Apertures back to front? (1 Viewer)

[pete schofield]

Hi all
I have been using a coolpix 995 for about 18 months but only for digi-scoping and previous to this used nikon slr's. On my recommendation my wife (also uses nikon slr) bought a 4500.

So here's one from the wife that I couldn't answer.

Why when zooming does the aperture get smaller as you zoom in and larger as you zoom out?

Now I am no expert but on all the zoom lenses I have used the opposite is true i.e. 100-300 zoom lens max aperture at 100 F4 at 300 F6.

Because I have only used mine for digi-scoping this has not bothered me, needing max shutter speeds at all times but she who must be obeyed uses her camera mainly for point and shoot and landscapes therefore requiring max depth of field.

Also how come we can only get upto F10 aperture on a digital or is it the same as with the lens add about a third (F10 = F16) or is it that digital technology just isn't good enough yet.

Hope someone can answer this as her indoors is not talking to me (some may say that's an advantage).

Happy Birding
Pete

o

 

[Adey Baker]

Pete

According to the spec, the Nikon 4500 has a maximum aperture of f2.6 at the wide end going down to f5.1 at the telephoto end so that should accord with what you expect.

As for minimum apertures, you do well do get f10, many only go down to f8 or even f6.7. I think this is due to the relative short focal length of lenses on digicams compared to 35mm, etc. As the aperture size is directly related to the focal length it can be very tiny at, especially, the wide end. A 7mm focal length at f8 would require an aperture of less than 1mm, which, presumably, would start to introduce degradation of the image due to diffraction. Also keeping the aperture a constant shape could be more of a problem at this sort of size.

Hope this doesn't bamboozle 'her indoors' - I would hate to be the cause of any 'deaf and dumb' mealtimes!

Adey

 

[Paul Rule]

As far as the zoom is concerned it obeys the same rules as any SLR zoom f2.6 at the wide end f5.1 at max zoom. .

As far as depth of field is concerned the f10.3 should give no problem for landscapes. This is more likely to be a problem with macro photography but in practice I have found the CP4500 to produce some nice macro results.

Havent done that many digital landscapes as yet but I think you will see from the following example (f7.7 @ 1/651sec) that you wife has nothing to worry about

Paul

 

[Paul Rule]

The following shows selected foreground middle and background from the above at higher magnification & resolution