Extension Tube Math?

Decided to cut this elephant up into bite size pieces by testing three Canon lenses with five Extension Tube combinations plus "no tube."

HERE'S the link to the results.

Due to the extremely shallow DOF, the focusing point was usually easy to determine. However, manual focusing was usually required.

PrimoFelis, hope this gives you enough empirical data to test your calculations. We appreciate your good work! (Even if some thing this isn't necessary at all )

Should those sizes be 12/20/*36*/48/68 rather than 12/20/*32*/48/68?

Hate to be picky but I suspect it will be material to the next batch of calculations....

Pete

Daytripper wrote:
Should those sizes be 12/20/*36*/48/68 rather than 12/20/*32*/48/68?

Hate to be picky but I suspect it will be material to the next batch of calculations....

Pete

I tried to select a variety -- not all 8 combinations (7 + "none".) I chose not to use both 32 and 36 since they are so close. In the end I chose this set because it is close to 1.5x steps. 20 = ~ 1.5*12; 32=~1.5x20, etc.

So what I've really used is:

none
12
20
12+20
12+36
12+20+36

But if our math-king wants them, he shall get them!!

awesome thread, I know it's old, but I found it in Google and it helped

Has anyone found a site where you enter in the lense focal lenght, MFD, amount of extension and then it gives you the new MFD

Thanks

Brandon

I read a review a couple of months ago (can't remember who/where) and the guy basically said he couldn't tell the Keno's from the Canon's except for the names.

The comment that stuck in my mind was, "There appears to be no difference between Kenko air, and Canon air".

I have the Kenko's - for the price of all three of these, I could have had one small Canon ring.

Sorry Canon, I'm not that loyal.

Glenn NK wrote in post #2453552
The comment that stuck in my mind was, "There appears to be no difference between Kenko air, and Canon air".

The only knocks I've seen about the Kenko set is that they don't seem to positively lock on the lens/body as do Canon's. This has apparently resulted in lenses dropping off at times. Then there are also those who do something ridiculous like place all three tubes on and mount something like a 500mm on the end and try to handhold the entire assembly, which winds up snapping off somewhere in the assembly.

Of course there are advised alternatives to using tubes with zooms. I believe Askey (among quite a few others) advises the use of close up 'filters' with zooms. These 'filters' don't degrade the IQ much, provide more consistent AF function (if you use AF for macro work), and eliminate the need to refocus when zooming to different focal lengths.

JKSeidel wrote in post #2454040
The only knocks I've seen about the Kenko set is that they don't seem to positively lock on the lens/body as do Canon's. This has apparently resulted in lenses dropping off at times. Then there are also those who do something ridiculous like place all three tubes on and mount something like a 500mm on the end and try to handhold the entire assembly, which winds up snapping off somewhere in the assembly.

Of course there are advised alternatives to using tubes with zooms. I believe Askey (among quite a few others) advises the use of close up 'filters' with zooms. These 'filters' don't degrade the IQ much, provide more consistent AF function (if you use AF for macro work), and eliminate the need to refocus when zooming to different focal lengths.

Wish this post had started sooner - I received a set of Kenko tubes yesterday (belated Xmas gift). Tried all three at once with my 24/105 on a tripod, and nothing fell off - yet.

Interesting comment about a close-up lens - I bought one a few weeks ago - a Canon 500D. Seems OK, but the term DOF is completely meaningless.

In time I will test the IQ with both systems for close-up work.

PrimoFelis wrote in post #104542
Hi Littlebike,

I have had the Kenko extension tubes (a set of 12, 20, 36mm extension) for use with my Canon film camera bodies. I have been happy with them.

I'd point out, however, there are two potential issues that may or may not be a conern for you depending on which lenses and camera bodies you plan on using it, now and future:

1. EF-S mount (in)compatibility issue.

As most of us know by now, Canon introduced a new EF-S mount for the Digital Rebel "kit lens" (18-55mm f3.5-5.6).

If you plan on using your extension tube with this (or any other future) EF-S mount lenses, you will need to get one of the new Canon extension tubes that were also recently introduced. The older Kenko/Vivitar/Canon extension tubes won't work with the EF-S lens(es). (It won't fit -- physically.)

2. The (potential) vignetting issue

I don't know about Vivitar or Canon tubes (new or old), but my Kenko tubes have a circular opening of 35mm in diameter. (I measured mine.)

I know that, with some lenses (e.g., 600mm f/4) his turns out to be too small an opening to clear all the light going toward the image corners of a full-size 35mm format film/sensor. This results in a (mild) vignetting in the image corners.

This is NOT an issue with most smaller/slower lenses. Further, it should NOT be an issue with 10D/Digital Rebel users (probably with ANY lenses) thanks to the 1.6x "cropping factor".

But if you are a current/future user of 1Ds (and possibly 1D too?) you should be aware of this. (Film body users as well.)

(That said, I'm not entirely sure if the genuine Canon extension tubes do not have this same vignetting issue. A tiny picture of an allegedly Canon extension tube that I saw didn't look much different from my Kenko. Can anyone out there with the Canon or Vivitar extension tubes measure their tube opening?)

Although the Kenco tubes do not take EF-S lenses as they stand, I have enlarged the hole in the plastic of my 12mm tube to take my 60mm EF-S macro.
You need to be sure to clean the tube after you make the hole bigger (I used a drill), otherwise you could get chaff inside your camera. Also make sure that the new hole is not so large that it affects the contacts.

The end result is a tube and lens combination that gives great results not only on a 350D but on a 5D as well. The EF-S lens does not give significant vignetting when it is on the end of the tube with the 5D.

This won't help with "math" but will give a visual idea . Something I did the first of the year.. Gerry

http://imageevent.com …er/crazycritter​firstalbum

Glenn NK wrote in post #2453552
I read a review a couple of months ago (can't remember who/where) and the guy basically said he couldn't tell the Keno's from the Canon's except for the names.

The comment that stuck in my mind was, "There appears to be no difference between Kenko air, and Canon air".

I have the Kenko's - for the price of all three of these, I could have had one small Canon ring.

Sorry Canon, I'm not that loyal.

I agree that for the most part the Kenko set is 100% fine. Image wise of course there is NO difference at all.

Where the Canon extenders become important is when using them along with a heavy lens like the 500mm-600mm lenses that birders use tubes with to0 get closer to the smaller perching birds. Combining a 1D, a 600mm and a t-Con with a Kenko extender becomes a recipe for disaster, as they simply aren't beefy enough to offer rock solid connection. For all other applications I'd agree the Kenkos are the way to go.

Glenn NK wrote in post #2462873
In time I will test the IQ with both systems for close-up work.

Be interested in seeing your results. I'm in the process of considering the purchase of a close up lens/filter for use with my 100-400mm. I'm having a tough time believing all the claims about the lack of IQ degradation by adding what amounts to an additional optical element over the use of air (extension tube). Please post some images when you get to the testing.

Sorry to bump up a 5 year thread. Just want to know if there's an online calculator available that determines the MFD of 'tubed' lenses.

The formula for magnification is here:

http://www.peterforsel​l.com/macro.html

Given the magnification you should be able to re-arrange one of the formulas on here to yield the MFD:

http://photo.net/learn​/optics/lensTutorial

This is single handedly the most confusing thread I've ever read. I just want to knows how much mag. a set of tubes will give. Is it dependent on the lens, or will the tubes give a set magnification?

And as to the OP saying that "why should I pay for metal, theres no optics" I agree. I bought some ebay hong kong extention tubes, $9 with shipping. It's metal, and doesn't allow lens to camera commo, what could it possibly do? I see no need to spend $100 or more on hollow aluminum tubes.