Why isn't 300 mm always 300 mm?

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Gregstx
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p.1 #1 · Why isn't 300 mm always 300 mm?

I have 3 different 300 mm lenses. An AF-S 300 F4, a 70-300 non VR G lens and a 28-300. Out of the 3, the 28-300 lens has much less magnification than the other 300 mm lenses. As a matter of fact, the 28-300 has slightly less magnification than my old 80-200 2.8 D lens. I really like my 28-300 lens and it is the lens that is usually on my D7000 but I kinda feel like I got cheated on reach. Oh, and FWIW, my 18-200 has noticeably less reach than my 80-200. There is a pattern here.

Jan 13, 2013 at 06:17 PM

Avi B
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p.1 #2 · Why isn't 300 mm always 300 mm?

Good observation. However, have you tried this exercise at various subject ranges? I would hazard to say the effects that you observe are probably in the short-to-medium range (<10m). Try something farther out.

Jan 13, 2013 at 06:24 PM

Gregstx
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p.1 #3 · Why isn't 300 mm always 300 mm?

Thanks. I'll try that. My test shots were at short range.

Jan 13, 2013 at 06:26 PM

Gregstx
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p.1 #4 · Why isn't 300 mm always 300 mm?

OK, I re-tested at longer ranges and got completely different results. The 300 f4 still has the most reach but the 70-300 is very close. I would guesstimate that I got maybe 5% less reach with the 28-300. That is OK with me. At longer ranges, the 80-200 has obviously less reach than any of the 300mm lenses. But it is still slightly more reach than the 18-200 lens.

Jan 13, 2013 at 07:09 PM

jhinkey
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p.1 #5 · Why isn't 300 mm always 300 mm?

Keep in mind that focal lengths are never exactly that stated on the lens. You are also seeing "lens breathing" - i.e., for some lens designs the focal length decreases as the focus distance gets shorter.

Jan 13, 2013 at 07:21 PM

mfletch
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p.1 #6 · Why isn't 300 mm always 300 mm?

This is a phenomenon sometimes referred to as lens breathing. It's normal for your lenses. When close focusing, the element groups in the lens have to move so far that the effective focal length is altered.

EDIT: I guess I type too slow.

Jan 13, 2013 at 07:22 PM

Avi B
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p.1 #7 · Why isn't 300 mm always 300 mm?

Yeah, what they said

You'll find that the 300 f/4 is the truest 300mm though

It also has the best IQ out of the bunch that you list.

Jan 13, 2013 at 07:30 PM

Smiert Spionam
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p.1 #8 · Why isn't 300 mm always 300 mm?

Virtually all zooms show this to some degree, and it's especially pronounced with those that are internal focusing.

Jan 13, 2013 at 08:01 PM

Lee Saxon
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p.1 #9 · Why isn't 300 mm always 300 mm?

I wonder how big and expensive a 70-200 2.8 with the same resolution and correction as the VR II would have to be to eliminate / mostly eliminate breathing.

Pretty big and expensive, I bet. Cine guys, at least, would probably still want it, though. Maybe not anybody else, but the cine market is very is willing to pay the low volume premium...

Jan 15, 2013 at 04:40 AM

Iris Chrome
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p.1 #10 · Why isn't 300 mm always 300 mm?

Lee Saxon wrote:
I wonder how big and expensive a 70-200 2.8 with the same resolution and correction as the VR II would have to be to eliminate / mostly eliminate breathing.

Considering that they have to take away a feature...

Jan 15, 2013 at 01:53 PM

asiostygius
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p.1 #11 · Why isn't 300 mm always 300 mm?

Avi B wrote:
Yeah, what they said

You'll find that the 300 f/4 is the truest 300mm though

It also has the best IQ out of the bunch that you list.

I suppose the truest Nikon 300mm focal lenght is in fact this one:

300mm/4.5 K or AI ED

This image is copyrighted by the owner

or the 300mm/4.5 AI or AIS non ED:

This image is copyrighted by the owner

Both are non IF focusing designs, the old helicoidal one, so at short focus distances there is none or minimal focus breathing.

Jan 16, 2013 at 04:10 PM

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