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03-17-2014, 07:40 AM   #16
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QuoteOriginally posted by Giklab Quote
"If a native lens requires 10 turns to move from 5ft focus to 7ft focus then providing there is no reduction in gearing the same lens with a 2 x converter attached wiil require 5 turns to move from 5 ft to 7ft."

This is where you are incorrect. A 'native' lens will ALWAYS take the same number of turns to focus from 5ft to 7ft, no matter how many teleconverters, filters or lens caps you stack on top. The TC simply extends the focal length, the focus range remains identical (except with the AFA 1.7x, but that's the one and only exception).
7ft away is 7ft away no matter what.
Your confused between you focusing the lens and the camera focusing the lens.

It's not even a point of argument, Take a converter any converter and count the camera side turns to lens side they are not 1:1.

If you were right they would be as it would just be a straight shaft , it isn't and so your wrong.

As these image clearly show

1st image native lens 3ft focused lens distance reads 3ft
switch to MF attach "x converter
2nd image the results out of focus lens reads 3ft
3rd image refocused with 2x converter lens distance now reads 2ft

Every 2 turns on camera side results in 1 lens side on this 2x converter

You are sort of right in saying focus range remains the same as the near field min focus remains constant , but far field range is constrained by the focal multiplier a pretty mute point as were at infinity.!

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Last edited by awaldram; 03-17-2014 at 08:19 AM.
03-17-2014, 08:27 AM   #17
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With a properly designed and constructed TC,here should not be any impact on focus distance (3m without a TC is 3m with TC) or SDM focusing. That the TC is there STILL doesn't change the fact that the AF system in the lens needs to travel an identical distance (reducers in the TC would slow down an AF system, but only because the camera needs to do more turns).
QuoteOriginally posted by awaldram Quote
Every 2 turns on camera side results in 1 lens side on this 2x converter
Assuming the TC has reducers (Please read what you quoted again), then this is absolutely correct. But not because the lens AF has to turn more.
What you are seeing above is the change of the optical formula, which results in the lens focusing at a different distance with the TC. Please, could you find the MFD with and without the TC?

Last edited by Giklab; 03-17-2014 at 08:35 AM.
03-17-2014, 08:45 AM   #18
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QuoteOriginally posted by Giklab Quote
With a properly designed and constructed TC,here should not be any impact on focus distance (3m without a TC is 3m with TC) or SDM focusing. That the TC is there STILL doesn't change the fact that the AF system in the lens needs to travel an identical distance (reducers in the TC would slow down an AF system, but only because the camera needs to do more turns).

Assuming the TC has reducers (Please read what you quoted again), then this is absolutely correct. But not because the lens AF has to turn more.
Scuse me ???

"but only because the camera needs to do more turns"
and
"But not because the lens AF has to turn more"

Your confusing me now !!


Anyway to prove further I have run a test having previously proved to my satisfaction that SDM through the converter did not introduce a reduction (as per my points on requirement)

I have now tested between two focal point 6ft and 15ft repeatedly (10 times to remove test margins)

If your correct then if the the native take 10 seconds then the converter has to be slower (losing a stop , Chromatic errors , dropped contrast etc etc ).

If I'm correct then the converter should be as faster than native !!! despite all the (losing a stop , Chromatic errors , dropped contrast etc etc).

and the results

Converter = 19.07 seconds
native = 20.78 seconds

this is in lowish light .

As I keep pointing out all my evidence can be tested by anyone so is pretty much incontrovertible

Yet you keep offering no evidence to your point whatsoever ??

It doesn't matter how many time you try and say "STILL doesn't change the fact" it still is not a fact at all .!

In this test the cards were deliberately stacked in 'Native' favor still the converter managed to show a clear 10% speed advantage with SDM lens, Given this I think it fair to say 'early reports' are based on reproducible evidence to back up their statements.

Whilst your theories appears not to have a shred of evidence.
03-17-2014, 08:50 AM   #19
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QuoteOriginally posted by awaldram Quote
Converter = 19.07 seconds
native = 20.78 seconds
OK now that's interesting. How did you measure it?

03-17-2014, 09:12 AM   #20
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QuoteOriginally posted by Giklab Quote
OK now that's interesting. How did you measure it?
I have now tested between two focal point 6ft and 15ft repeatedly (10 times to remove test margins)

Pretty rough left hand start stopwatch right hand acquire close target on beep release af acquire fare target on beep back to close etc etc 10 times

As were looking for 40% speed discrepancy (would be 6 seconds in this test )its close enough


Further testing I'll grant you 1m is 1m irrelevant of converter ( think my previous example was crxp optics)

I think what were seeing is SDM lens will operate without any usual slow down associated with converter use this gives the impression of improved AF relative to screw converter (due to physical gearing)

One other thing I noted the converter can fool PD for any approaching target and drive the AF the wrong way !!

Not consistent and I can't repeat it but happened 3 -4 times in 700 shots on the weekend and has never happened before.
03-17-2014, 09:18 AM   #21
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QuoteOriginally posted by awaldram Quote
I think what were seeing is SDM lens will operate without any usual slow down associated with converter use this gives the impression of improved AF relative to screw converter (due to physical gearing)
I agree completely on this. I think you can disregard my PM then .
03-19-2014, 10:47 PM   #22
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regarding the conversation above, I though a TC only magnifies the image.... meaning like x1.4 "bigger".

So focal length still remains the same.

I imagine it being like looking at the moon, the moon is 384,400 km away, even if you have a massive telescope, you still need to focus at 384,400 km, and not 300,000 km. Am I right?
03-19-2014, 11:40 PM   #23
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QuoteOriginally posted by leungclj Quote
I imagine it being like looking at the moon, the moon is 384,400 km away, even if you have a massive telescope, you still need to focus at 384,400 km, and not 300,000 km. Am I right?
The focal length of the lens remains the same, but the FL of the entire setup changes. Yes, you still need to focus at the same distance, although some TCs might affect that and the 300 000 km mark on the lens might mean something else.

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