Kenko Pro v Canon converter test Results

[Roy C]

Kenko Pro arrived today so I have tried some quick tests to compare against my Canon Converter. All tests were done using a 30D camera and 400mm f5.6 Canon lens. The pics were all shot in RAW with no processing whatsoever except converting to jpeg and resizing in CS2. Both sets of shots were taken with a few minutes of each other. All shot were taken with spot metering and single shot AF mode selected and central focus point only. I realise this is not a technical test but hopefully it gives some indication.


AF Test
For this test I hand held the combo and from the same position tried focusing on about 20 different objects which were at a range of between 5 and 100 metres. For most of the objects the AF locked on very quickly. A few took a little while with some mild ‘hunting’ before AF was achieved and one object in particular (a pottery flower pot) would not AF at all. I found both converters to be identical in their AF ability, the objects that locked right on with one converter did the same on the other converter. Those object that took a little longer to lock-on with a little hunting was again the same for both converters and the couple of objects that would not AF with one converter did not AF with the other converter also.

Optical Quality
For this quick test I set-up a sturdy tripod and fired off three images of a chimney stack with each converter. Below is the best pic from the three for each tc but to be honest for each tc there was nothing to choose between the three pics.
The first set are full frame shots resized in CS2 and the second pair are 100% crops of those images. In both cases the Canon is the first image and Kenko the second.
I will leave you to judge which one is best but I reckon the Canon is noticeable better in the cropped shots.
P.S. I notice the Canon shot was 1/640 sec and the Kenko was 1/500 sec not sure what influence this would have had.

It should be noted that the Kenko pro is less than half the price of the Canon.
I paid £51 + £18 P& P for the Kenko (ordered on the web from Hong Kong on Sunday evening and arrived on my doorstep Thursday morning!).
There are two more 100% crops from the same images on the next post.

[Roy C]

Here are a couple more 100% crops - again the first is the Canon and second the Kenko.

I know this test does not prove a thing and there are probably those that would dispute these results but this is how my images came out. I will do more test in the field pretty soon.

[Keith Reeder]

Yep, I'm seeing a difference too, Roy.

I reckon the chimney was moving when you took the Kenko shot!

;)

[Roy C]

Yep, I'm seeing a difference too, Roy.

I reckon the chimney was moving when you took the Kenko shot!

;)
Could explain the difference Keith |:D|
I still reckon the Kenko is a good tc - I snatched this shot this afernoon and it looks pretty good to me.

[shoshone]

Could explain the difference Keith |:D|
I still reckon the Kenko is a good tc - I snatched this shot this afernoon and it looks pretty good to me.

Great pix Roy..he's a little stonker.

Jamie

[citrinella]

Thanks for posting this Roy, not often you get a chance to see a direct comparison in real world, ordinary photographer terms.

You said the Canon shots were at 1/640, Kenko at 1/500. Did the light improve for the Canon ?

I wouldn't be surprised if that difference in shutter speed was enough to make that difference in the shots. If that difference is a fluke - the test is hard on the Kenko. If it is because the Canon transmits light a whole lot better, I wouldn't want a Kenko if the lens would take a Canon. We're all looking for as fast a shutter speed as possible. That difference is a lot cheaper than buying a faster lens esp. at birding focal lengths.

Evidence in favour of it being a fluke - you couldn't see any difference in AF performance. But how sophisticated were your metrics ? I'm not saying the test is no good, because I like tests that are more like what I actually do than a laboratory. All I mean is the difference in shutter speeds might be real without you being able to detect a difference in AF performance.

Mike.

Competing interests - I have a Canon 1.4 but not a Kenko ;-)

[Roy C]

Thanks for posting this Roy, not often you get a chance to see a direct comparison in real world, ordinary photographer terms.

You said the Canon shots were at 1/640, Kenko at 1/500. Did the light improve for the Canon ?

I wouldn't be surprised if that difference in shutter speed was enough to make that difference in the shots. If that difference is a fluke - the test is hard on the Kenko. If it is because the Canon transmits light a whole lot better, I wouldn't want a Kenko if the lens would take a Canon. We're all looking for as fast a shutter speed as possible. That difference is a lot cheaper than buying a faster lens esp. at birding focal lengths.

