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08-19-2011, 06:44 AM   #1
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Pentax-F 35-70mm

Hi,

I bought this lens on ebay and got it today.

Besides that the rear cap is missing (which the seller did not mention), the zoom ring is rough-running somewhere between 35-50mm.

I tried rotating the ring back and forth a few times to see if this changes something. Sometimes it got even harder to move between 35-50mm, but then got loose again.

I checked the lens database and found only one user mentioning this, too:
"Build quality is generally good but the zoom ring feels a little cheap and mine sticks a little as it moves through the mid (50mm) range... "

Is this "sticking" of the zoom ring normal for this lens or is my copy broken/too old?

Best wishes,
Klaus

08-19-2011, 07:19 AM   #2
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Hi Klaus,

My F 35-70's zoom requires more effort to turn at 40mm, when zooming from 35-70mm. Curiously, when zooming the other way (70-35mm) it's pretty smooth.
08-19-2011, 07:41 AM   #3
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Mine is pretty smooth throughout the range. However, to turn it to "macro" it feels pretty rough.
08-19-2011, 08:13 AM   #4
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Mine is smooth throughout its range also, including the 'macro' region, with no sticking at all, except for the macro transition bump. Your "rough feel" does not sound good. I don't really know what to suggest. Do you have the option of returning the lens?

08-19-2011, 08:32 AM   #5
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QuoteOriginally posted by RioRico Quote
I don't really know what to suggest. Do you have the option of returning the lens?
Fortunately, I bought the lens from a commercial seller and have a 14-day return policy (this is by law in germany).

Thus, I will return it. Mainly because of the sticking zoom ring, but also because the seller sold it without the rear cap without mentioning it. I feel a little bit fooled.


Thanks!

Klaus
08-19-2011, 04:57 PM   #6
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the lens probably came off a SF-X camera that's why no rear cap.

my 35-70 is quite smooth when turning the zoom ring however i remember it is quite difficult to turn the zoom ring when i first receive it.

the problem only went away when I turned it to macro mode and back a few times, (turn macro to 70 to 35 and back) the first time going into macro mode was really tough (i read up on the forum a few times on how to get in to macro mode before i have the confidence to do it)

I thought i am going to break the lens. Now it's working good. The only complain i have is the focus ring is noisy when turning. seems like some kind of sand is stuck in it.

It's good that you have the return policy, gives u the peace of mind

QuoteOriginally posted by kdre Quote
Fortunately, I bought the lens from a commercial seller and have a 14-day return policy (this is by law in germany).

Thus, I will return it. Mainly because of the sticking zoom ring, but also because the seller sold it without the rear cap without mentioning it. I feel a little bit fooled.


Thanks!

Klaus
08-21-2011, 01:51 AM   #7
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it's should be smooth through out the 35-70 range.

It's easy to take it apart tho. I am sure it's dirt that makes the friction.
08-21-2011, 02:12 AM   #8
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I've had 2 copies of this lens. One behaved like yours for the most part and I sold it for parts or repair. The other worked fine and left here a couple weeks ago so I guess you could say I have a 50% success rate with the F35-70. I think the zoom ring problems with this lens are more common than the lens database would have you believe. The database is a fantastic and vast resource however. I'm always leery about buying used zooms online, especially in this day and age of estate chasers who buy lots and have no clue of what they are reselling (though sometimes a bargain can be found that way too).



08-21-2011, 01:08 PM   #9
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QuoteOriginally posted by MegaPower Quote
it's should be smooth through out the 35-70 range.

It's easy to take it apart tho. I am sure it's dirt that makes the friction.
I was also thinking on taking the lens apart, but

a) Disassembling is usually easy. Is it complicated to assemble the lens once I cleand it inside? Can the lens get (easily) decentered or misaligned during this process?

b) Are there springs that can fly around as soon as I open the lens?

c) Which side (front or rear or both) should be opened?

d) Can you explain a little what should be done as soon as the lens is open? Just use a rocket blower and blow the hell out of it? Or a slightly wet tissue?

As you can see there a few questions that blew away my thoughts on taking the lens apart. I prepared the package today and will ship it to the seller tomorrow or the day after.
However, if someone answers the questions above before I bring it to the post, I could be tempted to give it a try :-)

Best wishes,
Klaus

PS: I have no problems doing handicraft work, but I never opened a lens, so if the risk that I destroy it is high, then I just should get my money back...
08-21-2011, 04:07 PM   #10
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I haven't taken this particular lens apart, but here's some general advice. Older primes tend to come apert from the front. Newer lenses are more likely to come apart from the back, except for the very frontmost elements. The mount screws are JIS standard, and Phillips screwdrivers won't always work. The screws will tear the head off a cheap Phillips screwdriver and not budge. The F and later lenses have lots of electrical contacts in the mount that can be really annoying to reassemble. The zoom mechanism is often several concentric barrels, and the fault might mean a lot of disassembly. For example, my FA 28-105 Power Zoom has four concentric barrels. Sometimes the barrels have to be in a specific place to access the screws holding them together. Most lenses have something like a pair of nylon rollers in a spiral groove. One roller might crack and the lens stil works but sticks. The next roller will wear out eventually and cause a more permanent failure. You might find the broken roller but then you have to figure out what to replace it with. Photos and notes help with reassembly. The lenses I have in my failed repair box are all zooms.
08-22-2011, 07:09 PM   #11
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QuoteOriginally posted by kdre Quote
I was also thinking on taking the lens apart, but

a) Disassembling is usually easy. Is it complicated to assemble the lens once I cleand it inside? Can the lens get (easily) decentered or misaligned during this process?

b) Are there springs that can fly around as soon as I open the lens?

c) Which side (front or rear or both) should be opened?

d) Can you explain a little what should be done as soon as the lens is open? Just use a rocket blower and blow the hell out of it? Or a slightly wet tissue?

As you can see there a few questions that blew away my thoughts on taking the lens apart. I prepared the package today and will ship it to the seller tomorrow or the day after.
However, if someone answers the questions above before I bring it to the post, I could be tempted to give it a try :-)

Best wishes,
Klaus

PS: I have no problems doing handicraft work, but I never opened a lens, so if the risk that I destroy it is high, then I just should get my money back...
take it apart from the front first. that will get you to the zoom ring/element.
turn the first element by the little 2 slot.
the hardest part to do is to clean the third and forth glass for me because there are oil at the edge of the glass.

I dont know what's causing your zoom ring hard to turn so i cannot suggest anything on there.

no springs on the front side, there are springs flying from the rear side.

if you have the right tools to open a lens, go ahead and do it.
be careful not to scratch the glass.
08-29-2011, 01:19 PM   #12
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Hi,

I just wanted to let you all know how my story ended.

I sent the lens back to the seller and got my money back. At the same time I found a guy in a german forum who sold me his 35-70 lens. I bought it, after he promised me that everything runs smooth and that (t)his lens has no problems at all. I got the lens today and it is as promised: Everything runs smooth like a hot knife into butter :-) I am happy now :-)

From my experience with two copies of this lens, I would say that a rough running focsring is definitively not normal and there are better copies out there. So, if you bought this lens and the focusring feels strange: Send it back and watch out for another copy. The good ones exist :-)

Best wishes,
Klaus

Last edited by kdre; 08-29-2011 at 03:03 PM.
08-30-2011, 03:07 PM   #13
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This is a very good lens, its IQ is almost as good as a prime. The first is taken with 35-70 at 50mm f/8, the 2nd with 50mm/1.7 at f/8. (Dwarf apple in my yard)

Last edited by violini; 11-24-2012 at 07:51 PM.
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