3" lens Worthwhile for Direct Shooting?

[Alwyn Adkins]

Gday all, I've just received a 2" Simpson 16mm lens for direct-shooting-capture from my projector and am very happy with the results, especially after I took Nantawat's advice and "peered" into the lens to get it sorted out!

I then got to thinking... would there be any benefit in going to a 3" lens? My logic is that the film image would be further enlarged, meaning less zoom on my camcorder and therefore better quality. But I'm no expert on optics so can't say whether a 3" lens would be better (or even work).

Any thoughts from the floor on whether a 3" lens would be better?

Thanks very much for any input.

[Stan Jelavic]

Hi Alwyn,
By 2" lens you are referring to 2" focal length which is around 50mm. Then yes 3" focal length would give you more optical magnification. It is similar to using the long focal length camera lenses for tele photography. But the things are not as simple. There could be complications.
- Longer FD lenses will sit further away from the gate and could produce vignette. You can search on that if not familiar with the term. Essentially the edges of the picture will become dark.
- Obviously you need a good quality lens and it has to work good with the camera-to-gate distance.
- The longer FD lenses give less light to the camera and you may have to increase exposure which may require lower scan speed.

There are more issues, but if not too expensive, the best way is to get one and try it.

[Alwyn Adkins]

Thanks Stan, that gives me food for thought.

[Nantawat Kittiwarakul]

I think it would be other way round - longer FL lens would give you smaller images.



For example, I'm also using 50mm lens on the projector side but a short (35-70 mm) zoom lens on the camera side. I've found that if I zoom all the way in at 70 mm (hence 70/50= 1.4:1 magnification), the image would nicely fill the entire frame nicely plus some borders for further cropping. But if I zoom out to 50mm (1:1 magnification) the image would be rather small, with large borders left in.

So my conclusion is that you may instead need shorter FL lens on the projector side, in order to get larger image on the camera side. However I've found that 50mm lens seems to work equally well with all cameras/camcorders I've tried. Even a camcorder with relatively short (10x) zoom lens seems to work OK too.

[Stan Jelavic]

Ok good point Nantawat. I forgot that this uses the virtual image. But anyways I ran the optical simulator and it shows that the magnification change is insignificant if you go shorter or longer FD. But the camera image distance to the camera lens (not 50 mm lens) changes significantly. So if you go with a 3 inch lens it the camera may not be able to focus. So, no significant benefit and potential focus problems. Thanks for the heads up.

[Alwyn Adkins]

Thanks Nantawat and Stan. I appreciate your feedback.