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-   -   Micro photography with extension tubes. (https://forums.steves-digicams.com/general-discussion-11/micro-photography-extension-tubes-188942/)

hanalwala Jun 13, 2011 6:41 AM

Micro photography with extension tubes.
 
2 Attachment(s)
Please pardon my ignorance as this will be my learning experience in micro photography.

I have just got a set of extension tubes and would like to use them along with my Sigma micro 105mm f/2.8 lens to take pictures of small insects. I use a Canon 60D.

I fitted the ET on my camera body and then fitted the lens in front of the tubes. I was not able to use the Aprature mode. Is that correct ? Or did I do something wrong? I had to go on manual mode with manual focus as well. I took these pictures but I am not at all happy with the results. Please advice where I have gone wrong and what is the setting recomended.Image no:286 is the screw of my glasses and image no:292 is the roller ball of my ball point pen. please advice...

TCav Jun 13, 2011 7:18 AM

Extension tubes give you a VERY shallow depth of field. That is why, for instance, the screwhead in the hinge of your glass frame is sharp, but the frame in front of and behind it is blurry.

Not having autofocus or autoexposure makes me think that the extension tubes you're using are the inexpensive ones that don't support those functions.

While extension tubes have no optical elements of their own, so they won't, all by themselves, degrade image quality, they most definitely magnify the flaws in the lenses you use them with. The Sigma 105/2.8 Macro you're using is very good, but under the circumstances, I'd keep the aperture between f/5.6 and f/11, instead of the maximum of f/2.8. Unfortunately, since the Sigma 105/2.8 Macro doesn't have an aperture ring, and your extension tubes don't support communication between the lens and the body, you can't control that.

And, again, since you can't control the aperture, your depth of field is always going to be razor thin.

Bob Nichol Jun 13, 2011 7:32 AM

Extension tubes such as the Kenko DG Teleplus Extension Tube Set allow for TTL exposure and diaphragm coupling, many other brands don't. Sounds like you have the latter so the camera can't control the diaphragm so the camera won't let you use Aperture priority. http://www.thkphoto.com/products/kenko/slrc-04b.html The lens does have an aperture ring (at least my copy does) so you could use manual mode.

The Sigma 105mm f/2.8 EX Macro is capable of 1:1 macro work as it is so adding extension tubes will allow even closer work with more magnification. More magnification means shallower depth of field as shown in your sample photos. More magnification also means you need to use a more solid support for your camera or resort to macro flash to freeze the image.

There is software to merge multiple photos to give the impression of greater depth of field but good results require the use of special stands that move the camera or specimen in precise increments.

TCav Jun 13, 2011 9:17 AM

Quote:

Originally Posted by Bob Nichol (Post 1233587)
The lens does have an aperture ring (at least my copy does) so you could use manual mode.

My bad. Thanks for catching it.

PeterP Jun 13, 2011 10:09 AM

Bob and TCav have covered it pretty well!
One issue not mentioned is light loss with tubes, there used to be formulas for calculating bellows extension loss but that should be now handled automatically by the camera.
Point is to get bigger DOF you need to use very small apertures and to get more magnification through extension tubes you lose even more light.
So things can get very dark, external light sources designed for macro work can be a beneficial addition to your kit.

This the the extension tube set that Bob mentioned at B&H Kenko Auto Extension Tube Set DG

An article about focus stacking it has a nice section on focus stacking software (some of it is free!) to assemble all the image slices.

And here is one of the automated rails Stack Shot Definitely not inexpensive piece of gear.
It is possible to do it manually but very tedious.

TCav Jun 13, 2011 10:30 AM

1 Attachment(s)
Quote:

Originally Posted by PeterP (Post 1233619)
One issue not mentioned is light loss with tubes, there used to be formulas for calculating bellows extension loss ...

Light loss varies with the telecentricity of the lens design and the size of the exit pupil. Perfectly telecentric lenses (which are rare) don't lose light when used with extension tubes. Light loss cannot be determined ahead of time, but only through experimentation.

PeterP Jun 13, 2011 10:51 AM

Bellows extension exposure compensation formulas (primarily for Large Format cameras)

As mentioned modern slr cameras will work out any compensation for you, that simplifies things a lot! :)

hanalwala Jun 13, 2011 10:58 AM

Thanks guys for your quick replies. I went across to the Camera store to check for the Kenko extender tubes and took my camera with me and yes the auto focus works. that means that the tubes I had were of poor quality. I purchased this Kinko set and will take pictures with this new set and see the results. For the loss of light issue.....Can I use a flash gun ? Since as of now I avoid using the flash as far as possible.... Please advice

TCav Jun 13, 2011 11:21 AM

The subject will be so close to the lens that the lens barrel will block the flash. You can use a macro flash or a ring light, but a conventional flash, especially one mounted on the accessory shoe, won't work very well.

PeterP Jun 14, 2011 9:14 AM

Wow, I never realized the name-brand macro flashes were that expensive!

You can make your own DIY with a double flash bracket, a flash splitter cord and a couple of small inexpensive flashes. There are many hits on google for making your own, just make sure the flashes you use are compatible with the dslr.
And they will most likely be manual mode, not ttl.

Or
a thrid party macro flash like the Sigma EM140DG are much less expensive.

Or
a strange adapter called the ray flash that converts a normal flash to work like a ring light.,

Myself I've been using a Alien Bees ABR800 ring flash, 320 W/S, fast recycle, modeling lights, and can take accessories like softboxes and grids, but on downside it does need 120v power and is a bit heavy.
(the alien bees vagabond mini power supply will run it for hours but costs almost as much as the ringflash itself :( )


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