50mm lens discussion - film or digital lens?

[jim_higgins4]

Recent discussion about the Nikon 50mm (1.4 vs 1.8) has me confused as to

whether we are talking about a digital lens or film lens. If a film lens, then

isn't it closer to a 75mm? I own a 50mm 1.4 AF lens that I assume if I put on my

D300 or D70 will "become" a 75mm lens and thus lose that fixed

50mm. But if I want a true 50mm lens on a D300, I have to buy the digital

version of the 50mm. Is that correct?

 

Jim Higgins

[blumesan]

Jim,

 

When you put the 50mm lens on a 1.5x cropped (digital) camera it is still a 50mm lens in every respect but one. It will capture the same field of view that you would obtain if you put a 75mm lens on a film camera.

[michael_darnton1]

So, it you want the equivalent of a 50mm lens on your digital camera, you need to buy a 35mm lens: 1.5 X 35 = 52.5mm.

[Two23]

Buy either the Tamron 17-50mm f2.8 or the Nikon 17-55mmn f2.8 and don't sweat it. You'll have both covered. And they have modern coatings designed for digital cameras and ED glass to cut down on CA too!

 

 

Kent in SD

[racksonc]

50mm refers the the physical focal length of the lnes. Putting it on a camera with a smaller sensor (than film) does not change that focal length, it has the effect of cropping. That is, the sensor only captures part of the image. On a D300 you get the same field of view as a film camera would give you with a 75mm lens.

 

Perspective is determined by the location of the camera. if you stood in the same spot, you would get the same perspective with a 16mm lens as you would with a 600mm. It's the field of view that changes.

 

A "digital lens" is one that projects an image that only covers a small sensor. A 50mm "digital lens" has the same focal length as a regular 50mm. That is, it would still "become" a 75mm lens with regard to field of view. To get a 50mm field of view on a DX camera, you would have to use a 33.333... lens.

 

I myself have a D80 with a 50mm f/1.8 Nikkor. I REALLY like the field of view - great for portraits and fairly good for general photography. With this set-up you still get the "normal" perspective (at a given distance). With a 33mm lens, you would get a wide angle perspective which would be terrible for close portraits (unless you want that effect).

 

I suggest that, unless you really need that field of view, you just get a 50mm and don't worry about it.

[User_276104]

I think the fact that DSLRs began with smaller sensors than 35mm film has had a positive effect on photographers as far as envisioning the effect of focal lengths.

 

It takes a bit to get used to, but eventually becomes second-nature for most film and digital SLR photographers.

[jerryjohnson]

Everything is pretty much covered, so I'll just add that the difference between 'digital only' lenes and 'fim' lenes. It was explained to me by a Nikon rep once that the DX (digial only) is optimized for APS-C sensors, such as the D70,80, 100, 200,300, etc, if you tried to use a 'digital only' lens on a film camera you will get vignetting really bad because of the film's wider dimenions. The "film" lenes are designed around a 35mm plane. The physical focal length stays the same.

 

Next time you're in a camera store, as to see a DX lens and a regular full frame lens at the same time. If you look at the rear cell of the lenes, you'll see how the DX lenses' rear cell is further back than the regular lens. Although the focal length stays the same, moving back the rear cell optimizes the image for digital sensors. In some cameras, I forget the models at the moment, the digital only lenses have a rear cell that sticks back so far that it could actually damage the mirror on some older film bodies. Keep in mind, the focal length, eg 50mm, 85mm, etc, is measured from where the lens mounts to the body to the end of the lens, not from the rear element to the front of the lens.

 

Hopefully I didn't confuse you even more, lol. Like I said, stop in a camera store and look at the same size lenses, one DX, the other regular and you'll see the difference. Personally, I just get lenses that will work on 35mm and ignore the DX lenses. That way, I know the lens will work on both my D80 and F100. Such as the case with the 50mm f/1.4, on my F100 it's a great general purpose lens, on the D80 it's a very decent portrait lens because of the crop factor.

[radfordneal]

The above post contains various misconceptions.<P>

 

The definition of a DX lens is that it does not work completely on a full-frame camera. Whether or not it has been "optimized" for APS-C sensors is known only to Nikon, and irrelevant to the customer, who should care only about price, performance, weight, etc.<P>

 

The position of the rear element of a lens depends on the optical design. There is no consistent difference in this regard between a DX and a full frame lens. All the lenses are constrained by having to avoid the mirror. Usually wide angle lenses will have the rear element as far back as possible, whether DX or full-frame.<P>

 

Focal length is <I>not</I> measured from where the lens mounts to the body. In a simple one-element lens, focal length is the distance from that one element to the sensor. In more complicated lenses (all the ones that anyone actually uses), there's no simple way to measure focal length from physical dimensions.<P>

 

All Nikon DX lenses can be safely mounted on any full-frame digital or film SLR. I believe that Canon EF-S lenses cannot, however, so maybe that's

what the poster was thinking of.<P>

 

The original poster's confusion comes from thinking that, like some P&S cameras, Nikon labels their DX lenses by their "35mm equivalent" focal length. They don't. They might have, but they don't. A Nikon DX lens labelled 50mm gives the same field of view as a full-frame lens labelled 50mm.

