Do we still need a TC?

Started Nov 11, 2013 | Discussions
MightyMike
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Re: Do we still need a TC?
In reply to awaldram, Nov 11, 2013

awaldram wrote:

MightyMike wrote:

Alastair Norcross wrote:

awaldram wrote:

Anastigmat wrote:

If your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

Only if you own a Canon, a Pentax will Auto focus an f5.6 + 2x converter with ease.

Really? A Pentax will perform phase-detect auto focus with a lens whose widest aperture is F11? I didn't know that. How fast is it?

Actually things have changed... It used to be (K10D to K-5) F8 with ease, F9 with little issue and F10 was pushing your luck, F10.7 only in the most extreme cases. When the K-5IIs came out F9 started to become a lot more difficult to focus... I don't think the K-3 has been fully tested for this yet.

K3 , 50-500 f6.7 + 2x converter

F 13.4 = no issue

Nothings changed as far as I can see maybe you need better quality converter ?

Sorry about subject matter but it's dark out and hand holding 1000mm Auto focusing indoors take some light.

Confirmed... i tried focus trap at F11 with one and 2 1.4x TC's on mirror lenses and it does focus trap! Sorry i don't have a 2x TC or a lens that is slow that would accept both 1.4x TC's as the one is the Sigma with protruding element. I bet Ron could do a heck of a lot more testing

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Mike from Canada
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klavrack
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Re: Do we still need a TC?
In reply to Anastigmat, Nov 11, 2013

f your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

If so, wouldn't focus peaking perhaps minimize that drawback, at least for relatively stationary subjects?

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Alastair Norcross
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Re: Do we still need a TC?
In reply to MightyMike, Nov 11, 2013

MightyMike wrote:

awaldram wrote:

MightyMike wrote:

Alastair Norcross wrote:

awaldram wrote:

Anastigmat wrote:

If your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

Only if you own a Canon, a Pentax will Auto focus an f5.6 + 2x converter with ease.

Really? A Pentax will perform phase-detect auto focus with a lens whose widest aperture is F11? I didn't know that. How fast is it?

Actually things have changed... It used to be (K10D to K-5) F8 with ease, F9 with little issue and F10 was pushing your luck, F10.7 only in the most extreme cases. When the K-5IIs came out F9 started to become a lot more difficult to focus... I don't think the K-3 has been fully tested for this yet.

K3 , 50-500 f6.7 + 2x converter

F 13.4 = no issue

Nothings changed as far as I can see maybe you need better quality converter ?

Sorry about subject matter but it's dark out and hand holding 1000mm Auto focusing indoors take some light.

Confirmed... i tried focus trap at F11 with one and 2 1.4x TC's on mirror lenses and it does focus trap! Sorry i don't have a 2x TC or a lens that is slow that would accept both 1.4x TC's as the one is the Sigma with protruding element. I bet Ron could do a heck of a lot more testing

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Mike from Canada
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So, just to be absolutely clear, these are using phase-detect AF, not live view AF? So everything I read about the PD AF system needing lenses with a maximum aperture of F5.6 or faster in reviews of the K5 and K5II was wrong? Or is this with a non-reporting TC? What is the AF speed like?

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awaldram
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Re: Do we still need a TC?
In reply to Alastair Norcross, Nov 11, 2013

Alastair Norcross wrote:

So, just to be absolutely clear, these are using phase-detect AF, not live view AF? So everything I read about the PD AF system needing lenses with a maximum aperture of F5.6 or faster in reviews of the K5 and K5II was wrong? Or is this with a non-reporting TC? What is the AF speed like?

I don't think I've ever read a review stating f5.6 for Pentax cameras , as I say the only cameras this applies to is canon and even there it's a deliberate limit set in firmware of the converter.

I can't confirm what the k5ii will focus to but pretty obviously its greater than f5.6 else Bigmas , sigma super zoom etc would all be useless as there slower than that.

Maybe you or the reviewer are mis-understanding the specs.?

Pentax cameras upto and including the k5 have f5.6 sensors this means the base line extends to a max aperture of f5.6, So any lens faster cannot be more accurate than that from readings.

Later cameras have varying numbers of f2.8 sensors which means they have a wider baseline and can achieve higher accuracy reading from faster (2.8 and better) lens.

Neither of these directly reflect the max PD lens aperture that the camera can focus though it is related. the point 'blackout' occurs is the point the lens will no longer focus.

This point is dependent on sensor baseline + lens contrast +t stop + af module light losses.

As F stop goes up light requirements also rise to maintain decent AF speed, I can't tell you how fast AF is as indoor hand held at 1000mm is very sluggish but that is more related to my ability to hold target than the AF lock period.

