Originally posted by Rondec For whatever reason, Sony seems to have some of the worst (most expensive) new prices for top end glass. Also, they don't have as long a history of FE mount lenses and so there aren't many used copies of those lenses running around either. I think you could make switch to Canon or Nikon for a more reasonable amount if you are buying used glass.
As far as Pentax glass selling, I think the Marketplace is usually the best option, but often lenses do sit for awhile before they move. Regardless, I'm glad the move has been good for you. The A9 is a serious camera and certainly is more than enough for most situations I can think of.
The A9 is a great specialized camera. For architecture or landscape photography there is no better option than the K-1. I photograph people and they are always moving. The eye AF really is a big deal. The silent shooting and black-out free EVF is really nice. I don't need 20fps, but I have see a lot of shots in the A9 groups when that came in very handy for getting the perfect shot. It has its place.
I'm sure you could make the switch to Canon or Nikon for less. If someone made a smart adapter for Pentax glass like they do for Canon/Nikon/Sigma I wouldn't need to sell any. I had a chance to use a Nikon 105mm F/1.4 on my A9 with and adapter and I was surprised that it was focusing faster than my friends Canon 5DIII with 85L. If I was a Canon or Nikon shooter the switch to Sony would be very smooth. Again.... There just aren't a enough K-mount users out there for anyone to invest in developing a smart adapter for K-mount. I thought about sending my Sigma 85mm back to Sigma and have them change the mount over to a Sigma mount and buy the Sigma to Sony adapter. But by the time I paid to have the mount changed and buy the adapter it wasn't worth it.
The Zeiss Batis 18mm F/2.8 can be bought for $1,200 - What is the Pentax option?
Search: batis 18mm | Flickr
The Zeiss Batis 25mm F/2 can be bought for around $1,000 - What is the Pentax option?
Search: batis 25mm | Flickr
The Zeiss Batis 135mm F/2.8 APO can be bought for $1,600 - What is the Pentax option?
Search: batis 135mm | Flickr
How much will the D-FA* 50mm F/1.4 lens cost? I bought the Sony-Zeiss 50mm F/1.4 for $1,500 while it was on sale, but I expect that the new D-FA* lens will be priced very similarly. I expect the D-FA* lens to be a premium quality lens and prices according.