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Old Sep 25, 2011, 7:38 PM   #1
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Default 600mm fz100 vs 300mm kx

Hi All

Hopefully someone can explain simply the comparison of 600 mm on the FZ-100 vs a 300 mm lens on a Pentax K-x. As far as I can tell they are pretty equal in there magnification of a subject. I'm confused.
I realize there is difference in quality. I just thought if one is 600 mm it would magnify twice what the 300 mm would be able to see. I doesn't seem so. I know the image quality is suppose to better with the Pentax. For me that has not been the case.
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Old Sep 26, 2011, 3:18 PM   #2
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Hi popellis

It's all to do with the sensor size. Most lenses are still quoted as 35mm equivalent focal lengths.

It becomes a little tricky at this point, if you had a 35 mm full frame sensor then a 300mm focal length lens would focus 300mm from the ccd sensor surface. If the sensor was replaced with a one of exactly half the dimensions of the 35mm one then the lens would would focus at 600mm from the ccd surface.

The smaller the sensor, the further away the lens needs to be from the sensor. That is how the zoom lens of the FZ series (for example) manages to have such a large zoom range with a small physical lens.

Hope that helps, and even more, hope I got the facts correct.
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Old Sep 26, 2011, 3:21 PM   #3
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whoops forgot, that does not explain why your results from the Pentax (or for that matter any larger sensor camera) are not better than the FZ100, 40/45

Are you sure the lenses, sensor and if the Pentax K x has a mirror, are clean.
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Old Sep 26, 2011, 3:48 PM   #4
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Given the sensor size on the Pentax,the equivalent zoom range will be roughly 450mm- also bear in mind that one is in 4/3 format and the SLR in 3/2 format.
In the real world that is not a huge difference...
I can't comment on the Pentax's image quality,but if I compare my Canon 20D's images with a Tamron 270mm lens fitted- no bridge camera will come close in image quality at the equivalent 430mm setting..!
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Old Sep 26, 2011, 6:10 PM   #5
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Thanks Square one and simon 40

I realize quality is not the same and it seems zoom may not be that much of a difference either. The pictures I posted below the 1st is the FZ-100 at 24X zoom and the 2nd is the Pentax 300 mm.

Now that I look at them more closely the zoom maybe close to 200 mm more. Of course this subjective just by my sight, nothing was used to measure for comparison.
Please I know these are lousy pictures it was just a quick shot on a very dark day. I wanted show distance and not really show how bad of a photographer I am.
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Old Sep 27, 2011, 5:11 AM   #6
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For a fair comparison I would suggest selecting an identical iso setting,set the focus area so that the mailbox numbers are in focus and try and capture a similar exposure- utilising a similar aperture setting,if possible. Also crop out a given area so that the two images appear the same size.... then see which one wins..!
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Old Sep 27, 2011, 5:57 AM   #7
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Quote:
Originally Posted by Square one View Post
Hi popellis

It's all to do with the sensor size. Most lenses are still quoted as 35mm equivalent focal lengths.

It becomes a little tricky at this point, if you had a 35 mm full frame sensor then a 300mm focal length lens would focus 300mm from the ccd sensor surface. If the sensor was replaced with a one of exactly half the dimensions of the 35mm one then the lens would would focus at 600mm from the ccd surface.

The smaller the sensor, the further away the lens needs to be from the sensor. That is how the zoom lens of the FZ series (for example) manages to have such a large zoom range with a small physical lens.

Hope that helps, and even more, hope I got the facts correct.
Sorry to say I don't think you did get this info correct.

All lenses are the focal length they are and it doesn't matter what size sensor they are put in front of the lens itself will perform the same. What will be different is the field of view. The smaller the sensor the narrower the field of view and thus it looks like the lens is acting like a longer lens.

The lens on the FZ-100 is actually 4.5mm to 108 mm, however, due to the size of the small sensor this makes the field of view look similar to a 28-600mm lens on a 35mm camera. Most people now use this 35mm equivalent as it is helpful to compare things, but the only element that is comparable is the field of view. For things like depth of filed then you are basically still back to the actual focal length of the lens.

The 300mm lens on a kx gives the 35mm equivalent of 450mm is it has a sensor that is 1.5x smaller than a 35mm camera. So this is why the focal length looks longer on your FZ-100 over the kx as the field of view is equivalent to 600mm rather than 450mm.

Just picking up the first point made in the quote about the sensor size affecting how far the lens focuses, how would it know that it had a small sensor to suddenly change

Simple thing to remember, lens properties don't change no matter what sensor or film is behind it, that just changes is the field of view captured. Same basically if you take an image that you've captured and then crop in onto a smaller section in the middle. You've not altered anything in the photo apart from how you now only see a smaller portion. I won't get onto circle of confusion or other slight differences as this is enough for now.

Hope that helps a little.
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Old Sep 27, 2011, 3:23 PM   #8
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Hi Mark

Thanks for straightening out the details, last thing I wanted was to put the wrong info into peoples minds.
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Old Sep 27, 2011, 3:33 PM   #9
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Quote:
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Hi Mark

Thanks for straightening out the details, last thing I wanted was to put the wrong info into peoples minds.
No worries, it is something that is pretty confusing as many people explain it in different ways so not always do the correct bits get picked up. That's what makes it fun to me, I love the technical/gadget side of things...... sometimes I wish I was more arty.
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Old Sep 27, 2011, 7:28 PM   #10
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Mark

Thanks for the reply. That explained it a little better. The KX 300 mm lens is more like a 450 mm in 35mm terms. That is why fz-100 does not appear to be twice the zoom (for lack of a better term) as the KX 300mm lens.
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