Galileo's Original Telescopes: New measurements of  their dimensions  with special optical rulers.
Click here to see the errors in the literature about the optics Galileo used in his telescopes v1

Galileo's Telescopes: To Date These Are The Worlds Finest Museum Quality  Replicas 
Made to Order by Jim & Rhoda Morris

 Jim & Rhoda Morris   781 245 2897

We have built  a number of these very fine replicas  for the the IMSS in Florence Italy, Griffith Observatory, the  Adler Planetarium, and President L. B. Johnson's Library and Museum in Austin, TX. A number, in various configurations, of our replica's IMSS inv #2427 and 2428 were  on the exhibit at Beijing Planetarium and are now at the Franklin institute in Philadelphia. We were able to successfully make them to high standard of accuracy after spending a  significant amount of research of the literature  and  making measurements of these instruments using some interesting techniques that we developed for this task

An issue in dimensions and the  solution;
As we progressed through the task of making  creditable replicas of Galileo's surviving telescopes we found  significant  ambiguities in the  physical dimensions of Galileo's telescopes IMSS 2427 and 2428 as reported in in a wide number of sources of the  literature.

Basically we found that the published physical dimensions for the length and diameters of various  components of the telescopes when compared to the dimensions required by the reported optics  were inconsistent and would have given significant blurring of the images  and distortions of the outer appearance of the telescopes if used in  making  replicas. .  

These errors were too large to be ignored in building and using our replicas. It was clear that the lengths and diameters of the various components had to be checked out with new measurements. So with the help of Dr. Giorgio Strano - Curator and the staff  at the IMSS we  made measurement  of  the instrument on  a number of visits to the IMSS for  both the IMSS 2427 and 2428 telescopes. Our measurements did show clearly that both telescopes were considerably shorter than reported.  The  methods that we employed are discussed below along with the the current dimensions of both telescopes

In addition to our work and impart as a result of our work; . IMSS on (12/4/2008) made new and more accurate measurements of the length of both telescopes   The new   lengths for  IMSS inventory 2427 is (1273 mm not 1360mm) and IMSS inventory 2428  is (927mm. not 980mm). This is very good news for all of us especially those that build models of these famous telescope. We all appreciate the very careful and good work done by the staff at the IMSS.

These new data are reported  on their very  wonderful and lively web sites. Again thank you IMSS for your good work it is so very helpful. to all of us. and a wonderful example of scientist working together to achieve the best data. for our and others  projects to replicate these instruments.

Below are some of the far out avenues we used to search out the physical specifications from the literature for the original Galileo's telescopes at IMSS, information necessary for our replication project.

Original Galileo Telescopes in an earlier display at Florence Italy.  Top telescope is IMSS 2427, bottom IMSS 2428 The broken lens IMSS 2429 in the center of the decorated ellipse

From pictures such as the classic mount of the two telescopes and the broken lens above, we made detailed ratio measurements of all the dimensions of  both telescope.  Given a known measurement this method yielded specific values for all the dimensions.  With this method parralax errors had to be taken into account and it was not adequate for the precise data we needed for our work, but it provided good confirming data on the relative physical specifications. 

Another helpful source were the museums that owned  replicas by Cipriani  (c 1920/30's at Arcetri Italy)  and had them in their inventory and on display. For example with the help of the staff at the Adler Planetarium we were able to make detailed measurements on their Cipriani replicas and found that for some details they deviate significantly from the originals. 

On our trips to the IMSS we took up the challenge to make our measurements of the original instruments through the display case windows in the exhibit  hall before normal exhibit hours.

The windows of the display case are of adequate optical quality to make useful optical measurements. For these measurements  we designed and built our own special portable optical rulers  which are described below. We compiled  two sets of data, one in 2005, using a single telescope on a substantial tripod, the second in 2007, using two microscopes  connected to a rail and ruler. A pictorial description is presented below for both techniques. A comparison of the two sets of data showed an agreement to within + or - 3 mm.

