[cindygirl]

1. When zooming in, why must the minimum apeture get smaller and smaller as the camera zooms?
2. I have a Pentax K100D and I'd like to get a nice portrait lens. What would you recommend? How can I be sure the lens will fit on the camera, do I just go by the lens size (58mm I think on the k100D) or is there something else I should look out for?

[posimoka]

1. Its all to do with the way lenses are designed. Basically, if you want a lower F.stop (so faster) at longer focal lengths, you need a lot of expensive, heavy glass. Consumer grade lens tradeoff this fact, with the F.stop increasing as the focal length increases.

2. Not sure, as I'm not famaliar with that camera, although I'm sure others can help on that point. Basically you need to know what the mounting type is for your camera body, and then make sure you buy lenses that match that.

[DongoSab]

Most good portrait lenses come in the 35-85mm range and have max. apertures of f/1.8 or larger. A 35mm lens will exaggerate facial features nearest the lens element, so a hand held out towards the camera will be enlarged or 'foreshortened." A 50mm lens is generally considered standard field of view, although crop image sensors alter the FOV, making this focal range resemble that of a longer lens. Finally, longer focal lengths like 85mm will flatten a scene, reducing any exaggeration caused by close physical proximity to the lens; longer focal lengths also have a more shallow depth of field at any given aperture than do lenses with shorter focal lengths.

[Shemker394]

What is your budget?

The "58mm size" you're refering to might be the filter size. Different lenses might have different filter sizes. What you're looking for is a k mount lens, or screw mount one but you'll need an adaptor for that.

I've found 50mm to be a tad too long for across the table shots. A 30-35mm lens will be better suited on cropped sensor. Don't forget a normal 50mm lens becomes 75mm short telephoto on your k100d due to the 1.5x crop. If I had the money I'd get a Sigma 30mm f/1.4 EX DC lens. With the cropped sensor its fov is 45mm so closer to a normal lens.

Myself I have a Super Takumar 50mm f/1.4 as a portrait lens. Can be bought quite cheap on ebay. I got mine from a forum member over at pentaxforums.com (which I advise you to sign up) along with the screw to k mount adapter for about $80. It's fully manual though.

[bestonlinepharmasy2]

What is your budget?

The "58mm size" you're refering to might be the filter size. Different lenses might have different filter sizes. What you're looking for is a k mount lens, or screw mount one but you'll need an adaptor for that.

I've found 50mm to be a tad too long for across the table shots. A 30-35mm lens will be better suited on cropped sensor. Don't forget a normal 50mm lens becomes 75mm short telephoto on your k100d due to the 1.5x crop. If I had the money I'd get a Sigma 30mm f/1.4 EX DC lens. With the cropped sensor its fov is 45mm so closer to a normal lens.

Myself I have a Super Takumar 50mm f/1.4 as a portrait lens. Can be bought quite cheap on ebay. I got mine from a forum member over at pentaxforums.com (which I advise you to sign up) along with the screw to k mount adapter for about $80. It's fully manual though.

Thanks for the help, my budget is very cheap, as in, the cheapest lens I can get, less than $100 if possible. The Sigma is quite a bit more, and I looked for the Super Takumar on ebay and it only came up in a kit. I would probably be looking for something around 50mm and around f1.4-2.0. Any other suggestions?

[valiumcheapll]

For that price you can get only full manual lenses. But they're a joy to use. Check ebay. Any Pentax 50mm f/1.4 or f/1.7 is a good buy. They are very cheap as well. If you have secondhand camera shops close to where you live you can find them for very cheap.

[h4z1XBI7]

50mm manual lenses on ebay. Happy bidding [thumbup].

[Fdmnrnba]

1. Because you have cheap glass. Zooms with a fixed aperture are general counted among pro, or at least semi-pro lenses, and const considerably more than consumer zooms. Generally, they also offer improved image quality.

2. Seeing as you camera has a 1.5x sensor crop, for portrair work you'd be best off with a fast standard lens. I'm sure there's a 50mm or 60mm f/1.8 available in the Pentax line - that would be your best choice, because after including the sensor crop, the lens would have the proper focal lendth for portaiture.

