kit lens vs pro lens whats the major difference (newbie)

i have a pentax k7 and im beggining photography ..i have 2 lenses ones the stock 55mm and the other is a sigma 300mm.. i have no idea what other lenses i might require as i want to experiment in all types of photography over time :) are the pro lenses worth it on this camera?

The photographer makes far more difference to the image than the equipment, and anything will take a decent photo in good conditions - you pay for equipment that will take better photos in worse conditions. For example, if an owl lands on a post next to you, sits there, and you're in bright sunlight, anything will take a good photo of it (if you can). Tracking the same owl in flight in the distance as it flies erratically in twilight, that's more taxing on the equipment.

 

Firstly, I'd say don't spend money until you know it'll get you something. Try your existing lenses first, and bear in mind that stopping down to f/8 or so will probably hide many optical issues. Do you need something wider for a shot you wished you could take? Look at a wider lens. Realise your 300mm isn't long enough? Think about a 150-600 or similar. Realise you need a faster lens to separate the subject from the background? Then look into one. But I wouldn't go shopping, especially for expensive glass, until I knew what I wanted - a $3000 lens won't help you if you never take the kind of shot it would help with. And learn the basics first - an expensive lens with the wrong technique or settings will still be miles behind a cheap lens used properly. (Don't let me scare you with this - the basics aren't too hard, and cameras automate a lot, I'm just saying you shouldn't learn to drive in a Ferrari.)

 

Can you see the difference of "pro" glass on a K7? Absolutely. A fast (and therefore expensive) lens will let you blur the background more to make your subject stand out. It'll give you a better chance of focussing on your subject of it moves fast. You won't see as much colour fringing around edges. The image will be sharper, especially at the corners and if you crop the image down or pixel peep. You get what you pay for (although check reviews - no product is perfect and all lenses have trade-offs). But again, none of that helps if you don't have the right focal length or flexibility for what you want to shoot.

 

Having said all that, at the risk of attracting the ire of Pentax users, Pentax haven't exactly been rushing out products of late. It's been said they're effectively a "toy project" within Ricoh (who mostly make printers), and they're not really investing to stay cutting edge or expand the system. There's nothing wrong with the Pentax system other than being a little limited in its range and lacking a few technical advances, notably in autofocus (though there's a fair share of Pentax-specific niceties too, and if those matter to you, so be it) - but if you're choosing a $1500 70-200mm f/2.8 (say) "pro lens" on the basis that it'll fit into $200-worth of system, I'd at least try some other brands in a camera store first and see whether you'd rather switch to Canon/Nikon/Sony/Fuji/micro 4/3 before you commit the big bucks. Maybe you won't, and that's fine (many swear by them), but once you spend a lot of money (especially if you buy new) bear in mind that changing system gets expensive. I chose to switch to Nikon (from Canon) just before investing in my first relatively expensive kit, for example. Pentax equipment is still plenty available, and will be (at least used) even if Ricoh never give them more money, but you can't get everything for Pentax that you can get for Canon or Nikon, and there are no signs that they're rushing to fill the gaps - though I should be clear that the basics are all there. Their reduced market share also means that third party products often don't get made in a Pentax version - most of the recent Sigma lenses, for example.

 

Summary: yes, pro lenses make a difference even on a K7; don't buy expensive lenses until you know what you'll get from buying them (your current lenses will often do just fine, used in a way that hides their limitations); if you're with Pentax for reasons other than "you carefully researched the camera systems and want things uniquely available in Pentax" then be sure you wouldn't rather switch to one of the more active systems before you invest a lot of money - but for now, get comfortable with what you've got, it's perfectly capable of taking very nice photos.