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Anastigmat
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Re: Do we still need a TC?
In reply to Alastair Norcross, Nov 11, 2013

Alastair Norcross wrote:

I've done a bit of research, and from what I can tell, it looks like the Pentax has the usual PD limitation (for a crop camera) to F5.6, which means it won't AF an F5.6 lens with a 2X teleconverter. You might be able to trick the camera into not realizing it has a converter. You can do that with Canons too, and achieve some kind of AF, but it tends to be slow and hunt a lot. The 1DX and 5DIII will PD AF with an F8 lens, but even they won't do it with F11. Were you thinking of live view AF? If you use live view, of course, you can AF with as slow a lens as you like, but live view AF is pretty slow. The fastest I know of is the new 70D, with its hybrid live view system.

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For most cameras, regardless of brand, the excess hunting with a f/5.6 lens and a 2x teleconverter will force most users to give up and focus manually.

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fotobert
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There is a quite simple answer
In reply to Mark Ransom, Nov 11, 2013

...the Leica Extender R 2x

The original comment in a 80's Leica brochure was: The image quality of an extender is simply better than a crop. They would not have built it, if it would not work.

Albert

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Anastigmat
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Re: Do we still need a TC?
In reply to awaldram, Nov 11, 2013

awaldram wrote:

MightyMike wrote:

Alastair Norcross wrote:

awaldram wrote:

Anastigmat wrote:

If your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

Only if you own a Canon, a Pentax will Auto focus an f5.6 + 2x converter with ease.

Really? A Pentax will perform phase-detect auto focus with a lens whose widest aperture is F11? I didn't know that. How fast is it?

Actually things have changed... It used to be (K10D to K-5) F8 with ease, F9 with little issue and F10 was pushing your luck, F10.7 only in the most extreme cases. When the K-5IIs came out F9 started to become a lot more difficult to focus... I don't think the K-3 has been fully tested for this yet.

K3 , 50-500 f6.7 + 2x converter

F 13.4 = no issue

Nothings changed as far as I can see maybe you need better quality converter ?

Sorry about subject matter but it's dark out and hand holding 1000mm Auto focusing indoors take some light.

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Mike from Canada
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Exactly, the light is the problem. If you have a bright light with good contrast like that a f5.6 lens and a 2x teleconverter will still autofocus. Point the same combination at a hawk sitting in a tree outdoors even when there is sunlight, and the autofocus will still hunt back and forth. Hawks are not like lamps.  They don't come with LED or tungsten bulbs. With a f5.6 lens, a 1.4x teleconverter will still allow autofocus in real world situations with real world subjects, but not a 2x.

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awaldram
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Re: Do we still need a TC?
In reply to Anastigmat, Nov 11, 2013

Anastigmat wrote:

Exactly, the light is the problem. If you have a bright light with good contrast like that a f5.6 lens and a 2x teleconverter will still autofocus. Point the same combination at a hawk sitting in a tree outdoors even when there is sunlight, and the autofocus will still hunt back and forth. Hawks are not like lamps. They don't come with LED or tungsten bulbs. With a f5.6 lens, a 1.4x teleconverter will still allow autofocus in real world situations with real world subjects, but not a 2x.

I don't recognise anything your saying re Pentax cameras, Do you have any experience with Pentax AF 2x converters and decent lens ?

From a boat hence the camera shake

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Anastigmat
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Re: Do we still need a TC?
In reply to awaldram, Nov 11, 2013

awaldram wrote:

Anastigmat wrote:

Exactly, the light is the problem. If you have a bright light with good contrast like that a f5.6 lens and a 2x teleconverter will still autofocus. Point the same combination at a hawk sitting in a tree outdoors even when there is sunlight, and the autofocus will still hunt back and forth. Hawks are not like lamps. They don't come with LED or tungsten bulbs. With a f5.6 lens, a 1.4x teleconverter will still allow autofocus in real world situations with real world subjects, but not a 2x.

I don't recognise anything your saying re Pentax cameras, Do you have any experience with Pentax AF 2x converters and decent lens ?

From a boat hence the camera shake

This is an easy subject with bright illumination and high contrast subject. Try photographing a red tailed hawk sitting in a tree in the shade, with the same combination of lens and teleconverter and report to us the results. BTW, why do you use ISO 100? Only a beginner would do that sort of thing, unless of course your camera is so nosiy at high ISO settings that you dare not use ISO 400 or above. BTW, it looks out of focus as well, which is precisely my point. Manufacturers of 2xTCs all have instruction sheets that advise against using a combination of f5.6 and 2x teleconverters.  They don't want irate customers calling them and complaining that the combination does not work.

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Conjure
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Re: Basic error
In reply to James O'Neill, Nov 11, 2013

+1

But:

Lets say your TC can manage 1000 lines per image width ...

