The macro lens is still the Tamron Sp 90 but ...

[JBW]

As the time draws near I am wondering about the Tamron 70 - 300. Not that it is not a quality lens but it may not be the best for my needs.

I would like a good lens for moon and star-field shots. Manual focus is fine and the Sony Alpha a58 comes with a good steady shot system. And of course the lens must mount to a Sony 'A' mount.

Brian

[Manfred M]

As the time draws near I am wondering about the Tamron 70 - 300. Not that it is not a quality lens but it may not be the best for my needs.

I would like a good lens for moon and star-field shots. Manual focus is fine and the Sony Alpha a58 comes with a good steady shot system. And of course the lens must mount to a Sony 'A' mount.

Brian

I don't take a lot of moon and star field shots (although I am studying star fields and might start tackling that when I get the chance to get to a "dark sky" area). Night shots of this type (especially the stars) are taken with a tripod, which means your steady shot system will need to be turned off to maximize sharpness.

If all you are planning to do with a longer lens is to do this type of shooting exclusively, I might agree with manual focus, but if you are planning to do some normal shooting (birds and bugs, etc.), then you definitely won't want manual focus. You can always focus an autofocus lens manually (and I do), on the other hand, a manual focus lens always has to be focused manually, and especially with a longer focal length lens, that is not the easiest or fastest thing to do.

[rudi]

For wide field star shots I do use the 100mm f2,8 macro lens. For a 'bit closer' I do use the canon 100-400 at 400mm.
Take a look at Ian Norman website at http://www.lonelyspeck.com/
He also shoots with the Sony system.

[Tringa]

A 300mm lens will give you a reasonable shot of the moon, if you do some cropping. This shot was taken by a camera with a 1.5 crop factor and using a 55 -300mm zoom lens at 300m. It has been cropped fairly heavily and I think it is about as far as I can go.

If you want to take shots of star fields with a static camera (ie not guided by an astronomical mount or in some other way) I do not think a 70-300mm lens will be much use.

To prevent the stars appearing a trails (due to the rotation of the Earth) the 500 rule is a good place to start -

500/(focal length of the lens x crop factor of the camera) = max exposure in seconds to prevent trailing.

At 70mm and with a crop factor of, say, 1.5 the maximum exposure is about 4.7s (500/(70x1.5)). I think to record stars with an exposure of around 5s the ISO would need to be very high and/or the need of a very big aperture. As the focal length get longer the situation get worse. There is also the issue that the area of sky covered by longer focal length lenses is quite small.

The lenses that are well liked for star photography are those with short focal lengths wide apertures.

This is another guide from Lonely Speck which is very useful. http://www.lonelyspeck.com/lenses-fo...y-photography/

Dave

[JBW]

And things just got more complicated. At 16:00 this afternoon for the first time in 15 years we spotted a type of heron flying into our bamboo. I couldn't get a shot because I don't have the lens. it was about 30 meters away and just maybe with a good auto focus telephoto I could have got it.