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05-06-2015, 04:36 AM   #1
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Hunting lens or hunting camera?

Hello all,

In some reviews of some lenses users have reported lenses to be hunting for focus. Example FA*24 and DA18-135WR .


In pentax system, the AF logic and drive is in the camera. How can the focus hunting be a "feature" of the lens?

Regards

05-06-2015, 05:14 AM   #2
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I can't answer your question, but every lens I have reacts differently when it comes to focus speed and accuracy.
05-06-2015, 05:57 AM   #3
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Agree, but the lens is controlled from the body, either by the screw type focus, or by the electric contacts.

If the body tells the lens to focus closer, then the lens focussus closer. If the body tells the lens to focus further, then the lens focussus further. The lens does not have a mind of its own. The body gives the commands. The body gives the commands until the picture is focused.

So, it is the body that hunts.

Then why do the reviews say that the lens is hunting?

What is wrong here?
05-06-2015, 06:07 AM - 1 Like   #4
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Because focus doesn't work just " LOOK FOR FOCUS GO YES GOT IT ". There are algorithms and many factors that play a role. For example light conditions. But if you aren't in very bright light, a slower lens (higher minimum f-number) will have a harder time than a fast lens (like f2, f1.4). Secondly, contrast, colours, and flare are important. This can be a problem for film-era lenses with older lens coatings that have not yet been optimized for digital. Another problem can be the lens drive, gears, which might not allow such precise movements that are needed. Older lenses tend to have a longer focus throw, optimized for MF and DoF scales, this means the AF will be slower again.
And some lenses have their own lens motor, which is usually much more silent, but can be a little slower.
Live view uses a different type of AF again, which has other strengths and weaknesses.

AF is a very complex mechanism, the camera doesn't even know the distance of the object, it just tries to lock focus, and it uses various things to speed up the process. Sometimes these things can be fooled. And some lenses are not optimized for modern cameras, which can be problematic.

Think of it this way: Some cars drive more smoothly than others. Why? Because of a hundred reasons, different factors coming together that we ultimately experience just as "smooth drive". And its not just the road surface, even though it is important and most noticeable. Clutch, gears, engine power, torque, wheels, all make a difference. As does the driver.

Usually, you have there factors:
- Poor AF conditions. Sometimes the user doesn't know that AF has its limitations, and then gets made when it fails. This can happen in darkness, aiming at something with no detail/colours, aiming at something that is too near, and so on. This can often lead to hunting, as the camera simply cannot find something to focus on, even though it seems perfectly obvious to the human eye.
- Gear is not optimized for your camera. For example third party lenses might not work best on your camera, because those companies do not have the true K-mount camera specifications (Sigma reverse engineers the mount, btw), they make lenses and then slap on a variety of mounts, and so on. Or old film lenses, made to work well on old cameras and allow some MF, but they might not be best suited on modern digital cameras, since technology keeps being more and more optimized. Optimization means the tolerances are tighter.
- Macro lenses. This doesn't apply only to macro lenses, but it does to most macro lenses. Some lenses have a bigger focus throw, a long area where they have to look for focus. This will automatically mean the camera has to look for focus in a bigger range. And the other part is that some lenses actually can find focus in more than one spot within the same line of sight. A macro lens, for example, can focus on the small fly in front of the lens, or the tree in the background. This can lead to "hunting", as the camera goes between one or another spot. This is not limited to macro lenses, as it can happen with almost any lens, but it happens especially often with macro lenses. This is often the main technical cause for focus hunting


Last edited by Na Horuk; 05-06-2015 at 06:54 AM.
05-06-2015, 06:31 AM   #5
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Where did you see the 18-135mm as being prone to hunting? Mine certainly does not. It is easily my best consumer zoom for AF, and I've owned most of them. The DA 18-250 hunts. The DA 55-300 hunts.

I wonder if you are using some other definition of hunting? Hunting means the lens goes past the target and continues to rack all the way in or out, then reverses direction and tries again, sometimes repeatedly. This happens when the subject is too low contrast due to its nature (e.g. try focussing on a black bear with a DA 55-300), or because there's not enough light, especially with small aperture lenses.
05-06-2015, 06:56 AM   #6
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i think it may be a function of what data exactly gets fed back to the camera body from the lens, to help the focusing algorithm, along with the relationship between this data and how much the camera either moves the set screw, or tells the camera to adjust focus. Hunting normally is really oscillating focus between too far in front of the subject to too far behind the subject, which means the camera cannot make smaller adjustments or believes it should be making larger ones than it needs to
05-06-2015, 07:14 AM   #7
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Audiobomber,

Thanks for adding some vibration to the discussion. Your statements "The DA 18-250 hunts. The DA 55-300 hunts." are exactly what I mean. And I can add FA24* (F2.0) to that list.

And if you add your definition of hunting "the lens goes past the target and continues to rack all the way in or out, then reverses direction and tries again, sometimes repeatedly." it completes my misunderstanding.

