Posted 12/01/2012 8:39 pm
OK, here's the scoop.
Your 55-250 isn't relevant for coins. Its' minimum focus distance of approximately a yard is not going to do it for you.
The 18-55 has a usable minimum focus distance of about 12", and I've gotten sorta-favorable results with the exact camera-lens combination you're using. From my experience (and understand, other combinations of zoom and camera distance might work too):
I used it zoomed all the way in (55mm), with the front face of the lens when zoomed that much about 15"+ from the coin. I'm posting from memory; it could be slightly different either way. Shooting settings - you're going to have to learn these for your situation, no choice - were roughly ISO 400, f/8 at 1/80 with the lighting I had at the time, which was inadequate so you'll use faster exposures if your lights are better. But I was able to achieve sharp focus, and fill almost 2/3 of the sensor with a Morgan dollar leading to an actual coin image of 1800px diameter. That's enough to post whatever the heck you want here, and get applause for your image quality.
I used that combination to maximize the distance from the coin, which makes lighting a lot easier. You could do 18mm and set the camera maybe 10" the coin - somewhere in there - and possibly achieve better results, but lighting would be compromised.
Your 55-250 isn't relevant for coins. Its' minimum focus distance of approximately a yard is not going to do it for you.
The 18-55 has a usable minimum focus distance of about 12", and I've gotten sorta-favorable results with the exact camera-lens combination you're using. From my experience (and understand, other combinations of zoom and camera distance might work too):
I used it zoomed all the way in (55mm), with the front face of the lens when zoomed that much about 15"+ from the coin. I'm posting from memory; it could be slightly different either way. Shooting settings - you're going to have to learn these for your situation, no choice - were roughly ISO 400, f/8 at 1/80 with the lighting I had at the time, which was inadequate so you'll use faster exposures if your lights are better. But I was able to achieve sharp focus, and fill almost 2/3 of the sensor with a Morgan dollar leading to an actual coin image of 1800px diameter. That's enough to post whatever the heck you want here, and get applause for your image quality.
I used that combination to maximize the distance from the coin, which makes lighting a lot easier. You could do 18mm and set the camera maybe 10" the coin - somewhere in there - and possibly achieve better results, but lighting would be compromised.
