Short macro bellows lens recommendation for 35mm, beyond 1:1

Paul Furman writes:

What is the diameter of the projected image circle?
How much 'working space between the rear element and image plane?
(approximately)

A standard microscope objective has its best performance (least
aberrations) at a 160mm tube length, which means the shoulder of the
threads is held 160mm from the end of the eyetube, while a standard eyetube
positions the image 10mm inside the end of the tube, so the "flange
distance" (so to speak, in the term usually applied to camera lenses) is
150mm.

The useful image circle is a diameter of 18mm or 22mm or thereabouts, which
is what the field stop in an eyepiece would show you.

A Canon SLR has its focal plane back 44mm from the bayonet flange. So if
you hold a microscope objective (shoulder) 150mm - 44mm = 106mm away from a
Canon camera body, you have a direct projection photomicrography camera.

Here is an example which I manufactu

http://www.truetex.com/microscope_rms_tmount.pdf

Richard J Kinch wrote:
Paul Furman writes:

What is the diameter of the projected image circle?
How much 'working space between the rear element and image plane?
(approximately)

A standard microscope objective has its best performance (least
aberrations) at a 160mm tube length, which means the shoulder of the
threads is held 160mm from the end of the eyetube, while a standard eyetube
positions the image 10mm inside the end of the tube, so the "flange
distance" (so to speak, in the term usually applied to camera lenses) is
150mm.

The useful image circle is a diameter of 18mm or 22mm or thereabouts, which
is what the field stop in an eyepiece would show you.

So it doesn't quite cover DX/APS cameras, though close enough, but not
on FX full frame. Thanks for clarifying.


A Canon SLR has its focal plane back 44mm from the bayonet flange. So if
you hold a microscope objective (shoulder) 150mm - 44mm = 106mm away from a
Canon camera body, you have a direct projection photomicrography camera.

Here is an example which I manufactu

http://www.truetex.com/microscope_rms_tmount.pdf

Sounds like an SLR can't get close enough to a standard focusing rack
with the eyepiece removed so the adapter is needed.


--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

David Ruether wrote:
Paul Furman wrote ..
David Ruether wrote:
Paul Furman wrote ..
Richard J Kinch wrote:

(Just what is an "extreme" macro lens?)

I'm looking at about [5:1] now ..., which which looks interesting. I'm not sure how that translates into microscope
magnification _x. That's a 7mm wide photo, about a quarter-inch on a 36mm wide sensor. That should enlarge nicely to a 19 or 24"
wide print which works out to about 25x original size. I don't know how that math translates to microscopy.

It just dawned on me that if you do not need a wide aperture (and the
equivalent of f32 to f45 is OK),

I do need a fairly fast lens in order to focus. Are those f/32-45 numbers figuring that the extension makes it darker? Like how
some macro lenses will report a smaller aperture at closest focus?

Adding a front lens (achromat or camera lens) will not slow the
lens it is attached to (just shorten its effective FL, hence the
"close-up" effect with its given barrel length).

Ah, thanks for clarifying that point. Makes sense!


Adding a converter
will slow the resulting optics (1 stop with the 1.4X, 2 stops with
the 2X). Tubes will also slow the combination, depending on
the length of the tube(s) compared with the effective FL of the
optics mounted on their end.

Yeah, the darkness at long extensions is a hassle, more than I would
have guessed before getting into it.


The small stops may be useful both
for improving performance with "impossible" stacking of several
options, but also for DOF reasons.

One thing I'm not clear about... do I need a lens with an aperture that
stops way down to f/45 or whatever or does the extension skew the f-stop
math so it ends up a tiny aperture at those magnifications anyways?


there are other solutions. I based my
1:1 to 3:1 shooting on the Nikkor compact version of the 200mm f4,
which is quite sharp stopped down even with tubes, teleconverters,
achromats, and (also likely) with reversed camera lenses stuck on the
front, even with combinations of these. This solution also offers the
advantage of having the auto diaphragm for focusing.

That's a neat lens I've drooled about getting but for this setup I want something really small.

That likely limits you to mostly lenses specifically designed for
5X (for you), and these tend to be rather slow on the required
extensions (which may not be compact with the longer FLs...),
and you will have no auto diaphragm, making hand-holding
impractical. The only exception I can think of is the reversed
55mm f1.2 CRT Nikkor, stopped down a couple of stops, if
very shallow DOF is OK. It does perform very well that way,
and the VF image may be adequate.

Yeah that leads to the Canon 60mm MPE f/2.8-4.3 because it's a modern
design with good coatings and optimized for the range I'm looking at: 1x
to 5x.

BTW, another option I've
tried in the past is using reversed movie camera lenses. You can
now buy Zeiss and other good fast 25mm lenses intended for
16mm movie cameras at very good prices. Here is one at KEH,
http://www.keh.com/OnLineStore/Produ...BCL=&GBC=&GCC=
listing a Schneider(?) 25mm f1.9 Xenoplan for $53 which may
be worth a try. It will not be as sharp as the "fancy" and carefully
selected lenses made for your purpose, but it may be good
enough, and KEH takes returns if it doesn't work out.

