DX/FX Shoot-Out

[Black Pearl]

There was a (fun) argument on here a while back along the lines of a 50mm on a DX (cropped camera) body being the same as a 75mm on a FX (full frame) body.

Some will argue that if you use a lens on a camera with a smaller sensor then it will be the same as using the equivalent (longer) focal length on the full frame body. Some (me) argued that a 50mm will always be a 50mm and the photographs will aways look like they were taken with a 50mm. 

 

Yes they give the equivalent field of view but they are not the same - not at all - not in the slightest.

One is a moderately wide angle with its own particular set depth of field & foreground/background separation and the other is a standard focal length with its own set of characteristics. 

 

I finally got my D300s (12mp on a DX sensor) with my 35mm lens on the front together with a mate's D3 (12mp on a FX sensor) with his 50mm lens on the front. I know I started arguing about a 50mm/75mm but there are very few 75mm lenses about so I went with what I had.

 

Two shots with exactly the same settings, from the same position, with the same processing of the resulting NEF files. 

 

Both bodies set to 1/40 sec;   f/2.8;   ISO 400

Both files opened in Camera RAW 7.0, all settings synced and the WB manually set so both match perfectly, we did dial in the same manual WB on the cameras so all I did was tweak it slightly. 

 

Nikon D300s + 35mm:

 

Nikon D3 + 50mm:

 

As you can see the way the two lenses render the background is significantly different.

A 35mm lens gives a great separation between the foreground and the background than a 50mm and even though the equivalent field of view is the same they are still different.

 

Another thing to note (interesting but not relevant) is how the D3 with its massive pixels renders shadows far more gently than the D300s - if you look at 100% there is far less noise in the D3 file too.

 

So - A 50mm will always be a 50mm and a 35mm will always be a 35mm.

[ChrisLumix]

I'm not sure I follow this at all. My camera's true focal length at widest angle is around 5mm, but is the 35mm equivalent of 27mm and looks it. A full frame 5mm lens (if it even existed?) would be so fish-eye it would practically be 360º. 

 

So therefore I conclude that all 5mm lenses are NOT the same! 

 

You'll have to explain this to me more, as right now I am still endlessly frustrated by members here  who talk about their 50mm lenses, and I'm sat here going "Yes, but what's that in 35mm terms??". 

[Black Pearl]

But you wouldn't be putting the 5mm on a FF DSLR you would be putting a 27mm on it to compare to your camera with the 5mm - do that and I'll guarantee the images will look vastly different.

 

I didn't put a 50mm on both I put a 35mm on the DX body and a 50mm on a FX body to do a direct field of view comparison - the results are different. I would have got the same if I'd put a 50mm on a DX body and a 75mm on the DX one.

[ChrisLumix]

But you wouldn't be putting the 5mm on a FF DSLR you would be putting a 27mm on it to compare to your camera with the 5mm - do that and I'll guarantee the images will look vastly different.

 

I didn't put a 50mm on both I put a 35mm on the DX body and a 50mm on a FX body to do a direct field of view comparison - the results are different. I would have got the same if I'd put a 50mm on a DX body and a 75mm on the DX one.

 

Ah, so what you're saying is that a 5mm on my tiny sensor, would not produce similar results (i.e. field of view, depth of field etc) to a 27mm on a full sensor, even though they are theoretically equivalent? Now I'm beginning to get it ... but why would that be? 

[NannyFerret]

It looks like the lines are straighter with the 35mm lens.

[Black Pearl]

The Field of View (FOV) would be similar between the two (as they are on the two shots above) but the depth of field and the way the foreground and background are separated would be entirely different. 

Wider lenses tend to exaggerate foregrounds and diminish backgrounds whereas longer lenses tend to compress them. 

So when someone puts a 50mm lens onto a cropped body the FOV becomes the same as the FOV of a 75mm on a FF body buts its characteristics remain unchanged. 

 

I will try and do a comparison between a compact camera with a 5mm (ish) lens equating to the FOV of a 27mm on a FF body and an actual 27mm lens on an actual FF body. Might be a while before I can get the D3 again but I can do it using my D300s and a 18mm lens which will be similar though not as exaggerated. 

[FUJI]

Whoa!

All those numbers and techie talk does me old head in..............Me?

I fit a lens........look through the viewfinder or look at the screen, adjust the camera settings........then, if I like what I see.........I shoot it?

Can't be doing with numbers.

That said.......I have just ordered a Circular Polariser and a set of filter rings for potential landscape work.

FUJI

[Black Pearl]

Actually Fuji you could do this experiment without bludgeoning your noggin with numbers.

 

Get your Panasonic LX compact, your Panasonic G M4/3 camera and your Sony A55. Make sure they are all set to a 3:2 ratio - thats your Sony's native setting, the middle position of the slider on the LX lens barrel and somewhere in the menu of the G.

Pick a subject that won't move that has a detailed background a reasonable distance from it, bung each on your tripod and try to get the width of each shot exactly the same on each camera.

 

What you should end up with is three images that have the same FOV but with wildly different depth of fields and front to back separation due to the three sensor sizes and the three different focal lengths needed.

[ChrisLumix]

So it's mostly a DOF thing then? You would probably expect 5mm on my FZ to have more DOF than a 27mm FF shot? (Though at that level of wideangle it would probably be hard to tell the difference - a better comparison would be the 85mm of my full telephoto against a 485mm - call it 500mm, there's virtually no difference - on a FF camera. Then you would presumably expect to see shallower DOF from the 500mm, I'm guessing.)

[Black Pearl]

Buy me a http://www.wexphotographic.com/buy-nikon-500mm-f4-ed-vr-af-s-nikkor-lens/p1024132 and we'll give it a go 

[ChrisLumix]

Buy me a http://www.wexphotographic.com/buy-nikon-500mm-f4-ed-vr-af-s-nikkor-lens/p1024132 and we'll give it a go 

 

And all for less than £6000 - you're on! (Joke joke, in case any lawyers are given this post to peruse )