crop factor in non-cpu lenses?

[n8]

I've been playing with a view of my dad's old nikkor lenses, in this case testing a 3.5 70-200 against my 18-200. I'm aware of the 1.5x crop factor, and am now wondering if the new lenses are made to compensate for this. I ask b/c the non-cpu 70-200 has much more reach at 200mm then my 18-200 does. I'm thinking this is the case with all of my manual lenses compared to my cpu lenses. Am I correct on this?

[mjs1973]

My understanding is that a 200mm lens is a 200mm lens. You should get the same field of view from your dad's old 200mm lens as you do on your newer 200mm when used on the same body.

[OldClicker]

Most zoom lenses are only the claimed focal length when focused at infinity and the more the zoom ratio (11x vs. 3x) the more the difference at other focal lengths [EDIT focus lengths, not focal]. - TF

[n8]

My understanding is that a 200mm lens is a 200mm lens. You should get the same field of view from your dad's old 200mm lens as you do on your newer 200mm when used on the same body.

I would think, but there's a noticeable difference. I've posted a couple for reference, including the lens of interest. First is with my 18-200, then with the 80-200. I was sitting in the same spot for both of these and using identical settings (I'm thinking I'm rather fond of this oldie).

[gryphonslair99]

Focal length is focal length. When you are talking about a zoom lens or a prime, the listed focal length is only close in most lenses. There are certain long held focal lengths that lens manufactures make. No one wants to mess with say a canon 50.15mm f1.8 vs a 49.10mm f1.4. They are both listed as 50mm. The 50mm is considered to be a "normal" lens because it provides the closest view to what the human eye sees.

The actual view of the human eye is approximately 43.27mm. No one wants to make a 43.27mm lens, thus the 50.

The same thing goes for f stop as well. I have both the canon 70-200 f2.8L and the canon 200mm f2.8L. the 200mm is easily 1/3 to 1/2 a stop faster. Trust me, you don't want to pay for exact science and or manufacturing when it comes to things like lens focal length.

[n8]

So, you're saying that there may be a 15mm difference between my two 200mm lenses, but they're both 200's?

[Franglais]

You know this is nothing to do with the original post and only it's going to confuse people who imagine that the "crop factor" actually does something to the lens (it doesn't) or that "digital" lenses have something extra built in to make them work with digital (they don't).

Oldclicker is right. The design of some zoom lenses means that the focal length changes with focussing distance. The very pro, very expensive 70-200mm f2.8 VR II at maximum focal length setting is a 192mm at infinity, and only a 134mm at closest focussing distance.

See what Thom Hogan says about it. He says that the 18-200 is also affected, but he doesn't say how much

http://www.bythom.com/nikkor-70-200-VR-II-lens.htm

[n8]

That makes a bit more sense. I can grasp that the mechanics between my two lenses would be vastly different and would produce this difference. It just struck me as odd when I first noticed it. I think I'll compare my auto and manual 50mm's just confuse myself further.

[gryphonslair99]

So, you're saying that there may be a 15mm difference between my two 200mm lenses, but they're both 200's?

Yep, they are both labeled as 200mm lenses. Somewhere, If I can find it, I have an old article that showed the actual focal lengths of several of the top of the line Canon and Nikon lenses. I will post it if I can get my hands on it again.

[gryphonslair99]

You know this is nothing to do with the original post and only it's going to confuse people who imagine that the "crop factor" actually does something to the lens (it doesn't) or that "digital" lenses have something extra built in to make them work with digital (they don't).

Oldclicker is right. The design of some zoom lenses means that the focal length changes with focussing distance. The very pro, very expensive 70-200mm f2.8 VR II at maximum focal length setting is a 192mm at infinity, and only a 134mm at closest focussing distance.

See what Thom Hogan says about it. He says that the 18-200 is also affected, but he doesn't say how much

http://www.bythom.com/nikkor-70-200-VR-II-lens.htm

The only thing I would take issue with here on the difference between "35mm" glass and "Digital" glass is in the lens coatings. "Digital" lenses have a different formula for their lens coating to take into account the peculiarities of digital sensors vs film. Not much of a difference in the overall scheme of things.