I think these are like 10x or more which is a bit more than I need
perhaps. Interesting suggestion though! I have a small slide projector
lens that I used to use on a circa 2000 AD Oly P&S which vignetted badly
but made amazing closeups:
http://edgehill.net/California/Bay-A...n/other/pg1pc3
I guess that's about an 8mm image circle. Hmm maybe it was an 8mm
projector lens...

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

Paul Furman wrote:
Richard J Kinch wrote:
a standard eyetube positions the image 10mm inside the end of the tube

Now I read that more carefully!

Sounds like an SLR can't get close enough to a standard focusing rack
with the eyepiece removed so the adapter is needed.

Paul Furman wrote:
David Ruether wrote:

there are other solutions. I based my
1:1 to 3:1 shooting on the Nikkor compact version of the 200mm f4,
which is quite sharp stopped down even with tubes, teleconverters,
achromats, and (also likely) with reversed camera lenses stuck on the
front, even with combinations of these. This solution also offers the
advantage of having the auto diaphragm for focusing.

That's a neat lens I've drooled about getting but for this setup I
want something really small.

That likely limits you to mostly lenses specifically designed for
5X (for you), and these tend to be rather slow on the required
extensions (which may not be compact with the longer FLs...),
and you will have no auto diaphragm, making hand-holding
impractical. The only exception I can think of is the reversed
55mm f1.2 CRT Nikkor, stopped down a couple of stops, if
very shallow DOF is OK. It does perform very well that way,
and the VF image may be adequate.

Yeah that leads to the Canon 60mm MPE f/2.8-4.3 because it's a modern
design with good coatings and optimized for the range I'm looking at: 1x
to 5x.

Any other options with modern coatings that are optimized for this
magnification? (1x to 5x) That lens would mean also getting a simpler
focusing rail and dumping the bellows. I guess that's a better setup
though. Here's some more with the 35/3.5 Spiratone:
http://www.flickr.com/photos/edgehill/3278436532/

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam

Paul Furman wrote:
Richard J Kinch wrote:
Paul Furman writes:

What is the diameter of the projected image circle?
How much 'working space between the rear element and image plane?
(approximately)
A standard microscope objective has its best
performance (least aberrations) at a 160mm tube
length, which means the shoulder of the threads is
held 160mm from the end of the eyetube, while a
standard eyetube positions the image 10mm inside the
end of the tube, so the "flange distance" (so to
speak, in the term usually applied to camera lenses)
is 150mm.
The useful image circle is a diameter of 18mm or 22mm
or thereabouts, which is what the field stop in an
eyepiece would show you.

So it doesn't quite cover DX/APS cameras, though close enough, but not
on FX full frame. Thanks for clarifying.

A little more extension would provide both greater
coverage and more magnification. It also will cause an
increase in spherical aberrations, but most camera
lenses are rarely ever used precisely at the optimum
extension/magnification.

A Canon SLR has its focal plane back 44mm from the
bayonet flange. So if you hold a microscope objective
(shoulder) 150mm - 44mm = 106mm away from a Canon
camera body, you have a direct projection
photomicrography camera.

Note that 160mm is "standard", but there are many
variations. Tube lengths from 160mm to 210mm are very
common, but today "infinity-corrected" objectives are
the most used. (Generally you would want to use
objectives for a shorter tube design, but the Unitron
objectives that I previously mentioned using are all for
170mm tubes.)

Objectives will be marked in several ways. Usually the
magnification is of course there (5x, 10, etc), and
usually the tube length and slip cover thickness are
indicated with something like this: "200/0.17". Either
"inf/" or an infinity mark indicates an infinity
corrected lens, and a "-" for the slip cover thickness
indicates no slip cover correction.

Hence the more desirable objective for use as a camera
lens might be a "160/-".

Another point worth injecting here is that the marked
magnification and tube length are related directly to
the focal length.

tube_length
--------------- = focal_length
magnification

Hence if it is a 10x objective designed for a 160mm
tube, the focal length is 16mm.

Here is an example which I manufactu
http://www.truetex.com/microscope_rms_tmount.pdf

Sounds like an SLR can't get close enough to a standard focusing rack
with the eyepiece removed so the adapter is needed.

A number of possible variations exist. First, a
mounting adapter to fit on the end of either a bellows
or a set of extension tubes is more functional.

Microscope objectives are designed to be "parfocal",
which means the focusing rail need not change when a
different objective is selected using a rotating
nosepiece. That distance is usually 45mm, measured from
the lens mounting hole to the plane that is in focus.
Working distance then depends on the physical length of
the lens. Generally from 25mm to less than 10mm will be
the working distance when the extension is 150mm, or
less with more extension.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)