Evidence in favour of it being a fluke - you couldn't see any difference in AF performance. But how sophisticated were your metrics ? I'm not saying the test is no good, because I like tests that are more like what I actually do than a laboratory. All I mean is the difference in shutter speeds might be real without you being able to detect a difference in AF performance.

Mike.

Competing interests - I have a Canon 1.4 but not a Kenko ;-)
Hi Mike, both sets of three were shot within a couple of minutes of each other and I certainly did not notice a change in light but I guess the light must have been slightly better for the Canon which is why I noted this in my report, I certainly intent to do some more tests.
I have read a lot about the lens not 'hunting' as much with the taped Kenko as the Canon which is why I bought the Kenko in the first place but as I say I found no difference what so ever in the two converters in this respect.
Might try the barcode test from about 10 metres today.

[senatore]

Hi Roy,
Very interesting reading.I myself have got a Kenko Pro 300 DG that I also got cheaply (Couldn't afford the Canon).

I taped the pins but the AF and the pics were disappointing when used with my 350D.I have now got a 30D and wonder if I can expect better results with this camera when I attach the tc.

Max.

[Keith Reeder]

I have now got a 30D and wonder if I can expect better results with this camera when I attach the tc.

Dunno if this helps Max, but all of my recent Gallery pictures have been taken with a 30D and a Kenko Pro DG 1.4x (with my trusty 100-400mm).

Works for me..!

;)

[senatore]

Dunno if this helps Max, but all of my recent Gallery pictures have been taken with a 30D and a Kenko Pro DG 1.4x (with my trusty 100-400mm).

Works for me..!

;)

I'd settle for those Keith.

Of course I'd forgotten to mention in my post that I use the 400 f5.6 prime lens.When the weather gets a bit better I will have a go.Fingers crossed.

Max.

[Roy C]

Hi Roy,
Very interesting reading.I myself have got a Kenko Pro 300 DG that I also got cheaply (Couldn't afford the Canon).

I taped the pins but the AF and the pics were disappointing when used with my 350D.I have now got a 30D and wonder if I can expect better results with this camera when I attach the tc.

Max.
Max, I went from the 350D to the 30D.With the Canon 1.4 taped I certainly get better results from the 30D. I suspect the same will be true of the Kenko + 30D.

[Keith Reeder]

Yeah, I know you've got the prime, Max - that's why I mentioned mine.

You'll be able to do better than me!

;)

[Roy C]

I reckon expectations are sometimes to high when using a tc. I know when I first got a tc I thought I was going to be able to shoot birds from 100 metres - well it ain't like that, if the bird is a small blob in the middle of the frame with the bare lens then it is going to be a slightly larger blob with a 1.4 tc attached. You still need to get pretty near for decent bird shots.

Pre-digital everyone would have known this when they got their prints back but now with people doing their own processing the temptation is to crop very heavily for web pics, if you do this with a tc on board then results are not going to be very good (especially if you shot at a high ISO)

This ability to heavily crop an image for web display is one reason why it is very difficult to judge the merits of equipment from web shots ( because you never know how much a pic has been cropped). A shot from close range with a relatively cheap lens can easily look better than a shot with a top class lens which has been taken from,say, 50 metres and then very heavily cropped.

Just my thoughts B (:

[senatore]

Managed to give the 30D and the Kenko 1.4 a go with the 400 f5.6 prime this afternoon in the backgarden between the heavy showers.

You were right Roy and Keith the 30D preformed much better than my 350D with the tc attached (the pins were taped).The AF hardly hunted at all and only did so a little if there was little contrast on the subject.This was not the case when using the 350D which hunted a lot.

Didn't take many pics as there was only a Woodpigeon to aim at.Results not brilliant (800 ISO) but better than previously achieved and I take your point Roy that we shouldn't have our expections too high when using a tc.

Max.

[Roy C]

Managed to give the 30D and the Kenko 1.4 a go with the 400 f5.6 prime this afternoon in the backgarden between the heavy showers.

