An unplanned technical test for my telephoto

A glance up into the woods behind the house when I was working in the back garden afforded me the view of a rather splendid Red Kite perched in the trees. Not unusual, I think they roost in there, but on this occasion, it was sitting pretty much in the open and was bathed in warm winter sunshine.

An opportunity not to be missed I ran inside to get my camera; it fortunately had my new Canon 75-300 IS lens (not the expensive one!) attached, was set to AE mode and allowed me to shoot straight away. Although the bird was about 100 years away and high up in the tree, I could get a shot, but was nowhere near filling the frame, despite a 1.6X crops sensor.

My bird seemed quite happy sitting there so I went back in to switch over to my Sigma 150-600mm so an effective focal length of 840mm at the big end. And as I did this I thought I could do a little experiment I’d been planning for a while:

  • Was my Sigma lens a little soft at the 600mm end, as some commentators have suggested?
  • Is it better to use it at 500mm and then crop in post-processing?
  • Is the benefit of the shorter Canon telephoto allowing me to hand hold in a more steady way a benefit? And again if I crop into the same size, do I really lose much quality?

The three images

I’ve selected three photos which have been treated in roughly the same in Lightroom and then I’ve resized the photos so the bird is approximately the same size in the frame. It’s all a bit non-scientific but is also a “real world” test. The shooting data for each was:

Photo # 1 2 3
Focal Length Canon 300mm Sigma 500 Sigma 600
Aperture f/5.6 f/6.3 f/6.3
Shutter Speed 1/1250 1/5000 1/4000
ISO 100 640 640
Cropped? Yes A little No


Canon 300
Sigma 500
Sigma 600

In my view

In my view the two photos with the Sigma lens yield a little bit more detail in the birds’ chest feather and eyes than the photo from the Canon 300 which is essentially cropped to use only half the image. That said, I am still impressed with the quality of the “expanded” Canon lens image. I also cannot see any difference in quality between the two Sigma images re-assuring me that even at the far end of the telephoto range, this lens is capable of providing great results.

Note however that I was shooting at a superfast shutter speed; a next step in this experiment would be to decrease that speed and see how beneficial the 4 stop IS really is for handheld shots. I know I can hold the small lens a lot more steady and if I were following a moving bird, this would be a much easier lens to use.

So, this begs the question if other members have tried similar experiments over the years, or at least have anecdotal evidence that modern day lenses can allow for significant cropping without a major impact on quality? Maybe you could share these with us?

I am certainly going to try out the same sort of experiment photographing moving birds. Our membership secretary, Nikos, recommends the hillside at Turville, for great Red Kite photography.

I do also have a cunning plan to make a more scientific experiment of these lenses at different apertures. You know, the sort you see in the camera magazines, but without the graphs which never seem to bear any relevance as far as I can see.

Anyway, all for now.

Have a great and safe Christmas everyone

Gareth Fish
Club Secretary

Gareth Fish

Generally having fun, mostly outdoor genres of photography. I look after the Night Photography SIG for the club. If you are interested in going the DarKnights, give me a call