You will hear a lot of different opinion on one lens solution. Please don't take it personal from my negative opinion towards one single lens solution as I normally don't agree on one lens solution as I don't think that is the right idea to have in a dSLR system where you buy it to have the flexibility of using different lens designed for different specific purposes. But I will see the needs in traveling with less lens and minimal to zero lens change while in certain segments in traveling plan, weight reduction and easier usage with family as well as functional and quality compromises to have all-in-one zoom lenses
My version of 1 lens solution involves few combination to make the best use of my system with both zooms and primes
1. Weekend walk-around I like to spend quality time with my family where I compromise on focal range in using a range that I use mostly for candid, portrait and landscape
All shot with Sigma 17-70mm f/2.8-4.5


Fireworks with tripod

candid

decent outdoor portrait
2. For vacation that compromise towards 1 lens solution
I will take three lens to cover range with 2 zooms and make up the miss of speed and IQ with 1 fast prime

50mm is your friend at night

50mm in wedding candid shots

3. For the absolute elite travel with limited primes
I will bring a trio or quad of limited or fast primes and bring two at a time. Plenty to choose form subject to your own liking and how you see fit.
Prime trio samples -- You have to bust the prime in Pentax world as they offer the best and unique choices of primes
- #1: 21mm/40mm/70mm -- the most compact one due to Pentax pancake design
- #2: 15mm/35mm/77mm -- almost the widest range except with DA 14mm f/2.8
- #3: 21mm/35mm/40mm/50mm/77mm -- Hin's current limited trio/quad that key on functional in landscape, macro, and portrait in traveling, add 50mm for nighttime and need of fast speed.
- #4: 12-24mm/43mm/70mm -- ok, one zoom which is more versatile in landscape shots
- #5: 21mm/43mm/77mm -- a safe bet for a balance between FF and APS-C


Only carry two primes at a time to get close to 1-lens compromise while leaving the unlikely used prime in the car or hotel.
4. Popular 1-lens do it all lenses
- Pentax or Tamron 18-250mm
- Sigma 18-250mm
- older variants of Tamron or Pentax 28-300mm
I have seen a lot of outstanding shots from both Pentax and Tamron 18-250mm. It is one lens that is not to be missed in consideration if the strict criteria of 1 lens with no lens change is of utmost importance to you and that you don't mind lower speed and heavier lens to carry for the entire trip among other compromises in 1-lens do it all approach.
If I ever have accumulated enough fund, I would venture to get a used copy of either Pentax 18-250mm or the Tamron 18-250mm. And I wonder if Tamron 18-270mm will be made available for Pentax mount as that may change my LBA decision for the Pentax 1-lens selection.
With input from
Street_Vision and
RiceHigh in the comments to this article, I research more into both Tamron 18-250mm and Pentax DA 18-250mm. For a long time, I get the impressions that they are the same lens and re-badged in Pentax for the DA lens. When money suffice, I will invest on a used copy of either lens for 1-lens do it all purpose lens for traveling and weekend needs. My very admired friend in PentaxForums by the name of Robert Fortson often highly recommend this lens and so is this article from
http://dchome.net that is mentioned by RiceHigh in his valuable inputs in the comment of this blog post. Thanks to RH for the eye-opening link for great photos that one can do with this popular 1-lens do it all zoom lens.
http://www.dchome.net/viewthread.php?tid=761396Very impressive to say the least.
5. Your manual focus primesAnd last but not the least is in not forgetting your manual focus primes. They can easily rival the best and the latest. With careful planning to mix new primes with old primes, new zooms with old primes, you can achieve dynamic setup that the 1-lens do it all options will lack behind by a bigger margin in terms of quality, weight in carrying one lens at a time, and gain of speed and characters with the old charms. Use your creativity to make lens change to be functional segment in the day. For instance, morning indoor breakfast and late night dinner with a fast prime that adds wonder to your charming vacation.



You are not bound with rules in the mixing. The good old glass are not the limited lens that cost you a bundle and make you a cry baby if you drop or lose them. And the old prime may serve better as a thief deterrent scheme in both its appearance in disguise of its value and most have sheer solid metal body that can induce injury when you throw it to your harm's way.
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