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Photo Forum / Digital Photography / DSLR Cameras / August 2006Closeup comparison of 18-70 kit lenses, D70 and A100
I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit lenses, both set to 70mm. Both lenses focus up to about 8" from the front of the lens, which are both about the same length, however, the object image in the Sony is twice the size of the Nikon! If I blow up the image from the Nikon from 6m to 10m like the Sony, the coin is still smaller, about 60%! Weird! So why isn't 70mm = 70mm ?? > So why isn't 70mm = 70mm ?? When you focus closer than infinity the focal length changes. How much it changes varies from one lens to another.  SignatureJeremy | jeremy@exit109.com > I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit > lenses, both set to 70mm. [quoted text clipped - 9 lines] > > So why isn't 70mm = 70mm ?? Normal for IF lenses for focal length to reduce at close range. The 18-70 Nikkor doesn't focus as close as 8". >> I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit >> lenses, both set to 70mm. [quoted text clipped - 12 lines] >Normal for IF lenses for focal length to reduce at close range. The >18-70 Nikkor doesn't focus as close as 8". I got focus lock at 8" from the lens objective, at 70mm. >>> So why isn't 70mm = 70mm ?? >>> >> Normal for IF lenses for focal length to reduce at close range. The >> 18-70 Nikkor doesn't focus as close as 8". > > I got focus lock at 8" from the lens objective, at 70mm. It's usually stated as distance from the film/sensor plane. >>Normal for IF lenses for focal length to reduce at close range. The >>18-70 Nikkor doesn't focus as close as 8". > > I got focus lock at 8" from the lens objective, at 70mm. Focus is from the film/sensor plane. (usually market on top of the camera with a circle with a line through it). Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. >>>Normal for IF lenses for focal length to reduce at close range. The >>>18-70 Nikkor doesn't focus as close as 8". [quoted text clipped - 3 lines] >Focus is from the film/sensor plane. (usually market on top of the >camera with a circle with a line through it). OK, I know the mark on my Nikon, there seems to be no mark on the Sony... I'm used to measuring lenses from the front glass, which is done in my industry. > On Tue, 08 Aug 2006 19:30:34 -0400, Alan Browne >>Focus is from the film/sensor plane. (usually market on top of the >>camera with a circle with a line through it). > > OK, I know the mark on my Nikon, there seems to be no mark on the Sony... More proof that it's a glorified P&S. <g> Cheers, Alan Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. >> On Tue, 08 Aug 2006 19:30:34 -0400, Alan Browne > [quoted text clipped - 7 lines] >Cheers, >Alan Each day I'm starting to agree with you... the pictures I'm getting from the Sony are mostly sh.t... very disappointing... everything looks like it's exposed wrong, somehow, and everything is fuzzy... Whatever 'curve' is being used to create the final picture in this camera is flawed. And I think the kit lens was designed for Penthouse... I'm going to try to post some pics on Pbase... it was screwed up today... >>> On Tue, 08 Aug 2006 19:30:34 -0400, Alan Browne >> [quoted text clipped - 15 lines] > > I'm going to try to post some pics on Pbase... it was screwed up today... You should use the lens as designed [for Penthouse] and only then post the pics. SignatureThomas T. Veldhouse Key Fingerprint: 2DB9 813F F510 82C2 E1AE 34D0 D69D 1EDC D5EC AED1 >>>> On Tue, 08 Aug 2006 19:30:34 -0400, Alan Browne >>> [quoted text clipped - 18 lines] >You should use the lens as designed [for Penthouse] and only then post the >pics. I could, but would probably get banned! > Each day I'm starting to agree with you... the pictures I'm getting from the > Sony are mostly sh.t... very disappointing... Well, exposure is something where one has to outsmart the meter most of the time ... why I usually shoot manual. Esp. with digital as through the joys of chimping&histogram I can find an exposure setting I like for a given light and then shoot around that setting. By holding the AEL (in manual mode on the 7D) button in, any change in aperture or speed gives the corresponding change in aperture and speed for constant EV shooting in that light. High consistency follows... but trust the camera meter in aperture or speed priority? Nope. Cheers, Alan. Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. > I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit > lenses, both set to 70mm. [quoted text clipped - 9 lines] > > So why isn't 70mm = 70mm ?? It isn't that uncommon for mfgs to lie about true focal lengths. It's marketing. Thats why nearly every kit lens is marked as 18-55mm. >I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit >lenses, both set to 70mm. > >Both lenses focus up to about 8" from the front of the lens, which are both >about the same length, however, the object image in the Sony is twice the size >of the Nikon! Naturally... >If I blow up the image from the Nikon from 6m to 10m like the Sony, the coin is >still smaller, about 60%! You can't compare like that. >Weird! Not at all. >So why isn't 70mm = 70mm ?? It is still 70mm on both. The difference has nothing to do with focal length or reproduction ratio. You're seeing the difference between resolution of the sensors. More megapixels means more resolution detail and a larger image if the distance and focal lengths are the same. If viewed at 100%, subjects in the larger image will appear larger when compared to a smaller image. If you view both so the entire frame fits within the image viewer you're using, they will both be the same size. It's only when you view the image in respect to the number of pixels that the sizes appear to change. >>I just shot pic's of coins with the Nikon D70 and the Sony A100 using the kit >>lenses, both set to 70mm. [quoted text clipped - 26 lines] >If you view both so the entire frame fits within the image viewer you're >using, they will both be the same size. That's my point - I changed the size of one to match the other, as if they were both now 4x6 or whatever, and the coin in one was 60% smaller. But I think that one camera may have focused closer then the other, I'll have to do a better test with my ruler... I was kind of balancing a meterstick and the camera and getting as close as I could and still get focus lock. To test focus closeness I guess I should put it into manual and advance the ring as far as possible and then move the camera till I have focus. To compare the 2 camera I should set up a ruler to the focal plane of the sensor? > It's only when you view the >image in respect to the number of pixels that the sizes appear to >change. >>>So why isn't 70mm = 70mm ?? >> [quoted text clipped - 11 lines] >That's my point - I changed the size of one to match the other, as if they were >both now 4x6 or whatever, and the coin in one was 60% smaller. Exactly as it should be 6/10 is 60%. I don't know what you did, but you didn't change the image size, it sounds like you changed the print size or something, which is not the same thing. Hang on while I get two matching images for reference... Ok, from dpreview - two shots of the same scene, both using the Nikkor 50mm f/1.8 lense on the Nikon D50 and D200 cameras at the same distance resulting in 6mp and 10mp samples: http://www.dpreview.com/reviews/NikonD50/Samples/Compared/Studio/d50_iso0200.JPG http://www.dpreview.com/reviews/NikonD200/Samples/Compared/Studio/d200_iso0100.JPG If you view them at 100%, all objects in the D200 image will appear to be larger because it captures more information or detail. Now, guess what happens if you were to compare with a 3mp image (half the size of the D70) of the same scene? >But I think that one camera may have focused closer then the other, I'll have to >do a better test with my ruler... I was kind of balancing a meterstick and the >camera and getting as close as I could and still get focus lock. To test focus >closeness I guess I should put it into manual and advance the ring as far as >possible and then move the camera till I have focus. To compare the 2 camera I >should set up a ruler to the focal plane of the sensor? Ideally that is the way to do it since body and lense dimensions at 70mm could be different. But it doesn't really matter that much - both are about 0.38m so they're essentially the same, or close enough. |
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