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05-30-2011, 04:10 PM   #31
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In my opinion, Pentax (and other manufacturers) implementing quick-shift is their way of saying they don't recommend using the focus ring when the motor is coupled to the lens. It could be the lens gears, or the motor, but it's something.

An alternative interpretation is that you can just adjust focus faster (e.g. w/o resistance).

QuoteOriginally posted by atlnq9 Quote
If you are so concerned about stripping gears by turning the focus ring why aren't you concerned about this lens release button? Ever used a power drill with a screw bit and only had the bit partially engaged? Fastest way in the world to strip a screw. What happens if you didn't get the button pushed in all the way and the slot partially engages then the motor starts? Or your finger slips and the motor starts?

A very valid point. Personally, I decouple the AF button from the half-button press so this isn't an issue in my case.

I don't know Aussie; but "look after" in US English means maintenance/ take care of/ check on... And I have never had to do any maintenance to the AF system.

He means that he wouldn't buy any of equipment that you use based on his opinion of what is being discussed in this thread


Ever heard of a safety factor? Been doing it for 3yrs, not a problem yet. Best dampening to the focus system in the world.

Interesting advantage that I didn't think of.

Yes I am putting torque in ways that are not normal, but they are obviously not out of design limits since it still works. I don't agree with this logic

I don't even want to get started on how many things everybody uses all the time which are not the intended use but us engineers know it will happen so we design for it.

Then why do they design lenses with quick-shift?


This is how you start a car with a manual transmission when the battery is dead and nobody is around to jump you. Done it at least 10 times.

A car with heavy duty manual transmission and gears is a bit different, in my opinion. Btw, I've never pushed my manual transmission in 1st gear, seems a bit illogical. I push it in neutral, then use the clutch to drop it in gear and fire the engine. The clutch is designed to prevent high torque transitions between the motor and driveshaft. Also, the transmission is designed to have torque go both ways.

This can easily be the difference in time between having a publishable shot and having a POS. Hey if it doesn't last me but one more time I don't care because doing this has paid for my equipment 10 times over. I am hard on my equipment because I have to be. I shoot climbing/mountaineering/skiing/adventure photography. If it gets me the shot I will do it. Many of the shots are a once in a lifetime chance to get it.

I think this is the most important thing: getting the shot. I just use the lens release button. Others may use quick-shift lenses.



Last edited by Eruditass; 05-31-2011 at 10:06 AM.
05-30-2011, 07:33 PM   #32
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Could someone explain 'quickshift', as I constantly hear about it without explanation, and for the life of me I can't figure out what it means?
05-30-2011, 08:17 PM   #33
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QuoteOriginally posted by chiane Quote
Could someone explain 'quickshift'
In DA series lenses (but not in DA-L series) you can touch up the focus manually by turning the focus ring while the camera is still in autofocus mode. The AF mechanism disengages automatically.
05-30-2011, 10:56 PM   #34
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directly move the motor (drive)? I doubt that it would very harmful

While I am not an engineer, I can definitely see how things work when you try to focus a regular lens without the quick-shift function.

If you take the lens off, you can see that, when you rotate the focus ring, you are twisting the connector directly. That means, you are trying to rotate the electronic drive (motor) using the focus ring.

I guess that it would not harm the motor, because when you shut down the camera and focus the lens, the motor would give you the same reaction. The process is similar to rotating a stopped electronic fan. Maybe there would some resistance and even some noise, I doubt it is harmful.

However, I would not try to focus when in AFC mode. The motor will be constantly adjusting and rotating. Focusing may have a negative effect.

Bottomline is that The motor is perhaps one of the most reliable electronic part on the camera. I have never heard about focusing motor turning bad.

05-30-2011, 11:15 PM   #35
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QuoteOriginally posted by Marc Sabatella Quote
Might not "strip" anything, at least not right away, but you're applying torque in places the system wasn't designed to withstand, so I doubt it's good for the camera or lens.
Mark is absolutely correct. The mechanism is not designed to take that sort of stress.


