Why are +0.4, +0.5 diopters more desired than +1 diopters?

[harharj]

Can some explain to me why +0.4 and +0.5 diopters are more desirable than +1 diopters? Are +1 diopters terrible? I would assume using +1 would grant the user the the option of being able to shoot at the distance a +0.5 allows and closer since its +1. Maybe someone can enlighten me on the pros and cons of each diopter strength.

[richg101]

if you can find a +1 achromat it'll still be a great addition to any lens collection.  a +0.5 non achromat isnt really that special since it doesnt correct for CA and using on anything more than a small sensor/aperture it'll degrade the optical quality.  But the reasons a +0.4 achromat is more desirable than a +1 achromat is this:-

 

a +0.4 achromat will reduce the minimum focus distance of your lens to almost half it;s original minimum focus (if you have a 1m minimum, the +0.4 achromat will change minimum to 0.6m.  However due to the weak diopter value it will still allow focus to all the way to 2.2mtrs.  this is a really good focus range for racking indoors.

 

a +1 achromat will reduce a 1m minimum to 0.2m so can get closer, but maximum distance when the lens is set to infinity will be 1 meter.

As a result, your focus pull range is drastically reduced.

 

So to answer your question, the reason is that a weaker diopter value lends itself well for users requiring focus pulling between 0.6m - 2.2m - still a rather useful range for medium/close shots, or powerful closeups from fast 85mm lenses which tend to have a minimum focus of 1m or longer.

[ken]

The key word is achromat.   Here has a useful info: http://fuzzcraft.com/achromats.html

Even if I never use close up lens, but I think if you shot closest distance by 2x lens limit, mostly at 1.5m/5ft, you might get far less than 2x images, maybe 1.85x or even less.  The +0.5 lens might help to keep images as close to 2x as possible.

[Policar]

I'm yet to be convinced that the difference between an achromat and a good single-element close up filter is terribly substantial (I would be happy to be proved otherwise, if anyone wants to pit a Tokina 0.4 against a Tokina 0.5 I'd love to see the results!), but the 0.4/0.5 strength gives you a really useful focusing range with an Iscorama, whereas no filter gives you infinity to 6 feet (too far to too far) and a +1 gives you too close to too close.

I don't get it, though. Most lenses aren't apochromatic and a 0.5 filter won't ruin your optics much. I don't think a decent 0.5 single-element filter will ruin the party tremendously, though I guess if you're spending $4k on an Iscorama, why not drop a few hundred extra on the best CU filter you can find.