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Old 19th of February 2013 (Tue)   #1
tonylong
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Default Fun With a TC!

Hey All!

Recently I got involved in a Facebook "mini-discussion" about using TCs (teleconverters).

I had for some years used a Kenko 1.4x TC with my EF 100-400 lens for some of my wildlife/bird shooting. I had tried the Canon 2x TC but saw that there was too much of a hit to my IQ. I had also tried the Kenko 1.4x compared to the Canon 1.4x and decided the Kenko stood up well.

Well, over the past year I've had to sell off a lot of my photo gear...including the Kenko 1.4x and the Canon 2x, Oh Well...

Anyway, on to the discussion we had! The original poster (a solid POTN member) had shot something with a long lens and a 1/4x TC. Now the interesting part: when you use a Canon tC and I believe the Kenko 1.4x TC, the TC will communicate with the camera and the camera will automatically limit your widest aperture, for the 1.4x TC by one stop, and with the 2x TC by two stops. So, let's say you are shooting with an f/2.8 lens, with a 1.4x TC you can only open up to f/4, and with a 2x TC to f/5.6.

And then, shooting with a long lens that has say a max aperture of f/5.6, well, most Canon cameras will refuse to shoot an f/5.6 lens with a TC (they max out at f/5.6 max aperture). This was in fact the problem with me shooting with my 100-400 lens, since at 400mm it can only open up to f/5.6. Because of that I could not use my trusty ol' 5DC or 30D with that combo. I had gotten a 1D3 my wildlife shooting, though, and that body could handle a TC.

Anyway, I expressed some curiosity on the thread about what goes on "under the hood" with this situation. I was expecially curious because I remembered, when I was working with some older gear, I actually got a TC to work with my 30D, it was one of the Kenkos, but I figured it was the 2x because my 1.4x didn't play nice.

And then, I was wondering about what actually goes on there. I seemed to recall that the Kenko 2x was buried somewhere in the midst of all my miscellaneous photo gear, somewhere...

Well, tonight that thread came to mind, I had my 5D nearby with my 24-105 f/4 lens attached, and a few bags of "stuff" laying around, so I decided "what the heck" and I started going through bags of my "lesser-used" stuff. And lo, buried in a bag was my Kenko 2x TC!

So I decide to check things out using that camera/lens combo...

First, I hooked up the TC and the camera didn't crap out! In fact, I opened the "in-camera aperture" and it showed f/4! And I shot several shots at f/4, then f/5.6 and then f/11, all the shots turned out!

Now for another test which can at least shed a bit of light. The question: was I getting a "real" f/4? Well, I'm no optical engineer or scientist, and I do't know what goes on "inside" that setup, so I just figured I'd do one little check...

I set the lens to 25mm, the "aperture" to f/4, then adjusted my shutter speed to give a "medium" exposure. I didn't actually take a pic, I just wanted the exposure/metering info.

Then, I took off the TC, extended the focal length to about 50mm (the equivalent of the 24mm with the TC doubling the "effective" focal length, and checked the exposure/meter, and found what I was looking for -- the expsure without the TC was much brighter, in fact (you can guess) I quadrupled the shutter speed (two stops) to get the exposure equivalence!

Well, then, there is good news and, well, so-so news. First the good news, I can use the 2x TC with my present gear, including the setup in the garage here where I use my trusty ol' 30D with the 100-400 to get photos of the little critters that wander around this home I'm in, squirrels, birds, cats, and then at night racoons. Often, 400mm is not far enough, and the critters don't let me get closer (not to mention the rainy weather!). And then, "shooting the moon" with just the 400mm is, well, not so good...

'Course then there is the so-so news that I'm actually losing two stops of light with the TC, so the "effective" aperture of the so-called f/5.6 at 400mm is still f/11, but hey, at least I can shoot. And, I know I'll take a hit on IQ but, oh well....

Well that's all. If you appreciate the info, chime in, ask questions, argue with me, whatever!

