how closeup filters affect focal distance?


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denizenx

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#1
anyone can help regarding the hoya +4? how does it change the min distance? is it like the 500D where the range hovers around a fixed value? or it just magnifies the image?
 

azone

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#2
Originally posted by denizenx
anyone can help regarding the hoya +4? how does it change the min distance? is it like the 500D where the range hovers around a fixed value? or it just magnifies the image?
Yes, a close-up filter shortens the focusing distance to around a fixed distance. Of course, different diopter rating gives different distance. Just divide 1m by the diopter value and you'll get the focusing distance. E.g, A +1 filter will focus at 1m, a +4 filter will focus at 25cm, etc.

A 500D does so similarly too.

By reducing the focusing distance, logically the object is being magnified.
 

xdivider

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#6
Originally posted by denizenx
sorry again... so I can focus on 25cm and below or above? above right? but no infinity.
ard 25cm. Other than that blur. But very hard to estimate, usually i move the cam in until the insect becomes focussed. The higher the +, the closer u can move in but the easier for u to get OOF.
 

denizenx

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#8
aiyah I'm a bum...
been shooting food rencently, using my 19mm.. so +4 need to get 77mm also..
OR is an extension tube better?
alamak so fickle from ignorance...
 

Wai

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#9
Originally posted by denizenx
aiyah I'm a bum...
been shooting food rencently, using my 19mm.. so +4 need to get 77mm also..
OR is an extension tube better?
alamak so fickle from ignorance...
hmm....may be extension tube better??? i GUESS closeup filter are more suitable for DC user who can't take out the lens like SLR

somemore for extension tube, no glass is added and it can also use for ANY of your lens....not only 77mm one...and it is cheaper...less than $100 for a 3rd party one..

but usage and quality wise...i never try before...may be our insect king can tell us more??
 

xdivider

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#10
Originally posted by denizenx
aiyah I'm a bum...
been shooting food rencently, using my 19mm.. so +4 need to get 77mm also..
OR is an extension tube better?
alamak so fickle from ignorance...
Wah, u need to see microorganisms on your food is it? :eek:
 

denizenx

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#11
oh insect king insect king!
LOL I only UST found out that AH is really alex hosp... where's the gdn? I stay there before...
 

reflecx

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#12
Saying that using a +4 will focus at 25cm is inaccurate. The camera will focus at 25cm if you set your lens is focus at infinity. If you set your lens focus to less than infinity, then the actual focal point will be less than 25cm.

Using a +4 close-up lens changes the possible focusing distance from

a (where a is lens min focusing distance) to infinity

to

b to 0.25m

where b is

0.25a / (0.25 + a)
 

xdivider

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#13
Originally posted by reflecx
Saying that using a +4 will focus at 25cm is inaccurate. The camera will focus at 25cm if you set your lens is focus at infinity. If you set your lens focus to less than infinity, then the actual focal point will be less than 25cm.

Using a +4 close-up lens changes the possible focusing distance from

a (where a is lens min focusing distance) to infinity

to

b to 0.25m

where y is

0.25a / (0.25 + a)
Wow, where did u get that formula from? I only read about the 25cm at infinity rule from web pages.
 

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