Coin Photography Question

MarkInDavis

I took a bunch of photos of my slabbed coins yesterday. As usual, it was lots of headaches. I can't seem to automate the process. I did get photos and you'll see some in future posts.

Now for my question. I know little about cameras. I'm shooting with my son's Nikon D40x (D60 now) and I'm using the 18-55mm Nikon lens that came with it. (He doesn't have a macro lens). I set the thing to 55mm and move the coin as close as I can focus. I was taking a lot of photos so I wanted to use auto-focus which worked fine when I set the camera to auto, but shot with f/5.6. My understanding was a smaller aperture (higher f - like f/10) would give me sharper shots. When I went to aperture priority and tried to shoot at f/8 or f/10, the camera would not auto-focus. I could manually focus and the camera would take a photo with shutter speed of about 1/25th sec. When I used all auto, it was f/5.6 1/125sec. Why wouldn't the camera auto-focus when I used aperture priority? By the way when using aperture priority, the ISO was set to 100. In auto mode, the camera chose an ISO between 100 and 200 but usually closer to 200.

Here are a couple sample photos. The Morgan was manual focus aperture priority f/10, 1/25th sec, ISO 100. The Walker all auto f/5.6, 1/125th sec, ISO 180. To me, the Walker is a little soft. I want a sharper appearance.

mrpotatoheadd

<< <i>My understanding was a smaller aperture (higher f - like f/10) would give me sharper shots. >>

My experience with film SLRs is that exposures using either F stop extreme (open or closed) were not as sharp as using a a setting couple of stops opened up from the minimum.

PawPaul

pretty good pix I think !

LindeDad

I think that the camera focused on the slab not the coin. Normally in Manual focus you can tell the diference when focused on the devices or the field in the difference in the lustur level. I too use the auto mode but only when doing the whole slab shot for eBay listings. Manual all the way on close ups.

blu62vette

If you are not a very experienced camera person, dont be afraid of using auto. Practice on that and then start to test other methods later.

blu62vette

BTW....what is that 1880 coin?

MarkInDavis

<< <i>BTW....what is that 1880 coin? >>



It is an 1880-S PCGS MS64 PL. The reverse falls just short of DMPL I guess. The obverse is a no-brainer DMPL.

mgoodm3

not sure what the lowest aperture is at 55mm, but as you focus closer you lose light and the working aperture is actually higher (called effective aperture). When the effective aperture get a little higher, say much above f8, the auto focus will not work properly anymore, not enough light for it. That means that autofocus doesn't tend to work well for macro. The aperture you set the lens to doesn't really make a difference for the auto focus since the lens is wide-open when not shooting and deciding on the autofocus. It only closes down to make the exposure. The autofocus issue is probably just that it gets a little flaky as you focus close.

the sharpest aperture will typically be in the f5.6-f8 range for most lenses. This setting is a bit muddy if the camera shows effective aperture in the viewfinder - nikon macro lenses do this. You will see the aperture setting in the viewfinder change as the focus is changed. may not change a lot with a normal lens if it does do that. If it doens show effective aperture, you will want to set it to somewhere in the f8-10 range.

You will get a little faster shutter with a higher ISO. You won't likely be able to tell much difference between 100 and 200. As ISO goes higher you will start to see more noise in the images.

nice morgan

messydesk

The issue with the Walker and focusing is that much of the coin is in the dark. If the working distance permits on the 18-55, get the lights in closer, which will light up the coin more and make it easier for the camera to autofocus or indicate correct focus. The maximum aperture at 55 mm is f/5.6, which starts to make AF challenging unless there is a lot of light. Also, realize that the fine detail of a Morgan dollar is sharper than that of a Walker. When I'm assessing critical focus of shots I take, I look at scratches, hits, and hairlines and play the optometrist agame ("better, worse, about the same"). If the lens is the 18-55 VR lens and you're on a tripod or copy stand, turn the VR off (yes, off). Finally, I did an experiment once with the "Exposure Delay" mode on my D80, which trips the shutter 400 msec after flipping the mirror up. This has a significant positive impact on sharpness for 1/10 sec. exposures. I don't know if the D60 has this feature.

lcoopie

Mark,
wouldn't a higher f stop
give a greater depth in focus,
especially with a macro lens? (not this case)

mgoodm3

higher will give you more depth of field, but you will pay the price with less sharp images. At long (non-macro) range bumping up the aperture works OK becuase 1) you get a lot more DOF at long range and changing it makes a bigger difference, 2) the lens will have more resolution to work with and losing a little bit by bumping up the aperture doesn't hurt you any. WIth macro, the increase in the DOF is less and the fuzziness is worse.

lcoopie

thanks Mark