Do we still need a TC?

Started Nov 11, 2013 | Discussions
Mark Ransom
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Do we still need a TC?
Nov 11, 2013

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. For a high-quality primary lens coupled with a decent teleconverter this has been the case until now. But with the introduction of the K-3 at 24MP with no anti-alias, have we reached the point where cropping can do just as good a job?

I'd love to hear from someone with both the K-3 and a decent TC to do a direct comparison.

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Ian Stuart Forsyth
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Re: Do we still need a TC?
In reply to Mark Ransom, Nov 11, 2013

There are several test done on the canon forum with TC by Sheely & bobn2 with tc and even with a good tc on a cheap zoom you will still see an improvement. One of the biggest problems when people using tc is they never modify their technique when using a tc, what they will do is use a 2 Xconv on a 300mm 2.8 lens and still use that lens as if it was 300mm 2.8 and not change their methods of shooting to a 600mm F5.6 lens. I have some test with the D800 and a zoom with a 1.7 tc if you would like to see.

I don’t see that there would be any difference with a sensor W/o filters as both images are being shot with the same camera but at 2 different pixel density, I feel the more pixels you can put on a subject is always better, more data to work with for NR and other software adjustments. But then there is always the argument that a cropped 24mp image is good enough for most people’s uses.

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JNR
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Re: Do we still need a TC?
In reply to Ian Stuart Forsyth, Nov 11, 2013

The topic gets discussed endlessly. Certainly to the extent that sensors are packed tighter and lenses do not quite keep up, the usefulness of the TC becomes less and less. Along the same lines, I put a 40-year-old 50mm lens on a Q and came up with a super-sharp result. That's about the same as putting a 3x TC on a K3. Bottom line, if you have a very sharp lens (at least in the central area), the TC can be useful.

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

If you need 450mm to achieve a target large enough to focus on then no amount of Mp will save you, Only a 1.5 converter on your 300mm will get you where you need to be.

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Ontario Gone
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Re: Do we still need a TC?
In reply to Mark Ransom, Nov 11, 2013

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.

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.

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

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. For a high-quality primary lens coupled with a decent teleconverter this has been the case until now. But with the introduction of the K-3 at 24MP with no anti-alias, have we reached the point where cropping can do just as good a job?

I'd love to hear from someone with both the K-3 and a decent TC to do a direct comparison.

Packing more pixels onto the same sized sensor does not actually give you higher resolution. It just gives you larger files. How much resolution you get depend on how good your lens is, and also on diffraction. If you stop down your lens to f/11 or smaller, your resolution is limited to a few megapixels even if you have a super duper lens that can resolve over 100 line pairs per mm. Resolution aside, the greatest obstacle to sharp images when using teleconverters and long lenses is focusing accuracy. If your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

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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:

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.

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

Anastigmat 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. For a high-quality primary lens coupled with a decent teleconverter this has been the case until now. But with the introduction of the K-3 at 24MP with no anti-alias, have we reached the point where cropping can do just as good a job?

I'd love to hear from someone with both the K-3 and a decent TC to do a direct comparison.

Packing more pixels onto the same sized sensor does not actually give you higher resolution. It just gives you larger files.

You are talking about equivelant resolution, where certain technical flaws cause the photo to look as though it were a lower resolution than it is. While this is true, it only happens to the degree of the weakest link, be it noise, motion blur, lens flaws, or even lateral and spherical CA to an extent. Your statement about more pixels is wrong though, otherwise we would be just as well off with a 2mp sensor. If you are looking at files only in full view and only on a 1080 screen, yes, they would look pretty much the same with 2mp vs 20mp. In this world of digital virtual resolutions, it's not that simple. Many people crop, a lot, I would even call it a fetish. Many people print large. Some people have 4k TVs. If you can avoid diffraction, and with better glass, more MP does equal more resolution, but this is nothing D800/E users haven't been dealing with for a while now.

How much resolution you get depend on how good your lens is, and also on diffraction.

If you stop down your lens to f/11 or smaller, your resolution is limited to a few megapixels even if you have a super duper lens that can resolve over 100 line pairs per mm.

lens resolution has nothing to do with diffraction, a bad lens simply adds fuzzyness to an already soft photo. Imagine looking through one dirty window, that's diffraction. Now imagine looking through 4 dirty windows, that's diffraction+motion blur+poor lens rez+lots of noise. They are however not mutually exclusive.

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

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.

An f5.6 lens + 2X TC makes a F11 lens, much beyond diffraction limit on the K3, so result will be bad.

An 1,4 TC on a excellent, fast lens (F2.8 or F4) can be useful. This is the only case

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

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?

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

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

awaldram wrote:

If you need 450mm to achieve a target large enough to focus on then no amount of Mp will save you, Only a 1.5 converter on your 300mm will get you where you need to be.

Agreed, more or less. Unless you stick an 85mm on a Q to get to a 474mm equivalent FoV:

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paulkienitz
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Re: Do we still need a TC?
In reply to Mark Ransom, Nov 11, 2013

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. For a high-quality primary lens coupled with a decent teleconverter this has been the case until now. But with the introduction of the K-3 at 24MP with no anti-alias, have we reached the point where cropping can do just as good a job?