You were right Roy and Keith the 30D preformed much better than my 350D with the tc attached (the pins were taped).The AF hardly hunted at all and only did so a little if there was little contrast on the subject.This was not the case when using the 350D which hunted a lot.

Didn't take many pics as there was only a Woodpigeon to aim at.Results not brilliant (800 ISO) but better than previously achieved and I take your point Roy that we shouldn't have our expections too high when using a tc.

Max.
Nice one Max - I glad things are looking up on the tc front. I think there is no doubt that the 30D AF system is better than the 350D ( I had almost given up on a tc with the 350D).

P.S. Just done another test between the converters and things are looking a lot closer than my first test - will post the results this evening.

[Roy C]

Just done another test between the two converters - this time the target was a detergent box from about 8 metres. Taken on a tripod with the built in timer and a bean bag on top of the lens to dampen the bounce.
The Canon is the first pic in both pairs.
I can see no appreciable difference between these shots and if anything I would say that the Kenko shades it on the first set.

[senatore]

Went down to my local patch this morning to try out the Kenko 1.4 tc attached to my 30D/400 f5.6 prime.

Weather was dull so I cranked up the ISO to 800 and picked a low f number.The AF with the pins taped worked very well and there were only a few times when I had to manual focus first.

As Roy said the AF worked far better on the 30D than on the 350D and I am now encouraged to use it whenever the situation arises.The only trouble I had was that some Reed and Sedge Warblers posed too close for me to get them in focus.

Here a some examples.They have been fiddled with a little bit but not much.The Little Owl was a long way off.The Oystercatcher and Redshank were about 10 metres away and the Dragonfly was as close as I could get.

The pics were all hand held.Any helpful advice would be appreciated.

Max.

[mjmw]

Just done another test between the two converters - this time the target was a detergent box from about 8 metres. Taken on a tripod with the built in timer and a bean bag on top of the lens to dampen the bounce.
The Canon is the first pic in both pairs.
I can see no appreciable difference between these shots and if anything I would say that the Kenko shades it on the first set.

Interesting stuff Roy. To my eyes, viewing on a calibrated LCD monitor, the Canon tc shots are brighter with more contrast but not a lot more.

I would be interested to see comparisons of the convertors with a larger sensor like one of the 1 series bodies or 5D. I think they would show even more difference because they are using more of the tc's glass.

[Keith Reeder]

I agree Mark, there's a slight contrast/brightness difference, but nothing significant.

Sharpness is too close to call, really.

From what I've read, the Canon is better at the edges than the Kenko, though many tests give the nod to the Kenko at the centre - which suits me for bird photos.

[Roy C]

Took these two with the Kenko - don't think there is a lot in it when shooting birds at the normal distances. Certainly excellent value for money when compared to the Canon.

[Roy C]

Just tried the taped Kenko with my 70-200 f4 L - AF is Definitely better with the Kenko .With the taped Canon converter the lens hunted like mad but with the Kenko it locked on very quickly for most of the time with very little hunting. Have no idea why this should be so |:S| |:S| but it could explain why some people have report better AF with the Kenko and the 100-400 with regards to the hunting. It seems like zooms are not suited to the Canon tc.
As reported earlier, with the 400mm f5.6 prime both converters are the same as far as AF and hunting goes.

[shoshone]

Just tried the taped Kenko with my 70-200 f4 L - AF is Definitely better with the Kenko with the taped Canon converter the lens hunted like mad but with the Kenko it locked on very quickly for most of the time with very little hunting. Have no idea why this should be so |:S| |:S| but it could explain why some people have report better AF with the Kenko and the 100-400 with regards to the hunting. It seems like zooms are not suited to the Canon tc.
As reported earlier, with the 400mm f5.6 prime both converters are the same as far as AF and hunting goes.

Roy, A side question. The trial of the Canon 1.4x TC I did outside Jessops with & without the TC showed 560mm and 400mm respectively in shot settings. Now having purchased a Canon 1.4x TC and with the TC taped I lose this info in that all shots settings show 400mm....is this to be expected?

