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Old Jul 21, 2007, 11:24 AM   #1
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hello, could someone please put me straight on the subject of focal length of my new lenses to use with my NikonD100 SLR??, i have just purchased a Sigma 70-200 EX DG Macro lensand i have been told thatmy Digital sensor conversion equates to a !.5 x increase??:?so am I really shooting at approx 98- 280mm at the thick end , in real view terms, orjust indigital P&P.?

Also i have now purchased a 1.4 converter which added to the zoom at thefull end creates a ( without the 1.5 Nikon digi to 35mm conversion) approx (again) a 280ish lens conversion which i assume means that in reality this must also have the 1.5 factor added?? giving me a Digi equivalent of 392 mm ishF4 at the extreme end?.

please help me come to terms with this issue!, I have a number of pro photographer friends but they all use Canon "full" frame cameras and admit to knowing nothing (or refusing to be bothered with) LOL:lol:, my Nikon issues anymore:sad:.^Thanks in advance. Graham
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Old Jul 21, 2007, 11:36 AM   #2
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Lenses (designed for digital or not) are marked by their actual focal lengths.

What changes is the angle of view (apparent magnification), depending on the sensor or film size a lens is being used on.

For any given focal length on a Nikon DSLR, you'll have the same angle of view (apparent magnification) that you would use a 50% longer lens on a 35mm camera.

IOW, in order to see what focal length you'd need on a 35mm camera for the same angle of view, multiply the focal length by 1.5x (it's actually slightly more, but it's rounded).

So, a 70-200mm lens on a Nikon DSLR would give you approximately the same angle of view you'd have using a 105-300mm lens on a 35mm cameras.

The same thing applies to "digital only" lenses like Nikon's DX lenses, Sigma's DC Lenses, and Tamron's Di II lenses. You'll still have a narrower angle of view (more apparent magnification) for a given focal length lens compared to a 35mm camera (even though you're not cropping anything out of the view with these, since they are designed for the smaller APS-C size sensor).

The focal length is the same on both types of lenses on the same camera. Ditto for the angle of view. The only difference is that you're not seeing a so called "cropped view" on a DSLR with a smaller sensor with a digital specific lens. Everything else (including multipliers for comparisons) remains the same.

Only the image circle size changes with a lens designed for digital on a DSLR (so you can't use that lens on a 35mm camera without vignetting). The angle of view (what you get in the resulting image) for a given focal length remains the same with digital or non-digital lenses on a DSLR.

If you use a smaller sensor or film size, the angle of view will be narrower (more apparent magnification) for any given focal length.

If you use a larger sensor or film size, the angle of view will be wider (less apparent magnification) for any given focal length.

The only reason to even have a so called crop factor or focal length multiplier is so that users familiar with using lenses on 35mm cameras have a better understanding of how angle of view compares using a DSLR with a sensor smaller than 35mm film.

If 35mm cameras were not so popular, there would be no need to use them at all.

Since you have the same lenses for use on 35mm or smaller sensors with DSLR models from Nikon, Canon, Olympus and KM, giving angle of view is more difficult (since you don't know the camera the lens will be used on with most designs).

Nikon started giving Angle of View for DX lenses assuming an APS-C size sensor would be used (since their DX series are similar to Canon's EF-S series lenses, or KM/Sony's DT lenses, or Tamron's Di II lenses, or Sigma's DT lenses) and they will only work on a camera with a sensor smaller than 35mm film without vignetting).

For example, the Nikon specs for the widest angle of view for the Nikkor 18-70mm f/3.5-4.5G ID-IF AF-S DX lens is shown as 76 degrees at a focal length of 18mm (as you would expect when a lens with a focal length of 18mm is used on a DSLR model with a smaller sensor).

If you look at a non-DX lens, the angle of view shown in the specifications for a given focal length assumes it will be used on a 35mm model.For example, the Nikkor 18-35mm f/3.5-4.5DED-IF AF lens (non DX lens) shows an angle of view in it's specifications of 100 degrees at a focal lenth of 18mm (as you would expect when an 18mm lens is used on a 35mm camera).

The focal length at the widest setting for both lenses is identical. What changes is the angle of view, depending on the size of the sensor/film the lens is being used with.

If you used the non-DX lens (designed for 35mm cameras) on a DSLR, the angle of view would be identical to the DX lens (digital only lens design) for the same focal length setting.

Since we have lenses that can be used on cameras with more than one sensor or film size, it's tougher to give angle of view for these (although they could give multiple angle of views in the specs, showing it for multiple sensor/film sizes).

