Sometimes photos are overexposed using A or P mode on my Nikon D80 with 18-200 mm lens. I remove the lens, then re-attach it and all is fine. What is happening? Poor contacts?

Fisheye is the extreme of a wide angle lens. I think you are not using a fish eye lens, but a fish eye adopter. That is a lens that will "shorten" the focal length of a lens most of the time with 30 % sometimes with 50% when you put it in front of your lens. So you could make a 24 mm lens look or act like a 12 mm.
On your tele lens this only will slightly shorten the 55 mm, but even 50 % of 55 is 27 mm and can't be seen as a fish eye.
I think when you put this on a short lens, the picture you get will be round, like you were using a real fish eye.

What mode are you shooting in? if in manual, your shutter speed is to slow and your photos are probably overexposed. or if you are in one of the program modes you probably have exposure compensation turned up very high. so turn down your exposure compensation down by holding the button that has a plus and a minus on it and turn so that it is set to 0

The Rokinon lens does not have the electronics to communicate with the camera. You must set the camera to the Manual exposure mode in order to use this lens. You control the shutter speed on the camera and the aperture by turning the ring on the lens. You also will not be able to use the camera's exposure meter; you can use the LCD display and the histogram to fine-tune the exposure.

Refer to the manual for full details on using the Manual exposure mode.

Do you have it in aperture or shutter priority modes? If so, do you also have exposure compensation set to overexpose? If you have it in manual mode, then you will, of course, have to make the adjustments each time.

If you have it in auto mode, it should be correcting the exposure for you, unless you have manually set the ISO to some very high level. Another potential issue would be that you have selected spot metering and you are metering on a very dark area, hence the camera is overexposing to make up for that.

I'd recommend setting the camera to auto-ISO and auto exposure and see how it works. If that checks out, then you can correct any settings in other modes.

What lens are you using ?
For all functions to work you will need a cpu lens - ie; a hsm or afs lens,these are lenses with built in motors.

Also check the switch on the side of the lens is switched to (A)

Blades are dirty.

Test by setting up for 1" shoot and look into the lens.
If blades close late then they are in need of an PM.

I repairs & serivices cameras, flashes, lens and studio lighting.

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Switch to M (manual) mode.

Inside the lens mount is the stop down lever. As you look at the camera, it is at 9 O'clock. Move it a couple of times up and down. It is probably stuck.

Is the switch on the side of the lens set to manual or auto? Sometimes it's the little things like this that we don't notice.

Hey timrowan,
What you’re seeing is your playback mode is set to highlight, which flashes all the highlights (bright areas) of your images that are overexposed. If you don't like this viewing option you should be able to change your viewing mode by pressing mutiselector button to the right or left until you get to normal viewing. I hope this helps!

Sincerely,
Allan
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