2x magnification

Richard Dutton wrote:

Yes you are going †o lose light whatever.

You should be able to get good image quality certainly in centre frame with a good achromat. The Nisi 58mm is easily available and is 5 dioptres. Use a step down ring 62 to 58. You should get near to 2:1 with that according to the calculators but in my experience they overestimate and probably 1.7:1 is nearer to what you will get.

The Raynox DCR-150 ( 4.8 dioptres ) and DCR-250 ( 8 dioptres ) have excellent image quality. They are three element designs I think. Lose yet more light.

You can always get more light. What you can't get easily is more image quality and more working distance.

You need somewhere in the near vicinity of 7 diopters to get a 105mm Nikon to go to 2:1. The reason you don't need 10 diopters is that the lens shortens its focal length as it focuses closer. At infinity, it's a 105mm lens with its rear node 105 mm from the sensor, but at 1:1 it's more like a 70mm lens with its rear node 140mm from the sensor (magnification = (140mm/70mm) - 1 = 1).

You're stuck with the 140mm, that's internal to the lens, so to get 2:1 you have to shrink the 70mm to  46.7mm (140mm / (2 + 1) = 46.6mm). That's 1000/46.7 = 21.4 diopters. The 105mm which has shrunk to 70mm is about 14.3 doppters, leaving you 7.,1 diopters short of a full load.

The problem is that, when two lenses go walking, the stronger one does the talking. In other words, the one with the most diopters dominates the image quality.

But in this case, neither lens really dominates the balance. The 105 at 14.3 diopters isn't really that much stronger than the Raynox at 8 diopters. So your image quality is about half one, half the other. And "the other" is a simple 3 element/2 group achromat with a little bit of field flattening. It's nothing like the optical quality of the 105mm f/2.8 VR with 14 elements in 12 groups correcting field flatness, barrel, pincushion, spherical aberration, lateral and longitudinal chromatic aberration, comma, etc.

You're also dropping the working distance of 140mm from the front node (about 100mm from the front element) down to about 70mm from the front node, or around 45mm from the front of the Raynox.

So you've really killed both the image quality and the working distance with a closeup "filter".

Some other views using TC's instead here

Lots of other threads about getting higher mags from the 105 on this and other forums e.g. this thread

The optimal solution is a lower-power closeup lens (less destructive of image quality) and a short extension tube. Just working the numbers in my head, a 24mm tube and a 3.3 diopter closeup filter will hit 2x with a lot less loss of image quality or working distance.