My light meter is not reading accurately in Manual setting. My photos are totally washed out and the shutter is very slow. This just started happening. Could I have accidently switched something in my settings? I'm not very technical but I've not had this problem in the past.

Ahh, in camera or in a photo editor?

Ex. of in Camera

Adjusting the Image Brightness for Shooting Setting the Exposure...

Ex. of photo editor like Lightroom (a video!)

Lightroom 5 tutorial Improving exposure and color with the Adjustment...

You did not provide enough information to determine what your problem is. For example, were the pictures all light or all dark. Knowing this lens, I will assume that they were all dark. So...

1) This is a very, very slow manual-focus lens. It will not auto focus. It must be manually focused very precisely because it has virtually no depth of field.
2) Depending on your camera, your internal light meter may not work. On my camera (Nikon D-90), it does. If it does not on yours and I suspect that may be your problem, you're going to have to shoot everything manually, i.e. setting the shutter speed and lens opening yourself. You can use your internal light meter to help you get started by taking your light reading before you install the lens...preferably using the aperture only setting where you set the aperture at f8 which I think is the speed of the Opteka and let the camera set the shutter speed. Make a note of the shutter speed then attach the Opteka to the camera and mount the lens on a tripod with the camera attached.
Then set your camera mode to manual and set the aperture to match the lens (f8, I think). Set the shutter speed at the speed you noted earlier. Shoot a picture using a remote shutter release or the self timer. This lens is so slow that unless you're in exceptionally bright conditions you will get fuzzy pictures due to camera movement at full zoom of 1200m and above if you're using the 2X doubler. I would start shooting at minimum zoom of 650 without the 2X doubler. Shoot a picture. and check the result.

You should have an image but it may be too light or too dark.

If its too light you'll need to increase the shutter speed or stop down the aperture to, say, f11...or both. Make the adjustment and shoot another picture. Remember that if you increase the aperture, you increase your depth of field, making focus less critical. If you increase the shutter speed you make camera or subject movement less critical.

If it's too dark, you can only increase the shutter speed because you can't open the lens any wider than f8. Make the adjustment and shoot the picture.

Keep doing this until the pictures are the way you want them.

This is a decent lens for the price and worth the little money they cost if you can't afford $10,000 plus for a high quality telephoto lens of this size. I would forget about the 2X doubler because as others have said, it further reduces the speed of an already very slow lens with such a high rate of magnification that a knat landing on the lens could cause the picture to blur from movement.

Okay lets put some "joy" back into your photo's The reason you aren't getting anything is because your shutter speed is to fast. Your setting I think you are trying to say are F5.6 100 ISO and 1/100 shutter speed "M" manual setting. Actually if you looked closely on your "nothing there" there would be something. Anyway, Moon shots as simple as they look are anything but simple. The earth is moving and you are trying to take a still shot. I don't know where you are on this earth and every star system is different. Starting with a good solid tripod, next the lens needs to have a great enough focal length so the moon covers 2/3rds of the view (first shot) ISO 100 is good. In manual mode look at your light meter try to have your F-stop at F8 or F11 and adjust the shutter speed for proper exposure, you may need to adjust your aperture up or down once you have a "normal" exposure either increase your shutter speed or preferably stop down the lens two stops.
Your camera will meter down to 30 seconds if it goes below this then this is where you take your start (first shot) meter reading and count how many stops of light you require beyond 30 seconds.
For practice though attempt to stay within the 30 seconds by increasing the aperture but not wide open say F8 is as low as you go, need some speed adjust the ISO up to ISO 200 then ISO 400 don't go beyond this because other factors come into play at this point. the thing is you need to establish a metering point then stop down two stops and see what you have as far as exposure.

