TC or not TC ?

(2012-02-18)

     
 
TC or not TC? That is indeed the question raised and debated over and over again in photographers' fora.
 
And the common wisdom says: "Tele converters means extra glass not optimized for the lenses they are used with. You will furthermore loose one or two f-stops with tele converters. Results has to be degradation of image quality! Over and out!"
 
And much experience says: "I put a tele converter on my 200-300 mm lens and images were blurred and hazy. Tele converters are essentially useless and today - in the digital age - you might as well crop and enlarge to get equally good or better results."
 
And, of course, one could always go buy a longer and faster lens, a more powerful macro lens with or without extension tubes and.........
 
But mostly overlooked in this type of debates among us amateurs are amongst others:
  • We never test an individual component in its own right. We produce and evaluate results using a combination of "arbitrary" lenses, tele converters, camera bodies and sensors

  • We ignore special circumstances under which the "tests" were made. For example, we all know that tele lenses are sensitive to hot rising air -generally speaking whenever the seeing is poor - so why not expect that adding a TC would make matters even worse - in this situation, and maybe this alone?!?

  • We forget about certain possible constraints in our generalized discussions such as: How close can I get? Is that close enough?? Or, how close will I have to get? Is that too close??

  • There are other limitations than optical quality. For example most lenses will out-resolve almost any camera sensor available today. That is: The image of two close points may be resolved (:split) by the lens, but that image cannot be captured as separate points on the sensor because of the "coarseness" in the pixel-sizes. In technical jargon we talk about  poor sampling.

  • There may(?) be added benefits in certain cases, I'm almost sure: A TC may actually help flatten the field and help provide uniform sharpness over the entire filed.

  • And, finally, some very down-to-earth issues: What do I have? What can I carry with me? What can/will I afford?

The solution "go buy something else, more sophisticated and more expensive" (and more voluminous and more heavy) may be the ideal solution IQ-wise, but it needs not be the only realistic, practical and affordable solution.

 
The essence of it all is - given the gear that you have:
  • Ask yourself: Do I know my gear ? And, if so, can I produce better images with this accessory (in this case a TC) or not???

And my answer is: "Yes, you sometimes can!" There will always be other solutions. Surely some better and more costly; perhaps some cheaper; perhaps even some cheaper and better. But it all depends upon the circumstances and "common wisdom" and "self-evident" generalized rules are here to be always questioned and tested by yourself!!!

 

So, basically, the reason for using a teleconverter will almost always be to get a larger image of a subject that is too far away, whether we are talking tele- or macro photos. (And then, maybe also to get a flatter field in a few cases). Therefore one test is quite simple: Will a cropped photo without TC be as good or even better than a photo taken with a TC?

 

One area, where I find TCs useful is astrophotography, in particular lunar and solar photography with longer telephoto lenses: The lens outresolves the sensor and cropping to get the "last, minute detail" is not an option.

 

Another, more subtle, is certain, mostly hand-held, macro work: An extension tube - without disturbing extra glass elements - may appear better and will often be so, but in certain situations I appreciate that the TC retains a comfortable working distance + better lightning conditions, with or without flash.

 

So, here is a test that I made recently. You judge if it is "fair" or not. Because I did not test the "telephoto application" since seeing in my place (Danish City) is terribly lousy for the present (winter) time being and that degrades any telephoto test.

 

Rather, I went for the "macro application" and photographed a stamp as shown below. The image uploaded is an 19.1% crop taken with my Tamron Adaptall-2 SP 35-80mm Model 01A at closest focusing distance.

 

 

As adaptall-2.org says: "Amazingly, this lens yields very good macro performance across the entire film plane when used with Tamron's SP 2X tele-converter. "

 

Next, I took 5 images with very careful focus - using 8X and 10X liveview - and thereafter another 5 with the Tamron F-series 2X Teleconverter at same closest focusing distance excersizing the same care with focus in liveview.

 

What I present are 2 times 3 sets with and without TC. Images uploaded are actual 100% crops from images with TC and 200% crops from images without TC. Each crop is taken from different pictures randomly chosen.

 

 

Now then, which are which? Feel free to evaluate. So take a break from the reading here and make your qualified guess. I have shuffled the crops around to make your assessment a little less straightforward.

 

See the correct answer on next page------>

 

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Copyright 2012 - Steen G. Bruun