Correction for Nikkor AFS G type DX lens confusion?

[Garbz]

My camera is a Nikon D200 which has an APS sized sensor in it. Now the APS sensor being slightly smaller than 35mm requires correction for the scaling of comon lenses. When I put my old 50mm Prime Nikkor AI lens on it is definitely not 50mm through the viewfinder.

So the confusion starts. The AF-S DX G type lense I have here is 18-70mm. Now when I look through the viewfinder and zoom, the point where what I see in the view finder being the same size as what I see in my other eye is ABOVE 50mm.

Now I can't figure out exactly what that means. How do I go about correcting the Nikkor G lenses for APS sensors if I even need to at all?

 

[Artoo]

You have to multiply everything by 1.5... Your 50mm becomes something around 75mm. While that 18-70mm lens you mentioned, being a piece of equipment made especially (DX symbol) for digitals is exactly what it sais it is

Somebody correct me if I'm wrong on anything

 

[Big Mike]

You don't have to do anything. What you see in the viewfinder is what you get. Same as with a film SLR camera.

The confusion is when you compare focal lengths on a digital body to the same focal lengths on a film body.

When I put my old 50mm Prime Nikkor AI lens on it is definitely not 50mm through the viewfinder

Well, yes it is 50mm...just not the 50mm that you are used to from a 35mm film camera. The focal length does not change...but the sensor and viewfinder are only seeing the middle portion of the projected image circle.

You will need to adjust your preconceived ideas of what the FOV is for each focal length. The factor for your camera is 1.5. So your 50mm will have the FOV that a 75mm lens would have on your film camera. To get the FOV that you had on 50mm, you would need a 33mm lens.

 

[fmw]

The DX lenses also have the advertisted focal lenghts and those focal lengths are whay they say they are. The difference is that they have a smaller image circle designed for the area of the sensor. Your 18-70 is 18-70 regardless of the camera to which you mount it. On a 35mm camera it will vignette because the image circle is too small. If you wanted the same angle of view on a 35mm camera, you would buy a 28-105 zoom if such a thing existed.

 

[Mad_Gnome]

The AF-S DX G type lense I have here is 18-70mm. Now when I look through the viewfinder and zoom, the point where what I see in the view finder being the same size as what I see in my other eye is ABOVE 50mm.

Your viewfinder doesn't show images full-sized. Most viewfinders have a magnification somewhere between 50-98% of life-sized. Your D200 has a 60% magnification, meaning what you see through the viewfinder is only 60% as large as the actual image. This would account for the difference between what you see with your eye and what you see through the viewfinder.

 

[fmw]

Your viewfinder doesn't show images full-sized. Most viewfinders have a magnification somewhere between 50-98% of life-sized. Your D200 has a 60% magnification, meaning what you see through the viewfinder is only 60% as large as the actual image. This would account for the difference between what you see with your eye and what you see through the viewfinder.

According to Nikon, the D200 viewfinder shows 95% of the subject, not 60%

 

[LWW]

I think what they meant was that the VF image was 60% of the size of the sensor.

LWW

 

[Garbz]

Sorry for not replying earlier, internet cafes are hard to find in this city.

Unfortunately I am now more confused. I can believe what mad_gnome is saying, it is just slightly discering coming from the nikon FE where when I had my 50mm lens the scene matched perfectly with both eyes open.

fmw you have confused me slightly. You say the nikon DX lenses are advertised with a corrected focal length. So when I buy an 18-70mm I get 18-70mm for the digital bodies and it will not work on the film body, or a full frame body. I get that.
What I don't understand is what you said following that. Are The question comes purely from me trying to compare lenses from Nikons DX range to other second hand AF Nikkors and also non Nikkors for my next purchase (telezoom lens 200mm+ if anyone has any pointers).

Thanks for your replies.

 

[Digital Matt]

Every focal length on your digital camera is cropped from what it is rated. The sensor is 1.5x smaller than a 35mm negative. So if you multiple the rated focal length of a lens by 1.5, you'll find out what the equivalent field of view is for your D200.

The 18-70mm lens, when mounted on a 35mm camera, would give you just that, 18-70mm. On your D200, is gives you the approximate field of view that a 27-105mm lens would have on a 35mm body.

18 * 1.5 = 27
70 * 1.5 = 105

It's still an 18-70mm lens, but you just aren't seeing the full frame. Because it is a DX (digital) lens, it has a smaller image circle. While it's focal length is still determined the same way 35mm lenses are determined (and any lens for that matter), it is meant to serve the purpose of a wide angle zoom for your digital. It has to be wider than a normal wide angle zoom, to get around the 1.5 field of view crop.

 

[Garbz]

Ok so regardless of the DX designator the 18-70mm lens is still equivalent to a 27-105, and the fact that when I set the lens to 50mm and look through the lens with both eyes open and see a difference is due to the eyepiece.

Ok got it. So there are there any lenses that are corrected for the sensor size discrepency? I assume it is safe to simply multiply all by 1.5 to get the 35mm equivalent I am used to then.

 

[Digital Matt]

Nothing needs to be "corrected" for the sensor size discrepency. Any lens that's made for a 35mm SLR of your same mount type will work fine, but you'll have to just multiply it's focal lengths by 1.5 to determine what "field of view" it will show you. The one thing to be careful of is that some fo the DX lenses, or lenses made specifically for the smaller digital sensor, will not work well on a film camera because of the smaller image circle, or because they are not as sharp from corner to corner. When you put a 35mm lens on a digital body, you are only seeing a cropped rectangle from the center, which in effect hides alot of the problems that you might see in the corners of the lens when shooting film.

 

[Garbz]

Ok. I didn't know if the DX designator meant that the 70mm is the 35mm equivalent digital size or the 35mm size. That'll teach me for not buying a Canon 1D lol!

I won't be using the lens on my 35mm body. Afterall it won't work at all seeing how I would need an old AI lens.

Thanks for your help.