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Re: The highest aperture is not always the best

Posted: 17 Aug 2009, 08:35
by daniel_reetz
Also, we should consider that when zooming in the aperture decreases....
But that may be effective aperture VS physical aperture size. Effective aperture doesn't necessarily have such detrimental diffraction effects.

Re: There is no aperture

Posted: 17 Aug 2009, 08:42
by fbonomi
daniel_reetz wrote: 2. These lens mechanisms are extremely complex and very easy to break. ;)
Yes, it's (almost) the only moving part in those P&S camera, it's incredibly tiny and must be incredibly precise...

Therefore, it's the primary cause for camera mis-functions.

A while ago, Canon was giving (in case of a lens mechanism malfunction ) an error message saying "E18".

This became infamous, to the point that there is a wikipedia page devoted to this problem ( http://en.wikipedia.org/wiki/E18_error ) and a specific site ( http://www.e18error.com )

Newer cameras just say "lens error" but the idea is the same

http://www.google.com/search?q=e18+canon (91.000 hits)
http://www.google.com/search?q=canon+lens+error (183.000 hits)

Re: The highest aperture is not always the best

Posted: 17 Aug 2009, 08:46
by fbonomi
daniel_reetz wrote:Since many of us are using an A590, it would be interesting to know if it has an iris or not.
Yes it has.

sorry, my eyes were tricked by the long listing...

Re: The highest aperture is not always the best

Posted: 17 Aug 2009, 09:01
by fbonomi
daniel_reetz wrote:
Also, we should consider that when zooming in the aperture decreases....
But that may be effective aperture VS physical aperture size. Effective aperture doesn't necessarily have such detrimental diffraction effects.
Oh, I see ...

Actually, I almost see... I love the term "Circle of confusion" because it describes exactly how I feel when reading about that stuff :-)

Re: The highest aperture is not always the best

Posted: 17 Aug 2009, 10:49
by daniel_reetz
Actually, I almost see... I love the term "Circle of confusion" because it describes exactly how I feel when reading about that stuff :-)
Actual VS effective aperture is one of the most confused things in photographic lit, I swear. The general idea is simple, or at least it is off the top of my head. If you zoom way out, you are utilizing less of the lens surface in terms of degrees of visual angle. Because of that, the number of light rays collected is somewhat less. This reduces the amount of light hitting the sensor, thus "shrinking" whatever aperture value you initially picked.

But I could be wrong about the precise definition. I need to scan all my photo books. I need to put my book scanner back together very badly. And I'm tired of moving and stupid health problems keeping me from fun stuff like this. :)

Re: The highest aperture is not always the best

Posted: 17 Aug 2009, 11:06
by fbonomi
daniel_reetz wrote:Actual VS effective aperture is one of the most confused things in photographic lit, I swear.
That's my very intuitive and probably approximate way of seeing it.

Actual aperture (measured in millimeters) is the diameter of hour "hole". This hole collects light, the "paint" we will use for our image

If we have a short focal length, we are using this paint to paint a small image.

If we keep the hole the same size but a longer focal length, we are painting a larger image with the same amount of paint, i.e. the image is "faded"

Effective aperture, being "diameter / focal length" measures how effective we are in painting: higher focal lengths give a smaller effective aperture.

On the other hand, speaking of images being blurred by diffraction and similar stuff, you are saying that the smaller the hole (the smaller the actual aperture) the more diffraction we have, regardless of focal length.... This kind of makes sense.
daniel_reetz wrote:stupid health problems keeping me from fun stuff like this. :)
Sorry to hear this... I hope it's nothing too worrying and best wishes!

Re: The highest aperture is not always the best

Posted: 20 Aug 2009, 20:10
by jradi
This has been a fascinating read!! I want to encourage everyone's experimentation along these lines. I had noticed the same phenomena but I didn't understand what it was, I'll have to do some experimenting to see if a different f-stop will yield a better result in my situation. Thanks!

Re: The highest aperture is not always the best

Posted: 26 Aug 2009, 09:13
by tsttm
thanks for the info.

i went with a larger aperture but realized (after scanning a whole book) i had to increase the speed accordingly. Otherwise, the page came out too bright- kinda bleached out, so the text seemed faded & blurry. At first i thought i was out of focus, but it simply was too bleached out (maybe my light is particularly bright-500w halogen).

Anyway, after increasing the speed accordingly, the text was much crisper (although the pages end up kinda grey- but i prefer slight grey to blurry).

Re: The highest aperture is not always the best

Posted: 26 Aug 2009, 10:46
by fbonomi
tsttm wrote:Otherwise, the page came out too bright
but have you disabled the camera auto-exposure ?

I mean, the camera should compensate automatically...

what camera do you have? In wha mode are you shooting, and what are the settings?

Re: The highest aperture is not always the best

Posted: 29 Aug 2009, 13:47
by tsttm
I'm using A590s. how do you turn on/off the auto exposure?

I'm shooting in manual mode, so i set the aperture & speed. i was just following the suggestions in the instructables settings. So, when i increased the aperture, it turned out the speed was too low.

should i use a different mode?