Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

[Mark500D]

Has anyone discover the sweet spot of the Canon EF 70-300mm f/4-5.6 IS USM. And I know this sound daft but if not, how is it done?

[Hereford_EOS]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

f/5.6-f/8 at 70mm and f/8 at other focal lengths.

hope it helps

[celtex]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

And I know this sound daft but if not, how is it done?

Not sure if this is true but I recently heard that for all lenses the sweet spot is approx. 2 to 3 stops up from widest (at a given focal length)?

[colin C]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

Not sure if this is true but I recently heard that for all lenses the sweet spot is approx. 2 to 3 stops up from widest (at a given focal length)?

It depends on the lens, but the general rule of thumb used to be 2 stops down from wide open. Not necessarily true for L lenses and definitely not true for catadioptic mirror lenses.

[S_J_P]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

Mark,

My sweet-spot test methodology isn't very scientific but is a useful way to determine the areas in which my glass performs best and (more importantly) worst, so that I can make allowances for any deficiencies.

I use either a lens-test chart (available for download on-line, just google Lens Test Chart) or a newspaper or magazine shot at various focal lengths and apertures (Make sure you fill the frame with the same portion of the target image in all instances for consistency).

I then cut and paste a small section from the middle and the edge of the frame into a Microsoft Word document (labelled with the shooting information) which will be displayed at full-size (1:1), then, once all the lens' images are in one place and at the same size I go through the images and rate them out of 10. When testing a new lens I try to review my baseline images (from an EF-S 60mm Macro) as well, as this is the lens I rated 10/10.

When rating the images I assess the sharpness and contrast of the image at both the centre (C) and the edges (E) wide-open, at f/5.6, f/8, f/11, and f/16, at both ends of the zoom range and in the middle. This produces a table in Microsoft Excel which I colour-code from red to green.

I've attached my table for Canon's EF 70-300 IS below which shows my example is at it's best at the short-end, and as already mentioned, stopped-down by two stops. The centre is very-good/excellent most of the time, but the edges benefit from stopping-down. I try to avoid shooting wide-open at the long end of the focal length range for obvious reasons!

This method is somewhat subjective, but does give at least an assessment of my own lenses on my own camera. I've given ratings between 1 (for a Samyang fisheye) though to 11 (for Canon's EF 100 f/2.8 IS Macro), and it's quite noticeable that Canon's L series lenses offer very consistent sharpness across the range of apertures whereas the non-L glass benefits from stopping-down to a far greater extent.

70-300 Sweet-Spot.jpg

[colin C]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

I used to use a similar rate system Steve, but you are far more diligent using Excel and colour coding.

[Nathaniel]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

Wow! Too scientific and will certainly put me off photography for good, if I was to take all this into consideration- my opinion!

[S_J_P]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

It's all part of the fun of photography, and another layer of the onion of understanding :-)

It's just a question of knowing your equipment (and your own) limitations, and then making allowances for them. Avoiding one end of a zooms range (and cropping-in in post-production), avoiding using particular lenses wide-open (and ramping-up the ISO instead), or selecting one lens over another where their focal lengths overlap can be considered in the same way that you might take note of the fact that you can't hand-hold reliably at 1/FL, or that your horizons are usually wonky (so you use a gridded focussing screen).

[mikep]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

Hi Mark

I used to have this lens, used on my 550D and I un-scientifically reckoned about F8 (as per other replies).

I must admit, when I first read SJP's more scientific approach, I too thought it was a little bit over-kill, but on reflection, I think it's a good idea to do. Settings up a test like this (and performing all the shots) wouldn't take too long. The assessment of the results need care, but once done would give an important understanding of what your lens is good and bad at. All this could be done over an evening at home when you not too busy, so isn't too onerous.

Each to their own, and I've never done anything like this before, but perhaps I'll have a go... after all, you'd only need to do it once per lens!

Always interesting to find out what other people do! Thanks for the process description.

Regards, Mike

[Mark500D]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

Wow what can I say. It rather like the technical side of things, I just want to get things right, and want to get the best results out of what I have. When I take photos and I know I can do better I want to know how to do it. I subscribe to the EOS magazine, but it is always great to get other people thoughts on thing. For me getting the perfect shot is all part of the fun, and I really enjoy technical stuff and understanding the equipment I have, and getting the best out of what I have. So thank you everyone for replying, I really appreciate it. Especially for S_J_P's tech stuff and Mikep encouraging words. Keep the post/replies coming, thanks. Mark.

[Riggers]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

I love the idea of having S_J_P's knowledge of the limitations of each lense but I just know I could never be bothered to do it so carefully. There's never enough time in the day to get everything done and that would feature too far down the list. I know it may be seen as lazy but I'd just rather read that kind of data from reviews or technical data on the internet if it were available.

[Mark500D]

Re: Sweet spot for the Canon EF 70-300mm f/4-5.6 IS USM???

It is really good that S_J_P has done his home work, especially for the rest of us, and yes it is much easier to read it in a magazine, but isn't it much better to have someone like S_J_P show the rest of us what to do, and then we go get our own results. That way we have a great sense of accomplishment knowing that we have found the info for our selves, and then we can like S_J_P show other. We receive free, we give free.