I don't own a 200 mm macro -- only a 50 mm and a 100 mm. There is a
very good
logical reason for NOT pushing extending a lens beyond 1:1 extension.
the point here is that lenses are designed and optimized on the
assumption that they are going
to transfer a large image (your subject) to a small object (your film
plane).
Once you move beyond 1:1 you are tranfering a small object to a large
so you
can capture the optical optimization by reversing the lense.
Optical quality doesn't suddenly vanish by extending beyond 1:1 without
reversing
however. Clearly the practical lense for reversal is the 50mm focal
length.
If you want to 'see what happens' with additional extension on your
existing
lense you can always resort to a 'poor man's extension tube' which which
I did my first macro phtography. -- simply insert a toilet paper core
between the lens and the camera. You can reduce the issue of possible
light leaks by
draping a dark cloth over the top if you want.
You need about 3 hands to hold the pieces together
but it works fairly well, and you can learn from the exercise, and
decide if you want to buy a second set of extension tubes.
Shel Belinkoff wrote:
> "Robert P. VanNatta" wrote:
>
> > That isn't an unreasonable amount of
> > extension for a 200 mm lens, but
> > you won't get the magnification you
> > are expecting me thinks.
>
> Since I'm new to macro and close-up photography, I have no
> expectations, per se.
> What magnification do you think I'd be able to achieve with a
> 150mm extension tube set and the Pentax A*200 macro lens?
>
> > Longer focal length lenses require
> > more extension to achieve any given
> > magnification.
>
> More extension than what? I'd need 200mmm with a 200mm lens
> to get 1:1, is that correct? Since the lens in question
> already allows for (I believe) 2X life size, wouldn't I get
> about 4X life size with the addition of 200mm tubes?
>
> > My good book says that image quality
> > will degrade when you push magnification
> > beyond 1:1 with extension unless you
> > reverse the lens. Telephotos are not
> > suitable for reversal.
>
> To what book are you referring? Since the Pentax lens goes to
> greater magnification than 1:1, and is considered to be
> extremely sharp and offers quite high resolution, I don't
> understand how extension tubes would degrade the image more
> than just racking out the focus. Could you please explain how
> that is?
>
> > When you talk about image degradation
> > that means different things to different
> > people.
>
> To me it means reduced sharpness, reduced contrast, reduced
> resolution - anything that degrades the image from the optimum
> performance of the lens. Does degradation mean something
> different to you?
>
> > With macro photography something will
> > likely still be in focus and sharp, but
> > the depth of field becomes progressively less.
>
> Yes, I know that. Is that what you consider image
> degradation?
>
> > Shucks if you want to do super macro
> > photography you can stick your camera
> > on the end of a microscope
>
> No, I don't want to do that. I just want to get the best
> image possible at the highest magnification so I can fill the
> frame with the subject and make large, sharp, highly resolved
> prints.
>
> > but you have to face reduced depth
> > of field
>
> DOF is already pretty shallow at max magnification with this
> lens, and it's even a bit more shallow with a 68mm extension
> tube set. However, it's adequate for my purposes at f/8.0 or
> f/11.0
>
> > reciprocity failure
> > issues. when you compensate 19
> > f stops you have strained the
> > reciprocity characteristics
> > of your film
>
> Thus far reciprocity has been of no concern. Exposures are
> all less than one second. With three times the extension
> (68mm to 200mm) I can see where it might be a consideration,
> although I think the LX meter will handle that. Plus I'll
> bracket like crazy until I get everything down pat.
>
> > unless you have unless you are
> > using a critical mass of nuclear
> > fissionable materials at close
> > range as a light source.
>
> I only use fissionable material when I barbecue.
>
> --
> Shel Belinkoff
> mailto:[EMAIL PROTECTED]
> -
> This message is from the Pentax-Discuss Mail List. To unsubscribe,
> visit http://www.pdml.net and follow the directions.
-
This message is from the Pentax-Discuss Mail List. To unsubscribe,
visit http://www.pdml.net and follow the directions.
