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10-14-2010, 09:45 AM   #16
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I'm not sure we have really answered the "zoom factor" question of the OP fully and / or correctly in a consise single post.

P&S cameras are marketed on two key points, the zoom ratio of the lens and the megapixel count of the sensor.

Since the OP asked about zoom ratio and what lenses he needs for his new DSLR, here is what he has to do.

In the manual of the camera, under specifications there should be either the actual focal length of the lens, i.e. minimum and maximum, or the 35mm film equivelents.

dividing the maximum focal length of the lens by the minimum will give the zoom factor.

the 35mm equivelent is based upon the diagonal of the sensor.

sensor size should also be listed, and therefore you can compare the actual focal length to sensor size diagonal and scale this to the 24x36mm frame of a film camera or the 16 x 24mm frame of a DSLR to know where you stand

10-14-2010, 10:39 AM   #17
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I'm no expert, but I'll give a shot at a simpler response here.
I had been using a Canon A710IS which boasted a 6x zoom, but I too wanted more zoom. (Like cowbells, you always need more zoom... )
The zoom was listed as 5.8-34.8 (hence the 6x). Given the sensor size of 1/2.5" (5.75 x 4.31 mm, 0.24 cm²), this translates to 35-210mm equivalent for a 35mm film camera. (Ie, to compensate for smaller sensor, multiply focal length by a factor of 6. I think this is what others are calling the "crop factor.")

As I did my shopping, for example, I determined the following sorts of zoom range equivalences.

Panasonic FZ35 w/ 18x using a 1/2.33" sensor and a 4.8-86.4mm lens (use 5.6 factor to get 35mm equivalent) >> 27-486mm

I ended up with a Pentax K-x which has the APS-C sensor. (With a 1.5 factor for 35 mm equivalences)
Using the 18-55mm lens > 27-82.5mm
Using the 50-300mm lens > 75-450mm

I think this is a useful enough rough guide, and I do indeed have more zoom!
10-14-2010, 11:52 AM   #18
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Great info thanks...While my brain abosorbs all this, here are some specs of my current p&s camera:

Canon SD880 - 10mp - 1/2.3-inch CCD image sensor - 5.0-20.0mm f/2.8-5.8 (35mm film equivalent: 28-112mm) 4x zoom (for some reason i had 3.7 stuck in my head)
10-14-2010, 12:00 PM   #19
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That translates to a crop factor of 5.6. 112mm (35mm equiv) to 20mm (actual). The crop factor for the Pentax dSLR is 1.5. If you wanted the same Type of zoom that you have with your P&S you would be going from about 18mm to 80mm. The closes single range lens for pentax offered in that range is the 17-70, either Pentax or Sigma. That would give you a Close equivalent focal range or zoom range to what you have now. If you want to think of it in terms of Xx, 4.11 from 17 to 70 mm. That should at least put some perspective on it for you.

10-14-2010, 10:25 PM   #20
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So I was bloody close in post #9

For starters you can think of the new Pentax DA 18-135WR lens. It will (more or less) double the size of a subject at the same distance and maximum focal length. I haven't seen a price yet. I also can not say if this lens is suitable for sports in low-light (read indoors; widest aperture 5.6 at 135mm) but it is a very universal lens from a focal length perspective.

If twice as big is not enough, you can go for the DA55-300; it's considered very good value for the money (I have one and I can vow for it). Maybe not the most suitable for low-light conditions (only a widest aperture of 5.8 at 300mm) and you might want to add the 18-55 kitlens for your wide angle needs.
Or the DA50-200

If indoors sport is in the picture, others might be able to advise better than me. With the excelent high ISO performance of the Kx (and probably the coming Kr and K5) a Kx/DA55-300 might do. Else you might end in expensive territory (e.g 3rd party 70-200/2.8).
10-15-2010, 03:15 AM   #21
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Or if weather resistance is less important and saving money is more important, there is a Sigma 18-125 currently available in the Marketplace for less than $250 USD; that would also give almost twice the reach of your point and shoot camera, without forcing you to change lenses during a shoot. Like the new Pentax 18-135, this Sigma is not the best indoor lens . . . there are also 18-200 and 18-250 zoom lenses available, and the 18-200s don't cost any more than an 18-125, but their image quality is not as good. The 18-250, as a more modern lens, has better image quality than an 18-200 but probably still not as good as a 55-300 other posters have referred to, and more expensive than a two lens solution with 18-55 and 55-300.

So you will have to weigh the convenience of one lens (18-125, 18-135 WR, 18-200 or 18-250) against the possibly lower price and longer reach of a two lens solution (18-55 + 55-300). Also, the cheapest WR solution currently available is 18-55 WR + 50-200 WR, but the 50-200 is both shorter reach and less well-regarded than the 55-300. There is no reason why longer telephoto lenses would have to be better than shorter telephoto lenses in quality, it just happens to be the case with 55-300 vs. 50-200 and with 18-250 vs. 18-200, for Pentax.

Good luck!
10-15-2010, 02:35 PM   #22
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The good thing about Pentax is the choice of cheap lenses to try out.

The 3.7 Canon would have a lens that's around a 120mm (35mm full frame).

I would just try the standard kit lenses of 18-55mm and the 50-200mm

Using the Canon telephoto end at 120mm (approx) the 50-200mm would give the same as a 300mm on a 35mm full frame, or between 10 and 12x in the Canon case.

The 50-200mm should be quick and small enough for hand held outside daylight sports day photography.

Last edited by View; 10-15-2010 at 02:38 PM. Reason: didn't realise there was a page two :)

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