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Old Jul 26, 2007, 9:30 AM   #1
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I own a Pentax K10D DSLR, as well as a Pentax MX manual film SLR..

As I slowly acquire the pieces of glass that I wish to make up my lens arsenal, I am somewhat confused as to the type of teleconverter that Ineed to purchase..

Kenko, Tamron, & Sigma all market AF teleconverters for use on Pentax cameras..

If a person wishes to use a teleconverter on lenses both with modern digital construction, and with older manual focus construction ( A-series lenses or older), will this necessitate the purchase of different teleconverters??..

I am fairly clear on the characteristics of the teleconverters that Pentax once produced (available on the used market) ..

These are the: A 1.4xS-- Short, for up to300mm lenses, A1.4xL-- Long, for 300mm & over lenses,F1.7xAF-- to allow AF capability with manual lenses, A2.0xS-- Short, for up to 300mm lenses, & the A2.0xL-- Long, for 300mm & over lenses..

As I understand things, all four of the A-series teleconverters will only provide AF capability with A-series & newer lenses??..If used on older lenses they provide the appropiate magnification, but without AF..Correct??..

The F1.7x AF is where I become confused..As I understand things, this teleconverter is supposed to allow a manual focus lens to transmit AF data to bothPentax auto-focus film SLR's, as well as Pentax DSLR's..Is this correct??..

Where I really become confused is with the third-party teleconverters..

IfI was to have a collection of Pentax and third party glass, ranging in age from early M42 Takumar fully manual lenses up to FA & DA-series auto-focus lenses, how many teleconverters will I need to own to cover a lens selection such as this??..

Iwish to ownas few teleconverters as possible..

Will the modern teleconverters designed to work with digital lenses work with older non-digital lenses??..Or do they suffer from the same limitations as putting a digital lens on a non-digital camera??..

From posts that I have read, I know I want to own a 1.4x to 1.5x teleconverter, but I am not sure about the 2.0x ones..

Is cost of manufacturing the reason that a 1.4x to 1.7x teleconverter outperforms the 2.0x teleconverters??..

I see many posts referring to how people do not like to use the 2.0x teleconverters as performance drops off..Can I infer that in order for a 2.0x teleconverter to perform like one with lesser magnification, it would have aunreasonably high price tag??.. Perhaps weigh too much??..

As magnification goes up light transmission goes down, correct??..And is this is why the 2.0x teleconverters only work well with f2.8 & faster lenses, as only the fast glass will transmit enough light to allow the AF functions of cameras to work??..

Any other limitations that I need to be aware of when using a teleconverter??..

Thanks in advance to any & all who take the time to answer all of these questions..

Bruce


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Old Jul 26, 2007, 2:35 PM   #2
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Hi Bruce,

I use TCs pretty extensively, and have a few, so I'll relate what I know and think.

Kenko, Tamron, & Sigma all market AF teleconverters for use on Pentax cameras

Correct -- these are considered the best of the bunch

If a person wishes to use a teleconverter on lenses both with modern digital construction, and with older manual focus construction ( A-series lenses or older), will this necessitate the purchase of different teleconverters??..

Not necessarily -- the current AF TCs only differ from MF TCs in that they have the shaft to allow the in-camera motor to turn the focusing mechanism in the lens. The fact that this shaft is flush with the mounting flange on both sides means that it will also fit MF lenses and just becomes irrelavent when used on them. In other words, AF TCs can be used on either AF or MF lenses, retaining all the functionality that the lens originally had, "A" style (with the electrical contacts) MF TCs can be used with AF or MF lenses, but makes the AF lenses into MF,but otherwise retains all the original features of the lens, and M-style TCs (no contacts) can be used with all AF or MF lenses, but all will become totally manual lenses in both metering and focus.

Also realize that the current crop of AF TCs do not convert the focal length info for SR purposes, and that since DA and FA J lenses don't have aperture rings, they will only be able to be used wide open with a fully manual TC (with no contacts).

The SDM lenses will be different, and since the motor will be in the lens, an AF TC for them must have the additional contacts to power the SDM system. The assumption is that the mfgs will continue to provide the screw shaft so they'll be able to be used on AF1-type lenses as well as SDMs.