I'd love to hear from someone with both the K-3 and a decent TC to do a direct comparison.

Yeah, that is the question.  The particular case that's most interesting is probably: what happens when you combine the K-3, the DA* 300, and the not-yet-available Pentax 1.4x AF RC?

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

Anastigmat 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. For a high-quality primary lens coupled with a decent teleconverter this has been the case until now. But with the introduction of the K-3 at 24MP with no anti-alias, have we reached the point where cropping can do just as good a job?

I'd love to hear from someone with both the K-3 and a decent TC to do a direct comparison.

Packing more pixels onto the same sized sensor does not actually give you higher resolution. It just gives you larger files. How much resolution you get depend on how good your lens is, and also on diffraction. If you stop down your lens to f/11 or smaller, your resolution is limited to a few megapixels even if you have a super duper lens that can resolve over 100 line pairs per mm. Resolution aside, the greatest obstacle to sharp images when using teleconverters and long lenses is focusing accuracy. If your lens is f/5.6, a 2x teleconverter requires manual focusing, Unless you focus correctly, you won't get a sharp image.

Considering very few, almost nobody will use a 2x TC on an F5.6 lens then that is not the greatest obstacle, in fact a much bigger obstacle is trying to shoot through too much atmosphere, that can degrade IQ far more than A) a TC or B) diffraction.

Also of course one can now CDAF an F5.6 lens with a 2x TC, i think Ron successfully CDAF'd an F71 setup on his K-01

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

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.

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viking79
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Re: Do we still need a TC?
In reply to Mark Ransom, Nov 11, 2013

I did a resolution test of an SMCP-A 50mm f/1.7 and a Vivitar 2x macro focusing extender, and the TC was much better than cropping to 100 mm field of view. This was on a 16 MP Sony NEX camera, K-3 might differ for crop, but not enough to match the TC.

I haven't posted results for it, will try to soon. Been doing some other lens reviews.

However, the TC was only decent above f/4 on lens (f/8 including TC). This combination was similar resolution to the SMCP 100mm f/4 macro, but not at equivalent apertures. The macro at f/4 was more like TC+50mm at f/8 (set at f/4 - 2 stops for TC).

My point is, with a good sharp prime and quality TC should still be a little better than cropping. The trade off point with K-3 will mean you need even better TC and lens to get better results than cropping. TC on small aperture lens is probably no gain, but I haven't tested as I can't get that far away from my chart.  Your best bet is get a lens of the needed focal length of course, it might not be sharper than lens with TC but should be larger aperture.

Eric

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paulkienitz
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Re: Do we still need a TC?
In reply to viking79, Nov 11, 2013

viking79 wrote:

I did a resolution test of an SMCP-A 50mm f/1.7 and a Vivitar 2x macro focusing extender, and the TC was much better than cropping to 100 mm field of view. This was on a 16 MP Sony NEX camera, K-3 might differ for crop, but not enough to match the TC.

That sounds promising.  I have one of those Vivitar 2x Macro things in OM mount, and it got quite blurry when I put it behind the long end of a 28-200 zoom, but it seemed to work well enough when converting my 50/1.8 into a 100/3.5 macro.  If even as dubious a teleconverter as that is still doing good work on a K-5, then the K-3 can probably still benefit from the coming AF RC.  I may have to get one with a DA* 300, since Pentax isn't offering a 450/5.6 or the like.  Of course, first my budget has to recover from buying the K-3 after I just had to replace my car.

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

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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James O'Neill
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Basic error
In reply to Mark Ransom, Nov 11, 2013

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)

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JNR
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Re: Do we still need a TC?
In reply to viking79, Nov 11, 2013

viking79 wrote:

I did a resolution test of an SMCP-A 50mm f/1.7 and a Vivitar 2x macro focusing extender, and the TC was much better than cropping to 100 mm field of view. This was on a 16 MP Sony NEX camera, K-3 might differ for crop, but not enough to match the TC.

I haven't posted results for it, will try to soon. Been doing some other lens reviews.

However, the TC was only decent above f/4 on lens (f/8 including TC). This combination was similar resolution to the SMCP 100mm f/4 macro, but not at equivalent apertures. The macro at f/4 was more like TC+50mm at f/8 (set at f/4 - 2 stops for TC).

My point is, with a good sharp prime and quality TC should still be a little better than cropping. The trade off point with K-3 will mean you need even better TC and lens to get better results than cropping. TC on small aperture lens is probably no gain, but I haven't tested as I can't get that far away from my chart. Your best bet is get a lens of the needed focal length of course, it might not be sharper than lens with TC but should be larger aperture.

Eric

Seems to confirm the conventional wisdom. That is, a good, fast prime will benefit most. I suspect a few good zooms can benefit if they are fast. Diffusion limits are going to pose a problem as much as dark screen issues on the slower lenses. The resolution question is a real factor. I never hesitated to use a TC when shooting the Canon 5D - which had a larger pixel pitch than the original 6 mp sensors on Pentax and Nikon.

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