nsfbr Posted January 12, 2009 Share Posted January 12, 2009 <p>I've tried to find the answer to this question, but in all my wanderings I have not found an answer to it. And so fellow Nikon users here it goes: Is there a database on line that gives the maximum aperture for Nikon zoom lenses versus focal length? For example, the 24-85mm f/2.8-4.0 D IF seems like a nice lens that could behave like the 24-70mm f/2.8 up through 70mm and then in order to get the last 15mm, it then starts to drop the aperture down to 4.0. But it very well could be a lens that starts at 2.8 for only a bit, then ramps up to 4.0 for most of its focal length range.<br> How does one know without first hand knowledge? <br> This seems like a database that is begging to exist. If it doesn't I would love to help start it, but I only have a few variable aperture lenses that could be considered modern. Strike that, one. Perhaps it is this that keeps me away from them. I do have quite a few older Nikon lenses that are variable aperture and I'm pretty sure I could generate data from them. I could even run the results through Excel and generate curve fits and publish parametric fits for them. <br> So...anyone have any idea if this exists?</p> Link to comment Share on other sites More sharing options...
lex_jenkins Posted January 12, 2009 Share Posted January 12, 2009 <p>I'm not aware of any such study or database. It could be interesting.</p> <p>So far my casual observations of the variable aperture zooms I've used over the years indicate a linear relationship between maximum effective aperture and focal length. When checking the EXIF data for the 18-70 DX, 24-120 VR and 28-85/3.5-4.5 AF, all seemed to show a gradual reduction in maximum effective aperture as the lenses were zoomed toward the tele end. No indication of sudden shifts.</p> <p>It's a bit tougher to tell for certain with the manual focus lenses I've owned but between Nikon, Canon FD, Olympus OM and Minolta mounts, but effective apertures for all seemed to progress gradually along with changes in focal length. Since I shot a lot of color slide film and slow b&w film with those systems any sudden deviation in maximum effective aperture would have been apparent, but I don't recall any problems.</p> Link to comment Share on other sites More sharing options...
Matt Laur Posted January 12, 2009 Share Posted January 12, 2009 <p>Not that the 18-200 is going to behave the same way as those that have a more limited range of focal lengths, but in case you're curious: <br /></p> <table border="1" cellspacing="0" cellpadding="2"> <tbody> <tr> <td>18mm</td> <td>f/3.5</td> </tr> <tr> <td>24mm</td> <td>f/3.8</td> </tr> <tr> <td>35mm</td> <td>f/4.2</td> </tr> <tr> <td>50mm</td> <td>f/4.8</td> </tr> <tr> <td>70mm</td> <td>f/5.0</td> </tr> <tr> <td>95mm</td> <td>f/5.3</td> </tr> <tr> <td>135mm</td> <td>f/5.6</td> </tr> <tr> <td>200mm</td> <td>f/5.6</td> </tr> </tbody> </table> <p><br /><br />So, what you notice of course is that the lens gets pretty slow, pretty fast, relative to its overall range.</p> Link to comment Share on other sites More sharing options...
Matt Laur Posted January 12, 2009 Share Posted January 12, 2009 <p>Couldn't edit that last post fast enough... but here's the same data (for the 18-200) along side of the 18-70.<br> Not that the 18-200 is going to behave the same way as those that have a more limited range of focal lengths, but in case you're curious:</p> <table border="1" cellspacing="0" cellpadding="2"> <tbody> <tr> <td colspan="2"> Nikon 18-200 </td> <td colspan="2"> Nikon 18-70 </td> </tr> <tr> <td>18mm</td> <td>f/3.5</td> <td>18mm</td> <td>f/3.5</td> </tr> <tr> <td>24mm</td> <td>f/3.8</td> <td>24mm</td> <td>f/3.8</td> </tr> <tr> <td>35mm</td> <td>f/4.2</td> <td>35mm</td> <td>f/4.2</td> </tr> <tr> <td>50mm</td> <td>f/4.8</td> <td>50mm</td> <td>f/4.5</td> </tr> <tr> <td>70mm</td> <td>f/5.0</td> <td>70mm</td> <td>f/4.5</td> </tr> <tr> <td>95mm</td> <td>f/5.3</td> <td>--</td> <td>--</td> </tr> <tr> <td>135mm</td> <td>f/5.6</td> <td>--</td> <td>--</td> </tr> <tr> <td>200mm</td> <td>f/5.6</td> <td>--</td> <td>--</td> </tr> </tbody> </table> Link to comment Share on other sites More sharing options...
