I'm in error on the lens reversal results. I read off the wrong chart.
The 28mm f2.8 reversed with no extension produces magnification of 1.78
and requires an exposure compensation of 5.6 f stops.
The pentax bellows A provides enough extension to gain a magnification
of 6.6 with a 28mm f2.8 reversed---however this requires 50 f stops of
exposure compensation.--plus some more for reciprocity failure.
The focal point 'film to subject' with a 28 mm lense reversed is 139 mm which
is a pretty close working distance.
lenses 40 mm and longer will need extension when they are reversed
or they will provide magnification of less than 1:1--and shouldn't be reversed
under those conditions.
"Robert P. VanNatta" wrote:
> Satish Kumar wrote:
>
> > Hi PUG�s,
> >
> > 1. What magnification is obtained when
> >
> > A. I use a reversing ring on a Normal Lens, Zoom Lens, Tele Lens & Wide Angle?
> > B. I mate either of the two above lenses Back to Face in all possible
>combinations?
> > C. I mate either of the two above lenses Face to Face in all possible
>combinations?
> >
> > 2. What are the merits & demerits?
> >
>
> Lens reversal is only appropriate when the magnification exceeds 1:1
> (life size on the film).
>
> Current AF macro lenses will reach 1:1 and the older ones gethalf way
> there at 1:2 and you have to use extension tubes to get the rest of the way.
>
> If you use thru the lens metering exposure compensation will take
> care of itself unless you use a flash. If you have a flash system and camera
> capable of TTL flash support it will still take care of itself. Prior to the auto
>focus family
> of pentax cameras only the LX and the Super program were able
> to handle flash via TTL.
>
> If you want a full run down on the tables, magnification, exposure compensation
> etc. for a variety of lenses--- jump on ebay and buy a Carl Shipman book
> on how to select and use Pentax SLR cameras. --- you can usually buy one
> for under $15.00 and it contains all the information you ask.
>
> Watch the age of the books--- as the books were published from 1977 to1990
> in annual editions so it would be helpful to get one matching the age of your
> equipment.
>
> the basic problem is that lens reversal doesn't get you where you want to go
> if macro photography is what you have in mind.
>
> You first have to get extension--- via extension tubes, bellows, or
> a special macro lens --- which have extra long helicoids in them for extension.--
> as well as optical features to improve flatness of field which becomes very critical
> in macro work because the depth of field disappears.
>
> When you start 'magnification' of the image -beyond life size the exposure
> compensation issues get clear out of hand and getting enough light becomes
> a real problem. The object is also so close to the lense that a regular flash
> doesn't do the trick---unless you have the ability to remove it from the camera
> etc. Also the depth of field is so skinny at wide apertures as to be frustrating.
> For example in photographing a bug you wind up having to decide which part
> of the bug you want in focus.
>
> A ring light is the solution for this.--- a special flash that screws into the lense
> filter holder and has a range of a few inches. with heavy extension etc.
>
> My favorite 'bug phtotoghphy' combination is a Super Program, with a 100 MM
> SMC-A Macro lense plus extension tubes and a pentax ringlight. With fast film
> I can stop down to f16 for improved depth of field (still not much). this works
> well up to 1:1 (life sized on the negative).
>
> Beyond that a fairly hard to find on the used market 'bellows A' has all the features
> needed for additional extension and lens reversal. However it relies on a double
>cable release
> for lens automation which implies it works best on a camera that
> will accept manual cable releases. Since flash is almost mandatory unless
> you have studio lighting, and exposure compensation is difficult to calculate
> the practical choices of cameras for the task is narrowed to the Super Program
> and the LX as they are the models that have TTL flash support and will work with
> a classic manual cable release.
>
> >
> > 3. How to calculate the aperture & shutter readings?
> >
> > 4. Is it possible to shoot without a Tripod, by using a faster film (>400ASA) &
>reduce shake?
> >
> > 5. What is the formula for calculating the magnification?
>
> Magnification = Extension / focal length.
>
> >
> >
> > Thanks a ton
> >
> > Satish Kumar
> > Madras/India
> >
> > _____________________________________________________
> > Chat with your friends as soon as they come online. Get Rediff Bol at
> > http://bol.rediff.com
> >
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