[Mappaindy]

1. Its all to do with the way lenses are designed. Basically, if you want a lower F.stop (so faster) at longer focal lengths, you need a lot of expensive, heavy glass. Consumer grade lens tradeoff this fact, with the F.stop increasing as the focal length increases.

That's not correct. In high-grade zooms, the aperture stays fixed throughout the focal range.
I've yet to hear of lens with F-stop bigger at the long end of the focal range than at thw wide end, though it's not impossble the thing that such a lens was manufactured at some point... It's just not the standard.

[iiilizium]

That's not correct. In high-grade zooms, the aperture stays fixed throughout the focal range.
I've yet to hear of lens with F-stop bigger at the long end of the focal range than at thw wide end, though it's not impossble the thing that such a lens was manufactured at some point... It's just not the standard.

By lower F.Stop I mean NOT increasing as you zoom, as is the case with consumer lens.

I did not mean the F.stop going the other way as you zoom!

[disappointment2]

By lower F.Stop I mean NOT increasing as you zoom, as is the case with consumer lens.

I did not mean the F.stop going the other way as you zoom!

Lower than in a cheap consumer zoom?

[addyta.org]

Oh, my bad. I totally misread that.
I'm after like 6 bowls, so ...

[KongoSan]

So I went to the local camera shop and the guy there said he preferred 75-100mm lenses for portrait photography. I didn't really understand, why would you want a 75 or 100mm lens X 1.5 crop = 150 - 200mm lens for taking pictures? I asked him about a small lens like a 28mm and he said I wouldn't want 28mm because there would be too much distortion. Most of the posts here have said 50mm is the way to go, but why shouldn't I get a 28mm or less?

[herbalviagra]

So I went to the local camera shop and the guy there said he preferred 75-100mm lenses for portrait photography. Generally that would work in a studio so you don't have to be to close to the subject. For normal occasions 50mm is fine, maybe a tad too long for across the table shots.

I asked him about a small lens like a 28mm and he said I wouldn't want 28mm because there would be too much distortion. A cheap one yes, it will distort. A proper one, not really.

Most of the posts here have said 50mm is the way to go, but why shouldn't I get a 28mm or less? Price! A fast 28mm lens costs more than a fast 50mm lens.

[cheapphenonline]

A cheap one yes, it will distort. A proper one, not really.

Will there be significantly more distortion on a cheap 28mm than a cheap 50mm?

[XGoFivk7]

Will there be significantly more distortion on a cheap 28mm than a cheap 50mm?

Most likely, yes. Wy not test some lenses in the shop and see?

[ballingham]

Will there be significantly more distortion on a cheap 28mm than a cheap 50mm?

You know, if you have around $800 dollars, get a something like a Sigma 70-200mm f/2.8. I used to own it, and was very pleased with what it produced. 70-200mm is a very good range for general work, as well as portraiture when you stay in the bottom half of the range (70-135mm), which is perfect for this kind of shooting. And the relatively fast f/2.8 aperture will provide a good bokeh from a longer range.
I you can afford that, then that lens would be a very good purchase.
Here's a picture I took with it:




And 100% crops.






PS
The lens itself is also gorgeous.

[spacecrafty]

Will there be significantly more distortion on a cheap 28mm than a cheap 50mm? Well, you can't really take my words literally. There are cheap manual 28mm lenses that are excellent.

Like this Pentax M 28mm f/2.8


There's another problem with wide angle lenses, fast ones are difficult to come by. The fastest "affordable" wide angle lens I've found is the Vivitar 28mm f/2.5. They can be found on ebay for $60ish.

Check this pentax lens review page. It'll give you a general idea of pentax lenses.

If I were you I'd start looking for a Pentax or Takumar 50mm f/1.4 lens. They're great for their price (starting from ~ $30 to ~$200 for a fa50mm f/1.4).

[6ZCo3xuK]

Thanks for the help everyone! [thumbup]

[HagsPusia]

Also, not to sound condescending - I really am trying to help, buy a photography book that covers the basics and the more advanced topics.