What lenses should I get for a Pentax K5 II?

First I'd get something in 30-35mm range which would be equivalent to normal 50mm focal length. The DA 35 limited is an amazing lens. It has approximate 50mm focal length on the crop sensor, is pretty fast at 2.8, is light and small, is a 1:1 macro and has excellent image quality. If you only get one lens this would be it. [The alternative to the 35 is the FA 31 1.8. It's not macro, faster, bigger, heavier, more expensive, and very well regarded.] Second I'd get the FA * 55 1.4. It's big but light, fast, and weather sealed. I've used it in the pouring rain on my K-7 with no problems. [An alternative to this would be the FA 77 1.8. I recommend having at least one weather sealed lens (the 55) but the 77 is my favorite lens. Magic is the only way to describe it: challenging to use but results are so rewarding.] Lastly I'd get the FA 100 Macro F2.8. It's fairly big and heavy, but well regarded. There is a weather resistant and non weather resistant lens but I don't know the difference. I believe the weather resistant is a newer model that simply added the weather resistance. Note that this is not the same level as the weather sealing that the * series has. [The alternative to the FA 100 is the Vivitar 100mm F2.8 Macro available used that is well regarded, and of similar size / weight. If you want to go all out the Voightlander 125 mm Macro is expensive, only available used, and smaller as there is no auto focus. It is considered the best macro lens for Pentax.] The DA 35, FA* 55 and FA 100 Macro have my vote for you. It covers a good range (35, 55, and 100), has macro at both ends, covers you for low light, a good option or day to day normal focal length, and and a weather proof option so rainy days are no problem. If you can get away with just the 35mm for your macro use (you might as you are capturing small but not super tiny stuff) you can drop the 100 Macro from the lineup to save weight and money. Another thing to consider is a split focus screen and small tripod which can help with focusing for macro.

Number one, you haven't told us what kind of photos you like to take, and how you like to take them (i.e how much control do you have in the setting, do you take a lot of landscapes, portraits etc etc). That being said I'm going to go against what will no doubt be the grain here, prefaced with a justification. I am an experienced amateur photographer, and I'm relatively decent. I favour portrait photos predominantly, followed by smaller landscapes and animal photos. I had a Pentax kit for about four years. 1) I would forget about a dedicated macro lens. It's a huge amount of kit space devoted to something that can only take one kind of photo really well, and they are extremely pricey. Macro extensions will work great with a small prime, but I favoured - and continue to favour the http://www.amazon.com/exec/obidos/ASIN/B0007KS7D0/metafilter-20/ref=nosim/ and its big brother 250 sibling. These are diopter lenses - which are typically frowned upon - but they are much better quality than the usual, you can take quite incredible photos with them (see http://beingmark.com/macro-illustrated/ - most of those were with a diopter). Be aware they have an even narrower depth-of-field than a regular macro lens, but you can make it work. 2) Everyone is always talking about primes. I find primes a pain in the arse, frankly. Yes, they are portable. Yes, you get a nice wide aperture for the price. But there's a reason why zooms are the most popular lenses with professionals. They are versatile, extremely versatile. A zoom lens will give you flexibility to capture a range of types of photo, in quickly evolving situations, unobtrusively, much easier than a prime. Further, extremely shallow DOF can actually be problematic when they prevent you from getting all your subject in focus, and the low-light capabilities of a 1.4 lens, for example, are not as needed as it once was because sensors are getting so damned good. Yes, you generally give up a bit of sharpness but http://www.pentaxforums.com/userreviews/tamron-af-17-50mm-f2-8-xr-ld-aspherical-if-sp.html (comparison photos are just a little ways down). Additionally, given Pentax frigging insane over-pricing of their prime lenses now (if you want to be depressed, check out how much they used to cost), you can pick up one of the Sigma or Tamron 2.8 lenses for often less than a goddamn pentax prime with like three elements in it. These lenses give you https://lh5.googleusercontent.com/-m78_FNCJa2g/UQ9cc41GgDI/AAAAAAAAFJs/uA0V4RjtXOA/w799-h532-no/IMGP3505.jpg, are good for low light, and cover a wide range making them useful for landscapes to portraits, and I believe the 2.8 Sigma zooms have quite close focussing making them convenient for macro, too (don't forget you can crop to "enlarge" macro images as well - few people need all the resolution of modern sensors). I personally had the Tamron 28-75 f2.8. It suited me needs, was a terrific lens that I loved dearly. I have no reason to believe the 17-50mm is worse. 3) Re: the telephoto, things are starting to get pricey at 100mm over and minimum f4. Be sure you need the aperture because you pay a *huge* premium for it, and there's many a lens that's f5.6 that goes unloved despite no vignetting, few chromatic aberrations, and little distortion, all because of a few f stops. I have found only a few instances where I wanted a low f-stop on my zoom - and that was in situations like game drives at night. They are super expensive, which brings me to my next point: 4) Consider a flash. I've had a *decent*, ttl flash (honestly, manual is fine sometimes but if you're at a party and bouncing of the ceiling in fast-changing situations as I'm wont to do, it's a lot of stuffing around to feel good about yourself), with my last three kits and it is an absolute must for me. Regardless of how good a lens or sensor might be, if you are photographing at night, you will come up against the limitations time and time again. It's not a bad thing - you can take great photos without a good, tilt-and-swivel, bounced flash, but you can't take anywhere near as many. I love my flash. I value it as much as any one of my lenses, and in terms of pictures I get from it; it's got a much higher value/price-performance ratio. Consider a flash. check out Neil Van Niekerk's Tangents blog for what an on-camera flash can do. I know what you're thinking - that's a lot of crap to be carrying, which brings me to my final point : 5) Don't obsess about size. My kit rule has been, whatever fits in my small crumpler camera bag, is what I can take. If I can't fit it, I can't take it. But one small crumpler bag, stuff full, is much the same to me as one half empty in terms of weight, having to carry etc. You can go smaller, sure, but there comes a point where it's really diminishing returns and carrying less stuff is resulting in fewer photos. So, when I had Pentax my Kit was: Camera Sigma tilt-and-swivel ttl flash Tamron 28-75 f.2.8 Pentax DAL 55-300mm F4.5 to 5.6 I think (been a while, it wasn't wide. Protip: this comes as a kit lens, so you can often pick it up, or its 200mm brother quite cheaply secondhand) Raynox macro diopters 150 and 250 and finally: Pentax F 50mm 1.4 (sometimes). It's small so I often took it when I didn't really need it. You will note I had nothing with a wide angle - it just doesn't suit me and the kind of photos of I take; no dig on wide angle lenses. If it did, I probs would swap the 50mm for a DA15mm. Anyway, that's my reasoning and rationale for what I have and what I take with me. That kit took me throughout Namibia and Japan. It never felt heavy, and I used the zooms and the flash exhaustively. The diopters not as much. The Tamron was basically glued to my camera 90% of the time and I just wish they made one for the micro four thirds system I now have.