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Last edited by tonylong : 19th of February 2013 (Tue) at 22:58.
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Old 19th of February 2013 (Tue)   #2
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Default Re: Fun With a TC!

Quick correction!

In my post I said I had to double my shutter speed, actually I had to quadruple it to get the equivalent exposure without the TC!
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Old 19th of February 2013 (Tue)   #3
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Default Re: Fun With a TC!

Actually, I just re-did that test and it seems that my "judgement" was way off, now it looks like I have to either boost my f-stop or increas my shutter speed by way more than two stops, but I'll have to test things more in the daytime from a tripod.

Anyone with one of those Kenko 2x TCs who feels like playing around, join in!
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Old 20th of February 2013 (Wed)   #4
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Default Re: Fun With a TC!

Tony,

I'll be honest, this stuff is WAY too much for me nowadays, it's over my head! heheheh Really, I just fly/shoot by the seat of my pants, I don't think too much when shooting, I just 'do it'...

I will say though, I had a XSi (450D) and I tried using the Kenkos (1.4 300 and 2.0 MG) and let's just say they ended up in a bag in the closet, horrible results. Recently, (actually, last year) I upgraded to a T21 (550D) and tried again, same thing, both of them sucked, and the focusing was really slow. Both of these were with a 100-400mm too.

Now, since last June I have had a 1DmkIV with a 400mm 2.8 lens. so I tried the 1.4 Kenko 300 out, a BIG difference, I could not tell I have one on at all, and the shots didn't really suffer at all. Next I tried my 2.0 Kenko MC4, same thing, I couldn't tell that I had it on, it was fast and the shots looked very good, but not as good as without.

So, I've acquired the Canon 1.4III to go along with it, I did some (not so scientific) tests against the Kenko 1.4 300 and they were really (surprisingly) close in quality. Since that day I have literally left the Canon 1.4 on my lens, I love it that much, even for BiF. (Birds in flight)

Next I tried stacking the 1.4 Kenko and the 1.4 Canon, I was shocked at how good they were, not perfect at all, but it did allow me to get shots that I would have otherwise not taken at all. (Very good documentary shots) Up close, (20' or so) you can't hardly tell I had an extender on, I have some pretty danged good shots that let me get 'closer'... Pretty sharp.

After that, I tried stacking the Canon 1.4III with my Kenko 300 2.0, that left a little to be desired, and also I lost all ability to auto-focus, so manual focusing was all I had. I can stack a Kenko 1.4 and a Kenko 2.0 and have the ability to auto-focus, and it reports too.

Next I plan to get a Canon 2.0III and see what happens, I am not at all expecting perfect or even usable results stacked, but I have seen some really good results from a Canon 2.0 used alone. The stuff I shoot sometimes I need that extra reach. (I borrowed one a week ago and tried it out for a few minutes, I couldn't see anything wrong at all, but nothing that jumped out in a positive way at me either)

Really, I don't know where this falls in your questions, but I think it may qualify, if not, I can sure delete it, I don't want to detract from your thread.

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Old 20th of February 2013 (Wed)   #5
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Default Re: Fun With a TC!

Quote:
Originally Posted by tonylong View Post
I had tried the Canon 2x TC but saw that there was too much of a hit to my IQ.
FWIW, I ran some tests with the 70-200 & found that the IQ was pretty good at f/11, & the AF worked well, too.
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Old 20th of February 2013 (Wed)   #6
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Default Re: Fun With a TC!

Tony,

That's an interesting post - thanks for detailing your TC experiences - I'm sure that will be helpful info for many folks here.

I think the 2x will always "take" two stops away from you. That's just the physics of light at work, and should remain constant. Likewise a 1.4 TC will "take" one stop away from you.

However, as your post explains, the camera's computer doesn't "know" that the light is being taken away, when using the Kenko 2x, so autofocus still works. One just needs to be aware of the effect on exposure, and adjust accordingly, as you explained.
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Old 20th of February 2013 (Wed)   #7
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Default Re: Fun With a TC!

