Calculating the Focal Length

[Dee_000]

Hi

Although I've been a keen photographer for a few years now, there are still parts of photography that I struggle with and this is one! :bonk:

I have put an app on my phone to help me with DOF, Hyperfocal Distance etc, but the first thing it asks you to do is to populate the is the focal length field

I get it for a standard prime lens, eg that for my 50mm lens the focal length is 50, but what about when I use my 28-300 lens, how do I work it out then? I'm probably being very stupid and there is an easly solution but I've searched and searched the web and I cant really find anything to help me (or that I can understand!) or maybe I just think its more complicated than it really is, or not that necessary

does anyone have a formula or advise about how to do this Janet and John style??

BTW I have a full frame camera

D

 

[Russ77]

It will vary for any given focal length, whether it's a prime or a zoom.

The DoF and hyperfocal distance will change for any given focal length between 28-300mm, there isn't a one size fits all answer

 

[dinners]

Agreed - the hyperfocal distance will just be governed by what focal length your zoom is currently set at.

I guess the key (unless the zoom has scale on it) is knowing where you are between the 28mm setting and the 300mm setting.

 

[simonkit]

You're not stupid - it's difficult to implement hyp distance accurately on lenses that don't have a Depth of Field scale for the very reason you mention, you don't really known exactly what focal length you are at or not from reading the lens anyway.

A way around this may be to take an initial shot and then view it on the screen whilst displaying all the Exif data - it should tell you what focal length the shot was taken at - the difficulty is in keeping the lens at the same focal length whilst doing this:bonk:

Simon

 

[Dee_000]

You're not stupid - it's difficult to implement hyp distance accurately on lenses that don't have a Depth of Field scale for the very reason you mention, you don't really known exactly what focal length you are at or not from reading the lens anyway.

A way around this may be to take an initial shot and then view it on the screen whilst displaying all the Exif data - it should tell you what focal length the shot was taken at - the difficulty is in keeping the lens at the same focal length whilst doing this:bonk:

Simon

Thanks very much Simon (and for saying I'm not daft ) I will give this a try.

D