On 04/03/2011 16:29, Eric Weir wrote:
After reading Jostein's response to Mike I realized I shoulda been writing to
Mike! My apologies, Mike! Thank *you* for the very clear explanation.
Er, no. You were right the first time - I just clarified a small
technical point. Do you use google mail, by any chance?
On Mar 4, 2011, at 2:13 AM, AlunFoto wrote:
I find that the only way to achieve accurate focus is to home in on
the subject with fully open aperture and then stop down for exposure.
The guy in the video seems to work with the lens already stopped down
when approaching his subject. I think the viewfinder becomes too dim
and focus too inaccurate working that way.
....
Starting with the K-series DSLRs, Pentax abandoned its old TTL flash
metering all together. In the *istD, there was a separate light meter
for flash, measuring the incoming light onto the CCD chip and capable
of quenching flash output when sufficient illumination had been
provided. This system had been in use, in various incarnations, since
the Pentax LX (1980). The P-TTL system no longer meters flash output
during exposure, but use a preflash. For P-TTL to work, it needs
aperture and focal lenght information from the lens. Thus it can only
work with FA- series lenses and newer. So with a
reveresed-lens-on-tubes setup, there's no flash metering at all.
Would use of flash in this kind of photography be necessary?
It is absolutely necessary. To achieve at least a nominal depth of
field, you need to stop down to f/11 or f/16. In addition, you lose a
couple of stops worth of light through the extension tubes. However
it's not as bad as it seems. A good quality flash (just avoid Sigma
and you're good) will provide the same output every time when set to
manual. When you work with a reversed lens, your working distance is
constant. So effectively, the same combination of flash, aperture and
lens setup will provide the same result every time, regardless of
ambient light. You just have to work out the right combination in
advance. That's a breeze with histograms, you know. I'm old enough to
remember how frustrating that was with gelatine... :-)
Thanks for the very clear explanations, Jostein. I was going to try to quote
extracts of it in responding, but couldn't find a word to leave out. I've
flagged the message for keeping.
Real understand requires practice. I'm getting hardly any practice -- neither
shooting nor processing. I can imagine spending my time doing hardly anything
else, but there are other things that matter that I'm loath to give up. There
is not enough time for it all.
Get clear about priorities, be hard-nosed about it, bite the bullet.
------------------------------------------------------------------------------------------
Eric Weir
Decatur, GA USA
eew...@bellsouth.net
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