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Old Sep 15, 2007, 11:35 PM   #1
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After reading so much about the Vivitar Series 1 70-210 lenses, I bought one this week off e-bay...got it today. I know it is not the most preferred model of the lens, but mine is apparently the model 4, made by Cosina. (I found out about the different models after bidding, but, at worst, I got a zoom that is one stop faster than the ones I had at all ranges). One advantage, though, is the A-position on the aperature ring.

The question is this. The lens is rated at f2.8-f4. This would normally mean that at 210mm, I could expect an f-stop of 4.0. However, when I set it at f4.0 with the lens fully extended, I can then adjust the f-stop on the aperature dial all the way down to f2.8. At first I thought it was just a quirk of the indicators, but I also got an increase in shutter speed (Av Mode) with no loss of brightness in the pictures. Am I wrong, but does that not imply that the lens is actually going to f2.8?

May be a dumb question, but it has me puzzled.
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Old Sep 16, 2007, 12:23 AM   #2
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The newer lenses are 'smart', in that they have electronics which know the focal length and max aperture, and communicate this to the camera. Older lenses only have contacts which tell the camera maximum and minimum aperture, but that doesn't change with focal length. Which means you have to remember that when zoomed out, your lens is one stop slower than the camera sees. (I think)

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Old Sep 16, 2007, 2:51 AM   #3
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Most of the series 1 Vivitars are constant aperture lens...That means they can use a low f/stop number at the longer zoom ranges. If it is a f/2.5 or 2.8 then it will be a 2.5 or 2.8 at 210mm. That is the reason for the large outer lens. My 3.5 series 1 group 1 and group 2 lens are a f/3.5 at 210mm.

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Old Sep 16, 2007, 6:10 AM   #4
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bigdawg wrote:
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Most of the series 1 Vivitars are constant aperture lens...That means they can use a low f/stop number at the longer zoom ranges. If it is a f/2.5 or 2.8 then it will be a 2.5 or 2.8 at 210mm. That is the reason for the large outer lens. My 3.5 series 1 group 1 and group 2 lens are a f/3.5 at 210mm.
I think I have it figured out, and it's related to what VTPhoto said. What was confusing was that, according to the shutter speed readings it was relaying to me in the program line of the viewfinder, it was acting like a constant aperature lens. However, when I studied the EXIFs of some shots I took, I think the values reported back to me were based on a perception by the camera of constant aperature. That's because I told the camera it was constant aperature when I turned on the camera and set the focal length for purposes of shake reduction. Since it gets no information back that the focal length has changed, it tries to act like it hasn't.

The actual EXIF's on the photos show no change in the focal length, but a variance in the shutter speed in line with what would be expected with a zoom lens whose aperature varies in accordance with focal length.

Does that make sense?

BTW, Dawg, congratulations. Your Tide gave a magnificent example of execution of a two-minute offense, while Arkansas' secondary looked like it was playing Blind Man's Bluff.
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Old Sep 16, 2007, 8:16 AM   #5
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Cosina also made an Autofocus version of the Vivitar 70-210mm f/2.8-4 APO Series I, although I don't know if they released it in Pentax mount or not.

I got a Vivitar Series I 70-210mm f/2.8-4 APO Autofocus lens for only $79.95 a while back from Cameta (brand new in box with warranty) in Maxxum mount for use on my KM Maxxum 5D.

Center sharpeness is really not as bad as I expected with the aperture wide open. It's a bit flare prone, so it's not the best for harsher lighting (you'll sometimes get washed out images from loss of contrast in harsher daytime lighting)

But, for the price, I can't really knock it for the times I'd use a longer lens (very rarely do I use anything longer than 100mm), and the extra brightness compared to most inexpensive zooms in this focal range can come in handy.

From what I've been able to determine, this one is using probably using the same basic optical design as the Cosina based 70-210mm f/2.8-4 that you probably have. I've got a few snapshots I took at a concert with my AF version here:

http://forums.steves-digicams.com/fo...amp;forum_id=5

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Old Sep 16, 2007, 1:42 PM   #6
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TJ,
what happens with a vari-ap lens is when it's at the least zoom the aperture is big enough for that magnification at f2.8. the reason it varies, or shuts down more even tho the aperture is still at it's widest opening is because the barrel of the lens is only large enough to let in the amount of light equal to a f4 lens. did this make sense?? did it help??

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Old Sep 17, 2007, 9:02 AM   #7
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Trojansoc wrote:
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bigdawg wrote:
Quote:
Most of the series 1 Vivitars are constant aperture lens...That means they can use a low f/stop number at the longer zoom ranges. If it is a f/2.5 or 2.8 then it will be a 2.5 or 2.8 at 210mm. That is the reason for the large outer lens. My 3.5 series 1 group 1 and group 2 lens are a f/3.5 at 210mm.
I think I have it figured out, and it's related to what VTPhoto said. What was confusing was that, according to the shutter speed readings it was relaying to me in the program line of the viewfinder, it was acting like a constant aperature lens. However, when I studied the EXIFs of some shots I took, I think the values reported back to me were based on a perception by the camera of constant aperature. That's because I told the camera it was constant aperature when I turned on the camera and set the focal length for purposes of shake reduction. Since it gets no information back that the focal length has changed, it tries to act like it hasn't.

The actual EXIF's on the photos show no change in the focal length, but a variance in the shutter speed in line with what would be expected with a zoom lens whose aperature varies in accordance with focal length.

Does that make sense?

BTW, Dawg, congratulations. Your Tide gave a magnificent example of execution of a two-minute offense, while Arkansas' secondary looked like it was playing Blind Man's Bluff.
Both teams show a need for some improvment.

Dawg
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Old Sep 23, 2007, 6:35 PM   #8
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Have you visited this Page?

http://www.robertstech.com/vivitar.htm

Dawg
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