[MK-x]

Hi.
I'm new to Pentax and to world of DSLR. I bought the K-x model, and I like it very much. The camera came with a 18-55mm kit lens only, and now I want to buy a lens with telephoto ability.
Since I'm not a professional photographer, and I don't like big bags , I'd like to buy a lens with a wide range. My preferred one is Pentax DA 18-250mm f/3.5-6.3, but it's too expensive for me.
While searching on B&H website, I came across two brands, that make lenses for Pentax: Sigma and Tamron.
I have some questions :
1) Are there any significant differences between 2 lenses with the same zoom/aperture range, made by these brands?
2) Are these lenses 100% compatible with my camera? What should I check before buying one of them?
3) I've noticed (from lenses' pics) that they have a AF/MF switch, which is also present on the K-x's body. Does it mean that I have to use both of these switches in same positions, or one overrides the other?
4) (generally speaking) are there any other special dials/switches on these lenses, which I don't have on my DA 18-55mm?

Thanks

[Adam]

Sigma lenses are generally of higher quality, and may have move features (OS, HSM), but both brands should be fully functional on your k-x.

The AF/MF switch issue depends on lens. If it's a Pentax or a Sigma lens, setting the switch on the lens will suffice in going to MF. On some tamron lenses, such as the 70-200mm, you have to use both.

[blackcloudbrew]

Answers:

1. There is no general answer to this question. If you review the lens review data base on this site, you will see there are differences and different opinions on between similar lenses from both Tamron and Sigma.
2. If the lenses are k-mount lenses then they will be compatible with your K-x. If they happen to be older film lenses there may be some differences in the way you use them with your camera. This is true for older Pentax lenses as well but they will work.
3. See Adam's response.
4. This varies lens to lens. The newer Sigma lenses have optical stabilization (OS) in the lenses which can be turned on or off. Generally, you adapt / learn to use each lens with it's controls one at at time. This really isn't something that is a discriminator between lenses.

While I own several Tamron lenses, I have owned a Sigma lens. These two companies focus primarily on making lenses for most brands of cameras. Tamron is known for their long zoom lenses and Sigma for some of their specialty lenses (like the 50-500 zoom know as the Bigma). They are also known as generally costing less than branded lenses. I believe they offer a great deal of quality for the price. However, like all manufactures not all of there products are stellar and again, if you look through the third party lens data base on this forum, you will see a number of different opinions about both Sigma and Tamron.

Oh, Tamron lenses tend to weigh less than others due to their design.

Honestly, I have always gotten excellent results from the Tamron and Sigma lenses that I've owned.

[Ash]

No third party lens manufacturers make weather-sealing or quick-shift focusing on their lenses for Pentax. These are the drawbacks. However, the optical quality of most of their lenses are very good, each having their own reputation (which you should check for yourself on the forum's lens review database and on independent lens review sites).

Find what focal lengths you'd be after specifically (my thinking is a dual lens kit such as the Pentax 18-55, the best kit lens available, and something like a DA 55-300 if you can afford the combination) and then go out with your budget in mind for the lenses you're after.

[GerryL]

You can even buy the old Manual Focus lenses to use with your K-x if the Autofocus ones are not up to your budget.

[MK-x]

Thanks guys

Answers:

2. If the lenses are k-mount lenses then they will be compatible with your K-x. If they happen to be older film lenses there may be some differences in the way you use them with your camera. This is true for older Pentax lenses as well but they will work.

when you say that it is compatible, do you mean that all functions are supported?
As described in this table from K-x manual?

[blackcloudbrew]

Compatible...that is a very broad word in this instance. Basically it goes like this. If it's a k-mount lens it will fit on your Pentax camera. After that, it depends on what the lens communicates to the camera. Speaking generically here, if it's a completely manual lens like an M42 screw mount lens for example, there will be no communication with the camera of lens state (f-stop, auto focus, stop down aperture, etc.), whereas any current lens should completely communicate the the camera all things. Some older features like Pentax F/FA series with PowerZoom will only work fully with an older Pentax film body because newer bodies (like your K-x) don't understand all the PowerZoom lens features. So compatible here means that you can mount the lens on your K-x and use it in some way get properly exposed images. How you do that varies with the lens' ability to communicate with the camera.