All these lenses are screw type focus. It means that the camera decides to go backwards and forwards looking for the best focus distance, possibly because it can't decide which is the best or can't find a good enough focus length. The lens does not decide anything. So again, it is the camera that hunts, not the lens.

The FA24* F2 certainly is not a small aperture. The others are consumer zoom, with a relatively large depth of field and limited sharpness.
05-06-2015, 07:40 AM   #8
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I'm still not sure we're talking about the same thing. When I focus on a low contrast bird with the DA 55-300, sometimes it hunts. AF goes zzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzzt zt. That is hunting. Focus just blew right by the subject, racked all the way a couple of times.

Then there is the famous Pentax focus check, especially noticeable on a lens like the DA*50-135mm, where focus goes zzzzzzzzzzzzzzzzzzzzt zzzzzt zzzt zt. That is not hunting. Some have said that this focus check makes Pentax more accurate than other DSLR's. I can't say for sure, I've only owned Pentax DSLR's.

The 18-135mm goes zzzzzzzzzzzzzzzt zt. This is as good as it gets.

The above behaviours are mostly to do with the lens. There are significant differences in bodies, for example the K20D hunts in dim light, regardless of lens. The K-3 is stunning in dim light. It will focus on subjects I can barely make out with my bare eyes.

05-06-2015, 07:49 AM   #9
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QuoteOriginally posted by JohntheThird Quote
The lens does not decide anything. So again, it is the camera that hunts, not the lens.
But the lens provides the information the camera is making decisions on. Take for example the Pentax FA 28-105 f/3.2-4.5 SMC Pentax-FA 28-105mm F3.2-4.5 AL [IF] Reviews - FA Zoom Lenses - Pentax Lens Reviews & Lens Database
A good lens in most respects and one I have gotten good use from but it exhibits lower contrast images than some other lenses. Look at the reviews, many say "this lens hunts". And I can state from personal experience that it does. As noted above the DA 55-300 has a reputation for hunting and I can confirm from personal experience. But those lenses both "hunt" on different camera bodies. I have used k-x, k-5, k-5IIs and k-3 and those lenses "hunt" on all of those bodies. And other lenses do not "hunt" on any body.

But as you state the lens is not focusing, the camera is. And yes this is correct and we are falling afoul of semantics. Perhaps a more correct statement would be "the camera's auto-focus mechanism hunts with this lens". But the cause of the "hunting" is the lens, not the camera. We do not say "the k-7 hunts" because it does not universally but it might with a particular lens.

And that lens might "hunt" only under certain conditions. In very good light with a contrasty subject you are not going to have issues with any lens. In low light with fog on a gray dreary day many lenses will "hunt" for focus. Where a particular lens falls on that good<------->poor condition scale is going to be determined by physical factors of the lens such as the coatings, the light path internally, the design of the optics and so. So semantics aside, the lens "hunts" not the camera.

---------- Post added 05-06-15 at 07:50 AM ----------

QuoteOriginally posted by audiobomber Quote
I'm still not sure we're talking about the same thing. When I focus on a low contrast bird with the DA 55-300, sometimes it hunts. AF goes zzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzzt zt. That is hunting. Focus just blew right by the subject, racked all the way a couple of times. Then there is the famous Pentax focus check, especially noticeable on a lens like the DA*50-135mm, where focus goes zzzzzzzzzzzzzzzzzzzzt zzzzzt zzzt zt. That is not hunting. Some have said that this focus check makes Pentax more accurate than other DSLR's. I can't say for sure, I've only owned Pentax DSLR's. The 18-135mm goes zzzzzzzzzzzzzzzt zt. This is as good as it gets.
And the F 70-210 goes zzzzzzzzt BANG!!!
05-06-2015, 08:08 AM   #10
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OK Audiobomber, I understand you when you say that "zzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzzt zt" is hunting and "zzzzzzzzzzzzzzzzzzzzt zzzzzt zzzt zt." is not hunting but focus check. That is all clear.

And I agree that the 18-135 does "zzzzzzzzzzzzzzzt zt", most of the time, although silently (SDM). I have that lens. You can tell that it goes past the focus point a bit and then goes back.

Still, the focus actions, whether it is "zzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzt zzzzzzzzzzzzzzzzzzzzzt zt" or "zzzzzzzzzzzzzzzzzzzzt zzzzzt zzzt zt." or "zzzzzzzzzzzzzzzt zt", are initiated by the camera with the auto-focus hardware and software, not by the lens.

As a comparison, if you mount any AF lens with lens cap and try to focus, it will go to furthest, then closest, then stop, recognizing that there will not be a focus.
05-06-2015, 10:34 AM   #11
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Good and clear post Jatrax,


So something makes it for the camera difficult to focus a DA55-300 and much easier to focus a kit DA18-55.


Both are screw drive, consumer grade, modern lenses. Both F5.6 at the long end. The DA55-300 is indicated to be sharp so the AF system should find it easy to recognise an infocus image. The DA18-55 is not that sharp, which could be a reason for the AF system to continue to find a sharper image than the best image that is there.


