Originally posted by pentaxk3user I don't understand what you typed yet but I'm going to try to figure it out . I'm going to read the links Serkevan put above . I still have a lot to learn . So sorry if my questions and requests are stupid .
---------- Post added 11-01-19 at 07:11 AM ----------
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Kozlok will you take a photo with the 18-35 at 35mm and the sharpest f stop and then take the same photo with the 16-85 at 85 mm with the f stop at 2.8 . them crop the 35 mm photo so you see the same thing as you do with the 85mm . And post it here so I can see the difference in the two .
---------- Post added 11-01-19 at 07:21 AM ----------
I know the 200mm photo is better than the cropped 35mm to the same size fov as the 200mm and I can see it when I zoom in on flikr and lightroom but not zooming in it looks pretty close . I was just hoping to get 2 photos from you professionals that know what your doing to let me see what the difference is between a 18-35mm lens at 35mm cropped to the same fov as the pentax 50-135 at 135mm . or even the 85mmm from the 16-85 mm lens .
Well, when you are cropping you are throwing part of the picture away. When you crop a 35mm image to 200mm you are throwing away over 80% of the image - you are cutting it off. That is why you end up with a little over 4 megapixels on a 24 megapixel image. and 4 megapixels was state of the art... about 20 years ago when digital cameras first started and everybody still shot film.
Having said that, if you are printing 8x10 images, I would say anything over 8 megapixels is actually going to look fine. So you could be ok cropping to 85 or even 100mm. And if you are printing 4x6 then you are probably fine even with the 4MP image! Also, if you are just looking at a picture on a cell phone or small old laptop, you might be fine cropping to 200mm and still seeing a nice image. But if you have a 4K monitor the 4MP image will not look great.
The problem is, you are probably better off with a small $100 dollar point and shoot that goes to 300mm equivalent rather than having a DSLR and a big expensive lens like the Sigma 18-35, and cropping 82% of your picture off.
It's just mathematics...
EDIT: The 200mm crop would actually be around 0.7 megapixels, so fine only for cell phone viewing.