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Old Dec 7, 2007, 9:40 AM   #11
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vivitar made by ??????
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Old Dec 7, 2007, 3:41 PM   #12
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Another comment about lenses (this is in the "for what it's worth" category)- yesterday I was using the K10 and taking pictures of an unexpected bird. I hadn't particularly paid attention to the SR settings (I was using a manual focus lens) and had the camera set to 100mm but was using a 300mm lens. Most of the shots were blurry due to camera shake (too slow a shutter speed for such a long lens). I'm not very steady any more, so I can't reliably use anything longer than 200 without paying close attention to shutter speeds. How steady are you? There are many people who are steady enough to handhold 600mm without SR, so don't think you HAVE to have it for long lenses.But if you can't reliably use a really long lens without SR, you might want to think about sticking with something up to 200mm. That's what I did when I bought my DS - I got the DA 50-200 and was quite happy withthat set-upfor a long time.
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Old Dec 7, 2007, 4:24 PM   #13
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I just got a deal from a local guy; Brand new Tokina 70-210mm f4.5-5.6. Is that a telephoto or macro lens? He's selling it for C$60. The thing is it's manual focus only. Does it mean that if I put my GX-1S on Auto focus mode, the lens will not autofocus? Is C$60 a deal for a Tokina? Is it a good lens - I mean Tokina in general?

http://www.tokinalens.com/products/tokina/mfl-05.html

I have two questions.

1) What does f4.5-5.6 mean?
2) What does SR mean?
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Old Dec 7, 2007, 10:38 PM   #14
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SR = shake reduction, Pentax's designation for their image stabilization.

A lens that is a 70-210 is a telephoto zoom lens. It may or may not be a macro lens. The numbers identify how "long" a lens is - a small number such as 18 will be a wide angle lens, while a big number, like 300, will be a very long lens. In film days a lens was called "normal" when it would capture an image that would be the same as what you would see with your eye - usually 50mm. Because dSLR cameras have a smaller sensor, they give a narrower field of view, so "normal" would be less than that. Any number bigger than 50 will be considered a telephoto lens.

A macro lens allows close focusing. The lensname will say macro on it, and it could be many different focal lengths. A true macro lens allows you to shoot an item at 1:1 - a ratio where the image on the sensor is the same size as the object itself. An example would be the image of a half inch insect would take up a half inch on the sensor. There's no law that says a macro has to be capable of 1:1, so a number of manufacturers will advertise their lenses as "macro" when it will do 1:2 (the half inch subject takes up 1/4" inch on the sensor)or even 1:4. If you are taking pictures of flowers 1:4 might be OK, but it won't get you close to a dragonfly's eye.

The numbers f4.5-5.6 relate to the aperture of the lens. Aperture is the size of the opening the lens is capable of, and therefore how much light it will allow. A lens that is f4.5-5.6 would be considered a "slow" lens - smaller numbers mean larger openings (seems counter-intuitive). Aperture is important for a couple of reasons - a larger opening (smaller number) means more light so you can have a properly exposed shot with faster shutter speeds (exposure is based on how much light hits the sensor and is controlled by two factors - how big the opening is and how long the shutter stays open).

The other thing that aperture does is control the depth of field. A larger aperture (smaller number) means a smaller depth of field, while a smaller aperture (larger number) will give you a deeper depth of field. So if you want to isolate a small object from its background, you would use a small number (large aperture) to make the background out of focus.

I would recommend you go to a library and take out a basic photography book - it can be an older book about film photography because the principles are all the same. That can give you more detail than I can post here.

As far as the Tokina lens, I'm not familiar with it personally. It doesn't sound like an exceptional lens, but Tokina is Hoya's brand.
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Old Dec 7, 2007, 10:54 PM   #15
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Hi Dolce,

I see that Harriet has already answered while I was typing, but I'll add my more wordy, harder to understand version anyway. . . :-)

A 70-210 zoom is considered a medium to long telephoto zoom. The general focal length categories for a 1.5x crop factor DSLR like all the Pentax models goes something like this:

Up to 18mm is an ultra wide angle
from 18-28mm is wide angle
from [email protected] is "normal" or close to the human eye's Field of View
from 50-135mm is short to very long portrait telephoto
longer than 135 is usually considered long telephoto with lenses over 300mm being ultra teles.

