Q�s from my students #1 � re Nikon D cameras - 50mm lens to 75mm and lens portrait characteristics or not.

[james_sophist]

My Fine Art (not photo specialists) students are (on their own)

generally moving over to the Nikon D cameras. I am experienced with

film, thus they come to me, but I am not really experienced with

digital. My students are moving from the AIS lenses they (and I) have

been using to the fairly obligatory AF metering lenses for the Nikon D

cameras.

 

One question that has arisen is with the character of a �normal� lens

when the 1.5 view perspective moves it into a more traditional

portrait range. For example with 50mm 1.8 becomes a 75mm. 75 is into

the range of portrait lens, if on the low side. But out of the pure

�normal� range.

Characteristic of portrait lenses is the fact of their depth of field

out of focus � or what seems now to be called �bokeh�. And

particularly their comfortable and usually smooth area that is out of

focus, at least with wide apertures.

Normal 50mm lenses are rather less known for this particular portrait

characteristic.

When the 50mm 1.8 or 1.4 �normal� lens becomes, with the Nikon D

sensor size adjustment a 75mm, does it genuinely act as a portrait

lens, due to its effective length ? Or at least come close enough to

doing so. I / we hope so, but I do not know if the physical optical

glass components restrict the 50mm 1.8 lens from acting as a portrait

lens in its new 75mm effective size.

Or if the existing Nikon 60mm would have any better chance of

emulating a portrait lens characteristic, at effective 90mm, if the 50

does not.

[angel_o.]

Depth of field depends on the effective focal lenght and aperture, its "look" (="bokeh") depends on the construction of the lens (e.g. shape of the diaphragm blades and their number).<br>

If a lens is called for a specific format "normal" or not depends if its focal lenght is close to the hypothenuse of the frame (e.g. the hypothenuse for the 35mm frame is ~43mm, which is very close to 50mm). In other words, the 50/1.8 can be considered as a small tele and the 35/2 as a "normal" lens if they're used with e.g. a D100.

[angel_o.]

Forgot to add that DOF depends on the focussing distance too.<br><br>

Regards

[mskovacs]

I'm going to chime in that its my interpretation that depth of field depends on focal length, not effective focal length.

 

E.g. I have an 80mm normal lens for my 6x6 medium format camera that has much less depth of field than its effective 50mm equivalent in 35mm format. For one of the smaller sensor DSLR cameras, just imagine taking the shot with a 50mm, then cropping it down to reflect the difference in sensor size. Does cutting a print with scissors change depth of field in your experience?

[leslie_cheung]

why not just blur the oof area with photoshop considering they are

working with digital and it's "fine art" rather than photography.

[carl smith]

That characteristics of the lens cannot and do not change, but the whole system changes get confusing. Read <a href="http://www.photo.net/learn/optics/dofdigital/" target="_blank">this by Bob Atkins</a> which should explain the entire situation, both in depth and a little bit less so.

[todd peach seattle, washi]

I don't use Nikon 50mm lenses, but they have a reputation for harsh bokeh. In addition to the aperture construction, bokeh is a function of the optical formula of the lens. Nikon lenses in general are optimized for sharpness at the expense of the background rendering. The 50mm's are reputed to be the epitome of this philosophy.

 

I have had good luck with the 85mm f/1.8 AFD on the D100. The crop factor means you're looking at more like a 135mm lens, but it gives a pleasing image. Even the 85/1.8 is supposed to have harsh bokeh compared to the 85/1.4 AFD, but the 1.8 is a decent lens at a decent price.

[carl smith]

I've used the Nikkor 50mms of various vintage (including the newest). They're fairly sharp, but have rather unpleasant bokeh, so if that matters to you they may not be the most ideal lens. On the other hand I use a 50 1.4 USM from canon which is just a bit sharper than my Nikkor but the bokeh is often quite better, although still not necessarily great.

[Ed_Ingold]

The key parameter for portraiture is the perspective (vanishing point), which is affected only by the distance to the subject. That is the effect which determines the balance between exaggerating or flattening features of the subject's face.

 

You can use a D1x with a 60mm lens at the same distance as an F5 with a 90mm lens, and will achieve the same perspective.

 

Depth-of-field is a different matter. At the same camera-to-subject distance, shorter lenses have a greater DOF than longer lenses. You can overcome this to a certain extent by using wider apertures, but you can't duplicate the effect of a 105/2 using a 60/2.8. If that's important, you could use a softening filter (or film).

[bruce_rubenstein___nyc]

A 50mm lens on a D100 crops the image to have the field of view of a 75mm lens. It will look different (DOF) than a 75mm lens used on a 35mm film camera. Probably the best, moderate priced lens would be the 85/1.8. The 85/1.4 would be even better. It wouldn't hurt to actually try one the AF 50/1.8 lenses to see how it looks.