Lens and body "fit"

[jinky]

I`ve said a few times I have been trialling a Nikon 85mm 1.8 lens that a Leeds flickr mate has offered me cheaper than the going rate. I have had it to look at for a few weeks but done so little photography due to weather / illness that only today did I test it against my 70-200 Sigma F2.8 to make comparison. What I found amazed me and I nearly put this in the what bemused you today section. Despite all assumptions I found:
Wide open - images at 100% crop were very similar in terms of sharpness though I preferred the colour on the Sigma. That said I thought fine 1.8 is the way to go

At F2 the Nikon was so soft I took another 3 shots to test my technique and each was the same 
At comparable f2.8, 4, 5.6 and 8 my Sigma was sharper on every image looking at the 100% crop and using Nikon X2 for viewing to check that the focus point had been the same.

This amazed me and persuaded me to leave it for now as  have other wants competing for my limited funds. I would have bet money on the Nikon being the sharper but must conclude, as read elsewhere, that on this occasion the Siggy is the better fit with the camera body I have. With a D80 I am unable to adjust for different lenses. Does it surprise you?

[Hinfrance]

Not really jinky.

All of the manufacturers have made both excellent lenses and some real turkeys. I was offered a Pentax FA series short zoom lens the other day and checked it out on the Pentax forums - turns out this one was a real dog. I tried it briefly and the reviews were true. Given the premium price that the camera manufacturers charge for their wares one would hope they were always at the top of the game, but alas it ain't necessarily so . .

[jinky]

Daft thing is the guy offering me this finds it the sharpest lens he has. I`ve kept hold of it a few more days to do some shooting outside when there is decent light. I did shoot some nice stuff with it at Whitby when I first borrowed it and commented how sharp it was - have to look at them again at 100% crop

[Hinfrance]

Were the first shots you took with it stopped down a couple of clicks? It could be that it is really sharp then. Many very good lenses have a tendency towards softness wide open that more than disappears a couple of stops in.

I'm sure you'll do the right thing 

[Simple]

I remember selling a dedicated Canon Portrait lens once. It was very soft, and the softness was even adjustable. (Never tested it because I use Nikon) (sold it to a person I knew from very early DCM days and is now a Pro)
The 85mm 1.8 is a dedicated Portrait lens, so I can imagine that ultimate sharpness is not on the high priority list. (Personally I would never use a soft lens because I like portraits in the style of Abers, nice, sharp B/W)

So that could be the reason, or I am talking nonsense and you still have a filter on the front of the lens??

[chris@seary.com]

Wide open - images at 100% crop were very similar in terms of sharpness though I preferred the colour on the Sigma. That said I thought fine 1.8 is the way to go

At F2 the Nikon was so soft I took another 3 shots to test my technique and each was the same 
At comparable f2.8, 4, 5.6 and 8 my Sigma was sharper on every image looking at the 100% crop and using Nikon X2 for viewing to check that the focus point had been the same.

You should be comparing 2.8 on the Nikon to 2.8 on the Sigma. You'll find the Nikon very sharp at this aperture. The extra stop and a bit is what you're gaining, rather than sharpness, especially with a portrait lens.

Also remember that, at or around full aperture, the depth of field on the 85mm 1.8 is pretty much nil, so you'll have to be really careful how you position your test chart. You did use a test chart, didn't you? If not, then a fair comparison is very subjective and not accurate.