Stacking more than 68mm extension tubes

[averylowiq]

I was just curious, if anyone has tried stacking more than 68mm of extension tubes on their lens? If so, how did it work out? I think will make the focusing way too close to the subject. Any thoughts?

[LordV]

This can work but as you say you do get rather close focus distances. I've seen someone using a 500mm aluminium tube as an ext tube for extreme macro work but it was mounted vertically like a microscope. Main problem I suspect at least with auto ext tubes is getting contact problems.
Brian v.

[averylowiq]

Thanks for the reply Brian. Good point about electrical contact problems. If I can find some borrowed tubes I will try it out and share the results.

[averylowiq]

For what its worth, here are some experiments with greater than 68mm extension tubes.

I used a set of ancient 21+13+31mm (65mm) no-name extension tube set. All images are taken with Canon 40D in manual mode and are uncropped frames - just exposure is adjusted and shrunken in size. Canon 100mm f/2.8 lens is kept in manual focus mode at 1:1 magnification. The subject is the cm scale on a ruler so each line represents 1mm distance. Images were taken handheld that's why they are a little crooked and well the left edge of the image doesn't always fall on a line.

1. Canon 100mm f/2.8.
http://farm4.static.flickr.com/3636/3464595664_6e7df802d0_o.jpg

2. Canon 100mm f/2.8 and Kenko 68mm extension tubes.
http://farm4.static.flickr.com/3638/3463779531_7cd737e5ee_o.jpg

3. Canon 100mm f/2.8, Kenko 68mm extension tubes and 65mm (21+13+31) extension tubes.
http://farm4.static.flickr.com/3607/3463779633_3f06c2f300_o.jpg

4. Canon 100mm f/2.8, Kenko 68mm extension tubes, 65mm (21+13+31) extension tubes and 2x Quantaray tele-converter adapter.
http://farm4.static.flickr.com/3530/3463779379_0316f85909_o.jpg

If I am not wrong, here are the rough magnifications achieved (please correct me if I am wrong):

(size of sensor in mm units)/(mm captured in image):1
1. ~22mm/22mm:1 ~ 1:1
2. ~22mm/11.5mm:1 ~ 2:1
3. ~22mm/7.25mm:1 ~ 3:1
4. ~22mm/4mm:1 ~ 5.5:1

With 133mm of extension tubes attached to the Canon 100mm f/2.8 lens (manually set at its MFD (1:1 magnification)) the MFD is roughly 3" from the subject.

[marcoj70]

What's the MFD with only 68mm Kenko on the 100mm f/2.8?

[gasrocks]

If you do a lot of work with a lot of extension, think about getting a bellows.