Fotomacher Loc: Toronto

The focal length marked on the lens is the correct focal length OF THE LENS. It is a physical determination based on the glass elements and size of the lens. The fact that the lens produces a different field of view when mounted on a camera body is a function of the camera body, not the lens. I had been shooting with a D300s and a D700 and all “FX” glass. My Nikkor 50mm f/1.4 prime lens is a 50mm lens no matter what I put it on. If I mounted it on my D300s, the field of view was what I’d expect from a 75mm lens on my D700, but the lens did not magically become a 75mm lens.

Thomas902 Loc: Washington DC

so strange that no one has even mentioned that for so many of the newer digital zoom optics the actual focal length is incorrectly stated both on the lens markings and exif data...

This phenomenon is simply shrugged off by the lens "Manufactures" where in the case of Nikkors they state (directly from the product sheet for the AF-S 70-200mm f/2.8G ED IF VRII) "This lens is equipped with the Internal (IF) focusing system. As the shooting distance decreases, the focal length also decreases" like WTF? Yes my AF-S 70-200mm f/2.8G ED IF VRII reports 200mm in it's exif data at headshot distance however is ONLY equal to 135mm. FACT! I've verified this against my AF 135mm f/2 DC prime... the images are virtually identical at the critical headshot distance.

The inference about IF causing this is total BS! I have a film era AF 70-210mm f/4 (constant aperture) that is internally focusing and zooming... circa 1988 that is equally sharp as my AF-S 70-200mm f/2.8G ED IF VRII and DOESN'T suffer from "Focus Breathing" It is a real shocker to see a side by side comparison between this vintage Nikkor with the AF-S 70-200mm f/2.8G ED IF VRII... while both report 200mm in exif only the 1988 film era Nikkor actually is 200mm when focused close up at headshot distance...

I'm in the process or replacing my digital "Pro Glass" with film era "Pro Glass" since I nearly always use studio and/or speedlights thus VR is virtually useless to me... Wake up folks... You've been lied to for way too long... Are you really that addicted to VR? Nikon was in it's golden age in the mid 1980's and 1990's. Cash rich and designing the finest film camera optics available... the new bloated plastic optics are vastly over priced and many of the zoom optics seriously suffer from focus breathing... it is so bad that Nikon finally had to change the optical design of their flagship 70-200mm to allow it to actually be true to what is labeled on the lens when focused at headshot distance...

Oh well "There's a Sucker Born Every Minute"

Imageandart your first mistake is believing what Nikon states on it's lens... They have their own hidden agenda... and Nikon has finally owned up to its lies with the release of the current flagship 70-200mm

srt101fan

Interesting comments Thomas, but what are the PRACTICAL concerns about all that game playing with the numbers?

As others have said, look through the viewfinder, adjust the zoom if you have it, and take the picture. Why do we need to worry about numbers?

markngolf Loc: Bridgewater, NJ

The number of posts regarding this subject is voluminous. Here are a few former posts I found with a quick search.
https://www.uglyhedgehog.com/search-topic-list?q=focal+length%2C+crop+sensors%2C+actual+focal+length&sectnum=0&username=

Mark

NCMtnMan Loc: N. Fork New River, Ashe Co., NC

Because it is the actual focal length.

amfoto1 Loc: San Jose, Calif. USA

Because manufacturers DO use the "correct focal length" on their lenses!

An 18-200mm lens is an 18-200mm lens. It's NOT and never will be "actually a 27-300mm lens".

Focal length is focal length. A 50mm lens is always a 50mm lens, regardless what camera it's used upon.

Any given focal length will "act differently"... will render different angles of view... if it's used on different sensor or film formats.

This is nothing new. It was the same with film cameras for 150 years. It will be the same with a camera 150 years in the future, if they still exist and even use optics.

For example...

- A 50mm lens on a 4x5" film (approx. 100x125mm) view camera would act as an ultrawide (0.29X).
- 50mm focal length is also very wide angle on a medium format film camera that makes 60x70mm images (0.469X).
- And it's still wide angle on a medium format digital camera with a 33x44mm sensor. (0.78X)
- The same 50mm would be a "normal" or "standard" lens on so called "full frame" digital or a 35mm film camera that makes 24x36mm images. (1X)
- But on a so-called APS-C camera with sensor approx. 15x23mm, that same 50mm will behave as a short telephoto (1.5X or 1.6X depending upon system).
- Or, on the slightly smaller Micro Four/Thirds sensor (13x17.3mm) the same 50mm will behave as a slightly more powerful telephoto (2X).
- Or on a camera with even smaller 1" sensor("one inch"... 8.8x13.2mm), 50mm acts as a moderately more powerful telephoto. (2.72X)
- And on a camera using a tiny 1/2.3" sensor (4.55x6.3mm), that 50mm will behave as a rather powerful telephoto (5.64X)

Same 50mm focal length lens... different format sensors and film.

Obviously the exact same 50mm lens couldn't be used on all of those different formats. A lens needs to be able to produce a very large image image circle to completely cover a 4x5" (approx. 100x125mm) sheet of film and that will call for one design. In contrast, a 50mm for use with a 1/2.3" sensor - which is less than the size of your pinky finger nail - can be a very small lens and will use a different design.

