Macro shots. Help me understand the difference between these 2 FLs.

<p>Hello!</p>

<p>While doing some research on my first macro lens, I've come across this question:<br /><br />We have various focal lengths for macro lenses, like 60mm and 90mm.<br>

Well, if both lenses have the same working distance for 1:1, that means the image of a flower should be exactly the same regarding size, right?<br>

But how about DOF and other properties that were supposed to be affected by the focal length?<br>

<br />Are they the same? What exactly changes between an image shot at the exact same conditions, same working distance?</p>

<p>Some lenses lose focal length as they focus closer, so the 90mm may not really be 90mm at 1:1. I believe the 60mm Nikon AF-S does this. Which two lenses are you comparing?</p>

 

<p>You are half right. In general, macro lenses have the same maximum magnification at minimum working distance (1:1), but the minimum working distance varies with focal length. Longer focal lengths give you a longer MWD.</p>

 

<p>Well thats the problem. In my case, Im comparing the tamron 90mm and the tamron 60mm, both macro.<br>

They both have the same minimum working distance. However, since the tamron 90mm has an extending barrel, it's in fact longer. Consequently, the distance from the SENSOR to subject is bigger with the tamron 90mm than with the tamron 60mm.<br>

So far so good, but I didnt find anyone showing pictures of shots taken comparing both lenses. So I'd like to know, at least theoretically, what would be the differences in an image produced by these 2 lenses.</p>

<p>Hi Allan. The biggest change is in perspective - if you're shooting from farther away with the longer lens, while the subject may be the same size, the background will appear larger and the foreground smaller (because their relative distances to the camera are a different fraction of the subject's).<br />

<br />

At 1:1, let's assume that the two macros are simple and don't change focal length: the 60mm would reach 1:1 with the lens nodal point 120mm from the sensor (2 x 60mm), and the subject the same distance from the lens. The lens is f/4 at this point.<br />

<br />

The 90mm reaches 1:1 with the lens nodal point 180mm from the sensor, and the subject 180mm from the lens - and it's f/5.6 at this point.<br />

<br />

The depth of field is appreciably smaller with the 60mm lens if you shoot both wide open. Although to be honest the depth of field will be pretty tiny with either of them if you decide to shoot at full aperture - it's normal to stop down appreciably for macro shooting...<br />

<br />

At the same working distance, you'll not be at 1:1 with the shorter lens (or you won't be focussed with the longer one). The longer lens will give you a closer view, just like at infinity.<br />

<br />

If internal focus is changing the focal length, all bets are off and you might like just to look at photozone's sample images. :-) HTH. (I find more working distance to be useful, which is why I got the 90mm...)</p>

<p>The focal length of a lens as engraved on the barrel is a measurement taken when the lens is focused on an object at infinity ∞. On an optical bench, this subject point will be an artificial star (you can use a real star), a pinhole, some distance from the lens.</p>

<p> As you know, the modern lens consists of numerous lens elements some cemented together, some air-spaced, some with strong positive power, some with negative power. Such a design is necessary to mitigate aberrations (there are seven). The focal length will be a summation of all these different powers which includes air-spaces (they also act as lens elements).</p>

<p> If you use pen and ink make a drawing (a ray trace) as light transverses the lens, trace reveals a single point where all rays appear to radiate from. This is the point where the focal length measure is taken. It is called the rear nodal or emerging nodal. This point can fall anywhere within the lens system. Wide-angle lenses, being short may interfere with the mirror movement if too close to the camera body. These designs place the rear nodal far forward of center. A true telephoto differs from a long lens. This design has a short barrel allowed because the rear nodal may fall far affront of the lens.</p>

<p>What I am trying to tell you is, the working distance, distance from front element to subject is a variable based on lens design.</p>

<p>To obtain “unity” (1:1 or life size) the chip surface or film surface is 4x the focal length from the subject. Thus with the 60mm the focal plane to subject plane is 240mm. With the 90mm this distance is 360mm. While the working distance might be the same, the subject to focal plane distances is not. If the working distances are the same, it is due to differences in the position of the rear nodal.</p>

