imagemeister Loc: mid east Florida

Use with a step-up ring - https://www.ebay.com/itm/Top-Mint-in-Box-Canon-Close-up-Lens-500D-72mm-Screw-In-Lens-Manual-From-JAPAN/402390618949?hash=item5db0599345:g:iroAAOSwmqtfAuDD
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bleirer

That is cool you did that. The Canon 250d is 4 diopters and is a high quality double glass version. You can get 52 or 58 size threads.

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Diopter spec of any lens is the inverse of its FL (FL stated in meters). So a one meter lens is a one diopter lens. A two meter lens is half diopter lens. A half meter lens is a two diopter lens.

Diopter specs are additive. Thaz why diopter spec is more convenient than FL spec when combining lenses. Combine lenses of half diopter and one diopter and you have a 1.50 diopter lens, which acoarst has a FL of 1/1.50 meters which solves to 0.66666 meters.

Your camera lens in question thus has a diopter spec of 1/0.135 diopters which solves to 7.41 diopters. Combine a two diopter lens with that and you have a 9.41 diopter combined lens whose FL is 1/9.41 meters which solves to 0.106 meters.

Now you know why combining a “2 diopter” lens with “135mm” lens creates a “106mm” lens that focuses closer than the “135” did on its own. The lens barrel was built for 135 tele but is now carrying a 106 tele. The barrel puts the 106 tele 19mm beyond its infinity focus distance from the sensor. In effect you have a 106 at its infinity focus connected to a 29mm extension tube. Thaz why it’s focused to a subject distance of one half meter ... the extension tube.

By the same formula, a 3 diopter “CU lens” will produce a 10.41 diopter combined optic which is a FL of 93mm so your excess barrel extension is 42mm. The result will be approximately 1:2 image size. Your defacto “extension tube” is about half of your FL (93mm) which gets you “half life size”. Since 42 is not quite half the FL, just turn the focusing ring away from the infinity mark to get a bit closer.

But if you need 1:1 image size, you need to shorten the original 135 tele to waaaaaay shorter than 106mm. Conveniently, a 1:1 image size occurs when any lens is at “double extension” vs it’s infinity focus position. IOW you’re stuck with a lens barrel that provides an extension of 135mm, so you must alter the optics to a FL of 67.5mm which is better stated as 0.0675 meters, which is 1/0.0675 diopters. Ain’t that peachy ?

1/0.0675 = 14.8 (diopters). The original “135 tele” has a diopter spec of 7.4 so it needs a 7.4 diopter optic combined to it to reach 14.8 diopters. Thaz the whole set of three “CU lenses”, the +1, +2, +4 set which is optical hell. Maybe you can find a +7.4 “CU lens” somewhere ... rotsa ruck widdat. Didja notice that archive 1:1 (at inf’y position) the additional optics have the same FL as the original lens ? That acoarst is scalable.

Scaling away ... where’s your 0.30 meter tele ? You call it “my 300”. We can also call it your 3.33 diopter tele. So if you hang a +3.33 “CU lens” on it you have 150mm combined optic at double extension (300mm from the sensor) and acoarst since at 1:1 everything is symmetrical, the lens is equidistant from both the sensor and the subject. IOW the subject is 600mm from the sensor. If you can’t find a +3.33 “CU lens” just use a +3. You can move the focus ring off its infinity mark to get a bit closer.

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Typo in above post:

19mm should be 29mm.

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A +4 won’t get nearly 1:1. Would need about +7 or 8 for that.

blackest Loc: Ireland

beautiful but is it missing the native lens magnification?

RWR Loc: La Mesa, CA

I was going to photograph a scale with a single element 3 diopter close-up lens on a 135mm lens, but since you have tested with your own lenses there would be no point. I will only add that you would get better IQ with achromat close-up lenses. Good luck!

bikerguy

The website for Cambridge in Colour has a calculator that will help you decide what dipoter you will need.
By inputing the native magnification and focal length of the lens and the diopter the calculator will provide the maximum magnification and working distance.

https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm#calculator-closeup

bleirer

Seems his math also agrees with the OP's, but its cool the OP persisted in working it out. Looks like the OP would get close to .5x magnification with the 2 diopters.

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3 diopters will fall just short of 1:2 with a 135 set to infinity. The combined optic has a FL of 93mm but is located 135mm distance from the sensor. A 93mm lens needs to be 140mm from the sensor for a 1:2 image size. Most any conventional 135 lens has that 5mm available via its focus helical.

The math is slightly different for an IF lens, but close enough for rock and roll.

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Lenses in and of themselves have no magnification worthy of concern when at their infinity position. If you are referring to the magnification provided when a lens is extended past it’s inf’y position, that has been allowed for in minor mentions but it can only be considered a minor tweak. All the math relies on the lens at its inf’y position cuz the built in extension is an unknown dimension. IOW the lens’s focusing mechanism is basically just a “fudge factor” ... unless acoarst the mechanism is unusually extensive, such as in a macro lens.

bleirer

So can you explain 'native' magnification, as in they always tout the Canon 100-400 ii because it has something like .24x native magnification. And the Cambridge in color calculator linked above add in native magnification in the calculator.

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Already explained above.

fetzler Loc: North West PA

I really wouldn't waste money on such lenses they are almost always very bad. Raynox lenses are rather good however but they are not cheap. I have three they range from +8 to +32. I use them with a macro lens for high mag work.

I would invest in a good set of automatic extension tubes. These work well.

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Just as a reality check I put a 2.2 diopter lens (canon cu 450) on a very typical unit focusing 135 tele.

As per calculations for infinity position, it does not manage 1:2 image size. But with the helical maxxed out to the 1.5m mark on the focus scale you can get there.

Field of view at infinity and 1.5m (per the focus scale) measure about 4.5” and 2.8” (long side). So if you need a range of 1:3 to 1:2, this works well enough.