[WhimsicalV]

No need to apologise - questions are good

With the Sigma 17-50 f/2.8, the widest aperture setting of f/2.8 is available at all focal lengths from 17 to 50mm inclusive (it's therefore described as a "constant aperture" lens). Furthermore, the sharpness of the lens - even wide open at f/2.8 - is good right across the frame. As such, you can actually use the lens at f/2.8 and get decent photos, and by f/5.6 the image quality is really very good indeed.

The Sigma 18-300 has a variable aperture. At 18mm, the maximum available aperture is f/3.5, but as you zoom in to longer focal lengths, this quickly reduces to f/6.3. Worse still, if you use the lens wide open at those maximum apertures, image sharpness - generally, but especially in the borders and corners of the frame - isn't good. In all honesty, you need to shoot it at f/8 - f/11 to get decent frame-wide image quality. However, at these apertures the lens is letting far less light than the Sigma 17-50 at f/2.8 or f/5.6, which means you'll need to use higher ISO settings on the camera, resulting in photos with a lot of noise.

Does that make sense?

I appreciate all your information. Mostly it does make sense. I do want to know why the sharpness is reduced when the aperture is wide open? Is that because it gets washed out by the light? I guess I was not sure how important it was because with past zoom lenses, it seemed that the picture often came out better when I did not leave it wide open when zoomed in. Therefore, I felt the option to have that fixed aperture was nice, but not exactly necessary.

---------- Post added 05-26-18 at 11:05 PM ----------

Just reading over the thread.....

the 18-135 is the best cheaper alternative. Especially with it's pseudo macro capability.
The Sigma 17-50 is your best indoor, low light choice. I've crunched the numbers on this a million times and basically I don't really like Sigma, so this is hard for me to say.
I'd pair it with a 55-300 of some kind.

17-50, 55 300 and you 35 2.4 are a great team although I'd probably ad the 50 1.8 as well for really low light. That would be all the kit you'd need until you decide to get into real specialty items. It should all fit into one relatively small easy to carry shoulder bag.

I have two questions. What do you mean by pseudo macro capability? Why is the 18 to 135 mm considerably lighter than the 17 to 70 mm ones? Material? Something that affects quality that I should be concerned about?

---------- Post added 05-26-18 at 11:06 PM ----------

The DFA24-70 is a full frame lens. You are paying a lot more money for a lens that covers a 24X36mm sensor. A crop sensor lens is much more affordable and more compact. Right a Sigma 17-50 is about $369 and the DFA24-70 is over a $1000. Also 24mm on a crop sensor camera is way too narrow for a lot of shots. SDM is the Pentax trademark name for their Supersonic Drive Motors that in their high end lens. All DA* lenses feature these in lens motors rather traditional screwdrive. Some feature both. In lens motors are virtually silent making them very appealing for indoor work.

I own both the DA18-135 and the HD16-85. One thing everyone needs to do with all UWA (Ultra Wide Angle) lenses is test for decentering and for if any focus adjustment is needed. It sounds like your 16-85 may have been decentered. I have seen a few of them. This can happen with any lens. Keep in mind all the new DFA lenses use the HD coatings. I went through 3 Sigma 8-16's and 2 Tamron 70-200's before I had a good one of each. The 18-135 is still my goto lens if I can only take one lens. For all of its weaknesses it is still one of the best all around lenses for Pentax. The DFA28-105 is sharper overall but does cover the equivalent focal range of 28-200mm on full frame. I however would want to rely on the 18-135 for indoor photography unless I was using a flash.

Silly me. I did not realize that it was a full frame lens. Eliminated.

---------- Post added 05-26-18 at 11:07 PM ----------

Several points-

There is no such thing as a fast, f/2.8 zoom lens with a range of 18-100mm- not even close. The DFA 24-70mm does not come close because 24mm is only modestly WA on APS-C, and not comparable to 18mm, while 70mm is a ways behind 100mm. However, there is much importance as to which camera body you will be using. I refer to the fact that a KP or a K-70 body, which are capable of outstanding performance at higher ISO settings, can effectively achieve results at f/4 or higher comparable to what can be had with f/2.8 on other bodies, lens quality level otherwise being similar.

