Tamron 18-250 close focus distance

raider · 09-13-2009, 04:21 AM

Wifey asked me this question today but I am not sure what the answer is...so I think I better turn to the "Jedi Council".

The question is...what is the closest focusing distance a tamron 18-250 can focus to. The specification says it is 450mm but is this 450mm refer to the distance between the camera body and the object or the distance between the lens and the object.

I was informed (by wifey) that the nikon 18-200 VR can focus up to 200mm from the lens to the object. I googled this and I think she is right!

Anyone can confirm what is the case for the tamron 18-250?

newarts · 09-13-2009, 04:34 AM

0.45m from the sensor is the meaning of the specification.

Quote:

Minimum Focus Distance 17.7in.(0.45m)
Macro Magnification Ratio 1:3.5 (at f=250mm MFD 0.45m)

audiobomber · 09-13-2009, 07:24 AM

And here's what the 18-250mm looks like at maximum magnification.

raider · 09-13-2009, 04:29 PM

Thanks for all the replies.

audiobomber, nice shot! Is this an original size pic or a cropped pic?

If the minimum 450mm closeup distance is measured from the body to the object, then by the time the lens extended to its full zoom, the distance between the lens would be approx 200mm or so to the object? Is this a correct assumption?

newarts · 09-13-2009, 04:58 PM

Originally posted by raider

Thanks for all the replies.

audiobomber, nice shot! Is this an original size pic or a cropped pic?

If the minimum 450mm closeup distance is measured from the body to the object, then by the time the lens extended to its full zoom, the distance between the lens would be approx 200mm or so to the object? Is this a correct assumption?

That sounds reasonable to me: even closer than 200mm because the 250mm lens must be more than 250mm from the sensor when focused close. The thin lens prediction is:

Sensor_lens_distance=f(1+m)=250(1+1/3.5)=321mm

The front of the lens is likely at about 450-321=128mm from the subject

One can't say exactly, because real lenses aren't "thin".

Dave

audiobomber · 09-13-2009, 06:31 PM

Originally posted by raider

audiobomber, nice shot! Is this an original size pic or a cropped pic?

I'll try to measure subject distance tomorrow.

The posted photo was uncropped. Here's a 100% crop from the same series (K20D, DA 18-250 @ 250mm, F11, ISO 200, 1/500s).

raider · 09-13-2009, 09:11 PM

Thanks newarts for the explanation.

Audiobomber: now if that original pic is not a cropped version, then I think the 18-250 is really sharp for what it is worth!!

09-13-2009, 04:21 AM	#1
raider Veteran Member Join Date: Jul 2007 Location: Perth, Australia Photos: Gallery Posts: 1,989	Tamron 18-250 close focus distance Wifey asked me this question today but I am not sure what the answer is...so I think I better turn to the "Jedi Council". The question is...what is the closest focusing distance a tamron 18-250 can focus to. The specification says it is 450mm but is this 450mm refer to the distance between the camera body and the object or the distance between the lens and the object. I was informed (by wifey) that the nikon 18-200 VR can focus up to 200mm from the lens to the object. I googled this and I think she is right! Anyone can confirm what is the case for the tamron 18-250?

09-13-2009, 04:58 PM	#5
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	Originally posted by raider Thanks for all the replies. audiobomber, nice shot! Is this an original size pic or a cropped pic? If the minimum 450mm closeup distance is measured from the body to the object, then by the time the lens extended to its full zoom, the distance between the lens would be approx 200mm or so to the object? Is this a correct assumption? That sounds reasonable to me: even closer than 200mm because the 250mm lens must be more than 250mm from the sensor when focused close. The thin lens prediction is: Sensor_lens_distance=f(1+m)=250(1+1/3.5)=321mm The front of the lens is likely at about 450-321=128mm from the subject One can't say exactly, because real lenses aren't "thin". Dave Last edited by newarts; 09-13-2009 at 05:35 PM.

09-13-2009, 06:31 PM	#6
audiobomber Veteran Member Join Date: May 2008 Location: Sudbury, Ontario Photos: Albums Posts: 6,806	Originally posted by raider audiobomber, nice shot! Is this an original size pic or a cropped pic? I'll try to measure subject distance tomorrow. The posted photo was uncropped. Here's a 100% crop from the same series (K20D, DA 18-250 @ 250mm, F11, ISO 200, 1/500s). Last edited by audiobomber; 09-13-2009 at 06:50 PM.

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09-13-2009, 04:34 AM	#2
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	0.45m from the sensor is the meaning of the specification. Quote: Minimum Focus Distance 17.7in.(0.45m) Macro Magnification Ratio 1:3.5 (at f=250mm MFD 0.45m)

09-13-2009, 07:24 AM	#3
audiobomber Veteran Member Join Date: May 2008 Location: Sudbury, Ontario Photos: Albums Posts: 6,806	And here's what the 18-250mm looks like at maximum magnification.

09-13-2009, 04:29 PM	#4
raider Veteran Member Join Date: Jul 2007 Location: Perth, Australia Photos: Gallery Posts: 1,989 Original Poster	Thanks for all the replies. audiobomber, nice shot! Is this an original size pic or a cropped pic? If the minimum 450mm closeup distance is measured from the body to the object, then by the time the lens extended to its full zoom, the distance between the lens would be approx 200mm or so to the object? Is this a correct assumption?

09-13-2009, 09:11 PM	#7
raider Veteran Member Join Date: Jul 2007 Location: Perth, Australia Photos: Gallery Posts: 1,989 Original Poster	Thanks newarts for the explanation. Audiobomber: now if that original pic is not a cropped version, then I think the 18-250 is really sharp for what it is worth!!

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