Favoured Focal Length

It may just be that my Digital SLR is less kind to my ageing Tamron 28-200 zoom than film ever was, but since going digital last year I have become increasingly dissatisfied with the aforementioned lens. In short, it’s a load of garbage. Soft, lacking in punch, under-saturated colour, and no longer wide enough, because my DSLR’s 1.5 FOV factor turns it into the full-frame equivalent of a 42mm lens at the “wide” end. Mmm, that’s pretty much a standard lens.

I’m a little cross because the attraction of buying a Sony A100 (on holiday in the Far East last year) had been to go digital while saving on the cost of new lenses, but still benefiting from the Sony’s built-in image stabilisation. The Tamron zoom had been bought for my previous camera, a Minolta Dynax 7xi and Sony DSLRs take Minolta mount lenses. I admit the lens had been a reasonably cheap compromise at the time, to save changing lenses all the time, but it had always given reasonable results with film. However, if I’d realised how dreadfully my zoom would perform on my Sony DSLR I might have looked at switching to a different brand entirely; maybe Nikon or Canon.

The awfulness of the Tamron was brought home to me when I had occasion to use my other lens, a Minolta 50mm F1.7 standard lens. I was trying to take a portrait of my daughter wearing “African” make-up for a school dance competition. It was an indoor shot and all I had on the Sony was the built-in fill-in flash. The results were terrible so I popped the standard lens on and tried available light. The comparison with my zoom knocked me flat.

Sharpness, punchiness, contrast, beautiful colour. Nothing wrong with the camera, just the damnable Tamron zoom.

I’d like to ditch Sony altogether and go full frame with maybe a Canon 5D. It does raise the issue of what lenses I might go for. If you believe Ken Rockwell then any old glass will do for a 5D. I’m still pondering his logic, but I do not think there is any Canon mount zoom that covers the all-in-one range and is seriously up to the job of partnering a 5D.

I could go for a “walkabout” zoom and say a prime telephoto but will that match my natural usage of focal lengths? Question: what IS my natural usage of focal lengths?

I tried a free application called Smart Photo Statistics and set it loose on an archive of around 1,000 photos on my PC. The program reads all the EXIF data and charts the distribution of shutter speeds, focal lengths, apertures etc taken over the selected images.

This is what it produced for focal lengths:

If nothing else it confirms I have been hampered by loss of wide-angle capability. So many images taken on as wide a zoom setting as I can get. The peak at 50mm is mostly standard lens shots taken after I discovered how much better a lens it is than the Tamron.

What stands out is the polarisation between extremes of wide and telephoto. Most of my Tamron shots are either full wide or full telephoto. Maybe not so surprising. The most striking pictures either use wide-angle to exaggerate perspective, or telephoto to pick out a subject while blurring the background. Standard lens shots are often unmemorable.

It’s food for thought. My current thinking is a 5D with the 24-105 F4L IS walkabout zoom and the 200m F2.8L prime. And not bother with a flash. I far prefer images taken with available light.

First published here 5 June 2008 on my Windows & technology blog Hasta la vista, Vista!

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One response to “Favoured Focal Length

  1. I wondered whether it was common for lenses that were fine with 35mm film cameras to be shown up as bad performers on switching to a DSLR. I found this illuminating comment in a forum posting.

    “Modern sub-frame dSLRs have several characteristics that make them different than 35mm film SLRs. The biggest is that the image sensor/size is much smaller than a 35mm frame. While this results in extra magnification for tele work like wildlife and turns your 50mm into an 85mm, it also means you are cropping the image, and hence being a lot harder on the optics.”

    Yes, of course he’s right. My Sony A100’s small sensor is “pre-cropping” every shot and exaggerating the lens’s deficiencies. Obvious when you think about it. And it explains why Ken Rockwell (see link in main blog post) finds situations where a cheap lens can do better on a full frame DSLR than a more expensive lens on a small-sensor DSLR.