Really helpful post, YuengLinger...I wasn't going to be the first to bring up the Sigma 180mm, but since somebody did...
On my R5, the IBIS and IS are working together surprising well. I say surprisingly because the 180mm is an older lens and it is very heavy and long. But it works about as well as does my ef 100mm f/2.8L IS, when I take into account the longer focal length. In other words, I up the shutter speed by about 2/3 of a stop and seem to get the roughly same results. I do think that the IS/IBIS must be working better for me, as there are so many more pixels on the R5, and it stays sharp in my typical handheld range of 1/150th to 1/640th. My hands are not super steady, so I've gone with higher shutter speeds for years now.
One thing to note, though, is that the Sigma 180mm does have very good IS all on its own. Just a little noisy compared to the latest and greatest.
That said, I shoot with it primarily on a tripod. My little boy asked why I use such a long lens to take pictures of bugs, and I explained that I can be a little further back. Then last week he got stung--really stung--mid-thigh by a wasp as he was playing with some flower buds on a shrub. When he saw me yesterday with the 180mm he said, "That's for bees and wasps, right, Dad?"
It was my impression, when I bought the 180mm, that it was a step above other Sigma lenses at the time, both in terms of optics and build quality. About a year later I bought the Sigma 35mm Art when it came out, and sensed a lot of similarities. I never tried a Sigma 150mm with, but the only person I know who had one was frequently complaining about his copy's IQ.
I was sad to see the Sigma 180mm go out of production. It also takes wonderful closeup portraits! (But it is too heavy for casual use.)
I'd love to see both Sigma and Canon competing with some longer and lighter macros.
The attached was taken handheld some years back with a 5DIII at f/4, 1/640th, ISO 640. Same little boy who got stung last week!
Also attached is another shot, but this on a tripod. Just for fun. 5DIII, f/8, 1/15th, ISO 320. Focus is on Batman.
And, btw, nodding to the topic, I never noticed a focus-shift issue with this longer focal-length macro.
I appreciate you taking the time to write, and share your interesting experiences with the Sigma 180mm macro. I have also heard a number of others saying how much they like that lens.
When that lens first came out, I was also looking at that as a possibility (instead of the Canon 100mm macro) - but I decided to go with the Canon, because it was my first macro, and I felt maybe less specialist than the Sigma.
Great photos that you attached, both have high image quality (sharpness, contrast, great colour), etc. Thanks for sharing!