Long-time Pentax user here: currently use a K5, previously a K10D, *ist DS, MX-6, etc... Personally, I use a DA* 16-50mm about 95% of the time, but it's had the focus motor replaced twice. Not a good record on that lens. The focal length is perfect for my use, though. I do love wide lenses. I have a http://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-14mm-F2.8-Lens.html, but it's heavy. If I were to buy again I'd go with the http://www.pentaxforums.com/lensreviews/hd-pentax-da-15mm-f4-ed-al-limited.html It's remarkably small, and high quality prime lens. You mention taking photographs of "specimens". Are these alive? If so, you'll want a longer macro lens like the Weather Resistant http://www.pentaxforums.com/lensreviews/SMC-Pentax-DFA-Weather-Resistant-100mm-F2.8-Macro-Lens.html to allow greater distance. If they are not alive, then the http://www.pentaxforums.com/lensreviews/hd-pentax-da-35mm-f2.8-limited-macro.html is a sure fire hit. Alternatively, the http://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-L-35mm-F2.4-AL.html (non-macro) is a very light lens, inexpensive lens with good image quality. I have it myself. If you can afford it, you might look at the (weather resistant) DA* 50-135. It's http://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-Star-50-135mm-F2.8-SDM-Zoom-Lens.html.

Finally addendum: lenses like the FA77 are indeed amazing, but they are ball-shrinkingly expensive, and if you need four different Pentax primes you're suddenly looking at 2.5k in expenses. The kit I used, purchased secondhand would run you abouuut $550 - minus the 50mm as I think they are quite expensive now, though it was only one hundred when I bought it.

A couple of things to consider: - If you are getting a macro lens for photographing frogs, I would recommend something longer than 35mm... the issue with wide angle macros is that you have to get right up to the subject to take a photo and also there can be some odd perspective issues. - I use manual (M42 Takumar) lenses on my K-50 and K100D along with a set of extension tubes for macro. This is a very flexible and inexpensive solution (you can get M42 era extension tubes for 10 bucks) but is all manual and requires some patience and experience (and a static subject unless you're a ninja) to get good results. A dedicated FA or DA macro lens is going to be much easier but much more expensive. - For the camera to really be weather sealed you will need WR lenses as well, otherwise moisture will just get in that way. - At this point it looks like there is just something inherently wrong with Pentax's SDM lens motors (they break at a really alarming rate) so be aware of that. I have shot with the 50-135 (via rental) and it's a glorious lens optically but... has those damn motors. - Speaking of the above you might consider renting some lenses to try them out and see what works for your needs, if that's possible.

The specimens will be photographed under anaesthesia. They are small frogs, about 25mm long.

I've done a lot of buying from the http://www.pentaxforums.com/forums/24-photographic-equipment-sale/, with good success.

I'll add another telephoto "alternative" option to my answer above. It isn't macro, but it is super small as it is manual focus only, and is available used for maybe $3-400. The Voightlander 180 F4. It's another of my favorites, but a split prism screen is pretty much a required upgrade. The Pentax * Telephotos are also great, but big and expensive. Also for the Vivitar I meant to say Vivitar Series 1 105mm F2.8.