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I'm not really an absolute beginner, I've been using film SLRs for years but now I have finally upgraded to a d70 and 18-70 kit lens.

The next step was to replace my old SB24 with an SB800 and my first question - The lcd screen on the sb800 shows that the lens is set at 70mm but the actual effective focal length is equivalent to 105mm. Will this make any difference in practice?

Any comments would be welcome.

No, as far as I'm aware because although the cameras' FOV is 105mm, then lens' FOV is still 70mm.

Geoff Marland wrote:The next step was to replace my old SB24 with an SB800 and my first question - The lcd screen on the sb800 shows that the lens is set at 70mm but the actual effective focal length is equivalent to 105mm. Will this make any difference in practice?

Welcome Geoff!

I'm not very experienced flash user but very recently I've red Thom Hogan's D70 user guide and there he recommends to use 1.5x factor for manual flash settings

johndec wrote:No, as far as I'm aware because although the cameras' FOV is 105mm, then lens' FOV is still 70mm.

As I' said I'm not experienced flash user, so, I'll quote Thom Hogan again:
If you use it as with film camera "you normally be lightning a wider angle than D70 is taking in, wasting flash strength"

johndec, I think we are getting our focal length and FOV details confused here.

On a d70, the FOV using a 105mm lens is the same as the FOV using a 70mm lens on a 35mm camera. This is the multiplier effect which arises as a result of the size of the CCD on the d70 being 2/3 the size of a 35mm negative. (2/3 multiplied by 1.5 =1)

The SB800 uses the focal length of the lens - which relates to a 35mm camera - so therefore it will be lighting a wider area than the area covered using that focal length on the d70.

For what it is worth, my use of the SB800 which has mostly been in TTL mode (due to laziness on my part) has given outstanding results. The issue means that too wide an area rather than too narrow an area is being lit, so it doesn't matter unless you are trying to get the last ounce of power out of it for a distant subject.