Re: lens questions

From: Richard Knoppow ^lt;[email protected]>
Date: 07/06/05-02:05:55 AM Z
Message-id: <19612601.1120637155272.JavaMail.root@wamui-mouette.atl.sa.earthlink.net>



-----Original Message-----
From: Barry Kleider
Sent: Jul 5, 2005 11:31 PM
To: "[email protected]"
Subject: lens questions

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
  If you are asking about angle of veiw the ratio is based on the ratio of the diagonal of the formats. "Normal" for a 6x6cm is about 80mm. For a 35mm camera the diagonal depends on whether you crop the negative (or transparency) to another aspect ratio. Normal for the 24mm x 36mm frame is about 44mm. If you crop it to the dimensions of an 8x10 the "normal" lens is about 37mm. Since a 150mm lens is about twice the "normal" FL for a Hassy a lens somwhere around 75mm to 90mm would have equivalent angle of view for 35mm.
   If you want to compare the performance if various designs you are getting into something rather more complex. Most Hassy lenses and most fast 35mm lenses are of the same generic type known variously as a Planar or Biotar or Opic. This is a very powerful design. Nearly all lenses of f/2.0 or faster for 35mm cameras and many lenses of f/2.5 or faster for 6x6 cameras are based on this type. The performance of an actual lens is dependent on both the skill of the designer and the quality of manufacturer. Since modern lenses are designed with the aid of a computer the designs are generally good. That still leaves the quality of manufacture so you should really evaluate individual lenses by trying them.
   Despite the popularity of the idea that current lenses are much better than those of the past its simply not true. Good glass and computer aided design have been available for decades. In fact, some types of very desirable glass are no longer available because they contain toxic or environmentally destructive materials, for instance Arsenic. Many classic lenses could not be built today because the necessary glass is not available.
   I hope this is helpful to you.
 
 

--
Richard Knoppow
[email protected]
Los Angeles, CA, USA
Received on Wed Jul 6 02:06:14 2005

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