Horizontal DOF ?

[hjoseph7]

A few years ago I purchased a used Nikon D7000 DSLR camera because I wanted to use it with the collection of Nikkor Manual lenses(about 25 lenses) that have been collecting dust in my closet ever since I switched to Digital. Not only did I switch from film to digital, I switched from Nikon to Canon, so unless I use a manual camera there is really no use for those old lenses.

 

I don't want to get too deep, or start any Troll-wars, but the Nikon digital cameras are surprisingly more sophisticated if not more complicated than any of my Canon digital cameras. Even my 10+ year old Nikon D7000 is more complicated than my Canon 6D.

 

The other day, I downloaded the Manual for this camera so I could learn how to use it properly. Even though I only purchased this camera to give me 'instant gratification' with my old Nikkor lenses, I could not resist and purchased some modern AF lenses to use with it. I now have a total of 5 Nikon AF lenses to go with my 25 old Nikkor manual lenses .

 

To make a long story short, while going through the manual, I attached one of those AF lenses on the camera. An '85mm f1.8 D' and began taking some Test shots. There was a book lying flat on my dresser where you could see the Title of the book, so I took a picture of that. The camera was set to "P' mode. The lighting was pretty dim, so the camera decided to give me an aperture reading of 1/40 @ f3.5.

 

I clicked on the shutter button and looked at the back LCD. This is when I saw that the Title of the book was sharp in the center, but pretty blurred in the corners, both corners to be exact. I thought it might have to do with the focusing-points ? So I changed the lay-out of the focusing-points from single-center point to multi-point and took another picture. Again the Title of the book was sharp in the middle, but blurred in the far corners ? I thought maybe it was the lens, or maybe the camera, but something certainly was off.

 

Then I switched to Aperture-Priority and set the aperture to F8. I held the camera as still as possible, given the conditions and took another picture. This time the entire Title of the book was in sharp focus !

 

From my limited experience, I thought the DOF (Depth-of-Field) was supposed to work with far and near objects, reason why the word Depth is used. Does DOF also include Horizontal focusing, or am I doing something wrong ?

[Ed_Ingold]

Most lenses have some degree or curvature of field, which means the focal point of objects varies with distance from the center. Practical lenses are designed so that the plane of sharpest focus is parallel to the image plane in the camera. Deviations from this ideal will render objects near the edges of the field out of focus. This effect is exacerbated at wide apertures, and generally reduced by stopping down.

 

Besides curvature of field, there are other aberrations which makes lenses less sharp away from the center. These too tend to decrease as the lens is stopped down. Smaller apertures also increase diffraction, and eventually there is a net loss of sharpness (diffraction limited).

 

Finally, design compromises in older lenses, designed for film, are much more visible in high-resolution digital cameras. I find very few "legacy" lenses suitable for mirrorless use, compared to modern lenses designed for digital photography.

Edited April 7, 2022 by Ed_Ingold

[Ken Katz]

It would appear to me that the book title at the extreme corners were further away from the film plane than the center of the book title, so the corners were out of focus. At F8, there was enough DOF to get the title corners to appear sharp.

[hjoseph7]

Could be Ken, but here are samples of what I was talking about:

 

[Ken Katz]

You shot the images from the left side of the books, so they were absolutely not parallel to the film plane. The left edge was materially closer to you than the center and the right edge of the books was materially further away.

[SCL]

Normal expected behavior.

[hjoseph7]

You shot the images from the left side of the books, so they were absolutely not parallel to the film plane. The left edge was materially closer to you than the center and the right edge of the books was materially further away.

 

You are right about that ! I tried it again, this time sitting directly across the book and not at an angle. This time the entire Title was sharp even at f2.5. I'm still confused why the far left corner would be blurred and not the center since it was closer to the camera ?

[John Seaman]

It appears the camera has focused close to the "T" on the word Photography. Anything nearer to or further away from the plane of focus will be out of focus, the more so at large apertures.

[JDMvW]

In the hard, cold light of reality, there is very little you can do with one marque that cannot be done on the other - although you surely will have to learn something to do so.

 

In any case, if you really can't get the hang of the Canons, go back to Nikon. You seem to be "imprinted"

 

 

Except that it's difficult to use the old non-AI Nikkor lenses on newer Nikons, but with a simple adapter they can be used manually with TTL exposure on the various Canon cameras.

[DavidTriplett]

Ken's critique is perfectly on-point. It seems @hjoseph7 could benefit from a DoF primer. It's one of the more difficult principles to fully comprehend and apply. There are many, many good videos explaining all the details and applications on YouTube.

If your old Nikkor lenses are AI or AI-adapted they'll work great on your D7000. I use mine routinely on my D7100 and get excellent results (with the possible exception of that lens of ill repute, the early Nikkor 43-86mm/3.5 zoom, or the "zoom that shall not be named", because it gave a bad rep to every zoom that followed for more than a generation!).

[glen_h]

I suspect this one has been well answered, but do note that lenses have cylindrical symmetry.

 

Any such effects are radial vs. tangential.

 

Most lenses are designed to focus a flat object onto a flat image field.

(Though there are Kodak projector lenses designed to match the curvature

of a slide in mount.)

 

There are some cameras that keep the film in a curved (cylindrical) shape,

presumably with matching lens. I have one stereo camera that manages

to put two images onto two halves of a 24x36mm frame, with curved

film path.

 

And yes, using older lenses on newer DSLRs can be fun.

 

My best lens deal is a Nikon AI 80-200 push/pull zoom lens for $10.50

from a Goodwill auction.

[hjoseph7]

"the early Nikkor 43-86mm/3.5 zoom, or the "zoom that shall not be named", because it gave a bad rep to every zoom that followed for more than a generation!)."

 

Unknowingly I purchased the first version years ago. That was my first Nikon Zoom. Unfortunately, it quickly became a paper weight(literally). A few years later, I purchased the second version which is quite good and still sits in my bag.

[michael_goldfarb]

I'm an example of one of those photographers who was forever prejudiced because of that Nikkor 43-86/3.5 lens!

 

My parents were pros who'd been shooting mainly 4x5 from the forties, and they began buying Nikon equipment in 1963. We got a Nikkor 43-86 to put on our Nikkorex F, it was our second Nikkor lens after the great 50/2... And it was quickly consigned to use only for family vacation slides. It was marginally acceptable for that use - and quite convenient having a normal and tele in one package - even though it wasn't really sharp at any focal length.

 

Multiple Nikkormats and Nikons and many more Nikkor lenses would soon follow, but my folks never bought another zoom lens. And I have never bought a zoom myself, I'm still a totally prime lens guy.

 

Oh, and that 43-86 eventually seized up and sat in the back of the camera cabinet, not worth repairing. We ultimately put it on a similarly broken Nikkormat FTn and buried them alongside our dad to honor his lifetime as photographer. That was probably its most useful moment.

[glen_h]

I'm an example of one of those photographers who was forever prejudiced because of that Nikkor 43-86/3.5 lens!

 

(snip)

 

I thought about buying the AI 43-86 along with my (then) new Nikon FM, but instead go the AI 35/2.0 to go with it.

 

Someone had tried to convince me that 86 was close to the 90 you need for portraits,

but I didn't do portraits, so that wasn't a good reason. But it might be that 43 wasn't

close to 35, which is what I wanted.

 

Not so many years later, I bought a used AI 35-70 to go with my wife-to-be's

Nikon FM, which she bought before we met. Most of the time mine had slide

film and hers had print film (for the family pictures).