<p>At unity (1:1) the span of depth-of field is split 50% behind and 50% forward of the point focused upon.<br>

For the 60mm, this span at f/16 is 1.9mm. For the 90mm, this span is 0.4mm. (based on a circle of confusion 0.03mm in diameter). </p>

<blockquote>

<p>They both have the same minimum working distance. However, since the tamron 90mm has an extending barrel, it's in fact longer. Consequently, the distance from the SENSOR to subject is bigger with the tamron 90mm than with the tamron 60mm.</p>

</blockquote>

<p>You're mistaking here; the minimal focus distance is calculated from the plane of the recording media, NOT from the front of the lens. So the physical length of the lens does not matter.<br>

The thing that remains different between the two is their angle of view - and hence at an equal focus distance, both render a different perspective.</p>

<p>You have to understand that a lens focuses closer using extension so a 90mm needs 90mm of ectension to produce a 'same size.' image on the sensor whereas the 60mm only needs 60mm.</p>

<p>That is not quite correct becuase if 'extension' is something added such as an extension tube you need less due to the focusing ability in the lens itself.</p>

<p><strong>For a given image size on the sensor there is no difference in DoF irrespective of focal length.</strong><br>

Though some will query the simplification of that statement but it is mostly true :-)</p>

<p>However if you gain magnification in subsequent editing you will have a bit more DoF if you stay back and crop rather going in for the tight shot in-camera.</p>

<p>There is also the 180mm Macro lens to be considered ... the advantage of the longer len is the separation between lens and subject making lighting easier ... protecting camera and you from venomous insects. Avoid scaring the little creature by coming in close</p>

<p>Personally in recent years I have used a 430mm lens for tightly framed shots and currently with MFT and only a 280 lens having to revise my OS slightly.....I do not have a macro lens for all its convienience but use older ways acquired over the years prior to the macro lens coming on the market.</p>

<p>The message here is that you do not have to go in close to get tight framing and there are definite advantages of staying back When I used an SLR all I had were a 50mm lens, extension tubes and bellows but with digital and my bridge camera I have a much longer zoom without going overboard and can benefit from the narrow angle of view of the longer lens ... I would suggest with close-ups perspective isn't really a very serious consideration, for me anyway :-)</p>

<p>I find the use of a close-up lens on a long lens a quick and efficient way of getting tight framing and less expensive for me becuase I have it from way back than buying another lens ... imposssible to use with a bridge camera although possible now I am using MFT.</p>

<p>Yes sure but I was talking about WORKING distance, not focus distance. As I said, my body, the camera and the longer lens (90mm) would stay a couple cm behind compared to the 60mm one, but the end of the frond element would be at the same distance on both cases.</p>

<p>Well, Alan, your explanation was too technical for me. I understood there would be a difference in DOF but I couldnt visualize it in my head.</p>

<p>Andrew and Wouter, so you think there definitely will be a change in the perspective since the smaller lens would be fatally closer to the subject, and the longer, farther. Alright. But which kind of perspective gives the best macro shots? Or maybe values the subject the best? Im guessing the one that makes the background larger right? In other words, I should pick the 90mm due to how it render the image?</p>

<p>There is also an ecconomic aspect .... quoting recent prices if you want a CU lens for a large DSLR lens needing a 77mm mount the price was $144 whereas me needing only a 55mm for my MFT x10 zoom lens* the price was just $25. Both four dioptres from B+W at B&H NY.<br>

* 280mm AoV</p>

<blockquote>

<p>But which kind of perspective gives the best macro shots? Or maybe values the subject the best? Im guessing the one that makes the background larger right? In other words, I should pick the 90mm due to how it render the image?</p>

</blockquote>

<p>It depends on what you are going to shoot.</p>

<p>In terms of the subject itself, like a bug or flower, I really doubt you will notice a difference between the two. I switch between a 60mm and a 100mm entirely based on other factors, not how the bug or flower will look. The longer length will give a slightly flatter perspective, but because the depth of field at macro distances is so small, I doubt anyone will notice.</p>

