Canon 100mm Macro with extension tubes

[tim]

Has anyone use the 100mm macro lens with the kenko extension tubes? If you put all three tubes on it gives you a 168 mm lens, which would be handy. The problem I see is the DOF calculator (http://www.dofmaster.com/dofjs.html) says the depth of field at F16 at 30cm (1 foot) is 0.09cm - ie about 1mm!

Has anyone used this combination with good results?

[steven]

No, I have all the parts just have not tried that combination.

I will try and let you know.

[tim]

Thanks Steven :)

[steven]

I have never posted a photo before :shock: so lets see if I can get this right.

Shot at 30 second f/16 100mm Macro with kenko extention 66mm(12+20+36)

First the whole image :

http://www.steven-long.com/1E3X4222%20web%20800.jpg

Now a couple of 100% crops

First:
http://www.steven-long.com/1E3X4222%20web%20crop1.jpg

Second:
http://www.steven-long.com/1E3X4222%20web%20crop2.jpg

You can see that the DOF is extream.

[tim]

Thanks for that Steven... that's impressive results from the lens with all those tubes on it :) Are either of those crops from the focal point of the photo?

[steven]

And for comparison here is a picture that is 1:1.
Taken with the sigma 180 but still as close as I can get so should be 1:1.

http://www.steven-long.com/1E3X4218%20web%20800.jpg

[steven]

For most close up macro work I don't use AF.
For these pictures I moved the flower forward and back using split screen focusing.
This is the easiest way I know of getting maximum image size. Set the focus to the min and then move either the camera or the object (flower) until you get focus.

My focus point (split screen) was just inbetween the two 100% crops.

[tim]

Thanks Steven. The 100% crops don't look great, but I guess they never really do. It's hard to compare those pics, as they're different sizes. That 180 looks good, but since it has a minimum focusing distance that's longer it only gives the same resolution as the 100.

With the extension tubes, will I be able to get more of small objects into my frame? Right now at the minimum focusing distance I a drop of water takes up about 1/20 of my frame. Will I be able to get more of it with the extension tubes, or should I be considering magnifying filters for that?

[steven]

Yes you will get more. If you compare the first picture taken with the 100mm+extenders with the 180mm (no extenders) you can get a feel for the amount of image size increase, since the image size for 100mm and 180mm without extenders should be the same.

If you would like to get the originals let me know and I will make them available.

[kb244]

By the way without the extenders, its 160 , not 168, its 168 when you use the Sigma 105mm Macro. by the way whats with the lines in the crops, are they like scan ins from a print?

[tim]

I'd love to get hold of the originals steven. Just let me know where to download them, or email them to me - I have my own server so size isn't an issue. Downloading them is better though, huge emails can be a little unreliable. If anyone else wants 'em I can host them on my server too.

[Persian-Rice]

tim, try it with the Tamron, all three at 75mm is pretty much impossible as far as I have tried.

[tim]

tim, try it with the Tamron, all three at 75mm is pretty much impossible as far as I have tried.

Would you mind elaborating a little more? I'm not sure what you're getting at. I don't have the tubes, i'm considering getting them is all. Steven seems to have managed to use them all at once.

[steven]

by the way whats with the lines in the crops, are they like scan ins from a print?

What lines??
don't see any lines. Anyone else seeing lines?

None of the pictures are scan they are all digital.

[Jesper]

No, I don't see any lines. Maybe kb244 has some electromagnetic interference on his/her monitor .... ??

[Jon]

Has anyone use the 100mm macro lens with the kenko extension tubes? If you put all three tubes on it gives you a 168 mm lens, which would be handy. The problem I see is the DOF calculator (http://www.dofmaster.com/dofjs.html) says the depth of field at F16 at 30cm (1 foot) is 0.09cm - ie about 1mm!

Has anyone used this combination with good results?

Just for clarification, it's not a 168 mm lens; it's a 100 mm lens at 168 mm extension (with a lens-subject distance of 247 mm). On a 20D that gives you DoF of about 2 mm. At 1 foot (lens-subject), you'll get about 4 mm DoF. But DoF in the macro range is always pretty durn small.

[tim]

Just for clarification, it's not a 168 mm lens; it's a 100 mm lens at 168 mm extension (with a lens-subject distance of 247 mm). On a 20D that gives you DoF of about 2 mm. At 1 foot (lens-subject), you'll get about 4 mm DoF. But DoF in the macro range is always pretty durn small.