Steve
05-31-2011, 07:14 PM   #36
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Some good comments here in my opinion

QuoteOriginally posted by Eruditass Quote
In my opinion, Pentax (and other manufacturers) implementing quick-shift is their way of saying they don't recommend using the focus ring when the motor is coupled to the lens. It could be the lens gears, or the motor, but it's something.

An alternative interpretation is that you can just adjust focus faster (e.g. w/o resistance).

Originally posted by atlnq9

If you are so concerned about stripping gears by turning the focus ring why aren't you concerned about this lens release button? Ever used a power drill with a screw bit and only had the bit partially engaged? Fastest way in the world to strip a screw. What happens if you didn't get the button pushed in all the way and the slot partially engages then the motor starts? Or your finger slips and the motor starts?

A very valid point. Personally, I decouple the AF button from the half-button press so this isn't an issue in my case.

What if your trigger finger slips and re-engages... All I am saying is that really when you look at both methods they both have advantages and disadvantages. I see no clear winner. Sure everybody can have preferences. But there was so much un educated criticism to my method and nobody bringing up the disadvantages to others...

I don't know Aussie; but "look after" in US English means maintenance/ take care of/ check on... And I have never had to do any maintenance to the AF system.

He means that he wouldn't buy any of equipment that you use based on his opinion of what is being discussed in this thread.

Ever heard of a safety factor? Been doing it for 3yrs, not a problem yet. Best dampening to the focus system in the world.

Interesting advantage that I didn't think of.

Yes I am putting torque in ways that are not normal, but they are obviously not out of design limits since it still works. I don't agree with this logic

Hey, send me a camera body and lens. I'll tear them apart calculate the forces, do some metallurgy and determine if the material can handle it. I'll even tell you the design safety factor.

I don't even want to get started on how many things everybody uses all the time which are not the intended use but us engineers know it will happen so we design for it.

Then why do they design lenses with quick-shift?

Pretty sure the design wasn't to use the lens release. The last thing I can imagine is pentax recommending to unlock the lens and then turn the focusing ring to focus. Why do they make hammers when a wrench works half the time? Why do they make special pry bars for paint cans when a screwdriver works fine? Why do they make spoon with holes in it when a normal spoon can still drain liquid. Etc.


This is how you start a car with a manual transmission when the battery is dead and nobody is around to jump you. Done it at least 10 times.

A car with heavy duty manual transmission and gears is a bit different, in my opinion. Btw, I've never pushed my manual transmission in 1st gear, seems a bit illogical. I push it in neutral, then use the clutch to drop it in gear and fire the engine. The clutch is designed to prevent high torque transitions between the motor and driveshaft. Also, the transmission is designed to have torque go both ways.

Of course, still high forces on the drive train. And say you really slip the clutch, that is no better on it...

This can easily be the difference in time between having a publishable shot and having a POS. Hey if it doesn't last me but one more time I don't care because doing this has paid for my equipment 10 times over. I am hard on my equipment because I have to be. I shoot climbing/mountaineering/skiing/adventure photography. If it gets me the shot I will do it. Many of the shots are a once in a lifetime chance to get it.

I think this is the most important thing: getting the shot. I just use the lens release button. Others may use quick-shift lenses.
05-31-2011, 08:21 PM   #37
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Gents,
it appears that this thread is missing the straight answer to the original question: "What would happen if I put an auto-focus lens without quick-shift on a modern body (e.g. the K-5) and turned the focus ring with the lens set to auto-focus?"

