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05-10-2017, 11:44 AM   #1
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Stacking 1.4 Teleconverters

Hi all. I am curious if anyone has tried stacking 2 1.4 HD Teleconverters at all, and if so what were the results like.
If not, what effect would you expect it to have, if it's even possible.

Cheers

05-10-2017, 11:47 AM   #2
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normhead does stuff like this. You'll want some fast glass on the end due to the drop in equivalent f-stop. A couple really high quality TC's and good glass on the end shouldn't affect sharpness or diffraction much. Much.
05-10-2017, 11:59 AM   #3
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Well I was considering trying it on the 150-450, but I fear that it's probably not quite fast enough. I am guessing that you would lose 2 stops?
05-10-2017, 12:52 PM   #4
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Here's a thread from mflenses.com, stacking tc's on a 300mm

Fun with Teleconverters

05-10-2017, 12:54 PM   #5
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QuoteOriginally posted by Kevriano Quote
Well I was considering trying it on the 150-450, but I fear that it's probably not quite fast enough. I am guessing that you would lose 2 stops?
With a TC on a DFA150-450, sharpness gets restored between f10 and f14, with the consequence of having to use a fairly low shutter speed relative to the focal length or high iso at which sharpness drops. I'm able to get fairly good image quality at f11 / f13 and using the electronic shutter on the K1, AF still works, but shooting conditions are limited. Anything, I think it's more simple to use a crop sensor with higher density pixels.
05-10-2017, 12:57 PM   #6
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Let's say you're shooting at f5.6. The math as I understand it would be 5.6*1.4*1.4 which equals about f11. I also don't think it would be sharp like if you stopped it down to f11 without the TC's. If you had it out at 450 for this, your focal distance would be 450*1.4*1.4 which equals about 900. What might make more sense is a good 1.7 TC and just use it alone; f-stop with the above case would be 5.6*1.7 for about f9.5 and a focal length of 765.

Without bolting it all together, or seeing results from someone else that did, I don't know what path I would want to take.
05-10-2017, 12:58 PM   #7
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QuoteOriginally posted by biz-engineer Quote
With a TC on a DFA150-450, sharpness gets restored between f10 and f14, with the consequence of having to use a fairly low shutter speed relative to the focal length or high iso at which sharpness drops. I'm able to get fairly good image quality at f11 / f13 and using the electronic shutter on the K1, AF still works, but shooting conditions are limited. Anything, I think it's more simple to use a crop sensor with higher density pixels.
Yes, I currently use a TC on the 150-450, and actually it's perfectly sharp at f8 IMO, but curious about stacking 2...
05-10-2017, 02:57 PM - 1 Like   #8
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I've stacked 3 TCs - to take pictures of the Sun, where there is PLENTY of light: Magnification Factors for several Kenko Teleconverters on K5 - PentaxForums.com

The images were OK. The ability to see details was definitely improved - the gain in magnification more than made up for the loss in resolution due to the stacking.

If you already have more than one, go ahead and try stacking. You can't hurt anything.

05-10-2017, 04:32 PM - 1 Like   #9
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I own the D FA 150-450 and last year at Yellowstone I spotted a grizzly sow with three cubs way off in the distance. So I stacked a Tamron 1.4x with a Vivitar 2x macro teleconverter onto my 150-450 which was mounted on my K3. This gave me the equivalent of an 1890mm lens. i later measured the distance on Google Earth to be a bit over 1 mile (1.6 km) away. The results are below. Due to the distance involved, not a great shot, but I doubt that I will ever see such a sight again.
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PENTAX K-3  Photo 

Last edited by gaweidert; 05-11-2017 at 06:43 AM.
05-10-2017, 05:20 PM   #10
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Q7/QS1 is the best teleconverter!

Last edited by surfar; 05-10-2017 at 05:26 PM.
05-10-2017, 10:07 PM   #11
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QuoteOriginally posted by gaweidert Quote
I own the D FA 150-450 and last year at Yellowstone I spotted a grizzly sow with three cubs way off in the distance. So I stacked a Tamron 1.4x with a Vivitar 2z macro teleconverter onto my 150-450 which was mounted on my K3. This gave me the equivalent of an 1890mm lens. i later measured the distance on Google Earth to be a bit over 1 mile (1.6 km) away. The results are below. Due to the distance involved, not a great shot, but I doubt that I will ever see such a sight again.
From a mile away that's pretty remarkable! Thanks for the reply too. Interesting result.
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