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07-28-2015, 06:47 AM   #1
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Pentax-DA 1.4x AW AF Rear Converter Compatibility

I recently purchased a Pentax-DA 1.4x AW AF Rear Converter. Being a Pentax product I incorrectly assumed that it was compatible with all K mount Pentax lenses. The lens that I use the most is a discontinued SMC Pentax-DA 18-250mm F3.5-6.3 ED AL [IF] zoom lens and when I tried it with 1.4x Rear Converter the lens worked OK in auto focus but I couldn't turn the manual focus ring on the lens when I set my cameras (K7, K30, K01) to MF, it was frozen. RICOH support says The DA 18-250mm lens is not listed as being compatible yet it works when set to AF. Has anyone got a work around to use MF when using rear converter on the DA 18-250mm lens? From what I have read the newer DA 18-270mm zoom has the same problem.


07-28-2015, 07:30 AM   #2
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One of the reasons they list for being incompatible is that the rear element of some lenses can extend far enough back to hit the front element of the teleconverter. This can cause damage to both the lens and the TC. Not sure if that is the case with the 18-250 or not.

The other reason for being listed as incompatible is that slower lenses plus the TC do not let enough light through for the AF to function reliably. Note that it might still function, just not up to the standard RIcoh set for being listed as compatible.

As to the focus ring being 'frozen' when the TC is mounted I find that odd unless the rear element is indeed touching the TC. But if that is the case then I do not see how the AF is working.

Have you tried moving the focus ring with the lens mounted to the TC but not on the camera? Are you sure the screwdrive is being completely disengaged by the af/mf switch.
07-28-2015, 08:16 AM   #3
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There's no issue such as glass to glass distance with the 18-250. But when the camera AF is set to MF, the screw drive is disangaged from the camera body only. Screw drive transmission stays coupled between the converter and the lens. It seems that the output speed of the converter is slower than the input speed. Result is that screw drive turn easily when from body to converter , but hardly from the lens to the rear converter. This is the case for the Pentax 18-250 , but also for the Tamron 17-70, Tamron 28-75 and Tamron 70-200. When using the rear converter , it may be possible to MF from the lens focus ring with applying additional force, but I'd not recommend it.
07-28-2015, 09:11 AM   #4
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Pentax-DA 1.4x AW AF Rear Converter Compatibility

Thank-you for responding jatrax.
As you suggested I tried moving the focus ring of the lens mounted on the TC only. At first it appeared to be frozen, but as I applied more pressure it moved. Then I tried both the lens and TC back on the camera and was able to move the focus ring with the camera set to MF. It's still a bit stiff but appears to work OK, but just not a smooth movement. My hesitation to be forceful may explain the frozen description. In AF the ring moves freely as it always has. With the lens off the TC and camera the focus ring has a friction rubbing sound which it had before I got the TC.

I compared the back end of the DA 18-250mm to other compatible lenses and I don't think that clearance is a problem.

My Sigma DG 150-500mm APO HMS zoom appears to work OK with the TC in AF and MF. I took a few back-yard test pictures, but have not gone out in the wild to give it a real test yet.


07-28-2015, 10:21 AM   #5
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QuoteOriginally posted by biz-engineer Quote
There's no issue such as glass to glass distance with the 18-250. But when the camera AF is set to MF, the screw drive is disangaged from the camera body only. Screw drive transmission stays coupled between the converter and the lens. It seems that the output speed of the converter is slower than the input speed. Result is that screw drive turn easily when from body to converter , but hardly from the lens to the rear converter. This is the case for the Pentax 18-250 , but also for the Tamron 17-70, Tamron 28-75 and Tamron 70-200. When using the rear converter , it may be possible to MF from the lens focus ring with applying additional force, but I'd not recommend it.
I think the Pentax DA 18-250mm was made by Tamron for Pentax as a Pentax lens, so I think you are right on with your opinion and it makes sense. Until I replace DA 18-250mm I will avoid using MF when using the TC. Thank-you both for your help.
07-28-2015, 10:37 AM   #6
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Putting that expensive teleconverter on that zoom lens is like putting Michelin tires on a Yugo
07-29-2015, 08:29 AM   #7
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You go too far with your arrogance, are you related to Donald Trump? I thought this forum was here to help not ridicule.
07-29-2015, 08:57 AM   #8
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humm... believe it or not, the AF worked with HD TC + screwdrive DA 18-250 (actually a Tamron design), and I was not able to lock AF with the first copy of DA*300 SDM (which I returned).

