I have a simple question (newbie). I hope someone can share the knowledge with me. I have this Tamron lens stated 5-50 mm with:

Manual Iris: F 1.4-Close Auto Iris: F 1.4-360

What does it means?

I know that 5-50 mm refers to the Focal Length.enter image description here

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  • How about a photo of the lens to assist? – NULLZ Jul 9 '13 at 7:20
  • Well, I guess the specification hardcopy given does not show clearly which range it belongs too. – Mzk Jul 9 '13 at 14:15

You have a CCTV lens made by Tamron, possibly the 5-50mm here: http://www.tamron.co.jp/en/data/cctv/13vg550as2.html

The aperture values are read in the same way as on photographic lenses. In this case, your lens has a maximum aperture of f/1.4 to f/360. f/360 or even smaller apertures are necessary for CCTV cameras which may have extremely sensitive CCDs.

Auto iris lenses automatically stop the lens down or open it up when needed for outdoor CCTV applications; manual iris lenses are adjusted manually and used for indoor CCTV.

  • Now I can understand for the automatic aperture (max aperture:f/1.4 - wide opening, min aperture: f/360 - small opening). Correct? How about manual? max. aperture: f/1.4, min. aperture: close? or there is no min aperture at all? Just f/1.4 for manual iris? – Mzk Jul 9 '13 at 6:45
  • @MizukiKai I guess 'close' means that the iris can be closed completely, so there's no light coming through at all. If so, I assume all the intermediate apertures are available as well. – j-g-faustus Jul 9 '13 at 8:02
  • @j-g-faustus So, there is intermediate aperture values available? Having said that, how can I know the f-number? If there is no intermediate apperture and just close and f/1.4, can I use en.wikipedia.org/wiki/F-number N=f/D, where N is fix with f/1.4 (if no intermediate values), that's mean the D (effective diameter) change. Is this possible? – Mzk Jul 9 '13 at 8:11
  • There is something I want to share though @j-g-faustus imaging.nikon.com/history/basics/19/02.htm – Mzk Jul 9 '13 at 8:19
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    @Mzk 1) Formula for f-number is the same, independent of DSLR or CCTV. 2) Some DSLR lenses cannot change aperture directly on the lens, only indirectly from the camera. But 3) it appears that the manual iris and auto iris specifications are for two different lens models - one manual, one auto. So I guess yours is the auto iris model. See their catalog (pdf) - one auto, one manual iris version of each lens. – j-g-faustus Jul 9 '13 at 10:12

Aperture is the size of the opening through which light is allowed to pass. The smaller the number, the larger the opening and the narrower the depth of field and the more light gets in. The larger the number, the smaller the opening, the less light gets in and the bigger the depth of field. (Depth of field is the amount of distance which appears in focus.)

  • Thank you for the explanation. But what do the numbers mean (manual iris and auto iris)? In manual Iris, the f-number is either 1.4 and close or it varies from 1.4 until it close? how about auto iris? In the setting configuration, I saw it says OPEN, CLOSE, AUTO, PRIORITIZE OPEN, PRIORIZE CLOSE selection. At the lens, I couldn't see any adjustable f-number. It only have W-T (zoom i guess) and infinity-N (Focus). – Mzk Jul 9 '13 at 5:10
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    @Mzk - it is a range of possible values. Closed means that the aperture can be moved all the way to the point where it is letting in no light. When it is in manual mode you can specify the aperture from 1.4 all the way through to fully closed. For automatic mode, it will choose a value somewhere between 1.4 and 360. As far as how to make manual adjustments, I'm not sure, it varies from lens to lens. It may have to be electronically controlled. – AJ Henderson Jul 9 '13 at 14:02

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