 

Just to check: I'm guessing your "55" is an 18-55mm zoom and your Sigma is perhaps a 70-300mm? If so, that gives you a lot of focal length to experiment with and decide whether you care more about wider shots (maybe landscapes), tighter shots (maybe wildlife), mid-range portraits, etc. There are lenses that are just 55mm or 300mm and don't zoom, which have advantages but which would restrict your experimentation. Would you mind sharing some more specifics (the full lens names) so we can advise better based on what you have?

 

Best of luck, and enjoy your new hobby!

Wow thank you so much Andrew thats the most comprehensive reply i could of hoped for .. i had no idea pentax were so limited as i do have a canon 600D rebel also ..but it seems like a toy compared to the K7.. but it takes very good close up pictures as im still struggling with F functions and apertures setting etc im very new to this.. the pentax is showing me the differences where the canon couldnt ..but i would love a canon 6D or something in that range.. my lenses are for the pentax a DA 1:3.5 - 5.6 18.55mm Al WR stock lens and the sigma is @55mm 1: 4.5 - 6.7 DL 100mm to 300mm lens made in japan .. on my canon i have the EF-S 1:3.5 -5.6 IS 18mm - 55mm @58mm and the EF-S 1:4 -5.6 IS 55mm to 250mm .. The canon is a faster camera but the pentax seems much more sturdy ..but after learning about Pentax i guess im going to have to move to canon or Nikon ..

"Kit lens vs pro lens what's the major difference?"

 

- Short and smart answer: about $1000!

 

Seriously. I'm with Andrew in saying you shouldn't spend anything until you've properly explored what your existing camera and lenses can do.

 

The outfit you have is capable of delivering excellent pictures of almost any subject - macro excluded.

 

Maybe you're into wildlife pictures and you're not getting frame-filling pictures? Hone your stalking skills or bait the subject and learn to keep still and downwind.

 

Maybe you're not getting stunning landscapes? Get up earlier or stay later and learn to anticipate weather and lighting conditions.

 

Maybe your portraits are a bit meh? Learn to interact with your subject and to use lighting better.

 

You get the idea. Good pictures are most often not about the equipment you use, but how you use it, and the ancillary skills you have.

 

Put the time into learning about lighting, composition, posing, knowing your subject, etc. Rather than throwing money at equipment. Don't be the person with "all the gear and no idea".

Edited September 16, 2018 by rodeo_joe|1

The advice fromAndrew Garrard is quite valid--Canon and Nikon definitely have more lenses available and more pro oriented bodies at pro prices. The questions that you need to consider are: How serious are you about photography? Will you be doing the kinds of photography that necessitate large and expensive lenses like a 70-200 f/2.8 or fast long telephotos (birds)? Do you need pro level AF and high fps rates? If the answers to these questions indicate actual needs then his advice to switch systems before investing in more and expensive lenses is spot on--you will always lose money on buying new and selling used lenses. But as a long time Pentax user I concur with you about the solid feel and durability of Pentax bodies, and comparable Nikon and Canon bodies will cost quite a bit more the Pentax equivalents. Incidentally, if you think that a 70-200 f/2.8 is a lens you need, look into the Pentax 50-135 for your K7. It covers an equivalent focal length range and is a lot smaller and lighter than anybody's 70-200 f/2.8. My copy is excellent optically--just get a recent copy that fixes the problematic AF motor in that lens. And AF has improved a lot on newer bodies like the K3, which also has much better resolution and dynamic range than the K7.

Thank you so much Rodeo Joe and also AJG i will definitely try harder with what i have and look for some lenses like the 50 - 135 pentax.. im going overseas so i will look forward to trying out some ideas i have ..and ill keep everyones advice on hand its really good advice for me and i totally appreciate you all giving me the time and setting me straight ...my K7 is still young at heart only 7k actuations but i might replace the sigma lens as i really not comfortable with it.. and ill use my own imagination rather than rely on my equipment.to do the work for me..Yes i need patience for sure ,i have alot to learn regarding light ,speed ,timing especially thank you again ...out of curoisity will all pentax dslr k mount fit my k7 ? ..i hope pentax stay around its been 50 years basically and they havent vanished yet.. shame on ricoh they should give pentax more funding...i beleive they have the technology even the mirrorless cameras of today like the new canon and nikon are great ..but i think if pentax had the funds they could pose some serious competiton ..thank you guys ..your all wonderful :)

+1 to Andrew's and RJ's comments.