The change of magnification because of the TC will force that stop or two on aperture - 2x magnification could be seen as if the light that enters the lens will be used to light up a four times (2x2) as large image circle.

But then, the extra lens elements in the TC will add a bit of extra light loss. So the actual light measurement may indicate a bit more than 1 or 2 stops for 1.4x and 2x TC.

The smaller aperture means that the depth-of-field will increase. That makes it harder for the AF system to lock focus because you don't get nice distinct phase shifts to detect. That is why the camera refuses to AF - Canon decides to refuse to focus instead of the customers complaining that the focus feels "random".

A non-reporting TC doesn't have the extra connectors needed to inform the camera that a TC is used. So the camera will not know that the aperture reported by the lens isn't correct. So a non-reporting TC will make the camera try to focus. In good light, it should normally work well. As the contrasts gets weaker or the light levels gets lower, the camera may start to hunt for focus.

If having a reporting TC, it is possible to use a bit of document tape (that doesn't leave any glue residue on the connectors when removed) and put over the extra gold connectors, to block the TC from communicating with the camera. Then the camera will just see the transparent transfer of lens information on the ordinary set of connectors all lenses has. The disadvantage is that the EXIF data will lie - the camera can't put in information it doesn't know about.
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Old 20th of February 2013 (Wed)   #8
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Default Re: Fun With a TC!

Hey all, nice to have folks chiming in!

In my hurry to type out my little story, I should have been more clear that the "problem" with most of our Canon cameras using a TC that gives an "equivalent" aperture of narrower than f/5.6 and "reports" that to the camera is that the camera won't AF. You can take a shot, with the needed exposure "boost", you just won't have the AF.

Now, we could call that Canon making things "idiot-proof"...

But my little experiment last night was that I could actually get a pretty good AF performance with my 5DC and my f/4 lens using the Kenko 2x Teleplus Pro 300 TC. It was Kenko's top-of-the-line TC back in the day I picked it up...

Like pwm says above, the fact that the TC doesn't "report" to the camera means that the Exif shows the lens settings (focal length and aperture) without the TC, unlike a "reporting" TC that gives the "equivalent" aperture and focal lengths!

Anyway, it's a fun thing to play with, I think today I'll get my 30D, TC and 100-400 on my tripod and out where I can play around!
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Old 20th of February 2013 (Wed)   #9
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Default Re: Fun With a TC!

Quote:
when you use a Canon tC and I believe the Kenko 1.4x TC, the TC will communicate with the camera and the camera will automatically limit your widest aperture, for the 1.4x TC by one stop, and with the 2x TC by two stops. So, let's say you are shooting with an f/2.8 lens, with a 1.4x TC you can only open up to f/4, and with a 2x TC to f/5.6.
I'm afraid this is not what is happening at all, as you have learned by your hard work.

The T-Cons existence has no bearing on what the lenses physical aperture gets set to. The actual aperture iris behaves exactly as it does when no TC is installed.

Let's say we are using an f/4 lens with a 1.4 t-con wide open.

The Camera (not the lens) just notes the existence of the t-con, and takes it's existence into account and REPORTS the actual correct info to you about the T-Con impact on exposure. It tells you you are working with a t-con that reduces the amount of light by one stop to f/5.6. That is all. The lenses aperture is still wide open at the position that should give you f/4, but the t-con sucks up that extra stop of light, resulting in your sensor receiving approx f/5.6 of light.

With the non reporting TC, the exact same thing happens EXCEPT, the t-con does not report itself, your camera's info states the same f/4 the lens is set to, BUT your actual exposure is being made with the same f/5.6 of light getting through the lens / t-con combo.

You get the same exposure made with f/5.6 of light, but the camera can only tell you what it knows from the lens, thus you get told f/4. That the camera tells you differently, does not impact the actual look of the file. ie: what the camera reports to you has no bearing on what the camera does to get you the exposure based on it's metering. The camera does not know why it has less light (t-con vs. darker lighting ) so it just continues on it's merry way to make the same attempt to give a correct exposure.

