Ai and K Nikkors 400mm f5.6 ED "non-IF"

[Akira]

It is just math. f = focal length so f/2 means the aperture is half the focal length. Using a 200mm lens as example, f/2 =100mm,  f/4 =50mm. f/8 =25mm.

Aha, the "result" of the division, not the denominator.

[Jack Dahlgren]

Aha, the "result" of the division, not the denominator.

Yes. It is easy to miss that / is a mathematical operator since photographers talk about apertures using phrases like "F Eight"

[mxbianco]

Aha, the "result" of the division, not the denominator.

This brings an added benefit: you can estimate the size of the front element of your lens (practically, the filter size and/or the lens cap diameter...)
Your "new" 400mm/5.6 will have a front element of 400/5.6 =  71.42 mm. I'll bet the filter size of your tele is 72 mm.

Another example: a 600mm/4 will have a frontal element with a diameter of 150mm, just the same as a 300mm/2.

Ciao from Massimo

[David H. Hartman]

Without reference material: F over R equals D where F is the focal length (any focal length for generality), R is the aperture ratio and D is the aperture diameter. For example...

100mm/2.0=50mm, a 100mm f/2.0 lens.

The f-number is not the Focal Length as its name implies but it is the Aperture Ratio and should be called the "R-Number." f-number has got to be one of the stupidest terms used by photographers.

From grade school math "The larger the divisor the smaller the quotient."

"The larger the divisor (R value) the smaller the quotient (D value) where F (focal length) divided by R (aperture ratio) = D (aperture diameter).

The larger the f-number (cough, cough) the smaller physical size of the opening allowing light through the lens, e.g. 100mm/2=50mm v. 100mm/16=6.25mm.

I hope I'm not talking trash here. 

Dave

What we really need to know is any f/2.0 lens of any focal length will allow the same amount of light to strike our image sensors (ignoring f/stops v. t/stops). t/stops are relevant to videographers and cinematographers, not so much photographers.

[Jack Dahlgren]

Without reference material: F over R equals D where F is the focal length (any focal length for generality), R is the aperture ratio and D is the aperture diameter. For example...

100mm/2.0=50mm, a 100mm f/2.0 lens.

The f-number is not the Focal Length as its name implies but it is the Aperture Ratio and should be called the "R-Number." f-number has got to be one of the stupidest terms used by photographers.

From grade school math "The larger the divisor the smaller the quotient."

"The larger the divisor (R value) the smaller the quotient (D value) where F (focal length) divided by R (aperture ratio) = D (aperture diameter).

The larger the f-number (cough, cough) the smaller physical size of the opening allowing light through the lens, e.g. 100mm/2=50mm v. 100mm/16=6.25mm.

I hope I'm not talking trash here. 

Dave

What we really need to know is any f/2.0 lens of any focal length will allow the same amount of light to strike our image sensors (ignoring f/stops v. t/stops). t/stops are relevant to videographers and cinematographers, not so much photographers.

As someone who spent too long in engineering classes I prefer the derived number (what you call R) to be isolated on one side of the equation. f/D = R, or R = f/D  for example. f and D are physical measures, R is derived as the ratio of the two, is dimensionless, and does not exist alone.

I completely agree that the naming convention of "f stop" works against clarity.

[Erik Lund]

Hehe ~ Turning back photography calculus 150 years, maybe do it in inches as well good fun!
or
Follow standard aperture values f /n,,,  and accept that not all minds work alike   

[Birna Rørslett]

This brings an added benefit: you can estimate the size of the front element of your lens (practically, the filter size and/or the lens cap diameter...)
Your "new" 400mm/5.6 will have a front element of 400/5.6 =  71.42 mm. I'll bet the filter size of your tele is 72 mm.

Another example: a 600mm/4 will have a frontal element with a diameter of 150mm, just the same as a 300mm/2.

Ciao from Massimo

Unfortunately, this is not that simple. The entrance pupil is not the same as the front diameter of the lens. Thus it is entirely possible to have an entrance pupil vastly different from the size of the front element. Think of a 15mm f/3.5 lens with a large front. The numerical value of the entrance pupil can be larger than the physical diameter of the lens as well.

[fish_shooter]

The main benefit of f numbers is exposure equivalency among lenses. Take a light meter reading and the aperture indicated is the same for any lens set at that f number (plus or minus a tiny bit due to rounding, light fall-off, and some f number cheating) at a constant shutter speed and ISO.
I do not know why folks have such as issue since "shutter speeds" are also written as reciprocal values on their cameras. Shutter speed is actually the bigger nomenclature issue as exposure duration would be better. Shutters move at high speed but different shutters can move at different speeds to yield the same marked exposure duration.

[Jack Dahlgren]

I do not know why folks have such as issue since "shutter speeds" are also written as reciprocal values on their cameras. Shutter speed is actually the bigger nomenclature issue as exposure duration would be better. Shutters move at high speed but different shutters can move at different speeds to yield the same marked exposure duration.