I wonder how did you get the 55mm and 300mm? You had them before you had the camera? Those are strange focal length to buy for your K7.

Thank you so much Rodeo Joe and also AJG i will definitely try harder with what i have and look for some lenses like the 50 - 135 pentax.. im going overseas so i will look forward to trying out some ideas i have ..and ill keep everyones advice on hand its really good advice for me and i totally appreciate you all giving me the time and setting me straight ...my K7 is still young at heart only 7k actuations but i might replace the sigma lens as i really not comfortable with it.. and ill use my own imagination rather than rely on my equipment.to do the work for me..Yes i need patience for sure ,i have alot to learn regarding light ,speed ,timing especially thank you again ...out of curoisity will all pentax dslr k mount fit my k7 ? ..i hope pentax stay around its been 50 years basically and they havent vanished yet.. shame on ricoh they should give pentax more funding...i beleive they have the technology even the mirrorless cameras of today like the new canon and nikon are great ..but i think if pentax had the funds they could pose some serious competiton ..thank you guys ..your all wonderful :)

All Pentax K mount lenses will fit your K7, but older K mount and M mount lenses will not meter at full aperture. In my experience, the stop down metering that Pentax provided on its DSLRs for these lenses isn't as accurate as full aperture metering with A series manual focus lenses and AF lenses . Since you're just getting into this I would avoid K and M series lenses because of the metering issues.

BeBu: I'm guessing they might be the long end of zoom lenses - an 18-55 and a 70-300 or similar would not be uncommon zooms to have. (I retained these ranges, along with the 50 f/1.8, when otherwise replacing my Canon system.) It's be nice to confirm, though - 55mm and 300mm primes would be unusual, and worth discussion.

 

Deadalert: I don't want to over-state the situation, and as far as I know there's nothing much wrong with the K7, other than that it wasn't the top of the line body and it's from about 2009 (technology moves on). If the features you need are available in the Pentax system and the way their bodies work makes most sense to you, don't switch just because I said so.

 

When I say Pentax are more limited, I mean in the sense that, for example, you can buy a multi-flash off-camera rig, or tilt-shift lenses, or a range of big telephotos from 200in f/2 to 800mm f/5.6. And there have been several updates to these over time. If you need these for Pentax, your options are much more limited (I've not researched details). Pentax do, notably, have a set of small "pancake" lens's that aren't in other systems. What they have works perfectly well, but if you shoot Canon or Nikon you'll know you can hire pretty much anything for your system at no notice, and buy replacement bits in most camera stores/departments. If this matters to you, it's worth being aware.

 

If you enjoy the k7 more than the 600D, don't stop using it. But I would try out a Canon Eos 80D and/or a Nikon D7500 (or even a 7Dii and a D500) before deciding on how a system handles - the cheaper bodies (like the 600D) a built lighter and a bit less robustly (and yes, I have a Nikon D90 which feels like a toy alongside my D850, and more so a "pro" F5). The 600D isn't exactly Canon's latest either. So if you're deciding where to start dropping a few thousand dollars on lenses (when and if you want to), it's worth looking at the premium bodies which might suit it - even if you start out with something older.

 

Before I misrepresent that as "buy the latest": older cameras do take good images, but image quality, performance and plain handling convenience have improved over time.

 

If you'd like to see what "pro" glass can do, you could think about hiring something - though you may find that easier for your Canon than Pentax.

 

But practice comes first. Have fun doing that!

I have more than a handful of f/2.8 zooms and f/2 or faster primes.

 

There are times when they come out, and times when they stay at home in favor of lower end/less expensive glass.

