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03-31-2014, 02:16 PM   #1
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Best All-in-One Zoom

I need advice on a new lens. I shoot a lot of construction sites and use an all-in-one zoom lens for these shoots. It's tough to carry two cameras while wearing PPE (personal protective equipment), and I won't change lenses in those extremely dusty conditions. I normally shoot daylight hours, or with bright sodium lights, so I don't need a particularly fast lens. Thus my need for an all-in-one.

I'm currently shooting a Pentax 18-250 ED AL (IF). It is having trouble autofocusing at full zoom; I have to zoom out about a quarter of the way to get it to autofocus, which doesn't always give me the sharpest images.

I need a new all-in-one. I like the 18-250 range, but would be willing to sacrifice on either end to get a good quality lens (28 250 or 18 200, for example). It has to be parfocal (which why doesn't anyone include this in their lens specs?) since that's the way I was taught to focus way back in the dark ages of all-manual lenses.

Of the all-in-one zoom lenses available today (Pentax, Sigma, Tamron), which is the best quality parfocal lens?

03-31-2014, 02:34 PM - 2 Likes   #2
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QuoteOriginally posted by mwacht Quote
I need advice on a new lens. I shoot a lot of construction sites and use an all-in-one zoom lens for these shoots. It's tough to carry two cameras while wearing PPE (personal protective equipment),
I agree



(Top: Pentax K-30 + DA* 16-50, Bottom: Pentax K-5 + Grip + DA* 60-250)

I would recommend the DA 18-135. You shouldn't even need SUPER ZOOM where you are shooting from huge distances, and thus the 135mm will suffice more than well enough. On the wide side, the widest weather sealed focal length for Pentax right now is 16mm, which is only 2mm wider than 18mm. Yes, there's a difference between the two, but not enough to offset the difference between 50mm and 135mm (the longest end of each lens).

That and the 18-135 is FAR cheaper than the DA* 16-50.

-Heie
03-31-2014, 02:47 PM   #3
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QuoteOriginally posted by Heie Quote
I would recommend the DA 18-135. You shouldn't even need SUPER ZOOM where you are shooting from huge distances, and thus the 135mm will suffice more than well enough. On the wide side, the widest weather sealed focal length for Pentax right now is 16mm, which is only 2mm wider than 18mm. Yes, there's a difference between the two, but not enough to offset the difference between 50mm and 135mm (the longest end of each lens).

That and the 18-135 is FAR cheaper than the DA* 16-50.

-Heie
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03-31-2014, 02:58 PM   #4
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Regarding your parfocal requirement, there are a couple of threads on this, if you just search on "parfocal". Like this one:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/201887-list...om-lenses.html

That said, I do love my 18-135, even though it is varifocal. Guess I've given into autofocus.

03-31-2014, 03:21 PM   #5
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Superzoom lenses are always a compromise. As others have mentioned, I'd recommend the 18-135mm as well. Pair it with and K-3 and you'll have an easier time making tight crops

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03-31-2014, 05:04 PM   #6
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QuoteOriginally posted by mwacht Quote
I'm currently shooting a Pentax 18-250 ED AL (IF). It is having trouble autofocusing at full zoom ...
You don't mention the Pentax DSLR model you are using, but a newer body would give better results in focusing.

Since it appears you do use the 250mm range, the DA 18-270mm with its SDM internal focusing might be an option.

03-31-2014, 06:12 PM   #7
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Evening and Welcome to the Forum!

I too am going to take a slightly different approach and suggest taking a look at the bodies, which might be a better approach. Looking at your profile, I see that your shooting with a K10 and K100 Super. As much as I like the CCD sensor, the AF on the older bodies is probably a large contributor to the problem - at least that is my thinking. I too have a K100 along with a K5 and there is a substantial difference in the AF locking, between the two.

Rather than going for another lens, I am thinking that using your current lens and possibly either a K30 or a K5II would be an upgrade all around. Both bodies have been discontinued, and thus their pricing have dropped quite a bit on close out. The K5II has a f2.8 AF sensor, which I think would help in terms of achieving AF lock (will focus in darkness). Even though you are shooting with light, this should substantially help. The K30, should be a bit less of a hit on the checkbook, doesn't have the f2.8 AF sensor, but still should be significantly better AF than either the K100 or K10. Both the bodies would be more similar to the K10 than the K100 in terms of controls.

Of course, if your budget allows - my choice would be either the K5IIs (for a bit better resolution without the anti-ailiasing filter) or the K3, for all of the improvements up through the K5II/IIs, along with the new upgrades it brings.

