I have a Konica 57mm f1.4. Should I sell my Konica 40mm f1.8 & replace it with what?

probably depends how deep your pockets are, Joe ...

 

Why would you consider selling it?
It's worth much more than what you'd get for it.
I love mine on my e-pl1, and if you've already got the AR to M43 adapter...

Stop it down a little - it's as sharp as they get. And a handy focal length to boot.

 

I had similar feelings about the 40mm as well and had starting shopping around for alternative options. I decided to give it one last go around and use it exclusively for several weeks. It's now one of my favorite lens. It's quicker to focus since the focusing ring is around half a turn around the lens barrel from end to end.

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EXIF: Hexanon 40mm ISO 200 f4

I think it renders the colors of dusk/sunset better than any other lens I have.

 

I have a similar situation. I have a 50/1.4 that I use and a 40/1.8 that I do not. The 40 is a great lens and I would advocate keeping it unless you wan tot sell it in order to fund a different purchase. That gets a bit more complicated with lenses like the 40 as they are pretty common and don't sell for much. In fact, I just went through this same scenario. I sold my 40 and as soon as I did I had a reason to use it so I ended up buying another one. Lets just say it would have been better to keep the original.

I've had a 57/1.4 and I currently have a 50/1.4 and the 40/1.8 and when stopped down the 40/1.8 is just as sharp. What I like about the 50/1.4 is the that it can close focus where the 40 cannot. If you look to replace the 40 you should be willing to pay a good deal more in order to see much difference in image quality. The best option I found was a 40/1.4 Olympus PEN F lens but at $150 (and that was cheap for that lens) it is a lot more than a mint Konica 40 and while the image quality is better the Konica can hold its own.