Length Measurements

In the beginning of our project, making the most precise replicas of Galileo's telescopes, we found that the dimensions in the literature just  don't add up

The portable measuring stand we assembled and used to measure Galileo's  telescopes at the IMSS in Florence, Italy in September 2005

Making the actual measurements of the original telescopes in their cabinet with the telescope on a tripod method at the IMSS, September 2005.  Here we are measuring the diameters. Over its 400 year history, the leather covered telescope has become less round and no longer has a truly  circular shape.  However we have vertical and horizontal photos from which we have  made diameter measurements. It would be valuable to have measurements of the circumference at various stations along its length, but this was not possible on either of our visits.

Below Rhoda, Jim and the staff at the IMSS, July 2007, reviewing and comparing the data in the literature and records on the lengths of IMSS 2427 & 2428 telescopes.

Rhoda and staff checking out IMSS inventory catalogs at the  for information on Galileo's telescopes

Rhoda and Dr. Strano, curator of the IMSS , making a visual overall comparison of our replica of 2428 with the original Galileo instrument.


In July 2007 we repeated  and re-checked our earlier measurements for the dimensions of the 2427 & 2428 telescopes at the IMSS with new equipment. We found that both of our data sets are  in good agreement and they continue to show serious inconsistencies with those in  the literature.


The July 2007 repetition of our original 2005 measurements of the length of the Galileo's original telescopes using a new version of our optical ruler designed especially for this task of making the measurements from outside their cabinets. The optical ruler  is composed of two microscopes with cross hairs. One microscope views the left hand side of the telescope the other the right side. They are connected with a centimeter scale.

Below are some photographs of the equipment and measurement process.


Above: the cabinets containing the Galileo IMSS 2427 and 2428 telescopes with Rhoda and Jim literally on their knees measuring the length of IMSS 2427.
Above  is the eye piece side of our optical ruler with their sliding focus tubes, one was used to view the  left  side  of  the telescope the other  use to view the right  end of the telescope. Their fiducial cross hairs were used to register the microscopes to the ends of the telescope. They are connected with a scale to make the length measurements.
The  above photo shows the telescope side of  the optical ruler. It  uses two low power microscopes with cross hairs.  The microscopes are pressed firmly to the glass  of the cabinet making them perpendicular to the cabinet.

Corrections had to be made to our measurements for 2428 because it was not parallel to the case. This amounted to a fraction of a millimeters in over all length. The two arrows show the rotated position of the 2428 which is above the arrows. The objective end of the telescope is pointed at the camera.


On Jim's  80 th birthday and after after completing  the  delivering of several of our replica's to the IMSS we with with Dr. Strano, curator of the IMSS,  made one more fast measurement by a third technique of  the length of the  IMSS 2428 telescope.

We did this  using a draftsman right triangle, a tape measure, and a few strip of black tape. It was a bit crude certainly  fast and accurate to a few mm..

Using the  right angle drawing triangle shown above  to obtain a simple rough measurement of   the  length of Galileo IMSS 2428 telescope while it's   still in its the display case.

This was used to make a quick estimate of the overall length of the 2428 telescope during  our visit to the  IMSS delivering three of our replicas telescopes to them

The photo above shows the process from the telescope's point of view while positioning the edge of the right triangle to one end of the telescope. The narrowest end the drafting triangle (the blue line in the foto) is place on the surface of the display case window and slid back and forth while sighting down the right angle edge of the triangle at the telescope. . When the edge  is registered correctly on the end of the telescope a piece of black tape is fixed to the display cabinet's window at the intersection of the right angle intersection of the drafting instrument marking that end of the telescope. The process is repeated at the other end of the telescope and the distance between the tapes is measured with a tape measure.

The three photos below were taken in our laboratory using one of our reproduction of the original telescope and a  reproduction of the measurement conditions that we had at the IMSS on  12/07/07 with the original.  The length of our measurement of the original ( see the pictures below )using this technique was 925 mm. To determine the precision of this technique we made on our return from the IMSS  7 measurements in our laboratory, replicating the same setup as used on the original and  found  a  standard deviation   for  data gathered by this method. We report it for one, two and three sigma's.  One sigma there  is  a 65 % chance it was within   + - 1.61 mm.. For  two standard deviations there is a 95% chance it was   between + _ 3.22 mm. and  for three standard deviations    99.7%  chance it would be within + - 4.83mm . That is 925 mm +or -  4.83 with a confidence of 99.7 %.

