Hello From A Chinese Coin Photo Group

Just saw this response today for some reason...

There are two reflections in the lower left:
1) Off the denticles. This is the normal illumination from your light source
2) Off the raised portion of the field. This appears to be coming from a secondary light source. It is almost as bright as the reflection off the denticles so I don't think it is a re-reflection from the coin.

If you are 100% sure there is no other light source in the room that might be causing the problem, then it must be a re-reflection. I also assume the coin is raw, so reflections off the slab can't explain it.

One thing you might try is a black tube around the coin to eliminate possibility of extraneous illumination. Hamm and rocky have done that to good effect and Hamm published results in another thread.

Other than that, a higher angle to the light would keep the reflections down but would also change the look of image quite a bit.




Looks to me like those are die polishing/sanding marks. The areas you're showing are on the edges of raised die elements.




Nice pics. They appear to be mostly axial. I'd like to see them a bit brighter and with more contrast, but as always it's up to the photographer to match the image to the coin.

My "contrast" comments are of course imaging-related, and are independent of the look of the coin, just geared to presenting the best image of the coin. This is a subtle distinction. It's important in an image to ensure proper overall exposure (re: the recent thread https://goccf.com/t/246014&whichpage=4) but also to use the full dynamic range of the jpg medium. To illustrate, I adjusted the dynamic range of the first of your latest images in two ways. First, bringing the black level up until I see just the first glimpses of saturation:



The black level here is 192, so this means you can drop your white level as low as 192 and not see significant over-exposed highlights.

I also lowered the white level to see where the first shadows are lost:



In this image I lowered the white level to 16.

So this means your image dynamic range can be improved quite a bit without crushing blacks or blowing out whites.

Thanks again, Ray. I passed your comments on to the photographer of the Great Wall and the Spaceflights coins. He does not remember whether there was an extra lighting source on the lower left side of the Great Wall coin. Still he was very impressed by your attention to such details.

Any comment on the high mag pictures I posted earlier taken with Nikon objectives? I was kind of shocked when I read about the depth of field in Lefkowitz's book. I started on 10x without realizing what I was facing. Here are two pictures I took with the 10x objective, after a lot of sharping.

coinphotofan hello I worked in the electrical field. we did a lot of pressing 50 ton. with many dies over the years. what looks smooth to the naked eye. you will find is not smooth at all. we worked with various metals it does not matter is never perfectly smooth. it can be close but there will always be lines. from where the dies are made. when the machine them. there are lines. thou they be micro they are there. using the magnification your using. you are only seeing what is on every piece of metal. if you don't see it increase the mag and it will be there.

Thanks for the info!

I believe they are polish lines. Periodically a die will be "cleaned up" with a file, and followed by a finer polish. If you've ever done any metal working, you know that file marks do not polish out easily. While appearing in the protected part of the coin, they are actually on the exposed corner of the die. A closer look at other coins will show that they are fairly common. They can be used as a clue to identify the specific die used to make the coin.



These examples come from a Morgan dollar made at New Orleans. The close ups are of the wreath bow, below the eagle's tail. (Note: the "O" mint mark was hand punched into the die after the rest of the die was prepared, so its position isn't always the same.)

@Chute72: Thanks for the comment and for all the great images.

It is good to know that this image is doing justice to the 10x lens. I realize that for the full image to be sharp, I have to stack. The lens may not even be parallel to the coin. I will take care of these. At the moment, I still have problems with sharpness. Not all my 10x photos show this sharpness. In fact most do not. I am trying to figure out how I can consistently produce this sharpness. I am using a Nikon 5200, with remote shutter release and mirror lock-up. The shutter speed can be as low as 1/6 second as lighting is diffused. I can observe shaking of the camera body when the mirror is raised (and lowered). I am wondering whether increase shutter speed would help. As I have no control of the aperture, a friend suggested increasing ISO.

Another way to eliminate vibration caused by mirror action is to use LiveView. But in LiveView, the shutter speed is limited to 1/30 or faster. I found this afternoon that turning off Manual Movie Settings can override this limit. I still have to try it out.



I discovered that some light is reflected off the inside of the cone-shaped adapter. How can I add light absorbing material?



I have not changed the picture control setting in the camera. It is "Standard." I normally do some sharpening, exposure and contrast adjustment during post-processing.