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01-06-2011, 02:01 AM   #1
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DA* ZOOM and Pentax 1.7x AFA and SR info

Does anyone know for sure if the Focal Length info is correctly transmitted to the camera body (including the 1.7x magnification) when using such a combination, like with the 50-135 or 16-50 + 1.7x AFA? I am wanting accurate Shake Reduction when using the AFA with one of these SDM zooms.

According to the diagram on bdimitrov's web site, the digital info pin (7th) pin does seem to exist on both sides of the AFA (looking by eye on my copy). I am guessing/assuming that the focal length info would be passed through or processed by the AFA:

Features and Operation of the Kaf Mount

Also, does anyone know if the 1.7x fudge factor is calculated and passed along to the camera body correctly, too??? I am one of those type of people who needs to know for sure that something works correctly before spending any money. This is the theory, actual user experience would be appreciated to confirm my theory.

Also, this is not a question about autofocus and is not a question about other companies' TC's. Thanks for any help.

GA

01-06-2011, 01:07 PM   #2
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The Pentax 1.7X AFA blocks the focal length info from the lens to the body. The body will ask you to enter the focal length.

The AFA translates the aperture info from the lens to the correct value, e.g. if the lens max aperture is F/2, the info to the body will be F/3.5.
01-06-2011, 01:40 PM   #3
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QuoteOriginally posted by SOldBear Quote
The Pentax 1.7X AFA blocks the focal length info from the lens to the body. The body will ask you to enter the focal length.

The AFA translates the aperture info from the lens to the correct value, e.g. if the lens max aperture is F/2, the info to the body will be F/3.5.
That sounds correct. Taking it one step further, the question then becomes what value to enter for focal length when prompted by the body. If you are going to be at the long of end the focal range (which might be a fair assumption since you're using a TC), then I would enter 250mm (about 150 x 1.7 - for the DA*50-135). If you plan to zoom a lot, the general idea is to enter a value about half-way to two-thirds of the zoom range (multiplied in this case by 1.7x).

Also, it's not relevant for the two DA* zooms you asked about, but I was playing with the A50/1.2 + 1.7x last night and noticed that the 1.7x AF-A wasn't able to read and/or handle the really large apertures. Basically, I couldn't go below f/2.8 on the body, which is about 2.5 stops slower than f/1.2. So I don't know if the body is reading/calculating the wrong aperture or if it can't open the A50/1.2 aperture up wide enough. Not really an issue, just throwing it out there in case anyone knows the answer
01-06-2011, 01:56 PM   #4
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QuoteOriginally posted by dgaies Quote
...the 1.7x AF-A wasn't able to read and/or handle the really large apertures. Basically, I couldn't go below f/2.8 on the body, which is about 2.5 stops slower than f/1.2. So I don't know if the body is reading/calculating the wrong aperture or if it can't open the A50/1.2 aperture up wide enough.
When all else fails, RTFM

(Page 3, first paragraph, last sentence)

Pentax-F AFA 1.7X Manual

01-06-2011, 02:18 PM   #5
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QuoteOriginally posted by SOldBear Quote
When all else fails, RTFM

(Page 3, first paragraph, last sentence)

Pentax-F AFA 1.7X Manual
That would presume I had the FM

Thanks for the link.
01-06-2011, 03:09 PM   #6
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SDM lens and AFA

Thanks both for the info!

Very interesting. So, Pentax does not currently have a TC that will send proper Focal Length info to the camera body??? Seems strange to push DA and SDM lenses but not have a full complement of accessories that support the long-standing DSLR feature set (since SR was introduced)!!! I don't like having to guess what FL to enter manually into the camera. Zooms are supposed to make things easier, not harder. Are there ANY TC's that support Pentax SR on zooms???

I will confirm that using the AFA on fixed focal length lenses focuses fast (I use mine routinely on a 50mm A 1.4 and a 35 year old 300mm Super Tak - works really well with both - the 50mm 1.4 also has trouble wide open like your 1.2). But this thread's question is NOT about focusing or aperture. Strictly Focal Length and SR. So I guess there is no real solution but to make a guestimate using the zooms, wrt Focal Length.

Also, I have read somewhere that it is best to use the smallest Focal Length expected to use to use SR properly with zooms. Like the 50-135 example, using mostly 150-200, should enter closest setting on camera to 150.

GA
01-06-2011, 03:12 PM   #7
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QuoteOriginally posted by goldenarrow Quote
Thanks both for the info!