nsfbr Posted January 12, 2009 Author Share Posted January 12, 2009 <p>Matt, interesting progression there. Is it from Exif data or some other method? When I was thinking about testing my lenses, I was wondering if I would trust that or not. I was thinking I would do that but test the data with exposure value on a variety of light levels on a uniformly lit wall or something like that. <br> I do think this would be an interesting group project if a means of assuring consistent test methods could be developed (maybe with multiple users testing the same lenses to cross check).<br> Good stuff - learning new things always is.</p> Link to comment Share on other sites More sharing options...
mark_sirota1 Posted January 12, 2009 Share Posted January 12, 2009 <p>In general, it's a predictable mathematical progression (logarithmic, IIRC) on the lenses I've seen charts for.</p> Link to comment Share on other sites More sharing options...
Matt Laur Posted January 12, 2009 Share Posted January 12, 2009 <p>Yeah, that's from EXIF data. Obviously, that's only as good as the lens's ability to report it precisely to the camera ... but it can't be TOO far off. For what it's worth, that was done with focus at infinity.</p> Link to comment Share on other sites More sharing options...
Michael R Freeman Posted January 12, 2009 Share Posted January 12, 2009 <p>As others have noted, it is a somewhat linear progression. The aperture will be a full f/2.8 ONLY at 24mm. As soon as you start to zoom from 24mm it will start to drop gradually to f/4.</p> <p>If you stop and think about it, in over simplified terms the actual iris opening remains a fixed size (diameter) in a variable aperture zoom as the focal length changes, so the f/stop (focal length/diameter ratio) will change as soon as the focal length changes.</p> <p>More specifically, here is the chart for the AF 24-85mm f/2.8-4.0 D IF:</p><div></div> Link to comment Share on other sites More sharing options...
Michael R Freeman Posted January 12, 2009 Share Posted January 12, 2009 <p>Incidentally, a chart such as that shown above is included in all instruction manuals for variable aperture zooms. Nikon has many instruction manuals for current production lenses posted on-line, so the information can be found.</p> Link to comment Share on other sites More sharing options...
chris_werner Posted January 12, 2009 Share Posted January 12, 2009 <p>One would think it would be linear, and barring any unusual mechanics it should be linear, but if you look at the data Matt provided, neither set is close to linear. Could the reporting error be that much?</p> Link to comment Share on other sites More sharing options...
Ed_Ingold Posted January 12, 2009 Share Posted January 12, 2009 Joel, <p> <p> You can read the effective f/stop in the viewfinder or top LCD screen of most digital SLRS and the Nikon F100 or F5 film cameras (perhaps others too). Thats only for the maximum opening. The cameras I mentioned have a menu item whereby the aperture is automatically held constant whenever it is not limited by the lens design. Link to comment Share on other sites More sharing options...
akira Posted January 12, 2009 Share Posted January 12, 2009 <p>There should be another problem: zoom lenses (IF lenses?) vary its effective focal length according to the distance you focus at even though you stay with the same focal length setting, which should affect the working aperture of the lens. I don't know if there is any way or source to figure out this particular parameter.</p> Link to comment Share on other sites More sharing options...
Ed_Ingold Posted January 13, 2009 Share Posted January 13, 2009 <p>This is all of academic interest. If you use TTL metering, the actual aperture is moot. Whatever it is, the meter will read the amount of light getting through and calculate the correct exposure. For depth of field, use the DOF preview button.</p> Link to comment Share on other sites More sharing options...
chris_werner Posted January 13, 2009 Share Posted January 13, 2009 <blockquote> <p>This is all of academic interest.</p> </blockquote> <p>That's both accurate and perfectly legitimate in terms of your not being interested in this discussion, but neither is there anything wrong with others wanting to understand it in more detail.</p> <p>I prefer to control the camera myself, and to understand the value and weak spots in things like DOF preview. That has at times given me a leg up; more often it's made little difference; but never have I been worse off for the knowledge.</p> Link to comment Share on other sites More sharing options...
blumesan Posted January 13, 2009 Share Posted January 13, 2009 <blockquote> <p>If you stop and think about it, in over simplified terms the actual iris opening remains a fixed size (diameter) in a variable aperture zoom as the focal length changes, so the f/stop (focal length/diameter ratio) will change as soon as the focal length changes.</p> </blockquote> <p>If your assumption that the aperture size remains constant while the focal length is changed, then it should be very straightforward. Double the focal length = half the f-stop value. Unfortunately the data that Matt has provided are in stark contradiction to that theory. I am assuming that Matt held the focal distance constant. </p> <p>I am sure it would take someone very knowledegable about lens design to explain the how and why. But it would certainly valuable to have the data in some tabular form for each lens. For myself it would be an important consideration when (before) purchasing a variable aperture zoom.</p> Link to comment Share on other sites More sharing options...
