Woah... Something weird with quickshift lens

*GLXLR* · 09-02-2009, 08:26 PM

Ok guys.

I recently realized that my focusing ring on my DA* 50-135mm started feeling loose again and that was why I exchanged my first version. So as a normal, curious teen, I surreptitiously took some of my dad's little screwdrivers during the night (he doesn't like my touching my babies incase I break em after seeing the 50mm f/2 open on my table)

Anyways, I was desperate to see how I could tighten my focusing ring. After an hour, I was frustrated and decided to turn the focussing ring past infinity and past 1m (minimum focusing). Then i realized the lens no longer had any hysteresis.

And FYI, yes I do know that putting the camera on AF and lens on AF will naturally cause some hysteresis but there SHOULD be none during manual focusing.

Can anyone test this with their SDM lenses and see if they can get their ring more loose or tight (I think if you twist it the other polar end then it will do the opposite effect). I am curious as to how this QuickShift focus system works. If you have other Nikon/Canon glass, does it have the same effect or is it just for Pentax quickshift?

Thanks. Just an observation that I thought was strange. There is still some hysteresis on my lens still but this is much less than a 10th of a degrees worth since the only way I can tell is when I twist the focusing ring in the opposite direction, I can feel an opposing force within the lens.

*GLXLR* · 09-02-2009, 08:41 PM

Pentax DA* Series 50-135mm f/2.8 ED IF SDM *NEW-DEMO* - eBay (item 270450753777 end time Oct-01-09 14:19:04 PDT)

completely off topic, but holy crap. With Bing cashback, that lens comes out to like $585... $165 less than what I paid for 3 months ago.... ARG. Great deal for you guys that want one. Then you can help me test out this!

stevebrot · 09-02-2009, 10:36 PM

Let me get this straight...

You messed with your DA* 50-135 in an effort to figure out how it works and "tighten up" the quickshift
When you were done, the lens was acting differently
You want someone else to do the same thing with their expensive DA* lens to see if they get the same result

Say what????

Steve

*GLXLR* · 09-03-2009, 02:26 PM

Originally Posted by stevebrot

Let me get this straight...

You messed with your DA* 50-135 in an effort to figure out how it works and "tighten up" the quickshift

When you were done, the lens was acting differently

You want someone else to do the same thing with their expensive DA* lens to see if they get the same result

Say what????

Steve

It was like that when it came and since I already got two models with that same focusing ring "looseness" I am guessing it is normal. Either way, it shouldn't damage your lens unless you twist it extremely fast or with great force.

I am thinking that maybe Pentax designed the lens this way so that the user can adjust tightness or looseness depending on his preference, although I am not sure how quickshift lenses work so I am wondering if someone very knowledgeable can explain this to me.

*Igilligan* · 09-03-2009, 03:14 PM

Originally Posted by GLXLR

Ok guys.

I recently realized that my focusing ring on my DA* 50-135mm started feeling loose again and that was why I exchanged my first version. So as a normal, curious teen, I surreptitiously took some of my dad's little screwdrivers during the night (he doesn't like my touching my babies incase I break em after seeing the 50mm f/2 open on my table)

Anyways, I was desperate to see how I could tighten my focusing ring. After an hour, I was frustrated and decided to turn the focussing ring past infinity and past 1m (minimum focusing). Then i realized the lens no longer had any hysteresis.

And FYI, yes I do know that putting the camera on AF and lens on AF will naturally cause some hysteresis but there SHOULD be none during manual focusing.

Can anyone test this with their SDM lenses and see if they can get their ring more loose or tight (I think if you twist it the other polar end then it will do the opposite effect). I am curious as to how this QuickShift focus system works. If you have other Nikon/Canon glass, does it have the same effect or is it just for Pentax quickshift?

Thanks. Just an observation that I thought was strange. There is still some hysteresis on my lens still but this is much less than a 10th of a degrees worth since the only way I can tell is when I twist the focusing ring in the opposite direction, I can feel an opposing force within the lens.

I am familiar with magnetic hysteresis in yig tuned oscillators... but I can not figure out how it relates to the quick shift focus of the lens in MF or AF.

Please help me understand... Great 10 dollar word though~!

*GLXLR* · 09-03-2009, 04:21 PM

Originally Posted by Igilligan

I am familiar with magnetic hysteresis in yig tuned oscillators... but I can not figure out how it relates to the quick shift focus of the lens in MF or AF.

