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03-03-2012, 12:33 AM   #1
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Why longest focal distance only for macro?

I'm just curious why some lenses have an extended macro focusing range but only at the longest focal distance. For instance, on a vivitar 35-105mm 3.2-4 the extended macro focusing range is only available at 105mm? Is it because macro image quality would be poor at shorter focal lengths do to the lenses design or something? I have several lenses that do it including at least 2 auto focus and maybe at least a dozen manual focus (actually one of the auto focus allow it from 200-300mm if I recall right).

The reason I ask, is that I just got the above mentioned vivitar 35-105mm 3.2-4 and it had a bit of scratchiness in the zoom at about 50mm or less and the focus was a bit scratchy in those shorter distances too. It wasn't terrible and did not prevent the lens from being used but it was annoying. I tore it apart, and found the bar that limits the macro at 105mm only was a bit bent (the lens must have taken a smack at some time when it was in the macro focus range). The bar was just dragging the outer ring a bit. I could have tried a little trial and error bending to eliminate it, but instead I just removed it. Now the lens will focus into that macro range at any focal length, and so far as I can tell, it is fully functional. It is a canon fd lens so I can not just throw it on my camera to test it out right now.

03-03-2012, 01:03 AM   #2
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It's because to achieve high magnification at short focal lengths you would need to put have the subject very very close to the front of the lens.

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03-03-2012, 01:16 AM   #3
Col
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Macro Zooms are only working at a high enough magnification when at the long end of their range for a manufacturer to dare to use the epitaph "macro" (ie 0.2x to 0.33x).
03-03-2012, 05:32 AM   #4
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Lensmakers print MACRO on their zooms because that uses less ink than CLOSE FOCUSING and it's sexier, of course.

I know of just one (or two) actual macro-zoom lenses: the Schneider Betavaron 50-125mm enlarger zooms, both versions. And a Betavaron needs some extension to reach macro range on miniature-format (135/FF or APS-C) camera. Perhaps some long zooms might reach 1:2, the usual upper limit of what we call 'macro', but I don't know for sure.

Calculating magnification from focal length and distance: M = F/(D-F) where M is magnification, F is lens focal length, and D is subject distance.

If my 10-24mm has a close focus of 24cm then magnification at 24mm = 24/(240-24)= 1:9. My 28-90 'macro' zoom has a close focus of 30cm. At the long end, M= 90/(300-90)= 1:3 -- still not very macro, but any shorter focal length at the same focus distance would have less magnification. NOTE: "Close-focus distance" here is specified from the frame (film or sensor). I think.


Last edited by RioRico; 03-03-2012 at 09:51 AM.
03-03-2012, 08:03 AM   #5
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So basically they are limiting the lens to closer focusing at the focal length where its going to get the best macro performance, be able to get high magnification from a better distance etc? Wouldn't it be better to not limit what focal length you get that extra focus range at so that the user can make his own decisions on how to shoot based on the circumstances? I do very little macro so I could be missing something here, but I have had a couple of complaints about it. Sometimes limiting it to the highest focal length gives me much more magnification than I need and I have to back up further than I would like to get the shot composed like I want. Also at the longer focal length, its harder to get a stable shot.
For example, I have quantaray 70-300mm and 28-90mm AF macro lenses (both sigmas). The 70-300mm only allows macro at 200-300mm? Often, 200-300mm is too powerful so I use the 28-90mm for macro more often than the 70-300mm. It would have been nice to have been able to use the 70-300mm at focal lengths with less magnification (and in some cases closer might not have been an issue).

Long store short, I left the limiter out of the lens and it seems to work fine. It actually seems to have better contrast and sharpness at the shorter focal lengths that were previously limited, despite the fact that I had to get closer to use them.

