I believe I mentioned this before but, one of the draws to Pentax is the backward compatibility of their lenses. In my mind they make it the easiest to use old manual focus or even M42 lenses. Pentax was renowned for the quality of their lens coatings and lenses in the 60's through 80's especially. If you like rabbit holes here is a fun one, the Lens Database on Pentax Forums:  https://www.pentaxforums.com/lensreviews/ From the beginning of my journey into digital I have become more aware of the need to understand the performance of my lenses and how to use that to my advantage. I think I am headed there but still have a long way to go. Notwithstanding my limitations, I took the opportunity to pick up lenses from what are know as the Pentax K-Series. Being the lenses first produced with a bayonet mount instead of screwing on like the old M42 standard. This will probably tell you more than you want to know: https://photographylife.com/what-is-lens-mount 

I acquired over the last few years: 24mmf2.8, 28mm f3.5, 35mm f3.5, 50mm f1.4, 135mm f2.5 and 200mm f2.5 lenses from the Pentax K-series. There are many others to choose from, I looked closely at a 85mm f1.8 that I friend of mine had, and wish I had bought it. And there are other lenses with larger apertures that interest me, but I like what I now have. They worked reasonably well when I was using them on APS-c. 

What I started, but haven't finished with is seeing how those older lenses stand up to a full frame sensor with more resolution than film. In November of 2023 I decided to take a different lens with me when I drive to work on Saturday and try to take shots of similar scenes with each lens, mostly wide open. This didn't last more than a couple Saturdays but using my 200mm f2.5 lens was a whole new experience on Full Frame. As an aside, "200mm" is the focal length of the lens. https://en.wikipedia.org/wiki/Focal_length which puts it in the realm of Medium Telephoto, making things further away appear closer. the "f2.5" refers to the widest aperture which is related to how much light it can gather as well as other  qualities of the image it produces. https://photographylife.com/what-is-aperture-in-photography Smaller aperture, or f numbers, tell you not only how much light the lens can gather (Smaller numbers=larger apertures which can allow for photography in dark areas) but also indicate the depth of field. Smaller numbers=smaller or thinner depth of field of focus. It is a trade off, you can gather more light but less of the image will be in focus which can be good or bad depending on what you are trying to do. If you are trying to isolate a subject a smaller f-stop and smaller depth of field can help achieve that, if you are trying to place the subject in the context of the larger environment you may want a larger f-stop for greater depth of field, but you will have to trade off other elements to achieve a good exposure. i.e. longer shutter speed, or increase the sensitivity of your sensor, also increasing noise and degrading the image a little.

What I wanted to see first was simply how sharp of an image could the lens produce in the in-focus areas at f2.5, also known as wide open.

So far so good, another aspect of lens performance is what the out of focus areas look like, it is called "Bokeh" one of those hard to translate aesthetic Japanese terms that I love. Here is another rabbit hole: https://photographylife.com/what-is-bokeh In this photo I am happy with the bokeh both in front and behind the subject.

Again, I am pleased and think I can use this creatively in many ways in the future, I will also need to do some more experimentation with the aperture stopped down and see if the backgrounds are distracting and when. Lenses can behave differently in bright light vs. more soft shadowed settings like when I was taking these photos. The colors of the photos are good and I do hope to get out and play with it more. 

Two more photos from this day: As always, feel free to comment and ask questions, thanks for visiting & hope all y'all have a great day!