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1899 4" f/16 Cooke Photovisual Apo refractor

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#251 col

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Posted 01 September 2020 - 10:14 PM

Nice work Peter. Looking much better but still showing its history.



#252 col

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Posted 01 September 2020 - 10:54 PM

The finder amused me.

 

It was my first light with the Cooke telescope, and because the instrument was in the garage I pointed the telescope at a star low on the horizon through the open door. Of course I used the finder to point the scope, I was amused that the finder was mounted so close to the tube that the objective cell obstructed part of the field of view.

 

attachicon.gifCooke garden.jpg

 

attachicon.gif20200205_152356.jpg

 

As can be seen in the photo above, there is no way to align the finder tube relative to the OTA, it is bolted in place with the brackets. However the reticle can be offset from the finder's tube to make pointing coincident with the main scope.

In the photo below the main telescope tube would be a 6 o'clock, one can see the adjustments have bottomed out. Unfortunately, at first light, I didn't note how accurately the finder was aligned to the telescope.

 

attachicon.gifIMG_2504.JPG

 

Peter,

your comment about the obstructed finder field puzzled me as I have never noticed the problem. It appears the finder supplied with the 5" PV has taller stand-offs.

Col

 

 

Cols-Cooke-9.jpg


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#253 Peter Ceravolo

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Posted 02 September 2020 - 01:26 AM

Col I placed the 1.25" finder on the tube with the objective dew shield in place.

 

IMG_2654.JPG

 

Looking through the eyepiece the objective cell/dew shield blocks about 25% of the field, in the form of an almost straight line 25% of the way down from the edge of the field.

I tried to get a shot of the view through the eyepiece with no luck, those ancient eyepieces don't have enough eye relief. Below is a shot of the exit pupil that kinda shows the obstruction. It's greater in extent through the eyepiece.

 

IMG_2655.JPG


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#254 macdonjh

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Posted 02 September 2020 - 09:29 AM

Nice work Peter. Looking much better but still showing its history.

+1, clean and shiny but still with a bit of patina.



#255 Ben Bajorek

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Posted 02 September 2020 - 12:36 PM

Very nice Ben!

 

Would you mind posting a pic of the finders objective end?

 

Do you know your Cooke's history? Was it every refinished?

 

Peter

Here are some shots of my finder's objective.  You can adjust the lens focus position with sliding set screw.  

 

I believe my Cooke has not been refinished.  It was polished at the factory, but I don't think anyone has messed with it since.  

 

As far as the history, unfortunately I know nothing.  The person I bought it from said it was a gift from her father for her to sell and buy a wedding dress with the proceeds, I believe to be the case.  I imagine it came out of an estate of one of those 19th century Michigan industrialist, mining or timber.  One of the wealthy Chicago families that summered in Northern Michigan is another possibility.

Attached Thumbnails

  • Cooke Finder Objective 1.jpg
  • Cooke Finder Objective 2.jpg

Edited by Ben Bajorek, 02 September 2020 - 12:37 PM.

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#256 macdonjh

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Posted 03 September 2020 - 08:29 AM

Here are some shots of my finder's objective.  You can adjust the lens focus position with sliding set screw.  

 

I believe my Cooke has not been refinished.  It was polished at the factory, but I don't think anyone has messed with it since.  

 

As far as the history, unfortunately I know nothing.  The person I bought it from said it was a gift from her father for her to sell and buy a wedding dress with the proceeds, I believe to be the case.  I imagine it came out of an estate of one of those 19th century Michigan industrialist, mining or timber.  One of the wealthy Chicago families that summered in Northern Michigan is another possibility.

I think a nice finder for such a fine telescope needs to be refitted with a MoonLite focuser for precision focusing...



#257 Kasmos

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Posted 03 September 2020 - 01:17 PM

 

 

Here is an image of the objective cell pressed onto a thin tube that slides into the main finder OTA. The finder objective can be slid up and down the main tube so that it's focus can be made coincident with the retical position. The eyepiece then is focused in the retical and all is good. I'm not clear on why one needs the screw in the main tube to fit in the slot in the finder objective tube. Clearly this arrangement prevents rotation, but I don't understand why one must prevent rotation of the objective cell tube when focusing it.

 

 

The screw and slot seems like good engineering to me. The slot lets it have travel for adjustment while screw keeps it from accidently being pulled all the way out. Especially since it might have slid very easily when new.


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#258 Peter Ceravolo

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Posted 03 September 2020 - 03:30 PM

Yes, the screw constrains the motion, one cannot pull the objective cell out.

So one focuses the eyepiece on the reticle, then one focuses the objective. Then you paint all over everything... :-)

 

IMG_2486.JPG


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#259 col

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Posted 03 September 2020 - 07:22 PM

Start with the focuser and cap on my 4" telescope.  Cooke is an Ltd. at this point, so it dates around 1897 to 1915.  Parts of this scope have been lightly re-polished and re-lacquered before my time with the scope, it certainly never was subjected to much wear and tear.  I wish I knew the history of this telescope, but I could not get much of an answer out of the seller. 

Hi Ben, 

Your finder appears to have similar size mounting brackets to those of the 1.3/4" supplied with my 1902, 5" Cooke but the objective end is different in style from anything in my 1900 and 1908 catalogues. Also according to the 1908 cat, the 4" Cookes were supplied with 1.1/2" finders whereas yours appears closer in size to mine? My guess is that your scope is more "modern" and possibly dates somewhere between 1909 and 1915. Maybe a later catalogue can provide more detail.

Regards, Col Shepherd


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#260 Peter Ceravolo

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Posted 04 September 2020 - 12:00 AM

Dating the PV refractor is proving to be more complicated than first thought. Although Photo Visual objective #69 was recorded as being sold to Dr. Hugh Walsham in 1899, some of the telescope components may be older.

 

I discovered Cooke telescope expert Martin Lunn in the UK:

https://thomascooket....wordpress.com/

 

Martin told me that the name plates on the telescope suggest they were made at different times. The plate on the drive system dates from between 1855-1862, the focuser on the other hand is from a later period and covers a larger period of time from 1869-1894. And although the objective was sold in 1899, it may have been made earlier.

 

Cooke drive cover.JPG

 

focuser.jpg


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#261 Peter Ceravolo

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Posted 15 September 2020 - 12:08 AM

I've been too busy lately to spend a lot of time on the Cooke. However I'm able to steal a bit time now and then to clean up the small round parts on the tiny lathe.

 

IMG_2663.JPG

 

Here the exposed lip of the OTA end cap the focuser bolts to was dulled by exposure to the elements. Spining it on the lathe made short work of cleaning it up.

 

IMG_2669.JPG

 

Here you can see the knurled knobs that hold the OTA rings onto the Dec saddle.

The laqcuer on the flat faces has flaked off and the brass corroded in spots. The green kitchen scouring pads were quite effective in buffing the surface clean without removing material.

 

IMG_2665.JPG


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#262 Peter Ceravolo

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Posted 15 September 2020 - 12:16 AM

I like the scouring pads, they remove most of the corrosion without making the part obnoxiously shiny.

Here are the turret eyepiece holders.

 

IMG_9512.JPG

 

The steel parts are another story. Here we have the screw that adjusts the mounts polar axis elevation. The screw pivots on the spherical section as the polar axis is adjusted.

It's one of the most corroded parts, second to the drives worm. There's not much to do here other than buff up the mangled metal and apply some grease to preserve whats left. I would not entertain using the lathe to shave off the war wounds.

 

IMG_2667.JPG


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