Very interesting. So, Pentax does not currently have a TC that will send proper Focal Length info to the camera body??? Seems strange to push DA and SDM lenses but not have a full complement of accessories that support the long-standing DSLR feature set (since SR was introduced)!!! I don't like having to guess what FL to enter manually into the camera. Zooms are supposed to make things easier, not harder. Are there ANY TC's that support Pentax SR on zooms???
That is a fact that we are all complaining about here! And that has been an ongoing lament for the last three years or so - ever since the DA tc vanished from the Pentax lens roadmap...

Ben
01-06-2011, 06:45 PM   #8
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RTFM:

Manual? What manual???



01-06-2011, 06:55 PM   #9
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Ben,
Thanks for echoing my sentiments. I hear rumors that professionals snicker at the name of Pentax. Now I can see tangible proof that Pentax does not currently have the resources to compete on a pro level in certain areas. And that gives the willies to any budding pro, not wanting to get caught with a system that lacks anything one might need to get business and keep it. As an amateur, I can live without a fully functional TC for now. But I can see a day when I may not be so amicable. If the lack of this feature in a TC sways me away from the 50-135 I was thinking of getting, how little it would take to sway me to get the Nikon system I might want to switch to, dumping Pentax in the process because of lack of money. I don't have the money to switch, and I have no need to also. Just saying, if the opportunity arose, who knows? But that is also the amateur legacy of Pentax which keeps them around and makes uniquely useful products that they DO make. So, I appreciate what they are accomplishing with digital but also keeping my eyes open, too.

GA
01-06-2011, 07:34 PM   #10
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I don 't understand your reticence to use 3rd Party TCs. We all know that the only Pentax TC out there currently in production (yes the AFA is in production - just not exported to Europe / North America) is the AFA x1.7. Unless you count the Kenko 1.5 (Kenko = Hoya).

Then there is the Tamron x1.4 which I also have (in addition to the AFA) and this also works perfectly with Pentax lenses. And Sigma also make a x1.4 which works with some lenses. So what you want is out there - just not with Pentax written on the barrel.
01-06-2011, 08:01 PM   #11
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TC+zoom with respect to SR

Hi Frogfish,
I was focusing on the particular limitation of ALL TC's on Pentax AF zoom lenses that do not allow Focal Length information to be given to the camera so that Shake Reduction can be set automatically. I do use a Pentax 1.7x AFA, quite often. But I would like to know if ANY TC out there can transmit the Focal Length to the camera so SR can be set by the camera, not by me. Desirable feature on a zoom lens but the automated part of the feature is lost when attaching a TC. I am focusing on a particularly irksome problem that keeps me from spending money on Pentax zooms.

Also, I forgot to mention this, is the fact that I sometimes shoot very long range. The 300mm fixed lens + 1.7x + 1.5x crop = 765mm equivalent - HANDHELD. Proper SR becomes extremely important in order to get usable results. I almost never use a tripod when birding, must be moving and looking for my targets. Now, picture what kind of zoom to buy, finding out that I can only set one SR Focal Length! Very disappointing when considering that I depend on SR if I find targets at various Focal Lengths. One can set SR TOO high and cause more shake to be introduced into the picture, hence the advice I read somewhere which said that one should set SR too low in order not to introduce sensor-induced shake.

I hope this makes sense?

GA
01-06-2011, 08:46 PM   #12
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Thank you GA for the additional information. The Tamron x1.4 doesn't require that you input the FL : therefore I am assuming (dangerous) that this means the FL information is transmitted from the TC to the camera (I'm using K5).

If you are using the AFA with a (x-300) zoom then most of the time you are going to be using it at it's extreme end in which case setting the FL to between 450 and 500 makes more sense. Though inconvenient if you wish to vary this for an animal that's close then it can be done in under 10 secs (off-on - set new FL) I've also seen excellent shots from people doubling up the AFA with the Tamron x1.4 for 714 (with Pentax crop factor that is 1,085).
01-06-2011, 08:59 PM   #13
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Moved to the lens forum.

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01-06-2011, 09:00 PM   #14
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QuoteOriginally posted by Frogfish Quote
Thank you GA for the additional information. The Tamron x1.4 doesn't require that you input the FL : therefore I am assuming (dangerous) that this means the FL information is transmitted from the TC to the camera (I'm using K5).
I am pretty sure the Tamron 1.4x passes the focal length information to the camera body untouched (without taking the 1.4x into account).
01-06-2011, 09:07 PM   #15
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Thank you Adam for moving to the right forum, thought a TC was an accessory.
GA
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