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Old Apr 17, 2006, 7:54 AM   #1
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I have noticed that some lenses have no aperature ring and some do. I have a new Sigma EX 28-70mm f2.8 lens with the aperature ring which I set to A. I also have some older lenses like an M42 mount80-210mm f3.5.

Obviously this lens does not have an A setting so I manually set my aperature, which allows me to set it at 210mm F3.5.

I am assuming that the lens is marked as a 80-210mm F3.5 because I can manually set it F3.5 at the 210mm focal length.

Whereas say the Sigma 70-300mm f4-5.6 has no Aperature ring and when you zoom to 300mm the aperatue automatically adjusts to 5f.6.

Now, I have seen some earlier versions of the Sigma 50-500mm f4-6.3 with aperaute rings. So if you set the aperature to f4 and zoomed to 500mm do you have a 500mm f4 lensthe same as the earlier m42 lenses were marked?

Just curious :O
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Old Apr 17, 2006, 8:14 AM   #2
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nope if its a 4-5.6 its f4 on the wide end and 5.6 on the tele end
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Old Apr 17, 2006, 8:21 AM   #3
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So what you are saying is thet even though I set the aperature manually to f4 it won't actually go to f4 when I set focal length to 500mm?
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Old Apr 17, 2006, 8:26 AM   #4
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No!!! The old lens you have is a constant aperture lens if it is marked just f3.5. Cheaper lenses, or lenses with large zoom ratios, usually have a variable aperture which gets smaller as you zoom to longer focal lengths. These lenses may be set at f4 on the aperture ring but will actually be at f6.3 at the 500mm setting (a real nuisance on manual exposure cameras). This is simply due to the fact that the numbers printed on the lens barrel cannot change with the maximum aperture.

Constant aperture zooms are getting more rare and more expensive than they used to be, in many cases only the large aperture models are still available (like the 28-70mm f2.8 or the 80-200mm f2.8, both very expensive lenses). The Pentax A series lenses had a number of reasonably priced constant aperture zooms and there is the FA 28-70mm f4 but most lower cost zooms are relatively slow and variable aperture.

Ira
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Old Apr 17, 2006, 8:30 AM   #5
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No it is an old Tamron 80-210mm and is marked f3.5 on the end lf the lens but on the aperature ring it can be adjusted to f22.



I was just curious, like my new EX Sigma28-70 f2.8. *It is marked as f2.8 on the sie of the lens, but the aperature ring can go to f22 as well.

I was just curious how they can do that with some oenses but not others that all.
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Old Apr 17, 2006, 8:41 AM   #6
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Check out my article at http://www.k12.nf.ca/gc/photoclubweb/exposure.htm

This one http://209.196.177.41/03/03-03.htm

Or this http://www.reminiscingvisions.com/ar...nding_001.html

BTW, the lack of an aperture ring does not change the way the lens works, it just means that the aperture values are controlled directly by the camera.


The following definitions are from http://photonotes.org/cgi-bin/entry....erturezoomlens The Photonotes.org dictionary.


Constant aperture zoom lens.

Also "fixed aperture zoom lens." A zoom lens which has the same maximum aperture at all focal lengths.

Such lenses tend to be expensive professional lenses because of the optical complexity in designing such a lens. Consumer lenses tend to be variable aperture lenses - in other words, their maximum apertures vary with focal length - typically decreasing as the focal length increases.

For example, a professional lens might maintain a constant maximum aperture of f/2.8 as the lens zooms from 70mm to 200mm. A consumer lens might have a maximum aperture of f/3.5 at 70mm, f/4.5 at 125mm and f/5.6 at 200mm.

Variable aperture zoom lens.

A zoom lens which has different maximum apertures at different focal lengths.

This has been a very good question, one that a lot of people are probably unaware of. Hope this was helpful.

Ira
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Old Apr 17, 2006, 8:47 AM   #7
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It also means that you can not use the newer lenses without the aperature ring with older cameras. I don't like that feature since I many times like to set the aperture manually and at least right now will not purchase a lens without the aperture ring.

Tom
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Old Apr 17, 2006, 8:50 AM   #8
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Tom

I agree, my only lens without an aperture ring is the 18-55mm kit lens (cheapest wide angle solution).

Ira
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Old Apr 17, 2006, 8:53 AM   #9
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I am going to go and have a look at the links you posted Ira, but here is the same lens I bought for $30US being sold on Ebay for $199.

I am pretty happy I got mine so cheap, I was wrong about the focal length it is 80-250mm f3.5.

http://cgi.ebay.com.au/Tamron-Auto-Z...QQcmdZViewItem

It has an aperature ring like my 28-70mm Sigma EX, but both are marketed and sold as a constant aperature even though you can manually select a different f stop.
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Old Apr 17, 2006, 9:01 AM   #10
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Crashman, I have noticed that you have gotten some very good lens deals, good luck in future.

One last link, for any Pentax user one of the most useful sites out there is http://www.bdimitrov.de/kmp/ since it outlines almost all K-mount cameras, lenses and accessories that Pentax has supplied over the years, invaluable.

That Tamron looks like a real keeper, just two things to watch for, 1) lens flare is a bigger issue with older lenses so be sure to use a lens shade in bright sunlight. 2) Chromatic Aberration, some older lenses were designed with less colour correction (possibly because of the popularity of black and white film with amateur and professional photographers, or just because of the early zoom technology) and are more prone to CA in high contrast areas.

Ira
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