correct!Originally Posted by patrickv
The focal length of the lens has a meaning and it's exact in it's meaning. It's a measure of it's magnification onto the sensor plane(whether that sensor is film or digital or paper or whatever else can be used).
Basically it's ability to record an image of a particular size onto the sensing material.
it's way too complicated to describe examples of how this actually works and the technical benefits of choosing differing focal lengths over others, but you are partly correct in that the size format of the sensing material plays a factor in the lenses ability to record it's image as well.
But a 50mm lens is a 50mm lens, irrespective of the format used, if you want a lens to magnify a subject to a particular size.
I'm sure you meant to say the 30mm Sigma lens and not the 50mm version .. 50mm version is also a nice lens to have..... For Canon it's 1.6x and not 1.5x so the closest approximation is more 30mm. Canon don't make a 30mm prime lens, they only make a 35 f/2 and a 35 f/1.4L so to have a "normal perspective" on Canon crop, I would rather recommend the Sigma 50mm F1.4 EX DC HSM lens. ....
But lets not get bogged down in semantic discussions of technical reasoning as to why a 50mm lens is handy or vital to have. The OP's question didn't seem to bother about technical discussions as to why a 50mm lens was a must have.. and in reality there are none for it.
I don't use either of my 50mm lenses for the 'natural human eye perspective' they give me.
In fact I find it quite boring to be honest.
I like the individual lenses ability to render the scene in a particular manner .. whether that with subtle contrast and or colour nuances, or bokeh or just for the fast aperture they allow(at a reasonable price!).
I acquire my lenses due to what I believe will give me a particular look that it has proven to achieve, either via samples I've stumbled across from others, or for myself via testing.
My first 50mm was the Nikon 50/1.2 and I got it simply for the ability to render images in a particular way for a given price.
had price been no object, I can unequivocally state that I'd have got the 58mm f/1.2 instead.. but that would have cost me about 6x the price of the 50mm.(58 mm is by far the superior lens, in many respects).
Later on, I liked the image samples I saw from the Sigma 50mm, and walked into a shop and wanted to try one out for myself.
The shop also had the Nikon 50/1.4 AF-S as well in stock and a slightly cheaper price(back then) .. as the Sigma was more rare!!??
I tried them both and immediately I thought the Sigma lens produced nicer bokeh on the images I captured in the shop with both lenses. So I got the Sigma and not the Nikon version.
I wanted another 50mm fast lens that had an AF-S autofocusing ability as well.
I could have chosen the AF-D(screw driven version) as well, but that lens never entered into the equation at all due to it's older focusing system design.
Why did I get another 50mm lens? .. especially as I don't particularly favour the perspective it gives me!! ... simply because those lenses gave nice looking images that I now have the ability to capture.
( I suppose the onus is on me to capture those 'nice looking images' ... and hopefully one day I will!)
I suppose the terminology used may also be partly to blame for the confusing messages it implies:
'A must have' taken literally could be interpreted as expressing an idea or notion that can't be lived without for some reason.
If the term is taken with a different context, say as a colloquialism .. the way you can transfer this expression to another gizmo, gadget or idea .. eg: an iPhone(or more accurately a smart phone).
I resisted for ages getting a smart phone .. all I wanted a phone for was to make PHONE calls!! (kind'a makes sense really as that's the purpose of 'em).
But my PDA eventually died(or is playing up to a point where it's unusable) and they're no longer being made(for good reason).
So I ummed and ahhed and got myself an Android phone.
Now I can do my PDA tasks, log keeping, spreadsheet editing, and other personal files keeping on my phone with critical data backed up to the PC and so forth.
After years of resisting, it's now become a 'must have' for me as it's replaced the PDA that I used to store stuff on.
So, just like a smart phone is a 'must have' ... so is a 50mm lens in photography terms.
That is; it's not a vital instrument for every day survival ... but it's so well priced, that you'd be mad not to have one.
Even if it's only for occasional use, as mine get used.
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