Inexpensive macro experiment

A2000 wrote:

What do you think about the NiSi 77mm close up lens?

Let me start of by saying I rather like NiSi. I own two NiSi NM-180 macro focusing rails: they're well made, move smoothly and precisely, and impress me greatly.

So it's not the NiSi I object to, it's the 77mm.

TL;DR

Raynox DCR-250 gives you

• Better optical quality
• More magnification (it's a +8 diopter vs +3 for the NiSi 77mm)
• A lighter, more compact device to deal with
• A $70 price tag

The NiSi 77mm gives you

• The ability to shoot wide open with your f2.8 zooms, or even f1.4 primes, although the image is isn't the sharpest it could be.

And for that, you double the price, triple the weight, and lose a lot of optical quality compared to the Raynox.

And now, the whole story.

Am I saying the NiSi is "bad"? Far from it

The NiSi 77mm is a competent 2-element (achromat) closeup lens: it can hang in a fire fight along with more well-known achromats such as Marumi or my long-out-of-production Canon. But... 77mm diopters are a "one trick pony": they let you shoot wide open on big lenses. To get that ability, you pay a price in size, weight, optical quality, and, er, price (perhaps I need a different cliche than "you pay a price").

I'm weird: I own two 77mm closeup lenses:

• Marumi DHG Macro-200 (200mm or +5 diopter) at 174g.
• Canon 500D (500mm or +2 diopter) at 167g.

The NiSi is right in the middle of that:

• NiSi 77mm kid (300mm or +3.3 diopter), somewhere around 170g.

Why do I own two 77mm closeup lenses if I think that size is impractical? Because I like doing that one trick. I sometimes take a Nikon 85mm f/1.4, which becomes an effective 77mm f/1.4 when set to its closest focus (long story, not going to math you to death today). Those "diopter" numbers I keep mentioning are important. They tell you how badly you're screwing up. More on that in a sec.

When you add a 77mm lens (13 diopters) and a 200mm closeup (5 diopters) the diopter values add, and 13+5 = 18 diopters, or 50mm. With an effective f/1.0 speed. Add a modest 15mm worth of extension tube and it hits 1:1, while retaining that crazy speed. You can get the ultimate shallow-focus portrait of a butterfly that way, with tons of creamy bokeh. Not everybody wants this.

I also own two little closeup lenese:

• Raynox DCR-150 (208mm or +4.8 diopter) at 50g. (I need to find it!)
• Sigma "Life Size Adapter (200mm or +5 diopter) at 60g.

I won't get into the optical engineering issues, but when you make a lens larger, it has to be thicker, and that increases spherical aberration even at the same aperture. You would think that stopped down to the same final aperture, there should be no difference, but there is.

The Raynox is the shining star of this crowd. It's a three element design, and it's the smallest of the lot (the optic capsule is about 38mm in diameter). With a 208mm focal length, it about goes to 1:1 with a 200mm telephoto or a 70-200mm zoom (it was designed in the day where expensive f/2.8 "pro" zooms went to 200mm, but cheaper "amateur" zooms usually went to 210mm, and on a 210mm you get near exactly 1:1.

Isn't that bitty Raynox too small for your massive 70-200mm f/2.8, you ask?

Not unless you plan on shooting wide open. That's an aperture of 200mm/2.8=71.8mm

Stop down to f/5.6 and your aperture is 35.9, well within the 38mm Raynox path.

Yes, you say, but 77mm!

No, I say, but three elements instead of two. Given decent resources, if you tell any competent optical engineer to make you a 200mm single element lens, a dual element lens, and a triple element lens, the triple will be the best. Each new element is two degrees of freedom (focal length and distance from the other elements) that the designer can control. Two elements means I can correct four things: focal length, red/blue balance, and a bit of spherical aberration and field flatness. Three elements means I could correct color at a third wavelength (what they call "apochromatic" or flatten the field.

And you need it to be good.

Why?

When you combine lenses, the stronger lens dominates the optical characteristic of the team-up. You were talking about the B+W NL-4 "There's considerable CA, and the lens definitely seems to like shorter focal lengths". The NL-4 is a +4 diopter (250mm focal length). Your 70-200mm, at the longest setting, is +5 diopters. That's so close to the +4 of the NL-4 that the two lenses are contributing almost equally to the final image quality. You've basically limited your optical performance to that of a single element lens, which accounts for the "considerable CA" you mentioned.

Use it with your 17-55mm and, well, 17mm is +59 diopters, which totally dominates the equation, and even 55mm is 18 diopters, which puts much more of a fingerprint on the final picture than a +4 diopter closeup lens does.

Regards,

Ron