Crop vs. FF Basics

[skipd]

Bugger - WHEN WILL WE BE ABLE TO EDIT POSTS?

 

I meant Robin above, not Ron.

[wdgodwin]

Now I'm confused. Ref - "There is also more background blur with a FF compared to a crop". This is the reverse of what I've been taught. It seems to me that with the smaller sensor on the same glass would yield more DOF.

 

David Godwin

[robin_sibson1]

Sorry if I did not make myself clear. What you want and expect to see through the finder is what falls on the sensor (or 98% of that or 95%, or whatever). That depends on the focal length of lens you are using. The question is, how big does it look through the finder? Or, in more precise terms, what angle of view does the image seen through the finder subtend at the eye? On a film or FF digital SLR, this is usually most of the way out towards the peripheral-vision part of the field-of-view of the eye. On a smaller-format DSLR, it isn't, and you get a 'tunnel vision' effect. It doesn't have to be like that, but if you (or, rather, the camera manufacturer) chose to give you a bigger image, it would also be dimmer.

 

What confuses things is the convention of quoting the magnification factor of the entire system with a 50mm lens. That is, if you look through the finder with one eye and straight at the subject with the other, what is the scale factor relating an object in one image to the same object in the other image? That's how the magnification of a telescope is defined. The problem is that if you wanted to use a 50mm lens on FF you would want a lens of about 32mm on 1.6-factor to capture a similar image from the same viewpoint. So if, for example, a viewfinder magnification of 0.7 gives a nice image on FF, then following the usual convention for quoting VF magnification, you'd need a magnification of 1.12 on a 1.6-factor body, and actually you get something under 1.

 

That's the best I can manage - if you need any more help, someone else will have to provide it, I'm afraid.

[andy_witkowski]

RE: Viewfinder

 

I guess it really depends on what your previous camera experience is. If you came directly from 35mm film camera, then you'll think the crop dSLR's viewfinder is smallish and dim. Coming from many Point and Shoot cams, you'll love how bright the crop dSLR's viewfinders are.

 

Its all relative :)

 

 

Take the 70-200 f4 L and try both the 30D and 5D, you'll see the difference in the viewfinder.

[matthias_meixner2]

> Now I'm confused. Ref - "There is also more background blur with a FF

> compared to a crop". This is the reverse of what I've been taught. It

> seems to me that with the smaller sensor on the same glass would yield

> more DOF.

 

Things become clear if you consider that you have to scale everything to get from a crop camera to FF: Shooting a subject in 10m distance with a 50mm lens is equivalent of shooting a subject in 16m distance (that is by a factor of 1.6 taller and wider) with a 80mm lens. In reality things do not become larger just because you swap the camera, i.e. you will have to get closer with the FF camera to get the same image size of the subject (you will want to have it also at a 10m distance). But getting closer means getting more background blur.