Keep in mind this was late last night (grabbed the closest thing to shoot just to see). I had just reassembled the lens (rubber wasn't back on the zoom ring yet) and I had to use flash so there is some flare off the white lettering. I had to hand hold the lens to try and keep it at the right focal length and focus, and hold it to the camera (canon fd mount on a pentax camera). In other words the shots kind of suck because it was hard to operate, but the shots at 35mm (the first 2) look better than the ones at 105mm. The shooting conditions (operator error) may have effected that but the ones at 35mm certainly don't suck in comparison?

I really need to pay my pbase membership so I can have full size shots but here is something. I think this site compresses so I'm not sure you will see what I see, but hopefully it will show what I mean. First shot is at 35mm at normal focus range, second is 35mm at the newly gained macro range (didn't gain much but its something), and the third is at 105mm at the macro focus range.

marco limiter removed album | Ripit2 | Fotki.com, photo and video sharing made easy.
03-03-2012, 09:32 AM   #6
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There would usually be no point in allowing close focus at shorter focal lengths, since you wouldn't get as much magnification as at longer focal lengths. Even if they did allow the extra close focusing at shorter focal lengths, there's a good chance you wouldn't get as much magnification as you would *without* the extra close focusing at the longest length.
03-03-2012, 10:18 AM   #7
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QuoteOriginally posted by ripit Quote
For example, I have quantaray 70-300mm and 28-90mm AF macro lenses (both sigmas). The 70-300mm only allows macro at 200-300mm? Often, 200-300mm is too powerful so I use the 28-90mm for macro more often than the 70-300mm. It would have been nice to have been able to use the 70-300mm at focal lengths with less magnification (and in some cases closer might not have been an issue).
Neither of those is 'macro' -- they don't approach 1:1 magnification. As I said, I also have the Quantaray-Sigma AF 28-90 'macro' and its greatest mag is 1:2.3. I have four longer MF 'macro' zooms and their characteristics are like this (using the M=F/(D-F) formula:

lens -- close-focus -- approx. max magnification
----------------------------------------------------
Pemtax Takumar-A 70-200/4.0 - 90cm -- 1:3.5
Vivitar Series 1 70-210/3.5 --- 200cm -- 1:8.5
Sears-Samyang 70-210/4.0 --- 45cm -- 1:1.15
Sears-Samyang 80-200/4.0 --- 45cm -- 1:1.25

Those Sears-Samyangs come close to macro range. But they're still not edge-to-edge flatfield sharp, which may or may not be important to you, but that makes a difference when shooting flat subjects. Again, the magnification formula above shows that shorter focal lengths would give less magnification. And we use longer FLs for close work so we don't have to get TOO close. It's all a balancing act. And AF isn't really useful at macro distances -- you and the system may not agree opon what should be in focus! Details, details...
03-03-2012, 10:21 AM   #8
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Not all zooms offer maximum magnification at maximum focal length. My Vivitar series 1 70-210/3.5 version 1 lens has 1:2.2 macro at 70mm. Although this is a special manual switch mode where the lens offers macro focusing by using focal length changing as part of the process

03-03-2012, 10:47 AM   #9
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The Tamron SP 60-300 F3.8/5.4 (Model 23A) offers almost true macro at the short end (60mm) with magnification ratio of 1:1.55.
03-03-2012, 10:48 AM   #10
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Again, I don't do a lot of macro work so if I'm missing the big picture, please forgive me. I do understand that these lenses are not really macro, but rather are just closer focusing lenses due to the level of close focus they can do.

I get that you get the best magnification/focus ratio at the longest focal length. Do you always in every case want the maximum magnification? Wouldn't it be limiting for closer work if you only had the option of 1:1 focusing?

In other words, with the lens in question (vivitar 35-105mm 3.2-4). As it came from the factory, it only has the extra focus range at 105mm (when you zoom to 105mm, you can then turn the focusing collar further than you can at all other focal lengths). It is limited by an L shaped bar in the lens (at 105mm, a tab on the focusing collar gets past that bar so that the focusing ring can turn into the additional close focus range). If you remove that L bar which I did, You still have identical close focus operation at 105mm (nothing in the way the lens actually functions has changed). With the bar removed though, you have improved close focus at all focal ranges as the lens can now focus into that extra range at all focal distances. Sure it may not be macro or even a lot of extra magnification/close focus at the shorter focal lengths, but its still improved close focus. Why put that limiting bar there in the first place. You are unnecessarily limiting the close focus abilities of the lens.