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awaldram
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Re: Do we still need a TC?
In reply to Anastigmat, Nov 11, 2013

Anastigmat wrote:

This is an easy subject with bright illumination and high contrast subject. Try photographing a red tailed hawk sitting in a tree in the shade, with the same combination of lens and teleconverter and report to us the results. BTW, why do you use ISO 100? Only a beginner would do that sort of thing, unless of course your camera is so nosiy at high ISO settings that you dare not use ISO 400 or above.

At this point the discussion is over, You've posted your colours .

Foolish comments and moving goal posts as you try and justify your incorrect statements are childish and sorry your on your own.

Grey Manatee on a grey river.

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Anastigmat
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Re: Do we still need a TC?
In reply to awaldram, Nov 11, 2013

awaldram wrote:

Anastigmat wrote:

This is an easy subject with bright illumination and high contrast subject. Try photographing a red tailed hawk sitting in a tree in the shade, with the same combination of lens and teleconverter and report to us the results. BTW, why do you use ISO 100? Only a beginner would do that sort of thing, unless of course your camera is so nosiy at high ISO settings that you dare not use ISO 400 or above.

At this point the discussion is over, You've posted your colours .

Foolish comments and moving goal posts as you try and justify your incorrect statements are childish and sorry your on your own.

One more thing, 1/800 sec. should have frozen the action, so it couldn't have been camera shake.  Perhaps the AF system was fooled into thinking the subject was in focus when it really wasn't.  That is another reason not to use the combination of 2x teleconverter and f/5.6 lens. It is like fool's gold rather than the real thing.

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MightyMike
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Re: Do we still need a TC?
In reply to Alastair Norcross, Nov 11, 2013

So, just to be absolutely clear, these are using phase-detect AF, not live view AF? So everything I read about the PD AF system needing lenses with a maximum aperture of F5.6 or faster in reviews of the K5 and K5II was wrong? Or is this with a non-reporting TC? What is the AF speed like?

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Alastair
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Not sure where you read F5.6 or faster cause thats total bunk and has been for a long time, I think early on some reviewers just assumed it was the same restrictions as one sees on a canon system but that has never been true. don't read reviews from uneducated reviewers .

Also no teleconverter for the Pentax system actually reports to the lens or body that there is a teleconverter.

Another point, I found that on all teleconverters that use screww drive there is a gear in the screw drive path that slows the focus speed by 1:2 or 1:2.5 regardless of the magnification factor. It is my opinion that this is deliberate to convince people to rather buy a more expensive longer lens than a TC. However I will be contacting some technicians tomorrow to see if the can give a legitimate reason for slowing the AF down before i post a full report on this in the forum. For Pentax those TC's that also allow SDM don't have a chip telling the lens to slow the motor down so there shouldn't be a technical reason to do so and that at the moment is my opinion. If its true that the gearing down is not necessary I'll work on converting my TC's to have no gearing and just be 1:1.

For the most part but not always a 1.4x TC will still focus most lenses fast and a 2x TC some lenses fast, but now that i know of the gearing down I can guarantee you that with the TC will never be as fast as without. that doesn't stop me from using my Sigma 1.4x EX DG on the Sigma 100-300mm F4.0 EX DG and Sigma 500mm F4.5 EX DG with great success and little difficulty.

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Mike from Canada
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awaldram
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Re: Do we still need a TC?
In reply to Anastigmat, Nov 11, 2013

Anastigmat wrote:

awaldram wrote:

Anastigmat wrote:

This is an easy subject with bright illumination and high contrast subject. Try photographing a red tailed hawk sitting in a tree in the shade, with the same combination of lens and teleconverter and report to us the results. BTW, why do you use ISO 100? Only a beginner would do that sort of thing, unless of course your camera is so nosiy at high ISO settings that you dare not use ISO 400 or above.

At this point the discussion is over, You've posted your colours .

Foolish comments and moving goal posts as you try and justify your incorrect statements are childish and sorry your on your own.

One more thing, 1/800 sec. should have frozen the action, so it couldn't have been camera shake. Perhaps the AF system was fooled into thinking the subject was in focus when it really wasn't. That is another reason not to use the combination of 2x teleconverter and f/5.6 lens. It is like fool's gold rather than the real thing.

You are obliviously very inexperienced in the subjects you talk about.

The camera is obviously in TV mode set at 1/800 wide open with floating ISO.

In addition hand-holding 1000mm on a boat tracking a bird is unlikely to be sharp at 1/800

I wasn’t out shooting birds, as being on a boat might have clued you up.!

A casual glance at the image is easy to see the blur is shake not focus for even the most moderate experienced photographer.

