Some habits are hard to break.
When MFT format was first introduced, Olympus generally produced lenses that made sense to full frame users (35, 50, 90mm equivalents etc), well up until they produced the slightly odd* 75mm (150mm equiv). Personally, I wished they had made a 50mm f1.8 and 100mm f2, the classic 100 and 200mm’s, but the performance of this lens was just too good to ignore. At the time it was better on paper and in results at least equal to my favourite Canon lens, the 135 f2L.
18mm and wider were once considered the “weird” wides, true perspective benders. These days, zooms going to 16mm are common, but these were once special application lenses and as rare as they were expensive.
20mm gets you past 90 degrees and was once seen as the extreme end, almost too much for many.
24mm is just short of 90 degres coverage, and was a little too wide for a range finder camera (Leica M series etc) to take without a separate view finder. Ths was the landscape shooters standard.
28mm is a nice even 75 degrees, but is actually the limit of a non electronic, built-in range finder camera’s focussing coverage.
35mm makes a decent semi wide standard, especially if you accept the 50mm as standard.
40 (42mm) is the mathematical standard standard for 35mm, being the actual measured diagonal of the 35mm film frame and is visually the most realistic, some say boring of focal lengths. This one is the longest lens that does not compress in any way. If you like the 40mm as I do, then the 35 and 50 can be skipped.
50-55mm the “nifty” 50 or as I sometimes call it the 50-50, because it has no real optical opinion, but leans ever so slightly towards tighter-more compressed. A hard lens to master, but powerful if you do.
58-60mm is the other side of the compressed-not compressed threshold, genuinely stepping into the “portrait” range. Once popular, it was also a common Nikon micro lens.
75-90 are the work horse portrait lenses, all pretty similar depending on your working range, waht was avaialble and tastes.
100-105mm was the classic macro lens length.
135 was the longest a non modified length a range finder camera could take.
180-200, basically the same depending on your brand of choice (Nikon liked 105 and 180, others went 100 and 200).
300 and longer were a matter of application and availability, with the 300 f2.8 being the holy grail of most.
There were exceptions, but generally, these were the standard “steps” available.
Panasonic and Sigma on the other hand, started to choose focal lenths that made more sense to them and the format, with no allegiance paid to past standards. The 15 (30mm), 20 (40mm), 30 (60mm) and 60 (120mm) all made plenty of sense to an outsider, but possibly confused ex-full frame converts. They are nice even numbers, but they have another, more immediate effect. They actually make more sense in a kit.
One of the first images taken with the 15mm. It felt “roomier” than the 17, while still easily avoiding distortion.
For me, a 30mm equiv is the perfect standard wide. I find 35mm very comfortable, but feel it needs a wider partner like a 10-12 (20-24mm), which still leaves room for something wider still and some indecision, where the 30mm is just wide enough to be matched to a wider lens (the 9mm) without the need for a filler and is slightly more versatile in this space. The 30mm effectively covers two focal lengths, 28 and 35mm which for me seems to be a decision point.
The 20 (40mm) is the “true standard”, or at least a 42mm equiv is and was once a common focal length. I had the first version of this lens, sold it and never replaced it, because the Oly 25mm I have is actually closer to a 22-23mm (45mm).
The 30 Sigma (60mm) is also a better standard portrait lens than the official standard 25 (50mm), getting completely away from any hint of wide distortion, but less compressed and distancing than a 75-90mm equivalent. I find my 25 (50mm) lens is better for a two person shot, but a 15-17 (30-34mm) is better again for groups. Again, like the 15 (30mm), this gives me better coverage and a more confident solution. I can jump from the 15 to the 30 then all the way up to the 75mm rather than run the 12, 17, 25, 45 and 75.
Proper portrait performance from the Sigma 30mm. Very slight compression, good DOF drop-off and a natural feel, but not so tight it forces the shooter to disengage with the subject. As a “one lens” option, I prefer the 25mm Oly, but in tandem with a wide lens, the 30mm makes more sense.
The rule with a primes kit is to skip at least every other focal length. You are not trying to cover all focal lengths, just represent each type of perspective. Think less place holders and more super wide, gentle wide, short compressed and long compressed perspectives as story telling tools. With these new lenses and their re-imagined focal lengths, it is possible to fudge 2 into the space of 6 lenses. Feet and angles do the rest.
9 (super wide), 15 (standard wide), 30 (standard portrait), 75 (long) (18, 30, 60, 150 equiv). Is this the perfect primes kit for my uses? In reality, I will use a tele zoom, because “zooming with your feet” is less practical with long lenses, but in lower light, the 75mm is a life saver.
The only slight issue is the AF speed of the Sigma, but for sport I still have the 25, 45, 75 combo. For general use, the Sigma is at least 90% as fast as the better Oly lenses and basically the same performance as the Oly lenses on the G9.
I have some great zooms, but it seems now, I also have a workable primes kit.
*I say slightly odd, because the full frame equivalent was the more random seeming 135mm. This was the longest lens early range finder style cameras could practically take without special focussing attachments (28mm was the widest), so it was a matter of necessity, not some divine plan.