Did I explain that well enough or did I just confuse the issue more?

Edit:, I was thinking that perhaps the lens wasn't designed to focus close at shorter focal lengths, but based on the photos I took, that wouldn't seem to be the case. The middle photo is at 35mm with it at the closest focus (in the extra macro range). Perhaps its a flat field issue, which I at first didn't think of, but flat field or not, wouldn't the extra close focus be of benefit at all ranges in some circumstances?

http://public.fotki.com/ripit2/marco-limiter-removed/
03-03-2012, 11:06 AM   #11
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I can't say why lensmakers build 'macro'zooms as they do. I imagine that the designers think they get the best performance within those limitations. Send a query off to Sigma, eh? Or just merrily hack the lenses and see what happens! I do know that many 'macro'zooms show their close-focus range and magnification numbers on their focus or focal-length dials, or along the push-pull body, so we're not limited to a single magnification level.
03-03-2012, 11:28 AM   #12
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QuoteOriginally posted by RioRico Quote
I can't say why lensmakers build 'macro'zooms as they do. I imagine that the designers think they get the best performance within those limitations. Send a query off to Sigma, eh? Or just merrily hack the lenses and see what happens! I do know that many 'macro'zooms show their close-focus range and magnification numbers on their focus or focal-length dials, or along the push-pull body, so we're not limited to a single magnification level.
I might send a message to sigma just to see what the response is. I realized I might have confused the issue. The pictures of the sigma lens were taken with the modified vivitar so they are meant to be an example of pictures taken with a modified lens. The sigma lens was on the camera at the time and I took it off to test the vivitar. I only took pictures of the sigma lens as it was already right there (it might as well been something else like a toy). I don't think I would try and hack up an auto focus lens. The vivitar has already had the limiting bar removed as it was bent and scraping a little. It seemed easier to remove it as to try and bend it back, and he lens seems to work great at all focal distances including in he extra macro range that was intended for 105mm only.
03-03-2012, 02:05 PM   #13
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QuoteOriginally posted by Col Quote
Macro Zooms are only working at a high enough magnification when at the long end of their range for a manufacturer to dare to use the epitaph "macro" (ie 0.2x to 0.33x).
I was rereading everyones post to see if I missed or misunderstood anything and realize basically the same though had entered my mind. Perhaps it is that a lens labeled 1:2 macro can only do it at the long end, so they limit it to the long end to prevent being accused of false advertising, since its not capable of 1:2 on the short end. You would think they could put 1:2 macro available at xxxmm only in specs and advertising, but maybe this is just what their legal/marketing departments came up with.

The Tamron SP 60-300 F3.8/5.4 that demp10 posted about goes to show you can have some macro ability on the short end. My 70-300mm has macro at 200-300mm so maybe that is the part of the range that could do macro to the advertised spec. If that is the reason, then it kind of supports just tearing out the limiter if like in my case, you are taking it apart anyway.
03-03-2012, 02:16 PM   #14
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Most zoom macro lenses are generally the cheap lenses. It's quite easy to understand why macro is at the max length, because the max length provides the full magnification. The most probable reason why they dont have it so that it is macro at the shortest focal length is probably to save cost. My guess is adding the macro functionality while the lens is extended doesn't cost that much more (from what I understand the rear element only needs to move further away from the sensor), while making it so that it includes the shortest focal length might require more lens elements (because the lens is not extended enough there is no room to move the rear element away). The 60-300 is labeled SP (super performance), so it likely wasn't a budget lens and is the exception.
03-03-2012, 02:54 PM   #15
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I have the Rikenon 70-150, a copy of which is currently on the market; its 'macro setting' (1:5 or so) is at the 70mm end. So it can be done but it is less common.
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