The new DA55-300 is only a few years old, the kit lens in all the variations is much older. It could be that the camera "knows" the exact number of turns of the AF screw to get where it needs to be for the DA18-55, but not exactly for the DA55-300. This could clarify the hunting. A software update should be able to correct this.


I need a long light WR zoom to accompany my 18-135 on my next outdoor trip. This hunting problem of this lens (now I am doing it myself) is bothering me. The pour AF performance of the DA55-300 is still a mystery to me and stops me from adding it to my collection.

---------- Post added 05-06-15 at 07:51 PM ----------

I checked the screw drive turns for some of my screw focus lenses, summary below





DA18-55WR 0.25-inf. 90 deg 5.5 screw drive turns
DA50-200WR 1.1-inf. 180 deg 13 screw drive turns
FA28/2.8 0.3-inf 90 deg 3.5 screw drive turns
FA*28-70 0.4-inf 80 deg 5.5 screw drive turns
FA50/1.4 0.45-inf 100 deg 6 screw drive turns
FA*24/2 0.3-inf 90 deg 3.5 screw drive turns.




I am not sure what trend there is to discover, I just felt like investigating. Let me know what you think
05-06-2015, 11:00 AM   #12
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QuoteOriginally posted by JohntheThird Quote
Both are screw drive, consumer grade, modern lenses. Both F5.6 at the long end. The DA55-300 is indicated to be sharp so the AF system should find it easy to recognise an infocus image. The DA18-55 is not that sharp, which could be a reason for the AF system to continue to find a sharper image than the best image that is there.
Actually I think the answer to this is quite simple, put the 55-300 @ 55mm and it will not hunt. You are asking a very small lens to do a lot @ 300mm.
QuoteOriginally posted by JohntheThird Quote
The new DA55-300 is only a few years old, the kit lens in all the variations is much older.
Actually that is not true the kit lens was re-done and made WR not that long ago. But I believe the optical formula for both 55-300 and 18-55 have remained the same for some time. So they are about the same age. But I don't think that is a factor. I suspect there are many variables and it might be difficult to point to any one thing as the issue. One thing not mentioned is the length of the focus throw. A short focus throw lens snaps into focus faster and if it misses on the first pass has a shorter distance to return back. A long focus throw lens, like the 55-300 has to go all the way out and back if it misses and that is really the reason it has a "hunting" reputation. It may not really be hunting any more than another lens, but when it misses it takes too long to get back. Another lens with this issue is the DFA 100mm macro, once it misses it racks all the way out and then back which can be frustrating.
QuoteOriginally posted by JohntheThird Quote
It could be that the camera "knows" the exact number of turns of the AF screw to get where it needs to be for the DA18-55, but not exactly for the DA55-300. This could clarify the hunting. A software update should be able to correct this.
Doubt this, the 55-300 has been out a long time, if a firmware update would have made any difference that would have been done years ago.
QuoteOriginally posted by JohntheThird Quote
This hunting problem of this lens (now I am doing it myself) is bothering me. The pour AF performance of the DA55-300 is still a mystery to me and stops me from adding it to my collection.
Just FYI, but the "hunting" problem of this lens is not really an issue IMHO. I used the 55-300 for years and my wife now carries it. Her kit is the 18-135 and 55-300. To give you an illustration using this lens for BIF shots at the coast I took maybe 300-350 shots one afternoon and had the lens "hunt" maybe 10-15 times. Is that perfect? Of course not. On the other hand on another trip using the DA*300 I did a similar shoot. Guess what? The DA*300 is not perfect either, I missed shots with it too.

If you want a small, light zoom that goes to 300mm there is nothing better. Learn to shoot with it and it will serve you well. Remember when people write reviews they start with perfect and then mention things that are less than perfect. In an ideal world the 55-300 would automatically lock on to sparrows at 10 miles. In the real world that isn't going to happen. And the variability of the skill of the photographer generally exceeds any issues the lens might have.
05-06-2015, 11:10 AM   #13
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I pretty much agree with everything jatrax said. Hunting is a lens issue, but Pentax has a fix for hunting, it's called Quick-Shift. When the lens misses focus, grab the focus ring and bring it back. Another trick is to reset focus to beyond the subject distance after each series of shots. because the camera usually starts to rack inward.
05-06-2015, 11:36 AM   #14
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So I definately need to buy this the 55-300 now.
05-06-2015, 01:49 PM   #15
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QuoteOriginally posted by JohntheThird Quote
So I definately need to buy this the 55-300 now.
Nah, you can wait until tomorrow if you want.
QuoteOriginally posted by audiobomber Quote
Pentax has a fix for hunting, it's called Quick-Shift. When the lens misses focus, grab the focus ring and bring it back. Another trick is to reset focus to beyond the subject distance after each series of shots. because the camera usually starts to rack inward.
I have the DA L version (no quick shift) and if I ever bought another it would be the version with quick shift. Makes tweaking the focus quite easy. Like most things there are tricks that make this or any lens work better. Part is knowing those, part is experience with a particular piece of gear and learning how to get the most out of it. Practice, practice, practice.
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