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The Classic Edmund Scientific Off-Axis Guider

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#1 amicus sidera

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Posted 07 May 2012 - 01:28 PM

In the late 1970's astrophotography was becoming of considerable interest to more and more amateur astronomers, and the Edmund Scientific Company responded to this increased interest by creating an off-axis guider for use with its then-new model 4001 8" fork-mounted telescopes. Part number 72,428 designated the new guider, which was offered by itself as a separate item for $250, or incorporated into a factory-made 8" OTA (model 4005) or complete telescope and mount (model 4004), at a cost of $625 or $1000 respectively.

The lineage of this guider is subject to some speculation... catalog descriptions of the item reference a Mr. Felix Blancha, a "noted astrophotographer", and that the guider was based on a concept of his, but my research has turned up almost nothing on him or his work, save for two mentions in Sky & Telescope magazine in the 1970's and an internet photo of him with his 12-1/2" reflector. On the other hand, it appears that the late Joseph Cocozza, a professional photographer, amateur astronomer and author of the 1977 book Astrophotography Near City Lights , was responsible for the basic design of this particular guider. An illustration in his book details the guider he built for his own 12-1/2" reflector, which looks nearly identical to the Edmund model that came out a year or so later. A recent conversation with Mr. Clyde Drauglis, a former Edmund design engineer, confirmed that the Edmund off-axis guider was based primarily upon Mr. Cocozza's design; Mr. Drauglis (who is also responsible for Edmund's tensioned-vane diagonal system, and who played a large part in designing the 3001 and 4001 reflectors, along with having a hand in the Astroscan design) related that he made a few changes to accommodate assembly-line practices, as well as for aesthetic reasons. Apart from those changes, the design seems to follow Cocozza's guider quite closely. There is also some speculation that Edmund's guider licensed concepts from an off-axis guider patented by Thomas Venable, U.S. patent no. 4,283,112, who references Joseph Cocozza in his patent. The trail is a bit cold at this late date; if anyone has more information related to this guider and the principals referenced here, please don't hesitate to add them to the thread.

According to Mr. Drauglis, total production numbers for the guiders totalled somewhat less than 150 units. They did not sell as well as expected, possibly due to the relatively high cost, as well as the introduction around this time of Lumicon's EZ-Guider Newtonian off-axis guider, which did not require permanent mounting on the telescope and was not model-specific. One wonders if Edmund ever broke even on their guiders, as they were not easy to produce and required, aside from the labor-intensive greensand casting process itself, a considerable amount of machining, finishing and assembly.

The photo below shows a late-production model of the Edmund "off-axis astrophotography guider", as it is termed in their catalogs. This pristine example was purchased from Sam, CN member "planet earth"... he had originally obtained it from Efstonscience in Toronto, circa 1981, who at the time were Edmund's primary - possibly only - Canadian distributor.

The guider consists of an upper and lower aluminum casting, two focusers (a 2" for the camera or visual use, and a 1-1/4" for the guiding eyepiece), a pick-off prism and a relay prism (both non-aluminized) and a fine-adjustment mechanism for the relay prism (not visible in the photo immediately below). The pick-off prism is fixed in place. Note the brass thumbscrews used for locking the focuser tubes in place once focus is achieved. The black-anodized adapters shown here in the 2" focuser were included with the guider from the factory.

The four brass thumbscrews spaced equally around the circumference of the guider are loosened slightly to enable the top part of the guider casting, which would be carrying the camera body and guiding eyepiece, to rotate for guide star selection. The bottom casting remains affixed to the telescope at all times.

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#2 amicus sidera

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Posted 07 May 2012 - 01:30 PM

A view of the guider from the other side. Note the black relay prism adjustment knob and lock nut at bottom left:

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#3 amicus sidera

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Posted 07 May 2012 - 01:30 PM

Looking down the two focuser tubes, showing the pick-off prism (right) and relay prism (left):

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#4 amicus sidera

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Posted 07 May 2012 - 01:31 PM

Underside of the guider, showing the prisms and part of the relay prism adjustment mechanism (this allows for a wide range of guide star selection). The mounting holes indicated are the attachment points for the lower casting onto the telescope tube:

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#5 amicus sidera

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Posted 07 May 2012 - 01:33 PM

A close-up view of the prisms and adjustment mechanism. The 30-year-old-plus epoxy used to attach the prisms seems to be holding, but safety wires are indicated with adhesive this old.

