Old pentax promaster lens
 

I was just offered the above mentioned lens for $100..its a 70mm to 300 zoom. 3.5 to 5.6. Is it worth it? is there a converter for use withe the af100?

thanks for your response

ric

Re: Old pentax promaster lens
 

Adapters are available for just about anything:
Fotodiox Professional Photography Supplies and Equipment

As to worth - I don't know, is $100 worth more than a 35mm-equiv 140-600mm zoom for your uses?

Re: Old pentax promaster lens
 

Ric,

If that's all you can afford that's one thing, but if your goal is to achieve the "fllm look" you won't get there with a lens with a relatively dark max aperture rating - especially that gets darker as you zoom further telephoto.

As a general rule it's best to have a zoom lens that can hold it's max aperture throughout it's range, such as a 70-200mm f/2.8, for example. Yes lenses of that type are more expensive - far more than $100, but you get what you pay for.

If you want to stay with a low-cost SLR-type lens there are dozens of older zooms with bright apertures all over the 'net from just about any brand you can imagine. In fact I saw a Vivitar Series 1 (which was really high-quality APO glass back in it's day) that was an 80-180mm f/2.8 selling for about $250. That would be a much better fit for video work - and affordable too!

Re: Old pentax promaster lens
 

My opinion, f3.5 should give you PLENTY shallow DOF at 70mm, and having a lens that can reach 300mm is always a nice touch. f5.6 is still fairly bright for 300mm/600mm equivalent. Also consider, what are the chances you're going to need that long of a lens indoors, where you might really need f2.8? Chances are, you'll be using it outside where you'll probably be stopping down well below even f5.6. Such a lens would be mighty good for wildlife work. Sure, maybe it doesn't have a constant aperture, but that's not a death knell if it's not necessary... most stills zooms are used like variable primes anyway, so holding aperture through zoom is often a non-issue.

One of my better outdoor zooms is a "crappy" Nikon 70-210 4-5.6. It's not ideal, but it's good enough for my uses and drains bank accounts less. No need to save up for a Mercedes when all I need is a Chevy.

Read some reviews (if you can find them), figure out if that's what's going to work for you, and either buy it, or don't.

Re: Old pentax promaster lens
 

Ric,

One thing I forgot to mention about having a constant aperture rating, is not so much that the lens needs to be bright to be really useful, but if you're doing a zoom during a shot you don't want the exposure to *change* during the shot, and that's what happens with lenses that have a variable f-stop rating.

It will make your footage look like it was shot with some type of auto-exposure turned on while the image brightness ramps up and down during your zoom move in the shot, and that's undesirable for any kind of work.

The only way around that gotcha would be to manually put the lens at it's *lowest* max f-stop rating (for example the Pentax would be f/5.6) and keep it there for the duration of your shoot. That way if you do choose to zoom in or out the exposure won't change up on you and keep your imagery professional-looking.