Dumb Question, I'm sure...

[MichaelHenson]

Just picked up my first full frame! I snagged a D750 and have some questions that I haven't been able to track down over the past week of searching.

How can I tell what lenses will work without switching into DX mode?

From what I can gather, I should be able to turn off the "Auto DX" mode in the camera, put a lens on and shoot stopped down and notice vignetting if the lens is inappropriate for full frame. Is this correct?

Obviously, any lenses from Nikon with DX on them will only work in DX mode or with vignetting...I'm wanting to ensure that I don't go out and shoot a session or something only to return and see that everything has been captured in DX at a max of like 10-12 MP.

I literally just picked up my camera from UPS, put on my Tamron LD DI SP 70-200/2.8 (IF) Macro, turned off Auto DX mode, and stopped all the way down to f32 (I think?), took some photos and noticed no vignetting. This seems to tell me that I can use this lens utilizing the full frame of the camera and @ the usual 24MP, correct?

Sorry if I'm missing something simple, just haven't been able to find a definitive answer that satisfies me...

 

[Designer]

From what I can gather, I should be able to turn off the "Auto DX" mode in the camera, put a lens on and shoot stopped down and notice vignetting if the lens is inappropriate for full frame. Is this correct?

No, the camera is much smarter than that. In DX or Auto DX, what you see is an image that is captured on only the middle (DX portion) of the sensor. You would see no vignetting unless you turn off auto DX and mount a DX lens.

 

[MichaelHenson]

From what I can gather, I should be able to turn off the "Auto DX" mode in the camera, put a lens on and shoot stopped down and notice vignetting if the lens is inappropriate for full frame. Is this correct?

No, the camera is much smarter than that. In DX or Auto DX, what you see is an image that is captured on only the middle (DX portion) of the sensor. You would see no vignetting unless you turn off auto DX and mount a DX lens.

I turned off "Auto DX" in the menu...If the lens isn't compatible, I should see vignetting at that point, correct?

 

[Designer]

I turned off "Auto DX" in the menu...If the lens isn't compatible, I should see vignetting at that point, correct?

I don't know, but I think it will be explained in the user's manual.

 

[MichaelHenson]

Agreed. Haven't had the chance to dig into it yet. I was hoping someone had a "rule of thumb" regarding lenses and FF or experience with how the camera would react with a DX lens attached.

 

[PaulWog]

Agreed. Haven't had the chance to dig into it yet. I was hoping someone had a "rule of thumb" regarding lenses and FF or experience with how the camera would react with a DX lens attached.

If you have auto DX mode on, the setup will be more or less like a DX camera with a DX lens. If you choose to shoot FX with a DX lens, then performance will be based on the particular lens. The 35mm 1.8G DX lens will have some vignetting, but it will perform very close to a full frame lens. The Sigma 10-20 f4-5.6 will have lots of vignetting, and at every focal length will need to be cropped due to completely black borders.

Here's your general rule of thumb:
- If you choose to shoot in DX mode, you will end up with a shot that has less megapixels. It will look like it was shot with a DX camera. You will achieve the same depth of field and field of view as a DX camera shooting with the lens. For example, if you shoot at 50mm and f4, then you will have a similar field of view and depth of field to 75mm and f6 on a full frame camera. You will also get a similar net ISO performance to a DX camera, due to the crop.
- If you choose to shoot in FX mode, you may need to crop in to what you would've gotten in DX mode anyways. You may be able to squeeze just a tiny bit more out of the lens and get a slightly wider field of view. However much you need to crop though, will reduce your depth of field, as well as your apparent ISO performance. Essentially, you will end up with something very similar to if you shot in DX mode. Do note that you won't be able to shoot with automatic exposure for the entire frame (you'll have to center-weight enough that you do not have automatic exposure account for the black borders).

 

[MichaelHenson]

So, since I've taken the Auto DX off, I should be in FF mode. If I then shoot with a lens and don't have vignetting, I'm good to go and will therefore be using the full sensor. Correct?

 

[manaheim]

You could just look the lens up and see if it is DX or FX.

 

[PaulWog]

So, since I've taken the Auto DX off, I should be in FF mode. If I then shoot with a lens and don't have vignetting, I'm good to go and will therefore be using the full sensor. Correct?

If you take auto DX off, it should shoot in full frame mode. I remember having it automatically switch back on me once or twice though (without knowing), something to do with switching to video mode or something. I can't remember, I don't have any DX lenses any longer.

I highly doubt your 18-55 will work in FX mode, nor your 55-200.

Isn't your 70-200 Tamron a full frame lens? As well as your 70-300, and 50mm 1.8. What lenses are you trying to shoot in full frame mode that you think are crop?

 

[KmH]

Tamron Di = Nikon FX
Tamron Di II = Nikon DX

 

[MichaelHenson]

Welp, that clears that up! Thanks @KmH!

 

[wfooshee]

Vignetting also changes with focal length with zooms. My ancient kit 18-55 fills a full frame image space when zoomed past 24 mm focal length. Since I don't actually have an FX wide-angle lens, I can use that to get the traditional 24, 28, and 35mm views. Just not at really nice large apertures!

 

[Derrel]

So, since I've taken the Auto DX off, I should be in FF mode. If I then shoot with a lens and don't have vignetting, I'm good to go and will therefore be using the full sensor. Correct?

Yes. Go by what you see on the rear LCD. "Some" DX-specified lenses will have terrible vignetting; others will have moderate vignetting; some DX lenses will have unacceptable vignetting at the wider-angle range, but at the mid- to longer rangers, may very well fill the entire 43-mm diameter FX-sized image circle. Some DX lenses will fill the 5:4 aspect ratio that some of the 1-digit Nikon bodies offer in-camera.

Not all lenses are created the same. Ken Rockwell and Thom Hogan both offer lens reviews where lens performance/coverage is discussed as it pertains to using a DX-optimized lens on an FX sensor Nikon.

 

[MichaelHenson]

Cool. Thanks, Derrel!