07-29-2015, 09:10 AM   #9
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QuoteOriginally posted by PaPa Quote
You go too far with your arrogance, are you related to Donald Trump? I thought this forum was here to help not ridicule.
Did you see the smiley? It was meant to be funny. Apparently you have no integrity or class.
07-29-2015, 07:54 PM   #10
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QuoteOriginally posted by Driline Quote
Did you see the smiley? It was meant to be funny. Apparently you have no integrity or class.
There is a risk to telling jokes even with a smile. Your joke wasn't funny and your timing was off. My reaction was a bit harsh and I'm sorry for that. If I tell a joke and it offends, I immediately apologise.
07-29-2015, 08:19 PM   #11
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QuoteOriginally posted by PaPa Quote
There is a risk to telling jokes even with a smile. Your joke wasn't funny and your timing was off

So says you. Me....I'm laughing hysterically
07-30-2015, 12:47 PM   #12
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QuoteOriginally posted by Driline Quote
So says you. Me....I'm laughing hysterically
Papa, you don't realize how blessed you were receiving advise from Driline. In one truthful and direct sentence he saved you from many hours of "trial and error" frustrations.
(Check out Pentax lens reviews.)
Yes, other members gave you good insight, but it all sounded rather like, blah blah blah to me.
Driline, maybe next time you can enlighten us with your wisdom and skills by using simple parables, rather than one liners!


ps Does Donald Trump drive a Yugo?
07-30-2015, 06:12 PM   #13
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QuoteOriginally posted by PaPa Quote
There is a risk to telling jokes even with a smile. Your joke wasn't funny and your timing was off. My reaction was a bit harsh and I'm sorry for that. If I tell a joke and it offends, I immediately apologise.
07-31-2015, 08:10 AM   #14
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QuoteOriginally posted by Crayfish Quote
Papa, you don't realize how blessed you were receiving advise from Driline. In one truthful and direct sentence he saved you from many hours of "trial and error" frustrations.
(Check out Pentax lens reviews.)
Yes, other members gave you good insight, but it all sounded rather like, blah blah blah to me.
Driline, maybe next time you can enlighten us with your wisdom and skills by using simple parables, rather than one liners!


ps Does Donald Trump drive a Yugo?
Here's some more blah blah blah for you.

I am not a professional photographer and joined Pentax Forums for help and I appreciate the answer that explained my MF problem with the DA 18-250mm lens.

Could someone please interpret what Driline was trying to say by his comment "Putting that expensive teleconverter on that zoom lens is like putting Michelin tires on a Yugo".

I know that the Yugo is a car with a bad reputation. I purchased the DA 18-250mm lens in January of 2009 for CAD$550.00 at Henry's after reading reviews and it's the lens that I use the most. I have taken thousands of images with DA 18-250mm lens. Comparing the DA 18-250mm lens to a Yugo is a bit of an insult. I paid CAD$550.00 for the 1.4xTC from Amazon.ca in June. They are both Pentax products and both expensive (For my budget).

Pentax boasts that you can mount any Pentax lens (thread mount or K mount) on any K mount camera, yet there is a problem with MF of the DA 18-250mm when using TC. I am aware that lenses should be F4 or faster, but a F3.5-6.3 zoom should still work using the TC and it adds 100mm.


PS: Trump only drives his Yugo when he's with Larry, Curly and Moe.
07-31-2015, 09:34 AM - 2 Likes   #15
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QuoteOriginally posted by PaPa Quote
Could someone please interpret what Driline was trying to say by his comment "Putting that expensive teleconverter on that zoom lens is like putting Michelin tires on a Yugo".
Just in case you are serious: The 18-250 is a fine lens for what it is, a slow consumer super-zoom. It is not, most definitely, a lens most would use a TC on. The HD 1.4x RC is a professional level teleconverter designed to be used with high end glass such as the DA*300, the DFA 150-450, the DFA*70-200 or other high quality lenses. So while Driline's comment may have been a bit of an exaggeration (hence his use of the smiley) there is a lot of truth to it.

There is no reason you cannot use the TC on the 18-250 if you are happy with the results. Just like there is no reason you cannot put Michelin tires on a Yugo. They will both work just fine, you just will not be getting the most out of the TC or the tires.

Hope that explanation helps, it is not my intention to get involved in this particular spat and if you were only trying to prolong the argument instead of looking for a serious answer then my apologies for being gullible.
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