Sharpness test recommendations please

[digiman]

I have become increasingly bothered by the sharpness of my 70-200f4L, and wondered if anyone knew of a downloadable test card I could use. I have read on this forum previously of people using various objects to test, but can't find the threads It may be my technique etc with the lens, but, I have been getting sharperer images with the 18-55EFS kit lens, so thought I would try a more scientific route to rule out the lens! I downloaded this but wondered if there was a better option.

Also, are there any tutorials on testing the lens that anyone can recommend?

Thanks in advance,

Garry

[AndyA]

Re: Sharpness test recommendations please

Garry, I'm very much a novice and can only offer limited advice.

When I thought that my 24-105 was producing soft images, I set my camera on a tripod to eliminate any camera shake from the results, I then focused on a lens box across the other side of the room. I set the camera to use a 10 second timer (again to eliminate camera movement) and took multiple shots using different f-stops. I then compared them on my pc.

Hopefully someone will be along soon to offer better advice.

[antoeknee]

Re: Sharpness test recommendations please

Using mirror lockup would help with minimising camera movement when testing like this.

[MX5]

Re: Sharpness test recommendations please

You can use a broadsheet newspaper ... but (big but) you need to ensure everything is perfectly flat (same applies to using a test chart) and likewise the camera is set up okay (yes mirror lockup, tripod, remote, IS-OFF, etc). So a spirit level is essential!

But ... another big but however you test your lens ... how are you going to recognize a problem (unless you have a 'good' example to compare against) from how the lens normally performs.

btw - Unless you can print A2 or A1 (A3 at a push) ... an A4 test chart on its own isn't much use. But you could use a matrix of A4 test charts at a push.

[S_J_P]

Re: Sharpness test recommendations please

Hi Garry, Canon Rumours have a decent article on lens sharpness testing which is worth a read.

I do things much more simply though, using something with fine-print which is a minimum of A3 in size (the last set of tests I did used an EOS-System list which was printed on glossy paper and listed all the EOS bits and pieces in A2 format). Try to fill the frame with the target at whichever focal length you're using.

The key to getting a representative image is is make sure your chosen target is flat (BluTak it to a wall) and that the camera is square to, and centralised over, the target. Use a tripod and live-view at 10x magnification to manually focus (to eliminate any autofocus effects), use a low ISO, and a highish shutter speed. Use a flash if necessary to maintain a high shutter speed, but beware of reflections and/or uneven lighting. Use self-timer with a 2 second delay to allow any vibrations to subside after pressing the shutter button, and use a remote-release if you have one to further reduce the impact of any vibration. Take a series of images at a variety of apertures and assess them at the centre and the edge/corner at 1:1 magnification on your computer. I've found it useful to note down the aperture, focal length, and any other relevant information on a Post-It note near the centre of the frame to make individual image identification simpler at the reviewing state (The EXIF data contains all you need to know, but having it there on the image helps!)

Hope that helps!

[Hereford_EOS]

Re: Sharpness test recommendations please

Some Canon cameras have a micro-adjustment facility (7D, 1D-X etc..), I'm not sure about the 500D.
If you are not into DIY calibration then send the camera and lens off to Canon for calibration.
I suspect there may be a small fee for the this.

[digiman]

Re: Sharpness test recommendations please

Thanks all for your quick responses.

MX5, with regards to comparing it to a known quantity, this is more to see whether I can improve on the sharpness in a controlled test. This way I will confirm to myself that the lens is fine and it is, as I suspect, my technique that is at fault. I have used this lens extensively since I got it a year ago, using it in over 1/3 of all my shots. Some of the results I achieved were disappointing, despite doing everything I thought was right, hence the test!

Steve, thanks for the link, and method. I am currently photographing a newspaper, camera tethered to my laptop. So, once taken and checked, I'll see if sharpness is improved.

Stephen, I have no idea about micro adjust! I am a have a go type of person, but not with an L lens!

Thanks all again,

Garry

[digiman]

Re: Sharpness test recommendations please

Well, I just carried out some tests on my 70-200f4, and, as I thought, this is an awesome lens! I think I need to do a LOT more practising, and maybe use my tripod more! I attached a shot I took during the test. I know, it's an awful shot but it does show a good level of sharpness, straight out of the camera. So, I am happy now

Lens Test001-071.jpg

Thanks all again for your excellent, as ever, input.

I hope one day I can return the favour!

Cheers,

Garry

[AndyA]

Re: Sharpness test recommendations please

Well there you go, that's proof enough Garry!

[MX5]

Re: Sharpness test recommendations please

Good result.

[colin C]

Re: Sharpness test recommendations please

Confidence in your equipment is everything and you are right to prove the point.

[digiman]

Re: Sharpness test recommendations please

Thanks Andy, MX5 and Colin.

[MartinR]

Re: Sharpness test recommendations please

I have become increasingly bothered by the sharpness of my 70-200f4L, ........... but wondered if there was a better option.



Garry

I have come to this thread a bit late, but for what it's worth here is another idea.
Extend a DIY tape measure diagonally across a table and mount the camera 8 to 10 feet away so that it is on the same level as the tape measure. Focus on a point about mid-way down the extended measure and expose (following all the other advice about keeping the camera free from vibration). The human eye tends to lose its ability to differentiate between parallel lines at about 1700 times the distance between the lines, so not only will you be able to check how well your lens can see the millimetere divisions along the measure, you can compare its performance with your own!

Martin

[digiman]

Re: Sharpness test recommendations please

Thanks Martin, I'll keep this one in mind!