 

As an example, one of my most used lenses on both my digital cameras and my late model film cameras is 24-85mm f/3.5-4.5 AF-S Nikkor VR. This lens definitely has its weaknesses, and I don't get the most out of cameras like my D800 when I use it. None the less, it's a lens that covers a very useful range of focal lengths for me, has a feature I consider important(VR), and probably most importantly it's small and light enough that I don't mind hauling it with me everywhere. The comparable "pro" lens to this would be the $2K AF-S Nikkor 24-85mm f/2.8E VR. I don't own that lens, or anything comparable to it. It's an optically excellent lens that also weighs a lot-and for someone who shoots film it's not a film friendly lens(no film cameras can control the aperture). The non-E version of the lens also lacks VR, and I'd rather have a lens a stop slower with VR(something not as much of aa concern when you have in-body stabilization).

 

Just this past week, I picked up a thoroughly consumer grade Nikon lens, the AF-P DX 10-20mm f/4.5-5.6 VR. I have a bunch of ultra-wide lenses, including among them the "king zoom"-the 14-24mm f/2.8. I absolutely love the 14-24mm, but it weighs a ton(nearly 1kg, or a bit over 2lbs), has a huge, bulbous front element, and no official ability to use filters. I paid $1200 for it used. The little 10-20mm runs a bit a bit over $300 at new discount retail, and I paid around $250 for a gently used boxed example. Even though it's sold and advertised as a lens for crop-sensor cameras, it's actually usable-and at least respectable-on full frame cameras(not a concern to you) at 13mm and longer. Its biggest downside for me is that-in one of those Nikon quirks-it will only focus on relatively new cameras, and in fact I had to update the firmware of both my D600 and D800 to get it to focus(manual focus is "focus by wire" so will also only work on a body that supports autofocus). Still, the lens weighs almost nothing, is tiny, and uses conventional 72mm filters.

We fit lenses based on the size of the image they record. The Pentax K7 sports an imaging chip that measures approximately 24mm length by 16mm height. This size camera is labeled “compact digital”. This is because this size is 66% of the venerable 35mm film format which measures 36mm length by 24mm height. When we talk about lenses we generally classify them as wide-angle, normal, and telephoto.

 

First we find out what is normal. To do this we calculate the corner to corner measurement of the image. The venerable 35mm image measures about 45mm and the compact digital measures 30mm thus 30 ÷ 45 = 0.66 X 100 = 66% ( percent means per 100).

 

For the 35mm classic camera we fit them with a 50mm focal length lens. This is a slight rounding up of the 45mm diagonal measure. What I am saying is, a “normal” lens is one with a focal length about equal to the diagonal measure of the format. A “normal” lash-up delivers what we call “the human perspective”. This will be an angle of view of about 45° with the camera held in the landscape (horizontal) position.

 

For the Pentax K7 compact digital, we mount a 30mm focal length lens and this lash-up delivers the “human perspective, an angle of view of 45°. Why is this important information?

 

The realm of wide-angle is a lens about 70% or shorter of “normal”. For the Pentax K7 wide-angle starts at 30mm X 0.70 = 20mm. Normal = 30mm and telephoto is 2X normal which is 60mm or longer.

 

To recap, for the K7 wide-angle is 20mm or shorter – normal is 30mm and telephoto is 60mm or longer.

 

The K7 is thus normally sold with an entry level lens that covers this range it is 18mm thru 55mm. This is a carefully chosen zoom range because it covers the basics. The 18mm thru 55m starts at the beginning of wide-angle and extends thru “normal” and extending to the beginning of telephoto. The idea is to expose the beginner to these key realms

 

You have a 55mm which is on the start of telephoto. You also have a 300mm which for the K7 is an extreme telephoto 10X normal 300 ÷ 30 = 10.

