I guess it depends on how much you want to zoom in but in my experience so far the quality of the lens is not as important as light, composition and magnification.
Here is a comparison:
Canon5dsr+tameron90mm | a6000+Sony90mm | a6000+55-210
The Canon was obviously using a flash and if you zoom in you can see a bit more detail but the setup is around $4000+ compared to the 55-210 setup around $850
the 55-210 shot was at 210mm and if I had kept it in it's sweet zone (around 80-140) and got the ISO at 100 instead of 400 it would have been better
The a6000+90mm can actually do better than the picture here but it goes to show how other variables can effect the IQ.
I can see now right away that image stacking is going to play a much bigger role in IQ particularly with very small things where the DoF is so narrow
Here is a flower with a 3 photo stack from the 5018 vs single shot from the 55-210
For taking pictures of insects the long focal lengths are much better but also tubes because the raynox250 will require the front of the lens to be within 6 inches and two sets of tubes will allow to to focus between a few inches and a few feet on the 55-210
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-Chris
https://www.flickr.com/photos/cspics/albums
But for lighting wise. Effective diffusing of light can be achieved if your diffuser is nearer to the subject? Having a longer distance allows you to shoot at ease but lighting wise greatly depend on the flash power if its sufficient enough to reach the subject.