Jamie

[Keith Reeder]

That's normal, Jamie - taping stops the lens and camera talking to each other, so the camera doesn't know the TC is there.

[Roy C]

Roy, A side question. The trial of the Canon 1.4x TC I did outside Jessops with & without the TC showed 560mm and 400mm respectively in shot settings. Now having purchased a Canon 1.4x TC and with the TC taped I lose this info in that all shots settings show 400mm....is this to be expected?

Jamie
As Keith say's Jamie that is normal. This is what taping is all about, you are fooling the camera into not knowing there is a tc present therefore it can only report the aperture of the bare lens - if it reported 560mm and f8 you could not AF.

[mjmw]

Just tried the taped Kenko with my 70-200 f4 L - AF is Definitely better with the Kenko .With the taped Canon converter the lens hunted like mad but with the Kenko it locked on very quickly for most of the time with very little hunting. Have no idea why this should be so |:S| |:S| but it could explain why some people have report better AF with the Kenko and the 100-400 with regards to the hunting. It seems like zooms are not suited to the Canon tc.

I don't think it is to do with the zoom but 'speed' (max aperture) of the lens. I would bet that a 300/4 and Canon tc with taped pins would hunt just as much as a 70-200/4.

[shoshone]

That's normal, Jamie - taping stops the lens and camera talking to each other, so the camera doesn't know the TC is there.

Thanks Keith & Roy for those prompt responses.

Jamie

[mjmw]

I agree Mark, there's a slight contrast/brightness difference, but nothing significant.

Sharpness is too close to call, really.

Surely sharpness is much to do with contrast at this pixel-peeking level? So the Canon TC is 'sharper'... ;)


From what I've read, the Canon is better at the edges than the Kenko, though many tests give the nod to the Kenko at the centre - which suits me for bird photos.

Exactly where I was going - there is a reason the Canon is more expensive and it isn't just badge and weather-sealing.

[Roy C]

I don't think it is to do with the zoom but 'speed' (max aperture) of the lens. I would bet that a 300/4 and Canon tc with taped pins would hunt just as much as a 70-200/4.
You could well be right Mark but how come it does not hunt with the Kenko?

[bisto]

Hi everyone, I have just been reading this post with great interest, I am relatively new to Digital SLR's after coming from a point and shoot camera, I have the Canon 400D and for wildlife shots I have been using the Canon 70/300 IS lens sometimes attaching the Kenco Pro 1.4, and have found it auto focuses quite well in good light, so I am interest to know whats meant by taping the pins, which ones and what with, also what would the difference be.

Hope this is not a silly question.

John.

[mjmw]

You could well be right Mark but how come it does not hunt with the Kenko?

OK, this is going to get a little long and complicated but please stick with me till the end! I will say straight away though that I am not 100% sure why the Kenko does not cause as much hunting, nor have I fully considered all the details of tcs and AF system interaction before now but I will try to explain my thoughts.

Lets start with a fundamental and often misunderstood concept: hunting is caused by the camera's AF system not the lens itself - the camera can't find the correct focus point so tells the lens to 'scan' so it can try and find it - notice how the lens AF motors work more slowly when you have little light or 'low contrast' situations? The AF sensor needs more time to find focus.

(D)SLR AF basically works using a phase detection system. Keeping it simple, a pair of sensors measure the light received from each side of the lens. The system then 'measures' the light and dark areas and compares the readings from both sensors – i.e. each side of the lens. If they are the same ('in phase'), correct focus has been achieved (it works in fundamentally the same way as a split focus screen on a manual focusing SLR). You can imagine that each of the focus points you see in the view-finder is a pair of those sensors, so when the light is 'in phase' for that focus point, the camera has achieved focus.

The AF system will work better the greater the distance between the sides of the lens (just trust me on that - this is getting too complicated to explain without pictures). So the widest aperture of a lens determines how far apart the sides of the lens are (that is a huge over-simplification but you get the idea). Most AF systems require an aperture of f5.6 or bigger because any less and the AF sensors won't get enough 'separation' to allow a good comparison. This means that, as well as greater amounts of light (more light means easier determination of light/dark areas), lenses with wider maximum apertures have a greater distance between the lens sides, so faster/better AF operation.

