Lower quality zoom lens or cropping higher quality wide angle?

Assuming your lenses perform anything like the lenses PZ tested:

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

the 55-250 at 130mm will deliver significantly more resolution

Based on PZ, I also bought  the 55 250. My findings are similar to yours. The pictures looked flat. For that reason, I returned it. If that was just coincidence, I dont know.

Great Bustard wrote:

Assuming your lenses perform anything like the lenses PZ tested:

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

the 55-250 at 130mm will deliver significantly more resolution.

The 15-85 at 85mm resolves (lw/ph -- center / edge) 2362 / 1846 at f/5.6 whereas the 55-250 at 135mm resolves 2157 / 2069. So, the lenses resolve essentially the same.

However, if you crop 85mm to 130mm, you retain only 65% of the resolution, which means that the 15-85 cropped to 130mm will have only 65% the resolution as the 55-250 at 130mm.

I note that you say how the 15-85 has "much higher IQ" than the 55-250. The possibilities are:

• Your 55-250 is substandard.
• The 15-85 PZ tested was substandard.
• PZ's test was either jacked or the MTF-50 measurement does not accurately represent IQ.
• The AF of the 55-250 is spotty compared to the 15-85, causing lower IQ in many photos.
• Your assessment of the relative IQ of the two lenses is in error.
• The types of pics you take with the 15-85 have more appeal to you than the types of pics you take with the 55-250.

In any case, if I had to bet, I'd certainly bet on the 55-250 delivering the better photos in the circumstances you describe.

Wow - thank you for the detailed and number-heavy reply! It was very useful. I think it's quite possible that my assessment could be partly to blame - I bought the 7D and 15-85 at the same time, which gave me a pretty big jump in IQ from the old 450D anyway, so that may also have influenced my perspective. Mind you, I've tried taking photographs of the same subject using both lenses and I still personally feel as though the 55-250 gives a 'duller' raw picture than that with the 15-85. It could also be that the 55-250 I own is substandard but I'm probably not enough of an expert to judge effectively!

Given that I'm using Lightroom, I would hope that any photos taken on the 55-250 for the display could be given the extra punch - crunching the numbers to show that I'd only be at 65% resolution if I cropped the 15-85 made me realise quite how much of the resolution I stood to lose! It sounds as though the 55-250 would probably be a wiser choice given the circumstances. Thanks again for your time and useful suggestions.

BengtS wrote:

Assuming your lenses perform anything like the lenses PZ tested:

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

the 55-250 at 130mm will deliver significantly more resolution

Based on PZ, I also bought the 55 250. My findings are similar to yours. The pictures looked flat. For that reason, I returned it. If that was just coincidence, I dont know.

It makes me feel a little better that I'm not the only person that thought that!

HappyHiker wrote:

Great Bustard wrote:

Assuming your lenses perform anything like the lenses PZ tested:

http://www.photozone.de/canon-eos/465-canon_1585_3556is?start=1

http://www.photozone.de/canon-eos/411-canon_55250_456is_50d?start=1

the 55-250 at 130mm will deliver significantly more resolution.

The 15-85 at 85mm resolves (lw/ph -- center / edge) 2362 / 1846 at f/5.6 whereas the 55-250 at 135mm resolves 2157 / 2069. So, the lenses resolve essentially the same.

However, if you crop 85mm to 130mm, you retain only 65% of the resolution, which means that the 15-85 cropped to 130mm will have only 65% the resolution as the 55-250 at 130mm.

I note that you say how the 15-85 has "much higher IQ" than the 55-250. The possibilities are:

• Your 55-250 is substandard.
• The 15-85 PZ tested was substandard.
• PZ's test was either jacked or the MTF-50 measurement does not accurately represent IQ.
• The AF of the 55-250 is spotty compared to the 15-85, causing lower IQ in many photos.
• Your assessment of the relative IQ of the two lenses is in error.
• The types of pics you take with the 15-85 have more appeal to you than the types of pics you take with the 55-250.

In any case, if I had to bet, I'd certainly bet on the 55-250 delivering the better photos in the circumstances you describe.

Wow - thank you for the detailed and number-heavy reply! It was very useful. I think it's quite possible that my assessment could be partly to blame - I bought the 7D and 15-85 at the same time, which gave me a pretty big jump in IQ from the old 450D anyway, so that may also have influenced my perspective.

Makes sense.  If you used the 55-250 on the 450D, then got the 7D and added the 15-85, the 15-85 would definitely appear to be the better lens when compared to how the 55-250 performed on the 450D.

Mind you, I've tried taking photographs of the same subject using both lenses and I still personally feel as though the 55-250 gives a 'duller' raw picture than that with the 15-85. It could also be that the 55-250 I own is substandard but I'm probably not enough of an expert to judge effectively!

Well, when it comes to your pictures, it's your opinion that matters in the end, right?  That said, maybe sometime you could post a pic of the same subject with the same settings (focal length, aperture, and shutter speed) -- might be interesting to compare.

