Extension tube on Nikon 500 F4

Dave Semmens

Dave Semmens

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A few of the hides I shoot from are quite enclosed after around 25 yards and I was wondering if anyone had tried fitting an extension tube to a Nikon 500mm F4 to reduce the close focus distance down from around 4 metres.

I know that it will limit the focus at longer range - that is not a problem in these hides.

What I ideally need to know is:

What size tube gives the best results?
Any particular make recommended?
Is focus speed / image quality affected (assuming not - but worth checking)?
Anything else I need to know?

Thanks

Dave.
 
Dave Semmens said:
A few of the hides I shoot from are quite enclosed after around 25 yards and I was wondering if anyone had tried fitting an extension tube to a Nikon 500mm F4 to reduce the close focus distance down from around 4 metres.

I know that it will limit the focus at longer range - that is not a problem in these hides.

What I ideally need to know is:

What size tube gives the best results?
Any particular make recommended?
Is focus speed / image quality affected (assuming not - but worth checking)?
Anything else I need to know?

Thanks

Dave.
Click to expand...
I use a helicoid extension tube that "zooms" between 46 and 68mm. It's got good (almost) all metal construction and electronic communication. I would not be concerned with hanging a camera body w/ grip off of it (I've hung the D4 off of it).
The first one I got was assembled wrong... the second has been fine. It's sold under several brands. I use it for macro work as the "zooming extension" acts like a bellows rail. I haven't had much use for it on long lenses. (but even the shortest setting is too long for short lenses (<~35mm)).

Other than that, the Kenko versions are good and allow for shorter extension.
No IQ issues.

Extension tubes cause a loss of light, but even 68mm on a 500mm lens won't amount to much. (68mm is ~13%= ~1/3 stop loss, 40% = 1 stop loss).

The bigger issue is that focusing shorter will significantly reduce your DOF. To get it back you have to stop down..combine that with a light loss and you are looking at possibly needing significantly higher ISO's.
Extension tubes have an "effectiveness" equivalent relative to the overall FL increase... I.e. 68mm is a huge effect on a 50mm (minimum focus distance/light loss) where it is much less significant on the 500mm. 68mm might result in a 50% reduction in the minimum focus distance for the 500mm (I don't actually know).
To equate that change in MFD to ISO: If you cut the focus/subject distance in half you change the DOF by a factor of ~4 (1/4 the DOF). But doubling the aperture (2x) only changes the DOF by a factor of ~2.... So, to get the DOF back for 1/2 reduction in the subject distance you would need to stop down 4 stops. That's potentially a very big hit...

I would only use them if the light is very good and they are absolutely necessary.
 
Thanks for the info - the old saying that "you don't get something for nothing" proves true again :(

Some of the areas the hides look out onto can be quite dark - especially in spring / summer with the foliage cover.

So I would not like to lose more light.

Looks like I need to live with it for now and look into another plan :)

Dave.
 
Dave Semmens said:
Thanks for the info - the old saying that "you don't get something for nothing" proves true again :(

Some of the areas the hides look out onto can be quite dark - especially in spring / summer with the foliage cover.

So I would not like to lose more light.

Looks like I need to live with it for now and look into another plan :)

Dave.
Click to expand...

I'm not sure there's anything significant to worry about. Steven is right in theory, and all lenses lose light/transmission when focused close. With a macro lens for example, at 1:1 the effective aperture is reduced by two stops (Nikon reports this in the viewfinder, Canon chooses not to). And by the same token, depth of field is also reduced.

But what you're doing by adding a short extension tube to a 500mm lens is a very small change, and in terms of effective aperture and depth of field reduction, what you'd get is no different to the lens doing it natively.
 
HoppyUK said:
But what you're doing by adding a short extension tube to a 500mm lens is a very small change, and in terms of effective aperture and depth of field reduction
Click to expand...
And a short tube would also be a small change in the MFD.

I found a calculator on this site/page that allows you to determine the MFD/Magnification with different extension tubes: http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

BTW, the native magnification ratio for the Nikon 500/4 VR is .145 (1/6.9) and the native MFD is 4000mm (4m AF).
The calculator shows that 25mm extension gives .2x and 3662mm MFD; and 68mm extension gives .28x and 2920mm (less MFD reduction than I guessed).

We can now use a DOF calculator to see how the different MFD's affect the DOF.
Using a FF camera (more DOF for a fixed distance/settings than APS) I get these numbers w/ a 500mm set to f/8.
00mm extension @ 4.0m MFD= .03m DOF
25mm extension @ 3.7m MFD= .02m DOF
68mm extension @ 2.9m MFD= .01m DOF
To get the .01m DOF back up to .03m you have to stop down to f/16... and .03m DOF is awfully thin already.

BUT, keep in mind that this DOF penalty is primarily due to working at shorter focus distances. If you add the 68mm extension tube and shoot at the same 4m distance the reduction in DOF is much less notable (~.025m instead of .03m). The further the focus distance is, the less the DOF penalty is. And the loss of light is only ~1/3 stop (maybe less).
This is (probably) the point Richard was trying to make. When working out at the focus distances you can currently use there isn't much loss/penalty from adding the extension.

The real penalties only come when working at the shorter distances that you can't currently use.
So the question becomes, are the small penalties overall worth the increased usability/range/cost? IMO, the increased focal range isn't very "usable" for what you're doing, but the costs aren't very great either... IMO, it probably really isn't worth it and a better choice would be a different lens (probably even if it requires cropping). Tough call really.

BTW, I found an interesting tidbit about the Nikon 500/4. You can reduce the MFD to 3.85m just by making a manual focus override (FWTW).
 
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how close do you need to focus ? (remmber its from the sensor plane mfd is measured)
cokin made a P size macro len's, ive got one but never used it...
 
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