zoom lens question

[powell7]

hi all,not been doing this long so i have a question.
i`v got a 75-300 sony lens http://www.jessops.com/online.store/products/35807/show.html.i know theres a huge difference in price and size but when this http://www.jessops.com/online.store/products/46812/show.html says its a 300mm,will this only zoom in as far as mine or just give much better quality ?
i`m asking because i`v seen all these monsters but when i look at the tag they dont seem to be much stronger than mine or am i totaly wrong like normal ?

 

[JackMcIntyre]

The big 300mm is a prime that doesn't zoom, its a fixed focal length. They're generally much bigger because they have a much wider Aperture, in this case it has F/2.8 as opposed to the F/5.6 of yours.

I'm not sure about Sony lenses as I've never used any but in the Canon range - generally speaking, the more expensive the lens is - the better its optical quality.

 

[powell7]

thankyou. so would the big one produce a closer image than mine,by this i mean go in closer to the subject i.e a bird ?

 

[HoppyUK]

If you set both lenses at 300mm f/5.6, the images would be identical in terms of what you see (both framing and depth of field).

The difference is that the 300mm prime can go four times brighter at f/2.8 (compare the size of the front glass). Plus the 300 is very high quality and the image would have noticeably more sharpness and contrast.

Edit: minimum focusing distance is something different - you'll see it in the lens spec. It's usually not a deal breaker as it's easy to get any lens to focus pretty much as close as you like with a simple extension tube on the back, or maybe a supplementary close-up lens on the front for a few quid.

 

[powell7]

thats great,thankyou for your help.