Extensions for Macro

[480sparky]

ET's don't change the focal length. Nor the 'crop-factor multiplier'. They only change the magnification ratio.

70mm is 70mm is 70mm is 70mm all day long.

 

[Overread]

Ignore crop factor.

Crop factor ONLY applies when you are comparing lenses between different sensor sizes in order to get an idea of the difference. So you don't need to factor it into the calculation; just use the actual focal length of the lens itself. The calculation I posted is to calculate the magnification of the lens

So for example a 50mm lens with 25mm of tubes would be

(tube length in mm/focal length) + lenses native magnification = power to :1

We shall assume native magnification is 0. It won't be, but if its not a macro lens it won't be a typically high value

(25/50) = 0.5:1 - or half macro.

If we push the tube length up to 50mm then

(50/50)+0 = 1:1 (ergo true macro that a macro lens would give)



Now if we used a 50mm macro lens with 50mm of extension tubing at the lenses closest focus (ergo maximum magnification) we'd get

(50/50)+1 = 2:1 ergo twice the magnification! (also called twice life size as now the subject is being reflected twice its original size on the lens)

 

[smoke665]

@Overread ok that makes more sense. In your first post you had divide the "focal" length by the "extension" .

Reversing those and using my lens example above 12mm extension/ 70mm focal length = .1714. Add the inherent magnification of .12 and I now have an effective magnification of .2914.

Using the first math I was coming up with almost 6x. No wonder the brain was overheating.

 

[Gary A.]

smoke665, it's only $125 ... you blow that on gasoline every other day. Stay home one day and just get the damn tubes. Hands on testing is the best way to figure out what works and what doesn't. I have a garage full of slightly used stuff that doesn't work for me.

 

[Overread]

oooops - I'll go change that!

 

[smoke665]

oooops - I'll go change that!

Decimal points and The Order Of Operations are the downfall of us all! LOL

 

[Derrel]

Smoke,
If you want to get into high-magnification macro work, the best course of action is to use a long lens on the camera, and then a reverse-mounted (filter thread-to-filter-thread reversed), short-length lens on the front of the long lens. Something like say a 24mm mounted in-reverse on the front of a 200mm lens.

Please check out some of the great stuff that comes up on the web and YouTube!

reverse-mounting a lens on another lens for macro photos - Yahoo Search Results Yahoo Search Results

Now, as far as extension tubes go: the 12mm and the 20mm lengths (approximate range; may vary by 1 to 5 mm, based on brand! There are 12mm and 13mm and 20,24,and 25mm tubes, in different brands!) are the MOST-useful, so a whole set of three is not a necessity! The 36mm tube that comes in 3-ring sets? That tube has been, in a practical sense, utterly useless to me, for decades. Seriously.

Another option is to use a 1.4x teleconverter and a telephoto lens, along with a short 12- to 20-mm extension tube; the TC increases magnification, the extension allows close-than-otherwise focusing distances to be used. The Nikkor 300/4 AF-S + TC14e-II has worked well for me in the past in this manner with the Kenko AF tubes.

Speaking of which....if you have a tele-converter, many people have suggested breaking the glass out of it, and using THAT as a de facto extension tube. I mean...it has the front and rear lens mounts! Perhaps you'd feel more comfortable buying a low-cost, used Pentax AF-capable 2x teleconverter, and removing the glass elements? Maybe use the truck and a block-and-nail to run over it? lol!

 

[petrochemist]

@Derrel so if I understand correctly what you and @Overread are saying, the use of extension tubes on a lens like my Pentax 35 Ltd macro, wouldn't really be of significant benefit as it's already 1;1 and has a minimum focus distance of just under 6 inches?

A longer lens would benefit much more from extension; the 70 or 77mm lens length would make much more sense to use with an extension tube. I think the 35mm lens length would likely not work very well with extension.

When reversed a 35mm works VERY well with extension.
Longer lenses need more extension to reach a set magnification, so extension can get very unwieldy with longer lenses. A 300mm lens would need 300mm extension to go from infinity focus to 1:1 with older lenses that move the entire lens to focus that makes the lens around a foot longer for 1:1. Possible with bellows but not practical.

If the working distance isn't an issue short focal lengths can easily get very high magnifications. IIRC my microfiche lens (~17mm focal length) gave me 4x easily enough.

 

[adamhiram]

The bottom line with extension tubes is they just allow for a shorter minimum focusing distance. I actually found the lenses that work best to be the opposite of what I would expect. For example, a 35mm that already has a 12" min focusing distance actually benefited quite a bit from extension tubes, provided you are actually able to get extremely close to your subject; I'm not sure the difference would be so dramatic if you can already focus at 6". I found 50mm to be the ideal focal length for extension tubes - with 68mm of extension tubes (all 3 stacked), I can get about 1.5x magnification at a distance of 1.5" - just enough to let in some light. I can get the same with a 35mm lens and 56mm of extension tubes, but am literally 1/8" from the subject, which is not really practical.

