This review will cover the Hoya 3 piece close-up set with diopter ratings of +1, +2, +4.  The lens used will be the Minolta 35-70mm F/4 for the most part, and a few comparison shots at the end with the Sony 28mm F/2.8, each mounted on the Sony A700 DSLR.   The little lenses reviewed here are a good way to save money, weight, and space on photo expeditions instead of packing an expensive macro lens, though they really won't replace a good macro lens.    My set appears to be plain clear glass.  The Hoya manual doesn't say anything about them being coated, but eBay dealers are listing the items as "coated" so I'm not sure about this.  My set was purchased in the late 1980s, though they look exactly the same today.  Update; newer sets are multi-coated.  Quality seems good, they look and feel like glass with a metal ring,  but I didn't try any destructive testing to confirm the materials used.  The set comes with an instruction manual and nice carrying case.  There isn't much else to describe about the lens set or filters as they are sometimes called.  They sell on eBay for around $20-$50 depending on the size, mine are 49mm.   These single element lenses are nothing more than a magnifying glass mounted to the front of your camera lens.  You can use them singly, or stacked in any combination, though image quality degrades significantly when all three are mounted together.  Also, like a magnifying glass, you can't focus to infinity, or much farther than close focus on your lens.  Depending on the diopter rating, focusing will extend to just a few feet (a meter or two).  The higher the rating, the closer your focus can be etc.  On a minor note; the +4 lens does a good job at starting fires using the sun!  That's another reason to carry one with you on your photo outings should you get lost.   Flare and ghosting are strong when near the sun, but it shouldn't be a problem in actual use.  Since the main objective of this set is to shoot close-ups within obvious reach, you'll probably be shooting at subjects on a level to downward angle, with the sun coming from your back or sides, so the only bright points of light would be the occasional reflections.  On the Sony 28mm F/2.8 lens, the built-in hood will extend over one close-up lens only, but it doesn't help curb reflections.     CA is surprisingly absent from the images using only one lens.  I see a little secondary lateral in the crops from the corners with two lenses stacked, and here it isn't bad at all.  It probably is originating from the lens itself.   The corners are pretty sharp, even with two stacked, and I noticed no light fall-off to speak of.    Bokeh seems about the same when the lenses are used.  I thought initially it would be a bit smoother because the close-up lenses can't focus more than a few feet away.   There's a loss of contrast when using more than one lens at a time (stacked).    Auto-focusing works with the lenses in place, but it's not really practical for close-up work, use manual and move closer or farther away as needed.    Let's begin our review with a few product shots.   Box and set. Good fold-up carrying case. Three lenses Inside the vinyl pouch.   Let's look at the differences as each close-up lens is added and stacked.  Lens used is the Minolta 35-70mm F/4 in macro mode with a magnification of 0.25x.  Full images below, not crops.  The subject is a standard US stamp 1" x 3/4" (25.4 x 19mm), the same one I use for my macro pictures.   None +1 +2 +4 +4, +2 +4, +2, +1   Now you know how close you can get with each lens, let's look at crops to see the detail.   None +1 +2 +4 +4, +2 +4, +2, +1   Everything is pretty sharp up to the last image, where you have 3 lenses stacked, so don't bother doing this.  You can also see the contrast drop when you stack 2 as in the +4, and +2.  I'm off a little on my exposures from the top, so don't pay attention to that.    None +1 +2 +4 +4, +2 +4, +2, +1   Again, the last shot sucks, 'nuff said.  Realistically speaking, it would be hard to use the +4, +2 in the field.  I'm thinking it would be just as good to keep the +4 alone as the next step up requires you to be so close it's tough to get anything in focus, since you have little DOF, and you're going to be dealing with shading from the lens itself.  I had to stop down one or two stops from normal for maximum sharpness when stacking the lenses.    Below I've made a chart to show the actual distance from the front of the lens to the subject.  This will vary depending on your camera lens model.  I used the Minolta 35-70mm F/4, so these are the figures for that lens.  All figures are for the minimum focusing distance.  You can probably use the diopter ratings and percentages based on the figures below to estimate distances-to-subject with your own lens.   Lens Minimum distance from lens to subject None 7 7/8" (198mm) +1 6 1/2" (165mm) +2 5 3/4" (146mm) +4 4 7/16" (113mm) +4,+2 3 9/16" (90mm) +4, +2, +1 3 1/8" (79mm)   Below, check out the cropped shots with the Sony 28mm F/2.8 lens.     Sony 28mm @ F/5.6 None +4   The wide angle Sony 28mm has an anemic magnification of 0.13x, but turns in a decent close-up using the +4 diopter, with an approximate magnification of 0.23x.   Conclusion.   These little close-up lenses are actually quite usable in my opinion.  Ultimately, you're not getting true macro performance with these lenses, but for the price they're very good, and they're very convenient.  Would you rather haul around a medium sized macro lens with your regular walk-around lens while hiking or vacationing at the tourist traps, or just slip a little close-up lens in your shirt pocket just in case?  I was surprised at the quality results, good color and contrast using one lens, and the corners held up nicely, though for close (not flat) work corners rarely matter.  This is a super-cheap way to go, and I highly recommend them.