[GR Jim]

Hello,

These are probably very silly questions that show my inexperience with digital photography, having mostly lived in the film camera world.

I just recently purchased a K-70 and a Tamron SP AF 17-50mm F/2.8 XR Di-II LD (non-VC to get a sharper image), thinking I'd get the uncropped equivalent range of 25.5-75mm, mild WA to mild Telephoto. However, after mounting the lens on the camera body and doing some practice shooting at the lens' 50mm focal length, I noticed both in the viewfinder and in Live View that the image is the same as I see it without the camera. Shifting my eyes away from the camera to the actual subject (a house across the street, shooting from within my home office), I do not see a mildly zoomed-in image. It's as if I were shooting a film camera with a 50mm 'normal' lens rather than a 75mm mild telephoto which I had expected.

So am I missing something with the whole cropped sensor technology? Do you think the lens is defective and not giving me the entire zoom range out to 50mm (75mm cropped)? How can I verify the proper functioning of the lens zoom range?

Any assistance I can get with this would be greatly appreciated.

[robiles]

The easiest way to explain it is they are both the same (50mm lenses) and the difference is that edges of the frame are covered in an aps-c camera.

[pschlute]

So am I missing something with the whole cropped sensor technology?

Any 50mm lens will have the same magnification whatever format (aps-c or FF) it was designed for. As robiles said above, the difference with a crop sensor is that you are recording a smaller chunk of the image circle than you would have done with either a 35mm film camera or a FF DSLR.

The narrower angle of view is what is referred to as FL "equivalence". There is no magnification factor when using aps-c format.

Where you will see a difference is if you look at two images taken by two formats (aps-c versus FF) on your computer screen at the same image size. The aps-c image will appear to have been magnified/zoomed/enlarged, but that is because it is a smaller crop of the FF image and is therefore enlarged more to keep the image size equal.

[UncleVanya]

The magnification doesn’t change but the angle of view is narrower. Because there’sa high density of pixels you can also crop the frame more and get detail that wouldn’t be available with the focal length on ff without going to very high density sensor. Even though your view through the finder doesn’t seem different in practice it is.

[Bob 256]

It sound's a bit like you're comparing the image on the LCD screen to the visual presentation of the same. That really isn't a good comparison and depends on how close or far away the LCD screen is. When the term "telephoto" is used, it is a comparison of one lens to another and the magnification of the image it presents in a (typically) uncropped print or display relative to that other lens. I'm sure your camera/lens is performing properly, and taking a photo with the lens adjusted to the sensor cropped 50mm equivalent setting should produce the same image as a 50mm lens on a full-frame camera (which you probably don't have to compare), so you shouldn't worry. The same would apply to your lens in the telephoto or wide angle range. Just take the LCD view with a grain of salt and use the actual image for comparison purposes.

[Parallax]

cropped sensor

Cropped sensor.
Crop factor.
FF equivalence/equivalency.
Do yourself a favor by forgetting you've ever encountered those terms. Once you focus (no pun intended) on what YOUR lenses do on YOUR camera I think you'll find photography a lot simpler and more enjoyable.

[aslyfox]

if you ignore Parallax's wise advice

and want to " research "

The Crop Factor Explained: An Animation - Tutorial Videos | PentaxForums.com


The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

[tibbitts]

Hello,

Tamron SP AF 17-50mm F/2.8 XR Di-II LD (non-VC to get a sharper image)

Also non-VC to avoid needing a very large wrench and maybe a hammer to attach it to your camera. Updated versions of Tamron lenses like the 17-50mm aren't available for Pentax mount.

Having had experience with that lens, and had mine serviced a couple of times by Tamron (the warranty terms are excellent vs. shorter warranties on, for example, Pentax lenses), I would be very careful to verify how well it's focusing, especially when not using live view. It's challenging to get most lenses focusing correctly at every focal length, especially lenses as fast as f2.8. Also make sure you're familiar with the focus field curvature and how that applies to how you use the lens.

As for the focal length, since you compared it to a 50mm on a film camera, what happens when you look through the K70 with the 50mm zoom and the 35mm camera with a 50mm? Not using a camera at all and comparing what you see is pretty meaningless.

[ramseybuckeye]

You are seeing the same as full frame with slight tunnel vision.

[aaacb]

I also like to ignore everything about crop factor and such. Instead I think about perspective, it's an essential compositional tool. You're noticing the same perspective as for your eyes. That's expected, because perspective depends on the distance between the viewer and the subject(s). The angle of view is determined by the focal length and the sensor size. In practice, we move farther back from the subject the smaller the angle of view gets, so then you get a different "compressed" perspective.

[stevebrot]

A crop is a crop is a crop...

Focal length and magnification stays the same. I do both-eyes-open technique at times with my K-3 and 50mm lens mounted sometimes just for the novelty, the 0.95x viewfinder magnification being close enough to 1.0x to allow it.


Steve

[GR Jim]

Thank you everyone for your explanation, viewpoints, and wise words. I didn't expect such a long thread. But basically, this 17-50mm lens is a starting point for my system as I'm starting over in my photography life after leaving film shooting. I now see what to expect with future lenses. I think the Tamron is a great lens and it has very good reviews, both by professionals and down-to-Earth users, but it's still a zoom. I have always favored prime lenses before, especially Nikon primes. I was looking for an ultra wide angle prime for expansive landscape photography in Arizona and couldn't find anything I liked that was affordable, so I compromised with a zoom. But I think photography, as in life, is a bunch of compromises anyway.

[Bob 256]

................................ But I think photography, as in life, is a bunch of compromises anyway.

Enjoy your "photography life". You'll begin to really believe that when you compromise on spending on your significant other so you can buy a new lens or camera

[pschlute]

I think the Tamron is a great lens and it has very good reviews, both by professionals and down-to-Earth users, but it's still a zoom. I have always favored prime lenses before

The zoom versus prime debate is not the same now as in the film days. Tech has changed so much. Like you I still favour primes, but my favourite UWA on the FF K-1 is the D-FA 15-30 zoom.

[Parallax]

For many years I was a proponent of primes and zooming with my feet. I have the 15, 21, 31, and 40 Ltds
Then my feet got old and tired like the rest of me.
I love my 16-85. It hasn't been off of my K-5 IIs since I got it