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Old Mar 11, 2006, 2:29 PM   #1
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I have been looking for a simple explanation for the relationship between Focal Length and Magnification and have not found one I understand.

My DSC-H1 has a 7.19mm CCD and a 6mm to 72mm 12x zoom lens. The book says that the 6-72mm equates to a 35mm equivalent of 36 to 432mm which means a conversion factor of 6... so far so good.

Now, reverting back to my film 35mm SLR days, a 50mm lens was considered "Normal" or eye view where the picture is the same size seen with the naked eye. So applying the conversion factor of 6, the Normal lens size for the H1 should be 50/6 = 8.33mm. Using the EVFin one eye, looking at the object with the other, and rocking the zoom in and out, I end up with 23mm as giving me a view of the object in the EVF the same size as I'm seeing with the other eye, not the 8.33mm I figured it should be. So, is the 23mm the "Normal" Focal Length for this camera/CCD?

Secondly, once the Normal Focal Length is determined, howcan I determine the +/- magnification factors of the zoom lens? If 23mm is indeed the Normal size, can we then say that the H1 has a + magnification of 3.13x (72mm/23mm) at max (Tele) zoom and a - magnification of 0.26x (6mm/23mm) at minimum (WA) zoom? If I add my 1.7x Tele lens is the + magnification now 4.83x (3.13 + 1.7), or 5.32x (3.13 x 1.17). The 5.32x sounds right because looked at another way of ((72mm x 1.7) / 23mm)) = 5.32x. In other words, with the 1.7 Tele lens on, does the object appear 5.32 times closer to me than seen with the naked eyes? ...... How about with my glasses on ?? :-)

I'm trying to relate the view thru the camera lens to the view thru my 7x binoculars.

Sorry for being so long winded.

George
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Old Mar 13, 2006, 9:25 AM   #2
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George – Here's how I understand it:

In 35 mm formatthe 55 mm lens is generally considered "normal" – the image is rendered at 1 X (ie. no magnification)

Now the H1's published max optical zoom 35 mm equivalent is 432 mm. This works out to about 7.9 X magnification (432mm / 55mm = 7.855)

Therefore the H1's maximum optical magnification is a bit more than for your 7X binoc's. However depending on the design of the binocular's optics, the field of view (the diameter of the image seen by the viewer) may be vastly different between the H1 and the binocs. (I'd suspect the binoc's havea larger field of view). But the apparent magnification of images as seenthrough eachwill be about the same.org



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Old Mar 13, 2006, 10:14 AM   #3
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FarmallBob tnx for the reply...

Yes, what you came up with is what I originally thought also, but there is a big difference in the magnification between my 7x binoc's and the H1 at full zoom, even with the 1.7x tele lens the binoc's are stronger.

I'm going to email sony support and see if they can tell me what mm would equate to the 1X position.

tnx agn

George
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Old Mar 13, 2006, 1:50 PM   #4
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I think your numbers are right and the observation off for some reason. You get a much brighter and clearer view through binoculars, but I don't think the magnification of 7X binoculars is greater than the magnification of your 432mm equivalent camera lens.
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Old Mar 14, 2006, 11:59 AM   #5
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George55 wrote:
Quote:
FarmallBob tnx for the reply...

Yes, what you came up with is what I originally thought also, but there is a big difference in the magnification between my 7x binoc's and the H1 at full zoom
George - I fooled around a bit this morning with my H1. Set the H1 to maximum OPTICAL zoom (set the zoom indicator at the line between optical and digital "smart zoom"). Then focused on an object about 15 ft distant that just about filled the viewfinder/LCD screen. Next I refocused on a similar-sized object about 100' distant and just to the side of the first object. I then observed the relative size (height) of the distant object relative to the near one.

Now without changing my position I took my my wife's 7 x 26 birding binoc's (7x magnfication) and repeated the above. Not surprisingly the size of the near object relative to the distant one was nearly identical when viewed thru the binocs as when viewed thru the H1. This tells me the magnification level provided by the H1 and the 7x binoc's are approximately the same.

However.... The images as perceived by my eye through the binoc's APPEARED to be much larger (brighter and sharper too...) than when viewed through the H1.

-----

This all tells me the H1's magnification at max zoom is as claimed. However due to differences in the apparent image sizes (and quality) between the H1 viewfinder and the binoc's, the binoc's will appear to provide more magnification than the H1.

-----

Incidentally I am fully delighted with my recently purchased H1. (It replaces an Olympus C2100 Ultrazoom that simply wore out mechanically after shooting nearly 30,000 images, many under harsh conditions of snow, windblown dust, etc.) The zoom range and image quality of my H1 is everything I expected. ...FB
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Old Mar 14, 2006, 7:01 PM   #6
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Yup, I re-thought the whole thing again and also came up with the fault being the way I perceive what I am seeing thru the EVF.

I did the math one more time and if the 35mm equivalent of our 6mm - 72mm is 36mm - 432mm as stated, then the 35mm equivalent of the "Normal" 50mm lens would be 8.33 (50/6) on the H1. So if 8.33mm is ground zero (1X) then 8.33mm to 72mm is 8.64X which is better than my 7x binoc's. It really gets fun when I plug in the numbers for the 1.7x Tele I bought.... 8.33mm to 122.4mm = 14.69x. Wowzer!!

I did email Sony with this question so we'll see if they agree with the 8.33mm as 1X.

We're Have'n Fun Now :-)

George
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