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12-24-2009, 05:14 AM   #1
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20-80mm redundant?

Hi, I'm new to the world of dSLRs with the recent purchase of a K-x with the standard kit lens. I have a few lenses from my 35mm days and am a little confused by the focal length equivalents of the new format. I have the following 35mm lenses:

- Pentax KA 50mm f1.7 with a broken "A" setting - I think it makes sense to keep this lens for speed in low light and shallow DOF.

- Vivitar 70-210mm - I think it makes sense to keep this for the reach (I had to modify it to fit the K-x but it works)

- Pentax SMC-A 28-80mm - This one I'm not so sure about. Is this focal length redundant if I already have the 18-55mm dSLR kit lens? I currently have it up for sale but I'm having second thoughts. Does it make sense to sell this one or is there value in keeping it?

Thanks!
Les

12-24-2009, 05:31 AM   #2
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Just compare the numbers themselves. Any lens, even one "designed for APS-C", which is commonly though of as being the opposite of a "35mm lens", will have its effective focal length cropped by 1.5x on a Pentax APS-C camera compared to how it would look on a 35mm sensor. That is to say, if you put your 18-55mm lens on a full-frame film camera, at 18mm it would give an even wider FOV than on digital, but it would suffer from heavy vignetting.

So, an 18-55mm lens and a 28-80mm lens only are redundant through 28-55mm, which is a fairly small range. Personally, I would consider it large enough though to sell the 28-80mm. The 18-55mm kit lens is very good quality for what it is, and the 28-80mm isn't, really. 28mm is also not nearly as useful for wide shots as 18mm is. So, I would keep the 18-55mm and use your other lenses (specifically the 70-210) to cover the range you used to have with the 28-80.
12-24-2009, 08:37 AM   #3
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You may want to hang on to that 28-80 for a while until you get a handle on what you are going to be using. I currently don't have anything in the size between 55-70 and am seriously considering a purchase as I think it would be very usefull. Probably the only thing stopping me is the current state of my finances. I had a Nikon 24-70 which I used on a Pronea (aps film SLR) and I loved using it. I miss that size.
12-24-2009, 08:47 AM   #4
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My understanding was that the 18-55 on the APC-C is equivalent to the the 28-80 on the 35mm. But based on the responses here, it sounds like this is not the case and that there is no conversion necessary, I should really be comparing the focal lengths directly. If this is true, then there really is a bit of a gap that would be covered by this lens. Hmmmm... so much to learn...

12-24-2009, 09:40 AM   #5
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QuoteOriginally posted by Nameles Quote
My understanding was that the 18-55 on the APC-C is equivalent to the the 28-80 on the 35mm. But based on the responses here, it sounds like this is not the case and that there is no conversion necessary, I should really be comparing the focal lengths directly. If this is true, then there really is a bit of a gap that would be covered by this lens. Hmmmm... so much to learn...
An 18-55mm on digital is roughly equivalent to 28-80mm on 35mm. But a 28-80mm will "become" (not really, but its images will look like) those from a 42-120mm lens. So exclusively when using APS-C digital with those two lenses, you have a 27-82.5mm lens and a 42-120mm lens (again, not literally, but the 1.5x crop factor will make them work like those focal lengths do on 35mm). So there's still about half the range doubled up no matter how you look at it, and I personally would get rid of the non-AF, less-wide lens and use what you have or look around for a nice prime around 80mm.
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