Lense aperature numbers

[NCHornet]

I am trying to decide on a new DSLR and I have a question about the aperature numbers. I moving uo from a Minolta TSI Plus SLR camera. I have used a light meter to shoot some studio type work with some strobes I purchased. Usually the meter will recommend a F 8-11.5 aperature at 1/90th sgutter speed. I have just been using the kit lenses that came with the camera. I noticed on the 35-75mm that my lense only has a aperature rating of 3.5-4.5 . However when I would set the camera for F8 ( if that is what the light meter told me to do) I would always get good results. Was I actually shooting in F8 or F4.5? Just a little confused and want to get this clear before I take the plunge.

Also I was looking at D90 and if it says it comes with a 18-105 lense, has this already been adjusted for the sensor since it's on a DSLR camera or do I need to mulitply these numbers by 1.5 (IIRC)
Thanks for the answers to my beginner questions.
Kevin

 

[NCHornet]

Ok I think I have answered my own question, when the lense says F3.5-4.5 this is the maximum aperature size throughout the focal area, the min isn't listed on the lense but would probably be above F 22. I am I right about this?

 

[Steph]

Ok I think I have answered my own question, when the lense says F3.5-4.5 this is the maximum aperature size throughout the focal area, the min isn't listed on the lense but would probably be above F 22. I am I right about this?

You are right.

 

[Steph]

Also I was looking at D90 and if it says it comes with a 18-105 lense, has this already been adjusted for the sensor since it's on a DSLR camera or do I need to mulitply these numbers by 1.5 (IIRC)
Thanks for the answers to my beginner questions.
Kevin

The focal length is a physical characteristic of the lens, which does not depend on the camera it is mounted on. In terms of field of view, you have to multiply by 1.5 to get the focal length that will give you the same field of view on a 35mm (or full frame) camera. For example, a 18mm lens on a D90 and a 24mm (18mm x 1.5) on a D3 will give the same field of view.

 

[NCHornet]

Thanks Steph!!

Kevin

 

[Pure]

Lens usually have a 22 or 32 minimim aperature, but that isn't labeled on the lenses

 

[skieur]

. For example, a 18mm lens on a D90 and a 24mm (18mm x 1.5) on a D3 will give the same field of view.

I believe 18mm X 1.5 = 27mm NOT 24mm, as you have indicated.

skieur

 

[Steph]

I believe 18mm X 1.5 = 27mm NOT 24mm, as you have indicated.

skieur

Well spotted!