How to choose a diopter ?

[Pirate]

I hope that someone has the advice that I am looking for here. I recently bought a new 2x tc, and I find that at the extreme focal lengths I have a little trouble getting my focus as sharp as I would like. Since I have to manually focus at these ranges I would like to buy another diopter for my cameras. My question is how to know which one you need. Can my optomitrist help me with this ? Where do I turn ? If I had a shop near that had them all then this would not be an issue. However I have to know if I'm going to order them from Canon. Any help here folks ?

 

[darich]

It could be that the image IS sharp but the additional glass degrades the quality a bit and you lose some sharpness would have without the TC.
As far as i know you can't buy a diopter - it's built into the camera but it's not a thing i've ever thought about buying so can't say for sure.

Try focussing on something without the TC in place. Leave the focus on the lens and then use the TC. Does the sharpness drop? if so then it probably is the quality. Especially if you have expensive lenses and a cheaper TC.

What about using a wide aperture and using autofocus to see what the camera comes up with?

 

[Pirate]

darich, you can buy them from camera shops, but they never have many is stock. Canon's website have many, many to choose from. But I will go out and try your suggestion today as we have thousands of sandhill cranes in the area right now. Thanks !

 

[mysteryscribe]

If you call you optomitrist he can give you the perscription for your reading glasses or the bifocal reading perscription that is what you buy for a diaopter correction. I use them with film cameras because my eyesight changes daily they are getting less useful. But thats the one you need.