[bmm]

Jim - this issue had me beat for a while but then it was explained to me this way and it became clear.

 

A 50mm lens is a 50mm lens period.

 

Imagine if you could use it as a projection lens, to focus an image on a piece of white sheet.

 

A film (or FX digital) sensor is like having enough white sheet to capture pretty much the whole width and height of the image, so that it is not 'cropped' too much.

 

A digital (or DX) sensor is like having only enough white sheet that, if put as much in the middle as possible, it captures the middle 2/3 or so of the projected image with the rest being 'wasted' off the sides - i.e. a fair bit of the full image is 'cropped' off due to the smaller sensor size.

 

So when people say that a 50mm lens is "like 75mm on DX" they only mean that a smaller, narrower bit of the picture is captured - a similar smallness/narrowness in fact to what you'd see if you used a 75mm lens on an FX sensing area. But the glass is still creating a 50mm image overall.

 

Does that help?

 

Oh, and if you see DX-specific lenses don't get confused. All that has happened is that the manufacturer has made the lens a bit lighter and cheaper, since it only needs to create an image on the smaller sensor size. The image is still the same focal length - there's just less of it to 'fall' off the sides of the sensor!

[peter_nelson1]

Just to confuse things even further (I play such a productive role in these discussions 8-) ) . . .

 

Some manufacturers, e.g., Tamron, have produced lenses that they claim are "digital" lenses in a different sense. Due to the 3D surface geometry of sensors there has been some concern that light hitting the sensor obliquely might not illuminate the entire sensor element surface so some makers have claimed that their optical designs result in the light hitting near the edges of the sensor to be more at right angles to the sensor surface than competing brands. I've never seen these claims tested or verified.

[wentbackward]

Jim, This is a very valid and confusing point.

 

When you put the 50mm on the D300, think of it this way. The viewfinder is probably

smaller on the D300 than on a film camera. The 50mm is still 'What you see is what

you get' but the D300 can't capture as much of what you see as a film camera

because the sensor is smaller. If you're the type of photographer that keeps both

eyes open, the 50mm will look close to normal, as you've probably come to expect.

 

The reality of course, is that what you captured is at the full 12 MPixels detail so the

picture is said to be cropped equivalent to a 75mm lens.

 

This is not poppycock. The viewfinder on a D3 full frame camera is much larger!!

[alex_lofquist]

Gee. I was hoping that when I put my 500mm lens on a digital camera it would grow into a 750mm lens. I waited and waited but it refused to do anything. Should I just keep waiting?

[peter_nelson1]

<i>Gee. I was hoping that when I put my 500mm lens on a digital camera it would grow into a 750mm lens. I waited and waited but it refused to do anything. Should I just keep waiting?</i>

<br><br>

 

There's stuff you can buy that will help there. But if it stays at 75mm for more than 4 hours send it back to Nikon.

[jim_higgins4]

I feel like Frozen Caveman Photographer. Let me see if I understand your ways.

The discussion recently about the 50mm 1.4 vs. 1.8 was about the lens I already own---AF 50mm 1.4 used previously on my Nikon 8008. Since most of the discussion in the forum is around digital lenses and cameras, I assumed there was a parallel universe and a 50mm digital lenses lived there. So, if I understand correctly, I have the 50mm lense that I need on my D70 or D300. All my other AF lenses are fully functional on a digital body but with the 1.5 cropping issue understood. So, now my search has narrowed to a good wide angle and a good long telephoto because I can use all my AF lenses (28, 85, 50, 70-210, 105) on my borrowed D70 and soon to purchase D300. I think I get it now,

 

Jim "Caveman" Higgins

[bmm]

Spot on - the great news is that you have a fantastic bag of lenses that will come across with you just fine in your switch from film to digital.

 

Have a quick peek at a compatibility chart to make sure you know of any potential limitations (eg AF, metering, distance) but none of these issues are deal-breakers.

 

Personally I'd just go a wide angle - or even maybe not for a while as you learn the digital body. Oh, and if your copy of the 70-210 is anywhere near as sharp (albeit still slow) as the one I recently inherited for free from a friend, you'll love it on a digital body.