300mm verses 400mm

Here's another thread, which might be a good read...with the same debate. Searching helps..

http://www.photography​-on-the.net/forum/showthre​ad.php?t=226589

johnstoy wrote in post #2124232
This is a picture taken with the Canon Zoom EF 75-300mm 4-5.6III at 1/1600s, F 14, ISO 1600, at 300mm...This $150 dollar lens makes a reasonable image...I used Canon's Zoom Browser EX to trim and sharpen the image taken this afternoon...

My question is: will the 300mm or the 400mm produce a considerably higher IQ?

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You'd get a better quality image if you lowered the ISO to 200 and reduced the shutter speed, is there a reason you needed to shoot at 1/1600th?

JuZ wrote in post #2128142
You'd get a better quality image if you lowered the ISO to 200 and reduced the shutter speed, is there a reason you needed to shoot at 1/1600th?

This was just a quick test shot and the squirrel happened to walk by...I never use this lens, expecting it to be of poor quality...I purchased it at a clearance sale at Walmart for 35% off...

Since I'm buying a long L lens, I thought I'd try some low light outdoor shots...the ISO was pre set from indoor concert theater shooting in low light, earlier in the week...

I'll next test the lens threshold, by shooting with minimal ISO, and best depth of field, to obtain optimal IQ...

Still, for taking two minutes to try out the light demands of an average 300mm lens, the picture looks pretty good...