Quote Originally Posted by Tannin View Post
.... With photographic gear, I'm perfectly happy paying a first-class manufacturer with excellent quality control to get it right the first time. ....
In terms of allowances for the 0.0001 mm discrepancies require to allow easy fitment .. this is nigh on impossible. If the disparate devices are to be easy to fit and need to account for wear over time, built in allowances will always be an issue.
In terms of build quality .. the sky then needs to be the only limit as to what it's going to cost(to build) and obviously sell .. think Zeiss/Lieca etc.
Actually think of it as the difference between NASA putting people into space with equipment they build where tolerances need to be spot on .. or if they got Yongnuo to build the this NASA hyper-titanium space pod that connected too the space drive to get those folks into space.

Nasa has the money to spend billions .. Yongnuo will find ways to cut costs to make money on the project.

Disregarding mirrorless systems, DLSRs have to focus using the additional focus module. If that is out by an estimated 0.001mm to where it's supposed to be, you get misfocus on a lens.

It's common knowledge that many cameras focus slightly differently due to these allowed tolerances .. add the allowable tolerance between camera and lens, and the tolerance numbers add up quickly.

You can see that adding one tolerance value to another is leading to possible focus issues somewhere down the line.
Spot on, ridgy didge, true blue manufacturing can only do so much .. but some of it HAS to be there due to the modular nature of the systems we prefer..
Take mirrorless and the entire premise is eliminated(PDAF on sensor!)

But, we haven't yet taken into account the possibility that over time gear gets a knock here and a whack there .. and those knocks all add up to move bits out of whack.
Bodies may have 0.0005mm of focus module misalignment at some point in the years ahead .. lenses will have 0.00001mm of misaligned lens elements over time too.

if you don't follow LensRental's ongoing blog I suggest you check it out.
Roger is a major fan of Sony(mostly) and Canon(recently).
Canon have been doing good things recently re lens realignment systems, making it easier for non Canon experts to realign lenses to better than new performance.
Sony has many plastic parts contained within, but on the whole their lens adjustment systems are faves of his, being simple to work on.
Nikon just make things sturdy but true to Nikon style .. hard to work on for non Nikon service folk.

So my thinking is more along the lines .. if I knock my large Sigma .. and it now focuses a little out of whack .. can I tinker to make it not out of whack. If not, then do I have to take it to the service centre. .. etc.

For a bit more clarity: my trusty little most hevily used Sigma 10-20 lens has taken it's fair share of knocks. Being an UWA it's not obvious. But for sure a lens realignment is necessary as it's out of whack .. tilted lens, decentering or whatever it is .. it's only when I try a pano and find that one side is crystal clear, but the other side(of the image) is blurred like an 85/1.2's bokeh! .. and this is all at infinity.
So the poor little Sigma needs TLC, or is that SLA
The 12-24 took over as UWA of choice tho and I haven't even touched the 10-20 other than moving it once to dust of the shelf it sits on.
But I'm going to do it one day .. not for the sake of usage but for the sake of TLC

I'm still a bit sceptical of IS elements they move, do they move properly all the time? is it going to park properly every time. Do I need to worry about it .. etc.

I'm thinking that your concern about Tamron and Sigma may no longer be valid. Maybe many moons ago when they may have made less durable looking products.
But the 24-70 Tammy is quite solid... Plastic! but still quite solid. I used to worry about some things being plastic, but when you see what parts in trucks ar emade of engineered plastics it helps you sleep at night.
Kev will hopefully chime in to back that statement up .. I remember the 70-200USM lens felt metal like. I'm sure it's plastic but felt very strong.
With Sigma Art and Sport products think all metal .. cold hard metal. To me they feel no more solid that Tamrons plastics.
Personally in varied heat I prefer well engineered plastics .. for the thermal transfer properties.
Sigma 150-600 Sport is one huge ##### of a lens. All metal rock solid build.
I also have Tamrons really old all cast iron 300/2.8 lens to(still). Feels more solid(to me) than Nikon's old bluestone lumps of 300/2.8 tho, I cam close to getting an old Ais version.
Sigma 150-600 to me .. feels more solid than both.

Nikons 105VR OTOH feels cheaply made., Focus ring is simply crap. No fluidity, lens hood is worse than Chinese made tissue products for the same purpose. How Nikon got away with that lens hood is a mystery. Doesn't sit at all on my 105VR now.

In terms of lens-body tolerance, I've yet to find any lens with more slack than the all metal solid as a fort Nikon 50/1.2 lens. It mounts well and feels tight in terms of horiszontal/vertical movement, but it has way too much rotational slack for al all metal lens.
No other lenses I have show this much play in the mounting lugs.

sorry for the long reply, but just some of my observations over time.