Macro with a 180mm

[DonSchap]

I know that several of you have been shooting macro with various lens lengths.

I was recently entertaining the idea of buying the 180mm f/3.5 Macro 1:1 for my FIRST true macro lens. Is there any reason this would be a preferred lens over the 90mm Macro or a 50mm f/2.5 with life-size extender?

Thanks in advance and afterwards (cover the bases)

[adam75south]

yea, it's so the spider doesn't jump on you.

[Prospero]

Adam is right, the working distance of a 180mm macro is much larger, which can come in handy with subjects that scare easily (e.g. insects). A disadvantage is that the DOF you get with such a long focal length will be much smaller than with ~100mm, and thus the lens needs to be stopped down a lot more, sometimes giving shutterspeeds requiring a tripod.

[coldrain]

I am not sure about a shallower depth of field. Normally when you talk about wide angle vs longer focal lengths that is that way, but we are dealing with lenses that all get used to make 1:1 images... I have the feeling (but can't get it figured out right now) that the tele macro's actually allow for a bigger depth of field?

[Prospero]

I may be wrong about the shallow depth of field, it is what I kept reading everywhere when I researched into these lenses (I might get one myself somewhere this year). I believe that what makes macro lenses different from normal lenses (focussing distance aside) is that they can be stopped down a lot more without showing signs of diffraction. Not that they give more depth of field at equal settings as regular lenses. Therefore, normal depth of field formulas should apply.

[coldrain]

What makes a macro lens a macro lens is basilaclly being able to get closer than a normal lens of same focal length to a subject. What exactly causes one lens to diffract more than another is not totally clear to me. What diffraction basically is, is light behaving quite strangely like water when entering a narrow mouth of a harbor of something. Along the edges (the pupil or aperture of the lens) the light gets bent a bit more or a bit less, and this causes light to hit neighbouring pixels at certain aperture settings.

Probably the positioning of the aperture (diaphragma as we call it) has to do with it, but for the rest I have no idea.

I do know that I like longer focal length "macro's" I make with my 70-200 f4 L + 1.7x TC more than with my 90mm macro most of the time, because of compositional and tele shortening reasons.

[Prospero]

What makes a macro lens a macro lens is basilaclly being able to get closer than a normal lens of same focal length to a subject. What exactly causes one lens to diffract more than another is not totally clear to me. What diffraction basically is, is light behaving quite strangely like water when entering a narrow mouth of a harbor of something. Along the edges (the pupil or aperture of the lens) the light gets bent a bit more or a bit less, and this causes light to hit neighbouring pixels at certain aperture settings.

Probably the positioning of the aperture (diaphragma as we call it) has to do with it, but for the rest I have no idea.

I do know that I like longer focal length "macro's" I make with my 70-200 f4 L + 1.7x TC more than with my 90mm macro most of the time, because of compositional and tele shortening reasons.

Both types definitly have their uses, when taking 1:2 macros, the closest my kit comes to real macro, in some cases I really like the perspective of the 17-70 when compared to the 70-300. On the other hand, the 70-300 is more convenient, I can use the flash without the lens blocking the field and the background can be less distracting due to the smaller angle.

It turns out that my point about DOF is not valid, I read it a lot on the internet, but it turns out to be a misconception based on comparing lenses at similar focussing distances rather than similar magnifications. The issue is more complex, as can be read here: http://www.vanwalree.com/optics/dof.html, basically both types of macro have the same depth of field, but distributed differently (in the link it is explained better).

[DonSchap]

One of the aspects to this particular lens is that is uses two LD glass elements to compensate for the chromatic aberrations that "Coldrain" spoke of. Image sharpness tends to fall off as chromatic aberrations become apparent with closer focusing of telephoto lenses.

If this sharpness is the real difference between the 90mm and the 180mm, other than the lens not changing physical size during focusing and it weighing more than twice as much, then maybe it's worth the extra coin. Speaking of which .... I came across this visual comparison ...

Courtesy of Tamron Lens Company

They are listing the minimum focal distance for the 180mm as around 18.5" (versus 11.4" for the 90mm). You will definitely have to back up a bit ... but with the doubling of the focal length ... the result seems to be about the same, except for the perspective.

[coldrain]

No Don, I did not talk about chromatic aberrations here at all... just about diffraction. And that is something that occurs at the diafragma/pupil/aperture, chromatic aberrations are when different wave lengths of light travel to glass in different paths.


They have nothing to do with eachother. And no, the 180mm tamron is not sharper than the 90mm tamron. The difference is just that one is a 180mm tele lens that allows you to focus closer than other 180mm lenses, making it a 1:1 macro, and the other is a 90mm "portrait tele" lens that allows for closer focussing than a normal 90mm lens... making it an 1:1 macro.

As you can understand, since the field of view of a 90mm lens is WIDER than the field of view of a 180mm macro... you NEED to get closer with the 90mm lens in order to get the same 1:1 magnification.

And here in lies the biggest difference... the 180mm macro allows a bigger distance to the subject to get the same magnification. And the field of view of the background with the 90mm will be wider than the 180mm lens.

Simple. Nothing to do with CA, diffraction or what not. Just with size, weight, funds and focal lengths.

[adam75south]

fear the spider.