Focal length in SR for manual lenses

One of the really good things about my newly acquired K100D is the compatibility with my old K-lenses.

Now I have learned that there is a 1.5 factor to the focal length for lenses made for 35mm film as compared to digital lenses. E.g. my old 50mm "analogue" lens is the equivalent of a 75 mm "digital" lens.

So what do I input as the focal length for SR, the actual focal length or multiplied by 1.5?

Always use the actual focal length - in this case 50mm.

Any 50mm lens on your digital camera acts like a 75mm lens on your film camera.

Digital specific lenses have the same focal length, just a smaller image circle.

Thanks for the responses, folks

This can be read two ways!! Perhaps it might have been better phrased:

'Any 50mm lens on your digital camera acts like a 75mm lens would act on your film camera.'

Because, of course, if you're used to the 'digital' angle of view, and you put your 50mm lens on a film camera, it will be acting like a 35mm lens* (well, 33)!

It all seems very complex, but the good news for the OP is that it doesn't take very long (if you're taking pictures mostly with the digital camera), for the brain to completely make the switch to finding the narrower angle of view perfectly normal.

But yes, actual focal length for the SR (thank goodness!!)

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* would act on your digital camera

That's definitely a better wording.

Sure you would enter the actual focal length - simply because that does not change? The 50mm lens from a 'film' SLR acts as a 75mm lens on a digital SLR only in as much as the field of view approximates the FOV of a 75mm lens. The 'reach' is no different........it does not bring your subject any closer.

Mike

A 50mm lens is always a 50mm lens regardless of what film or sensor size you put behind it.

All this is completely moot these days.

I guess for those still taking pictures with film and digital it prolongs the need for mental agility, but in the year I've now had the K10D I've looked through a 35mm viewfinder perhaps four times, and each time it's made me think, "blimey that's wide".

It's just a question of what you're used to - I simply expect to see what I see now. 18mm is the start of wide, whereas 28 was before.

It's getting there, certainly for the APS-C sized sensors.

The problem really arises with compact cameras as the size of the sensor is so variable. As a consequence it's difficult to relate to the actual focal length, hence the reference to "35mm-equivalent". Some are even marked up in 35mm-equivalent focal lengths.

This was never a problem with film because although formats were different they were at least a defined size. It's probably also true that the buyers were mainly enthusiasts and so they had a good knowledge of photography. There may now be quite a few non-photographers who are actually very good indeed at producing great images but who have limited technical knowledge.