35mm lens vs digital lens---opinions please.

[blakjak8]

I purchased a Sony a200 a year or so ago partly because I already had Minolta equipment. The transition to digital was a bit less expensive that way. My Sigma 70-300 lens has died and I am looking at replacing it. Using it on the a200, it performed similar to a 105-450 due to the 1.5 times crop factor. I may mis-speak here due to some confusion on my part so feel free to correct me. I liked the "extra" telephoto of the Sigma and am looking at the Sony 70-300, Tamron and Sigma lenses also. Does the "crop factor" always come into play on all lenses? How do I determine which lens is unaffected? Is one of these lenses much better or worse than the others? Any and all opinions and info is much appreciated. The sticky about the DSLR Sensors is much appreciated and informative. Thanks!

 

[Johnboy2978]

The crop factor is a function of your camera because the sensor is not a full frame.

 

[Big Mike]

That's correct. It's the camera, not the lens.

Imagine, if you will, how the lens works. Light comes in the front and exits out the back, projecting an image into the camera. The lenses project an image circle that is big enough to cover a frame of 35mm film. That doesn't change just because you put the lens onto a digital camera.

The difference is that the digital camera's sensor is smaller than a frame of 35mm film...so it only 'sees' a portion of the image that is projected....the rest is 'cropped' off....which is why we call it the 'crop factor'.

Now, there are some 'digital only' lenses...and the difference is that they project a smaller image circle, only big enough to cover the size of the sensor.

 

[rpm]

every lens will be affected by it be it aimed for crop-factor or ff digital slrs (well with Nikon at least. not sure if the fitting is diff between the lens types for sony/minolta)

even those designed specifically for the non-FF sensors will have that crop factor influence them. i think its a matter of 'ease' keeping them and it will be less of an obstacle when it comes to the marketing of the lens. so they simply add a specific name system for those lens line up..so even tho its a, Nikon for example, DX lens aimed at a DX-camera (read crop sensor), they will still advertise it as 18-55mm lens instead of 27-83mm but at least with Nikon, it can still be used on an FF system (with more negatives than positive implications).

 

[Big Mike]

they will still advertise it as 18-55mm lens instead of 27-83mm

That's because it physically is, and always will be, an 18-55mm lens. Changing the camera that it's attached to, does not change the focal length of the lens. That seems to be the big misconception that many people have.

Really, the 'crop factor' is only useful for people who have a previous expectation of what they will see from a particular focal length...a.k.a. people who have been shooting with 35mm film SLR cameras.
When those people pick up a 50mm lens, they expect a certain field of view...but with digital SLR cameras like the one in question here, there is a 'crop factor', which affects the effective field of view. The result is that it FEELS like a longer lens. But the focal length is still 50mm. So the magnification and perspective are still what you would expect from a 50mm lens.

To the many, many people who have never used a 35mm film SLR (or full frame digital), they should forget they ever heard of the crop factor.

 

[rpm]

i know it doesn't and all in all it is 18-55mm in terms of physical attributes etc im not saying it does, but all in all, to not confuse people who are not in the know and more importantly since they do aim it primarily at DX users and hope it stays within DX cameras cause of the negative impact on FF cameras (for the most part), theres nothing wrong with actually stating what they would actually reflect on a DX camera. i mean it is a DX lens...i know that is a common sense mentality and not a technically correct or accurate depiction of the lens. but when you use it, it wont be behaving like a 18-55mm lens ever on a DX camera. but like i said...im not misconceiving what the crop factor does, im just using a common sense mentality instead of the technical realities lol

 

[Big Mike]

I think I know where you are coming from...but I think you are also unnecessarily confusing the issue.

but when you use it, it wont be behaving like a 18-55mm lens

That's where you're wrong. Of course it will behave like an 18-55mm lens. How could it do otherwise?
You don't need to cling to the 'old standard' of 35mm film, where 18mm would be ultra wide and 50mm would be 'normal'...especially if you don't use a film SLR (or never have).

