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Message: <blockquote data-quote="dwever" data-source="post: 3537760" data-attributes="member: 118803">MFT measurements (sampled a few paragraphs down) make the fact of compromise regarding sharpness with this and virtually all teleconverters objectively undeniable.  How much compromise makes one put the teleconverter down is subjective.Some would say magnification for some sharpnesss loss is well worth it; others such as Photozone in their MC-14 MFT measuring say use the MC-14 teleconverter as a last resort (<a href="http://www.photozone.de/m43/945_olympus40150f28pro?start=1" target="_blank">http://www.photozone.de/m43/945_olympus40150f28pro?start=1</a>).  At any rate, all agree there's a penalty to pay when you use the 1.4X; and, that penalty is quantifiable in MTF with the right instruments which I'll get to.In a perfect world, for birding I would own the $2,300 Olympus 300mm f4 PRO but I don't because Birding is my only need for it, so I use the 1.4x w/40-150 because I pay less in image quality with it than without it.  Without it I would be cropping the heck out of a shot even more to see the bird in some detail.  And with the 1.4 as the bug pursuer below shows, I still have have to crop a lot.Having said that, the results are usable, and the objective measurement comes from testing using instruments that measure MTF**.  Lenses will have usually three numbers associated with each f stop, one for the center where sharpness is usually best, one for the edges (lower), and one for the corners or extremes(worst).  With zoom lens you get even more variations, and with the Olympus 40-150 f2.8 it's sharpest images come at about 100mm at f4.  The MTF there is a whopping 3,124.Here is an example of the penalty charged by using the 1.4x: the 40-150 f2.8 at 150mm gives a best resolution for that power at the center of the lens of 2,987 at f/4.  Then, with the TC-14 at it's full power, it gives it's highest resolution at f5.6 in the center at 2677.  Penalty: a 10% drop in sharpness at full power with the teleconverter attached.  When using less than full power, say 100mm, the penalty in sharpness with the teleconverter is not as great, but it is always there.  There is no focal length and f stop combination with the 1.4 that gives equal sharpness to use without.  So, the subjective question is, are you still pleased with your images with it on, is the extra focal length worth the loss of sharpness?  Most of us say heck yeah, while others are like I only use it man if I have to.  When shooting birds, the less magnification you bring to the game, the more you will crop.  The image below is the 40-150 f2.8 with 1.4x at full power.  In the original shot the picture is 5184x3888, the crop is less than 1600x1200, just a small piece of the original frame (1/3200 of a second at f5.6 ISO 800 March 10).Birding is one application where a 34mp sensor like on a Nikon DSLR 8100 can make a lot of sense where images are 7,360 x 4,912.  But, and it's a big butt, 8100 plus 300mm f2.8 is North of $8,000.  For half that, get an OM-D E-M1 Mark II and a 600mm equivalent 300mm f/4 PRO.  Images are grabbed at twice the power by the Oly at 5,184 x 3,888. But comparisons are highly nuanced so let met get off that path.**The sharpness of a photographic imaging system or of a component of the system (lens, film, image sensor, scanner, enlarging lens, etc.) is characterized by a parameter called Modulation Transfer Function (MTF), also known as spatial frequency response.  MTF is a way to incorporate resolution and contrast into a single specification.  <a href="https://www.edmundoptics.com/resources/application-notes/optics/introduction-to-modulation-transfer-function/" target="_blank">https://www.edmundoptics.com/resources/application-notes/optics/introduction-to-modulation-transfer-function/</a> and <a href="http://www.normankoren.com/Tutorials/MTF.html" target="_blank">http://www.normankoren.com/Tutorials/MTF.html</a>For a number of reasons, for birding in good light I like to be a stop away from wide open if I have a fast lens like a 2.8 or 4.0 if possible.Under what conditions would lower MFT numbers (penalty) not have application unless they were to become so close with and without the teleconverter as to be of virtually of no consequence to the human eye?  I think the point is that the 300mm or 40-150mm with the 1.4x and the accompanying lower MFT, that is generally a better image of a small bird than without the 1.4x and the more extreme cropping that would accompany it.</blockquote>

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