Crop Sensor Camera with Full Frame Lens Question

[ACHILLEAS]

focal lengths lead to a lot of confusion for many people. it is an engineering problem. photographers don't need it. if lenses were sold with an advertised angle of view it would be far more practical. it will also eliminate the confusion what cropping does. which is digital zooming. in the exif data the focal length did not change because it is a physical property of the lens not the sensor. but the angle of view changed. ignoring resolution you can simulate a longer lens.

 

[greybeard44 17]

Your math is correct. A 30mm lens on your canon aps-c would give you the FoV (field of view) of a 50mm on full frame. A 35mm would be pretty close and there are many available.

 

[Ysarex96 91]

focal lengths lead to a lot of confusion for many people. it is an engineering problem. photographers don't need it. if lenses were sold with an advertised angle of view it would be far more practical.

I have a 35mm lens I'm fond of. I use it on my FF cameras and it has an angle of view of 54 degrees. But I also use it on my APS-C cameras where it has an angle of view of 38 degrees. But wait, I also use it on my MFT cameras where it has an angle of view of 29 degrees. Now that's a bit more complicated than just saying no matter what camera I use it on it's always a 35mm lens.

The confusion in all of this derives from the term "equivalent focal length." Way back in the film era before anyone ever said "equivalent focal length" I had an Arca camera. It was a 35mm, 6X6.45, 6X6, 6x7, 6x9, and 4x5 camera depending on the back I put on it. It had a plate for the back that would mount my Nikon F, a plate that would hold any 120 roll back, and a plate for 4x5 sheet film. I had a 90mm lens I used on that camera. It was a wide angle lens as well as a short telephoto lens as well as a normal lens all at the same time. I don't remember folks being confused about that back then because it was always a 90mm lens.

it will also eliminate the confusion what cropping does. which is digital zooming. in the exif data the focal length did not change because it is a physical property of the lens not the sensor. but the angle of view changed. ignoring resolution you can simulate a longer lens.

 

[Don Fischer]

So regardless of the lens whether or not it's for crop or full frame, it's always going to be what actual focal length of the lens is but crop sensor lenses have smaller image circle so on full frame sensors they will leave a heavy vignette or a circle as they can't cover the entire sensor but the focal length remains the same.

You are right that there is a crop factor, canon crop sensors are a hair smaller than Nikon which is 1.5x while canon is 1.6x.

So yes a 50mm x 1.6 = 80mm so you getting an 80mm full frame equivalent focal length on crop but it's still 50mm just cropped in.

So if you want an equivalent focal length of 50mm on your crop sensor you'll want a 30mm lens, I'm not sure if there is one for that mount otherwise a standard 35mm prime works as well. However those lenses will still bring along the characteristics of a 30mm/35mm lens, it won't match 50mm because what you are getting effectively is an equivalent field of view of a 50mm lens but not actually 50mm.

For an example. If I take my 50mm lens on my full frame camera and crop it in 1.6x to get an equivalent field of view of an 80mm, it would be essentially identical to one taken with a 50mm on an APS-C size sensor camera.

Hopefully this makes sense.

Just one more thing wrong with modern camera's. Everything related to 35mm but different!

 

[petrochemist127 152]

Your math is correct. A 30mm lens on your canon aps-c would give you the FoV (field of view) of a 50mm on full frame. A 35mm would be pretty close and there are many available.

A 28mm would be closer & there's loads of those too

 

[petrochemist127 152]

I have a 35mm lens I'm fond of. I use it on my FF cameras and it has an angle of view of 54 degrees. But I also use it on my APS-C cameras where it has an angle of view of 38 degrees. But wait, I also use it on my MFT cameras where it has an angle of view of 29 degrees. Now that's a bit more complicated than just saying no matter what camera I use it on it's always a 35mm lens.

The confusion in all of this derives from the term "equivalent focal length." Way back in the film era before anyone ever said "equivalent focal length" I had an Arca camera. It was a 35mm, 6X6.45, 6X6, 6x7, 6x9, and 4x5 camera depending on the back I put on it. It had a plate for the back that would mount my Nikon F, a plate that would hold any 120 roll back, and a plate for 4x5 sheet film. I had a 90mm lens I used on that camera. It was a wide angle lens as well as a short telephoto lens as well as a normal lens all at the same time. I don't remember folks being confused about that back then because it was always a 90mm lens.

I have loads of lenses that can be used on any of 7 different sensor sizes in my collection, so strongly agree that quoting the lenses FOV doesn't work! My Pentax Q lenses are actually designed to be native on two different sensor sizes, and there are loads of lenses designed for FF yet used natively on APSC (I don't think Canon allow this but Nikon & Pentax do).

I don't agree that "equivalent focal length" is the issue, I find it a useful concept, that .I also use to visualize the results from large format lenses...
The issue is more one that photographers who've only ever used APSC are hung up on the FF equivalent. That and perhaps that Math is no longer something people do in their head!