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06-23-2014, 06:58 PM   #1
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K3 with Stacked 1.4 and F1.7X Rear Converters

I tried the Pentax 1.4X rear converter and the Pentax F1.7X converter with the K3 and DA 300 today to see what is would do. This combo creates an effective focal length of 710mm. Does it work? Well, since the F 1.7X converter allows only centre point AF, it only can AF in good light. However, it worked better than I expected so it is worthwhile to continue some experiments. An example shot from today of a goldeneye.


Dale

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06-23-2014, 07:20 PM   #2
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I hope you didn't have SR on - the FL is reported as 24mm!
06-23-2014, 08:59 PM   #3
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That would effectively double the hit you take to maximum aperture. That said, I've seen articles by George Lepp where he said he has stacked 1.4x and 2x tele-extenders when no other option would work. He warned about softness in the images due to twice as many glass elements being added but if the option is a slightly soft image at f/11 or no image, it might be worth it.

Last edited by abmj; 06-23-2014 at 10:36 PM.
06-23-2014, 10:26 PM   #4
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False choice though, right?

Let's say the TC's give you exactly what you want. Some choices:

1) 300+1.7+1.4 = 714mm F/9.5 @ 24 MP
2) 300+1.7 = 510mm F/6.8 @ 24 MP, or cropped to 714mm F/9.5 @ 17 MP
3) 300+1.4 = 420mm F/5.6 @ 24 MP, or cropped to 714mm F/9.5 @ 14 MP
4) 300 = 300mm F/4 @ 24 MP, or cropped to 714mm f/9.5 @ 10MP


Personally I'd bet that image #4, even cropped that far, would likely be better than image #1.

06-24-2014, 01:01 AM   #5
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QuoteOriginally posted by ElJamoquio Quote
False choice though, right?

Let's say the TC's give you exactly what you want. Some choices:

1) 300+1.7+1.4 = 714mm F/9.5 @ 24 MP
2) 300+1.7 = 510mm F/6.8 @ 24 MP, or cropped to 714mm F/9.5 @ 17 MP
3) 300+1.4 = 420mm F/5.6 @ 24 MP, or cropped to 714mm F/9.5 @ 14 MP
4) 300 = 300mm F/4 @ 24 MP, or cropped to 714mm f/9.5 @ 10MP


Personally I'd bet that image #4, even cropped that far, would likely be better than image #1.
I agree on this one. I have a print made from K-5 crop, just 4 megapixel, made into A3 and it looks fine. So I turned my 300mm lens into 600mm without use of a TC.
06-24-2014, 05:01 AM   #6
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I've been doing some experiments along similar lines, I will do a thread for it but trying the 50-135 at 135 with the old 1.7 AFA, the quality captured with the 1.7 AFA far exceeds the cropped image quality in the early test.

I would be interested if the OP could try these combinations suggested above, based on my experiments my money is going on option #2, and you get AF too.

QuoteOriginally posted by ElJamoquio Quote
1) 300+1.7+1.4 = 714mm F/9.5 @ 24 MP
2) 300+1.7 = 510mm F/6.8 @ 24 MP, or cropped to 714mm F/9.5 @ 17 MP
3) 300+1.4 = 420mm F/5.6 @ 24 MP, or cropped to 714mm F/9.5 @ 14 MP
4) 300 = 300mm F/4 @ 24 MP, or cropped to 714mm f/9.5 @ 10MP
By the way, the AF I got on the 50-135+1.7AFA was really easy to work with, setting the lens to the rough length is pretty damn easy then let the AFA do its thing. Very glad personally I got the AFA, its what I'm planning to use at kids football etc, to give me some extra reach without big investment.
06-24-2014, 05:02 AM   #7
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While I haven't printed this picture yet, it will print fine and I have 24 MP to work with.

Dale
06-24-2014, 09:41 AM   #8
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You shoot wide open and with both adapters? If so, at f/9.5 there is diffraction for 24mp aps-c sensor. And I am not sure that combo is enough for 24mp resolution. So I dont think you really have 24mp for printing, watch the size and viewing distance

06-24-2014, 11:57 AM   #9
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I had the 1.4 and 1.7, and tried them stacked.

The 1.4 gave better performance, and more accurate AF than the 1.7, and sharper images that revealed more detail cropped than the stacked combination at full resolution. This was using a K3 which obviously will have a crop advantage for optimally focussed shots over other bodies.

The contrast and sharpness of the 1.4 won over the 1.7X and also the stack. I didn't hesitate to sell the 1.7X after a few tests - getting a 'closer' image (filling the frame) is no advantage if less detail is revealed.

Last edited by johnc; 06-26-2014 at 12:31 AM.
06-24-2014, 01:05 PM   #10
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I find that both the new 1.4X and the F1.7X work well but is was fun to try them together.

Dale
06-24-2014, 02:41 PM   #11
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Definitely, it was one of the first things I tried! They are both very useful, and the 1.7x has some advantages, but personally I couldn't justify both. I do wonder if I will regret the sale one day.
06-24-2014, 03:10 PM   #12
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QuoteOriginally posted by johnc Quote
I do wonder if I will regret the sale one day.
I don't yet, and I sold mine perhaps 2 years ago. I might have a different opinion if I had some A* glass... but the A*600+F1.7x I tried was way-too-purple-fringy for me. No thanks!
06-25-2014, 05:24 AM   #13
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QuoteOriginally posted by johnc Quote
Definitely, it was one of the first things I tried! They are both very useful, and the 1.7x has some advantages, but personally I couldn't justify both. I do wonder if I will regret the sale one day.
I also think the 1.4 gives better AF accuracy so I sold my 1.7. Despite it's limitations, I am already beginning to regret letting the 1.7 go.
06-25-2014, 05:33 AM   #14
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I've got both, and would never let one go. The 1.4 gives me full AF on my electrical lenses, and the 1.7 converts my A-lenses into AF lenses. Mind you, on my A_400 I find unless it's broad highlight blasting daylight, I have to manual focus anyway.
06-26-2014, 12:37 AM   #15
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QuoteOriginally posted by normhead Quote
I've got both, and would never let one go. The 1.4 gives me full AF on my electrical lenses, and the 1.7 converts my A-lenses into AF lenses. Mind you, on my A_400 I find unless it's broad highlight blasting daylight, I have to manual focus anyway.
I have a fair number of MF lenses but never used the AFA much for that purpose, partly due to my manuals being in the 50mm range.

I have the samyang 85 1.4 and DA* 50-135 to cover the combination of my MFs with the 1.7x, at some weight penalty.

I might feel different if I had longer manual primes to hand. The AFA 1.7 performed well with the DFA 100mm for example, more detail revealed at the expense of some CA.
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