Worth Buying?

[Cricketboy]

I'm looking for a telephoto lens on a budget. I want to photograph the moon during the day, and maybe at night. I'm currently looking at a 70-250mm f/4 lens. Would this be adequate with a 2x teleconverter on the camera? Would that put to much stress on my camera's mount with 1 or 2 teleconverters without a tripod mount on the lens?

BUT, I saw this lens, but it doesn't seem like a good lens. Kimunor 500mm Lens F/8.0 Canon-Pentax-Minolta Mounts - eBay (item 320639689908 end time Jan-13-11 21:47:40 PST)

It's fixed at f/8, and I heard it only has two elements, and someone called it a "chromatic aberration tube." Probably not worth buying?

 

[Jeatley]

How much are you looking to spend and what camera do you need it for?

I took this image a few weeks ago with a tripod and nikon d90 and sigma 70-200mm 2.8

PS not sure but I am pretty sure you can not put 2 teleconverters on a camera.

Also I would have to say that that KIMUNOR is not worth buying

 

[Cricketboy]

I need it for a Pentax K1000 bayonet mount. I've been looking at this one for a while. Pentax PK Mount Rokinon 80-250mm Macro Zoom f4.5-4.8 - eBay (item 230569996709 end time Jan-08-11 20:58:20 PST)

 

[John Mc]

The link you posted is pritty much a telescope,just get a 2x tc and you should be set.

 

[maris]

A useful rule is the size of the moon's image is obtained by dividing the lens focal length by 100. A 500mm lens will give you a 5mm diameter moon image, for example.

For a fixed camera, like on a tripod, earth rotation will shift a moon image by its own diameter in 120 seconds. Really sharp moon images need a fast shutter speed or an equatorial tracking mount. For example a moon photographed with a 500mm lens and then enlarged to 40mm diameter on an 8 X 10 photograph needs a shutter speed of 1/2 second or faster to look sharp.

 

[Cricketboy]

A useful rule is the size of the moon's image is obtained by dividing the lens focal length by 100. A 500mm lens will give you a 5mm diameter moon image, for example.

For a fixed camera, like on a tripod, earth rotation will shift a moon image by its own diameter in 120 seconds. Really sharp moon images need a fast shutter speed or an equatorial tracking mount. For example a moon photographed with a 500mm lens and then enlarged to 40mm diameter on an 8 X 10 photograph needs a shutter speed of 1/2 second or faster to look sharp.

Thanks! I'm assuming you would want to use the widest f stop you can? I ended up getting an f/4.5 80-250mm lens. I also found out from another thread that you can stack teleconverters, although not recommended due to the light loss.