This view the triangle is too far to the right of the end of the telescope. For this view the triangle is too far to the left of the end In this view The triangle is very close to being on target at the end of the telescope and will be marked with a strip of black tape by a colleague while the observer maintains the position of the drafting square.

When the  drafting square  is registered a piece of black take is fixed to the display cabinet's window marking the end of the telescope and the observers move on to the other end.
The telescope is cantered in its case so that it is not parallel to the window.. Additional measurements were made from the side of case making it possible to correct  this potential error.

Again we very much thank the staff  of the IMSS in Florence Italy for their help and patience during this projects especially Dr. Giorgio Strano  Curator of IMSS who is on the left of the photos  above helping with the measurements. The photo on the right shows the team  including Rhoda getting data to correct for the angular displacement about the vertical plane of leather telescope.

The data in the literature  generated for the focal length of the objective of 2428 and 2427  around the first quarter of the last century by Ronchi is 95.6 cm and that by Molesini etal in the last quarter is 98.0 cm. We had chosen to favor the latter data because it is the most recent and must certainly have been check because the authors must have been aware of the difference and checked their results carefully. We authors' are looking forward to a resolution of these figures which maybe done in the near future. It is important fro a number of reasons among them the eye piece nub!

The eyepiece nub?

Side view of the eyepiece nub on the original. IMSS.

c 1930  overall view showing  of Guilio Cipriana replica now at Adler Planetarium.  No nub. as an  eyepiece

End view of the nub on the original. IMSS

c 1930  Eyepiece and its decorations of Guilio Cipriana replica now at Adler Planetarium. Note  No nub. as an eyepiece

The authors believe that there is a convincing set of arguments that can be made for getting rid of the little paper covered eyepiece holder, that we call a nub, and move the lens back into the original mount. this would shorten the optical length about 21 mm  which would then accommodate a 956 focal length objective  the data  that Ronchi reported in 1923. The telescope would then be short enough to accommodate this lens and still be able to focus at infinity.   In fact the old inventory data at the IMSS records a total telescope length of 0.92meters.  We assume that this measurement is without the nub, since it is so much shorter than our measurements of the original telescope length which includes the nub.  If this assumption is true  then it is further evidence that the nub  was not considered a part of the original parts list.  It is also consistent with the overall lengths we measure with the nub since adding the nub length of 1.6 cm to the 0.92 meters gives us an overall length of 93.6 cm, a value that falls within the range of  measurements we have made on the lengths of the original, namely from- 93.3 to 93.9cm.


The little piece now holding the eyepiece is out of style with the rest of the decorations of the red leather telescope. It has been reported the present eyepiece lens s not an original. Guilio Cipriana in building his replicas in the 1920 and  30's did not include it in his replicas. Why not?  He appears to have had  access to the original because his art work  while not exact is similar. His  construction details, such as the diameter along the length  of the telescope, do not follow the original that closely but have been good enough to satisfy a number of museums around the world for their collection.

It seems worth while to see if their is any information available about Cipriani and his  work at Arcetri, Italy in the 1900's . that could shed light on this issue. The little nub just does seem right. Its time to clear this issue up for the up coming year of astronomy. in the mean time we have made some pieces to hold the lens in the exiting mount along with a leather decoration to convert the lens so that it would be  keeping the style of the objective end..

 Our end result for the length of the Telescopes!
and science in action!

Our measurements and their comparisons with the literature
were made with three types of apparatus described above on three occasions. We are reporting in this table  our average measurements. Look above again to see us measuring the lengths of the original Galileo's Telescopes at IMSS in Florence Italy.

