In focus moon
Tonight I took several pictures of the Super Moon, I am a novice practicing in manual mode. Can someone explain why these photos are drastically different. The out of focus was shot with a Nikon D3200 55-200mm telephoto kit lens at ISO 200, 200mm, f/10, 1/125 sec. The in-focus ISO 200, 200MM, F/9.0 1/400 sec. I don't think the settings are drastically different are they?
The biggest clue is the fact that the out of focus shot makes the moon appear to be significantly smaller than the in focus shot. With many Nikon telephoto zoom lenses as the focus distance is reduced the field of view is expanded. Some versions of Nikon's 70-200mm f/2.8 series of lenses have field of view of only about 140mm at the minimum focus distance when set at the maximum focal length of 200mm. This is referred to as focus breathing. If the effective focal length does not change, then the out of focus shot would make the moon appear slightly larger.
Based on the relative sizes of the two images and assuming both are at the same focal length when shot and at the same enlargement it seems something caused the focus distance to be greatly reduced in the out of focus shot.
It is almost always necessary to manually focus astronomical subjects. The AF systems in most cameras can't focus on small, dim objects in the sky. Even when they can, their margin of error is usually too great to give the kinds of results most people desire when doing astrophotography. Because infinity focus changes with focal length and other environmental factors, most lenses allow the focusing elements to go past infinity. Many lenses with high speed AF motors allow an even greater buffer past infinity focus so the focus motor is less likely to bump against the end of travel when trying to focus at infinity.
With digital cameras manual focus using the viewfinder can be difficult even in bright light. It's even harder in dim light. Fortunately there is a better way if your camera has a Live View shooting mode. Set the lens to "manual focusing", use the Live view magnifier to zoom in on a section of the sky (in your case the moon) and manually focus until it is as sharp as you can get it. Since AF is turned off, the lens will stay focused at that distance as long as the focus ring is not moved. You can then exit live view and shoot using the viewfinder to compose. Just be careful not to touch or move the focus or zoom rings on the lens.