 

Now what you do need is kit lens 18mm thru 55mm. Such a lens will provide you with an entry level lens that will allow you to experiment and learn. After a learning curve, using this kit lens, you will then be in a position to choose focal lengths as required for your new passion which is photography.

as im still struggling with F functions and apertures setting etc im very new to this.

 

Frankly, if you're struggling with these settings and features at this point, buy nothing for now. Keep the money safe in a bank account, until you are more familiar with photography basics and better understand your own needs and photography style. Only at that point, start spending money on gear again, so you'll be sure to spend the money on the items you will benefit most. Might be that 50-135 mentioned, but it could also be a macro-lens, or a wide angle.

 

This article is a good start on photography basics. If you prefer a book, I'd recommend to start with Understanding Exposure, which happens to be from the same author as that linked article.

 

after learning about Pentax i guess im going to have to move to canon or Nikon ..

 

Don't. Not yet anyway. Even if Pentax isn't as rapid releasing new cameras as some of the others, and may have a lesser current catalog of lenses, it is still a very viable system.

Most important is that you like using the camera, and it sure sounds like you like using the Pentax better than the Canon - stick with what you like. Also again it matters to first understand your needs, based on your photography. Maybe Pentax has all the lenses you need, and will work just perfectly fine for you. There are also tons of old(er) lenses for Pentax that will work, so plenty of options.

Seriously, make no decisions to buy/sell until you grasp better what your real needs are; it's easy to spend a load of money on lenses and cameras you don't need, and your photos will be no better for it. Spending money where it counts for your needs, though, can help make better photos.

Alan: I'm still assuming that when deadalert said "i have 2 lenses ones the stock 55mm and the other is a sigma 300mm", that was just reading the long end of the zoom, and the 18-55mm and (presumably) 70-300mm was meant. Pentax do make an f/1.4 55mm prime lens, but I wouldn't describe it as "stock". I don't know that Sigma make a 300mm prime lens other than the 2.4kg, $3400 f/2.8, which is the kind of lens you'd know if you had. We're admittedly having a somewhat different conversation if deadalert already has about $4000 invested in the Pentax system. But if so, yes, an 18-55mm would be a good idea. :-)

 

deadalert: Could you please confirm what your current lenses are with their full names (whatever's printed on them)?

 

Wouter: Agreed wholeheartedly, and apologies if I misled by indicating otherwise. Pentax have a reasonably complete system, it's mostly the more exotic stuff that Canon and Nikon offer. So long as you never need to go outside your bounds, go with what feels right.

"Pro" lenses worth it? Depends on a whole lot of things! I am not familiar with the K7 but have K20, 10 & 100 + *ist D. Any of these cameras reveals a difference between images by my old Pentax FA 100/2.8 macro (the big heavy one) and 2 copies of Sigma 70-300/4-5.6, where results don't look good enough to convince me to use the zooms frequently.

Pictures taken at f2.8 look sharper from my 50/2.8 macro than from a 50/1.4. - OTOH the macro lens takes longer to rack through it's focusing range, when it didn't lock at first attempt, which can lead to a missed chance, in portraiture for example.

 

Not every lens with a nasty price tag on it will necessarily improve your photography. - Some folks like insanely fast glass. Older constructions in that field tend to be less sharp, even stopped down, than their saner counterparts. Fast lenses are likely to reveal shortcomings of your AF system. - Performing micro adjustments might fix some but having very close to "no DOF at all" doesn't make photography easier.

 

While other camera brands get seriously catered by third party lens makers, Pentax look a bit neglected. - Outsourcing production of their native lenses to those companies might have gone along with contracts stopping them to offer glass under their own label or Pentax don't sell enough cameras to lens shopping enthusiasts to still be an interesting market.

 

Use what you have to figure out which focal lengths you might like to own. Then start researching through DxO's database and as many reviews as you can find online, who might offer something great, bang for the buck (and maybe even still portable?) for which camera brand.

