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12-29-2006, 11:06 AM   #1
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Lens and coverted distance

I was told that the K100d converts the lens at a 1.5 rate, so the 50-200 actually shoots at a 75-300 range.

Advertised at Adarama.com ( Equivalent focal length to 75mm-300mm in the 35mm format )Is this correct or not?

If this is then if you put a teleconverter 1.4 won't it extend it to a
105-420

12-29-2006, 11:19 AM   #2
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in simplistic terms yes it will.. but someone is bound to complicate things by saying a focal lengh is always a focal length film or otherwise..

so from where u are standing yes it will.. the 200 becomes plus 1.4 and then u add the 1.5 digital crop factor..

trog
12-29-2006, 11:43 AM   #3
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Well actually no. The camera doesn't magically give your lens a greater telephoto "reach". What it does mean is that the "field of view" is different than the lens would show on a 35mm film camera. The field of view (FOV) is greater by a factor of 1.5, not the telephoto reach, tho some think of it that way. In other words what a 50mm will show on a DSLR with an APS sized sensor is the same field of view that a 75mm lens would show on a film camera.

NaCl(hope that helps)H2O
12-29-2006, 12:06 PM   #4
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QuoteOriginally posted by NaClH2O Quote
Well actually no. The camera doesn't magically give your lens a greater telephoto "reach". What it does mean is that the "field of view" is different than the lens would show on a 35mm film camera. The field of view (FOV) is greater by a factor of 1.5, not the telephoto reach, tho some think of it that way. In other words what a 50mm will show on a DSLR with an APS sized sensor is the same field of view that a 75mm lens would show on a film camera.

NaCl(hope that helps)H2O
I would have thought that yes it does give your camera "magically" extra reach.

12-29-2006, 01:46 PM   #5
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It is not really the extra reach. It is the image being cropped out at the periphery because of smaller sensor size - light from subject falling outside the realm of sensor; the remaining image needs to be enlarged much more to "fit" into an actual image of 35mm SLR.

Though the amount of light going through the lens remains unchanged as designated by the aperture of the lens, DOF and sharpness are altered bceause of APC sensor.

Cheers
12-29-2006, 02:27 PM   #6
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Hi peted,
Let me try to explain it another way. Say you have a 200mm lens and a 300mm lens both exactly equal except for their focal lengths. Say you take a photo of an eye chart with the 300mm lens and a film camera. Now you take the same picture with your 200mm lens and a dslr. Examine the two photos. The eye chart will be the same size (field of view) BUT!!!! you will be able to read a smaller line of print with the 300mm lens and the film camera than you will with the 200mm lens and the dslr. (reach)
Putting a lens on a dslr does not magically increase it's resolving power. The resolution of a 200mm lens stays the same whether it's attached to a dslr or a film camera, even though the objects appear bigger. And, like roentarre has said, the DOF are somewhat altered.

NaCl(I hope I haven't confused people more)H2O +
12-29-2006, 02:43 PM   #7
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QuoteOriginally posted by NaClH2O Quote
Hi peted,
Let me try to explain it another way. Say you have a 200mm lens and a 300mm lens both exactly equal except for their focal lengths. Say you take a photo of an eye chart with the 300mm lens and a film camera. Now you take the same picture with your 200mm lens and a dslr. Examine the two photos. The eye chart will be the same size (field of view) BUT!!!! you will be able to read a smaller line of print with the 300mm lens and the film camera than you will with the 200mm lens and the dslr. (reach)
Putting a lens on a dslr does not magically increase it's resolving power. The resolution of a 200mm lens stays the same whether it's attached to a dslr or a film camera, even though the objects appear bigger. And, like roentarre has said, the DOF are somewhat altered.

NaCl(I hope I haven't confused people more)H2O +

Absolutely agree. Thats why it all seems to be "magic", you of course don't get any free lunches and there is always a cost.
12-29-2006, 03:23 PM   #8
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Well, actually I believe that our salty friend is wrong this time.
1. The field of view is the same. It means that if you had 6MP full frame sensor on 300mm, it would give exactly the same picture as 6MP APS sensor on 200mm. Resolution has nothing to do with this (apart from quality of lenses and sensors - my assumption is that they are of the same quality). Tiny letters would be the same on both pics. The reason is that it is a picture of the same spatial angle. Only you have more dense pixels in APS sensor than in full frame sensor of the same "megapixelness"
2. The difference is DOF. It means that hiperfocal lengths are different and therefore DOF is different.
That is my opinion. Having tried none so far, this comes only from my meager theoretical knowledge of geometric optics.