It just so happens that "full frame/35mm film", APS-C crop and Micro 4/3 crop digital sensors are close enough that it's possible for them to share some lenses.

Another way of looking at this, say you want a "normal" or "standard" lens for your cameras. For a full frame/35mm film camera you'll simply buy a 50mm lens. For APS-C, you'll want a lens approx. 30mm focal length. Or for Micro 4/3 you'll want a 25mm lens. But if you are using a medium format digital, better look for a lens around 65mm. Or, for a 6x7cm medium format film camera, you'll want a 100 or 105mm lens, while for use on a 4x5" large format film camera you'll need a lens in the 160 to 180mm range.

Here's a news flash... NONE OF THIS MATTERS if you only use one format of camera.

If you only use an APS-C format digital, that's all you've ever used and all you ever will use, you can safely ignore all the above and you don't need to "constantly figure" anything at all.

All you need to know is how any given focal length "acts" on your particular camera. Or, in the case of a zoom, how that range of focal lengths that it offers works on your camera.

The only time you need to be concerned about how focal lengths behave on different formats and get out the calculator to "do the math" with those multipliers is if you're changing formats or are using multiple formats side-by-side. For example, I use both full frame and APS-C digital for different purposes. In the past I used 35mm film, medium format film and large format film cameras alongside each other. Even so, I don't sit around "doing the math". I've learned through experience how lens focal lengths perform on each system. The only time I might "do the math" is when I'm seeking a specific type of lens for a different format camera and need to know what to shop for. The rest of the time, I hardly ever think about it.

BTW, it's a notable benefit today that in some cases the same lens can be used on multiple digital formats. Back in the days of film, with very few exceptions, you needed a set of lenses for each format. That was costly and made for a lot more stuff to haul around!

frankraney Loc: Clovis, Ca.

The focal length of a lens does not change. What is marked is what it is........ And what you get......

boberic Loc: Quiet Corner, Connecticut. Ex long Islander

Another way to look at it. If you were to crop a photo in post, you have a crop factor. So when a camera has a crop factor equal to the cropped photo, it is exactly the same thing except the camera does the cropping

Blair Shaw Jr Loc: Dunnellon,Florida

As I have come to understand it: Cropping doesn't change Focal Length....only the Viewing Angle.

So your assumption & subsequent statement that Manufacturers Don't Use Correct Focal Length on their lenses is Not Factual and Incorrect.

Maybe others , more skilled at this have a more precise explanation for your inquiry but I am only an amateur at this craft and only 73 years of it I might add. And the Jelly Fish have survived nearly 650 million years with No Brain at all....??? Gives the rest of us Hope .....at least it does for me. I just take pictures and don't bother with the infinitesimals.

photoman022 Loc: Manchester CT USA

I agree! Those of us shooting CS cameras have to stop "overthinking" things!

pendennis

It would behoove photographers to go back to the basics when referring to focal length of lenses.

The focal length of a lens is the distance from the film/sensor plane, to the optical center of the lens. In the case of "normal" and "wide" lenses, the optical center of the lens is where the aperture is. This is true for most lenses, except for true telephoto lenses. Telephotos have an optical center in front of the aperture; and in some cases in front of the front lens element. "Long" lenses are those whose focal length is longer than "normal" but which cover the image circle. In the case of wide angle lenses, the focal length will be true, only to around 24mm, after which, a wide angle lens will have to be of the retro-focus type, since the rear element of the lens would interfere with the camera's mirror movement.

A "normal" lens will cover an image circle equal to the diagonal distance of the film/sensor. A "35mm" lens will have a focal length of approximately 43mm. Anything longer or shorter will be "long", or "wide". Lenses are designed to provide complete image circle coverage, regardless their focal length.

waynewiz

Thanks mwsilvers.
You are abosultely right.
Marketing people invented the equivalent focal length to make us think that smaller sensors are better.
Taking this to an extreme, what if the sensor were 0.35 mm instead of 35mm. Would a 50 mm lens act like a 5000 mm lens ? I think not :)

anotherview Loc: California

From experience, I've found that some matters in photography rest on assumptions that not everybody knows in the first place. Confusion and frustration follow. Then others try to clarify but include another assumption or two.

I can relate because when I started doing photography seriously, I confess my confusion as to the function of Aperture, Shutter Speed, and ISO. Reviewing the Exposure Triangle and practicing while learning from my mistakes and successes developed my skills over time.

Suggestions. Join a camera club and ask your questions there. Look up terms and issues on the Internet.
Consult other sources of information as needed. Keep at it.

Please know that nobody ever said photography was easy. It's a craft that one learns by doing.

LarryFB Loc: Depends where our RV is parked

Focal length is a parameter of the lens and actually has nothing to due with the size of the sensor. So you lens is a zoom lens that can go from a focal length of 18mm to a focal length of 200mm. It make no difference what camera you use, you lens is an 18-200 mm lens and always will be.

ggab Loc: ?

Come on Hoggers, we can do better than only 3 pages with this subject.
FOV vs Focal Length. FF vs Crop. Canon Crop vs Nikon Crop vs......