Originally Posted by
arthurking83
one thing to be careful of(in terms of technical specifications) is not so much the minimum focus distance, or MFD(close focus distance .. same thing) .. but more important is the minimum working distance of the lens.
What happens as some lenses focus closer, is that they shorten the focal length .. that's how the manufacturers get these macro lenses to focus close AND create lenses that are internal focus.
In the old days of lenses in general, and macro in particular, was that lenses used to grow really long as you focused closer.
Longer focal lengths more so than shorter ones .. but in general you had pretty good working distances from the front of the lens.
I think the elder type Tammy 90/2.8 ... not the newer one with VC .. has a good sounding MFD in that it sounded reasonably long at about 30cm, but as the lens extends forward to achieve macro magnification, the distance from subject to front of the lens starts to look quite small This lens also has a design where the front lens element is deeply recessed too tho!
This doesn't mean that the lens is no good .. tried it and is very good to excellent!
But the problem with short MWD values is that light shading can be an issue to account for.
That is, as the front part of your lens gets closer to the subject, you can block out quite a substantial amount of light sometimes.
Having said that, there is also the issue of trying to find such information too tho .. most manufacturers don't publish it .. but you can estimate it to a reasonable level.
Sigma 105OS macro lens length = 126mm + distance to film plane = 46mm total distance = 172mm
MFD of this lens = 312mm. Therefore MWD of the lens (for 1:1 obviously) will be 312-172 = 140mm
Sigma 150OS macro lens length = 150mm + distance to film plane = 46mm total distance = 196mm
MFD of this lens = 380mm. Therefore MWD of the lens (for 1:1 obviously) will be 380-196 = 194mm
You can see you get 54mm more working space between front of lens and subject in using the 150mm macro.
BUT!!! if you tend to use the lens hood as well(which I tend to do a lot on my Nikon 105VR!) .. be mindful of the length of the lens hood too.
** (just found some specs re the lenses with hoods attached .. the 180 is 40mm longer with hood .. so it still gives a 14mm advantage)
The reason I mention all this, is that it's really annoying to have to occasionally need to remove the lens hood from the 105VR as shading on the subject is so easily seen sometimes.
In terms of using the lens at 1:1 .. I doubt you'll see much difference(other than those extra 54mm of space to your subject without using a lens hood).
They're both going to be as sharp as each other .. give or take a few hairs here and there.
If you're just chasing insects around the garden .. I think the even greater working distances differences may be more obvious .. in that it won't scare all your favourite little bugs off as you try to get closer.
@ 150mm(as opposed to 105mm) you already are closer.
If you can justify the extra $400 expense .. always go for the longer macro(it's generally more of an advantage).
As for portraits .. both focal lengths work well ... 150mm on Fx is actually quite easy to do given enough space to work with.