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06-21-2009, 01:59 PM   #1
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K7 is 1.5 x focal length?

The K7 sensor produces images at 1.5x focal length, right?

e.g. 300mm X 1.5 = 450mm?

thanks

06-21-2009, 02:01 PM   #2
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yes

(ten characters)
06-21-2009, 05:01 PM   #3
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Yes, if you mean, you are accustomed to 35mm film focal lengths and are looking to compare between them. If you don't need to be comparing focal lengths between film and digital cameras, you don't need to multiply anything. A 300mm is a 300mm lens, period. It just happens to have a field of view similar to what a 450mm lens would have on film - something that is mainly of interest normally to people who shoot film. Or, I suppose, if you have some other camera with a different "crop factor" and are looking for a basis for comparison.
06-25-2009, 12:39 AM   #4
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Just to go a bit south here But in reading a article(whatdigitalcamera.com) on the K7 about a altering the sensor,any one here have more info on this



Quote


For those who may not see my response in the Pentax forum to the comments on our Pentax K-7 review, I have posted it again here. Thanks.

In response to some negative publicity for our Pentax K-7 review we would like to clarify a few points.

Firstly, the camera reviewed was given to What Digital Camera as a ‘full production model’ directly from Pentax UK and contained the very latest firmware (version 1.00) at the time of testing. Today however, it has been announced that Pentax may be altering its sensor before this goes on sale, presumably recognising themselves that some improvements can be made.

We appreciate all comments about our reviews and have clarified a few points, including a part in the review that claimed that this was the first Pentax to feature a battery grip. What it should have said is that the D-BG4 is the first Pentax battery grip to offer a choice of AA battery or rechargeable Li-ion use.

Our review of the K-7 is generally very positive and this is reflected in its 86% score, and What Digital Camera Recommended Award. However, a camera that is due to cost £1199 in the UK ($1975 USD as of 22/6/09) should expect to be pulled up on its shortcomings, especially when other cameras in this price bracket do not suffer the same afflictions.

We appreciate photographers are very passionate about their cameras and have strong brand loyalty but we strive to offer fair independent testing to all the cameras we test and feel it is more honest to point out any faults than find ways to overcome them.

If the camera is now due to be updated before its launch we will amend our review once we have used the new version.


cheers

06-25-2009, 02:41 AM   #5
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QuoteOriginally posted by rdrum76 Quote
The K7 sensor produces images at 1.5x focal length, right?

e.g. 300mm X 1.5 = 450mm?

thanks
give this a read. it's a few years old, but explains with pictures the differences between sensor crop & pixel density.



notice the magnification never changes, just a fov crop based on sensor size.
06-25-2009, 01:45 PM   #6
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QuoteOriginally posted by rdrum76 Quote
The K7 sensor produces images at 1.5x focal length, right?

e.g. 300mm X 1.5 = 450mm?

thanks
No. 300mm = 300mm.
Learn to use the equipment you are using rather than equipment you are not using.
06-25-2009, 04:23 PM   #7
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OP - yes the K-7 is a cropped sensor @ 1.5, much like the K10, K20, etc.

c[_]
06-25-2009, 04:31 PM   #8
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"No. 300mm = 300mm.
Learn to use the equipment you are using rather than equipment you are not using."

Misdirected hostility HA!

06-25-2009, 07:30 PM   #9
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Here's a good article concerning FOV/AOV relative to sensor size.
Memeber noblepa deserves the credit.
06-25-2009, 07:33 PM   #10
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Keyword should be "behaves". A 300mm lens on the K-7 behaves like a 450mm.
06-28-2009, 01:50 PM   #11
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QuoteOriginally posted by K-9 Quote
Keyword should be "behaves". A 300mm lens on the K-7 behaves like a 450mm.
In terms of reach, yes. dof at equal aperture, no. Unless you're figuring in a larger sensors possible ability to blah blah blah...

Let's not start these arguments again.

Lenses put on a K-7 will behave the same way as lenses of the same focal-length used on any other pentax, nikon, or sony crop-sensor camera. That's all you really need to know to take pictures (if that).
06-28-2009, 02:19 PM   #12
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rdrum76: the K-7 is still an APS-C or "cropped" sensor - no change there from previous models in terms of sensor dimensions.

Unfortunately nothing changes in terms of focal length, "reach" or optical magnification. I wish it was that easy instead of buying a longer, more expensive lens! As already stated by several folks, not much else needs to be added. Those linked articles summarize it nicely too.

To clearly illustrate this situation: during a class someone brought up that question. To avoid any further argument or discussion, I put the same lens on both a K10D and then an MS-Z SLR and asked them to look at an object in the distance using both bodies with that same lens. They saw immediately that the objects are not any closer than before with with the DSLR. What changed was the viewing angle or FOV (field of view). Case closed, back to photography... Normally you get higher pixel density with the APS-C sensor but the subject is not closer.

Only the FOV (field of view) is affected with a sensor smaller than the 35mm standard of 24x36. In this case, it's 1.5x the focal length of the lens. Nothing more.

It's still a 300mm lens.

Regards,
Marc

Last edited by Marc Langille; 06-28-2009 at 02:24 PM.
06-29-2009, 03:38 PM - 1 Like   #13
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QuoteOriginally posted by Marc Langille Quote
Unfortunately nothing changes in terms of focal length, "reach" or optical magnification.
Depends on what you mean by "reach", though. I measure it by the results on the print, not by how big something appears in the viewfinder. And for identical sized prints, then of course APS-C does indeed make a pictured object appear larger. That's why the "crop factor" does indeed makes sense as a way of comparing between formats for many people.

Of course, whether or not making an object bigger on the print also makes it more detailed is also a function of the sensor resolution and the specific lenses being compared.
06-29-2009, 05:56 PM   #14
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I quoted another poster, nothing more.

Very good points Marc! Now the OP's question is evolving into additional comments and answers, so it's beginning to go beyond the focal length issue by including pixel densities of the sensor on APS-C, etc. It is an inherent benefit in that regard. You might have more resolution, but it's not optical magnification and then the lens optical quality becomes a more important factor.

I agree with most of your points and bottom line is that I'll stand by my post. The lenses' focal length remains unchanged regardless of sensor size and the object is no closer.

Regards,
Marc

Last edited by Marc Langille; 06-29-2009 at 06:02 PM.
06-29-2009, 06:33 PM   #15
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Huh. Funny how all my Pentax exif info always states stuff like:

Focal Length In 35mm Format : 300mm

...for a 200mm lens.
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