<p>You may notice a difference in backgrounds. Because depth of field at macro distances is VERY shallow, backgrounds will tend to be quite blurred in either case. However, if you have a detailed background, you might notice a small difference. Longer focal lengths produce more background blur, which is not the same thing as depth of field. Because longer lenses have a smaller field of view, they effectively spread out the background more to fill the frame, creating more blur. You can see examples if you go to toothwalker.org/optics/dof.html and search for the section on background blur.</p>

<p>I never bother about depth of field as I know that it is unlikely to be <strong>that</strong> soft out of the camera and I can handle any need for softness in editing ... that is as a result of using bridge cameras until recently although I did have an APS-C DSLR for awhile but rarely used it. MFT made it redundant and it has been disposed of to a good cause :-)</p>

<blockquote>

<p>I switch between a 60mm and a 100mm entirely based on other factors,<br>

</p>

</blockquote>

<p>So these factors would be how much blurry you want the background to be? Or there are other things?<br>

<br>

ALso, at 1:1, you think Id be able to see an actual difference regarding background blur when comparing 60mm and 90mm? Cause I really like blurry backgrounds.</p>

<p><em>ALLAN M. Yes sure but I was talking about WORKING distance, not focus distance. As I said, my body, the camera and the longer lens (90mm) would stay a couple cm behind compared to the 60mm one, but the end of the frond element would be at the same distance on both cases</em><br>

don't think that is correct but I have no way to prove either way. Working distance and focus distance are the same. My bridge camera set-up with a two dioptre CU lens and the focusing ability of the lens gives me both a focus distance and working distance of between 20 inches with the camera thinking it is infinity and 13 inches which is at the camera's minimum focus distance at full 430mm zoom. Another of my cameras gives me a range of 20>9 inches but doesn't give me any more magnification becuase it is only a 280mm lens ... of course things vary when one zooms back for the composition required.<br>

I would have said that the back of the lens stays in the same place becuase it is attached to the camera ... perhaps I am being perverse with that comment ... sorry .... but most definitely I am sure the front of the longer lens will be further back from the subject than the shorter one becuase that is one of the arguments for using a longer lens is that you are using the narrower angle of view to achieve the same framing.<br>

We come back to the common misconception that for a tight framing you have to get in close ... you can do it that way but there are advantages in using the longer lens with a CU lens to overcome the inherant problem that long lenses are not made to focus close. An alternative of course is to use an extension tube.</p>

<p>As I previously posted: At 1:1 “unity”, the chip plane (focal plane) will be exactly 4x the focal length from the subject plane. If the focal length of a lens is unknown, one can set up a 1:1 situation, measure the distance, focal plane to object, divide by four, and derive the focal length with accuracy. The optical center (rear nodal) will fall exactly between the focal plane and the subject plane. Thus the location of the rear nodal can also be derived.</p>

<p>The length of a lens barrel is highly dependent on the location of the rear nodal. It is common practice when making a telephoto to set the rear nodal far forward of center. This design shortens the barrel making the camera with lens mounted more compact thus more manageable.</p>

<p>What I am trying to say, the working distance, front element to subject, is dictated by focal length and the position of the rear nodal. It is highly possible that a 60mm and a 90mm will have nearly the same working distance at a given magnification.</p>

<p>One more thought, the modern wide-angle is a short focal length lens, thus it has a short barrel. This places the rear lens very close to film or chip. This closeness can interfere with mirror swing on an SLR and the back focus distance being short may not adequately cover the frame. The solution is to shift the rear nodal so that it falls in air behind the lens. This spaces the lens far forward creating more back focus distance via a longer barrel. Such a design is commonplace and it is best described as an inverted telephoto.</p>

