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Smallcreep
14th January 2012, 04:19 PM
Rotating the zoom ring of my newly acquired 70-300, I see that extending the lens fully reveals the 1:6 mark just in front of the locking ring, with the 150mm line exposed by about 5mm. Gently twisting the barrrel reveals a 1:2 mark about 15mm below the 300mm mark. The overall length of the lens is now 225mm. Would I be right in thinking that the barrel would extend further if an extension tube were added to the lens? Or is there some other explanation?

PeterBirder
14th January 2012, 11:34 PM
Rotating the zoom ring of my newly acquired 70-300, I see that extending the lens fully reveals the 1:6 mark just in front of the locking ring, with the 150mm line exposed by about 5mm. Gently twisting the barrrel reveals a 1:2 mark about 15mm below the 300mm mark. The overall length of the lens is now 225mm. Would I be right in thinking that the barrel would extend further if an extension tube were added to the lens? Or is there some other explanation?

Firstly, do not rotate the barrel of the lens by hand as you are adjusting the focus mechanism of the lens which is designed to be operated by the built in motor and you may damage it.:eek:
Put the lens on the camera and set the little switch on the lens to MF (Manual Focus) and rotate th focus ring. You will see that rotating the focus ring will then rotate and extend the barrel between the three ratios marked for the focal length you have set. eg between 1:16 and 1:8 for 70mm focal length. These ratios are the range of "magnification" that the lens produces at the focal length you have set. This is significant for close focus or macro shooting and is the ratio of the actual size of the subject to the size of its image on the camera sensor. A ratio of 1:2, which the 70-300 can achieve at 300mm means that an object 2cm long will give an image 1cm long on the sensor. A 1:1 ratio, which is often regarded as the start of the macro range would produce an image 2cm long.
An extension tube is a relatively simple "spacer" which fits between the camera body and the lens and causes a larger image to be projected onto the sensor, thus increasing the "magnification". This has no effect on the length of the barrel of the lens which is determined by a combination of the zoom and focus settings. The 70-300 is a "front focusing" design because focus is achieved by adjusting the front elements of the lens whereas the "kit" lenses are "back focus" or "internal focus" designs where elements further back in the lens body are moved to adjust focus.

Hope this helps. The 70-300 is a great lens IMHO but you do need decent light to get the best from it.

Regards

Ross the fiddler
15th January 2012, 05:27 AM
Rotating the zoom ring of my newly acquired 70-300, I see that extending the lens fully reveals the 1:6 mark just in front of the locking ring, with the 150mm line exposed by about 5mm. Gently twisting the barrrel reveals a 1:2 mark about 15mm below the 300mm mark. The overall length of the lens is now 225mm. Would I be right in thinking that the barrel would extend further if an extension tube were added to the lens? Or is there some other explanation?
Do take note of Peter's advice.

Firstly, do not rotate the barrel of the lens by hand as you are adjusting the focus mechanism of the lens which is designed to be operated by the built in motor and you may damage it.:eek:

A safe practice to have when using this lens is to never move the lens barrel by hand & it will last a long time, but others that haven't been so careful have had motor/drive gear failures.

My method of removing the lens hood without rotating the lens at all, is to press on the lens cap (with lens attached to camera body) & with a quick anticlockwise movement, rotate the lens hood to remove it. Another method is to extend the zoom & hold the moving barrel while removing the hood. It is a good practice to get into (using either method) to avoid any damage to the lens. I also use a little pencil lead (graphite) on the lens & hood at the points of contact etc. to help.

Further to Peter's comment, the lens will AF to 1:3 ratio which is about 1.2m (from the sensor) when at 300mm zoom & with MF it will focus closer allowing 1:2 ratio. See the compatability charts here (http://www.olympus.co.jp/en/support/imsg/digicamera/compati/di004042e.cfm) & it will show the details for when using the (Olympus) EX25 extension tube (cheap extension tubes will not work with this lens).

Hope that helps.

*chr

Barkly
15th January 2012, 07:40 AM
After having damaged mine twice in 15 months by not doing what Ross suggested - but having it repaired by OLLY Oz both times for free (once under warranty) I now ONLY remove the lens hood the way Ross suggests.

Smallcreep
15th January 2012, 11:49 AM
Many thanks for your replies. I can assure you that I only moved the barrel gently and will now desist. No damage to the lens. An added bonus of auto-focus, I have discovered, is the nostaligic sound effect of a steam train shunting as the mechanism hunts for sharpness.

Ross the fiddler
15th January 2012, 12:07 PM
Many thanks for your replies. I can assure you that I only moved the barrel gently and will now desist. No damage to the lens. An added bonus of auto-focus, I have discovered, is the nostaligic sound effect of a steam train shunting as the mechanism hunts for sharpness.

Ah yes, it might be a good value lens, but a little frustrating when the focusing noise frightens the birds (both kinds ;)) away before it locks onto focus. :D