I am a novice photographer looking to get into DSLR photography. I have an old Maxxum 5 and a couple lenses for it: a 75-300 zoom and a 28-80 zoom. After reading this question, it is clear that these lenses will work with a Sony a57 (let me know if I'm confused on that point). My question is, is there any reason to buy the a57 with a new lens, or are my existing lenses just fine? It looks like I can purchase the Sony with an 18-55 lens for about $100 more than just the body. Other than the shorter focal length, which I don't care much about at the moment, will this lens perform better than the 28-80 I already have? It looks like the lens will cost me about $200 separately so if it is worth getting I am better off buying it with the body. But if it isn't better than my current lenses I'd rather save the $100.
The A57 - which got a DP Review Gold rating is a superb photo making system (as opposed to just being a camera) and you will be astounded at what it can achieve once you get used to it. The seamlessly integrated live view made possible by the Pellicle mirror, what-you-see-is-what-you-get EVF and constant phase type focusing transforms the overall taking experience compared to that from a "normal" DSLR. Note that more than for some cameras, the A57's RAW output is far better than JPEG*.
Overall, you will not regret buying the 18-55 lens in the circumstances.
The Sony 18-55 kit lens is better than may be expected with 78 user reviews giving it a 3.99/5 average rating. In this case it is superior to 3 of the 4 Minolta lenses in the 28-80 range so is worth having. Sharpness is good for an entry level lens, with "build" being what you'd expect in a modern plastic entry level lens.
While it is a matter of personal preference, when I am doing casual candid 'street photography, for general scenes I most usually use 18mm focal length on an APSC camera. The change from 18mm to 28mm gives you 18/28 = 64% of the width and angle of view and only 40% of the area. The difference is very substantial. 18mm on an APSC (equivalent to 27mm on a 35mm full frame) is on the upper end of what is classically accepted as "wide angle". 28mm APSC = 42mm FF is definitely not.
The following applies more genrally. In many cases my advice would be that the old Minolta lenses are good value for money and superior to kit alternatives. This casse is a welcome exception.
Quality wise the older Full Frame Minolta lenses are liable to be of equal to better quality than entry level "kit" Sony DX lenses.
You can find user reviews and discussion for all things Minolta, including much information re lenses at www.dyxum.com (aka Dynax + Maxum). DYXUM homme page here
Lens page here - accessed by tastefully small and easily overlooked top right menu entry on home page.
Use selector guide at right to narrow range.
There are 4 x 28-80mm lenses listed, with ratings of 3.44, 3.5, 4.22, 3.62
On the review page note where it says "total: 22 reviews". The "reviews" is a live link - click it and you get to read the 22 reviews.
Do I "need" an 18mm lens when I have a 28mm one?
An 18mm lens on an APSC camera with a 1.5 crop factor is the equivalent of a full frame 35mm camera with a 1.5 x 18 = 27mm lens. A 28mm lens on an APSC camera is the equivalenbt of a 42mm FF lens. The difference is extremely significant.
The 4 photos below were taken "while wandering around" using an APSC camera with 18mm fical length setting. The rectangles marked on each show the area would be covered if a 28mm lens had been used from the sam position. While "foot zoom" will allow you to obtain approximately the same result with a 28mm lens, circumstances and sheer physical constraints often make this completely impractical. Also, a 28mm lens shot covering the same area will change the perspective - for better or worse.
The top left shot has the camera held at arms length. MUCH longer arms would be needed to use a 28mm lens in this manner.
Some have the 28mm effective area marked - in others it can be readily envisaged. Most of these are street scenes where a 28mm shot would have been limiting or impossible.
If you don't think you'll go wider than the full-frame equivalent of 42mm, save the $100.
I'd say you've got two things to consider:
First, field of view:
The sensor on an a57 is an APS-C size, which is smaller than the full 135 format frame that your Maxxum 5 would have used. So your lenses on the a57 will be effectively 'longer' than they were on the Maxxum. This is a dark rabbit hole to get sucked in to. For more, see What is the difference between focal length and crop factor? and What is “angle of view” in photography?.
With the 1.5x crop factor, your 28–80mm will have a field of view like a 42-120mm on film, and your 75–300mm will be effectively a 112.5-450mm lens. On the a57, the 18–55mm kit lens will have a near-identical field of view (27.5–82.5mm) as your 28–80mm did on film.
So if you liked shooting wider than 42mm (on film), you won't have that wider field of view available with your current lenses on the digital camera.
As for size and weight… well, typically I'd say that lenses for the smaller APS-C sensor can be smaller and lighter than lenses with the same field of view on larger formats, but according to Dyxum the 18-55 is actually slightly heavier than your 28-80. So I guess there's no weight savings to be had.
So, yeah, if you didn't ever use the 28–42mm range of your 28–80 zoom, save the $100.