Given that I'm using Lightroom, I would hope that any photos taken on the 55-250 for the display could be given the extra punch - crunching the numbers to show that I'd only be at 65% resolution if I cropped the 15-85 made me realise quite how much of the resolution I stood to lose!

Yep -- cropping robs a lot of resolution.  Something to keep in mind when discussing primes vs zooms.

It sounds as though the 55-250 would probably be a wiser choice given the circumstances.

The resolution loss from cropping is not quite as severe as I made it out to be, since you'll be keeping the central portion of the photo which resolves better than the edges that are going to be cropped off.  So let's say you'll retain 75% of the resolution, rather than 65%.

That said, assuming the PZ test is representative of your lenses and also representative of perceived resolution in the photo, the 55-250 at 130mm will still be the better choice, by far, than the 15-85 at 85mm cropped to a 130mm FOV.

Thanks again for your time and useful suggestions..

Of course, you could always test it for yourself.  Choose a scene at distance that has a lot of detail in it, and take a pic at 85mm with the 15-85, then at 130mm with the 55-200, crop the 85mm pic to the same framing, display (or print) both at the same size, and compare.

Great Bustard wrote:

Given that I'm using Lightroom, I would hope that any photos taken on the 55-250 for the display could be given the extra punch - crunching the numbers to show that I'd only be at 65% resolution if I cropped the 15-85 made me realise quite how much of the resolution I stood to lose!

Of course, you could always test it for yourself. Choose a scene at distance that has a lot of detail in it, and take a pic at 85mm with the 15-85, then at 130mm with the 55-200, crop the 85mm pic to the same framing, display (or print) both at the same size, and compare.

I did just that this morning, and was a bit shocked at the results! Using a tripod and the same aperture/shutter/ISO settings for both lenses (at approx 85mm), I've ended up with two pictures that are pretty much impossible to tell apart when using the comparison mode in Lightroom. In fact, when viewed at 1:1 or 3:1, the 15-85 is producing worse chromatic fringing than the 55-250. Maybe when I first used them both on the same day, I got a couple of duff pictures from the 55-250 and decided to blame the lens and not the fact I took some bad pictures compared to the shots I took with the 15-85! I think I might have been underrating my 55-250 for quite some time now!

Thank you again for the time you've taken to respond, and the thoroughness of your replies. I'm lucky(!) enough to be in Sydney for New Year's fireworks, so we get two displays - one at 9pm and one at midnight. I might give the 15-85 a run at 9pm as I'll get more of the twilight and city skyline in, and use the 55-250 for the big display at midnight as I'll be able to centre it more on the opera house and harbour bridge.

photonius wrote:

I think that is not unusual. Recently posted comparisons of the 18-55 IS to the 15-85 also showed the 18-55 IS be "flatter". The two kit lenses are good for the price, and the resolution figures are good. But I think one area where they are inferior to lenses such as the 10-22, 15-85, or 17-55 f2.8 IS is the contrast. The 18-55 IS and 15-85 handle contrast rich situations less well and tend to flare more. Images will be more "flat", i.e. less contrast rich when bright light comes from the front (e.g. overcast cloudy white sky can be enough for this). You can correct for this to some extend of course in postprocessing in the computer.

I think that's probably what threw me in the first place - the pictures where I'd originally compared the two lenses were bright days and high contrast situations. This morning it's dull and cloudy and both the 15-85 and 55-250 are producing images that are almost identical.

Given the limitations of the kit lenses (18-55 IS, and 55-250 IS), you might perhaps be better off with the 15-85 for fireworks in terms of contrast (not resolution wise), because there you will have strong light against black sky (presumably). I have never tried my 55-250 IS with fireworks, but presume you should be able to find samples on the internet.

I'll have a hunt online and see what I can find. As I said above, the fireworks are against the backdrop of Sydney harbour and skyline so there's less flat black background to work with. It's a combination of the fireworks themselves and the landmarks of the city.

Freneticburn wrote:

Using a remote and bulb is THE only way to photograph fireworks. I've only gone twice with my DSLR but both times I used a Canon 50mm 1.4 (speed doesn't matter since I think I only used f/11 anyway) on a tripod with a remote and bulb mode. I think opening the shutter right before the fireworks explode and closing about half way through the expansion created some of my cooler looking fireworks photos. Opening up for the launch just makes your photos look like trees made of light which can look cool but not when every photograph looks that way. Going too long and trying to get too many in one photograph gets too busy and the smoke starts to show. In my opinion your choice in lenses isn't going to matter. Just your timing of capturing the light. You're overthinking it. Even if you crop that loss in resolution isn't going to matter much when you're going for streaks of light. I personally would like to go wider angle and get closer the next time I try it. Here's a few from my 50mm 1.4 here:

I was absolutely going to be using a cable release and bulb mode. I think my best pictures with the last set were at around 2 seconds at f/10. Next year I want to be much closer but - funnily enough - getting a great close-up location at Sydney's New Year celebrations tends to require either being very rich or camping out the night before!

Thanks again for all the responses.