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#6 amicus sidera

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Posted 07 May 2012 - 01:33 PM

Tension adjustment allen screws for the 2" focuser; these tighten to increase tension on the pinion shaft:

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#7 amicus sidera

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Posted 07 May 2012 - 01:34 PM

Tension for the 1-1/4" focuser is provided by a wave washer riding between the casting and knob on one side... the tension can be increased simply by loosening the focuser knob and retightening it closer to the casting, thereby compressing the washer.

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#8 amicus sidera

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Posted 07 May 2012 - 01:35 PM

Side view of the guider, showing the radiused cutout on the bottom casting. Early, or Type I models of this guider continued the curved radius all the way out to the sides of the bottom casting. This had two drawbacks: it added unnecessary weight to the guider, and also prevented its ready use on any telescope other than one having a tube larger than the 9-1/2" outside diameter of the 4001. It is suspected that the change to the Type II base casting occurred after the main production run, and that only new bases were cast, without new top castings being produced. This modification allowed the guider to be used on a much wider variety of tube sizes.

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#9 amicus sidera

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Posted 07 May 2012 - 01:35 PM

Close-up of the relay prism adjustment shaft... this moves a mechanism which allows for repositioning of the prism across the field of view, which increases the number of available guide stars considerably. The large knurled, round nut below the knob is used to lock the shaft to prevent movement after a guide star has been selected.

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#10 amicus sidera

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Posted 07 May 2012 - 01:36 PM

Here the four circumferential brass thumbscrews have been removed, allowing the separation of the top and bottom castings. The top casting rotates in the machined groove on the bottom casting. The original lubricant used appears identical to water-pump grease, and is likely the same as the grease originally used on the worm drives and shafts of Edmund telescopes - a smear test on white paper bears this out.

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#11 amicus sidera

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Posted 07 May 2012 - 01:37 PM

Closeup of the relay prism adjustment mechanism:

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#12 amicus sidera

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Posted 07 May 2012 - 01:37 PM

Along with the previously-mentioned differences in the lower casting, here are some other salient differences between early production and later guiders, Type I being earlier than Type II displayed here:

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#13 amicus sidera

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Posted 07 May 2012 - 01:38 PM

The photographs shown here do not truly convey the precision and mass of this piece of equipment... the machining tolerances were kept very tight, and the whole assembly works exceptionally smoothly, with a "Swiss watch" feel to it. Total weight for the unit exceeds four pounds.

How well does it work? I have yet to place it onto my Edmund 8" f/5, as I am attempting to obtain a spare tube for it, so as not to modify the original. To all appearances it should work exceedingly well for its intended purpose as an off-axis guider. One possible drawback to using this guider assembly for both visual and astrophotographic purposes is that there seems to be no way to retract the pick-off prism from the light path... I have yet to determine whether or not this will have a detrimental effect on visual observing.

There are mentions in the CN archives regarding this guider; Neil (apfever) has one of the rare Edmund model 4004's that came from the factory with a late-model, Type II guider installed; photos about halfway down the following CN page:

Edmund model 4004

Jimegger has several related posts starting a little more than halfway down this page, with photos showing his Type I, earlier production guider on his telescope:

CN Forums Archive - related post


I trust that this series of posts was found to be enlightening, if not useful... I would especially welcome reports and comments from anyone who has or is using this guider, or had one at one time.

Special thanks to CN members Neil (apfever) for his continued assistance, encouragement and considerable Edmund knowledge, and Sam (planet earth) for making the guider available for sale in the CN classifieds and for providing an ultra-smooth transaction.

#14 tim53

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Posted 07 May 2012 - 01:58 PM

Thanks for posting this! I remember when these came out. I wanted one more than you could imagine, but the cost was too high. I ended up making an off axis guider from an old SLR mirror and thin plywood. Only used it a couple of times, but it worked okay.

