Focus problem - Lens or my eyes?

[Big W]

Most good cameras do have an adjustment for the view finder to adjust the focus (as seen through view finder) for your eyes.

My question is how do you know the camera is actually in focus when you adjust it? Will it not be possible to “compensate” for a slightly out of focus camera and you will be lead to believe that it is actually in focus?

Not sure if it makes sense, but after being at the optometrist and seeing him stacking different lenses to get the correct focus for my eyes I got thinking…

I used a 100-400mm L lens the weekend and I had a lot more good shots – using the AF, than I would have with my Sigma 150-500mm that have an AF issue and I use MF. I know that most people will say that it’s obvious – the Canon is a better lens, but I have noticed a drastic increase the quality of the photos. I have taken my time manual focusing to ensure that it is in focus (when using the Sigma), but never have I had anything near the quality.

[Anonymous]

You don't need a lens on it to see if the diopter is set correctly. The illuminated focal points should be enough of an indication.

[Big W]

You don't need a lens on it to see if the diopter is set correctly. The illuminated focal points should be enough of an indication.

even in MF?

[Leo Theron]

As Wiliams said…

The lens project the focussing image onto a viewing screen via a mirror. To get the image sharp on the screen, you turn the lens focussing ring.

There is another clown inside the camera that steals part of the image, look at it and tells the focus motor what to do. Looking through the viewfinder, you can see the result of the Focussing Clown's work (in focus image). Your diopter setting has NOTHING to do with this result.

To see the image on the screen at the best - you need to focus FOR YOUR eye, using the diopter setting.

The two are not linked.

HTH

[Anonymous]

even in MF?

MF? There is no "F" at all when the lens is off!

[Big W]

As Wiliams said…

The lens project the focussing image onto a viewing screen via a mirror. To get the image sharp on the screen, you turn the lens focussing ring.

There is another clown inside the camera that steals part of the image, look at it and tells the focus motor what to do. Looking through the viewfinder, you can see the result of the Focussing Clown's work (in focus image). Your diopter setting has NOTHING to do with this result.

To see the image on the screen at the best - you need to focus FOR YOUR eye, using the diopter setting.

The two are not linked.

HTH

I understand that if Focussing Clown is working and the image is in focus and you then adjust you will see the the "perfect" picture.

So I need a lens that can AF, let focussing clown do it's work and then adjust?

Adjusting it when a MF lens is fitted is not going to work?

[Big W]

MF? There is no "F" at all when the lens is off!

I know... Manual Focus. The AF is not working!

[Anonymous]

I know... Manual Focus. The AF is not working!

If you need to set the diopter take the lens off the camera, look through the viewfinder and adjust it until the points illuminated on the focusing screen are crisp.

Depending on your camera you might also be able to do a micro-focus lens adjustment. What camera do you have?

[Leo Theron]

I understand that if Focussing Clown is working and the image is in focus and you then adjust you will see the the "perfect" picture.

So I need a lens that can AF, let focussing clown do it's work and then adjust?

Adjusting it when a MF lens is fitted is not going to work?

As some other people have said - you must use the diopter focussing (to adjust for YOUR eye) to see the screen (and focussing marks) properly. No lens required, NOTHING/NADA/F******. Now put the lens on the camera, and use.


Note the following:

- 'Focussing' screens fitted to modern DSLR cameras are NOT optimised for manual focussing - the DSLR's Focussing Clown does that for you, you only need to see the brightest picture. (MY 1969 Nikon F had a focussing screen with a rangefinder type split prism in the middle surrounded by a sea of very fine prisms around it followed by a with a ground glass circle surrounded by a fresnel lens. Easy to use - but if the lens dropped below f4, it all went dark on the one side! of those prisms! Also - the modern DSLR cannot meter properly with such a screen fitted - possible to buy a reftrofit screen.)

- Manual focussing is something you will need to learn! It takes practice to make it work.

[Big W]

OK.... now get it! Lens off!!

[Peter Veitch]

May be coming in at the doff end but try manual focussing using live view if you have it. That's what I do shooting macro and I've seen avian guys doing it trying to shoot MK's diving.