Macro lens; what acc. to increase magnification?

frons

I have a Sigma 150 macro and would like to increase the magnification I can get. I have a Nikon 6T, but am wondering if the Sigma 1.4x teleconverter or a set of tubes would be the next best step.

Anyone ever use this combination? Would the glass in the TC degrade the sharpness of the lens itself? If not, it seems the better choice since tubes wouldn't noticeably increase the magnification for this focal length.

The one stop of light loss wouldn't likely be a factor since I'm usually stopped down pretty far when shooting, though manual focusing in the early morning light could be a bit harder.

If I'm missing something, let me know. thx

BigAl

Set of tubes.

ziggy53

The optical design of a macro lens usually allows the use of extension tubes and bellows with little degradation. At full extension there is a considerable loss in light efficiency due to the expansion of the image circle.

A teleconverter will work but it introduces optical elements that usually degrade the images somewhat. For simple subjects it probably wouldn't be too bad.

For really large magnifications and little cost I recommend a DIY project similar to the one I posted here:

http://www.dgrin.com/showthread.php?t=69392&highlight=microscope

... Darkdragon (Lisa) version:

http://www.dgrin.com/showthread.php?t=96883

... or the Lord Vetinari version:

http://www.dgrin.com/showthread.php?t=152544
http://www.dgrin.com/showthread.php?t=153900

... or adapt a microscope:

http://www.dgrin.com/showthread.php?t=28810

frons

Thanks, Ziggy, those links are pretty cool. However, I'm trying to photograph live dragonflies, so those setups are a bit more than I need. I guess I'm hoping to get to about 3x.

I've poked around the web a bit but can't seem to find a formula for calculating by how much either a set of tubes or a TC would increase the magnification. I'm using a 1.5x crop sensor, and am looking at the Kenko tubes with a total of 68mm stacked, or the Sigma 1.4x TC. Here's the lens link.

Thanks for pointing me in the right direction.

ziggy53

frons wrote: »

... I guess I'm hoping to get to about 3x.

I've poked around the web a bit but can't seem to find a formula for calculating by how much either a set of tubes or a TC would increase the magnification. I'm using a 1.5x crop sensor, and am looking at the Kenko tubes with a total of 68mm stacked, or the Sigma 1.4x TC. ...

The teleconverter calculation for potential magnification is rather easy.

If you start with a lens capable of 1:1 magnification on FF camera, put the lens onto a crop 1.5x camera body along with a 1.4x teleconverter, the formula is just:

(1 x 1.5) x 1.4, or simplified 1.5 x 1.4. That equates to around 2.1 magnification of lifesize.

Of course printing allows a much greater magnification still, which is why many zoom lenses have a "Macro" designation, which is really just a "Marketing Macro" since few zooms do better than 1/3rd lifesize.

Extension tubes are a bit trickier and you generally use a measuring target to determine magnification empirically. An approximate calculation is located here:

http://www.earthboundlight.com/phototips/closeup-choices.html

Remember that you need to measure from the nodal point of the particular lens to the film plane. Since the nodal point may be difficult to ascertain (unless the lens has a marking), you may have to guess the nodal point position, usually close to the diaphragm location. Remember too that a macro lens extends to focus closely, so take that extension into account.

---

A FF - 35mm image is 24mm x 36mm. A US quarter is close to 24mm in diameter, so a life size image of the quarter fills the short dimension of the frame (1:1 macro). For a crop 1.5x/1.6x camera a US dime works pretty well to fill the short dimension of the image frame at life size. (This is just to illustrate the concept of true "macro" sizes for photography.)

paddler4

I'd go with tubes. A set of Kenko tubes will give you three lengths, which you can stack in any combination. I would suggest starting small, with no more than 20mm, and gradually build up, because the loss of light and the shallower DOF make it hard going as the length of extension gets longer.

nightowlcat

You might also try one of these: http://www.bhphotovideo.com/c/product/87500-REG/Canon_2823A002.html

basflt

in addition to what is said above ;
with teleconverters the working distance is increased by the same amount [ 1,4 1,7 2,0 ]
this can be an advantage , i think
with tubes , working distance of the used lens remains the same

[ thats my own experience though ]

fldspringer

A teleconverter magnifies while in maintains the same working distance of the original lens.

Tubes increase magnification by reducing the working distance. You also loose focus at infnity. It doesn't always work with short focal lengths.

Close up lenses do the same as the tubes, you get more magnification because you get closer to the subject. You also loose focus at infinity.

I use a combination of teleconverters and a Canon close up lens and am pleased with the results. Your mileage, of course, may vary.

Working with high magnification is tough work. DOF gets tiny, stopping down pushes you into difraction and requires flash to supply light and support to eliminate camera shake. I can do about 2.25:1 plus a 2x crop factor, and I don't need more. DOF is maybe a millimeter and thats when I stopped down about three or four stops past where diffraction starts to degrade the image.

catspaw

echoing others, get a set of tubes. priceless for what you get out of them.