Help me understand DOF a little better

[Don Kuykendall_RIP]

Surely this hasn't always been true, and I don't know that it is now of most lenses, though you're probably right in characterizing it as being associated with lower-priced modern lenses.

Back in the days of manual-only cameras, I think it would have been prohibitively difficult to manage exposure properly with a zoom lens that changed aperture as it changed focal length, in the manner that some modern zooms do. This seems like something that could only be made workable by modern electronics that can keep track of this change and account properly for it.

I ma not sure how long ago you are talking about but the ones I had when I started out 35 years ago they did have variable apertures. Also when I started working in labs about 30 years ago and selling lenses they did have variable apertures then.
I still have my Zuiko AUTO-Zoom 35-105mm f/3.5~f/4.5 MACRO from 1984

 

[skater]

A couple of my threads from a while back exist to illustrate this relationship. In each of these threads, with a different lens, I give a practical demonstration of how depth-of-field and other aspects of the image quality change with the aperture setting. It's probably worthwhile for the OP, @DonnieZ, to have a look at them…

• http://nikonites.com/education/25599-aperture-depth_of_field-relationship-nikkor-s-50mm-f1-4-a.html
• http://nikonites.com/education/2552...tionship-vivitar-85-205mm-f3-8-tele-zoom.html

These are good examples, but I took the question to be asking whether a different focal length, with the same aperture, would have a different depth of field. I don't know the answer to that, and I don't think the examples you posted in those threads (which are good!) demonstrate that. (Unless they were farther down in the threads - I only looked through the first posts.)

 

[Bob Blaylock]

A couple of my threads from a while back exist to illustrate this relationship. In each of these threads, with a different lens, I give a practical demonstration of how depth-of-field and other aspects of the image quality change with the aperture setting. It's probably worthwhile for the OP, @DonnieZ, to have a look at them…

• http://nikonites.com/education/25599-aperture-depth_of_field-relationship-nikkor-s-50mm-f1-4-a.html
• http://nikonites.com/education/2552...tionship-vivitar-85-205mm-f3-8-tele-zoom.html

These are good examples, but I took the question to be asking whether a different focal length, with the same aperture, would have a different depth of field. I don't know the answer to that, and I don't think the examples you posted in those threads (which are good!) demonstrate that. (Unless they were farther down in the threads - I only looked through the first posts.)

The thread about the Vivitar lens shows this, but perhaps not as well as one would like.

It's particularly noticeable to me in the ƒ/8 pair, that the nearest pieces of candy are fairly sharp in the 85mm shot, but still very much out of focus in the 205mm shot.

But the answer is that all other things being equal, a shorter focal length will give you greater depth-of-field, while a longer focal length will give you shallower depth-of-field.

 

[DonnieZ]

From your EXIF data, I see that you had the lens zoomed to 34mm. It seems obvious enough that it seems stupid to ask, but did you try zooming out to shorter focal lengths? At shorter focal lengths, depth of field is greater, which isn't what you want, but I think you'd more than make up for that by being able to get closer to the bra.

I did try zooming out a bit, but I gained some DoF that I wasn't looking for.

If you have determined that 34mm is about the focal length with which you want to work, then you might as well switch to your 35mm prime. That way, you should get somewhat better image quality, and you've got more aperture range to work with.

And to repeat a suggestion I made before, consider using a pair of panties instead of a bra. Same idea, same “feel”, but the panties will be more compact, and easier to get entirely in the field of view.

I did try the 35.. With both the bra and a pair of panties... However I didn't like the result as much with the panties. Partially because of lighting concerns and my ability to hand hold and get the sharpness I wanted. Shooting it wide open not only softened it up a bit, but also gave me such a thin DoF that parts of the panties were in focus but parts were not. I'll have to set the shot up again and play with it.

Since I'm a little new to the D7100, I've also read a lot about "fine tuning" the focus on all my lenses. I'm going to try that some night, as I think that would have a huge effect if it were "off" a bit when shooting wide open.

Thanks for all the suggestions everyone - kind of a fun little experiment that I didn't think would spark this much discussion!

 

[Daz]

Partially because of lighting concerns and my ability to hand hold and get the sharpness I wanted.

Can you not shoot it on a Tripod ?

 

[DonnieZ]

Can you not shoot it on a Tripod ?

Space in the hallway is a little tight.. I might be able to make it work.

 

[Bob Blaylock]

Here's my latest take on the sort of thing @DonnieZ was trying to do. Somewhat different. My apartment has a bathroom off the bedroom, so I am shooting across the bed, into the bathroom, where my wife is in the tub.

The cat got in the act, during part of the shoot.

50mm ƒ/1.4 lens on my D3200, with a heart-shaped cutout on the front to shape whatever bokeh there might be (not much, really). 1/15 of a second, ISO 200.

 

[Bob Blaylock]

So, @DonnieZ, did you ever go any further with this pursuit?

Any results that you can share with us?