The focal length of 2428 objective (Ronchi 956 mm ref 6a) and  (Greco etal 980 mm ref 7). The focal length of the eyepiece of 2427 (Ronchi-48.8mm) and  (Greco etal-47.5)

Source of data and telescope


Our measurements:
Telescope barrel length for IMSS # 2428
826 mm  3 mm. one sigma corrected for typo error 12/05/08
IMSS web site: 
Telescope barrel length for IMSS # 2428
835 mm. plus or  minus?
Our measurements
Total length for IMSS #2428

925mm. plus or minus 3 mm. corrected typo error 12/05/08

IMSS  web sites:
Total telescope length for IMSS #2428  
927 mm plus or  minus? an updated value will be published on  IMSS web site shortly12/05/08
 STScI web site  now quote IMSS new data
Our measurements : 
Total telescope length for IMSS # 2427
1265 mm.  plus or  minus 3 mm one sigma
IMSS web site:
Total telescope length for IMSS # 2427 
1273 mm.  plus or minus
an updated value will be published on  IMSS web site shortly shortly12/05/08


Bottom line on length: 12/05/08 IMSS has made new measurement for both telescopes that will appear on their web site shortly.

For the #2428 telescope we measure the overall length to be 925 mm plus or minus  3 mm.  This value is consistent with the value we obtain from our measurement of the barrel (which agrees with the IMSS barrel length) and the two lens housings all added together.  IMSS and a NASA affiliate, STScI, report 980mm, a difference of 45 mm 1  3/4 "or nearly 5%. of the total length.  The overall length  depends, of course, on the position of the eyepiece and objective tubes and they were pushed all the way in when we made our measurements.  For the #2427 telescope the offset is 95 mm or almost 4 inches or 5.5 %.

The importance of these numbers for the total length is that when one uses the longer lengths and the focal lengths for the lenses published for these telescopes it is an optical impossibility for the telescopes to focus at infinity! If they are made to the published data the view of the planets and stars will be blurred out of focus images.

Another point using our measurements it is possible to use the current lens without it present little holder which may  also not be original. Doing this one could use  objectives  lens that has  Ronchi focal length measurements of 956mm The end result is a telescope that dimensionally does not have this out of style extra piece holding the eyepiece and it will still focus at infinity.

Click on the picture to make it bigger

A review; The distances between the eye piece and the objective lens, in a Galilean design, is calculated from the sum of the focal length of objective and and the focal length of the eyepiece. Remember that Galileo used a negative lens i.e., -47.5mm. so the values are subtracted.  (See standard text book on optics)

Both IMSS and we, as partners in science, strive for accuracy in our work. We understand that errors such as this can and will be copied over and over again with repetition like a domino effect.  They will even find their way into other publications to which people will look for good data on the Galileo telescopes such as NASA's  affiliate, STScI, which reports on Hubble data and  identifies itself as "the Formal Education Group of the Space Telescope Science Institute's Office of Public Outreach," see Hubble.                                         


Tube Radius Measurements. IMSS 2427 & 2428


This animation  of the IMSS 2428 telescope shows that by preferentially increasing the magnification of the diameter but not its length we can get a much better appreciation of the shape of  the telescope along its length including some dents along the body. One can see the cone like shape at the objective end.

With the apparatus described above we measured the cross section of the telescope at a number of points along its length.

In addition we were able to get an overall measurement along its length . using a high resolution photographic view of both the side and the top.   The photo above is one of a number of examples of this technique which  enhance, by  photographic means, the relative measurements of the dimensions of the telescope. We enhanced the cross sectional shape of this photo by magnifying the diameter ten times the length. giving the fat photo shown above.  One has to be careful taking dimensional data from photographs because the camera can bias the image from any number of lens distortion issues. One of the most important  correction is  for barrel distortion caused by the camera. 



 Notice how this method accents the irregularities of the cross section of these telescopes. We also contrasted the image to bring out  the surface irregularities.  It is more than interesting how much more  information of the telescope shape is demonstrated  through this process. Further, by normalizing the photo and making  the rather small corrections for our  camera perspective i.e. Barrel distortion to our measurements we get detailed quantitative  specifications for the cross sectional dimensions of the telescopes. 

Throughout the life of the telescope it has been flattened in several places along its length.  Combining data  from  photos of  the top and side   gives a good approximation to the lack of roundness of these telescopes. Many professional photos of these telescopes have been made over many years allowing one to study these telescopes aging with time. We have done a little of this  from photos before and after the last restoration . for example the sliding tubes seem to be stuck from some where after 1920's. Could it have been a result of Dr.  Hales visit in the 1920's?