Bottom line:
- it mainly depends on the camera model and its condition. In some cases you'll be able to pull it all the way from stop to stop, in other cases you'll be able to twist it a few millimeters (tenths of inch) only (the amount is determined by the freeplay in the gears and between different gear units)

An answer to another question arisen: will it be damaged?
Bottom line: it depends on several factors:
- the force applied
- the speed you're trying to twist it with
- the camera model and it's condition (see below re reduction gear)
- the lens model and it's condition (see below re reduction gear)

The 3rd question: is it recommended to do such things?
Answer: no, these things can at some conditions handle such application, but they're not designed for it. If you need the ability for quick manual focus w/o necessity to flip AF/MF switch, then you'd better invest into DA or DA* lens(es)

Here goes some 'how things work' stuff (it's amazing to see no real engineer here on PF who could chime in and break down all these simple bits).
When two bodies are in contact and one is trying to move relative to another one of three possible scenarios can happen:
- if the force (actually it's longitudinal projection, but nevertheless) applied is less then stationary friction coefficient (that depends on the material combination of those two bodies) multiplied by... something (I'm trying to keep things simple) then nothing happens, these two bodies will behave as they're stuck together
- if the force applied is greater then that friction coefficient then one body will be moving relatively its counter-part
- if one body is already moving relatively to another body but motion friction coefficient happened to arise then the speed will be reduced and at an extreme case the motion will be cancelled and two bodies will behave as a single solid one

A reduction gear assembly follows these basic physic rules. There're plenty of gear reducer designs, but all of them follow the friction rules above.

Spur gears can handle input force on both ends (in theory this is true for all designs of this type; in real life it doesn't work in a case of extremely huge gear ratios). In one case it works as a reducer and in the other one as an increaser\multiplier


The same goes for bevel gears


Worm gears work in one-way only, they got locked if input force is applied to gear, not the worm


Worm gear can be considered as an extreme of helical gear. It depends on the ratio (which in turn also depends on the angle between the teeth of both gears) whether this design works one-way only or both ways


So, what's up?
- it mainly depends on the reducer type used in your particular camera. I didn't get that far, but it appears that ist DS doesn't use worm gears and I'm able to twist the focus ring of non-QS lens with the body in AF mode. In a case of modern K-5 this doesn't work (it really looks like gear ratio in the AF drive has been increased comparing to old ist DS and probably this was done with a help of worm gear - K-5 has much stronger and powerful AF screwdrive)
- it has nothing with the DC motor in the camera. Actually, it does a little bit (strong motors create more mechanical resistance when one tries to twist the rotor), but here it can be considered that it doesn't
- since it depends on the friction coefficient between those two surfaces riding on each other then two identical gear-assemblies can show different results (in a terms of rear-drive availability) cause of different lubrication used in them; a lubricant goes worse with the age so this means that two identical cameras (e.g. ist DS) can show different results cause of the lubricants in AF gears just happen to be of different conditions
- all the screw-driven AF lenses that I'm aware of have a simple spur-gear reducer inside. You can check it yourself: take the lens off the camera and twist the focus ring while checking AF coupler on the lens bayonet - it'll be rotating as soon as you twist the focus ring; if they had worm gear then you wouldn't be able to twist the focus ring on the lens even if it's not mounted on camera

If you have read all the stuff to this line (which means you've got lots of free time!) then it's obvious that the bottom line for 'can I twist the focus ring on non-DA lens and what can go wrong' goes the following:
- it mainly depends on your camera. The old ones (probably expect z-1p) tend to 'allow' this while the latter ones forbid it just by the AF gear design
- I'd say that it's the lens gears that should fail 1st (should a failure happen or if you apply to much force). But in a case of extremely well-built (and designed) lens it's the dslr's AF gears to withstand the force applied (and to go south in a case of you're not that sensible or lucky).

so
can I? - yes
will it be fatal? - not really... usually
should I? - eh.. you'd better buy DA (or DA*) lens

Zig

Last edited by Siegfried; 05-31-2011 at 08:29 PM.
05-31-2011, 09:07 PM   #38
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QuoteOriginally posted by Siegfried Quote
Gents, it appears that this thread is missing the straight answer to the original question: "What would happen if I put an auto-focus lens without quick-shift on a modern body (e.g. the K-5) and turned the focus ring with the lens set to auto-focus?"
The focus changes

Maybe I just got a rare model that was properly designed and nobody else did or actually believes that pentax knows something about how people use their equipment or how to engineer cameras.