03-31-2014, 07:10 PM   #8
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QuoteOriginally posted by mwacht Quote
I'm currently shooting a Pentax 18-250 ED AL (IF).
This is one of the best super zooms around.

It is probably the best value for money proposition since more modern superzooms typically cost more because they add shake reduction that you don't need as a Pentax shooter.

I do not believe that the Pentax 18-135 is going to be an improvement for you. It has been measured to be pretty weak at the long end by Photozone. When Photozone enquired with Pentax about the subpar measurements, they received the response that the lens performed according to specification.

The 18-135 has its place with its weather-sealing and silent motor, it also has very decent bokeh from what I've seen but a good copy of a Pentax/Tamron 18-250 should be at least as good optically.

Note that focusing is performed by the camera body, not the lens. You may solve your problems by switching to a K-30, K-50, K-5 II, or K-3. Having said that, I have used a Tamron 18-250 (the Pentax 18-250 is just a rebadged Tamron) with a K100D and I don't remember any focusing problems at the long end. Maybe your 18-250 copy has optical issues at the long end that prevent proper focussing but such issues should then also manifest themselves in poor image quality.

What you certainly cannot do is to combine the 18-250 with a teleconverter. Even a 1.4 x TC would eat too much light for the AF system to work. This is because the 18-250 is already at f/6.3 at the long end and the AF system is not designed to reliably work at an effective aperture of f/8.8 anymore.

QuoteOriginally posted by mwacht Quote
It has to be parfocal (which why doesn't anyone include this in their lens specs?) since that's the way I was taught to focus way back in the dark ages of all-manual lenses.
If you use AF then it really does not matter.

With manual focus lenses it was a good method to zoom in, obtain focus and then zoom out again. With a properly adjusted AF lens (some copies require AF micro adjustments), you simply focus at the focal length you need for framing. There is no need to zoom in first.


Last edited by Class A; 03-31-2014 at 07:23 PM.
03-31-2014, 07:17 PM   #9
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QuoteOriginally posted by interested_observer Quote
The K5II has a f2.8 AF sensor, which I think would help in terms of achieving AF lock (will focus in darkness).
I agree with your other statements, but note that "f/2.8" in the context of an AF area refers to the base length of the phase difference measurement, not the sensitivity in terms of light. This one f/2.8 AF area allows focusing with better accuracy; it does not help to focus in lower light levels.

The f/2.8 AF area of the K-5 II won't help in case of the Pentax 18-250 at the long end, because the latter has such high f-ratios wide open at the long end. (The f/2.8 AF area will only improve on regular AF areas between f/5.6 and f/2.8).

Having said that, the K-5 II's AF system is indeed more sensitive and will help to focus the 18-250 with more speed and less hesitation even in lower light.
03-31-2014, 07:58 PM   #10
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I agree with the previous comments; the K10D and K100D Super are great cameras, but AF performance is a weak point.

I also say it's worth considering a body from the last two generations (K-30, K-50, K-5 II or K-5 IIs, K-3), where AF is really improved. And the DA18-250 is one of the better superzooms, so I wonder if something is wrong with your copy.


FWIW, the 18-270 is marked down to $600 right now (which should have been the price in the first place, IMO), so it's a consideration. But I think it's only a little better than a properly functioning DA18-250.
03-31-2014, 07:59 PM   #11
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QuoteOriginally posted by Class A Quote
I agree with your other statements, but note that "f/2.8" in the context of an AF area refers to the base length of the phase difference measurement, not the sensitivity in terms of light. This one f/2.8 AF area allows focusing with better accuracy; it does not help to focus in lower light levels.

The f/2.8 AF area of the K-5 II won't help in case of the Pentax 18-250 at the long end, because the latter has such high f-ratios wide open at the long end. (The f/2.8 AF area will only improve on regular AF areas between f/5.6 and f/2.8).

Having said that, the K-5 II's AF system is indeed more sensitive and will help to focus the 18-250 with more speed and less hesitation even in lower light.
Thanks for the correction. I got home and everyone was out and about, so I was grabbing dinner while doing some reading.

04-01-2014, 10:39 AM   #12
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Hi mwacht,

I'd also consider a new body. For me, the K-5 breathed new life into My DA 18-250. The increased low light sensitivity of the AF sensor and the high ISO IQ made this lens much more usable, especially in lower light -- even indoors in a normally lit room. The added AF sensitivity of the K-5 II series and K-3 over the K-5 just make it better. The difference in AF sensitivity between the K100 and K10 and the newest bodies is very significant. At f6.3/250mm, it will still hunt in very low light, but manually prefocusing it close enough so you can make out the general shapes of the subjects usually allows the AF system to gain a lock easily, even in pretty dim scenes. Unfortunately, the 18-250 doesn't have QS, but it's easy enough to just press the lens release button with the right hand to allow MF temporarily.

