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12-20-2009, 09:20 PM   #1
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Lens =

With a Kx we talk about a kit lens being the full 35 mill equivilant not sure of the ratio, I understand this is to to with the sensor area being smaller than the a full 35mm DSLR does this work the other way with a manual lens does a 50mm stay as a 50mm or change focal length the same as a kit lens .

Cheers MARK

12-20-2009, 10:15 PM   #2
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https://www.pentaxforums.com/forums/photography-articles/49560-crop-factor-field-view.html

The focal length of the lens is always the same no matter what camera you use, but using a sensor smaller than 35mm results in a "crop factor" of 1.5, therefore a 50mm lens on your Kx will look like it's cropped to a 75mm lens on a 35mm camera. It doesn't matter whether you have a manual, DA or FA lens, just use 1.5 as your crop factor.
12-20-2009, 10:24 PM   #3
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Mark, the focal length of a giving lens never changes from one format to another, a 50mm lens will be a 50mm lens on a APS-C camera as well as a 35mm camera. What changes is the Field of View. On a 35mm camera a 50mm lens has about a 40 degree Feld of View, on an APS-C camera the same lens has about 27 degree Field of View. So a 50mm lens on APS-C has roughly the same Field of View as a 75mm Lens on 35mm format.
Hope that makes sense,

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12-21-2009, 12:17 AM   #4
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Thanks guys for the info when i had my fathers lenses available my favourite lens was a Tac 28mm. to get the same field of view I will have to look for a 21,22,23, is that right !

12-21-2009, 12:18 AM   #5
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Thanks guys for the info when i had my fathers lenses available my favourite lens was a Tac 28mm. to get the same field of view I will have to look for a 21,22,23, is that right !

Cheers Mark
12-21-2009, 05:22 AM   #6
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If your old film favourite was Tak 28, you should be looking for K18 or K/M/A/FA 20.
DA21 would maybe do...
BR
Peter
12-21-2009, 07:08 AM   #7
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QuoteOriginally posted by wedgetail Quote
Thanks guys for the info when i had my fathers lenses available my favourite lens was a Tac 28mm. to get the same field of view I will have to look for a 21,22,23, is that right !

Cheers Mark
Mark, it would be 18. 28/1.5 = 18.66667 so 18 is close enough, so the bottom end of the Kit lens provides you with what you are looking for.
12-21-2009, 04:03 PM   #8
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..or just use the 28mm and take a few steps back to get the same FOV.
This is call zooming (in or out) with your feet!

12-22-2009, 01:02 AM   #9
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QuoteOriginally posted by GerryL Quote
..or just use the 28mm and take a few steps back to get the same FOV.
This is call zooming (in or out) with your feet!
problem with this method is that changing the subject/camera distance will change the perspective!

BR
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12-22-2009, 06:07 AM   #10
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QuoteOriginally posted by GerryL Quote
..or just use the 28mm and take a few steps back to get the same FOV.
This is call zooming (in or out) with your feet!
Nope. Google "perspective"
12-22-2009, 06:08 AM   #11
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QuoteOriginally posted by GerryL Quote
..or just use the 28mm and take a few steps back to get the same FOV.
This is call zooming (in or out) with your feet!
Also, many times you can't take a few steps back. There's a BIG difference between 28mm and 18mm.
12-22-2009, 08:21 AM   #12
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QuoteOriginally posted by GerryL Quote
..or just use the 28mm and take a few steps back to get the same FOV.
This is call zooming (in or out) with your feet!
Every year up at the Grand Canyon, there are tourists that try that - sometimes with disastrous results (either for themselves or their subjects). There was one tourist (according to the newspaper article) - a lady, who kept telling her husband to back up - just a little bit.... She went home sans husband.

Guys - you gotta watch out!!!
12-22-2009, 07:13 PM   #13
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QuoteOriginally posted by axl Quote
problem with this method is that changing the subject/camera distance will change the perspective!

BR
Peter
That is actually what a zoom lens does.
If however you have already been stuck with one lens focal length, you have to zoom with your feet to frame (or move your head forward or backward a bit) no matter what.
You don't just stick that camera to your eye and not frame your subject and say each time..aha, I don't have to go near or move back!
12-22-2009, 07:37 PM   #14
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QuoteOriginally posted by GerryL Quote
That is actually what a zoom lens does.
Not sure what you mean here. Unless you are referring the couple of *inches* a zoom lens might shift while zooming, which would have a practiclly imperceptible effect, zooming definitely does *not* change perspective. Only changing your position does that. There is no way to get a 28mm lens to emulate what an 18mm lens does by stepping back.

QuoteQuote:
If however you have already been stuck with one lens focal length, you have to zoom with your feet to frame (or move your head forward or backward a bit) no matter what.
True. This can *partially* mimic the effect of a shorter focal length, although really, only with subjects that are close enough to you for the change in position to seem significant. Might take *hours* to back up enough on a subject at the horizon to get the same effect, and everything else about the picture would be changed drastically too.
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