[Melanie Crause]

Hi every one, I have just stumbled upon a site explaining diopter lenses. Have any of you tried it? did you get good or bad results? do you think it's worth the effort?

[RioRico]

+Dioptre closeup lenses are cheap fun. They aren't optically corrected, so they have aberrations, especially around the edges of an image. You get cleaner images using macro tubes or bellows -- but such extension eats light, which +dioptres don't. Corrected versions are made by Raynox and others, which can produce brilliant macro results, but cost rather more. Price comparisons:

* Set of +1+2+4 dioptre lenses, maybe US$12-20
* Stronger +10 dioptre lens, maybe US$10-20
* Corrected Raynox DCR-150 or -250, US$60-75

The dioptre lens cost vary with their size. Those meant for host lenses with 49mm threads are smaller and cost less than those for 62mm threads. The Raynox lenses come with a snap-on adapter that fits anything from 52-67mm threads, and can be forced onto a 49mm thread.

But the main advantages of +dioptres are: cheap; simple; don't eat light. I have several sets. I write about these a little here: https://www.pentaxforums.com/forums/pentax-lens-articles/152336-cheap-macro-b...lose-work.html and I'm writing articles now specifically about putting stuff in front of and behind camera lenses. Stay tuned!

[Lowell Goudge]

as the title implies, this is a quick and easy introduction to macro and lens magnification.

there are basically 3 ways to get increased magnification from your lens
1) use extension tubes to allow you to focus closer.
2) put another "lens" in front either a diopter lens or a prime lens with a reversing ring as they are effictively the same
3) put another lens behind your lens (teleconverter)

option 1 allows you to focus closer than the lens focusing helix would otherwise permit, since magnification is the ratio of lens to focal plane / subject to lens adding an extension tube and focusing closer increases magnification.

using another lens in front of your lens alters the maximum focusing distance, and reduces the effective focal length of your lens, however, as you increase magnification the image gets darker

Option 2) achieves magnification by modification of the lens focal length. if you consider that the diopter number is really 1/focal lengh of the add on lens, and that when you add diopters (or a reversed prime) to the front of your lens, the resulting focal length is 1 / ( 1/FL1 +1/FL2) but you now are at the distance from the focal plane of the prime lens (FL1) which is greater than the new focal length, you no longer focus to infinity but your close focal distance is now FL2

so you achieve close focus by changing your focal length. The advantage here is that the lens actually gets faster, because you have not changed the physical aperture diameter of the lens,and the focal length is shorter (Remember F number is focal length over aperture)

option 3 a teleconverter basically spreads the image out further, i.e. it multiplies the focal length by between 14x and 2x depending on teleconverter, but because your physical aperture does not change, the F number gets bigger (i.e. slower and less light) and the image gets darker.

[Melanie Crause]

Thanks guys!!

I'll visit the camera shop next week and keep you updated!!