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09-14-2012, 02:39 PM   #1
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Enjoy Pentax

Hi all,

I am an avid Pentax fan for years. I am requesting suggestions regarding an inexpensive useful lens for my Pentax k100d. I am looking to have great depth of field/bokeh effects. Have a great day and thanks in advance for your help

09-14-2012, 02:53 PM   #2
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Wider lenses have more depth of field than telephotos at the same aperture.

You will have to give a focal length and budget to get any useful help, though :-)
09-14-2012, 03:09 PM   #3
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Thank you,

I only recently realized that my kit lens f5.8 and up to f22. I guess I need a lens that is f1.3 to about f5.8. Is that about right?
09-14-2012, 04:26 PM   #4
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Ideally one would want a lens that has a fixed aperture.. and fast (so f/2.8 or less).

The problem is the smaller the aperture value, the more expensive the lens. Note this rated aperture of the lens is only it's minimum possible aperture. It will go well above that (f/4, 5.6, 8, 11, etc) but will not go lower than that rated value.

So if you had one that is f5.8 to f22 then you cannot adjust it (via lens or in the camera itself) to any lower value than 5.8.

You're not going to see an f/1.3 lens -- the smallest you'll see for Pentax is 1.4 and very rarely. Please note this value means the size of the opening allowed for light to pass through to the sensor. 1.4 is a large opening while 22 is a tiny one.

And that said.. you probably will want to stop down to f/2 or f/2.8 anyways unless it is a really nice (read: expensive) lens as stopping down will improve corner sharpness in general.

You still have not shared what kind of lens you want.. there are Primes which have a fixed focal length (for instance, 55mm) or Zooms which have a range of focal length (for instance, 18-55mm). It might also be helpful to share what lenses you already have.

Apologies if this seems a bit elementary, but from your posts I read that you are new to the technical side of shooting. Please accept my apologies if you are not.

09-14-2012, 05:59 PM   #5
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@Idea, please describe your current lens in more detail. Is it the DA 18-55 zoom?

I am going to try to touch on some of the photography buzzwords that confused me when I started. Sorry if you already know this. Larger aperture = less depth of field = narrower focus = more bokeh. A larger f-stop number = smaller aperture.

With respect to photo composition, as you get closer to your subject you'll get more background bokeh. As an experiment, use your existing lens. Find a scene with a mix of near and far objects. Set the camera to Av mode and the largest aperture (smallest f number) the lens allows. Focus on a near object and take a picture. Then increase the aperture to f11 and try another picture of the same object. Compare the backgrounds of the 2 photos. The small f number blurs the background more and makes your subject stand out more.

Assuming you have the 18-55 zoom, repeat the experiment at 18 and at 55.

As far as an upgrade lens for narrower focus and more bokeh, the "best" choice depends on what you like to photograph, budget, whether you want a single focal length or a zoom, and other factors.
09-14-2012, 08:25 PM   #6
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Also, if you want "great depth of field", this is sort of opposite to "great bokeh". Depth of field makes foreground and background more in focus, bokeh is (simplified) more out-of-focus. For deep depth of field you should shoot at maybe f8 or f11, so getting a "fast" lens with a large maximum aperture such as f2.8 is also not what you need (though they are generally better quality).

Also, I think there is actually a Pentax 55mm f1.2 out there.
09-18-2012, 04:10 PM   #7
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Hi there,

Thanks for getting back to me. I am more familiar with film cameras. I recently replaced my Pentax Asahi with the Pentax K100d, several years before that, I had a most dependable Fujica 35mm. I am sure I am dating myself but that is ok My current Pentax k100d serves me well. I only recently found time to pay attention to realize that the kit camera starts at f5.8. I have a Tamron that is a modest and useful telephoto lens that worked with my old Asahi, but does not work with my current Pentax. A few months ago, I also purchased a Nikon 3100D. This one also starts at f5.8, which I was not aware of as various lower lens apertures escaped me when going from film to digital over the last few years. All of the comments I have read have been very helpful, educational and useful to me. I thank all of you for your kind attention and information.
09-19-2012, 04:34 PM   #8
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You guessed it correctly that is my current lens

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