jim_momary Posted January 13, 2009 Share Posted January 13, 2009 <p>It is straightforward, in trig. Assume that the dark vertical represents half of the max physical aperture of the lens, here called one unit. In case A, let this be the min focal length of your zoom, which conveniently happens to be one unit too. The angle created as shown is 45 degrees.</p> <p>Crank the lens out to 2 units, 'B'; the angle becomes 26.56 degrees ( and assume the max physical aperture remains the same, it moves further from the film/sensor/eyeball plane is all ).</p> <p>Crank the lens out to 3 units, 'C'; the angle becomes 18.42 degrees.</p> <p>Crank the lens out to 4 units, 'D'; the angle becomes 14.04 degrees. Etc.</p> <p>Now, you see that the largest change in apparent aperture occurs when moving from the smallest focal length outward. As the focal length gets longer, the 'rate' of change in apparent aperture decreases as one takes equal but progressive steps. It is all related mathematically this way to the perspective as seen from the viewpoint of the the place the image is being recorded. Hope this helps a bit and doesn't confuse.</p> <p>Jim M.</p> <p>.</p><div></div> Link to comment Share on other sites More sharing options...
Matt Laur Posted January 13, 2009 Share Posted January 13, 2009 <p>Holy Pythagoras, Batman! Nice illustration, Jim. You also get a gold star for using "dagnabit" in a technical discussion.</p> Link to comment Share on other sites More sharing options...
Ed_Ingold Posted January 13, 2009 Share Posted January 13, 2009 <p>Thank you, Chris, for your dismissal. However there is no general solution to this quest for knowledge other than measuring and plotting the data. The behavior depends on the lens design and the compromises made to effect zooming and various focusing mechanisms, as well as the nominal focal length and focusing distance. At one design extreme the aperture remains constant throughout the zoom range. At the other, you lose two f/stops each time the focal length doubles.</p> <p><br />We laugh at medieval philosophers who argued over "How many angels can dance on the head of a pin?"</p> Link to comment Share on other sites More sharing options...
nsfbr Posted January 13, 2009 Author Share Posted January 13, 2009 <p>I'm glad this inspired some interest. Some thoughts:</p> <p><strong>Michael Freeman:</strong> I did not know that some lenses included that data. Good to know. The manuals on the download page do not, at least not for the ones I've looked at. Here is a link to the download page:<br> http://support.nikontech.com/cgi-bin/nikonusa.cfg/php/enduser/std_adp.php?p_faqid=13948&p_created=1143233777&p_sid=ANFl8Rnj&p_accessibility=0&p_redirect=&p_lva=13948&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9NTksNTkmcF9wcm9kcz04MSZwX2NhdHM9JnBfcHY9MS44MSZwX2N2PSZwX3NlYXJjaF90eXBlPWFuc3dlcnMuc2VhcmNoX25sJnBfcGFnZT0x&p_li=&p_topview=1#Anchor-lenses<br> (And now I know that photo.net blocks tiny url links!)<br> and for that particular manual:<br> http://www.nikonusa.com/pdf/manuals/lenses/AF/AF-S_24-85mm_G.pdf<br> I do know enough about lenses (and Optics given that my degree <em>way</em> back when was in Physics) to know what it "should" be if everything is simple and all that, however, my experience, and it would seem Matt's is that quite often it isn't. There are many possible reasons for this, but the simplest, and probably most common, is that some light may be, and probably is, falling outside the image circle on these lenses. More relevantly, the amount that is doing so is probably changing with focal length, and unfortunately probably with focussing distance. So the objective/focal length rule is probably not going to work at both ends. This may explain the flat region in the middle. (It certainly has to happen on fixed aperture zooms, right?)</p> <p>As to whether or not this is of any merit to discuss, aka, why do I care? I'm well aware of how our camera's work and how they will automatically account for this in the exposure, etc. My interest is in helping to choose a lens to purchase viz a viz weighing the performance vs. focal length. I'm aware of no camera that will tell me how the unpurchased lens will perform until it is mounted on it. ;-)</p> <p>I may attempt to begin as a personal project the recording of the lenses I own that are variable aperture zooms. If I do so, the aims would be 1) to compare the Exif data versus other information to decide if the Exif is good enough going forward, and 2) build a database to see if there are trends and characteristics that could be used to predict other lenses depending on various items (like DX, IF, RF, push pull vs. two touch). Any other ideas would be welcomed. <br> From my perspective, there are no bad questions, especially when it is clear that the answer is not well known, or unclear. Thanks for the responses everyone.</p> Link to comment Share on other sites More sharing options...