If 645 format was more popular than 35mm, we may have be seeing "focal length multipliers" to help medium format users make the transition to 35mm, so that users could understand that a lens will have more apparent magnification (narrower angle of view) for any given focal length when used on a 35mm camera versus a medium format model. ;-)


If you really want to know the forumla, here it is:
  • Angle of View = 2 * ArcTan(Film Dimension / (2 * Focal Length * (1 + Magnification)))[/*]
If you want some simple formulas for how larger format films compare to 35mm for a given focal length lens, here some are::

645 focal length x 0.62 = equivalent 35mm focal length
6x6 focal length x 0.55 = equivalent 35mm focal length
6x7 focal length x 0.48 = equivalent 35mm focal length

If you use a lens designed for a given format (as in the new "digital only" lenses designed for a DSLR with a smaller sensor), you don't crop it (as the image circle is designed to match up to the film or sensor). But, you still have to use the exact same formulas for angle of view comparisons for a given focal length lens.

For example, if you use a 50mm lens on a 645 format camera, you'll have a wider angle of view (less apparent magnfication) compared to a 50mm lens on a 35mm camera (it would be like using a 31mm lens on a 35mm camera from an angle of view perpective). You'll have a wider angle of view on 645 film.

Or, to put it another way, you'd have a narrower angle of view (more apparent magnification) using any given focal length lens on a 35mm camera versus a medium format model. You'd need to multiply the focal length of a lens used on a 35mm camera by around 1.7x to compare to the focal length needed on a 645 camera for the same angle of view.

Now what format are we "cropping"? That's one of the biggest misconceptions about digital around.

A lens designed for a 35mm camera will behave exactly the same on DSLR from an angle of view perspective as a digital only lens of the same focal length on that same DSLR from an angle of view perspective (apparent magnfication, what you see on the resulting image).

You'd still need to multiply the actual focal length of the lens by 1.5x if a lens is used on a DSLR with an APS-C size sensor to see what focal length you'd need on a 35mm camera for the same angle of view.

Where the confusion comes in, is because lenses designed for a 35mm camera have a larger image circle compared to lenses designed for a DSLR with an APS-C size sensor.

That doesn't have anything to do with the angle of view you see for a given focal length lens. In the case of a lens originally designed for a 35mm camera, the extra space in the image circle just isn't used with a DSLR using an APS-C sensor.

Does any of that make sense? ;-)

Short answer (repeated from above):

If you use a smaller sensor or film size, the angle of view will be narrower (more apparent magnification) for any given focal length.

If you use a larger sensor or film size, the angle of view will be wider (less apparent magnification) for any given focal length.

The only reason to even have a so called crop factor or focal length multiplier is so that users familiar with using lenses on 35mm cameras have a better understanding of how angle of view compares using a DSLR with a sensor smaller than 35mm film.

If 35mm cameras were not so popular, there would be no need to use them at all.

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Old Jul 21, 2007, 2:37 PM   #3
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Thank you Jim for you very comprehensive explination:-), i'll read it another dozen times and i'm sure it will sink in LOL.Kind regards Graham.
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Old Jul 22, 2007, 9:04 AM   #4
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Hello JimC,

I am dumbfounded as to the mm talk. :?

I have Nikon F80 (Film camera) with the following lenses.

1) Nikon AF Nikkor 24-85mm 1:2.8-4 D.
2) Sigma zoom 100-300mm 1:4.5-6.7 DL.

I intend to buy Nikon D80 (DSLR) without the kit lens.
Are the above lenses compatible with D80? Will they both autofocus?
I think the 24-85mm lens will behave like a 36-130mm (approximately) lens?
and 100-300mm will work like (if at all) a 150-450mm lens?
What about the kit lens?
Will 18-135mm lens work like a 28-210mm? or what?

One more thing. I have Nikon SB22s flash. Can I use it with D80 with TTL function, or should I get SB-600/800? What about SB-400? Is it any good for heavy duty use, such as wedding?


Please help.
Thanks in advance.
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Old Jul 22, 2007, 9:26 AM   #5
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Pamo27 wrote:
Quote:
I have Nikon F80 (Film camera) with the following lenses.

1) Nikon AF Nikkor 24-85mm 1:2.8-4 D.
2) Sigma zoom 100-300mm 1:4.5-6.7 DL.

I intend to buy Nikon D80 (DSLR) without the kit lens.
Are the above lenses compatible with D80? Will they both autofocus?
Probably. Sometimes you see some compatiblity quirks with some of the Sigma AF lenses (they tend to reverse engineer the lens mount protocols and sometimes miss a feature that's included in newer camera bodies).

When that happens, Sigma can sometimes rechip them for better compatiblity (but, not always). Your best bet would be to try it on a demo camera in a store and make sure it works.

Quote:
I think the 24-85mm lens will behave like a 36-130mm (approximately) lens?
and 100-300mm will work like (if at all) a 150-450mm lens?
What about the kit lens?
Will 18-135mm lens work like a 28-210mm? or what?
Yes, to all (from an angle of view/apparent magnification perspective). They will all appear to have a 1.5x longer focal length on a DSLR, compared to using them on a 35mm camera.