<p>Some gobbledygook from Alan Marcus </p>

<p>I wouldn't call it gobbledygook but a much deeper knowledge than I have although it reminded me of the exam question C&G set me back in 1953 when I had to set up a focusing scale for a bellows camera and I found infinity by halving the extension required for double extension :-)<br />Suggesting a tape measure for the intermediate distances they asked for They passed me with what I gather was a better than psss grade :-)<br />For some reason I didn't hear about nodal points until several decades into my carear.<br />Interesting reading<br>

edit ... you make a good argument for getting the 180 macro for practical use.</p>

<p><em>Well, if both lenses have the same working distance for 1:1, that means the image of a flower should be exactly the same regarding size, right?</em><br>

If the distance from the sensor to the flower at 1:1 is the same for both lenses then the image will look the same.<br>

<br /><em> But how about DOF and other properties that were supposed to be affected by the focal length?</em><br>

Same as above. And as others have pointed out the "official" focal length of a lens is only valid at infinity. At macro distances the focal length can vary depending on how the lens is designed. So the 90mm at infinity could easily become a 60mm at 1:1 if that's how it was designed. <br /><br /><em>Are they the same? What exactly changes between an image shot at the exact same conditions, same working distance?</em><br>

If the lens quality is the same then nothing changes.<br>

Again, the reason a longer focal length macro lens over a shorter one is preferred is because <em>if the focal length doesn't get reduced on focusing closer</em> then you have more working distance. But if it does then you gain little or nothing (depending on how much it's been reduced).</p>

<p>Guys Im lost now. Some of you are saying background perspective will change, like Dan M said, Id get a blurrier background with the longer lens; while other are saying nothing will change at all.<br>

Remember we are talking about 1:1.<br>

Can we reach a consensus regarding that?</p>

<p>Minimum focusing distance (MFD)=minimum distance from sensor to subject<br>

Mininum working distance (MWD)=minimum distance from front of lens to subject.<br>

<br />A longer focal length (FL) will give you a longer MFD. It will usually give you a longer MWD, but that depends in part on lens design, including whether the lens extends to focus. I don't know those details for the two lenses in question, so let's stick with MFD.</p>

<p>If you take a photo of a bug with these two lenses, both at MFD, the image size on the sensor will be identical. Because the image is framed the same, depth of field (DOF) will be similar. Perspective will be slightly different. Longer FLs flatten perspective, shorter ones do the reverse (e.g., bulbous noses in pictures taken with a wide angle lens). I doubt you will notice the difference.</p>

<p>A longer FL will give you more background blur, which is not the same as 'less DOF'. Please read the relevant section of the article I linked for you last time, which gives a clear explanation of this, along with photos demonstrating it.</p>

<p>You asked how I choose between my macro lenses. I choose almost entirely based on the working distance I want (MWD). Usually, I use plain backgrounds, so background blur is not an issue. When it is, I would see that as a reason to prefer the longer length.</p>

<blockquote>

<p>Can we reach a consensus regarding that?</p>

</blockquote>

<p>You've been around PN for a few years, and should know better than to expect a consensus here, on just about anything :-)</p>

<blockquote>

<p>We have various focal lengths for macro lenses, like 60mm and 90mm.<br /> Well, if both lenses have the same working distance for 1:1, that means the image of a flower should be exactly the same regarding size, right?<br /> But how about DOF and other properties that were supposed to be affected by the focal length?<br /> <br />Are they the same? What exactly changes between an image shot at the exact same conditions, same working distance?</p>

</blockquote>

<p>How about showing us a couple of shots using the two lenses with the same setup? Then tell us if you think they are the same, and see if we can agree, or most likely, disagree.</p>

<p>Well see, now that's a nice clarification. Cheers Dan M. I probably mixed up the MFD and MWD terms, now I got that. And I also thought there would be a significant difference between blur caused by those "30mm", but as I understand, at 1:1, it won't be relevant. I also understood that DOF will be the same.</p>

<blockquote>

<p>How about showing us a couple of shots using the two lenses with the same setup? Then tell us if you think they are the same, and see if we can agree, or most likely, disagree.</p>

</blockquote>

<p>I actually started the topic to help me choose the right lens, if I had the means to get by hands on both I would sure do the testing myself.<br>