Please help me understand... Great 10 dollar word though~!

Lol.. that's the thing. I DON'T know how quickshift works, let alone know if it is even RELATED to the problem, although I thought it was. I remember that when in AF mode, there is a bit of hysteresis because of the "loosening" (if this is even the right word) of the quickshift motor.

stevebrot · 09-03-2009, 05:30 PM

Originally Posted by Igilligan

I am familiar with magnetic hysteresis in yig tuned oscillators... but I can not figure out how it relates to the quick shift focus of the lens in MF or AF.

Please help me understand... Great 10 dollar word though~!

I am familiar with the word in an engineering context as well and was unsure what was meant here. I think he means lag, slop, or latency.

Steve

wasser · 09-03-2009, 05:41 PM

Originally Posted by GLXLR

completely off topic, but holy crap. With Bing cashback, that lens comes out to like $585... $165 less than what I paid for 3 months ago.... ARG. Great deal for you guys that want one. Then you can help me test out this!

Bing cashback at Ebay requires payment through Paypal. That seller doesn't accept Paypal. Still, it's not too bad a deal.

kjellhar · 09-04-2009, 01:15 AM

If I understand it right, what you want people to try is not to take the lens apart, but only to rotate the focussing ring past the infinite or close range stops and see if that somehow tightens things up?

I have not seen how Pentax have solved the Quickshift stuff, but I know how Canon does it on their USM lenses, and I guess that is also how the rest is doing it. It's not that easy to explain in words, but I'll try.
The lens assembly that is focused is in the middle, and has some ball bearings attached to it. The USM motor ring is pressing at one side of the ball bearing, and the manual focus ring is pressing on the other. If the motor stands still, and the focus ring is rotated, the ball bearing will roll against the motor ring, and drag the lens assembly along. The same happens when you do the opposite. The lens assembly will rotate at half the speed as the focus ring, which can be seen on the distance scale. So, on these lenses there are no clutch systems or anything. When you rotate the manual focus beyond the stops, you will notice that the friction increases, which is caused by the fact that the ball bearings are slipping instead of rolling since the lens assembly refuses to move any further. This should not harm the lens as it is designed to take it.

The Quickshift on the screw drive lenses is a different deal though. On these lenses the focus ring moves when the autofocus is working. My guess is that there is some sort of autoclutch system that is activated when the screw drive starts to spin, and disengage when it stops. Maybe some friction coupling that expands when it starts to rotate. Or maybe a gear that is pushed in, like in the electrical starter engine of a car.

*GLXLR* · 09-04-2009, 05:42 PM

Originally Posted by kjellhar

If I understand it right, what you want people to try is not to take the lens apart, but only to rotate the focussing ring past the infinite or close range stops and see if that somehow tightens things up?

I have not seen how Pentax have solved the Quickshift stuff, but I know how Canon does it on their USM lenses, and I guess that is also how the rest is doing it. It's not that easy to explain in words, but I'll try.
The lens assembly that is focused is in the middle, and has some ball bearings attached to it. The USM motor ring is pressing at one side of the ball bearing, and the manual focus ring is pressing on the other. If the motor stands still, and the focus ring is rotated, the ball bearing will roll against the motor ring, and drag the lens assembly along. The same happens when you do the opposite. The lens assembly will rotate at half the speed as the focus ring, which can be seen on the distance scale. So, on these lenses there are no clutch systems or anything. When you rotate the manual focus beyond the stops, you will notice that the friction increases, which is caused by the fact that the ball bearings are slipping instead of rolling since the lens assembly refuses to move any further. This should not harm the lens as it is designed to take it.

The Quickshift on the screw drive lenses is a different deal though. On these lenses the focus ring moves when the autofocus is working. My guess is that there is some sort of autoclutch system that is activated when the screw drive starts to spin, and disengage when it stops. Maybe some friction coupling that expands when it starts to rotate. Or maybe a gear that is pushed in, like in the electrical starter engine of a car.

Wow! Thanks. Anyways, for some odd reason, my lens tightens or loosens when pushing past infinity. Maybe it's because the ball bearings get closer together when you tighten the focusing ring and the opposite when you loosen. Anyways, this is a non issue and I have it all resolved.