To many people, 18mm is just moderately wide...and that's OK. They don't need to know that it 'feels like 24mm would feel on a film SLR'. I think it's just confusing and pointless to try to explain that to them.

 

[rpm]

i understand what you're saying as well but when you look through the viewfinder, its not 18mm at its shortest length and it wont be 55mm at its longest...you wouldn't confuse anyone if all DX-crop lenses stated what they would reflect on the crop sensor on the package...whats happening is that people are asking how the crop-factor affects the lenses (case in point this thread)...it doesnt simply 'feel' like a 24mm lens...the picture taken would be as if it was a 24mm lens on a FF body and on a DX body it 'acts' like a 24mm lens while having the technical attributes of a 18mm lens

we dont need to cling onto it but its still around, in the form of the FF bodies, but now you also have the crop bodies and threads like this come up. now...if the DX lenses reflected how they behaved on a DX body, i guess you could argue we would find ourselves with threads asking about how a DX lens behaves on a FF body...but hey we still have that too lol....

but we can easily go round in circles how this should be handled by the companies and how we the user-base should understand it as but all in all, maybe we both can agree its an unneeded complication for anyone coming from the SLR side of life and anyone wanting to get their feet wet...

 

[enzodm]

i understand what you're saying as well but when you look through the viewfinder, its not 18mm at its shortest length and it wont be 55mm at its longest...

If you crop a picture taken on FF with a 18mm, you still have a picture taken with a 18mm. The kind of distortion available will be the same, DoF will be the same, etc. And those are features of that 18mm, different from those of a 24mm.

If lenses should begin to be named after what they look like on some specific body (not considering that a FF lens can be typically used on a crop body), you could have also to take into account Megapixels - because same detail will be rendered in different digital size.

 

[rpm]

like i said, we can go round in circles on this topic with diff arguments, counter-arguments and go bonkers trying to prove one point or another, all in all, i think we can all agree that its an unneeded complication for consumers that will persist...

 

[enzodm]

i think we can all agree that its an unneeded complication for consumers that will persist...

I agree only on circles . If I buy a Canon L lens, I could use it on a crop body but also on a FF body. So? How do I call it when I upgrade body from crop to FF?

 

[Big Mike]

I agree that we could go around in circles...but I still think there is a point where you are incorrect...

but when you look through the viewfinder, its not 18mm at its shortest length and it wont be 55mm at its longest

Yes, it will.
It doesn't matter if it's a film camera, a digital camera or a rhinoceros behind the lens...it's still 18mm.

 

[prodigy2k7]

its really simple and people are over complicating it...

Checkout this image
http://upload.wikimedia.org/wikipedia/commons/f/f5/Full-frame_vs_APS-C.svg

On a crop body, you are doing exactly that, CROPPING some of the image. The mirror and sensor are smaller, and are literally cutting off some of the lens image circle, so it appears to give it an additional zoom, when in fact its the same focal length, just cropped.

 

[supraman215]

Welcome back OP, joined in 04 with 35 posts!

 

[skieur]

I purchased a Sony a200 a year or so ago partly because I already had Minolta equipment. The transition to digital was a bit less expensive that way. My Sigma 70-300 lens has died and I am looking at replacing it. Using it on the a200, it performed similar to a 105-450 due to the 1.5 times crop factor. I may mis-speak here due to some confusion on my part so feel free to correct me. I liked the "extra" telephoto of the Sigma and am looking at the Sony 70-300, Tamron and Sigma lenses also. Does the "crop factor" always come into play on all lenses? How do I determine which lens is unaffected? Is one of these lenses much better or worse than the others? Any and all opinions and info is much appreciated. The sticky about the DSLR Sensors is much appreciated and informative. Thanks!

I have the Sony 70-300mm and it is very good at resolving detail and colour even at a considerable distance. The autofocus is fast and silent and although it may seem heavy, it has good balance and I have not had blurred shots due to camera movement. It is also great for doing close-ups of plants, etc. from a distance with good depth of field.

skieur