I just made these up, but they are close to the what have been considered the traditional ranges for photography.

I've got a Tokina 70-210 f4-5.6 SZ, and it's an okay lens, but not great. Its advantages are low cost, good build quality, and small size. The major disadvantages are manual focus, speed (for me, at least), just average optical quality, and low resale value. I bought this lens at a camera meet, and used in mint condition, it was $30 USD.

It is a manual focus lens, so it's always manual focus since there isn't any mechanism in the lens to allow auto focusing. Your camera body, however has a focusing indicator that can signal you when the camera finds optimum focusing, so you're not completely on your own. If you use an MF lens with your GX1S in AF mode, your shutter will only fire when the lens is optimally focused and the focus indicator is lit in the viewfinder. This is actually a feature (called focus trap), and can be used to your advantage, but most of the time, for most people, and in most shooting situations it's a PIA, so MF mode in the camera is usually a better bet for MF lenses.

A much better lens in this range would be the Pentax A 70-210 f4. It's also manual focus only, and you should be able to find one for reasonable money (less than $100 USD), but it's much sharper, and has the advantage of having a constant maximum aperture of f4, in addition to the SMC coatings, which are generally regarded as the best. It is bigger and heavier than the Tokina by quite a bit, but the tradeoff in size for optical quality is worth it, IMO, and if you can find a good copy for a reasonable price, you will probably be able to resell it for at least the same amount as you paid.

The "f#" are ratios of actual aperture (lens opening)to focal length and provide photographers and their metering systems a relative standard to guage the amount of light that the lens can capture regardless of the size of the lens. A 100mm lens with an actual max aperture of 25mm would be an f4 (100/25=4), as would a 200mm lens with an actual aperture of 50mm (200/50=4) -- you can see the need for an "effective aperture" standard since you couldn't use the actual aperture measurement without considering the focal length for the purpose of metering exposure.

A lens with a max effective aperture of f1 would capture about the amount of light that the human eye can detect. There have been a few f1 lenses made, but very few, and they were expensive at the extreme to produce.

Every step that reduces the amount of light by one half decreases the effective aperture by a factor of 2 (halving the area of the opening) and increases the ratio (f#) by a factor of 1.4x (the rounded square root of 2 since you're cutting the area of the opening by a factor of 2, and the area of a circle is = pi X radius squared), so the standard "f-stops" are all multiples of 1.4.

The f-stop value(s) used in the lens's name are the largest opening (smallest f-stop values) that the lens is capable of. It is usually expressed as a ratio as in "1:4" for an f4 max aperture lens.

Starting at f1, they are f1.4,f2,f2.8,f4,f5.6,f8,f11,f16,and f22. In other words, an f4 lens captures twice the light as an f5.6 and half that of an f2.8.

The reason most "consumer grade" (read less expensive) zoom lenses have an f-stop range like f4.5-5.6 is that designing and building a lens where the actual aperture can vary in direct proportion to the focal length is both difficult and expensive, so one of the compromises made is to limit the amount that the actual aperture varies with focal length, so it ends up having a max aperture range instead of being a constant. In the case of the Tokina lens you mentioned it's max aperture at 70mm is f4.5, and at 200mm, it's f5.6, or about 2/3 stop slower. To figure fractional f-stops, you need to find where the f-stop value falls in relation to the nearest standard f-stops above an below the value you have, so in this case, f4.5 is between f4 and f5.6, and the .5 difference is about 1/3 of the 1.6 actual difference in the two values.

SR (Shake Reduction) is Pentax's name for its version of "image stabilization" where the effect of camera shake is reduced by moving the sensor in the camera body to counteract the natural motion of the shooter when handholding the camera.

Sorry if I didn't explain this well -- it's a difficult subject, since it's so phototechnically oriented. Feel free to ask more spcific questions if I've confused the situation even more.

Scott
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Old Dec 8, 2007, 12:39 AM   #16
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Hi mtngal.

Thank you for the infos - I can call it a small crash course. I will go to the bookstore sometimes this weekend to look for a book on photographies.

And Scott, thanks also for your explanation. And also for your opinion on the Tokina I was going to get. I guess, I'm gonna hold on for something else to come up (local sales), or even on Ebay. I'll shop around.


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