[Franglais]

The only thing I would take issue with here on the difference between "35mm" glass and "Digital" glass is in the lens coatings. "Digital" lenses have a different formula for their lens coating to take into account the peculiarities of digital sensors vs film. Not much of a difference in the overall scheme of things.

I was trying to use vague marketing terms like "digital" meaning in this case "designed to be used only on a 'crop' APS-C sensor and not for use on a 'full-frame' 24x36mm sensor or on 35mm film".

People seem to think that there's a magnifying glass or something on the end of the lens that changes the view to adapt it to a digital sensor. There is no such thing - a magnifying glass would change the focal length.

I don't think anyone designs lenses for film any more. The manufacturers are gradually renewing their whole range of lenses (including primes) for digital. I can think of a few more changes they are making:

- avoid designs where the rear element is very small. If the light hits the sensor at an angle then it may not get into the individual photosites. This is a problem with 24x36mm sensors at the edges of the field. Many Leica rangerinder lenses have small rear elements. The M9 has specific sensor design with microlenses that are modified on the edge of the filed to look towards where the light is going to come from
- better lens coatings as you said. The sensor is shiny and reflects light back onto the rear lens element. If the rear element reflects the light back onto the sensor you get ghosting
- lower chromatic aberration. This is where a while line is split into a rainbow-coloured line. Each "pixel" on the sensor is actually four elements of different colours side-by-side, splitting the colours makes a mess of the fine detail in an image
- increase definition at the expense of contrast. You can always put the contrast back in postprocessing in the camera, but you can't invent detail that isn't there. Same with light falloff and distortion - if the designer knows that the lens is going to be used on a DSLR then he can leave some errors uncorrected (to improve other things) knowing that it can be fixed automatically in the camera without the user even knowing. (Don't ask me for examples - this is just something that the French press have been hinting at in the latest Nikon DSLR's)

[gryphonslair99]

I was trying to use vague marketing terms like "digital" meaning in this case "designed to be used only on a 'crop' APS-C sensor and not for use on a 'full-frame' 24x36mm sensor or on 35mm film".

People seem to think that there's a magnifying glass or something on the end of the lens that changes the view to adapt it to a digital sensor. There is no such thing - a magnifying glass would change the focal length.

I don't think anyone designs lenses for film any more. The manufacturers are gradually renewing their whole range of lenses (including primes) for digital. I can think of a few more changes they are making:

- avoid designs where the rear element is very small. If the light hits the sensor at an angle then it may not get into the individual photosites. This is a problem with 24x36mm sensors at the edges of the field. Many Leica rangerinder lenses have small rear elements. The M9 has specific sensor design with microlenses that are modified on the edge of the filed to look towards where the light is going to come from
- better lens coatings as you said. The sensor is shiny and reflects light back onto the rear lens element. If the rear element reflects the light back onto the sensor you get ghosting
- lower chromatic aberration. This is where a while line is split into a rainbow-coloured line. Each "pixel" on the sensor is actually four elements of different colours side-by-side, splitting the colours makes a mess of the fine detail in an image
- increase definition at the expense of contrast. You can always put the contrast back in postprocessing in the camera, but you can't invent detail that isn't there. Same with light falloff and distortion - if the designer knows that the lens is going to be used on a DSLR then he can leave some errors uncorrected (to improve other things) knowing that it can be fixed automatically in the camera without the user even knowing. (Don't ask me for examples - this is just something that the French press have been hinting at in the latest Nikon DSLR's)

:thumbsup: Yep

What I find amazing these days is the number of people that seem to believe that Digital re-invented the photographic wheel. All digital sensors did was make the ride better, the physics/science of photography stayed the same.

Just as the putting of an iron band on the first wooden wheels just made the wheel last longer. The wheel was and still is round. Still is after the addition of rubber, pneumatic tires, tubeless pneumatic tires etc. Of course the old wooden wheel, iron wheel and rubber wheel didn't need a tube or a valve stem. Those are just slight differences with the different road contact surfaces of the wheel.