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Extension tubes calculation

Erik DeBill

New member
Is there a formula for how much minimum focus will be affected by adding extension tubes?

I do a lot of my photography while hiking and I'd like to add some macro capability, but carrying my 100mm adds too much weight, when I won't use it most of the time. I was thinking that extension tubes on a 70-200 zoom might get me close enough (not necessarily 1:1 - even 50% life size would be fine).

Is there a way to calculate the effects of adding tubes, without having to test them myself?
 

Erik DeBill

New member
Thank you. That's exactly what I needed.

Looks like I won't be able to get serious macro capability, but I can come close (and 1:1 usually requires too much light for hiking anyway). The second link with the ability to do calculations helped me understand the relationships involved much more than just looking at the charts (that didn't have 2/3 of the lenses I'd have with me anyway).
 
Erik DeBill said:
Thank you. That's exactly what I needed.
You are welcome. :eek:)
Erik DeBill said:
Looks like I won't be able to get serious macro capability, but I can come close
A +10 dioptric correct lens is inexpensive and should get you close without loss of light. Albeit, infinity focus will be long gone. Take a look at B&H if you are stateside.
Erik DeBill said:
1:1 usually requires too much light for hiking anyway

A 550 EX plus batteries weighs little and is powerful enough to provide decent light with the EF 100/2.8 USM Macro lens at 1:1. Truth be told, I find daylight a bit dim on a bright day to get decent DoF on a bright clear day. Most of my macro work is using the 550 EX with a Lumiquest Softbox (4x8 in softbox) with daylight fill. The Lumiquest softbox is not vital, but it does soften specular highlights on wings and other specular insect surfaces yielding better detail. Add in that the 100/2.8 Macro is my "normal" lens and I am used to hauling a lot of mass in my hands for shooting when the flash is added (especially with my lightweight XT/350D). Nonetheless, the 550 EX plus batteries weighs far less than my tripod. And as a "normal" lens (not normal focal length, just my normal non-portrait lens) the 100/2.8 is fantastic as it is sharp wide open unlike the 50/1.4. Albeit, these two lenses mixed with the dim XT viewfinder have left me with a taste for fast glass.

Erik DeBill said:
The second link with the ability to do calculations helped me understand the relationships involved much more than just looking at the charts (that didn't have 2/3 of the lenses I'd have with me anyway).

The charts work well for me, but my only lens I want extension tubes for is the 100/2.8 and that is for getting to 2:1 for extreme macro work. Though the 50/1.4 might be fun up close with its razor thin DoF.

Nonetheless, I highly recommend the 100/2.8 USM Macro. The images are sharp and focus is mostly fast except the occasion hunting in low contrast scenes. I would expect the 5D to have better autofocus making that less of an issue. But even with the XT's tiny dim viewfinder an f/2.8 lens is enough for manual focus and that means a body upgrade's cost can buy a new lens.

enjoy,

Sean
 

Asher Kelman

OPF Owner/Editor-in-Chief
Great information, Sean!

Do you use a 500D or extension tubes with your 100mm Macro?

Now has anyone used the 150mm Sigma Macro and can gove experience v. the Canon 100mm Macro?

Asher
 
Asher Kelman said:
Great information, Sean!

Do you use a 500D or extension tubes with your 100mm Macro?

Thanks Asher.

I only have a set of Tiffen dioptric correction lenses I bought long ago (+1, +2, and +4) and the single lens dioptric correction is allegedely inferior to the 250D and 500D. As the 250D is has the stronger correction I would favor that over the 500D in spite of Canon's recommendations for longer focal lengths as the goal is to get closer. But that will not work for larger filter threads. An interesting and helpful distallation of this info with Chuck Westfall's input can be found at:

http://bobatkins.com/photography/eosfaq/closeup2.htm

I have thought about getting extension tubes, but truth be told I only rarely want to get that close and I have the inexpensive filter set of close of lenses and I can always use a reversed 50 mm. And the reversed 50 mm seems to retain optical quality. As the season has started to turn from our 3-4 months of dry back to wet again I cannot place much value on getting closer as it is time to start shooting mushrooms again and that rarely involves getting below 1:2 as my interest is ground level macroscapes. Though I may look into getting extension tubes next spring and chase the tiny hoppers (1-5 mm long) for some full frame shots.

You can currently at B&H get a 58 mm B+W +10 close up lens for $45.95 or a 77 mm +5 for $52.95. Canons two element close up lenses cost about double that.

some thoughts,

Sean
 
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