can someone explain this

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billybob99

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Andrew
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Hi I was bored and was playing around both of the below images where taken at exactly the same distance No1 is with minolta 50mm no2 with sony 18-70mm set at 50mm both f5.6 iso 200 no PP apart from resizing for web why is one a closer image than the other i have included exif data below

no 1 minolta 50mm

DSC03571.jpg


no 2 sony 18-70mm set at 50mm

DSC03572.jpg


exif data no1: minolta
Compression - 6 (JPG)
ImageDescription - SONY DSC
Make - SONY
Model - DSLR-A200
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
Software - DSLR-A200 v1.00
DateTime - 2009:07:19 11:49:41
JpegIFOffset - 155683
JpegIFByteCount - 324688
ExifOffset - 316
ExposureTime - 1/100 seconds
FNumber - 5.60
ExposureProgram - Aperture priority
ISOSpeedRatings - 200
ExifVersion - 0221
DateTimeOriginal - 2009:07:19 11:49:41
DateTimeDigitized - 2009:07:19 11:49:41
ComponentsConfiguration - YCbCr
CompressedBitsPerPixel - 8 (bits/pixel)
BrightnessValue - 5.75
ExposureBiasValue - 0.00
MaxApertureValue - F 1.70
MeteringMode - Multi-segment
LightSource - Auto
Flash - Flash not fired, compulsory flash mode
FocalLength - 50.00 mm
UserComment -
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 3880
ExifImageHeight - 2600
InteroperabilityOffset - 30544
FileSource - DSC - Digital still camera
SceneType - A directly photographed image
CustomRendered - Normal process
ExposureMode - Auto
White Balance - Auto
FocalLengthIn35mmFilm - 75 mm
SceneCaptureType - Standard
Contrast - Normal
Saturation - Normal
Sharpness - Normal

Maker Note (Vendor): -

Thumbnail: -
Compression - 6 (JPG)
Make - SONY
Model - DSLR-A200
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
DateTime - 2009:07:19 11:49:41
JpegIFOffset - 32770
JpegIFByteCount - 2190

No2 sony 18-70
Compression - 6 (JPG)
ImageDescription - SONY DSC
Make - SONY
Model - DSLR-A200
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
Software - DSLR-A200 v1.00
DateTime - 2009:07:19 11:51:00
JpegIFOffset - 155683
JpegIFByteCount - 330047
ExifOffset - 316
ExposureTime - 1/100 seconds
FNumber - 5.60
ExposureProgram - Aperture priority
ISOSpeedRatings - 200
ExifVersion - 0221
DateTimeOriginal - 2009:07:19 11:51:00
DateTimeDigitized - 2009:07:19 11:51:00
ComponentsConfiguration - YCbCr
CompressedBitsPerPixel - 8 (bits/pixel)
BrightnessValue - 5.87
ExposureBiasValue - 0.00
MaxApertureValue - F 5.60
MeteringMode - Multi-segment
LightSource - Auto
Flash - Flash not fired, compulsory flash mode
FocalLength - 50.00 mm
UserComment -
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 3880
ExifImageHeight - 2600
InteroperabilityOffset - 30544
FileSource - DSC - Digital still camera
SceneType - A directly photographed image
CustomRendered - Normal process
ExposureMode - Auto
White Balance - Auto
FocalLengthIn35mmFilm - 75 mm
SceneCaptureType - Standard
Contrast - Normal
Saturation - Normal
Sharpness - Normal

Maker Note (Vendor): -

Thumbnail: -
Compression - 6 (JPG)
Make - SONY
Model - DSLR-A200
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
DateTime - 2009:07:19 11:51:00
JpegIFOffset - 32770
JpegIFByteCount - 2222
 
Sorry Billyboy but I dont really have the time to explain :D
 
I think the explnation is about extension.

John Shaw explains it in his book "close ups in nature". Do not think closer or further away, think magnification. And magnification rates in photography are governed by (amongst other things) lens extension (not purely focal length). As Shaw says "extension is extension", what this means is that lens extension comes from a variety of lens mechanisums, one of which is often forgotten about which is the focus ring.

As the lenses are mechanically different it is likley that the focus mechanisum is providing a different lens extension in each lens - hence the different magnification.

Of course there may be a completey different explanation .... anyone.
 
I Have wondered about this too after noticing the diffrence between my 50mm and my 24-70mm both at 50mm. I think it's because even though they are the same focal length the fact that one lens is longer than the other the front element is closer to the object. having the same effect as moving slightly towards the object thus looking larger.

You could try this again but try making the front of each lens the reference point. see if you get the same results.
 
onform said:
I Have wondered about this too after noticing the diffrence between my 50mm and my 24-70mm both at 50mm. I think it's because even though they are the same focal length the fact that one lens is longer than the other the front element is closer to the object. having the same effect as moving slightly towards the object thus looking larger.

You could try this again but try making the front of each lens the reference point. see if you get the same results.
Click to expand...

sorry, I am probably being dim, but if that was the case [and it sounds totally plausible to me btw] wouldn't the shots be the other way round, the zoom would seem to be closer in, not the 50? :shrug:

Another thing that might be worth mentioning, someone, I think Puddleduck, mentoned a week or two ago about sigma zoom lenses not necessarily being the actual length they are said to be, so for example, when it says '50mm', what you ae actuually getting in reality is 48 or 52mm, or similar. So maybe that is th ecase here, the zoom isn't totally accurate and you are getting a different length than it would suggest. Just an idea to throw into the pot, there may be a very good explaination, I just don't do 'technical' if I can avoid it, its a man thing :naughty:
 
There's various reasons they may be slightly different, all hinted at above.

The short answer, especially with a difference this large, is that focal lengths are rounded, especially at either end of zooms or with primes. There'll be small differences here and there.
 
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