Its not a holy grail.
But because older users since film want back the same FOV from their old lenses, they have wailed about it for a long time and this has passed on into a sort of self created legend.
With all formats, there are advantages/disadvantages.
I took this on Friday with a Soligor 17/4.
This lens was quite pointless to use on APS-C, being not too wide being about the FOV of a kit 18-55 but the size of a Sigma 10-20 and the weight of 2 hand grenades.
But on FF, its totally transformed to wide and worth the trouble.
The same can be said of other wides like 15 and 20mms (and maybe 24mm)
But, then, my friend who shot with me had a K01+10-20 and he shot this :
Vesak Dawn | Flickr - Photo Sharing!
Pano stitch of course, but nice shot (and better than mine, imo).
Basically, he got the job done on aps-c and a 'non-true FL' for all it was worth.
So to me, landscapes, no big deal, aps-c with the modern UWA lenses, do the job fine.
This sort of thing (studio type portraits), its a matter of trade offs too.
Often stopped down for more DOF, rather than less.
And on a strobist setup (ie. less powerful), aps-c stops down less for the same DOF, meaning I use a lower power setting on the flash (eg. 1/4; 1/2) and get better recycle times.
The advantage to FF for the same shot would be a shorter working distance for the same FOV and less DOF if needed.
Low light, depends and user standards too.
I don't have too high a requirement.
Shot this in a very dim night market in Indonesia with the K5+FA35.
For this who are not familiar with less developed countries, the street lamps are as good as none and the market either has its own weak light or an oil lamp or none.
For me, don't think I need much better ISO performance since I don't plan to shoot a documentary about mammal mating habits in the dark
DOF (less of)
Now, here's were I think FF does have an advantage.
Especially so as the working distance is also shorter for the same FOV as the same lens on aps-c.
The humble 50mm gives a nice wide FOV while giving less DOF and can often convey a sense of subject isolation that is harder to achieve on aps-c
With the A50/1.7 at f2 on FF (at the working distance we'd associate with a 31/1.8)
This (wider FOV and less DOF) applied on lenses like the FA ltds and many of the nice small Pentax lenses.... I think it will be SUPER.
Then there are shallow DOF shots too with short tele lenses, but nearer working distances that we are used to on aps-c
S.Tak 85/1.9 on FF (at about the working distance we'd associate with the 50mm on aps-c)
though I may comment that since this was a candid, I might have preferred the longer working distance.
S.Tak 135/2.5 on FF (standing the distance that I would have using a 85mm)
But not all is black and white cause I've shot rather 'like' (not not 1:1 similar) stuff too on aps-c, just maybe a longer working distance (usually more problematic) and maybe more expensive or longer lens. (and sometimes in portrait orientation)
31ltd
M85/2
Revuenon 55/1.2
But often on a tour, I find that I want to retain environmental context and FF/APS-C matters not that much.
I doubt the following few shots would have benefited with even less DOF. (my back and legs certainly benefited from it being Pentax aps-c though)
this one, certainly the smaller than aps-c sensor helped
Pentax Q+100mm macro