I am looking for a T4 or TX mount in a Pentax K mount

Sorry, cannot locate San Antoino

Sigma makes their lenses with a variety of mounts. If the lens has a Pentax mount then it will work with your K20d.

Sorry, no. If it fit onto a Pentax camera then the lens has a Pentax mount. The Nikon (I assume you mean the D80 digital camera, or perhaps the N80 film camera) has a Nikon mount. Since the Nikon mount has a deeper flange distance than the Pentax mount, there are no adapters available to allow you to fit a Pentax-mount lens onto a Nikon camera.

Vivitar makes lenses with a variety of mounts. Lenses with the Pentax K-mount can be used on the K1000, lenses with other mounts can not.

Olympus lenses will not mount onto a Pentax camera.

You can sell the lenses, give them to someone with the appropriate camera(s), or use them as paperweights.

Unfortunately, it is not possible to mount Minolta lenses on a Pentax K mount camera and retain either auto-focus, metering, or the ability to focus at infinity.
The reason for the loss of the ability to focus at infinity is because the distance from the mount to where the image forms on a Minolat lens is 43mm, whereas on a Pentax it is 46mm, so the Minolta lens glass would need to be 2mm into the body of the Pentax camera in order for the image to form on the sensor (i.e. have a clear image that is in focus).
The only solution to this is to purchase an adapter with an optical element such as this: http://photo-adapter-llc.amazonwebstore.com/Zykkor-Minolta-MD-Lens-to-Pentax/M/B004PB8142.htm?traffic_src=froogle&utm_medium=CSE&utm_source=froogle This will allow you to focus at infinity, however you will have to use stop down metering and manual focus, as the electrical contacts will not connect. Also, you can expect a slight loss of image quality when using an adapter.
I personally have a few Minolta lenses that I have wanted to use on my Pentax, so I understand your pain. It is a shame they don't work better.
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The hard part will be getting a T-mount for the old Pentax screw mount. If you already have one, you should have no trouble. It won't even matter which one you buy, since you'll be removing the mount that comes with it and using the old Pentax screw instead.

If you don't have a T-mount, then you're going to have to hunt for one. You don't want to buy anything that's marked "for Pentax", since anything current will be the Pentax-K bayonet mount, not the old Pentax screw mount.

Quantaray makes lenses with a variety of mounts. If the lens has a Pentax mount then it will fit onto your camera. If it has a Canon mount, for example, then it will not.

Hi rlopez117,

Congratulations on the aquisition of such a great vintage camera!

Pentax cameras use a mount known as M42. This means it is a 42 millimeter diamater. You may also find this referred to as the Pentax mount, as Pentax (Asahi Optical) made this popular in the United States. With any camera, any lens you purchase should match the mount of the camera in order to be used together.

Thank you,
Jason,
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Greetings fffffjffffff,

It would really depend on the mount the previous lens has versus the mount on the new body. The advantage is that majority of the time you can utilize lenses on different bodies of slr cameras, as long as you stay within the same manufacturer.

Thanks,

Dorothy
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No. Unless the lens has a generic T-mount with a Minolta adapter. In that case you can replace the T-mount with a Pentax adapter.