Quote:
One more thing. I have Nikon SB22s flash. Can I use it with D80 with TTL function, or should I get SB-600/800?
It's not going to work in TTL auto modes for sure. Flash systems have been redesigned for Digital.

But, it looks like that flash model has both non-TTL Auto (using the built in sensor to measure reflected light) and manual modes. So, you could probably set the camera and flash to match for Aperture and ISO speed and get it working that way (although you may have to tweak the settings a tad on one versus the other).

I'll let some of the Nikon shooters comment that may have some experience with one. My only Nikon gear is film (other than one old Coolpix 950). lol


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Old Jul 22, 2007, 9:46 AM   #6
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Hello JimC,

Thanks a lot for the reply.
I read in an old thread that D80 used to have an exposure problem with Matrix Metering. Have they (Nikon) rectified it in the newer models of D80?

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Old Jul 22, 2007, 10:03 AM   #7
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Well, if you read enough threads, you'll find reports of exposure issues with just about every camera model from every manufacturer. :-)

I'm not aware of any specific quirks. But, as a rule, the newer matrix metering systems tend to weight things like your focus point more. So, it's not uncommon to see exposure complaints from users of a variety of camera brands when they don't realize that kind of thing is happening.

Also, some cameras tend to try to protect the highlights more than others, and this can lead to a bit of underexposure in some high contrast shots (since it's usually easier to pull detail out of the shadows and mid tones with a bit of post processing versus losing it entirely in the highlights if an image is overexposed). Ditto if a model tends to lean towards a normal exposure (sometimes a model like that will tend to overexpose the highlights, if it's designed for less post processing). Digital more closely resembles shooting with positive film in that respect (i.e., your slide film).

So, you really have to take some time to get used to the metering behavior of any new system you use, and they each tend to have a personality of their own (especially since the algorithms used by a manufacturer's matrix metering tend to be very proprietary in nature). You may find Center Weighted to be more consistent with some models. But, Nikon has a very good reputation for their metering overall, and I doubt you'd have much trouble becoming accustomed to any of the metering modes.

Again, my only Nikon gear is film. So, I'll let Nikon shooters here comment anything specific to the D80's metering behavior that may be of interest.

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Old Jul 22, 2007, 10:27 AM   #8
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P.S.

We're hijacking the original poster's thread. So, you may want to start a separate thread with questions you have about the D80, etc.


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Old Sep 13, 2007, 10:57 AM   #9
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I think this would be returning closer to the OP's interest. So I'll ask this question. I have a nice collection of Nikkor WA, Macro, Tele, and Zoom lenses that I've used with my Nikon F2A Photomics and Nikkomat EL. I'm seriously thinking of going beyond my Nikon CP990 and looking into a Nikon DSLR.

So the question of the hour would be can these non-AI manual focus lenses be adapted to function with a new DSLR? I have heard that they can be used as is but it would mean some manual adjustments (cheez, perish the thought of changing an f/stop manually) and maybe using a handheld light meter... is this true? Kinda'going back to "real" photography huh?

But could someone explain the conversion process and approximate cost? I have a significant investment in this fabulous old glass, and if they are useable... well, I'd have a nice jump start.

Doc
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Old Sep 13, 2007, 1:03 PM   #10
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Using them on a Canon DSLR via a lens adapter would be your best bet unless you want to move into a higher end Nikon body and convert your lenses to AI.

You can get adapters for some of the other bodies, too (but, make sure to check and see if you'd have infinity focus through any adapter you buy).

You'd be shooting blind (no metering) with the entry level Nikon DSLR models. So, you'd need to estimate your exposure setttings for aperture and shutter speed, or measure it with another camera or meter.

You'll need to go with a Nikon D200 or higher to get metering with non-CPU lenses. But, you'd have metering with any of the Canon DSLR bodes via an EF Body to Nikon F Mount adapter and you wouldn't need to convert your lenses.

If you go Nikon, it's a good idea to convert them to AI first to keep from damaging the camera or lens (although I don't think that's a problem with some body/lens combos now, Nikon warns you about needing AI lenses to prevent damage). But, it's my understanding that only the higher end Nikon bodies would meter with them, even if you converted them to AI first.

Here's a page showing lens/body combinations that need conversion if you don't want to risk damage. The older non-AI lenses are in the right hand column.

http://www.aiconversions.com/compatibilitytable.htm

Here's an example of an inexpensive adapter ($27.95) to let them work on a Canon body (and you'd have metering, too).

http://www.fotodiox.com/shop/product...roducts_id=718

Or, if you wanted a higher end Nikon body anyway, check out the D200 and higher Nikon DSLR bodies so that you'd have metering. But, I'd convert them to AI first.

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