Variable aperture lens question

mopar_guy · Aug 25, 2012

I have a couple of Tokina variable aperture zooms that I bought new in about 1984. During this period, most consumer oriented 35mm SLRs had some kind of TTL metering as well as Auto exposure modes. These lenses both have two aperture index marks. The first mark in white indexes the aperture for the shortest focal length of the lens and the orange index mark indicates the aperture for the longest focal length. There is a one stop difference when zooming all the way from shortest to longest focal length.

One lens is the Tokina SZ-X210 which is a 70-210mm lens with a variable aperture of f/4-5.6. So when you would use this lens at 70mm and f8 and the you zoom to 210mm you get an aperture of f11 if you don't change the aperture setting. This was a fairly common design for the mid 1980's. There were also zoom lenses that had constant apertures throughout the zoom range. These were generally built to a higher standard and sold for two or three times the amount each.

Diapositivo · Aug 26, 2012

Mopar_guy, thanks for the clarification.

As said, I have two zooms: one is a Minolta Rokkor MD 100-200/5.6 (fixed aperture). The other is a Minolta Rokkor MD 28-85/3.5-4.5 (variable aperture). It is interesting to know that while using an external lightmeter the actual aperture is actually 1/3 EV more when at 28mm and 1/3 EV less at 85mm than what is indicated, at any aperture. The difference is not dramatic but it must be there.

A day spent without learning something is a wasted day

cowanw · Aug 26, 2012

So, I did as you suggested and put my Zeiss Jena 28-210 f 3.8-5.6 on a Contax S2 (all manual).
And, indeed a clear blue sky metered about 2 stops differently between 28mm and 210 mm.
Not quite what you asked for, but the S2 would not meter at all with the depth of field button stopped down.
So I tried the lens on a Contax 159 and it does read stopped down, which at 28mm was 3 stops less than wide open and 1 more stop less when zoomed. Not all perfectly consistent, but good enough for government.
When you set the F stop on the manual camera, you are not so much setting an F stop as you are setting an aperture diameter, which the mechanical linkages stop down to, at exposure. The conversion of that aperture to an Fstop requires the assumption of a focal length of lens.
The flip side of this is interesting as well. It means that at 200 mm I have lost 2 stops of speed if I want to maintain the same aperture.
Thanks for asking the question

Sirius Glass · Aug 26, 2012

nwilkins said:
If using TTL metering then this obviously isn't a problem, but I use an external meter so I need to know what the actual effective aperture is. Also, how do I tell at what point in the lens's zoom range the aperture switches from F4 to F5.6?

No, it is not a dumb question. None of us was born with photographic knowledge; we all had to learn from others at some time.

No, it is not a bad design, just a result of the change in the focal length.

You can do some test with the TTL and an external meter.

Set both the TTL and an external meter to the same ISO.
For each f/stop from f/4.0 to f/22:
1. Take a reading at 70mm and write down the shutter speed
2. Take a reading at 140mm and write down the shutter speed
3. Take a reading at 210mm and write down the shutter speed

Next to each f/stop and each focal length write down the change in effective f/stop

Repeat for several different scenes with the same illumination.
Repeat for several different scenes with the different illuminations.

A clear pattern should emerge. If not post a photo of each scene and a table of the results, and we will help you find the pattern.

Chan Tran · Aug 26, 2012

I can't say for all variable aperture zoom but I think they are similar. I have made a test with my Nikon 70-300mm f/4-5.6 IF-ED-D lens. I put this lens on a Nikon FM, set the focus at infinity, pointing the lens to my enlarger color head. I remove the color head from the enlarger and power it up putting in horizontally. With my dicrho DG head for the 4x5 enlarger I have about 6" circle of intense and quite even light area. I checked with a spot meter and there is less than 2/10 of a stop from center to the edge. I position the lens about 6" from this and this lighted area would completely cover the full frame. I removed the back of the camera and put the Minolta booster II unit with a film plane attachment and connect this to the Minolta flashmeter III. Zooming the lens at various aperture I can confirm that at all apertures there is about 1 stop of light loss from 70mm to 300mm. The drop in illumination seems to proportion to the amount of zoom setting although not exactly.
When I mount this lens on the Nikon F5, set the aperture ring at minimum and set the aperture via the dial on the camera. The aperture stays constant if I set it to anything between f/5.6 and f/32. Aperture larger than f/5.6 is possible at the shorter end and smaller than f/32 is possible at the long end. I can't do the same at the film plane measurement with the meter on the F5.

John_Nikon_F · Aug 29, 2012

On the aforementioned Tamron 70-210, which I have in front of me, there are two white lines between the focusing ring/dof scale and the aperture ring. When the lens is at 70mm, the thicker white line shows what the aperture is. At 210mm, the thin white line is the effective aperture. If you're shooting at f/8, set the ring to 5.6 when you're approaching 210mm. Meter reading should be the same with the ring at 5.6 and the lens zoomed out to 210 as it would be with the ring at 8 and the lens set at 70mm.

Just verified this with my F FTn. At 70mm, f/11 gave me 1/8 second with ISO 100 film. At 210mm, f/8 gave me 1/8 second. When shooting at the intermediate settings, set the ring between numbers to get correct exposure.

-J

nwilkins · Aug 29, 2012

thanks for the input everyone - I haven't had time to do thorough testing, but my rough tests have confirmed a difference of about 1-1.5 stops (depending on aperture setting) between 70mm and 210mm. So I guess TTL is the best way to go until I can get a prime portrait lens.