There is no limit imposed by the Canon t-con on the lenses aperture setting, there is only the camera doing the math for you to let you know you actually have less light to work with.

this continues as you stop down. When your camera tells you you are shooting f/8, your lenses iris is actually at it's f/5.6 opening, add to that the 1.4x t-con, and you are shooting f/8 and that's what the camera tells you.

Last edited by CyberDyneSystems : 20th of February 2013 (Wed) at 14:35.
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Old 20th of February 2013 (Wed)   #10
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Default Re: Fun With a TC!

CDS, It's good to see your smiling mug shot! How've you been?

I've missed you. Nobody's tried to ban me in months! Jon does keep an eye peeled my way, though....
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Old 20th of February 2013 (Wed)   #11
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Default Re: Fun With a TC!

Jake/CDS, yeah, thanks for making things more clear! It's hard to put things together in a single sentence, hence my garbled "Long...winded" first post and your much better explanation!

Well, I have my setup reasy to go standing in the living room, I just have to get it set up for shooting some critters!

By the way, a note on shooting with those long/magnified focal lengths:

The times when I've shot with a setup using my 300mm f/2.8 IS lens, a 2x TC, on a tripod, I've noticed that the IS being on helps (for stationary subjects at least). This goes contrary to the general suggestion to turn the IS off when shooting with a tripod. But I noticed that at a 600mm focal lenth/magnification that vibrations were very noticeable through the viewfinder, but once the IS got activated, they noticeably died down! That was a lesson learned!

My next little project with this "kit" will be to dig out one of my Better Beamer flash extenders. They are useful for putting some "fill" light on the little "out there" critters and that will help to compensate for the light lost from the TC. Also, if I put my flash on High Speed Synch, I'll also benefit from being able to use a faster shutter speed! WhooHoo!
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Old 20th of February 2013 (Wed)   #12
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Default Re: Fun With a TC!

Quote:
This goes contrary to the general suggestion to turn the IS off when shooting with a tripod.
Tony Tony tony, you've really never read the FAQ on this?

http://photography-on-the.net/forum/...75#post1066324
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Old 20th of February 2013 (Wed)   #13
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Default Re: Fun With a TC!

....Well, it's a little out of date now with a lot more new 3rd gen IS lenses out, but the principles still apply, and I can't edit my own posts when they are that old to update.
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Old 20th of February 2013 (Wed)   #14
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Default Re: Fun With a TC!

Just FYI, the reason the TC changes the lens maximum f/stop value is specifically because it does not change the aperture.

Simple example - suppose you have a 100mm focal length lens with a 50mm aperture. This lens is capable of f/2 since 100mm/50mm = 2.

If you add a 2X TC then the teleconverter changes the focal length to 200mm. But the teleconverter cannot change the aperture so that is still 50mm. So now what is the f/stop?

It is f/4 since 200mm / 50mm = 4.

As CDS noted, when you use a non-reporting teleconvertor the camera will tell you that you can still shoot at f/2, but that is only because the teleconvertor is lying to the camera and telling it that it is still shooting a 100mm lens with a 50mm aperture. But it isn't, the camera is just not being informed by the TC that the focal length changed to 200mm.
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Old 20th of February 2013 (Wed)   #15
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Default Re: Fun With a TC!

Quote:
Originally Posted by CyberDyneSystems View Post
....Well, it's a little out of date now with a lot more new 3rd gen IS lenses out, but the principles still apply, and I can't edit my own posts when they are that old to update.
Heh! Jake, I'm sure I've read it, somewhere back in time!

Now, the old 300 is on that list, although I sold it back in '08...but the IS was a help when the TC made it 600mm!

I'll have to try out my other two lenses with IS. I don't think either one has the "special" IS funtionality, I'll have to see...both of them are "older", the question will be whether they turn of the IS when on the tripod! More stuff to play with!
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