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06-28-2015, 11:14 PM   #1
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Sigma DC 18-250mm 1:3.5-6.3 HSM lens

Hi all Please explain to me why the Sigma DC lens will work on auto focus on my K-50 but will not work on my older K 20-D?


Is there a setting I must change on the K20 to accept the lens?

06-29-2015, 03:25 AM   #2
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If the AF/MF switch on the K-20D is set to autofocus, then the lens should autofocus. Does other AF lenses with internal AF motors work correctly with AF on the K20D? Dirty contacts perhaps?
06-29-2015, 04:22 AM   #3
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There is IIRC a cutoff before which HSM and other such fancy stuff is not supported by older camera bodies. This is why I would want future Pentax lenses to have a screwdrive fallback position with the HSM/screwdrive option to be decided in firmware.
06-29-2015, 08:50 AM   #4
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Hi When the Pentax DA lens is fitted and the Autofocus switch is set at AF.S the auto focus works fine When fitting the Sigma nothing???? Fitting it to the K50 and the Sigma works with beautiful pictures!!!!!!!


Pathdoc are you saying my K20D is too old to read the HMS lens? Both were on the market at the time?

06-29-2015, 10:04 AM   #5
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I don't understand this. Lenses with an internal motor should work fine on a K20D
06-29-2015, 11:17 AM   #6
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Neither do I so where are the gurus to tell me what I must do. I want to use the Sigma on the K20D when going on my cruise in October but the motor will not turn It works on the K50 so is not bust!!!!!
06-29-2015, 01:44 PM   #7
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QuoteOriginally posted by LOBO RSA Quote
Hi all Please explain to me why the Sigma DC lens will work on auto focus on my K-50 but will not work on my older K 20-D?


Is there a setting I must change on the K20 to accept the lens?
If this is the lens you are talking about -

Amazon.com : Sigma 18-250mm f3.5-6.3 DC MACRO OS HSM for Nikon Digital SLR Cameras : Camera Lenses : Camera & Photo

I have this lens along with the K20D with firmware 1.00
I just tried this combination and all focus modes work properly.

Last edited by wildman; 06-29-2015 at 01:54 PM.
06-29-2015, 10:46 PM   #8
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Sigma HSM AF uses the two PZ (power zoom) contacts located just slightly inside the lens mount.

The K 20D does not have these two separate contacts; therefore HSM AF will not work on that model.

06-30-2015, 07:15 AM   #9
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Yes, that is the same lens What is firmware 1.00


Hi Kevin Actually you are wrong My K20 D does have the two PZ contacts The K50 and the K20D are identical to the last screw It may be that the pins are not connected or must be activated ?
07-02-2015, 06:04 AM   #10
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So, to the few that have been following this I went to Sigma here in Cape Town with little hope. Way and behold what a wonderful experience. Not only were they friendly and helpful they went the full mile and will be replacing the PCB in the lens to recognise my K20D at no cost. Excellent service at the tip of Africa
07-02-2015, 06:07 AM   #11
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My Sigma 18-250 is off at Sigma right now, as it's slowly stopped working on all my cameras. originally it worked on my K-5 but not my wife's, then it stopped working on my wife's and my K-3. IN the end it wouldn't AF on anything. Sigma is sorting it out.
07-02-2015, 07:33 AM   #12
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QuoteOriginally posted by LOBO RSA Quote
Yes, that is the same lens What is firmware 1.00
I was referring to firmware on the K20 camera body (it might make a difference).
BTW I like this lens very much - I hardly use anything else for just general family and walkaround photography.

Last edited by wildman; 07-02-2015 at 07:44 AM.
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