Personally, the table you've displayed is for me one of those WTF items in the manual. Yes, the exact version of the K mount does make a difference particularly with older lenses. But once you use an older lens and learn how to do stop down metering, all of that stuff above is really not that important.

Look at it this way, the current Tamron and Sigma lenses will work just fine with your K-x. Older k-mount lenses by any manufacture will work but the way you use them with the camera may be a bit different.

[Marc Sabatella]

1) Are there any significant differences between 2 lenses with the same zoom/aperture range, made by these brands?

One stats with an "s", the other with a "t". Aside from that, there is no general answer to this. You'd have to check the reviews for the *specific* lenses involved.

Note, though, that an 18-200 or 18-250 weighs are much as the two lenses it would be replacing (18-55 and 18-200) combined. And that you'd still be stuck with no lens suitable for use in low light, so don't blow your entire budgt on one 'superzoom".

2) Are these lenses 100% compatible with my camera? What should I check before buying one of them?

All AF lenses sold for Pentax cameras are 100% compatible with your camera. The only time you need to worry about the various limitations are with manual focus lenses.

[MK-x]

And that you'd still be stuck with no lens suitable for use in low light, so don't blow your entire budgt on one 'superzoom".

Do you mean that all 'superzoom' lenses are not suitable for low light?
Actually (a dumb question ) , what does it mean "not suitable for low light"? In what way?
I've seen many good reviews on Tamron's 18-200 (AF 18-200mm F/3.5-6.3 XR Di II LD Aspherical (IF); Tamron USA, Inc.).
As I've mentioned, I'm not a pro photographer (but I do have a good sight )

All AF lenses sold for Pentax cameras are 100% compatible with your camera. The only time you need to worry about the various limitations are with manual focus lenses.

can you give me an example of a "manual focus lens"? a model or a link.
Thanks

[RioRico]

Do you mean that all 'superzoom' lenses are not suitable for low light?
Actually (a dumb question ) , what does it mean "not suitable for low light"? In what way?

You should read up a bit about the elements of exposure: aperture (f-stop), shutter speed, and sensitivity (ISO). To shoot in low light, you need to do some combination of:

* a wide aperture (but superzooms don't open much),
* a slow shutter (which may require a tripod), and
* boosting ISO (which increases noise in the image).

A superzoom is "not suitable for low-light shooting" because its aperture cannot be opened very far -- its best is typically f/3.5 to f/5.6, which is pretty 'slow'. A 'fast' lens may have a maximum f-stop of f/2 or f/1.7 or f/1.4. [NOTE: an f-stop is a fraction, the ratio of a lens' maximum opening to its focal length. Just as 1/2 is a bigger fraction than 1/4, so f/2 is a larger opening than f/4, letting more light in.]

Faster lenses are expensive to design and build. Fast zooms are even more complex and expensive. Fast superzooms are virtually impossible to produce economically, which is why they don't exist. So, superzooms are necessarily 'slow'.

And some superzooms show "zoom creep". Put an excellent DA18-250 onto a tripod-mounted camera, aim it downwards, and it will tend to 'creep' out to 250mm, no matter where you actually want it. So in low light, it's not suitable for handheld use; and it's not suitable for tripod use unless it is kept absolutely level, or taped into position, or sandbagged.

So you can either boost the ISO (and get more noise), or use a faster lens. Those are the cold hard facts.

can you give me an example of a "manual focus lens"? a model or a link.

Look here: [ Pentax Reviews - Pentax Lens Reviews & Pentax Lens Database ]
Everything below the entry F-SERIES ZOOMS is a manual lens.

A manual focus lens is just that -- you manually twist it to focus it, no electric motors involved. Many of us prefer older manual focus lenses because 1) they have a different 'look' than newer lenses, and 2) they can cost much much less. Of my over 200 lenses, about 10 are AF, the rest are manual focus (MF). On average, AF lenses cost me US$330 each, and MF lenses cost me US$20 each. I can buy many many old MF lenses for the price of one new AF lens. I'm a cheap bastard, so that is important to me, eh?

[MK-x]

You should read up a bit about the elements of exposure: aperture (f-stop), shutter speed, and sensitivity (ISO). To shoot in low light, you need to do some combination of:

* a wide aperture (but superzooms don't open much),
* a slow shutter (which may require a tripod), and
* boosting ISO (which increases noise in the image).

