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Greetings from North East England

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#21 Andy Perrin

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Posted 12 January 2018 - 04:15

Maybe she meant because the lens is not an ideal lens so with different aperture the CA is different? CA can cause some blurring-like effects. I guess we will wait for Andrea to explain!

#22 Andrea B.

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Posted 12 January 2018 - 22:08

https://photographyl...-is-focus-shift

I have often encountered this when shooting in UV. I can usually see well enough at f/4 to focus through the UV-pass filter via Live View but there is not enough UV light to be able to focus through the UV-pass filter via Live View at f/8 or f/11. So I must set focus wide open then stop down to my desired aperture to shoot. A good dedicated lens like the UV-Nikkor will not produce any focus shift after stopping down. However, many of our UV-capable wider (28mm or 25mm) lenses have significant focus shift between f/3.5 and f/11 so a slight adjustment of the focusing ring must be made.

IIRC, the Novoflex 35/3.5 was not troubled much by this stop-down kind of focus shift. And also did not shift very much at all if focused in Visible light then shot in UV light.

There can also be focus shift even in some of the newest AF lenses as the camera makes the auto-focus wide open and then stops down to make the shot.

**********

**I was thinking that for landscapes at smaller aperture maybe there is sufficient depth of focus for a lot of subjects to not have to worry about focus shift too much?

Jim - indeed, focus shift, if present in a lens at all, may not be troublesome for a distant landscape. I don't have a working definition of "distant" here -- probably something like 30 feet to infinity, I suppose. It is much more troublesome in close UV work if not compensated for. Too many times I have shot a UV documentary series or test -- working a few inches from a flower -- while forgetting to review for stop-down focus shift and later kicked myself for the misplaced focus.
Andrea G. Blum
Often found hanging out with flowers & bees.

#23 Andrea B.

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Posted 12 January 2018 - 22:32

https://diglloyd.com...FocusShift.html

Another link. :D
Friend Lloyd also notes that Live View is not managed the same way in all cameras. In his particular example, if there is very bright light, the camera stops down beyond the desired shooting aperture in order to focus and focus shift occurs when the aperture is opened up to make the actual shot. Sort of the reverse of what I mentioned above. Geez!!

I suppose the moral of the story is always review your shot for focus before leaving the field. B)
Andrea G. Blum
Often found hanging out with flowers & bees.

#24 Andrea B.

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Posted 13 January 2018 - 19:50

Hey, did I provide sufficient documentation? Anybody follow up on this?? Just curious....... :lol: :lol: :lol:
Andrea G. Blum
Often found hanging out with flowers & bees.

#25 UlfW

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Posted 14 January 2018 - 10:47

Hi Andrea,

Thank you very much for the links.
Now I understand how this could happen.
I warned that I sometimes are a bit slow.

It is always nice to learn something new and your experience combined with the technical explanation are very valuable.
You made my day! :)
Ulf Wilhelmson
Curious and trying to see the invisible.

#26 Andrea B.

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Posted 14 January 2018 - 16:51

Thank you, Ulf. :) On a forum like this it is wonderful that we can share knowledge and learn. It never stops.

The "angled ruler" set-up is a good one for testing for focus shift because it helps to distinguish between actual focus shift and over-all diffraction degradation.

Roger Cicala over on Lens Rentals has a great write-up about lens testing. Go to Step 2 to read about testing for focus shift.
https://www.lensrent...to-test-a-lens/
Andrea G. Blum
Often found hanging out with flowers & bees.

#27 Jim Lloyd

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Posted 14 January 2018 - 17:19

ThankyouAndrea
Ihavelostspaces
Doesanyoneelsehavethisproblem?

#28 Jim Lloyd

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Posted 14 January 2018 - 17:24

Thank you Andrea
As In previous post I have sometimes found on this site that I suddenly lose the ability to enter spaces.

Anyway, This is all very helpful information.
I am hoping that by next weekend I will finally have all the equipment (and time) to finally make my first UV picture - Not that there is much UV in these parts at this time of year!
I think I will find these issues easier to understand by practical experiment than theory alone (although of course that helps)

#29 Andrea B.

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Posted 14 January 2018 - 23:26

Jim, such transmission corruption is caused locally. What to do: reboot your ISP and/or wireless routers and clear your browser caches. It never hurts to reboot your computer. If the problem continues and you are using the Microsoft IE browser, try a different browser like Chrome, Firefox or Safari.

We have no browser related settings in the forum software that would account for spacing problems or other such transmission errors between your keyboard and the post display here on UVP. If such problems were due to forum sofware, then we would all be seeing the same thing at the same time. :D
Andrea G. Blum
Often found hanging out with flowers & bees.