OK, assuming that made any sense at all, let’s look at using teleconvertors (tc). I am going to assume we are using a 1.4x tc, which reduces the aperture by one stop. Take one f5.6 lens, add a tc and strap it to a 30D…the AF system is disabled because the lens/tc combination is reporting a maximum aperture of f8 to the camera. The AF system is not ‘designed’ to work with that small a distance between the lens sides and the light may miss the sensors all together!

When you ‘tape the pins’ on a tc, the lens/tc reports that the combo is f5.6 and the camera leaves the AF system switched on. As luck would have it, the AF sensors on the 30D seem to be able to handle an f8 lens (makes you wonder if the next generation of the 30D will support AF at f8 as a ‘new’ feature…). From memory, the 350D didn’t handle the f8 combo as well – I can only assume that the AF sensors are even less designed for that small a gap between the lens sides.

Finally I can try to answer Roy’s question. For lenses faster than f5.6 the AF sensors are ‘adjusted’ to handle the extra light and greater distance between lens sides. A slight side note - one of the ‘breakthroughs’ on the EOS 3 was that the AF sensors could work even faster for f2.8 lenses – which has now been carried on in the 1 series bodies and even the 30D (I think).

Why does this matter with taped pins? When using an f4 lens (like the 70-200/4) Canon’s AF system will ‘adjust’ the sensors for the light and width from the f4 lens. By adding the tc you are making the lens/tc combo f5.6 but by taping the pins on the tc, the AF system is still expecting an f4 lens…so the sensors are going to have a tough time with less light and less distance between the lens sides - it is going to cause the sensors to hunt.

Now, why does the lens hunt less with the Kenko and taped pins? I don’t honestly know. I can only assume that the Canon tcs send extra data or manipulate the data from the lens in some way whereas the Kenko one doesn’t (Kenko will make the insides of their tcs the same irrelevant of the camera manufacturer the mount is for to keep costs down). Does this mean that the Canon AF system is designed to work fastest with Canon branded tcs and lenses? Probably – it gives them a competitive advantage! Following that thought through, having the Kenko tc on the camera may mean that the AF system is operating in a generic ‘safe’ mode that allows AF at any aperture of f5.6 or wider…so taping the pins has little effect on the faster lenses.

Whew…I went on longer than I intended and congratulations to anyone who read through to the end and I hope it made some sense to someone.

BTW, before any ‘well actually’ responses, I know that ‘distance between the sides of the lens’ is not a strictly accurate description, but it is a simple way to think/write about it without diagrams… ;)

[Roy C]

OK, this is going to get a little long and complicated but please stick with me till the end! I will say straight away though that I am not 100% sure why the Kenko does not cause as much hunting, nor have I fully considered all the details of tcs and AF system interaction before now but I will try to explain my thoughts.

Lets start with a fundamental and often misunderstood concept: hunting is caused by the camera's AF system not the lens itself - the camera can't find the correct focus point so tells the lens to 'scan' so it can try and find it - notice how the lens AF motors work more slowly when you have little light or 'low contrast' situations? The AF sensor needs more time to find focus.

(D)SLR AF basically works using a phase detection system. Keeping it simple, a pair of sensors measure the light received from each side of the lens. The system then 'measures' the light and dark areas and compares the readings from both sensors – i.e. each side of the lens. If they are the same ('in phase'), correct focus has been achieved (it works in fundamentally the same way as a split focus screen on a manual focusing SLR). You can imagine that each of the focus points you see in the view-finder is a pair of those sensors, so when the light is 'in phase' for that focus point, the camera has achieved focus.

The AF system will work better the greater the distance between the sides of the lens (just trust me on that - this is getting too complicated to explain without pictures). So the widest aperture of a lens determines how far apart the sides of the lens are (that is a huge over-simplification but you get the idea). Most AF systems require an aperture of f5.6 or bigger because any less and the AF sensors won't get enough 'separation' to allow a good comparison. This means that, as well as greater amounts of light (more light means easier determination of light/dark areas), lenses with wider maximum apertures have a greater distance between the lens sides, so faster/better AF operation.

