diopter

I've heard discussed many times on this site the need for some lenses to have a diopter . Measurements have been state of +1 to +4 and I'm sure there are others.

I'm not really sure I understand what is being talked about.

I thought a diopter was an adjustment that can be made to the view finder and have nothing to do with the actual image, its use was only to adjust the view finder for people with different eyesight.

So I am most likely wrong since my understand does not flow with the way the term has been used on this site.

From what I am picking up, I now think that a diopter is an adjustment to focal length made by attaching a lens filter. Is this correct?

Supplementary diopter lenses have been called everything from close-up lenses to close-up filters to supplementary lens attachments. Actually, supplementary diopter lenses are not filters but are actual lenses with long focal lengths and are attached to the front of a camera lens by screwing into the camera lens' filter threads. (That is probably how they have become known as "close-up filters". They really aren't filters because don't filter anything!)

For the sake of clarity I will refer to supplementary diopter lenses simply as "supplementary lenses". Cameras lenses are like "farsighted" people and we add positive diopter supplementary lenses to camera lenses to allow camera lenses to focus closer than normal. The use of supplementary lenses is an inexpensive method of decreasing the minimum focusing distance of a camera lens. (In the photo, on the left, the diopter lens is on the right along with a 55mm/52mm adapter ring on the left.)

For macrophotography, I have a Nikon D70 with a 60mm Macro lens which allows me to focus as close as 1:1, and I can take a fine image of the hair on an insect. I also have a 28-300 mm Tamron zoom lens, and it is extremely versatile, but it will not focus close enough for macrophotography. So I add a Canon 500D "close up" suplemental lens attached to the front of the Zoom lens and I can now focus that lens to a magnification of 1.2:1 and I do not have to carry around the extra macro lens. I cannot tell the difference. The cost of the diopter was about $100 while the Nikon Macro lens was near $300 and adds weight to my kit.

Hope this helps.

The diopter has been the subject of a lot of discussion because of the use of dome ports with housed wide-angle lenses: the dome port acts like a lens itself, and not all housed lenses can focus on the image made by this extra optical element. Lenses that focus at short distances and big domes don't need diopters, but smaller domes and lenses that focus at greater distances do. Wide angle lenses need dome ports, so you can't escape from this topic if you want to take "seascape" pictures.

Some of the best explanations are in the "Features" menu on Wetpixel.

I have a 170mm dome and though a Nikon 10.5mm fisheye lens doesn't need a diopter, a 12-24mm lens works best with (I think, others argue about it) a +3D close-up lens behind this port and an extension ring. I'm trying to investigate the use of a mid-range wide-angle lens with a +2D close-up lens behind a smaller dome to take undistorted images of shipwreck artefacts.

I used to have a compact digital camera (Nikon Coolpix 5000) that had such good close-up capabilities that it didn't need a diopter, but with a DSLR I'm grappling with diopters now. You should be able to work out what is needed by calculation, but some trial-and-error is needed (and an excuse to do some more diving?).

Since "diopter" is just an optical term (the reciprocal of a lens' focal length in meters), any lens can be described as a "diopter", and that's why the name is also given to the variable correction applied to some viewfinders.

B)

thanks for clearifying this.