QuoteOriginally posted by Siegfried Quote
no real engineer here on PF who could chime in and break down all these simple bits
I'm a metallurgical engineer, not a mechanical. If you tell me the metal chemistry, manufacture method and heat treatment I can tell you what the mechanical properties are. If I dust off the old books I can calculate the gear ratios...

Trust me pentax knew it would happen. The safety factor on the system will encompass this. This is called a design criteria. Did pentax design the system to do this, no. Did they plan on it happening, yes. This is extremely common when engineering systems. This is engineering design 101.

05-31-2011, 10:31 PM   #39
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Andrew,
I'm sorry I don't quite follow your input. Lemme breakdown mine.

My idea - if in short - goes the following: in some cameras (my bet goes for ist series for sure plus some K1(1)00, K200 and K2000, probably also k-r/x) focus ring of non-DA lens can be twisted all the way from MFD stop to infinity stop while in others (K10-20-7-5) the gears inside the cam will 'self-lock' (mostly due to gear design chosen) and the available focus ring motion will be determined by the free-play in the lens gear and af-screw-coupler-to-main-gear-unit gear freeplay. This should be safe if the force applied will not exceed some threshold. And should a break-down happen it most probably be the gears in the lens, not the body.

On the other side: the equipment mentioned isn't designed to be used this way. It depends on the margin of safety (e.g. gears should be able to handle X nm/lbft of torque when working under normal conditions, but pentax engineers increased the gear strength by N per cent for safety purposes or dummy-proof) implemented on how long it gonna last being used this way - it's a significantly increased load (comparing to usual AF operation) that the gears handle when working under conditions we're talking about.

Zig
06-01-2011, 05:59 AM   #40
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QuoteOriginally posted by atlnq9 Quote
I'm a metallurgical engineer, not a mechanical. If you tell me the metal chemistry, manufacture method and heat treatment I can tell you what the mechanical properties are.
Are you sure the gears are even made of metal? I've obviously never opened up my camera body, but I think there's at least a decent chance the gears are actually plastic.
06-01-2011, 07:19 PM   #41
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QuoteOriginally posted by Siegfried Quote
(K10-20-7-5) the gears inside the cam will 'self-lock'
Not the K-7. This is what I use. I have no idea what gear configuration they use but I doubt there was any changes between k-5 and 7.

QuoteOriginally posted by Siegfried Quote
On the other side: the equipment mentioned isn't designed to be used this way. It depends on the margin of safety (e.g. gears should be able to handle X nm/lbft of torque when working under normal conditions, but pentax engineers increased the gear strength by N per cent for safety purposes or dummy-proof) implemented on how long it gonna last being used this way - it's a significantly increased load (comparing to usual AF operation) that the gears handle when working under conditions we're talking about.
You pretty much said what I have been trying to explain in the last couple posts. If gears are metal then if it designed to withstand the force a couple times it will take many thousands. Fatigue although it does exist and many cases is a critical design variable is a low issue here. Things that really require fatigue calculations are cyclical loadings (plane wings, piston rods, bike frames, springs, etc.)

QuoteOriginally posted by dgaies Quote
Are you sure the gears are even made of metal? I've obviously never opened up my camera body, but I think there's at least a decent chance the gears are actually plastic.
At least with my FA lenses they all have at least one metal gear, likely a chrome plated copper alloy but no guaranty. The point that couples drive likely has a gear directly encorporated... Same with the coupling on the camera. Plastics can be quite strong these days as well.

Last edited by atlnq9; 06-01-2011 at 08:35 PM.
06-01-2011, 07:28 PM   #42
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QuoteOriginally posted by atlnq9 Quote
Plastics can be quite strong these days as well.
Agreed. There would be quite a few advantages (including cost and weight) to using a properly designed plastic gear.
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