Parsed below...
Regards,
Bob...
--------------------------------------
"Those who say that life is worth living at any cost
have already written an epitaph of infamy,
for there is no cause and no person
that they will not betray to stay alive."
Sidney Hook
From: "Ayash Kanto Mukherjee" <[EMAIL PROTECTED]>
>
> .............. I am using close up filter kit to achieve magnification as
great
> as 1:1. There are two basic problems that I encountered while using this
> kit. One is however, the depth of field is not enough for apertures like
> f/8. I have to stop down to f/16 and sometimes f/22 to get acceptable
> depth of field.
Depth of field is a function of achieved focal length, distance to subject,
and aperture. How these are constructed (single macro lens or additional
lenses) is irrelavent. What is acceptable depth of field depends on the
subject and the desires of the photographer.
> ........................... A related problem is that the plane of focus
is just
> one.
I don't understand the above sentence.
> A very slight motion of the hand is enough to throw the subject out
> of focus. Therefore, I always use tripod while doing macro
> photography. Yet there is another problem that persists and it is low
> shutter speed that I have to choose for an aperture of f/16,
> 22. Sometimes, it goes to as low as 1 second (I use 200 ASA speed films).
> In this time period, if the subject moves either intensionally or
> unintensionally (say, because of gentle wind), it is impossible to take a
> shot.
The tradeoffs between DOF, shutter speed and ISO always exist. This is why
many nature shots of, say very small frogs, do not have the entire animal in
focus. The eyes (at least one) are always in tack sharp focus though. Decent
bokeh is often important here too. As to the wind, try using a wind block.
> Another problem that I face is poor colour rendition.
Color rendition is a function of many things. Using any single element lens
attachment will add some color aberation. To avoid this (and other
aberations), it's usually better to use extention tubes or bellows rather
than macro lens kits. Bellows are unwieldy contraptions, but are very
flexable. Lens extention kits are easier to use, but a full kit with
helicoid can be expensive and they are not as adjustable.
> Now, I have certain questions regarding a real Macro Lens, before
> purchasing it. It will be great if I can purchase a macro lens of
> magnification ratio of 1:1 but sometimes it is not possible.
The following lenses are excellent at 1:1 ratio, all require an extension
(tubes or bellows) for 1:1 ratio:
SMCA 100/2,8 Macro
SMCK 100/4 Macro
SMCM 100/4 Macro
SMCM 100/4 Dental Macro (identical to SMCM 100/4 Macro, but with different
markings)
SMCK 100/4 Bellows (requires bellows or hellicoid to focus)
>
............................................................................
..............Macro lenses
> having magnification of 1:2 can be converted to 1:1 by including an
> adapter at its filter thread, e.g., Vivitar 100 mm f/3.5 Macro.
Yes. These add some curvature of the field of focus, and if they are not
achromatic (having at least 2 elements of differing index of refraction)
they will add color aberations.
>
> How does a macro lens with 1:1 adapter on behaves with respect to an
> ordinary lens with close-up filter stacked on it as far as depth of field
> and colour rendition is concerned ?
Difficult to tell. Possibly better. Better to have an extension tube.
> Do I have to go down to smaller
> apertures to achieve acceptable depth of field ? If yes, then there is
> virtually no difference in using a macro lens and an ordinary lens with
> close-up filters. Please note that low apertures demand low shutter speed
> and here is the problem.
Well, the answer is the DOF will be the same. On the other hand, normal
lenses will not have the flat field of focus that a macro lens is supposed
to have and my experience is that most add-on lenses for "macro" make this
worse. In fact, this flat field of focus is the sole reason for the macro
lens's existance. Curvature of the field of focus is often mistaken for poor
DOF as the results are often similar. As to your using the smaller
apertures, remember that the f/stop is relative to the focal length of the
lens at infinity. At 1:1 the actual focus is doubled so that the f/8 marked
on your lens is really f/16. When you are using what is marked as f/22 your
lens is really f/44. What is "acceptable depth of field" is up to your
creative talent.
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