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I am a noob in photography and don't have any idea of lenses and optics...

Recently though I was looking out for some camera modules and couldn't understand some of the specifications mentioned in the data-sheet.

One of them stated that the Lens construction is 4P + IR, what does this mean?... To an extent I understand the IR part indicates to some filter in the lens.

I searched for the term "4P Lens" on the web but it didn't return relevant results either?

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    \$\begingroup\$ One answer appears in the first hit when you Google "4P + IR lens": "4P = four plastic lenses; 1G = one glass lens; IR = infrared filter" \$\endgroup\$
    – whuber
    Commented Oct 14, 2010 at 14:51
  • \$\begingroup\$ @whuber: Thanks, so why exactly do we need these four plastic lenses or glass lenses? Is there some reference that explains the construction and understanding of lenses. \$\endgroup\$
    – Kevin Boyd
    Commented Oct 14, 2010 at 17:56
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    \$\begingroup\$ You might start at the Wikipedia article and then explore whatever interests you in the links from it. en.wikipedia.org/wiki/Camera_lens \$\endgroup\$
    – whuber
    Commented Oct 14, 2010 at 18:00
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    \$\begingroup\$ It might be useful to add a link to the data-sheet you mention \$\endgroup\$
    – Rowland Shaw
    Commented Oct 15, 2010 at 18:48

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I don't know about 4P, but at least in CCTV IR lenses are lenses that are corrected for infrared wavelengths, which means you can use them with day/night cameras that switch to IR when it goes dark (see Tamron site for examples of these).

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  • \$\begingroup\$ I may be wrong, but my thinking was that the IR part was a filter attached behind the lens and it was to remove the IR component of light entering the camera. \$\endgroup\$
    – Kevin Boyd
    Commented Oct 14, 2010 at 17:58
  • \$\begingroup\$ Tamron explanation at tamron.co.jp/en/data/cctv_ir/ir_series2.html suggest that at least for Tamron it works the way I described. \$\endgroup\$
    – che
    Commented Oct 14, 2010 at 19:04
  • \$\begingroup\$ I think you're both correct: you need to remove the IR filter from the sensor in order to shoot IR, and having an IR-corrected lens helps with focusing. \$\endgroup\$
    – Reid
    Commented Oct 14, 2010 at 22:44
  • \$\begingroup\$ Kevin's link actually says 4Plastic + IR; so I'd say you're spot on. \$\endgroup\$
    – Rowland Shaw
    Commented Oct 16, 2010 at 14:14
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I think f/4P should be read "f/4" + "P". f/4 is clear, "P" according to this documentation means:

P lenses are manual focus AI-s lenses that have had the electronic contacts of an AF lens added to them.

There are only a few of these: the 500mm f/4 P from 1988, the 1200 - 1700 mm f/5.6-8.0 P ED and the new 45mm f/2.8 P.

They allow Matrix metering and I believe the addition of all the automatic exposure modes on AF cameras.

Again, these are manual focus lenses that are unique in their ability to take advantage of exposure and metering modes usually reserved only for AF lenses on AF cameras. You still have to focus them by hand.

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  • \$\begingroup\$ I'm a bit confused now after reading this, whuber mentions that 4P means a 4 element plastic lens. The datasheet of this particular camera states that it is fixed focus, I don't know about manual focus adjustment and the electronic contacts of AF as said in your answer. What conclusions should I come to? \$\endgroup\$
    – Kevin Boyd
    Commented Oct 15, 2010 at 15:33
  • \$\begingroup\$ The naming is very confusing. The same letter has several meanings. Maybe if you show the full name, someone will give you a better answer. \$\endgroup\$
    – asalamon74
    Commented Oct 15, 2010 at 16:48
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    \$\begingroup\$ This wasn't a question about Nikon lenses, I think. \$\endgroup\$
    – James Youngman
    Commented Mar 4, 2012 at 16:37
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By the broken link you mention in your comment, it looks it's a specific naming for Truly company about the CCM (Compact Camera Module). I would recommend to edit your question to be more specific about where your find those mentions as it does not look to be an official standard. (And anyway each brands have their own nomenclature).

As the other answer mention Nikkor AI-P my answer will not mention this as it does not look related to the Nikon / Nikkor nomenclature.

I do not find the exact pdf specifications you mentionned but by looking to another similar document here they mentions: 1/4 inch 4Plastic+ IR which looks like 4 plastic elements and IR filtering. What the specification does not mention is how the IR filtering is exactly done: a specific lens element or just a filter behind the lens.

But the 4P in that context means for sure 4Plastic elements.

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