RE: lens questions

...and this leads me to recall that the only successful photo I've seen
of someone welding was taken using fill-in flash...
Kate

-----Original Message-----
From: Harry Smart [mailto:harry@harrysmart.plus.com]
Sent: Thursday, 7 July 2005 2:22 a.m.
To: alt-photo-process-l@sask.usask.ca
Subject: Re: lens questions

I've tried shooting welding a couple of times, and, assuming you're
talking about arc welding, the arc itself and the area around it are
going to burn to solid black on the neg pretty much whatever you do. I'd
consider metering from that area as completely pointless. How wide that
area is and how bright it is at its core will depend largely on what's
being welded, the size of the rods, the current the welder is using,
etc. and will also vary substantially during the weld as the
conductivity of the joint that's being formed changes substantially. If
they're working along a seam, then once you've got over striking the
arc, and if they're good (i.e. they keep a constant rate of movement to
achieve a consistent depth of weld ... and most welding is actually
pretty rough work, so don't count on consistency unless you know your
guys are good and are working to close tolerances) then you should get
fairly steady illumination. The falloff of light from the arc itself
will be very steep, so, if you can protect your eyes, you should be able
to use a spot meter to get values for areas close to the arc ... I'd
suggest you equip yourself with one of the masks that are clear up to
the moment the arc is struck, and which then darken immediately. I've
used one when welding myself and they really are magical ... I got mine
on ebay quite inexpensively ... they cost hundreds when they first
appeared a few years ago.
 
However, even so, I think you'll find there's a lot of wasted shots.
Quite apart from the consistency of the light output from the weld, your
welders will probably be continuously varying the angle at which the
present the rod to the joint, you'll find that sometimes the workpiece
itself is masking part of the arc .. and you'll just have to shoot a lot
to get the occasional good result.
 
Cheers,
 
Harry

----- Original Message -----
From: HYPERLINK "mailto:jdos2@mindspring.com"Jeff Sumner
To: HYPERLINK
"mailto:alt-photo-process-l@sask.usask.ca"alt-photo-process-l@sask.usask
.ca
Sent: Wednesday, July 06, 2005 2:35 PM
Subject: Re: lens questions

On Jul 6, 2005, at 2:31 AM, Barry Kleider wrote:

Last week, I was shooting some welders.

My ultimate goal was to shoot them with a Hasselblad and a 150 f4 lens.
(No internal meter.)

Since these exposures are obviously tricky, I started with my Nikon D-1
and a Tamron 28-70 f2.8

I was getting some decent exposures - nothing great, but certainly
within tolerance for a first attempt. So I decided to switch over to the
Hassy using the same readings.

Since the Nikon was running at ISO 200 and my provia is 100, I gave it a
full stop. I got the lab results today: $%#^$%. (Translation: way too
dark and looks like s**t.)

So my question is: what's the relationship between a medium format Hassy
with a 150 f4 lens, and a 35mm Nikon with a 28-70 f2.8 lens (running
close to 70 if not full on)?

I assume there's a very straight-forward (though possibly hard to
follow) explanation having to do with the difference in lens designs
rather than a format comparison or a digital vs. analog thing (as my lab
guy surmised.)

Barry

Lens speed and shutter speeds are constants between the format.
Measuring with a meter through one in any format will work fine in
another, depending on what you are metering.

You say the prints are too dark- how do the negatives look? Are they
thin? Did you take pictures metering with that actinct light from the
welder? That brightness can easily fool the folks doing the printing (or
much more likely, the machine doing the printing)

f-Stops is f-stops.

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