I originally assumed my longer telephoto lenses would be perfect - imagine a 200mm or 300mm lens that could focus just a few inches away - but that just wasn't the case. Besides only giving slightly closer focusing distances on longer lenses, they tended to be too heavy and put a lot of strain on the camera's mount when used with extension tubes.

The other path many people go is to get a reversing ring, typically used with a 50mm prime with manual aperture ring, along with a bellows which is basically a much longer adjustable extension tube. You can still do this without breaking the bank, but of course it's not nearly as affordable or simple as just adding extension tubes to what you already have. Honestly I would recommend just picking up the Kenko extension tubes to play around with for $124. You'll use them eventually...

 

[smoke665]

@Derrel, I've looked at that option also. Just somehow seems wrong, like going in the back door and backing out of the front door. LOL I already have some close up filters that provide magnification without a substantial degradation in image.

 

[petrochemist]

Smoke,
If you want to get into high-magnification macro work, the best course of action is to use a long lens on the camera, and then a reverse-mounted (filter thread-to-filter-thread reversed), short-length lens on the front of the long lens. Something like say a 24mm mounted in-reverse on the front of a 200mm lens.

Please check out some of the great stuff that comes up on the web and YouTube!

reverse-mounting a lens on another lens for macro photos - Yahoo Search Results Yahoo Search Results

That's my most commonly used technique as I usually have both long & short lenses with me.
I find Coupling lenses for extreme macro to be a great resource on this technique & the rest of Johan's site explains the other options pretty well too.

Macro does get very tricky at higher magnifications whatever technique you use, even the tiniest movements become critical.

 

[Derrel]

@Derrel, I've looked at that option also. Just somehow seems wrong, like going in the back door and backing out of the front door. LOL I already have some close up filters that provide magnification without a substantial degradation in image.

YES--the high-grade, two-element "achromat" type close-up filters, also called close-up lenses, can work wonderfully! Canon makes the 250D and the 500D models, and Nikon made the 5-T (52mm threaded) and the 6-T (62mm threaded). These are NOT THE CHEAPIE sets of three, thin, plus-diopter filters that screw onto the front of a lens, but THICK, heavy, two-element, front-thread-mounting close up "LENSES"....these are a VERY viable option. The achromatic lenses remove/eliminate chromatic aberration...it's a pairing of two different glass types, like crown glass and flint glass...and they can work absolutely spectacularly on some lenses, including the older Nikkor zoom lenses that were designed, specifically, to use the 6-T lens, and the lens's built-in macro-range settings in the orange-painted range; these Nikon manual focus zoom lenses were designed with one, specific, Nikon-made, two-element close-up lens pair (ie, the 5-T and then later, the 6-T) as part of the overall lens designs. The Nikkor 100-300 f/5.6 Ai-S and the 6-T mounted on the front of that lens (in reverse) produces flat-field, extraordinarily crisp macro images of a level that is fully professional in quality (See Bjorn Rorseltt's Nikkor Lens Evaluations Page). I was FLOORED with the 100-300/5.6 conventionally mounted to camera + 6-T Reverse-mounted on lens front performance on shots of dollar bills and stamps,etc..

The Canon 500D is another one, 2-element achromatic close-up lens that I have kicking around...mine is in 77mm thread, and it works quite well! The 500D is stronger than the Canon 250D.

Raynox likely also has a high-grade, two-elelement close-up lens available as well.

I think even inexpensive plus-diopter filters might be amply good on 1.5x APS-C cameras...I do not have any of those older sets around any more to try out, but I think the old problem, of weak corner performance from the plus-diopter filters would be moot on a 1.5x crop-frame body, since the corners would not even be seen by the sensor!

 

[480sparky]

Reversing a single lens is another way to get über-close. The shorter the focal length, the closer you can get. I usually use an old botched-Ai-conversion 28/2.8 Nikkor reversed on my PB6 bellows. I can easily get 2x to 7x magnification. I once bought a special step-down ring and tried my Tokina 17/3.5 reversed. Although I had some vignetting due to the ring, I managed 15x.

 

[smoke665]

I think even inexpensive plus-=diopter lenses might be amply good on 1.5x APS-C cameras.

I have a set of inexpensive ones that I played with a couple years ago, till the ADDHD kicked in and I moved on to something else. As I recall they weren't that bad, however I've become more critical on image quality since then. Might be a good time to pull them out and try them again.

 

[pez]

I went through a phase of using some vintage Pentax tubes on various lenses up to 70mm, with mixed results. The Cosina 55mm f1.2, for one, was a spectacular tool for the manual tubes, as was my Helios 44 58mm. The tubes made for Lensbaby lenses did an amazing job on my Sweet 35 lens.