Ok, it turns out that a friend of mine has the PK-11A (8 mm) so I will test it and see what the results are and if I get anything nice, I will post them here for you to see also :)

You guys can look up bellows extension factor- it's well known that as you focus closer, your effective aperture decreases and you require more exposure.

As far as using wide angle lenses goes, one thing you have to worry about is the maximum extension you can get while still being able to focus. As you add extension, the distance to the subject decreases. At some point the location your lens is focused on is actually before the front element of your lens, meaning you can't focus at that magnification. Since the focal length is shorter, this happens sooner with wide angle lenses. Of course, the solution in this case is just to use a reversing ring.

Dont know if the coin example is valid :-) (I am no math nor physic guru!) but I think that its darker because the distance of the lens aperture to the sensor is farther away so you have lost some light that way. similarly if you have a f2.8 macro lens. it is a well known that at 1:1 magnification your aperture is not F2.8 but more like F5.6 though your camera will lie to you and say its still F2.8 :-)

monty11 said:
The bit about it getting darker has something to do with physics, which I'm not really at home with :) Maybe someone else can shed some light on it.

Imagine you want to take a photo of a coin. With a regular lens the coin would be e.g. on an area of 100 x 100 pixels. So the light that the coin reflects into the camera is spread on these 10.000 pixel. Now you get closer and make the coins larger, so it is 1000 x 1000 pixels in size. This means that the light is spread on a bigger area leaving less light for a single pixel: the image gets darker.

Btw it does not matter if you use extension rings or if you use the extended mechanics of a dedicated macro lens. The math is:
e = (m + 1)^2
where e is the extension factor (multiplier for exposue time - just as with dark filters) and m is the magnification.

monty11 said:
What length of Kenko ring were you talking about? The Kenko rings that I have, are 12, 20 and 36 mm. Those have no problems and I haven't seen any shake when only one ring is used at a time. There are some shake problems if you mount several rings at once.

I meant hand shake not a wobbly or mounting problem.

Tubes to make the images flatter in color in my experience. I too have seen the darker image but really that dealt with available light and the small f-stops needed for close up work. Below average light and above F8 AF is not real reliable.

There are no aperture problems on coupled extension tubes, only focusing is tricky on zoom lenses.

The bit about it getting darker has something to do with physics, which I'm not really at home with :) Maybe someone else can shed some light on it.

NSXType-R said:
Are there any problems with mounting G lenses with any extension ring? Are there extension rings with contacts to change the aperture?

Hmm, maybe I'll try them with the 105mm macro.

heartyfisher said:
I have the kenko 12,20,35 set. Works fine with my lenses. except its pointless putting the the longer ones on my kit zoom 18-70 18-200 as lens is physically long and the focus point is so close it is within the lens! esp at the wide angle side. I did stack all 3 on my 200-400 to get closer. It works but but its too dark to auto focus. However, the single 35mm one on the 200-400 is good.

Why does it get dark? There's no glass in an extension tube right?

I have the kenko 12,20,35 set. Works fine with my lenses. except its pointless putting the the longer ones on my kit zoom 18-70 18-200 as lens is physically long and the focus point is so close it is within the lens! esp at the wide angle side. I did stack all 3 on my 200-400 to get closer. It works but but its too dark to auto focus. However, the single 35mm one on the 200-400 is good.

Well the only problem the Kenko (perhaps also others) have is that AF becomes almost unusable with zoom lenses.

But these are not the ones I'm talking about :)

The Kenko kit I have has a 12mm, 20mm, and 36mm ring. They can be used alone or in combination, although I rarely use them together, the 36 seems to be more than enough in most cases. I have tried them with a G lens and they worked fine.

Are there any problems with mounting G lenses with any extension ring? Are there extension rings with contacts to change the aperture?

Ok, I did some more research and the problematic ones are the Nikon K-rings (I'm especially interested in the K1 ring) that could scratch the camera bayonet contacts unless it is carefully mounted. The latter is a Nikon warning. There are no problems with the PK-11A.

I found quite an extensive information archive on this site: http://www.mir.com.my/rb/photography/hardwares/classics/michaeliu/cameras/shared/ff2macro/

What length of Kenko ring were you talking about? The Kenko rings that I have, are 12, 20 and 36 mm. Those have no problems and I haven't seen any shake when only one ring is used at a time. There are some shake problems if you mount several rings at once.

I have the kenko ring set and used it with my 17-35 with no problem. The smallest extension ring in the kit is 12mm. You have to get real close (2-3cm) to focus.

I have not heard anything on extension ring damaging a camera. Is that a Nikon or 3rd party manufacture? Nikon part #? (i.e. PK-XXX)

I have borrowed a friends Kenko set before and they were ok (non AF version used with AFD 24mm lens). They are used more for macro work and shake comes into play very fast. I have never used it with G lenses though.

I have used this as a reference for long lenses before. It is probably the same for wide angles. http://kenmcvayphoto.clymbers.com/articles/extensiontubes.html

Monty, this is interesting, as the wide angle lens would mean you have to get real close for focusing, I think.

post some pictures if and when you try it.

perspective would be different and interesting.

I've been thinking of using extension rings on wide angle lenses.

Does anyone have any experience with this? Or perhaps can someone tell me how to calculate the closest focusing distance with an extension ring?

I've read on the internets that the 5 mm one can damage the camera bayonet (DSLR), is this true?