For future considerations, the best bet from a compatibility standpoint would be to get an SDM capable AF TC with the screw shaft as that will allow all the types of lenses to work as they should. I believe that the current production Kenko and Tamron TCs are like this, but I'm not sure.

As I understand things, all four of the A-series teleconverters will only provide AF capability with A-series & newer lenses??..If used on older lenses they provide the appropiate magnification, but without AF..Correct??..

No -- All the A-series TCs are just like the A-series lenses, and do not allow AF (Auto-Focus) -- they do, however, allow AE (Auto Exposure) which is what I think you meant -- that is, metering with the lens wide open and controlling the aperture through the camera body instead of only with the aperture ring on the lens with the aperture ring set on "A".

The F1.7x AF is where I become confused..As I understand things, this teleconverter is supposed to allow a manual focus lens to transmit AF data to bothPentax auto-focus film SLR's, as well as Pentax DSLR's..Is this correct??..

If you think about it, in the KAF system (in-camera motor -- as opposed to the KAF II -- in-lens motor, or SDM), there is no AF data transmitted to the lens -- it's all done in the body. The F 1.7x AFA turns MF lenses into AF by focusing within the TC. It's unique in that it has a focusing group of elements inside it.

Depending on the lens, it has the ability to either focus for the lens, or focus within a limited range of distances. If you use it with a 50mm, you would set the focus on the lens for infinity, and the TC will do all the focusing at all distances. I'm not sure at what FL the ability to focus from all the way from minimum focusing distance to infinity is lost, but on longer lenses, it will only be able to focus within a range of distances, let's say for example sake, from infinity to 50', so for closer distances, you would have to manually turn the focus ring on the lens to get it within range so the TC can focus automatically.

This may sound like a hassle, but I found it easy to get used to, and use the 1.7x AFA all the time. In practice, it's actually a benefit, as the limited focusing range and the physical lightness of the focusing group allows for a very quick lock to lock time, and virtually no hunting so it can cut down on focusing time significantly, and when you have the lens within the focusing range of the TC, the AF is very quick and positive.

IfI was to have a collection of Pentax and third party glass, ranging in age from early M42 Takumar fully manual lenses up to FA & DA-series auto-focus lenses, how many teleconverters will I need to own to cover a lens selection such as this??..

Need and want are two different things. . .:-) Technically, if you only want the 1.4x multiplier, then if you can get an SDM compatible AF TC, then you only need one. . .

. . . but there are some other possibly interesting considerations. . .

The 1.7x AFA's advantages have already been mentioned. The Pentax TCs are probably the best as far as optics, and there are some specialty TCs, like the Vivtar 2x Macro Focusing TC -- manual focus only, but it also has a helicoid which allows you to close focus any lens to 1:1 macro in addition to doubling the FL, so it would, for example, make a 50/1.4 into a pretty competent 100mm f2.8 1:1 macro. If you're interested in one of these, be aware that they were made in both A and M styles -- you want the A-style with the contacts.

Will the modern teleconverters designed to work with digital lenses work with older non-digital lenses??..Or do they suffer from the same limitations as putting a digital lens on a non-digital camera??..

I've not heard of TCs being APS-C specific, and doubt that there would be any advantage to designing one, so I believe that the answer is no. . .


From posts that I have read, I know I want to own a 1.4x to 1.5x teleconverter, but I am not sure about the 2.0x ones..

Is cost of manufacturing the reason that a 1.4x to 1.7x teleconverter outperforms the 2.0x teleconverters??..

I doubt it -- OEM TCs have always been pretty pricey, and the Tamron SPs have always been expensive as well. I think it's more a matter of not being able to make the optics work.

I see many posts referring to how people do not like to use the 2.0x teleconverters as performance drops off..Can I infer that in order for a 2.0x teleconverter to perform like one with lesser magnification, it would have aunreasonably high price tag??.. Perhaps weigh too much??..