I don't think people actually have much issue. We are just being pedantic.

[mxbianco]

Unfortunately, this is not that simple. The entrance pupil is not the same as the front diameter of the lens. Thus it is entirely possible to have an entrance pupil vastly different from the size of the front element. Think of a 15mm f/3.5 lens with a large front. The numerical value of the entrance pupil can be larger than the physical diameter of the lens as well.

True with wide angles and fisheyes, but beyond 85mm this simple rule-of-thumb works,

Ciao from Massimo

[David H. Hartman]

Somewhere in the back of my head I'm hearing something like "Pupillary magnification" that applies to telephoto lenses. I believe that's telephoto lenses but not long lenses of non-telephoto design. Anyone care to take this further?

Dave

If memory serves me it seems the 180/2.8 ED with tubes looses more light than if it were not a telephoto design. A TTL meter takes care of the exposure change. Calculation is only needed for a hand held meter. I'm away from home and can't check my references, probably one of John Shaw's books.

[David H. Hartman]

I found my Nikon TC-14B and tried it with my 400/5.6 ED AI Nikkor. The focus distance was near the minimum. I shot from a Bogen 3021 tripod which is much less than ideal for a 560mm lens. The shutter speed was 1/2000th and the aperture was f/8.0 (f/5.6 as marked on the lens). The ISO was 800. Focusing was damned near impossible for me on a D850 using the LCD monitor at 100%. I tried focus bracketing. The original focus seemed best, not the plus or minus focus settings. This crop was produced by Capture NX-D set to "Latest Picture Control" and using the "Standard Picture Control" with no additional adjustments by me.

I said I'd get out my TC-14B and try it so here is a 100% crop of the frame. On a D850 I don't find the combination of a 400/5.6 ED AI and TC-14B practical. I suspect cropping maybe more practical. Down sampling to 50% (4128x2752) looks pretty good (not shown here). This test may indicate my limitations more than anything else.

Dave

[Akira]

I found my Nikon TC-14B and tried it with my 400/5.6 ED AI Nikkor. The focus distance was near the minimum. I shot from a Bogen 3021 tripod which is much less than ideal for a 560mm lens. The shutter speed was 1/2000th and the aperture was f/8.0 (f/5.6 as marked on the lens). The ISO was 800. Focusing was damned near impossible for me on a D850 using the LCD monitor at 100%. I tried focus bracketing. The original focus seemed best, not the plus or minus focus settings. This crop was produced by Capture NX-D set to "Latest Picture Control" and using the "Standard Picture Control" with no additional adjustments by me.

I said I'd get out my TC-14B and try it so here is a 100% crop of the frame. On a D850 I don't find the combination of a 400/5.6 ED AI and TC-14B practical. I suspect cropping maybe more practical. Down sampling to 50% (4128x2752) looks pretty good (not shown here). This test may indicate my limitations more than anything else.

Dave

Dave, thank you for taking time to test the lens with TC.  I found the lens even used without TC is not very good at its closest focusing range.  So, it is understandable that TC will exaggerate the flaw.   That said, considering that the lens performs quite nicely at distant scenes and objects, a 1.4x TC might make a bit more sense, I guess?  Of course, you would need a really sturdy tripod even with a mirrorless camera in the electronic shutter mode.

[David H. Hartman]

Of course, you would need a really sturdy tripod even with a mirrorless camera in the electronic shutter mode.

Sometimes extraordinary measures can yield good results from a less that ideal tripod. A counter indication is a Linhof tripod I own that is light and very rigid. The legs are extruded aluminum and can catch a breeze and resonate. A work-around is to stuff socks in the channels to dampen vibrations.

Tripods that allow spreading their legs wide can help if the lowest legs are not extended. I was testing a lens with my heavy Bogen 3068 video tripod. The wind was so strong that even this tripod was showing vibrations. I might have. been testing my 300/4.5 IF-ED AI with my TC-14B or TC-16A. Lowing the rig to about 1 meter (39") helps greatly.

A way to test a tripod, head or lens collar is attach a laser pointer to a lens. I've used a laser pointer on my 200/4.0 Micro-Nikkor with various cameras. The light from the pointer will dance indicating vibrations. I found my F2, FM2n and FE2 vibrate more on tripping the shutter compared to later cameras like my F3 and F5. This type of test and show if vibrations can be tamed with a self timer with early mirror release or mirror up mode will solve tripod and camera vibrations. I found the lower legs on my Bogen 3021 and vintage C. M. Marchioni Tilltall are really squishy.

I wish I had several thousand dollars to spend on a couple of really rigid and stable medium and HD tripods.

Dave

[Akira]

Here is a result of a kind of "torture test" for flare and ghosts in an extremely high-contrast situation, with shooting earthshine on the moon in mind.

I think the simplistic 3g5e optical design almost like those of astronomical telescopes and multi-coating are working nicely...