very basic Crop vs Full-Frame questions

[Ronaldo]

From what I understand a 35mm lens on a Nikon D90 is roughly equal to a 50mm lens on a Nikon D700.

But what exactly does this mean?

If you put a 35mm lens on the D700 from a specific distance to the subject, it would project a certain image size onto the sensor.

Now, if you keep the exact same lens and distance to the subject but switch the camera to a D90 - - won't the image size projected onto the sensor be the same size as with the D700? Except that with the smaller sensor on the D90 only the central part of the image is recorded?

So, if the projected image size is the same between the two cameras (crop and full) with the same lens - - how come the 35mm on the crop is considered roughly equal to the 50mm on the full??

I understand that the 35mm lens on a D90 might fill the viewfinder roughly the same as a 50mm lens on a D700.

But the 35mm lens on a D90 is not magnifying the image at all, compared to the 35mm on the D700, right?

So a 35mm lens on a D90 is not roughly the same as a 50mm on a D700 in terms of image magnification and projection onto the sensor, right??

So if you took a pic from the same distance using the same 35mm lens on the two cameras. And you cropped the pic from the D700 to compensate for the smaller D90 sensor size. The pics would then look the same???

Can someone please help sort-out my confusion on this?

:scratch:

thanks

 

[BuS_RiDeR]

Crop factor - Wikipedia, the free encyclopedia

 

[table1349]

This should answer all of your questions nicely. Digital Camera Sensor Sizes: How it Influences Your Photography

This is a good site for all kinds of basic questions. Digital Photography Tutorials

 

[molested_cow]

I posted a reply earlier but realized a mistake. I basically said the distortion between a 35mm and 50mm is different therefore it's not fair to say that they are "equivalent". I used CAD to simulate this but used the wrong method.

I redid the simulation and it appears that the distortion is the same between full frame and cropped. In any case, I don't have the equipment to test it in real life, so I cannot confirm it.

 

[kundalini]

From what I understand a 35mm lens on a Nikon D90 is roughly equal to a 50mm lens on a Nikon D700.

But what exactly does this mean?

If you've never shot 35mm film, don't worry about it. The focal length IS ALWAYS the focal length.

 

[molested_cow]

Ok let me do this again.

Here's a cube at 50mm full frame.

Here's the same cube at 35mm full frame.

Here's an overlap of the 50mm at full frame vs 35mm at cropped frame.

You can see that the overlap is actually exact. Now, this is just a simulation with CAD. I don't know if the software uses accurate way to simulate the visual perception or if they are just bull****ting.


Here's 50mm at full frame vs 35mm but moved closer to the subject for similar coverage.

It will be great if someone who has both FX and DX DSLRs can do this test so we have real life comparisons.

 

[kundalini]

No simulation involved.


http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

 

[djacobox372]

TS understanding is 100% correct. Cropping results in the same image, but resolution is lost if u crop a full frame image-- I can shoot my d700 in crop mode, but it turns it into an expensive 5 mp camera.

The only thing that is not equal between a 35mm on aps vs. 50mm on full frame is dof at a given aperture--longer focal lengths give a tighter dof.

 

[molested_cow]

Okok, I did a quick one using my point and shoot. In theory this should work too.

What I did was, I took a shot at 1X, then the same shot at 3X. I then enlarge the 1X image to match the 3X to see if there's any difference in distortion. Well, there's none!

Ok I think I can sleep well tonight.

 

[molested_cow]

No simulation involved.


http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

Nice! My criticism will be that you should have used something with parallel edges as the subject so you can see the difference in perspective distortion. In this case, there's none.

 

[fokker]

I always thought that a good way to help yourself understand the effect that focal length has is to play around with a zoom lens doing 'dolly zoom' motions. Effectively you are focused on a subject and zooming in at the same time as you are backing away (or vice versa) to keep the subject the same size while altering the appearance of the background. They do it on Top Gear a lot, if you've ever watched the show you'll know what I mean.



Once you understand this effect, then the crop body effects will make a lot more sense I think.

 

[radiorickm]

A very basic answer to your question

What happens, when you blow up an image. When you crop it, you are only USING part of the image. The same exact thing on the sensor. It is projecting a full image, but because the sensor is smaller than a frame of film, you are only using PART of the image. How much depends on the size of the sensor.

BASIC answer.

 

[Ronaldo]

Crop factor - Wikipedia, the free encyclopedia

Okay - - but let's look at what this article contains:

The crop factor is sometimes referred to as "magnification factor", "focal length factor" or "focal length multiplier". This usage reflects the observation that lenses of a given focal length seem to produce greater magnification on crop-factor cameras than they do on full-frame cameras. This is an advantage in, for example, bird photography, where photographers often strive to get the maximum "reach". A camera with a smaller sensor can be preferable to using a teleconverter, because the latter affects the f-number of the lens, and can therefore degrade the performance of the autofocus.

Why is a crop frame an "advantage" in bird photography - - if the image projected onto the sensor (and the viewfinder?) is the exact same size on a crop camera as a full-frame camera (since the focal length of a lens is just that)? How does the crop camera provide extra "reach"???

Wouldn't the full-frame camera (with the same lens and distance) have exactly the same reach as a crop camera? And wouldn't the bird be the same size on the sensor and in the viewfinder (although the full-frame sensor and view-finder would contain greater total area)??

As with this article, I often hear/read that crop cameras are great for birds, etc. But this is not making any sense to me.

thanks for letting me ramble about this here. . .