Conclusion? You do get magic boost in reach due to smallness of the sensor - compared to full frame sensor of the same "megapixelness". You also do not get the same DOF. Therefore it's better to treat 200mm lenses as 200mm lenses (for DOF calculation), especially if you do not have experience with 35mm film or full-frame sensor. You'll get used to the reach you're getting. So, after a while you'll get 300mm lenses
to get that extra reach and different DOF etc.

12-29-2006, 03:32 PM   #9
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well i did try and keep it simple.. i should know better .. he he..

so when the world and his dog says "35mm equivalent" and normal people know what they mean are they all wrong or are just some folks too anal for their own good.. ??

trog
12-29-2006, 04:35 PM   #10
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I love these threads. They make me smile each time there is one on this subject. So if we say the lenses and sensors are of equal quality the FF picture will have more resolution and detail because of the size of the pixels.

regards,
12-29-2006, 04:43 PM   #11
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Well, I hope pixel quality could be better improved. The research should be concentrated on the quality of pixels rather than more pixel count with higher pixel density.

I guess everyone was forced to learn arithmatics with compulsory education in childhood. We always count numbers from the lowest number onwards. "More" is better
12-29-2006, 05:11 PM   #12
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QuoteOriginally posted by Branimir Quote
Well, actually I believe that our salty friend is wrong this time.
1. The field of view is the same. It means that if you had 6MP full frame sensor on 300mm, it would give exactly the same picture as 6MP APS sensor on 200mm. Resolution has nothing to do with this (apart from quality of lenses and sensors - my assumption is that they are of the same quality). Tiny letters would be the same on both pics. The reason is that it is a picture of the same spatial angle. Only you have more dense pixels in APS sensor than in full frame sensor of the same "megapixelness"
2. The difference is DOF. It means that hiperfocal lengths are different and therefore DOF is different.
That is my opinion. Having tried none so far, this comes only from my meager theoretical knowledge of geometric optics.

Conclusion? You do get magic boost in reach due to smallness of the sensor - compared to full frame sensor of the same "megapixelness". You also do not get the same DOF. Therefore it's better to treat 200mm lenses as 200mm lenses (for DOF calculation), especially if you do not have experience with 35mm film or full-frame sensor. You'll get used to the reach you're getting. So, after a while you'll get 300mm lenses
to get that extra reach and different DOF etc.
Some will argue that the Depth of Focus may or may not be the same but others will argue that the Depth of Field has changed or hasn't. ;-)
12-30-2006, 01:54 PM   #13
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Nice one Peted.

Well, I understand that we need to have some measurement about what is equal. I understand that neither one of us at this forum invented "35mm equivalent" (correct me if I'm wrong), but that is what is. We cannot run away from it. My old Canon A70 has 5.4-16.2mm zoom lense. What does it tell you? Wow what a wide lens on that little camera! I think not.

And there are all the other P&S cameras with similar numbers on their lens. I believe that we need a number that would say how wide lens are, compared to another camera.
Of course, F2.8 on my A70 and F2.8 on film camera are very different.

Yep, I know that I sound anal retentive or whatever the phrase in english is, but I needed that and this post to clarify the complete picture to myself as well
And to end my rant, I will make a New Year Promise not to rant about crop factors ever again. (Unless very seriously provoked )

And trog, I admire you for trying to keep it simple. I saw a polemic about it on a newsgroup lasting some 30+posts...
12-30-2006, 02:45 PM   #14
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i do the same "mistake" with dof.. i tend to think "depth of focus".. which to me makes sense.. but never say it in a forum.. he he

it will always get the correction.. depth of field.. circle of confusion and 1/3 in front and 2/3 behind but thats wrong and run on for thirty posts.. he he he

i am not that clever and understand complicated things in my own mind by simplifying them..

trog
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