Fixed aperture lenses?

Hi all, trawling through Pentax fit lenses I have come across a couple at fixed apertures of f4.5

Are there any advantages/disadvantages with such fixed apertures?

Deryn

Can you elaborate please, which lens/lenses?

The only fixed aperture lenses I'm aware of are mirror/reflex lenses, but these are usually fixed at f8, not f4.5

Hi Peter, Pentax 75-250, Soligor I believe.

Advantages/disadvantages?

Deryn

That's not a fixed aperture lens. It's largest aperture is f4.5 but it closes down to f22. That makes it a bog-standard zoom lens. As I wrote previously, the only fixed aperture lenses that I know of are the mirror type, AKA reflex lenses.

Advantage? - - - It's cheap.

Disadvantage? - - - It's a Soligor, hence the advantage above.

I have no other experience of third party lenses but just remember, "you gets what you pays for". If it's cheap, it's cheap for a reason.

Thanks Peter, the lens was advertised as 'fixed aperture', so obviously wrong!

Deryn

That can mean one of two things:-

1: The seller hasn't a clue about what he/she is selling. Or

2: The lens is faulty and the aperture is stuck on some random setting.

Whichever is true, avoid.

Pre-set anybody? I've no idea how they work though.

I wonder if the seller is getting confused with constant aperture, such as F4 max aperture through the zoom range. Which the Soligor isn't anyway