I purchased a generic Pentax K-mount 100-300mm Quantaray lens for my K-70 for $15 on Ebay! Was it worth the hassle of ordering and testing? Check out the video for my comments, and resulting images.
My goal was birding. It's a simple term that describes taking photos of birds. There are a lot of youtube channels devoted to birding, not so much when it comes to the Pentax K-70, and almost nothing when it comes to the Quantaray 100-300mm lens.
So I pulled the trigger, assuming for $15 I had nothing to lose, and bought the lens from an Ebay seller. The lens arrived in great condition, and I was surprised how solid, clean and firm it felt. There was a bit of a jiggle or shaking sounds inside the lens when attached to the camera, but doesn't seem to have any effect on the results of the images.
There was absolutely no zoom creep (when you turn the camera upside down and cheap zooms will start extracting), and the manual focus ring, which I'd likely not be using anyway, was fine and workable if needed.
At first inspection, while surprised how nice the condition and grip were, I didn't expect sharp details, and didn't know how the auto-focus would react. On both counts, this lens passed with flying colors. I don't shoot in jpeg, so all of my images are edited in lightroom using RAW files.
This test didn't deep-dive into details, just situations that I would find myself using the lens. So if you shoot in jpeg, this review and the out-of-camera results might not answer some of your questions. But as stated, the test is for my personal use, not universal situations that others might want to use it for.
On my first outing with the Quantaray 100-300mm attached to my Pentax K-70, I came away with just one image that would be considered decent, and it was just a simple profile of a duck. I was disenchanted with the lens at first, but decided to jump back out the next day adn try my luck again, assuming the results, or lack of, from the day before was my fault. I was right.
Day two turned in much better results than the first attempt. My biggest mistake on day one was shooting at a slow 1/320 shutter speed. This in no way would freeze the action of a bird in flight, and blew my chances of capturing a really cool, large crane that was wading in the pond, and took flight as I approached. Every one of my images were blurry, as would be expected, at 1/320 second.
One day two, I raised my shutter speed up to 1/1000 second to catch the blur of the wings, but found even this not high enough in most instances. I was trying to keep my ISO down to avoid excessive noise, but this was a bad idea. So I upped my ISO range to 1600 on day two. While this worked much better, I still needed to go higher with my shutter speed to completely freeze the action of the wings (that will be my next outing).
In retrospect, I found that when I edited the images, I was able to get rid of a lot of the noise that I feared, and therefore used the lower shutter speed. Lesson learned here is that I need to be closer to 1/2000 or 1/2500 second to get a better chance of freezing those wings in flight.
A Workable Aperture of f/4.5 at 100mm, and f/6.7 at 300mm
I went with as shallow depth of field that I could muster. Several shots would have benefited from a higher aperture to add more dof, but most of the birding images I see online or in videos are shot with a very small dof, and a ton of bokeh (blurry background). So that's the avenue I tried and was pleased with not only the bokeh I achieved with this inexpensive lens, but the clarity of the subject as well.
Fully extended to 300mm, the Quantaray 100-300mm lens has a minimum aperture of f/6.7. In general, most recommendations are to not use a cheaper quality lens at it's largest or smallest focal length, or the lowest aperture available. But that didn't seem to matter much with this lens. If one were pixel peeping I'm sure it would show signs of vignetting and not as sharp as center, but those issues don't even enter my mind when purchasing a lens for $15. With a little post-editing sharpening, along with any other adjustments that need to be made, I feel like the $15 was justified just on this first outing alone. But I'll be using this for more adventures for sure.
Limitations of 300mm
While 300mm gives you a nice reach for most situations, including landscapes and wildlife, and is equivilent to 450mm on a full frame camera, it's still a little short for proper birding. I consider proper birding to be the small birds, and not just the larger ducks, fowl and geese that I feature in my first attempt.
Check out the video, and sample photos from my first outing with this lens, and let me know if you have any questions, comments, suggestions!