Therefore either your a complete NOOB about photography or your your being deliberately obstinate in the face of obvious facts.

1 you claim Pentax cameras can;t shoot f5.6 +2x

I show image f6.7 2x

2 you claim camera only focused due to light and couldn't shoot a hawk in flight

I show hawk in flight f6.7 2x

3 you claim due to bright weather and couldn’t shoot low contrast target

I post grey on grey f6.7 2x

4 you claim wouldn't work in coal cellar with black cat

I agree.!

Never the less your talking complete twaddle.

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awaldram
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Re: Do we still need a TC?
In reply to MightyMike, Nov 11, 2013

Well at least this thread hasn't been a dead loss.

I was about to argue the point on geared AF but thought I;d check before making a fool of myself.

Good job I did and I've learnt something new ....Thanks Mike.

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MightyMike
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Re: Basic error
In reply to James O'Neill, Nov 11, 2013

James O'Neill wrote:

Mark Ransom wrote:

A teleconverter works by magnifying the image that it gets from the primary lens. You could get the same effect by simply cropping, but the assumption is that the magnified image will be higher in quality than the cropped image.

No that's not the assumption. The TC can't possibly out put an image of any higher quality than went into it. So why do we have one ?

If you record 1/2 the image with all the pixels (or all the film area) you will get better results than if you record all the image with all area and print half the result.

The net resolution is normally given as 1/net = 1/medium + 1/lens
for simplicity assume sensor and lens have equal res if the smallest the medium can resolve is 1/100th mm and the smallest the lens can resolve is also 1/100th mm the dot you can get when you put them together is 2/100mm. -i.e. 1/50th .

So lets say your lens can manage 1000 lines per image width and so can the sensor, net you get 500 lines per width. Crop to half the width you get 250 lines.

With a TC you're putting 500 of the 1000 lines onto 1000 lines of sensor res - net you 333 lines with the TC (less any loss from the TC itself)

If the parent lens out resolves the sensor by a factor of 2 then adding a 2x TC will still net you more detail than cropping. I'd suggest that many lenses still out resolve even high pixel count sensors by a good margin.

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Mike from Canada
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MightyMike
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Re: Do we still need a TC?
In reply to awaldram, Nov 11, 2013

+1

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Ontario Gone
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Re: Do we still need a TC?
In reply to klavrack, Nov 12, 2013

klavrack wrote:

f your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

If so, wouldn't focus peaking perhaps minimize that drawback, at least for relatively stationary subjects?

Peaking helps with things like this but at such small apertures the contrasting lines would be much less visible, which is what peaking is based on.

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paulkienitz
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Re: Basic error
In reply to MightyMike, Nov 12, 2013

MightyMike wrote:

I'd suggest that many lenses still out resolve even high pixel count sensors by a good margin.

This is getting harder to believe.  Today's crop-format sensors have a photosite spacing between 3.5 and 4 microns.  I don't think there are a ton of lenses out there that can resolve finer than that.  For one thing, the diffraction blur circle at f4 is already over 5 microns in theory, and f2.8 lenses are not usually sharper than f4 ones.  In practice it seems possible to extract smaller detail than this, but it's an uphill fight.

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Mark Ransom
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Re: Do we still need a TC?
In reply to Ontario Gone, Nov 12, 2013

Ontario Gone wrote:

Don't have a K3 yet, but I will offer my 2. one thing is inevitable, eventually we will see sensor resolutions that are too high for either diffraction limits, or lens resolutions, or both. Even the high end glass. When that happens, a TC will just be magnifying an already fuzzy image, and so will cropping, but at least the TC will give more pixels on the subject.

If you want more pixels, you can just upsize the cropped image. Once you've captured all the detail that comes from the lens it doesn't matter how many pixels it spreads out over.

That hard answer here is it depends. If technical aspects are spot on, meaning almost no motion blur, focus is sharp, low noise, cropping should be "sharper" as you are not adding any glass. The key word is IF. AFAIK, most people use TC for things like birding, or astrophotography, and these things are usually limited by the situations. Action shots are going to have some traces of blur, always, and the sky can get real turbulent. In these cases it's probably better to have a little extra glass than to magnify the pixel level flaws of motion blur and high iso.

I can see that spreading high ISO noise out over more pixels would be desirable. But since the TC forces you to bump up a stop in ISO to keep the same shutter speed, might it not cancel out?

If conditions are ideal, I would rather crop and use optimal settings in camera. Are there TC that are so pristine you can hardly tell they are on? I don't know and likely don't want to pay for one. I kinda agree with your idea here that more MP is allowing us to crop more and more for reach. It's one of the reasons I love filterless sensors so much, but I honestly think there is a tool for every job. TC when things are sloppy, cropping when you have complete control.

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