Photographers are fickle creatures. They want supreme optical quality, top notch mechanical quality, tiny lenses, and fast bright apertures but they don't want to spend a lot of money for it. Alas reality doesn't agree and so compromises are necessary. The Minolta Celtic line are a great example of this. Minolta sacrificed some mechanical quality to reduce the price of the lenses without losing much in the way of optical performance but of course photographers turned their noses up on them. Even today in the vintage lens market the Celtic lenses don't receive respect. Their loss - this lens is fantastic. It's a great portrait lens and is extremely affordable. I found mine at a photo show for just $20 and don't regret it in the least.
Mount: SR Mount
Focal Length: 135mm
Aperture Range: f/2.8 - f/22
Minimum Focus: 1.5m
Filter Thread: 55mm
Date Acquired: 06/01/19
Serial Number: 1323671
Purchase Price: $20
Going Price: ~$35
Condition: Some small stains but optically perfect
The Celtic line is Minolta's equivalent to Nikon's Series E lenses. They're economy variants of Minolta's famous Rokkor line. There are some obvious compromises in the build quality - especially the focus ring. It's still smooth to focus but instead of the distinct diamond texture found on Rokkor's you have this very slippery rubber that doesn't age well. Most copies will have some kind of damage to the ring. On mine there's a split where the rubber became stuff with age. Despite these compromises though it still has an integrated lens hood which is always appreciated and the aperture ring is easy to use.
Despite being an economy lens the performance is quite solid. Wide open at f/2.8 the lens is tack sharp in the center and only slightly soft in the corners. Stopping down to f/5.6 the corners are now tack sharp as well. Flare is decently controlled though not amazing as there is definite veiling and a yellow arc being faintly visible. Vignetting is definite at f/2.8 but disappears by f/4. Bokeh is exceptionally smooth at f/2.8 with large bokeh balls rendered from point lights sources.
In the hand the lens is very comfortable. The focus is a little slippery but not bad. It's not the most confidence inspiring experience in use but decent all the same.
Should I get one for photography?
If you're in need of a fast 135mm lens and on a budget I think this is a fantastic option. Performance is fantastic and the price is very low thanks the Celtic line being less popular than the Rokkor line of lenses. If you already have 135mm lenses it's a bit harder to recommend but at the price it's worth it.
Should I get one for a collection?
The Celtic line unfortunately isn't very interesting visually and doesn't hold much value in a collection. There's a reason why the lens is cheap - people just aren't that interested in them. If your goal is collecting the Rokkor line is probably what you should look for.