Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-13-2009, 04:21 AM   #1
Pentaxian
raider's Avatar

Join Date: Jul 2007
Location: Perth, Australia
Photos: Gallery
Posts: 1,931
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, 04:34 AM   #2
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.

QuoteQuote:
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
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
And here's what the 18-250mm looks like at maximum magnification.

09-13-2009, 04:29 PM   #4
Pentaxian
raider's Avatar

Join Date: Jul 2007
Location: Perth, Australia
Photos: Gallery
Posts: 1,931
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, 04:58 PM   #5
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by raider Quote
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
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,631
QuoteOriginally posted by raider Quote
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.
09-13-2009, 09:11 PM   #7
Pentaxian
raider's Avatar

Join Date: Jul 2007
Location: Perth, Australia
Photos: Gallery
Posts: 1,931
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!!
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
450mm, distance, focus, k-mount, lens, object, pentax lens, question, slr lens, tamron, wifey
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Minimum focus distance - Tamron 70-300 flippedgazelle Pentax SLR Lens Discussion 2 09-30-2009 05:55 PM
Sigma 20 1.8, nails close focus, back-focuses at a distance. What to do. adhall82 Pentax SLR Lens Discussion 1 05-07-2009 11:38 PM
Tamron 18-250 won't focus - PANIC ! glanglois Pentax SLR Lens Discussion 11 07-24-2008 03:05 AM
For Sale - Sold: FS: Tamron SP 300/5.6 close focus (1:3) + Tamron SP 2X TC aegisphan Sold Items 3 04-11-2008 08:55 AM



All times are GMT -7. The time now is 08:40 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top