I'm familiar with these terms , just wanted to be sure what exactly "not suitable for low light" means. My current (kit) lens is 18-55MM F3.5-5.6, so it's also not suitable, but till now I haven't seen any problems with it.

And some superzooms show "zoom creep". Put an excellent DA18-250 onto a tripod-mounted camera, aim it downwards, and it will tend to 'creep' out to 250mm, no matter where you actually want it. So in low light, it's not suitable for handheld use; and it's not suitable for tripod use unless it is kept absolutely level, or taped into position, or sandbagged.

are there any models without this problem?

A manual focus lens is just that -- you manually twist it to focus it, no electric motors involved.

Are these lenses found only as 2nd hand, or there are also new ones?
Thanks.

[Frogfish]

You have had many excellent replies already but I'll try and simplify it for you, without being in any way condescending, as it seems you are not yet familiar with lense terminology and design.

If you buy any recently made Tamron or Sigma that has a Pentax mount (that is it will fit to your Kx without an adapter and it states 'Pentax' or "made for Pentax') then you don't have to worry that it will or will not work on your Kx .... they all will. And all your camera's features will work except probably the lense correction function (this is not an important consideration at this point). If you are buying older 3rd party lenses (such as the Tamron 'Adaptall' systems) then you may need to investigate further but you can buy any modern Tamron / Sigma with confidence.

Go to the Tamron and Sigma websites and you'll see which models (most) are made to fit Pentax cameras. Ignore the prices though as those are often far off 'street' prices !

As far as a suitable lense is concerned then give us a budget, there are many knowledgeable people on here that can offer you valid suggestions. You don't have to buy new if you don't have the budget - if you are in the USA then KEH or B&H are very reputable stores to buy from that will sell you used lenses in excellent condition, and in the UK - there's SRS amongst others, so that you don't have to worry.

[MK-x]

And some superzooms show "zoom creep". Put an excellent DA18-250 onto a tripod-mounted camera, aim it downwards, and it will tend to 'creep' out to 250mm, no matter where you actually want it. So in low light, it's not suitable for handheld use; and it's not suitable for tripod use unless it is kept absolutely level, or taped into position, or sandbagged.

There is a "lock" button on some of zoom lenses. Is it used to lock the lens while in bag only, or the lens can be locked in any position (zoom extension)?

[MK-x]

As far as a suitable lense is concerned then give us a budget, there are many knowledgeable people on here that can offer you valid suggestions. You don't have to buy new if you don't have the budget - if you are in the USA then KEH or B&H are very reputable stores to buy from that will sell you used lenses in excellent condition, and in the UK - there's SRS amongst others, so that you don't have to worry.

I'm thinking about buying a Tamron/Sigma 18-200mm. It covers the range I need.
I've seen on B&H website that there is a "rebate" on Tamron, when buying in US. I couldn't understand whether the buyer must be a US citizen (or buy in the store) to receive it (because I'm not), or buying online from B&H is sufficient...

[Marc Sabatella]

Do you mean that all 'superzoom' lenses are not suitable for low light?
Actually (a dumb question ) , what does it mean "not suitable for low light"? In what way?

Just to summarize what has already been written: I mean, since they don't have a very large maximum aperture, you're stuck shooting very high ISO in hopes of getting a fast enough shutter speed to avoid blur. If you only do that sort of thing occasionally, or aren't very demanding about the results, you can certainly do it - the lens doesn't just stop working - but you get much better results with a "faster" lens.

When I say "much" better, I mean, whatever difference in quality there might be between the 18-55, the Tamron 18-200, the Sigma 18-200, or either 18-250, multiple that by 50 and you'll get an idea of the amount of improvement there is to be gained by using a faster lens.

I've seen many good reviews on Tamron's 18-200

As others have said, in general, the 18-200's aren't as good as the 18-250's, but I recently got the Tamron 18-200 for my wife, and in my playing around with it, I have to say,it does what it says it will do. Only place I see any real issues are at 18mm fully wide open where the corners are indeed quite soft, and there is more distortion than I'd prefer at that focal length too.

can you give me an example of a "manual focus lens"?

There are *tons* of them. Anything in the Pentax K, M, or A series (see the Lens review Database on this site for more specifics), for example. Basically, all lenses made before 1980-something. Nothing you'd be buying brand new except for a couple of very expensive lenses made by Zeiss and a few others made by Samyang.