[Not a Number]

Pressing the INFO button on my K10D shows the zoom setting on AF lenses the entered setting for MF lenses.

Why not in the viewfinder or top LCD panel? Lack of space or lack of connections on the controller chip. If you're looking at the top LCD it's easy enough to look at the zoom setting on the lens at the same time.

[Wheatfield]

Hmmm...I guess I never noticed that before. If I zoom, it is seldom to a particular focal length.


Steve

I sometimes think that if everything that everyone wants in the viewfinder was in the viewfinder, there wouldn't be any room left to compose an actual picture. It would all just be a jumble of dancing lights.
Do people not just take pictures anymore?

[RobA_Oz]

I sometimes think that if everything that everyone wants in the viewfinder was in the viewfinder, there wouldn't be any room left to compose an actual picture.

It’s one of the advantages of mirrorless bodies, of course.

[Wheatfield]

It’s one of the advantages of mirrorless bodies, of course.

I'm sure.

[jumbleview]

Do not most zooms have a scale written on the lens itself ?

They have, but:

• Scale is non-linear usually
• Precision is not very good compare to aperture scale for example

[vonBaloney]

Zooms can be particularly prone to focus breathing, so except at infinity even an "accurate" number is often not very indicative of the actual angel of view you are getting on your subject.

[pschlute]

Zooms can be particularly prone to focus breathing, so except at infinity even an "accurate" number is often not very indicative of the actual angel of view you are getting on your subject.

True, but neither will any digital display of the FL in use. I had the DA* 60-250 which at closest focus distance had a real FL of about 190mm. EXIF still told me it was 250

[vonBaloney]

True, but neither will any digital display of the FL in use. I had the DA* 60-250 which at closest focus distance had a real FL of about 190mm. EXIF still told me it was 250

Yeah, that's what I'm saying. Don't worry about the number -- no matter how you get it, it will be wrong half the time anyway.

[alfa75ts]

Pentax uses a set of switches in the lens to give an approximate focal length, usually 4 or 5 switches giving 16 or 32 steps. How the length is calculated for each step I do not know.

As an example the DAL 55-300 and the 55-300 PLM both have 16 steps while the 18-250 has 32 steps (I just checked these lenses).

Edit: The Sigma 50-500 Mk1 has 15 steps.

[Not a Number]

Simple, represent the steps in binary.. 5 witches = 11111 binary = 31 decimal include 00000 and you have 32 steps. Four switches 1111 = 15 decimal including 0000 for 16 steps total.

So you just turn the switches on or off for each of the steps. I don't know about the newer lenses but the older lens had four or five parallel strips of contacts and four or five brush, comb or finger contacts that slide along the strips. It's just a matter of insulating parts of each strip along the length to represent the binary numbers between zero and 15 or 31. Insulated = off or a binary digit 1.

[stevebrot]

It’s one of the advantages of mirrorless bodies, of course.

I'm sure.

Of course, if the feature was exposed on Pentax cameras, there would be endless complaints that there are not enough steps and the numbers are wrong. I like things the way they are


Steve

[stevebrot]

They have, but:

• Scale is non-linear usually
• Precision is not very good compare to aperture scale for example

If the scale is non-linear*, that is a pretty good indication that the reported EXIF will also be so. Ditto for precision.


Steve

* I'm not quite sure what that means in this context

[alfa75ts]

A plot of the above lenses, both 55-300s are the same:

[mikesbike]

Do not most zooms have a scale written on the lens itself ?

That is what I generally use to set a particular FL if I need to do so. This is usually close enough to meet my need. If I should ever want to get a more exacting reading for sake of comparison, I can always just shoot a quick test shot and get a reading in the full info screen.

[jumbleview]

If the scale is non-linear*, that is a pretty good indication that the reported EXIF will also be so. Ditto for precision.


Steve

* I'm not quite sure what that means in this context

If lens (like 18-135mm for example) has scale marking 35 and next one 50. And suppose you put the zoom in the middle. What would be actual focal length? 42.5? 43?. Camera reports 40 actually. Moving further to the long end it is even more confusing.