I think it's a matter of limitations in the glass -- TCs magnify the image (otherwise they'd have to be significantly bigger -- a 300mm f2.8 lens with a 1.4x TC [420mm f4] is always going to be significantly smaller than a lens designed as a 400mm f4 for example). I think it's beyond practical (or might not really be possible) to magnify the image 2x without significant resolution degradation or distortion.

Strangely, I've had good success with stacked TCs. I frequently use my Tamron SP 300/2.8 with the SP 1.4x Adaptall 2 TC on top of the Pentax F 1.7x AFA for a combined multiplier of @ 2.4x with good results. This yields a 714mm f6.7 that only (:-)) weighs @ 5 1/2 lbs and cost me significantly less than $1000 USD total. Compare this to the size, weight, and cost of the FA*600/4 that's been commented on recently here at @ 12 lbs and over $6000 USD, and the advantages of TC use for me becomes much clearer. Don't get me wrong, the FA*600 is clearly better, and if it were a matter of putting food on the table, I'd pop for the monster, but for my purposes as an amatuer birder, my combo serves very nicely.

As magnification goes up light transmission goes down, correct??..And is this is why the 2.0x teleconverters only work well with f2.8 & faster lenses, as only the fast glass will transmit enough light to allow the AF functions of cameras to work??..


Correct on both counts. As you increase focal length, light transmission drops proportionately since effective aperture is equal to the actual aperture x focal length. Since the max diaphragm opening and size of the front element of the lens are fixed, by increasing the FL, you decrease the light transmission by the same factor, so a 1.4x TC decreases the Ev by a factor of 1.4 (or one stop), a 1.7x decreases the Ev @ 1 1/2 stops, and a 2x decreases it by 2 stops.

Most AF systems start to struggle at f5.6 and stop working reliably at f8 max apertures, even in very bright light, so the fast glass is a definite plus for use with TCs. Other factors in AF performance are sharpness and contrast of the lens wide open, the sharper and more contrasty the better.

The multiplying effect of the TC also multiplies the optical faults of the lens, so for TC use, my rule of thumb is the better the lens, the less it will be degraded by using a TC with it.

Another lengthy post. . . and realize that much of it is only my opinion, so YMMV. so take it for what it's worth. . .

Scott






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Old Jul 26, 2007, 3:31 PM   #3
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Since Scott's answer is actually very well covering the subject, I'll just add my personal experience.

I have recently bought the Pentax-F 1.7 AF Adapter (the autofocus one), have just been able to try it a little with the A*85 mm and the A*200 mm lenses. I'm very satisfied so far, the AF really is fast just as Scott says, and I can see no problem with image quality.

I also have the Pentax Rear Converter A 2XS (manual focus, automatic metering with A-lenses and designed for shorter lenses <200 mm). It's physically possible to use with longer lenses too, but the manual gives a warning that you might get some light fall-off at the corners. I use this one with my 600 mm lens. Probably thanks to the smaller-than-film sensor I see no problem with the light fall-off. At infinity there is a recognizeable degradation in image quality, but it's not severe. At shorter than infinity, the image quality is nearly as good as withoutTC.

Both these converters are still available new from Scandinavian Photo (at least they are listed). For some reason the A converters (all four varieties 1.4XS, 2XS, 1.4XL and 2XL) are much more expensive than the AF Adapter 1.7, don't know why.

Kjell

Sample pic 600 mm+Converter A 2XS at about 7 metres:
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Old Jul 26, 2007, 4:00 PM   #4
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Your picture has convinced me Kjell that I really do need the auto focus converter, unfortunately the local shop who ordered one for me from Japanlater advised they were unavailable and Scandanavianphoto have not answered my emails.:sad:

I suspect if I had one it would become an almost integral part of my *ist DS. Poor focus is by far my greatest cause of failure plus of course shots missed through being too slow to do it manually. I get good results with full auto-focus lens but most of my lenses are "antique" or "junk" depending upon the point of view.:roll:
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Old Jul 26, 2007, 4:35 PM   #5
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Thank you, Thank you Scott & Kjell

Scott, your post was exellent, & answered all of my questions..

Now it's just a matter of finding the TC that I want & bidding for it..