I know this may all sound really complicated but it's not the most important thing is to have a good tripod use F8 as your widest aperture don't increase beyond ISO 400 and keep your shutter speed at 30 second or above. Another problem that will occur is focus actually the lack of, your camera requires contrast to focus one you have established this shift the lens into manual and recompose your scene. What we aren't done yet don't touch the camera when your release the shutter. Use the 2 second time delay to give the camera time to stop vibrating after the shutter has bee depressed remove your hand DON'T touch it until the picture is finished. If it were me I'd be looking at doing a few landscapes at night to get use to all this stuff then tackle the moon so to speak. In the mean time here is a picture of The Fork Of the Thames in London Ontario Canada.
Picture here

To take the kind of pic you want, you need a camera with manual control like a DSLR. You need to set the ISO to 100 and the aperture to f16 or f22 so that the shutter slows down to at least 1/4 second.

needs repairing at a qualified shop
when was it last cleaned or serviced ?
if you think the camera is worthy, since its old how much is it worth to you vs a new one

You can't meter through that lens. If the images are too dark, either slow down the shutter speed or open the aperture. Keep going until the picture looks okay on the monitor. If you know how to use the histogram, that's even better. If you go too far and get images too light, reverse the process (faster shutter speed or smaller aperture).

If you have another light meter, you can use that to get a ballpark exposure to start with. Alternatively, take a reading with your other lens at the longest zoom.

OM-20 was basically a upgraded OM-10 with the manual adapter built in and a number of other refinements.

The viewfinder has LED's to show the shutter speed recommended by the camera's lightmeter for the ISO and aperture selected. It also has an exposure compensation indicator (the +/- symbol) and an indicator for flash ready which doubles up as a post-exposure flash confirmation. There is also the indicator lamp to show manual mode has been selected. OM-10 lacks the manual mode lamp and the +/- indicator.

Like the OM-10, the OM-20 is primarily an aperture priority automatic camera. In this mode you set the ISO film speed, choose which aperture you wish to use (with the ability to use the lens depth of field preview button) and then the camera selects the correct shutter speed. The +/- exposure compensation control allows the user to tell the camera to modify the recommended shutter speed by up to two stops either way.

In manual mode, there is no manual metering. The light meter behaves exactly as it does in aperture priority mode and the viewfinder shows the recommended shutter speed and not the manually selected one. Correct metering is therefore a case of adjusting the aperture first, and then choosing the correct shutter speed indicated in the viewfinder. If the user then decides to select a different shutter speed, then the aperture ring must be adjusted to maintain the correct exposure. For example the aperture is set to f8 and the camera recommends 1/60th of a second. The user decides that a faster shutter speed is required and chooses 1/250th, but the viewfinder remains showing 1/60th. In order to keep the same exposure value the user must open the aperture by two full stops to f4. The camera's light meter will detect the new aperture setting and providing the light on the object is unchanged the viewfinder shutter speed display should now show 1/250th as well to confirm the correct adjustment. Alternatively, the user can choose the shutter speed first by looking at what has been set on the control ring (or by turning the ring to the end of its travel and then counting the clicks from there as all experienced OM users do) and then turning the aperture ring until the shutter speed shown in the viewfinder matches what's been manually set.

It all sounds clumsy and complex but is done far more quickly than I've taken to type this and becomes second nature.

Aperture priority metering is selected on the camera by choosing AUTO on the mode selecter. In this mode the shutter speed ring has no effect and the viewfinder always displays the automatically selected shutter speed.

The exposure compensation dial (at the back) doesn't work when you're in Manual. In Manual, you set the shutter speed and aperture to get an image with the amount of over- or under-exposure you need. In the view finder, the "exposure meter" at the bottom shows how much light there is where the lens is pointed. When it shows what you called "2-stops", its really underexposed. Thus your black images. You need to increase ISO, open the aperture and slow down the shutter speed (or a combination of these 3 options)

Set your camera to P or full-auto. Do the photos turn out ok? If they do, then there's nothing wrong with your camera and you just need practise on the Manual mode.

snoopytwo, jmv23 & guests,
Sounds like you have been taking photos in both auto & manual modes, make sure your f-stop is set at the range it needs to be to allow enough light for the camera to take the photo. Since the lens and the camera communicate, if the lens is closed down & not allowing enough light the camera will not take the photo - does that make sense - Look at the metering in auto mode and see what the camera says the conditions are for a specific lighting condition check to see if the lens has a aperture position for Auto, usually a dot on the lens ring to align with a setting in red or green (likely a F-22) depending on the make of lens, that has been moved to some place in the middle and not returned while trying other manual settings so the shutter won't release because the camera is told by the lens there is not enough light or slow enough shutter to take this picture.
randy320sgi

Can u provide us with a sample so that we can understand what u mean by by "washed out"