Thursday, 22 April 2010

Minolta 100mm F2.8 Macro D lens - comparison of magnifications with extension tubes and 2x teleconverter

Followers of this blog would be familiar with my macro equipment. For a long while I didn't have a Macro lens and managed my macro photography with an MD fit 58mm lens attached to a bellows unit.  However, I have recently taken the plunge and invested in a Minolta 100mm F2.8 Macro D lens. The Minolta 100mm F2.8 Macro D lens is essentially the same lens that is today sold as the Sony SAL-100M28.

I already had in my possession a set of Jessops extension tubes (12mm, 21mm and 31mm) which maintained electronic contact via 5 pins, as well as a Kenko 2x MC7 (8 pin) and I was curious to know what magnifications I could achieve using these in conjunction with the macro lens. The following is the result of my experiment to determine the resulting magnifications:

The setup:

DSC08137

A dead assassin bug served as a co-operative model. It was placed on a table, slightly elevated, to align it with the camera’s line of sight when placed on the same table. The Bug was illuminated using a Minolta 3600D flash, wirelessly triggered using the in-built camera flash. The distance from the bug to the front of the camera lens was measured approximately using a measuring tape stretched out along the table. images were shot as fine JPEGs with spot metering. Focussing was done manually using live view (manual focus check live view) on a Sony A550 camera.

Results:
1:2 magnification, f8,
focus distance: 9inches
DSC08140
1:1 magnification, f8,
focus distance: 6inches
DSC08143
>1:1 magnification, f8,
focus distance: 5.8inches
with 12mm extension tube
DSC08147
>1:1 magnification, f8,
focus distance: 5.5inches
with 21mm extension tube
DSC08148
>1:1 magnification, f8,
focus distance: 5.3inches
with 31mm extension tube
DSC08149
>1:1 magnification, f8,
focus distance: 4.8inches
with 12+21+31mm extension tubes
DSC08150
>1:1 magnification, f8,
focus distance: 6.25inches
with 2x Teleconverter
DSC08151
>1:1 magnification, f8,
focus distance: 4.5inches
with 12+21+31mm extension tubes and 2x Teleconverter
DSC08152

As you can see with the addition of each extension tube there is a slight increase in magnification. The magnification obtained with all three tubes stacked together was still less than that obtained when using a 2x teleconverter. To quantify the magnifications, I measured the increase in magnification in photoshop, taking the 1:1 magnification as my baseline. The highest magnification resulting from stacking all three tubes and the 2x TC was a 3x magnification.

Accessory used
Magnification
12mm extension tube 1.1:1
21mm extension tube 1.2:1
31mm extension tube 1.3:1
12+21+31mm extension tubes 1.6:1
2x Teleconverter 1.8:1
12+21+31mm extension tubes and 2x Teleconverter 3:1

magnifications scaled

One has to keep in mind that with the use of extensions and TCs, there occurs a loss of light and the viewfinder becomes progressively darker as the number of extensions increase. Considering this, and the higher magnification ratio obtained with a 2X TC, compared with 3 stacked extension tubes,  I would be inclined to use the former over the latter in the field. Although the disadvantages of a TC over the tubes being the presence of extra glass in the light path and the reduction of the maximal aperture from 2.8 to 4. The second disadvantage is anyway not really a con considering that one almost always employs smaller apertures in macro photography to maximise depth of field.

Shown below is another image at f8 using the 2x TC in conjunction with the macro lens:DSC08156

For greater magnifications, I would definitely use all three tubes stacked together with the 2x TC. However, I wouldnt recommend this for the field as the increased magnification makes it very hard to maintain focus (extremely narrow DoF) and the viewfinder is extremely dark with this setup. However, in a studio/controlled situation, the use of MFcheck live view can be really useful and can do wonders to improve visibility and focusing.

At 3x magnification, even a aperture value of f8 gives a narrow depth of field. Below is an image taken using  the above combination at f8:

DSC08153

…and the same shot using an aperture value of f32:

DSC08155

I hope the above article has been useful for people. If you liked this article, do consider bookmarking or subscribing to this site using any one of the numerous options in the sidebar and keep tuned for more macro experiments.


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