I've recently purchased an OM 135mm 3.5 that I'm using on a Canon 1D MK II. I like it quite a bit ... except for the MFD is around 5 feet. The resolution on it is quite good and I can crop quite a bit in PP, but I would like to get a bit closer, say 2 feet +/- (or closer).
If I use extensiontube(s):
1) How much can I reduce my MFD by ?
2) How much of a penalty do I incur in IQ ?
3) Do I lose contrast, like when using a TC, because the image is being spread over a larger area ... or is it nominal compared to a TC ?
4) Do I incur more diffraction because the aperture blades are further from the focal plane ?
5) Can I compensate for the diffraction losses by choosing a different f-stop, or will they all be effected equally ?
6) Is there a point at which I can expect minimal IQ losses vs. significant IQ losses ?
7) Any other considerations that I should be thinking of ?
Extension tubes will shorten both MFD and cost you infinity on the long end.
You might want to check out the Oly auto bellows. Ya, you gotta get a cable release to stop the lens down, but it gives you dramatically more flexibility than fixed length tubes.
BTW, if you go the tube route, you have to get Olys. A Canon tube will not work between the adapter and your camera body.
Congratulations on the new lens, it is a beauty for flowers.
Get the adjustable Oly tube which is more convenient to carry around but it can not extend as much as the bellows. This lens has great color and bokeh, especially with the tube which can give you some really nice flower blur shots.
Andreas (Anden) is of course the master of this but I have had fun doing some of my own.
Enjoy!
Extension tubes will not decrease IQ or diffraction significantly. However, they will show flaws in the lens at close focus distances, as most lenses are optimized for long distances, especially teles.
RustyBug wrote:
I'm not sure I understand why a Canon tube would not work ... other than electronics not controlling aperture, as with all MF lenses?
You get an error message, as the camera sees the extensiontube, but not the lens. Some get around this by unlocking the latch and rotating the extensiontube and lens back enough to move the contacts apart, others tape the contacts. I opted for a tube set that cost me $12 CDN shipped to my door.
I have tried extension tubes on all my lenses. Some can produce excellent results even with a lot of extension while others fall apart. You will need to hear from someone who has used the exact same lens with a tube to get a meaningful answer.
RustyBug wrote:
I've recently purchased an OM 135mm 3.5 that I'm using on a Canon 1D MK II. I like it quite a bit ... except for the MFD is around 5 feet. The resolution on it is quite good and I can crop quite a bit in PP, but I would like to get a bit closer, say 2 feet +/- (or closer).
If I use extensiontube(s):
1) How much can I reduce my MFD by ?
That depends on the length of the tube. If you want an object distance of 2 feet, you need 25 mm of extension in addition to the extension offered by the lens itself.
2) How much of a penalty do I incur in IQ ?
That depends on the lens design. Some lenses perform remarkably well on tubes.
3) Do I lose contrast, like when using a TC, because the image is being spread over a larger area ... or is it nominal compared to a TC ?
You will lose contrast, but not like when using a tele converter. A TC magnifies errors of the prime lens and adds some of its own; with an extensiontube you just use a lens outside the distance regime for which it was designed. The losses can be big or small, depending on the lens and the amount of extension.
4) Do I incur more diffraction because the aperture blades are further from the focal plane ?
You will get more diffraction, but you will get that with any lens at close focus.
5) Can I compensate for the diffraction losses by choosing a different f-stop, or will they all be effected equally ?
The influence of diffraction decreases with an increasing aperture, regardless of whether the lens is on tubes. What changes is the optimum aperture. If the best performance at infinity is obtained at, say, f/8, the optimum aperture at close focus might be f/5.6.
6) Is there a point at which I can expect minimal IQ losses vs. significant IQ losses ?
There is always a transition region.
7) Any other considerations that I should be thinking of ?
A macro lens might be more convenient in the long term.
