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10-26-2018, 09:05 AM - 5 Likes   #1
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a different tc challenge.

We always hear the cropping vs a tc debate. This thread got me thinking in a different way. Thoughts about using Pentax 1.4x HD PENTAX-DA AF Rear Converter AW - PentaxForums.com
The 55-300 plm is not as strong at 300 as it is at much less than that. So it got me wondering if the plm by itself at 300mm could be the combo which uses the lens at a much shorter length. So I did a quick and dirty test.
I put the 55-300 at 300 on camera on tripod and live zoomed to focus on the trademark TM from about 25ft. The TM is smaller than 2mm. I used f8 at I think 1/45 and 2 second delay. Next I added the tc and pulled the zoom until my frame was as close to it was before and pressed the button again.
I had to pull up the exposure about 140 in post with the tc. It was spotty overcast but I doubt there was that much change in light. I think the T stop is less with the tc at the same fstop. That makes sense since more glass eats light.

So the center crop of the zoom all out on the left vs zoom with tc and post gain on the right.


I call a sharpness dead heat. My test wasn't designed for contrast and color but I have to question the tc on those points.

10-26-2018, 10:27 AM   #2
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Photos to show what you're talking about. How Unique on this forum. Thanks swanlefitte
I get greater distance to the target with the crop & with the 55-300PLM & sometimes the 1.4 TC. I'm after the story that I see and I want the picture even if it is imperfect and this combo gives me the opportunity to get closer & to get it without being burden with a hugh amount of equipment. The IQ is usually excellent and there is always a chance of motion distortion on both ends .
I have 2 pictures on a recent Post : "Thoughts about using Pentax 1.4x HD PENTAX-DA AF Rear Converter AW" that show something similar. Both shots are cropped extremely. I have shots on My Flickr of Eagles Aerial Combat & grabbing Salmon out of the river mouth. Both shot in very poor light but with the combo Lens & Crop I got the Photos. I have other aerial shots that are bang on with light & the same combo. I need the flexibility of the 55-300PLM & cropping to catch the unpredictable flight & distance of these magnificant Raptors. These are all Hand held out of the window of my Truck.

Last edited by honey bo bo; 12-04-2018 at 03:34 PM.
10-26-2018, 11:08 AM - 1 Like   #3
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I think the 55-300 holds its sharpness up to about 270mm. It got to 300 with the tc at around 215mm. Extrapolating then with the tc at 380mm i could keep sharpness like pictures at 300mm without. I haven't proved it but that would be huge.
Then the question is if it's better to crop from 380mm or take a picture at 420mm. Even if that is the case the tc is still in effect a 1.26x.
A tc is mostly used on a prime so this consideration doesn't usually apply.
10-26-2018, 01:34 PM   #4
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TC's tend to work best with faster lenses. I have used my HD 1.4x on my 60-250 to extend range closer / past my 55-300. The results are sharper and better than cropping the 55-300 from earlier and they are quite useable overall. Using the 1.4x with an f2.8 200 is another good use. And yes sometimes I use it on the f4.5 300 FA* - but I have never been tempted to use it on the 55-300 (DA - old style).

10-26-2018, 02:38 PM   #5
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QuoteOriginally posted by swanlefitte Quote
think the 55-300 holds its sharpness up to about 270mm
Well, that's right about where you loose that last click of light that takes you from f5.6 to f6.3 as you zoom, so in a way, that's just fine.
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