 

I have no clue how "pro" my seasoned Pentax kit might be. Besides the 18-50/55/70 kit zooms (2 Samsungs, 2 Sigmas) and the IMHO quite decent 12-24/4 everything else's construction dates back to film days. Sigma 24/1.8 and Pentax 50/1.4 don't make me really happy. I bought them for low light concert / event photography. The 24mm is very bulky; I don't like to carry it around in broad daylight and being a somewhat affordable fast superwide FF lens, it doesn't knock my socks off as a moderate wide on the crop sensor. The macros are sharp, the 135/2.8 performs well enough (optically). Yes, I do shoot kit zooms in broad daylight, that permits stopping them down a bit. I once took a calendar front page shot with a very old plastic 35-80, that did cost about 25€ during sale out.

 

I pondered getting some long zoom for quite a while. - I ended getting into Canon with a 70-200/2.8 on 5D IV. That combo doesn't feel like a touristic walk around camera to me. But for sports and events I appreciate the frame rate AF performance and low light capability it provides. Otherwise (i.e. for landscape photography and anything done casually, as a pass time) I am happy with Leica M and the comparably compact half decent lenses available for that system. - Yes, I bought used old ones and 3rd party. - At the end of the day they are floating my boat. I am too unlikely to nail (manual!) focus in a portrait with a 90/2 I have, so I rather carry a significantly lighter 90/4. 50 & Konica35/2 are my moderately fast low light lenses, 21/2.8 Zeiss on the wide and 135/4 at the long end.

 

i would love a canon 6D or something in that range

Probably not the worst choice. Combined with bread and butter primes, (there are quite a few stabilized ones for Canon if you count Tamron's offerings in) it should work quite well. - Yes, dynamic range isn't it's strength, but we are probably used to shooting worse. - I am not sure if I 'd liked the comparably few AF spots scattered around the center of the frame. It is up to you and your research, to figure out what you want more and at which price point. - A Pentax K1 has a quite decent sensor and tosses in IBIS at a comparably low price tag. OTOH you'll pay for a 24-70/2.8 zoom that gets sold cheaper under a Tamron label, there even with OIS, to others and also might get faster AF elsewhere.

 

Whatever you'll end doing: Shop bulk & weight conscious; stay at home monstrosities don't take pictures. There is some truth in "f8 & be there".

Before you end buying expensive unfamiliar gear or even switching systems, ponder renting it first, to test out if you like it and will get along with it.

deadalert: Could you please confirm what your current lenses are with their full names (whatever's printed on them)?

He specified already:

my lenses are for the pentax a DA 1:3.5 - 5.6 18.55mm Al WR stock lens and the sigma is @55mm 1: 4.5 - 6.7 DL 100mm to 300mm lens made in japan .. on my canon i have the EF-S 1:3.5 -5.6 IS 18mm - 55mm @58mm and the EF-S 1:4 -5.6 IS 55mm to 250mm

To clarify something: I am no way suggesting to rush and buy a different "dream within reach" camera right now. Just put lens purchases into your big picture and great long term plans. - Maybe try out Pentax' affordable 50mm or any other prime catching your attention and figure out if mixing what you have might work for you, which way ever; short lens on Pentax, long on on Canon or the other way round.

a big thank you to everyone who has posted here for me , i have certainly got every angle covered with all these answers and i will stick with my pentax and learn more to understand the basics and the limits , maybe in the future i will upgrade once i feel that i cant do anything more with what i have but until then im staying with the kits i have and maybe grabbing the trusty 50mm lens for the pentax as it seems like a trusty lens for alot of people ..thank you all again you have been so very helpful ..excellent people :)

As for the actual question, 'kit' lens means that they make a lot of them. Economy of scale allows them to keep the price down. Some costs, such as designing the lens, and building the equipment to make it, (called NRE, Non-Recurring Engineering) only need to be paid once, no matter how many you make.