So will it act like a 168mm lens, or a 247mm lens? And where do you get the 247mm distance from?

[Persian-Rice]

Tim, when I use the 3 tubes on the Tamron I have to go so close that the subjects hits my UV filter. Mind you that is at 75mm. 28mm seems to be a little easier, nevertheless they are good. Not sure how they perform on other lenses, the already "okay" contrast of the Tamron becomes worse, the 50 1.8 is better then the tamron but still not great, but I noticed the contrast is still good with the 24-70 & 70-200. If you have good contrast on the 100mm macro, then you will really love the images, but I can't be sure, I have never used that lens.

[tim]

Why do you "have" to go in so close?

[Jon]

So will it act like a 168mm lens, or a 247mm lens? And where do you get the 247mm distance from?

It'll act like a 100 mm lens since that's what it is, with the focussing helical racked out to 168 mm. The 247 mm distance came from the formula 1/fl = 1/d1 + 1/d2 where d1 is the lens to subject distance and d2 is the lens to film plane distance. You use the 100 mm value for the focal length in the DoF calculator.

1/fl = 1/d1 + 1/d2
1/fl - 1/d2 = 1/d1 + 1/d2 -1/d2
1/fl - 1/d2 = 1/d1
1/100 - 1/168 = 1/d2
.01 - .006 = 1/d2
.01 - .006 = .004
.01 - .006 = 1/247

If the calculator expects the distance value to be the film plane to subject distance, not the lens to subject distance, results will be different. For "normal" working distances, it won't be a factor since the film plane to lens distance is small relative to the lens to subject distance. In macro mode, it becomes critical. In this case, it'd be the difference between a "distance" value of 247 mm and one of 415 mm. Of course in macro the indicated aperture isn't the actual aperture value since f/ stop is affected by the total distance between lens and film plane, not just the focal length. So your f/16 is more like an f/27 unless that compensation is built into the calculator.

[tim]

Interesting. In laymans terms, what will happen with the 100mm macro and the extension tubes on? Will the subject fill more of the frame, and will it be better quality than cropping the digital image? That's all i'm really worried about.

[Jon]

Why do you "have" to go in so close?

Lens to subject distance is calculated from the "nodal point", the optical center, of the lens. If the 28-75 zooms out so the front of the lens is well beyond the front nodal point, the lens will be eating up some of that calculated working distance.

A zoom, or a retrofocus, or a telephoto, lens will have two nodal points since the complex structure of elements and groups makes it look different to the front of the lens and the back of the lens. For an example, take your zoom off your camera. Then look through the front of the lens at the apparent diameter of the optical path (entry pupil). Turn it around and look through the rear of the lens at the exit pupil. On a symmetrical lens, like your 50 mm which is a standard Gaussian design, the difference will be minimal, and the front and rear nodal points will be just about the same. On a lens with an asymmetrical design, the entry and exit pupils will be fairly markedly different. The nodal points will also. Just about any lens of less than 35 mm will be a retrofocus design, where the rear nodal point is forward of the apparent focal point of the lens (because a 28 mm lens' optical center is 28 mm from the sensor, and that's well inside the amera's body - in a really great spot to slap the mirror whenever you tried to take a picture). On a telephoto, the situation will be reversed - the focal point of a 400 mm lens (on a classic telephoto design, not a "long focal length" lens) will be well in front of the front of the lens. For an extreme example of this, look at the Sigma 600 mm mirror lens. It's only about 120 mm long, coupled with about 40 mm body depth and you've got a total length front of lens to film plane of about 1/4 the actual focal length.

[Jon]

Interesting. In laymans terms, what will happen with the 100mm macro and the extension tubes on? Will the subject fill more of the frame, and will it be better quality than cropping the digital image? That's all i'm really worried about.

Yes it'll fill more of the frame. You're just focussing closer. And it will be better quality than a crop, since you'll be using more sensor cells to form the image than you would if you cropped a shot from further away.

[tim]

Your first post confused me slightly, i'm not up to speed in lens design, and the last time I did anything like that was during my engineering degree a bit less than 10 years ago. The second post answered my question and didn't strain my brain ;)