Kjell, you are the 2nd. or 3rd. person recently to say that Pentax was still making the TC's, but no place that has them listed actually has stock to sell..

Which is too bad as an adequate supply of these TC's would eleviate a lot of Pentaxians needs for larger glass..

Another case of Pentax dropping the ball..

Although from Pentax's point of view, until the K100D & K10D were introduced to their respective now impressive worldwide market sales, things must have looked pretty bleak as far as worldwide camera & accessory sales were concerned..

I would have liked to have been a fly on the wall in the meetings where the discussions took place to advocate discontinuation of all of the A-series, F-series, & FA-series lenses and accessories..I can only hope that those responsible for those decissions are no longer with the company..

Since digital lenses designed for less than full-size sensors allow for less than acceptable results when used on film cameras, we Pentaxians can only hope that the future holds in store for us full-size sensor DSLR's & digital lenses that will allow the same backwards compatibility of use on film cameras that we now enjoy with all but the DA & DA* lenses..

I for one will have to think long & hard before investing thousands upon thousands of dollars on a new digital only camera system that will not allow me to use the new purchases with my older film cameras..

Bruce
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Old Jul 26, 2007, 5:01 PM   #6
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Sorry John, but the picture was taken with the A 2XS converter, manual focus. The AF 1.7 adapter cannot be used with the 600 mm lenssince it's too slow, min aperture 5.6. According to the manual the adapter only works with lensesf2.8 or faster, but others on this forum reports that it works with f4-lenses too.

This is a sample with the AF adapter and the A*85 mm lens. Difficult light since everyone was standing under the trees while the sun (for once) lit strongly on the lawn. I didn't get any good shots from this event, there was also spectators in the background nearly all the time (standing in a ring around the kids). But it still shows what sharpness the AF adapter can deliver. Slightly cropped to get unwanted spectators out of the picture. Shotfrom a distance of10-15 metres.

Kjell
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Old Jul 26, 2007, 5:59 PM   #7
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bilybianca wrote:
Quote:
This is a sample with the AF adapter and the A*85 mm lens. Difficult light since everyone was standing under the trees while the sun (for once) lit strongly on the lawn. I didn't get any good shots from this event, there was also spectators in the background nearly all the time (standing in a ring around the kids). But it still shows what sharpness the AF adapter can deliver. Slightly cropped to get unwanted spectators out of the picture. ShotÂ*from a distance ofÂ*10-15 metres.

Kjell
Kjell

Wow the attached file is beautiful particularly with the back light. Was it some kind of a school play ? Well done. This is the sort of thing that one pict suffices to tell all. The A*85 has a lot of light for the TC to work in full force. Even 2x should not degrade it to a significant extent

Daniel
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Old Jul 26, 2007, 6:12 PM   #8
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Sorry Kjell, I should have read your post with more care.

I have read reports of the AF adapter only working with 'fast' lenses but surely the limiter is the amount of light available, otherwise perhaps it is best I dont have one. I certainly dont have any fast long lenses, my nearest would be a 300 f4 and the kit lens gives me autofocus in the shorter ranges anyway.
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Old Jul 26, 2007, 6:43 PM   #9
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Hi Kjell,

Tne pic of the kids in costume is a definite WOW! Talk about 3D appearance! I'm sure the patterning of the costumes added to it, but as soon as it appeared on the screen. . . it just popped out. . .

Okay -- now I'm gonna be more disappointed I didn't buy that one last year. . .

Scott
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Old Jul 26, 2007, 7:33 PM   #10
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I have the A*85 1.4 also and that is the reason I bought the AF 1.7 TC to use with my PZ-1P and it is a beautiful combination. Not to mention that the PZ focused so much faster than even the K10D that focus seemed like it was instantaneous.

The faster the lens, the better it works and the more contrast the lens has the better it works too. I have the A1.4X-L and the A1.4X-S and they both are great pieces of glass, but they are not AF and are a bit pricey.

The Tamron 1.4x TC is a close second and far less expensive than the Pentax versions so long as you get a current version, as some of the older ones were optically inferior.

Tom
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