I plan on buying a Sony a6500 (APS-C sensor) camera within 60 days. I want very much to work with just one lens, either the Sony DT 18-135mm (27mm -203mm) f/3.5-5.6 SAM, or the Sony E PZ 18-105mm (27mm - 158mm) f/4G OSS. This will give me a reasonably compact system that I wish to use for the following actives of my grand children. These activities are Football and Soccer (outdoors) and swimming and theatre (indoors)….The DT18135 may need an adapter? I realize that neither of these lenses are preferred for these activities. Am I asking too much of these lenses? I am open to an alternative lens, but wish to stay with a single lens solution. Also, for outdoor Football and Soccer, …..Would a 1.4x or 2x teleconverter be helpful? I am an older guy and wish to keep my system as light and easy as possible, yet, I am hoping to get decent quality.
The Sony E PZ 18-105mm (27mm - 158mm) f/4G OSS is a better lens optically than the Sony DT 18-135mm (27mm -203mm) f/3.5-5.6 SAM and the difference in prices reflect that.
You are correct that you would also need an adapter to use the A-mount lens on your E-mount body. Adapters can also introduce miniscule alignment issues that can actually be perceptible in photographs. From a blog entry by Roger Cicala at lensrentals.com titled "There Is No Free Lunch, Episode 763: Lens Adapters"
One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces. When you look at the thick metal pieces on the front of the camera and the back of the lens, and then consider that they have to be lined up exactly parallel to the image sensor, it’s kind of amazing it works.
Although it doesn’t always work. Lloyd Chambers first reported years ago that with high-quality, wide-angle lenses you could detect very small misalignments in the camera-lens mount. Misalignment of 10 microns from side-to-side was enough to cause blur on the sides of the image. Since then a lot of other people have confirmed the same thing.
So when I hear people cavalierly talking about putting an adapter on their camera I tend to cringe. When a single camera-lens interface has enough variability to sometimes be visible, adding another large piece of metal with another mount interface seems a recipe for problems.
Within the limits of the focal length ranges each lens you suggested offers, either one would probably give you acceptable results for outdoor daylight use. Even with a quality 1.4X TC the 18-105mm f/4 might do well at longer focal lengths in sunlight. Keep in mind that most wide angle lenses don't do well at all with TCs. There's never been a real impetus to design TCs that work well with wide angle lenses because most photographers already have normal focal length lenses that give better performance than what a WA + TC could possibly produce.
I'm not sure either of your suggested lenses would fare well with indoor sports. f/4 is fairly slow to shoot sports under artificial lights, f/5.6 is intolerable. For theatrical use, anything slower than f/2.8 is not likely to give you anything you'll be happy with. Fast primes with f/2 or wider apertures are the best way to shoot theater, although f/2.8 zooms can usually handle it well enough in the hands of a skilled photographer. Shooting theater is one of the most challenging forms of photography there is both in terms of the demands on the photographer's skill and knowledge and in terms of the limits of the equipment.
You'll also likely find that 105mm or even 135mm on an APS-C camera is not going to be long enough for shooting soccer or football from the sidelines and even less useful if you're shooting from bleachers further back. You're going to need to get in the 200-300mm+ range. Anything past 300mm for an APS-C or larger sensor camera is really going to start costing some money or the maximum aperture and/or image quality is going to start to suffer. Lower priced offerings at 200mm+ focal lengths have fairly narrow maximum apertures of around f/5.6-6.3 so they are pretty good in bright light but aren't very useful for sports/action under lights or indoor sports and they're near useless for theatrical work.
The entire point of an interchangeable lens system camera is to allow you to use different lenses that are better or even great at one thing but unsuitable for other things. Fixed lens cameras force you to use a single lens that is mediocre or worse at a lot of things but better at nothing. Insisting on using a single lens for everything on an interchangeable lens camera is not much different than a fixed lens camera. In some cases the fixed lens camera may meet your needs better than an ILC with only one lens.
The best lenses are all prime lenses. That means a single focal length. No.Zoom.At.All. They're really good when they provide the field of view and other characteristics you need. This is because they can be optimized to do one thing at one focal length. A good flat field 100mm macro lens is different from a good 85mm, 105mm, or 135mm portrait lens. But they are not very flexible, so you need a lot of them for various different things. Some are pretty good for not much money (e.g. EF 50mm f/1.8 STM @ $120). Others are incredibly good for a boatload of cash (e.g. EF 400mm f/2.8 L IS II @ $10K). Most fall somewhere in between.
Compared to their zoom lens counterparts, in addition to equal or better optical quality at a lower price prime lenses can also be smaller/lighter, have wider maximum apertures, and often still be much cheaper.
Short ratio zoom lenses, that is zoom lenses with a less than 3X difference between their longest and shortest focal length, can also be very good. But the best ones cost a lot. A lens like the Canon EF 24-70mm f/2.8 L II runs around $2K and can match the image quality, if not the maximum aperture, of a $120 EF 50mm f/1.8 STM. It's also built a bit better and can shoot at 24mm (with near the same IQ as a mid-priced 24mm prime) and 70mm and anywhere in between. The Sony FE 16-35mm F2.8 GM would be a comparable E-mount lens when used in an APS-C E-mount camera.
When you move outside of the 3x limit is when image quality really starts to noticeably go down. Some 4-5X zoom lenses that fall entirely in the telephoto range can be pretty good. But when you start trying to design a lens that goes from wide angle to telephoto and covers a 5X-10X or more zoom range, that is when it really starts getting difficult to keep it affordable and manageable with regard to size and weight and still provide excellent image quality. You'll usually get better image quality and spend less buying something like an 18-55mm and a 55-250mm pair of zoom lenses than you would get with an 18-200mm 'all-in-one'.
The other thing you must consider is that larger sensors require larger lenses to get the same field of view. Your 27-203mm equivalent superzoom is really an 18-135mm lens in front of a sensor that is 1.5X smaller in linear measurements and covers an area less than 1/2 the size of a FF sensor. There are tradeoffs with low light ability, noise level even when shooting in daylight, image sharpness, particularly at the telephoto end, etc. that were made to give you that "7.5X zoom." Even with the higher quality 18-105mm f/4, there are similar tradeoffs made to give you that "5.8X zoom."
From Michael Clark's answer:
In some cases the fixed lens camera may meet your needs better than an ILC with only one lens.
Speaking only about indoor swimming, since that's what I'm most familiar with, this seems to me to be one of those cases. With your proposed lenses, or with any large-sensor setup you can realistically purchase, for that matter, you are probably not going to be able to get shots of your grandchildren resembling those, because you can't get a lens long enough to provide such a narrow field of view.
(Sony RX10 M3, 220mm (600mm equiv.), 1/800s, f/4, 3200 ISO)
So you could compromise and go with a smaller sensor setup, so you can have the narrow FoV with a shorter lens. Fortunately, your budget is not so small as to force you to go microscopic, and you can go with a "mid-size" one (smaller than APS-C but larger than Joe Average's point-and-shoot) like the one in my RX10. Yes, image quality will probably suffer somewhat, but it's a trade-off you might find acceptable.