dan_brown4 Posted January 13, 2009 Share Posted January 13, 2009 <p>Holy moly! Did not know it was this complicated. Luckily, I can now dial-up the ISO of my D700 to overcome this maximum aperture problem ;-)</p> Link to comment Share on other sites More sharing options...
stevenseelig Posted January 13, 2009 Share Posted January 13, 2009 <p>I avoid variable aperture lens if possible. Think I have only one which I have not used for over a year, once I got the 24-70mm f2.8 lens. Steven</p> Link to comment Share on other sites More sharing options...
Michael R Freeman Posted January 13, 2009 Share Posted January 13, 2009 <blockquote> <p>I did not know that some lenses included that data. Good to know. The manuals on the download page do not, at least not for the ones I've looked at.</p> </blockquote> <p>I expect that the charts showing aperture vs. focal length are/were only included in the instruction manuals for AF and AF-D lenses (i.e. those with an aperture ring). Which makes sense, as G lenses will only function fully on modern bodies, and on all of those bodies the aperture at any focal length can be read in the viewfinder, and it is set electronically via the camera body computer. On many (all?) of those bodies you can also set the aperture to keep a constant fixed value as the lens is zoomed, provided the f/stop chosen is at least as large as the maximum value at the long end of the zoom.</p> <p>AF/AF-D lenses on the other hand can be used on manual focus bodies, and for those bodies it's necessary to know what the actual aperture is for various focal lengths for manual or non-TTL auto flash exposures, or for manual exposures determined (for whatever reason) by an external meter. And of course that aperture will not be the actual f/stop show on the aperture ring at mid-zoom positions, as there is only an index mark for the shortest/longest focal length.</p> <p>On other thing to note with regards to the aperture reported to the viewfinder and used by the camera computer / recorded in EXIF data with AF/AF-D/G lenses. AFAIK this is determined via an encoding strip in the lens barrel (that's how it was done, and probably still is). This encoding strip is set up in discrete zones, so although the aperture is continuously variable as the lens is zoomed, the value displayed only changes in discrete steps (1/3 stops probably). To use the data provided by Matt as an example, the aperture on the 18~70mm for example likely does not maintain a constant f/4.50 from 50mm to 70mm. At 50mm it's probably just a bit wider than f/4.5, but the difference is less than 1/3 stop and insignificant for exposure determination, so the encoding strip is set up with a single zone over this zoom range.</p> Link to comment Share on other sites More sharing options...
chris_werner Posted January 13, 2009 Share Posted January 13, 2009 <p>Well, I'm with Steven on variable aperture lenses. Don't like them, try not to use them.</p> <p>Edward - In my prior post I was just saying that I support people trying to understand the equipment they use. I don't see where I dismissed you, but regardless, that was not my intent.</p> Link to comment Share on other sites More sharing options...
nsfbr Posted January 13, 2009 Author Share Posted January 13, 2009 <p>Chris, the original reason I posted this thread was that I am for the most part like you and Steven - since I've been able to afford otherwise, and frankly as I've become a more serious (spoken in a deep, authoritative voice) photographer, I've also avoided variable aperture lenses. However, I'm trying to understand if this is always warranted. <br> To make the point, I really do find my 18-70 DX that came with my first dSLR kit a very nice lens. It is the only one I use, but not the only one I own as I have bought several older zooms back when I was shooting film and using ancient bodies (I own several N2020s for example). In any event, I as usual appreciate the thought that people have put into responding to my post - I find the Nikon users at Photo.net, and the entire Photo.net community a rare bunch of knowledgeable and supportive folks. </p> Link to comment Share on other sites More sharing options...
chris_werner Posted January 13, 2009 Share Posted January 13, 2009 <p>:-) Understood. I probably should have expanded on what I said earlier because you are right, the kit lenses today are generally pretty nice from an IQ perspective.</p> <p>My reason for not liking them is simply that the variability in the maximum f# makes me feel like I lose control, and I obviously have control issues since I've turned off almost everything automatic on my D300. ;-) I also prefer fixed focal length lenses because they provide me some additional structure and force me to concentrate on composition. As a former boss used to say, "Sounds like a personal problem to me!".</p> Link to comment Share on other sites More sharing options...
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