Reversed-Lens Aperture Controller

[Kevin Childress]

Looking for ideas ...

That device attached to the front of the lens (actually the rear of the lens) is designed to manually control the aperture opening on Nikon G lenses that are reversed for macro photography. Since the adapter works with many different lenses it has no f/stop markings or lines on it - those would have to be worked out for whatever lens its attached to. I'm looking for ideas for making the markings.

The aperture control ring definitely has to be marked. The outside of the aperture control ring has nice knurled lines machined into it. The recesses of the knurling seem to make great straight lines for marking the adapter ring with f/stop, but I can't decide how to transfer the f/stop lines from the adapter to the lens. I'd rather not engrave/mark the lens body at all. The forward-most section of the adapter doesn't rotate with the ring so maybe that's a good surface to transfer the stop lines to rather than the lens body. Here's an image of what I have in mind. I probably won't have room to write the stop numbers on that surface, but the dots should suffice - with a little cheat sheet for reference. I'm think of using something like a roller-ball paint pen for the marks once I have the stop positions worked out. Your thoughts???

[© Tom Cooper]

I have had some success marking textured metal and hard plastic surfaces with fingernail polish.

For best results, avoid cheap fingernail polish, and get a set of finer brushes than come with the polish. The brushes that come with the polish are too coarse for detailed work. You will not be re-using the brushes, so there is no harm in getting cheap ones. Small amounts of spillage can be cleaned up easily if wiped off _immediately._

It would work really well putting the lines between the ridges, but not so much trying to create an accurately placed nice round dot, especially if you want all the dots to be the same size. Time is a critical factor when working with nail polish. A bottle that has had the cover off for half an hour is going to be thicker and harder to work with. A bottle that has been opened for an hour is trash.

Also, I was thinking as I was reading that you might not be able to put specific f/stops on the adapter. That's because the positions for the same f/stop may be in different places for different lenses. You might want to confirm this before you do anything permanent.

Tom

[Kevin Childress]

Thanks for the input, Tom!

© Tom Cooper wrote:

...and get a set of finer brushes than come with the polish. The brushes that come with the polish are too coarse for detailed work.

Agreed on this. And its turning out the word "finer" is the operative word here. I'm finding that I'm going to need very, very fine and definitive lines/marks if this endeavor is going to be meaningful. Illustrated at bottom ...

© Tom Cooper wrote: 

Also, I was thinking as I was reading that you might not be able to put specific f/stops on the adapter. That's because the positions for the same f/stop may be in different places for different lenses. You might want to confirm this before you do anything permanent. 

Exactly right. As a matter of fact I won't be able to mark the adapter with f/stop numbers at all regardless of which lens its on. I'm finding that once the lens is reversed one has to apply a lot of difficult calculations to determine literal/accurate f/stops for the reversed optics and reversed entrance and exit pupils. Here's one long, very detailed explanation if anyone wants to read. The math is far beyond me so I won't be marking the adapter with any numbers at all. But I will be marking the adjusting ring with lines or dots and placing one dot on the forward bezel. I was testing yesterday using tape just to get a rough feel for making adjustments and it dawned on me that I only needed one line or dot out front. Here's the good news: In my first round of tests it does appear that I can get sharper pixels by stopping down the reversed lens instead of the main lens, which is not what I've been doing (another long and very detailed explanation here). The 5 lines you see on the adjusting ring represent the full range of the lens' aperture (which would be f/1.8 - f/16 in normal use). I measure the total range of rotation at only 6.5mm so I'm working within a very tight range. The middle line, or "line #3" as I know it, is producing the sharpest images so far. In normal use that would be ~f/8. The light I was using was AC power continuous light that I would use in some macro projects. With that light I'm seeing a consistent 1 2/3-stop exposure gain on the camera's exposure meter when adjusting to the 5 lines you see. I want to tighten that up to 1-stop increments. So I might end up with 8 or 9 dots or lines by the time I'm done which is a lot for a 6.5mm window! I'll then find the 'sharpest dot' and use that moving forward.