FX lenses on DX bodies

neilos100

neilos100

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Neil
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This may have been asked before and apologies if it has......cant find it searching though.
Would i be right in saying that (generally) you will get better IQ from using an FX or full frame lens on a crop body? My reasoning is twofold;

1. You will only be using the center part of the lens elements and will therefore not be subject to as much edge distortion and such like. I read somewhere that the middle of the element is the 'sweet-spot' and wondered if this were true.

2. Secondly, the quality of the lenses themselves seem to be better. Materials , mount, (elements??) Obviously, this is reflected in the price.

Now its the first reason that particularly interests me, as with anything you get what you pay for so the second reason above seems to be pretty obvious.

So is it worth using FX on a DX body or are you just wasting money?

Any thoughts??

Neil
 
I wouldn't say you're wasting money, but it depends on your motives and requirements.

I use the 70-200 f/2.8 VR, which is an FX lens, which some claim shows edge softness and vignetting on an FX body, but I experience none of this on the D100, D200 or D300s bodies (as I shouldn't). I've yet to try shooting it on my old N90s 35mm body, but one day I'll put a couple of rolls through it and see what happens.

So, yes, it will help get rid of edge issues that may normally show in an FX body.

I don't think #2 is necessarily a feature of FX glass, at least the fact that it's FX is not the primary reason. #2 is a feature of pro glass, but pros generally demand full frame lenses.

All of my lenses are full frame except for my Sigma 10-20mm f/4-5.6, and I don't regret the purchases for a minute. Given what a D2X costs second hand now, by the time the D4 has reached its second iteration, the likes of the D700 and D3 will have hit ridiculously low prices in the used market and many more people will have the chance to go full frame in a year or two.

Bodies come and go, but lenses can last for decades with proper care. It's definitely worth the extra money (to me anyway) to get a lens that's designed to go the distance, and "future proof" my kit to cope with whatever body I may purchase in the future.
 
...but on the contrary, DX lenses have a higher resolution (in theory anyway) because the image circle is smaller, so are better suited to small sensor high megapixel cameras, where the camera might out resolve even a very good FX lens.
 
huh?
 
It's been said loads on here before and I never used to believe it myself - but what part of my post exactly didn't you understand?
 
No, not a waste of money as you get what you pay for, ie pro quality. Then, there are some lenses, eg macro, that don't come in DX format.

That said, there are some DX stars. I only know about Nikon, so I'll mention the 35 mm f/1.8, the 10.5 mm f/2.8 and the versatile 18 mm - 200 mm VR all of which, I think, deserve a place in your camera bag.
 
trencheel303 said:
but what part of my post exactly didn't you understand?
Click to expand...
The theory behind it. You gave none.

A FX lens at 200mm and a DX lens at 200mm are both going to project the exact same thing onto a DX sensor.
 
The image circle for DX lenses is smaller than FX lenses, so the resolution of the lens is 'compressed' into the smaller image circle so that it fits the sensor it was designed for. None (or very little) of the lens is wasted - it's a more efficient use of the materials.

If you have an FX lens designed to outresolve the full frame sensor up to, say, 15MP, then placing it on a 15MP cropped sensor will cause it to be outresolved quite substantially, as it's 15megapixels but on a smaller format, plus, the outside of the lens is wasted by the crop factor. You're using 15MP, but ONLY on a centre crop of the lens - not the whole lens. This gives the lens a lot less effective resolution as you are only using some of it - but with still the same MP amount.

It's why you see folk constantly posting threads here about their 7D and the need to upgrade their glass - a lot of cheaper glass just can't cut it for high resolution small sensor because it gets outresolved by the sensor. I've even seen the 17-55 EF-S recommended over the 17-40 for a crop sensor, again because of the resolution - 17-40 is at the point of being out-done by modern sensors, particularly high MP cropped sensors.
 
But the glass itself inside a DX lens is physically smaller - that was their whole selling point when Nikon started making DX lenses "they're lighter, smaller, etc".

A DX lens is basically the same as an FX lens, except that they've shaved down the size of the elements so that it doesn't project as large an image as its FX equivalent.

Why you see folk constantly posting threads about their 7D and needing to upgrade their glass is nothing to do with FX vs. DX. It's to do with consumer crap vs. high end pro glass (regardless of their FX/DX format).

You don't think the fact that the 17-55 f/2.8 EF-S costs twice as much as the 17-40mm f/4 has anything to do with it? :)
 
Kaouthia said:
A DX lens is basically the same as an FX lens, except that they've shaved down the size of the elements so that it doesn't project as large an image as its FX equivalent.
Click to expand...

In which case I apologise as I have been misinformed. It sounded convincing so I believed it... but until then I had always asserted what you are now saying.


You don't think the fact that the 17-55 f/2.8 EF-S costs twice as much as the 17-40mm f/4 has anything to do with it? :)
Click to expand...

Twice as much is news to me... as far as I know (just did a quick check too) it costs around 250 more. But yes, I see your point.
 
The quick search I did showed the 17-55 at around £900, and the 14-40 at around £450-500, but I shoot "the other brand" so didn't bother to price check all that much. ;)
 
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