OK, assuming that made any sense at all, let’s look at using teleconvertors (tc). I am going to assume we are using a 1.4x tc, which reduces the aperture by one stop. Take one f5.6 lens, add a tc and strap it to a 30D…the AF system is disabled because the lens/tc combination is reporting a maximum aperture of f8 to the camera. The AF system is not ‘designed’ to work with that small a distance between the lens sides and the light may miss the sensors all together!

When you ‘tape the pins’ on a tc, the lens/tc reports that the combo is f5.6 and the camera leaves the AF system switched on. As luck would have it, the AF sensors on the 30D seem to be able to handle an f8 lens (makes you wonder if the next generation of the 30D will support AF at f8 as a ‘new’ feature…). From memory, the 350D didn’t handle the f8 combo as well – I can only assume that the AF sensors are even less designed for that small a gap between the lens sides.

Finally I can try to answer Roy’s question. For lenses faster than f5.6 the AF sensors are ‘adjusted’ to handle the extra light and greater distance between lens sides. A slight side note - one of the ‘breakthroughs’ on the EOS 3 was that the AF sensors could work even faster for f2.8 lenses – which has now been carried on in the 1 series bodies and even the 30D (I think).

Why does this matter with taped pins? When using an f4 lens (like the 70-200/4) Canon’s AF system will ‘adjust’ the sensors for the light and width from the f4 lens. By adding the tc you are making the lens/tc combo f5.6 but by taping the pins on the tc, the AF system is still expecting an f4 lens…so the sensors are going to have a tough time with less light and less distance between the lens sides - it is going to cause the sensors to hunt.

Now, why does the lens hunt less with the Kenko and taped pins? I don’t honestly know. I can only assume that the Canon tcs send extra data or manipulate the data from the lens in some way whereas the Kenko one doesn’t (they will make the insides of their tcs the same irrelevant of the camera manufacturer the mount is for). Does this mean that the Canon AF system is designed to work fastest with Canon branded tcs and lenses? Probably – it gives them a competitive advantage! Following that thought through, having the Kenko tc on the camera may mean that the AF system is operating in a generic ‘safe’ mode that allows AF at any aperture of f5.6 or wider…so taping the pins has little effect on the faster lenses.

Whew…I went on longer than I intended and congratulations to anyone who read through to the end and I hope it made some sense to someone.

BTW, before any ‘well actually’ responses, I know that ‘distance between the sides of the lens’ is not a strictly accurate description, but it is a simple way to think/write about it without diagrams… ;)
Very interesting stuff Mark - thanks.:t: :t: :t:
Re the Kenko hunting less than the Canon (certainly on my 70-200 f4) like you say, we can only assume that some different data is being sent to the camera. I see what you are saying about the faster lenses (f4).

Not so sure that this theory holds good for the 100-400 (f5.6 at the long end) but then again I have not tested this lens with the tc's myself. I can only take other peoples word for it that it hunts far less with the kenko.

[mjmw]

Not so sure that this theory holds good for the 100-400 (f5.6 at the long end) but then again I have not tested this lens with the tc's myself. I can only take other peoples word for it that it hunts far less with the kenko.

I haven't read the posts on POTN or elsewhere about this...but my instant reaction is the variable maximum aperture on the 100-400 and how the camera handles this. Also the smallest things can really impact the AF performance - a couple of the small screws near the camera mount end of my 400/5.6 had worked a little lose and AF was dreadful (light leak?)...I tightened the screws and all was perfect again.

On the same thought process, a small amount of dirt or grease on the camera end of the lens or either end of the tc could also have a huge amount of difference on AF...as could a UV filter on the front of the lens. I am also being cynical having not seen the 'evidence' of the Kenko hunting less than the Canon...especially when I can't think of a reason for it ;)

[senatore]

I don't know whether this birder I got talking to in a hide yesterday was taking the **** or not but he said that if your camera hunts a lot trying to get the AF you will eventually burn out the AF motors.I took far less pics after he said this.

