Closeup Lens Mathematics

[Trius]

Sometimes I like to do things the hard way, and I suspect that you might, too! 😛

Anyway, for some perverse reason, I would like to use close-up lenses on my Oly SP and RC. Since no one that I recall made a close-up set such as the Auto-Ups for other RFs, that means I would have to calculate coverage, minimum focus distance, etc. OK, I know this is stupid and I'll be lucky to have even a few "keeper" shots, but the thought of those sharp lenses with great bokeh and a lousy 1 meter closest focus distance presents a challenge, no?

So, how do I calculate all the factors based on the power of a particular closeup lens? Some are marked in focal length, some are marked as +1, +2 ... +10, etc.

I was at least average in maths, (but great in other sciences, with a degree in biology & chemistry, so I'm not a high school drop-out) but that was a LONG time ago, and I figured there are younger geniuses on this great forum that might want to wade in.

BTW, I'll be incommunicado after tomorrow around noon, travelling on business. So if I don't reply to specific posts, I'm not being rude.

TIA!

Trius

 

[pvdhaar]

I hope you're a metric person;

when the lens is set to infinity, a 1 diopter makes it focus at 1 meter, a 2 diopter at 1/2 meter, a 3 diopter at 1/3 meter etc. I'm sure you can work out the 10 diopter case..

You could bend a metal coathanger in an appropriate shape and use that as a distance and framing guide. Some close-up sets which were sold for rangefinder or scale focussing cameras had such a thingamajig..

Oh, by the way, when stacking diopters, add their values. A 1 stacked with a 2 gives a 3 diopter, albeit with a lower optical quality than a single one.

 

[Trius]

Thank you, Peter. Yes, I am a metric person ... actually, I can operate in both worlds.

Regarding adding diopter powers: Does it matter in which order they are stacked? I seem to recall from yearas ago that there is a difference in effect.

Thanks again.

Trius

 

[denishr]

If you don't have a proper "Auto-up" accessory, which consists of the "frame" with TWO close-up lenses (one for the lens, and one (or two) for the VF), the best way I can think of is to test the close-up accessory that screws onto the lens is to try a "quasi-ground glass" technique.

That is, open the back of the camera and stretch a piece of "frosted" sticky tape across the film gate (where the film usually sits), and check the focus using a loupe on the image that forms on the frosted tape as you focus the lens. The only thing that you have to be careful with is to put the frosted tape EXACTLY on the same plane where the film is. Most cameras I've worked with (Kiev, FED, Leica et al.) usually have two sets of "rails" where the film rests. The film actually stretches over the inner set of "rails". You can also check the exact film position using a piece of already exposed (clear) film.

It's the technique often recommended for checking the infinity alignment, you can find the illustrations on many Web pages dealing with VF/RF infinity check (I think I've seen it also on Matt Denton's Web site).

Since I'm kind of "hands-on" person, I'm usually sure only in the results I can actually see 🙂 More reliable than my math, I'm afraid 😉

Denis

 

[ErnestoJL]

I would recommend to use a small piece of fine frosted glass. I´ve ordered to an Optics technician one piece with small metal frame which seats exactly where film does allowing me to check lens adjustment. I was using a matte focusing screen (I don´t know where or when it came from) from an old SLR, but it had no means of holding it in place safely. The "Custom made focus check device" can go for just USD15 / 25.

 

[Trius]

Thanks to everyone. I will probably end up using a focusing aid at the film plane to get me started, do some testing, and record the results in some sort of table that I can refer to for actual shooting.

Triius