E. von Hoegh · Aug 29, 2012

nwilkins said:
thanks for the input everyone - I haven't had time to do thorough testing, but my rough tests have confirmed a difference of about 1-1.5 stops (depending on aperture setting) between 70mm and 210mm. So I guess TTL is the best way to go until I can get a prime portrait lens.

The 105/2.5 Nikkor is a lovely portrait lens, and is available at very reasonable prices. There are two types, a Sonnar and a Gauss. The AI versions will usually be the Gauss type.

nwilkins · Aug 29, 2012

thanks, that is the one I am looking at - seems like by far the best Nikkor for the money in the 85-135 group.

E. von Hoegh · Aug 29, 2012

nwilkins said:
thanks, that is the one I am looking at - seems like by far the best Nikkor for the money in the 85-135 group.

It's one of the best Nikkors, period.

Edit - Mir.com is a good source of info. re. Nikons and Nikkors.http://www.mir.com.my/rb/photography/companies/nikon/nikkoresources/6070nikkor/telephoto/105mm.htm

benjiboy · Aug 29, 2012

Speaking generally, if you are buying zoom lenses and want to use them with separate hand held meters, none TTL cameras or flash, (either portable or studio) variable aperture lenses are best avoided, it makes life so much simpler.

E. von Hoegh · Aug 29, 2012

benjiboy said:
Speaking generally, if you are buying zoom lenses and want to use them with separate hand held meters, none TTL cameras or flash, (either portable or studio) variable aperture lenses are best avoided, it makes life so much simpler.

Zooms are best avoided. They're a compromise at best.

benjiboy · Aug 29, 2012

E. von Hoegh said:
Zooms are best avoided. They're a compromise at best.

They are a compromise as you write, but I still find the two constant aperture Canon FD 28-85mm f4 and 70-210 f3.5 Vivitar Series I lenses I have invaluable when shooting slides because of the precise framing you can get with them and the image quality is to me very acceptable, and although have nine prime lenses for my SLR s I tend to use them for shooting negative films .

Sirius Glass · Aug 29, 2012

benjiboy said:
They are a compromise as you write, but I still find the two constant aperture Canon FD 28-85mm f4 and 70-210 f3.5 Vivitar Series I lenses I have invaluable when shooting slides because of the precise framing you can get with them and the image quality is to me very acceptable, and although have nine prime lenses for my SLR s I tend to use them for shooting negative films .

Ditto for my 28mm to 300mm zoom lens. Since I use the TTL meter, the exposures are allows correct. And I have made 24"x36" prints that do not show any signs that would imply that the prime lenses would have made a noticeable difference, even from 6" away.

MFstooges · Aug 30, 2012

Interesting thread. Pardon me for saying this but easiest way to find out is to put the lens onto digital body, take two shots at 70 & 210mm, with same flash setting and same camera to object distance. Then crop the 70mm to get the same field of view of the 210mm and finally check the histogram.

Diapositivo · Aug 30, 2012

MFstooges said:
Interesting thread. Pardon me for saying this but easiest way to find out is to put the lens onto digital body, take two shots at 70 & 210mm, with same flash setting and same camera to object distance. Then crop the 70mm to get the same field of view of the 210mm and finally check the histogram.

Yes but you have to set the camera in manual mode or the camera (digital or film doesn't make any difference) will compensate for the light loss.
But then, a histogram is not a "number" so it doesn't give you an idea of how much you have to compensate when using an external light meter.

E. von Hoegh · Aug 30, 2012

MFstooges said:
Interesting thread. Pardon me for saying this but easiest way to find out is to put the lens onto digital body, take two shots at 70 & 210mm, with same flash setting and same camera to object distance. Then crop the 70mm to get the same field of view of the 210mm and finally check the histogram.

I'll just stick whichever prime lens I think suits the scene on my Nikon, meter with my handheld meter, and expose the frame with utter confidence.

MFstooges · Aug 30, 2012

Diapositivo said:
Yes but you have to set the camera in manual mode or the camera (digital or film doesn't make any difference) will compensate for the light loss.
But then, a histogram is not a "number" so it doesn't give you an idea of how much you have to compensate when using an external light meter.

Histogram actually gives you more accurate number you just need to know the camera dynamic range and divide the histogram by how many stops you have.

lacavol · Aug 31, 2012

You might try adaptall-2.org as they give lots of information on Tamron lenses.

Diapositivo · Aug 31, 2012

MFstooges said:
Histogram actually gives you more accurate number you just need to know the camera dynamic range and divide the histogram by how many stops you have.

I see what you mean but does it work considering that the histogram is drawn after the gamma curve is applied and the data is non-linear any more?
Or is there a way to have the histogram of the "raw" file?
In my digital camera the histogram refers to the in-camera JPEG which naturally has the curves applied by the internal engine.

Chan Tran · Aug 31, 2012

You must have a curve although it could be a straight line before you can have histogram.

MFstooges · Aug 31, 2012

Diapositivo said:
I see what you mean but does it work considering that the histogram is drawn after the gamma curve is applied and the data is non-linear any more?
Or is there a way to have the histogram of the "raw" file?
In my digital camera the histogram refers to the in-camera JPEG which naturally has the curves applied by the internal engine.

Umm that's a good point but I think is not a significant issue since we are not comparing two digicams with different algorithms. That will be way off the analog photography area. My thought is just so he/she can use more accurate measurement for the vari-aperture lens and to save film lab time and cost.

benjiboy · Sep 3, 2012

I had two variable aperture zoom lenses that I sold and replaced with constant aperture ones because they weren't worth the hassle and mental arithmetic.

Variable aperture lens question

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