 

There are also ways to keep the costs down, such as using plastic in parts that might otherwise be metal.

There are good plastics now, so don't automatically rule them out, but sometimes they indicate a cheaper construction.

 

As above, many pro lenses have large apertures, which means very large glass lens elements, which cost more.

There are times when those are needed, though with increased sensor sensitivity, not as often as before.

 

Keeping the cost down, allows keeping the price for the whole kit down.

That helps when there are competing products that are similar.

 

But another way to keep your costs down is to buy used.

 

You might find some that are a step up from the kit lens, but not the overpriced pro versions.

 

But a lot depends on what kinds of things you like to photograph, and under what conditions.

. . . i will stick with my pentax [K-7] and learn more to understand the basics and the limits . . . and maybe grabbing the trusty 50mm lens for the pentax as it seems like a trusty lens for alot of people . . .

 

A 50mm Prime Lens, used on your Pentax K-7 will act as a Short Telephoto Lens: that may or may not be 'a trusty lens' for YOUR uses.

 

****

 

The history/back story is this - a 50mm Prime Lens was the most common 'standard lens' used on a 35mm film camera. 'standard lens' when used in that technical sense means it gives an approximate 'standard view', relative to what our eyes see. i.e. it is not acting as a telephoto lens, nor is it acting as a wide angle lens.

 

BUT - your Pentax K-7 has an APS-C sized sensor and a 50mm lens when it is used on your Pentax will act as a short telephoto lens.

 

50mm Prime Lenses, for SLRs and now DSLRs, have always been in abundance, and many are relatively inexpensive - because of the back-story, above - and these 50mm lenses are repeatedly advocated by commentators on the www as a 'must have' or 'a trusty' lens for everyone's DSLR usually without deference to the either camera's sensor size or the user's needs.

 

The typical other (main) reason for adding a Prime Lens to one's kit is to have a lens with a fast Lens Speed, that's a fancy way of saying the Lens has a fast (or big) Maximum Aperture.

 

For example you might get a Pentax 50mm F/1.4. This means that you can make photos using F/1.4 as the Aperture. On the other hand, the Zoom Lens you already have ('DA 1:3.5 - 5.6 18.55mm Al WR stock lens') allows you to make photos at 50mm, but using a Maximum Aperture of F/5.6.

 

A practical example comparing the uses of the above mentioned two lenses: you're inside your house and you want to make a photo of your dog being funny at the kitchen table. You frame the camera and the light meter tells you that you will have to use 1/20th @ F/5.6 @ ISO800.

 

You think 'holy molly, I know that 1/20th is a very slow shutter speed, the dog is so happy and he is moving around so much ... my picture will be all blurry. I have to make a faster shutter speed, so I will make the photo at 1/80th @ F/5.6 @ ISO3200, but perhaps I should use 1/160th @ F/5.6 @ ISO6400 just to be sure.'

 

OK that's good thinking, but your camera is now at the ISO limit (ISO6400) and the dog might still be blurred using 1/160th Shutter Speed.

 

If you had a 50mm F/1.4 lens you could make a similar photo using, for example, 1/320th @ F/2 @ ISO1600.

 

So, that is one advantage of having a 'fast lens' - so you can make photos of moving Subjects in low light, without capturing significant Subject Motion Blur.

 

But, another consideration is to remember that you are making this photo inside your kitchen and it is not a big kitchen and a 50mm lens might be too much telephoto to make a good shot of your dog . . .

 

it is important to note that it usually possible to move two steps closer to the Subject, or crop the image a bit, if the Subject is a bit too far away, but if your back is against a wall and you are too close to the Subject to make a good shot, it is difficult to move the wall.

 

So before you spend money on a 50mm Prime Lens, I advise that you be confident you do indeed want a short telephoto lens and it, will benefit your needs.

