A Nurse with a Gun

Thursday, April 16, 2009

When 85mm is Really 129mm

I make no bones about liking to isolate my subject in a photograph among an indistinct background of relative subdued colors. In the past, with film, that desire led to an appreciation for the 50mm prime lens. Click to enlargeTo gain the indistinct background, the depth of field must be narrowed by cranking open the aperture.

The 50mm prime lens not only frequently gave the sharpest details and less distortion of the form, but the larger f stops allowed me to isolate my subject as I desired. The ability to shoot in low light with a larger aperture was a bonus. As a result, I ended up with a small collection of 50mm lenses in the ƒ1.4 to ƒ1.2 range. I learned to fill the frame of my photos by shooting close, and moving.

When I purchased my Nikon D-200 complete with an 85mm ƒ1.8 prime lens, I was relieved to get some space between myself and my subject. I did not realize just how much space I was using until I took photos of people at the Tea Party.

I had an immediate advantage in that people thought I was photographing them with their sign when I was actually taking a portrait. When I wanted to get the entire person in the frame though, I had to back up to a distance that confused my subject.Click to enlarge Even my fast fifties seemed to need more distance to frame the same subject on the D-200.

After a bit of research at Ken Rockwell's website, I found that what I was sensing was reality. The Nikon D-200 is a DX camera. That means that its sensor is 1.5 times smaller than 35mm film. That is not necessarily a bad thing. What it means is that a lens with a 50mm focal length actually reads as a 75mm lens. My 85mm prime was reading as a 129mm telephoto on the digital camera. My 70-210mm zoom lens reads as a 105-315mm lens! Ken has a page at his website explaining the crop factor when SLR lenses intended for film are used on a digital SLR, as well as a chart to convert the focal lengths.

While I will likely continue to enjoy the 85mm lens for portraiture, I am considering purchasing a 50mm ƒ1.8 prime lens for when I am taking photos of people in tighter quarters. I already have a 18-70mm auto focus zoom lens that fills that focal length, but its aperture is a variable ƒ3.5-4.5. For the isolation of my subject, I want that big hole in the back.

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9 Comments:

Anonymous VariableFeedback said...

Xavier - You may want to try a 35mm prime - it would closely approximate your previous experience with a 50mm.

7:01 AM  
Anonymous 2yellowdogs said...

Xavier,
Just bought a 50mm f1.4 so have a surplus 1.8 with original box. Was going to eBay it, but if you're interested, let me know and I'll make you a good price.

7:20 AM  
Blogger Les Jones said...

The crop factor is very helpful on the telephoto end. You don't get something for nothing, though. At the wide end it makes your lenses less wide. That 18-70 becomes a 24mm at the wide end, which isn't what you want.

Still, horses for courses. DX is great for telephoto. Landscape photographers who need wide angles like the new FX cameras (or 35mm, if they haven't switched to digital.

8:48 AM  
Anonymous Anonymous said...

You're in luck since you are using a Nikon. Nikon is 2nd best in compatibility of old lenses to new DSLR models (Pentax is a little better on that). You've got a wide range of stuff availible in pawnshops and on ebay.

8:49 AM  
Blogger Les Jones said...

Er, wait, no. 18 becomes 27. Need coffee.

8:49 AM  
Blogger Chris Byrne said...

You may also want to consider the new 35mm f/1.8 that I wrote about a few months back. it's $200 and it's a DX specific lens; but it gives you the equivalent of a fast 50 prime on a DX camera.

11:12 AM  
Anonymous Anonymous said...

Xavier -
The 50mm will also come in handy if you are take indoor shots, by existing light. Emjoy!
~Sandee~

3:17 PM  
Blogger sandee said...

Xavier, you will like that 50mm for inside shots with existing light, also. Enjoy!
~Sandee~

3:19 PM  
Blogger Xavier said...

VF, I'm thinking the 50 on a DX will give me the distance I had previously wished for shooting film with a 50.

2YD, Many thanks for the offer, I figure I want a f1.4 with AF, one of the older Japanese ones with a metal barrel and mount.

4:59 PM  

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