DX on FX

thecageylumen · Jan 31, 2014

Hello,

I feel this isn't exactly an advanced question but is still technically beyond the basics so if im outside my category I apologize. Anyway. A couple questions. My first is if i were to take a dx lens and put it on an fx format body, while the viewing area would most definitely change, would the noise in lower light situations inherent to dx bodies return? Because you're now only utilizing a smaller area of your sensor does the image quality deteriorate as well, or is it just a matter of cropping. Does the fx body retain it's image quality.

Secondly why do zoom lenses with lower differences in focal range tend to be so much bigger? Why is a 70-200 so much bigger (and costlier for that matter) than a 55-300.

Thirdly, while I've got you here, thoughts on a good portrait lens 500 or lower? The nikon 85 1.8 seems like an obvious choice but the tamron 90mm macro seems pretty attractive as well. Both for the price and the macro capability. And then there's sigma altogether. Freaking. Choices.

jaomul · Jan 31, 2014

Noise is product of cameras sensor ability at selected setting. Using a dx Lens on fx will give you same noise at same settings.

70-200 lenses that are f2.8 are bigger as they have more mechanics in them to enable a large aperture at all focal lengths.

If you have an fx camera the 85 is better as a portrait Lens as it has a bigger aperture. However the macro Lens would be quite a good portrait Lens with the benefit of macro

480sparky · Jan 31, 2014

FX bodies will accept DX lenses with ease. They can be set three ways: Automatically detect a DX lens and shoot in DX mode, be set to DX mode regardless of lens attached, and set to FX mode regardless of lens attached.

Noise is not a function of the lens, so low-light capability is determined by the body.

The 70-200 class of lens tends to be faster (f/2.8 and f/4) than the 55-300 (f/4.5). Faster glass means larger aperture, and that required a larger diameter barrel. A wider focal range also required the glas to physically move further in the barrel.

Derrel · Jan 31, 2014

thecageylumen said:
SNIP>
Thirdly, while I've got you here, thoughts on a good portrait lens 500 or lower? The nikon 85 1.8 seems like an obvious choice but the tamron 90mm macro seems pretty attractive as well. Both for the price and the macro capability. And then there's sigma altogether. Freaking. Choices.

The Nikon 85mm 1.8 G is a VERY,very sharp, good-performing lens, and is affordable. I own one, and it is a very amazing lens for the price. I own the Tamron 90mm AF-SP, the model one version back. It's a good lens, but it is a MACRO lens, and the autofocus and the manual focusing action on this lens is NOT QUITE up to snuff at beyond about 1 meter; like most macros, the AF and manual focusing is HAIR-trigger at portrait ands outdoor distances, and can lead to the focus being MISSED many times, often by 10 inches to 2 feet at say, 30 feet. It can ruin shots when a regular, normal "field telephoto" design will NAIL the focus, because it is optimized for focusing at longer ranges like 6 feet to Infinity.

Where so,so many macro lenses fall flat is this side of infinity, but at distances of over 10 meters...it is in that range that it's VERY easy for the focus to be off enough to ruin shots. AF system work on a "close-enough" type basis...beyond 10 meters and out to say 1/4 mile, the focusing system will often decide that it's "good enough". Believe me--a macro lens is NOT a substitute for a field telephoto,like the 85/1.8 G, or for a portrait lens, like the older 85mm f/1.4 AF-D "aka The Cream machine" with its superb bokeh, nor the 105 or 135 DC Nikkors.

Sigma's 85mm 1.4 is a decent lens for portraiture. We have several members here who use that lens.