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Canon 70-200mm F/4 Manual Mode Questions Help!

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#1 RJMAstronomy

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Posted 21 November 2020 - 07:49 PM

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Hey everyone. I just picked up a Canon 70-200mm F/4 USM. It’s in great shape and works very well.

However when I was using it tonight to take some photos of the moon and test it out a little, I’m having a sort of strange issue.

For night and astrophotography, I always use manual mode, but when I move the lens to manual mode, the Moon seemed much further away that it was in automatic mode. In auto mode the moon was super close and bright. In manual mode it was maybe a 1/3 the size and in more of a wide angle try or setting, but I can figure this out.

This photo is 200mm F/4 ISO 400 if I zoom in and crop it, it looks good, but I feel like it should be bigger no?

 

This photo is at 200mm in auto mode. It’s bad because of the auto mode, but look how much closer the moon looks!

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#2 T~Stew

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Posted 23 November 2020 - 09:37 PM

If you are referring to autofocus vs manual focus I think its simply the out of focus image appearing larger (autofocus isnt actually locking on focus?). Its not closer its just creating an out of focus larger blob. Precise focus is usually when distant objects like stars are at their smallest size on the screen, just point at one of the brightest stars in the sky and adjust the focus from end to end it will be a large blurry blog until it shrinks to a tiny point of focus then turns into an enlarging blob again as you go past focus. Just the way optics work.



#3 LittleEd

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Posted 24 November 2020 - 11:42 PM

I have that lens. Using it on a full moon (or very nearly so) I found an exposure of 1/500 s at f/4.5 and ISO 100 was about right with my Canon 77D. I would expect you should need an exposure within a couple f stops of that.

 

As for focus, the moon is bright enough that I was able to use auto focus and it seemed to do a pretty good job.




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