 

WW

When you're starting out, the right camera and lenses are the ones you have! It helps if they give you some creative control -- the ability to set aperture or shutter speed or both so you can learn what they do. You might be able to find a class at a local school or camera store (if there still are any) or find some books to start with at the bookstore or library. The books might tell you want kind of photography appeals to you. Do you like to shoot people, or landscapes, or products or still lifes? Try a little of everything.

 

Professional lenses are typically equipped with brighter apertures and better quality lenses, but you don't need them for now. Wait to see what you enjoy doing and what kind of camera you like (and which are available to you at your price range). I started with a Konica I rangefinder and a GE light meter from my Dad. It was good enough to learn black and white for yearbook photography in high school. Maybe you can find good online classes, or just available videos that can introduce you to what's out there that you might be interested in.

 

Note that high school yearbook work is a good way to get introduced to people photography and if you're a college student, there's usually a fine arts department you can take a class from. But you'll probably learn more, even on your own, if you give yourself goals based on what you see in books and go out with your camera with that in mind. If you DO have something in mind, that is a good focus. Usually it's not the quality of your equipment that holds you back.

I basically agree with @William Michael above. Just: maybe stick to the 50mm f1.8. - The f1.4 doesn't really knock my socks off (rather) wide open and is twice as expensive. Use your kit zoom to figure out what you'll want more. - There is a moderately priced 35mm too.

personally I am a big fan of the fast short telephoto lenses since a really fast wide would most likely frame 2 people with only one of them in focus. - You aslo can't go anywhere without somebody else bringing a wide lens on their smart phone; so I am after differently looking pictures. But YMMV

Kit lenses do indeed tend to be very good for the money - not least because when you see a camera reviewed, it tends to get reviewed with its kit lens, so its in the interests of the manufacturers not to let a shoddy lens torpedo the camera. On the other hand, they also have to be pretty flexible, reasonably lightweight, cheap to produce, and competitive against other manufacturers' options in the same range. This basically means every manufacturer has run through several versions of an 18-55mm f/3.5-5.6 kit lens, and they're all more decent than you might expect.

 

The 50mm f/1.8 lenses tend to be fairly similar and unambitious in formula. They usually suck when shot wide open (some newer ones like the Nikkor AF-S version suck slightly less), and usually get extremely sharp when stopped down below f/5.6. It's common for the bokeh to be a little unpleasant, though. A 50mm f/1.8 is a cheap lens to buy - the "nifty fifty" is a common suggestion for a lens everyone should have - so if you can live with those limitations, go for it. At f/1.8 it might be a bit "dreamy", but at least you'll have the shot. Most f/1.4 lenses, especially older ones, are a bit better at these apertures - but often only a bit. (If you want to step up, the older pre-"Art" 50mm f/1.4 Sigma was pretty good to the edges of a crop sensor frame, although I don't know if it came in Pentax mount.) If you want a lens that actually looks good at this aperture, you're looking at more complex designs like the Sigma 50mm Art, the Zeiss Otus, or the latest HD Pentax-D FA* 50mm f/1.4. But they're all vastly larger and more expensive than the f/1.8, so you have to really love the focal length to want one.

 

In fact, this is a general guideline I came to when first buying camera kit. If you buy a reasonably cheap prime or zoom with a reasonable zoom range (so not something like an 18-200mm), they tend to be acceptable. They're not made to be very fast lenses, so you don't see the optical aberrations that come with speed. They're mass-produced, so they have to be decent. Shoot them at f/8 and basically everything is decent. If not, at least you didn't spend much money. If you buy a lens over $2000, it also tends to be decent. Money is relatively no object, the lens has to meet the demands of professionals, and the quality control is good. When I've had a problem with a lens, it's tended to be between the two - a lens that's trying to do more than a budget lens, but doesn't have the money in its manufacture to do it properly. That's a gross oversimplification (and I own and am happy with several lenses in this price bracket), but it's worth considering if you're going for the "a bit more money for a bit more performance" theory.