Combining the data we get a shape of two cones.. One starting from the eyepiece at 36mm  dia. growing linearly to 37 mm 150 mm from the objective end. A second stronger cone starting at 37mm and growing to 47 mm. We have encouraged the IMSS  at their next opportunity to measure the perimeter along the length of the telescope rather than the radius. Thus getting  of the out of roundness difficulty. as will be discussed further on in this site we measure n over length  of 935mm rather than the 980 mm reported on IMSS's  web site. This has also been reported to IMSS.


Example of Cross section measurements, using photo enhancement  of IMSS 2427 paper covered development telescope
Our data shows contrary to the data found in  Pettit, Edison. A Telescope of Galileo. Publications of the Astronomical Society of the Pacific 51 (June 1939) 147-150. (#301) (replica by Cipriani).. Our photos of IMSS 2427 show no linear cone shape over the total length of the telescope. Rather the objective end of this telescope is close to a constant diameter cylinder to the middle. Its purpose could  be to make it easier to use Galileo's Micrometer for angle measurements. This enhanced photo also helps in locating the position of the wires rapped around the telescope. Last but not least the  lower image of the telescope in this figure show in greater detail the warping found in this telescope.

All in all this type of photographic  enhancement has much to speak for it.




International Year of Astronomy

The IYA  impact of this dimensional difference for both Galileo's telescopes is that builders and enthusiasts will be absorbing these errors when they make there own copy of these very historical and beautiful telescopes for their IYA activities.  If they use  the longer dimension and published optics for the lenses they will find that their telescopes will not focus at infinity.   They will not be able to replicate the Galileo observations that he made in 1609 and later. 

Certainly having another though mini-Hubble-focusing problem in Galileo replicas in 2009 would not be appreciated by celebrating astronomers and educators. [:-) nor STScI

 It's not good for the "image" of sciences if we can't pin down how and where the image is focused for the worlds oldest, simplest, and historically significant telescopes, instruments we want to use as teaching tools for science.

On the other hand the process described above is an excellent example of science at work!  It starts out with a problem, an anomaly, or inconsistency to resolve and one has to determine the most probable cause.  Remembering Galileo's 1610 letter to the Tuscan court, substantial effort had to be spent honoring  the first principle of science, that is, to be right.  By searching the known data and making repeated measurements and with the help of other professionals in the field, we achieved consistent data.  So replicas can be made that will be working telescopes capable of operating the way they did for Galileo and to serve as the teaching tool to tell the "truth" he wanted observers to see in the heavens  The story of  building Galileo's instruments  is a classic example of how Galileo and his new methods of  science can be brought into action.


ref 1aa  Sidereus Nuncius Galileo Galilei Translated by Albert Van Helden1989 Univ of Chicago. p91
See our write up in "Galileo's Telescope The Instrument The Changed the World" edited by Giorgio Strano, Pub  Giunti 2008 (isbn 978-88-09-05938-2)
We cannot thank all those who have helped so much with all the work in these projects. If nothing else the authors hope that the non scientific reader will get a taste of the amount of work that goes into scientific projects to be sure they are test ably right.

THE so called
Audit trail that all  scientist automatically go though  in their  explorations of how things including science work.

Good luck.


Ref 1 The American Heritage Dictionary

1a. Catalogue of Early Telescopes by Albert Van Helden 1999 Istituto e Museo di Storia Scienza dell Scienza, Firenzze

2a. Sidereus or The Sidereal Messenger Galileo Galilei Translated with introduction, conclusion, and notes by Albert Van Helden The university of Chicago Press Chicago and London1989

We thank Paul Valleli of Amateur Telescope Makers of Boston for discussions on adjustments of the focal length of the objective, recommending several source of information and generally paving a path to many resources including contacting Peter Abrahams of the Antique Telescope Society who very kindly supplied the references below. Also the is a well rounded collection of references and relevant information  pictures plus  interesting critiques maintained by Jim Mosher. Tom Pope both experience scientist.