Has this ever happened ? Could it ever happen ?

Max.

[gmax]

Also the smallest things can really impact the AF performance - a couple of the small screws near the camera mount end of my 400/5.6 had worked a little lose and AF was dreadful (light leak?)...I tightened the screws and all was perfect again.


Aaaarghh, that's exactly what I found on my lens, but before realizing it I got mad and desperate .. now I always carry a small screwdriver in my backpack :t: ... it's the first time I hear of another 400mm's user having this problem: is it something common with this lens?

Ps good explanation of this hard to get theory, I appreciated your "distance between the sides" thing ;)

Max

[Keith Reeder]

Max (Senatore),

you hear that about burning out the motors a lot, but I've never come across a definitive "it happened to me!" posting or article.

I'm not sure how much of a "Real World" this is, but I'm not put off - let's face it, given how many TCs are out there, we'd be reading a lot more about self-destructing AF drives if it was happening anything like frequently.

[Roy C]

Keith beat me to it Max S. I have heard that motors could burn out but never heard of anyone that is has actually happened to. It has not put me off and I have been using a taped tc for more than a year.

[macshark]

One possible reason why the camera will hunt less with a particular 1.4x TC and more with another one may be that the two TCs in question may have slightly different magnification factors, and thus, slightly different effective apertures when combined with a f/5.6 lens.

The 1.4 comes from square root of 2 which is close to 1.414. Someone did a comparison of teleconverter magnification ratios a whlie back and found that the effective multiplier can be as low as 1.35 even though the label says "1.4". Unfortunately, I cannot seem to find the link.

[mjmw]

One possible reason why the camera will hunt less with a particular 1.4x TC and more with another one may be that the two TCs in question may have slightly different magnification factors, and thus, slightly different effective apertures when combined with a f/5.6 lens.

The 1.4 comes from square root of 2 which is close to 1.414. Someone did a comparison of teleconverter magnification ratios a whlie back and found that the effective multiplier can be as low as 1.35 even though the label says "1.4". Unfortunately, I cannot seem to find the link.

Interesting, that could explain it - if the Canon is nearer 1.414x and the Kenko less, it may hunt less - that small amount of difference would be much greater at the AF sensors.

[AC/DC]

sorry to sound stupid but why wont a camera af past f8?

[mike nesbitt]

I don't know whether this birder I got talking to in a hide yesterday was taking the **** or not but he said that if your camera hunts a lot trying to get the AF you will eventually burn out the AF motors.I took far less pics after he said this.

Has this ever happened ? Could it ever happen ?

Max.
I'm no optical person but I do know a bit about motors.
There's no chance of burning the motor out but you will subject it to excessive wear. this is in turn dependant on the amount of hunting involved.
You pays your money you takes your choice.
You know how it should function, if it's clearly struggling then it's not worth the bother.

[postcardcv]

sorry to sound stupid but why wont a camera af past f8?

As the aperture of the lens gets smaller (bigger f number) the light getting to the sensor is less... less light means slower and less acurate AF. So camera manufacturers will limit the system so it will not even attempt to AF if the max aperture is smaller than f5.6... using the taped pins trick you can fool a camera into thinking it's using an f5.6 lens when it's effectively using an f8 set up... above that and a standard body will struggle. Using my lenses and tcs (with pins taped) I've shown that my 400D will actually AF perfectly at f6.3, fairly well upto f8, but at f9 it is hopeless.

[AC/DC]

so with a lens of f4.5-f5.6 it will be alright?

[postcardcv]

so with a lens of f4.5-f5.6 it will be alright?

a f4.5-5.6 zoom will certainly work fine on it's own, however when adding a tc you can get variable, but it would be worth a try...

[AC/DC]

thanks very much postcardcv. I assume the aperture af thing is the same on all enthusiast dslr's, its just canon camera's actually wont let you, rather than letting you try, and failing ( if you know what i mean). Mike from ebbw has had some very good results with a tc, however i dont think i will be getting one yet - but i should be getting my new gear very soon!