50mm macros in general use

Started Jul 29, 2010 | Discussions thread
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RS_RS Senior Member • Posts: 1,773
Re: 50mm macros in general use

Just a few further comments to supplement my previous post.

When saying that some lenses designed for 1.6-factor Canon bodies would not fit at all onto FF bodies, I was, of course, referring specifically to EF-S lenses. If an off-brand 1.6-factor lens does fit onto a FF body, it will indeed almost certainly vignette at least at some settings, and image quality will drop away pretty badly as well.

My comments about the downsides of the 50/2.5 were clearly stated to be relative to the (original) 50/1.8, since that is the lens that the OP is looking to compare it with. The other disadvantages, such as slow noisy AF and lack of full-time manual focus, are shared with all EF lenses of that generation.

The comment that the 50/2.5+LSC package is expensive for what it offers is certainly right, but that's because the LSC costs silly money new for what it is, and may be hard to find s/h. If you are content to stay in the range to ×0.5, the lens alone is not an expensive option even new, and can be found s/h at quite good prices.

As I pointed out, the 50/2.5 does not have a focus limiiter switch. But then, neither does the EF-S 60/2.8, a defect on an otherwise excellent lens.

A simple 50mm lens at ×1 has the plane of focus 100mm from the lens. Since the lens is usually fairly deeply buried in the mount (to make room for the focusing mechanism), and for a real lens the nodal point is not at the very front of the glass, that can easily result in a working distance (from the front of the mount to the plane of focus) that is inconveniently short. It was probably the problem of trading off working distance against space needed for the focusing mechanism that meant early standard-focal-length macro lenses were usually limited to ×0.5 – they worked fine optically at ×1 on an extension tube.

The 50/2.5 is different. At ×0.5 the working distance is just over 100mm, and there is no problem for lighting (based on my own experience of using it both with natural light and with macro flashes over many years), only the quite separate problem that you may be too close to a live subject. Then you add the LSC, and you are then working with a 70mm lens not a 50mm lens. By that stage the lens is so complicated optically that you don't learn much from calculations, but the working distance at ×1 is actually 75mm – I just measured it. That's short, but perfectly adequate for a macro flash.

Interestingly, a typical 100mm IF macro lens focused at ×1 also has a focal length of about 70mm. However, the different optical design results in a better working distance – for the Caon EF 100/2.8L IS it is about 130mm, which does not do a lot to solve the live subject problem but does cope entirely adequately with lighting issues.

Finally, I agree with Steve Balcombe that one use where the 50/2.5 really shines is for copying work. It is my standard lens (on FF) for photographing oil paintings, which I do quite a lot. For most of my botanical fieldwork I use the 100/2.8L IS on FF, and for butterflies and dragonflies I use either that lens or even the 135/2 on an EF25 tube on 1.6-factor.

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