1, Baxandall, David. Replicas of Two Galileo Telescopes.
Transactions of the
Optical Society 25:3, (January 1924) 141-144. (measurements
Galilean optics)

2 Pettit, Edison. A Telescope of Galileo. Publications of the
Society of the Pacific 51 (June 1939) 147-150. (#301) (replica
by Cipriani)

3(Galileo) Barr, E. Scott. Men & Milestones in Optics, III: Galileo
Applied Optics 3:12 (1964) 1321-1328.

4(Galileo) Drake, Stillman. Galileo Gleanings VI: Galileo's First
Telescopes at
Padua and Venice. Isis 50:3 (Sept. 1959) 245-254.

5(Galileo) Drake, Stillman. Galileo's First Telescopes at Padua
and Venice. Isis
50 (1959) 245-54.

6(Galileo) Greco, Vincenzo, G. Molesini, & F. Quercioli. Optical
tests of
Galileo's lenses. Nature 358 (July 9, 1992) 101. <& .pdf>

6a V. Ronchi "Sopra i cannocchiali di Galileo," L 'Universo 4,791-804(1923)

7(Galileo) Greco, Vincenzo et. al. Telescopes of Galileo. Applied
Optics 32 #31
(Nov. 1993) 6219.

8(Galileo) Miniati, Mara. Examination of an Antique Telescope.
Nuncius 9:2
(1994) 677-682.

9 (Galileo) Ringwood, Stephen. A Galilean telescope. Quarterly
Journal of the
Royal Astronomical Society 35 (1994) 43-50.

10 (Galileo) Sonnefeld, August. Optical data of Galileo Galilei's
telescope. Jena Review #6 (1962) 207-212. <.jpg>

11 (Galileo)Westfall, Richard. Science and Patronage: Galileo and
the Telescope.
Isis 76 (1985) 11-30. <& .pdf,.tif>

12 (Galileo) Zik, Yaakov. Galileo and the Telescope. Nuncius 14:1
(1999) 31-67.
13 (Galileo) Dupré, Sven. Galileo, the Telescope, and the Science
of Optics in the
Sixteenth Century: A Case Study of Instrumental Practice in Art
and Science.
PhD Dissertation, Universiteit Gent, Belgium, 2002. 366pp.
14 (Galileo) Miniati, Mara, et al. Examination of a terrestrial
telescope with the
signature of Galileo. Optik 101:3 (Jan. 1996) 140-142.

15 (Galileo) Greco, Vincenzo et. al. Modern Optical Testing on the
Lenses of
Galileo. pp110-121, Paolo Mazzoldi, ed.; From Galileo's
Occhialino to
16 Optoelectronics, conference Padova June 1992; Singapore:
World Scientific, 1993.

17 Sidereus Nuncius Galileo Galilei Translated by Albert Van Helden1989 Univ of Chicago. p91

18  See the wonderful New book and catalog from the IMSS: "Galileo's Telescope The Instrument That Changed the World" edited by Giorgio Strano, Publ. Giunti 2008 (isbn 978-88-09-05938-2)  It covers the history of thought and technology in the development of the telescope over a broad spectrum of topics relevant to Galileo's time presented by a team of international experts.  It is an excellent historical and educational catalogue for their exhibition with wonderful technical analyses of the components of Galileo's telescope illustrated with magnificent photographs.

(We were privileged to be one of the collaborators)

Click to see Reference 1 resin composite construction

reference to a  replica Hale had made for himself. mid 1900's

1.   Smithsonian/NASA Astrophysics Data System (ADS)

Title: A Telescope of Galileo
Authors: Pettit, E.
Journal: Publications of the Astronomical Society of the Pacific, Vol. 51, No. 301, p.147
Bibliographic Code: 1939PASP ..51 .147P ..51 .147P



ref. 6a V. Ronchi "Sopra i cannocchiali di Galileo," L 'Universo 4,791-804(1923)

ref  7 (Galileo) Greco, Vincenzo, G. Molesini, & F. Quercioli. Optical tests of
Galileo's lenses. Nature 358 (July 9, 1992) 101.


All photos and written material are by Jim & Rhoda Morris unless noted otherwise. Free personal and educational use and reproduction is encouraged; We would appreciate an acknowledgement. all commercial rights are reserved. copyright 07-07-2007 Jim & Rhoda Morris

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