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11-11-2011, 09:00 AM   #1
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Does pentax-F 1.7x support SDM lenses?

Does pentax-F 1.7x support SDM lenses?Or it just does the normal/basic AF on SDM lenses?

Actually, I guess I got the answer already..... because the F 1.7x was built before SDM lenses release. Right?

11-11-2011, 09:04 AM   #2
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The AFA x1.7 works great with the DA*300 ... so yes it works just fine with SDM. I'm assuming that will be the same for all other SDM lenses.
11-11-2011, 09:05 AM   #3
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The Pentax-F 1.7 AF-A does the actual focusing, so it doesn't matter what's attached to it (in terms of focusing). DA* lenses work just fine with it, even ones with broken SDM motors
11-11-2011, 09:11 AM   #4
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The AF1.7 doesn't care about lens AF, it treats any lens as simple "A" style lens. It does the AF itself. User just needs to make sure the lens is focused slightly behind the subject and AF TC will use it's AF capability to compensate for this.

11-11-2011, 09:13 AM   #5
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So the AFA 1.7x will do the focusing job, not the lens anymore. Then it means NO SDM function comes with this combination. Correct me if I ama wrong, plz.
11-11-2011, 09:27 AM   #6
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QuoteOriginally posted by Kenneth3aracing Quote
So the AFA 1.7x will do the focusing job, not the lens anymore. Then it means NO SDM function comes with this combination. Correct me if I ama wrong, plz.
The AFA does the focusing. However, it can only focus over a certain range, and that range is usually smaller than from the MFD to infinity. Therefore, you typically have to pre-focus the lens you're using manually to get close, and then the AFA finishes the job (so to speak). There is no AF connection from the body to the lens (either screw or SDM) through the AFA. The body uses the screw drive to focus the elements in the AFA, that's it.
11-11-2011, 11:06 AM   #7
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1.7 teleconverter

Pentax needs to come up with a new dedicated teleconverter.
11-11-2011, 01:53 PM   #8
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QuoteOriginally posted by Kenneth3aracing Quote
Does pentax-F 1.7x support SDM lenses?Or it just does the normal/basic AF on SDM lenses?

Actually, I guess I got the answer already..... because the F 1.7x was built before SDM lenses release. Right?
Since no one has offered a proper answer I will do so.

The SMC-F 1.7x AF TC does not support any autofocus lens, It will convert any autofocus lens into a manual focus lens, and it will NOT transfer any Lens data to the camera through the data pin mounted as this pin is not carried through the TC to the camera.

The reason data from the lens is not passed to the camera, is that the AF TC needs to use the data pin for its own focus information, as it performs the focusing for the lens, once you get close to focus manually.

As a result, you need to enter focal length into the camera when you turn it on, which means that for zooms, unless you know what focal length you are going to shoot in advance, it is best to set to minimum (plus1.7x for the adaptor)

One thing the adaptor does do, however, is correct the reported aperture for the teleconverter light liss of 1.5 stops. This means matrix metering and P-TTL flash work as intended, and you do not get errors (constant offsets) due to the addition of this teleconverter, like you do when you add a teleconverter that does not correct the reported aperture.

as a result it is a mixed bag. Having said that, due to the small size and low mass of the focusing elements, focusing is very quick and reasonably quiet

Also, and we should do this as a project, since the AF TC has its own focusing range, we should do a test, perhaps using a K50mm or similar, to determine the equivelent lens extension that the focusing mechanism of the adaptor has. In that way you would know the (quasi) hyper focal distance of any lens. By this I mean the focusing distance for which the adaptor can focus out to infinity in one direction and down to some (to be determined as a function of focal length) minimum distance.

11-11-2011, 08:54 PM   #9
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QuoteOriginally posted by Lowell Goudge Quote
As a result, you need to enter focal length into the camera when you turn it on, which means that for zooms, unless you know what focal length you are going to shoot in advance, it is best to set to minimum (plus1.7x for the adaptor)
Why do you say that Lowell ? I have heard various theories on this and usually set mine to somewhere around the middle of the range + TC if I know I am going to be using the whole range or, more likely since the whole purpose of adding the AFA is to gain reach, set it near the end of the range + TC. Is this wrong ?
11-12-2011, 05:03 AM   #10
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See the first part of the comment. I said if you know the focal length you are shooting at........ If the intent is to shoot at the long end set it there, but if you are all over the range, slight under compensation is much better than over compensation, as the SR can and will induce blur if you set it longer than you are shooting. When I use my series 1 70-210/3.5. If I don't have a plan to use any one focal length I set the focal length to 129mm (minimum with adaptor) and rely on technique and slightly elevated shutter speed for the long end, but if i really want the full benefit of the focal length I set it for 350mm
11-12-2011, 06:44 AM   #11
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Thanks Lowell.
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