-Tim.

#15 amicus sidera

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Posted 07 May 2012 - 02:27 PM

I wanted one too back then, Tim, and yes, they were really expensive for their time! Corrected for inflation, that $250 figure for the 1979 price is equivalent to approximately $750 in 2010 dollars, according to the Inflation Calculator webpage.

#16 Nightfly

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Posted 07 May 2012 - 05:07 PM

An excellent and thorough report. I recall this guider when flipping through the 1980-81 Edmund's catalog while dreaming of doing astrophotography. A fast Newtonian such as the Edmund 8", coupled with the guider was a formidable instrument in its time. I looked at it very seriously before buying my Meade 8" SCT in '83, opting for the compact scope package as I believe many did at that time.

Looking at the guider today, I feel a loss for what was (and is) a beautiful instrument.

Thanks for bringing this lost piece of gear to our attention.

Now there will be one more piece to the story that I will find most delightful, taking a modern day astrophotograph with it. Not with a DSLR, but with keeping with the era that it came from, a film astrophotograph. That would be an fitting end to what so far is a great story.

Jim

#17 amicus sidera

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Posted 07 May 2012 - 05:45 PM

That's next on the agenda, Jim... and film it will indeed be! It would offend one's sense of the fitness of things for it to take its first astrophotos using anything other than analog media. :grin:

#18 Nightfly

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Posted 08 May 2012 - 06:14 PM

That would be a wonderful addition to your research on Edmund scopes, and a great story!

#19 apfever

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Posted 09 May 2012 - 11:36 PM

Thanks amicus,

I'll be using this thread for when I tear mine apart.

#20 dib2

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Posted 16 May 2012 - 11:15 PM

Greetings amicus sidera,

I have first-hand knowledge of the creation of the original off-axis guider you refer to. I introduced Joe Cocozza to Felix Blancha many years ago. Felix was a dear friend of mine, an optomechanical genius who had many other talents, astrophotography among them. I met Joe at an astronomy club meeting in Philadelphia, if I recall, and knowing they were both talented astrophotographers thought they should meet. At this point Felix and I had been friends for at least 15 yrs.

As a person, Felix had a magnetic personality: very outgoing, creative, generous, friendly, and energetic.

Blancha had developed (conceived, designed, built) the original guider for his own use on his home-built 14" telescope. He freely shared his design with Joe, showing it to him in detail. Subsequently, the concept, modified a little, showed up being produced by Edmund Scientific. I will say no more.

I would be interested to see the image of Blancha on the internet. If you'd send along a link I would be grateful.

Best,
dib2

#21 amicus sidera

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Posted 17 May 2012 - 09:29 AM

Dib2, many, many thanks for your response and clarification! This is wonderful information, and resolves some questions that have been tossed about. I found photos of Felix at the following link:

Felix Blancha - Ancestry.com

They consist of rather large thumbnails, and apparently registration with ancestry.com is required to see the larger versions.

So, his big 'scope was a 14-incher? Correction noted... also, reading between the lines, I think I see what you're getting at to regarding the design of the guider... at least Edmund did give him some credit in their catalog pages. Considering his proximity to Barrington, the general consensus was that he knew someone at Edmund... perhaps he simply apprised them of his priority in regard to the design of the guider?

I did find out a bit more about him than I alluded to in the original post as I felt it wasn't germaine to the topic at hand, such as his being an immigrant that arrived here in the U.S. in the early 1900's, that he held a number of patents, and was the grandfather of Steven Tyler, of the band Aerosmith... and article dealing with that is at the following link:

Huffington Post article

I'll send you a private message (PM) regarding other related items.

Again, thank you very much for your input!

#22 apfever

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Posted 17 May 2012 - 08:22 PM

dib2,

Thank you for the information on Felix Blancha. He was mentioned in the original Edmund ads for the focuser "Based on a concept developed by noted amateur astronomer Felix Blancha..."

Until now i've found no other explanation of his involvement. Again, much appreciated info.

Neil


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