It is also important, in view of the above facts, to zero in on the FLs where low-light work is mostly done. If you need that over the entire 18-100mm range, you'll need two fast zoom lenses. For that, I use the excellent DA* 50-135mm f/2.8, which is a great lens having top-flight construction and WR, and more recently combined with a Sigma 17-50mm f/2.8 EX DC, which I also highly recommend. They are great on my K-5 IIs, my K-S2, or even better on my KP! But the KP can do very well with f/4 or greater settings, which is very good, since then these lenses are not wide open, so their high quality level is elevated even more, and with the KP detail and quality are well-preserved at a greater ISO while noise is reduced.

You might also, for a budget compromise, consider a Sigma 17-70mm f/2.8-4, if 70mm is enough and you can get by with f/4 max in the tele range.

Appreciate it!

[aslyfox]

I have two questions. What do you mean by pseudo macro capability? Why is the 18 to 135 mm considerably lighter than the 17 to 70 mm ones? Material? Something that affects quality that I should be concerned about?. . .

IF you

go up to Lenses above and look at the reviews of the lenses

YOU

may be able to find info about the lenses so you can learn many of the answers to your questions

SMC Pentax-DA 18-135mm F3.5-5.6 ED AL [IF] DC WR Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database

Max. Magnification
0.24x

Diam x Length 73 x 76 mm (2.9 x 3.0 in.)

Weight 405 g (14.3 oz.)


Read more at: https://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-18-135mm-F3.5-5.6-ED-...#ixzz5GhFZyHR6

[jgnfld]

By your criteria, the 18-135 is a no brainer.

Personally though, I think you're dreaming. Your 35mm prime is a nice lens, and adding the zoom is great. BUT....

Then you need an ultra-wide. The DA15 Limited is the obvious choice.
Then you need something *really* long. The HD55-300PLM can't be beaten.

Job done.

I love my 55-300 PLM. It is a huge upgrade over its screw drive predecessor which I also owned and liked. But living in an often relatively dark environment in Newfoundland, I do find myself pushing it to its limits more than I'd like. Getting a K-70 has made shooting with it a bit easier as I can do 400 or even 800 ASA with no/little perceptible problem and higher yet with only a few problems.

I love my PLM but the truth is it can be beaten and possibly the OP's needs are one such case.

I could make basically the same comments about the 16-85. Modern sensors really up the value of these two lenses.

[mikesbike]

The DA 18-135mm has outstanding build quality, among AF models second only to the DA* and FA* range of zoom lenses and the DA 20-40mm Limited, all of which feature metal construction. Its compactness is near miraculous for such quality in a lens having this much range, while the aperture can keep to f/3.5-4.5 out to 70mm.

Quality control issues- decentering, loose parts, etc. seem to be rare for this particular lens, according to a lack of complaints that show up.

[mikesbike]

Also, the sharpness of lenses in general is reduced to some degree at wide open aperture compared to mid-aperture settings. The degree of this fact does, however, vary considerably between lens models. The Sigma 17-50mm f/2.8 EX DC that BigMackCam commented on its fast aperture f/2.8 performance, is above average for such a fast zoom lens in this regard- not perfect, of course, but very good. It is a bargain for the performance and quality it offers. Its FOV, being for APS-C, is comparable to about a 26-77mm lens on a FF body, just to compare to what the DFA 24-70mm lens will do on a K-1, and at a fraction of the size and weight.

[dstar]

I have one suggestions may be another option look sigma 18-200 contemporary. They redisign,now very light fast and very quiet. I bought months ago.Very happyPrice very attractive 399 included sigma dock for adjustment.Really worth to try

[WhimsicalV]

I have one suggestions may be another option look sigma 18-200 contemporary. They redisign,now very light fast and very quiet. I bought months ago.Very happyPrice very attractive 399 included sigma dock for adjustment.Really worth to try

What is the Sigma Dock? I have definitely airways been weary of purchasing lens outside of Pentax.

[dstar]

Sigma dock help calibrated several new lenses usually C-Art style and update software Adjustment focus system as needed. Look sigmaphoto .com
I have few Sigma lenses Art style and very happy I have Sigma 18-200 C may be 3 months Very happy with result
Open Sigma web and look sample 18-200 or 17-70 . Not too many done with Pentax but give you idea what you can expected
Money wise it was good choice