K rings on DX lenses

[ibargureni]

Hi,

 

I was thinking about how useful a DX lens would be in a film body. If

the light rays are proyected in a cone form, that would mean that

taking the lens away from the body would make the proyected circle

bigger and the light would cover all the film, wouldn't it? So could

these lenses be useful for macrophotography in film bodies using, for

example, K-ringsets?

 

A problem with this method seems to be telecentric designs. I don't

know very well how these lenses proyect the light in the film/sensor,

but if they proyect perpendicular rays, this system could be useless,

since film to lens distance wouldn't make any difference.

 

Well, I don't have any DX lens yet, but it would be useful to know how

this combination works. Any comments are welcome,

 

Ioritz.

[vivek iyer]

Futile idea. Forget it.

[briany]

Vivek's mostly right, I imagine. What you're fogetting is focus. Objects closer than your focus point are focused behind the film plane. In order to get objects at infinity well behind the normal film/sensor plane distance, your lens would have to focus well past infinity, and of course none do. If you added enough extension to increase the image circle to film size (if possible at all), you could only photograph extreme macro.

[vivek iyer]

Brian, Why "mostly right"?

 

Show me a non G, "DX" lens.

[bjørn rørslett]

Most DX lenses are only partially useful with extension rings. You would expect a lens giving a larger image circle when it is farther away from the film plane, right? Wrong with all DX lenses I've tried so far. Their image circle in fact gets smaller, not bigger, when extension is added to the lens. For some of them (zoom designs) the image circle may be adequate over part of the zooming range so you can at least use them for close-ups on a DX/DSLR camera, the 18-200 VR being an example. However, both the 12-24 DX and the 18-200 DX towards their shorter end will give focus inside the lens assembly if used in conjunction with extension tubes, which isn't very practical :(

[ibargureni]

Thanks for all the answers. Well, in fact, I obviously meant to use them for macro photography (as stated in the original post). However, it seems, as Bjorn confirmed, that the design of these lenses isn't done bearing in mind the use of extension rings. Moreover, as Vivek noticed, all the DX lenses (correct me if I'm wrong) are of the AF-G type, so their usefulness is quite limited and very impractical.

 

So, thanks for the answers again and contunue exploring...

 

Ioritz.