Soon after getting my K-5, my cousin (who knows nothing about photography) wanted to borrow a camera to cover her son's Eagle Scout induction. The lighting ranged from bright direct sunlight to a candle lit ceremony indoors. I set up the camera to Av priority, set the aperture to wide open, set auto ISO to 80-12,800, showed her how to zoom and activate the AF, wait for the beep, and shoot. She ended up with over 150 shots for the day, with only a handful of misses. There were a lot of cameras there that day, but her son later told me that his mom's were by far the best, and there were many requests for prints from the other families. A $2K super zoom P&S may be a little crazy, but that's what she had that day, and it served well.

There are a lot of other factors that recommend one of the newer models. Much higher ISO capabilities is the most noticeable, but there are also quite a list of features that you may or may not find useful -- LV and video capabilities come to mind easily.

Scott
04-01-2014, 11:04 AM   #13
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Thanks for the input. I haven't upgraded my information in a while. I still shoot the K10D, and have upgraded to a K5 II. The lens is sketchy on both cameras, so I know it's the lens. Other lenses are not doing the same thing on either camera.

At full zoom, it focuses in and out twice before deciding it can't focus. Once I zoom out a little bit, it focuses, but I'm not happy with the accuracy of the focus at that point. The photos are not coming out as sharp as they were before the lens started doing this. I did try the Sigma 18-250 lens (which is varifocal), and aside from being hard to break 30 years of focusing method (habit), I wasn't as happy with the focus as I have been with the Pentax lens.

That said, I will consider the 18 - 135, but would also like to know anyone's experiences with the Sigma 18 – 200, as I've heard the lens is parfocal, and it has been recommended as a good lens by a retailer, but I can't find any good online reviews of the lens
04-01-2014, 05:04 PM   #14
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QuoteOriginally posted by mwacht Quote
The photos are not coming out as sharp as they were before the lens started doing this.
Perhaps getting the lens repaired then or replacing it with another copy of the same model is an option?

Repairs can be tricky, though, if you get a lazy person who deems the lens "within factory specifications".

BTW, the Pentax/Tamron 18-250 is not parfocal. Between a thread about parfocal zooms and another dedicated to the 18-250 you have three posters stating that lens is not parfocal.

Unfortunately, I haven't read anything about the Sigma 18-200. I just know that you should stay away from the old Tamron 18-200 which was paradoxically not as good as the 18-250.
04-01-2014, 06:01 PM   #15
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QuoteOriginally posted by mwacht Quote
Thanks for the input. I haven't upgraded my information in a while. I still shoot the K10D, and have upgraded to a K5 II. The lens is sketchy on both cameras, so I know it's the lens. Other lenses are not doing the same thing on either camera.

At full zoom, it focuses in and out twice before deciding it can't focus. Once I zoom out a little bit, it focuses, but I'm not happy with the accuracy of the focus at that point. The photos are not coming out as sharp as they were before the lens started doing this. I did try the Sigma 18-250 lens (which is varifocal), and aside from being hard to break 30 years of focusing method (habit), I wasn't as happy with the focus as I have been with the Pentax lens.

That said, I will consider the 18 - 135, but would also like to know anyone's experiences with the Sigma 18 – 200, as I've heard the lens is parfocal, and it has been recommended as a good lens by a retailer, but I can't find any good online reviews of the lens
You won't find many 18-200 sigma contemporary reviews because this is a very new lens. I'm not aware that there are even any copies publicly available for sale, but of course that should change any day now if it hasn't already.

I've tested an 18-250 Sigma: while having some of the expected compromises of a superzoom, it didn't have any difficulties focusing in bright outdoor light on a K200. To the extent that there's a consensus, up to this point the Sigma appears to be the best available superzoom available in K mount, followed by the 18-270 Tamron(/Pentax.) When you say you weren't happy with the focus on this lens, are you saying you did controlled tests on a tripod, and that the focus, as opposed to the optical quality, was the problem? Was the lens locking, but not at correct focus? Could you determine that AF wasn't getting you as good results as LV focus on the K5? Is it possible that focus adjustment would have have resolved the problem? I don't think you'll achieve that much success with your "back off" technique, unless by accident. You should really focus at the focal length you're going to use.

Last edited by tibbitts; 04-01-2014 at 06:06 PM.
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