And what I asked did not involve an opinion like, which tripods is the best?, I was looking for precise answers based on facts. I think expecting a consensus in my case is fairly reasonable.</p>

<p>One last thing. Do you guys think having a larger aperture, like f/2, would be beneficial at all for macro photography versus an aperture of f/2.8?</p>

<blockquote>

<p>One last thing. Do you guys think having a larger aperture, like f/2, would be beneficial at all for macro photography versus an aperture of f/2.8?</p>

</blockquote>

<p><br />Not for any macro work I do. DOF is extremely thin at macro distances. Usually, you end up struggling to get enough DOF, not to minimize it. I never shoot macros wide open.</p>

<p>Yes Dan, that makes sense.</p>

<p>Well...besides the aperture and the focal length, which became clear not to affect macro shots, I dont see other differences between these 2 tamron macro lenses that could help me make a good decision.</p>

<p>Do you have any other tips I could be using to make the right choice? Should I be leaning towards the 60mm cause it would be useful for things other than macro photography? (Im with a DX here).</p>

<p>Sorry for the delay in joining in... If we're accepting that the 90mm macro has the same minimum working distance as the 60mm macro, I guess we're saying that the 90mm becomes the same focal length as the 60mm as it focusses closer.<br />

<br />

Would it help if I broke that assumption? According to Photozone, assuming not talking about the new (expensive, stabilized) 90mm Tamron, its minimum focus distance is 29cm, vs 23cm for the 60mm. The 60mm is not too hot in the corners according to their review, while we're at it. The 90mm probably does shrink a bit, given that 29cm is less than 36cm (90mm x 4), but not as much as the 60mm.<br />

<br />

The depth of field discussion should accommodate that the 60mm is f/2 and the 90mm is only f/2.8. However, as others have said, it's unusual to be at full aperture at macro distances. While I've argued about its mathematical accuracy in the past (there's a small difference based on focal length, unless the depth of field is big) depth of field is <i>mostly</i> dependent only on relative aperture for the same subject size.<br />

<br />

I wouldn't necessarily argue that the 60mm is more useful on DX. 60mm is 90mm in FX FoV terms, which is a short portrait length (slightly longer than the 85mm that Nikon tries to sell for this). 90mm is 135mm in FX FoV, which is a long portrait length, and Nikon will gladly sell you a 135 f/2 DC. It depends whether you need a decent longer lens (I've used a 90mm macro on my D800 when I was on a trip and realised that I was going to be unhappy with every shot I got from my 28-200) and how you like to frame your portraits. The 90mm will lose the background almost as well as the 60mm and be optically better (and have more depth of field) doing it - background blur does depend on focal length.<br />

<br />

As an aside, the older 90mm is a little prone to LoCA, which goes away if you stop down. Look at the 100mm Tokina or a Sigma if you want to avoid this.<br />

<br />

Which is better for macro depends on whether you want to include the background (which you might for flower shots) or isolate the subject (which you might want for insects). More working distance is better for insects too - some people use a 300 f/4, and I can confirm that a 150mm macro was appreciably less troublesome than a 90mm for this. Personally I tend to go with distance, if only so that I'm not blocking my own light. However, I should point out that the front element on the 90mm macro is very recessed, which is a bit annoying when you're trying to get close to something, so it's not as convenient as you'd hope.<br />

<br />

I'd go 90mm, but YMMV. Also, extension tubes are more effective on shorter lenses, so you have another way to get a short macro if you later find you need one...</p>

<p>Hi Andrew! Nice thoughts, as always :)</p>

<p>Well, when I think about a second use for a macro lens, I usually think about something all-rounder, like Im on a short 1-day trip and Im only with that macro lens. Could I use it for other stuff besides macro in that case?<br>

Not so much regarding portraits, since I have a nice 85mm 1.8.<br>

<br />So, Im aware Id probably rarely use the 90mm for stuff other than macro, but not so sure about the 60mm...that's the catch for me. When I simply do not want to carry more than 1 lens, but at the same time would not want to lose a shot.</p>