2x and 3x Teleconverters using 500mm 1:8 Lense

The use of a tele-converter will invariably reduce your f/stop count. The magnification value will correspond with the loss of f/stop. Reducing shutter speed wont change the f/stop count. For the lens you described, Annette, I see no problem with using a 2x tele as the f/stop will be around 4. That's more than adequate for such focal lengths

Art X
f 1:8 is my widest lense opening f 1:8, 11, 16, 22 , 32

With a 2x converter your aperture will change from f/8 to 6/16. Focussing will be very difficult. You can indeed use a slower shutter speed to compensate, or higher ISO but you will always lose 2 or 3 f-stops. No way to avoid that. Must be possible with a sturdy tripod and some luck with regard to focusing.

Can I use a slower shutter speed instead of losing 2 or 3 f-stops

No, you can't; the aperture really does change and you can't stop that. You shutter speed will be lower regardless to cover for that loss. So, it's going to require a really decent tripod for sure. As for the quality of a 500 f/8 with a 2x TC - I don't believe it will be very good; one should wonder if it is really worth the effort.
For what would you need the 1000 to 1500 mm length, combined with very slow film?

my mistake I misunderstood the f/stop count for this lens. Josh has correctly advised

It will work, but you will have to very slow shutter speeds with ASA 100 film. Best to use a very good tripod.

"... one should wonder if it is really worth the effort."

Discouraging advice I'm sure, but accurate advice nonetheless. But I guess it's your film to waste if you want to give it a go. But I expect you will be very disappointed with the results.

It sounds like you are using a 500mm f/8 preset / T-mount lens. If so, such a lightweight super-telephoto combined with a 2X teleconverter is going to be very, very prone to vibration. You're going to need more than a decent tripod ... you'll need a rock solid tripod with a rock solid head. Better still, you'll probably want a rig where you can brace both the camera base and the tripod mount on the lens.

In full, bright noon day sun with ISO 100 film and a 2X converter, your highest possible shutter speed is going to be around 1/60 sec, since your maximum effective aperture wide open will be f/16. But you're going to want to stop the lens down at least 2 stops to compensate for the aberrations from the teleconverter, so now your highest possible shutter speed in full sun is 1/15 sec with a 1000mm lens. That means using mirror lockup (and wasted shots on the F) to have any reasonable hope whatsoever of a passably blur free image. Doesn't sound like a lot of fun to me, but if you want to give it a try, damn the torpedoes and full (very slow) speed ahead. :)

I wouldn't even think of trying a 3X converter on such a lens.

Good luck! :)

A thought on focusing issues with such low light transmission. Some of the Nikon film cameras have user interchangeable focusing screens, and if yours does and you can find one for TELEPHOTO 400mm or better (they make it quite easy to focus in low light). I use that setup with my Nikon F3 and a 400mm f6.3 lens stopped down to f8-11. Unfortunately, the telephoto focusing screens have to be changed back for normal lens usage, as they vignette the viewing area of shorter focal lengths than they are designed for.

Ok shooting on top of a small mountain to the city below what ASA Film would yeld best results? In very bright Sun.