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by randyh on Sat Jan 20, 2018 12:28 pm
randyh
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Posts: 61
Joined: 14 Nov 2006
Location: Murrells Inlet, SC
I am interested in doing some bird photography with my Canon 7D ii with my Canon EF 70-200 f/2.8 IS. I have been using my Canon 1.4X tele extender giving me an effective focal length of 448 mm with good results. My question is would I be happy if I purchased a Canon 2X tele extender to use with that combination to give me an effective focal length of 640 mm ? I understand that I would be losing an additional stop of light, but would the image quality be degraded any by using that combination?  I would like to be able to purchase a longer lens, but that just isn't possible at this moment. Any advice? Any thoughts? Thanks in advance. 
Randy Hargett Photography
1136 Jumper Trail Circle
Myrtle Beach, SC 29588
704-589-0067
 

by E.J. Peiker on Sat Jan 20, 2018 4:08 pm
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E.J. Peiker
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Stacking TC's rarely gives you good results. Your f/2.8 lens would become an f/8 lens combination that needs to be stopped down as much as 2 stops before it is sharp so you are looking at f/16, f/11 if your sharpness needs aren't that high (for example if your end use is email and internet pictures) . Also AF would be marginal at best. The 2x alone with the 70-200 and then cropping the pictures would likely give you a better result than stacking converters.
 

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