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Post your Cat/Cass CO measurement

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63 replies to this topic

#1 TG

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Posted 04 July 2017 - 11:04 AM

Recently, a buyer wanted exact measurements for the C14 I was selling. He had measured dimensions from the ad pictures and arrived at 34.5%. Turned out my camera has barrel distortion! I think this comes up often enough for people that it might be useful to have a database of various scope vintages and their CO sizes. Here's mine

C14 Fastar, year 2000, 113mm (31.7%)
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#2 Guest_djhanson_*

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Posted 04 July 2017 - 02:32 PM

Here are two of mine that I measured (@ secondary baffle diameter):

 

CFF350 class cass, year 2015, 79mm (22.6%)
C14HD SCT, year 2014, 113mm (31.8%)

 

Looks like we agree well for the C14 measurements, which match Celestron's reported values (rounded).

 

cheers, DJ



#3 Asbytec

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Posted 04 July 2017 - 05:39 PM

Are we measuring the diameter of the useable secondary mirror or the baffle opening? The former has to do with back focus and field of view, the latter is often larger with added diffraction. What purpose are we measuring?  



#4 TG

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Posted 05 July 2017 - 07:44 AM

We're measuring whatever you can measure! :grin:

#5 JASmith

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Posted 05 July 2017 - 11:07 AM

From the bottom end of the SCT scale, I give you the Meade 2045:

 

  • Secondary mirror diameter (inside of cell rim): 1.3"
  • Actual obstruction (outside of baffle): 1.8"
  • Corrector aperture: 4"
  • Usable mirror diameter (due to bevel): 3.9"

 

Obstruction (baffle/usable mirror): 46%

 

- which is a not-at-all-negligible 21% of the area.


Edited by JASmith, 05 July 2017 - 11:11 AM.


#6 Eric63

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Posted 05 July 2017 - 12:00 PM

For my 2012 SW127 Mak I have the following from a flashlight test:

Actual aperture approx 118mm:
CO = 48mm

Therefore the CO is 40.7%.

Eric

Edited by Eric63, 05 July 2017 - 10:31 PM.

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#7 BWAZ

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Posted 05 July 2017 - 12:24 PM

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%


Edited by BWAZ, 05 July 2017 - 12:27 PM.

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#8 Kevin Barker

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Posted 05 July 2017 - 01:47 PM

Meade 8 LX90 37%

Intes Micro IM 603 33%, IM 703 33%, IM 815 24%

Questar 3.5 33%



#9 Special Ed

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Posted 05 July 2017 - 03:17 PM

The owner's manual for my CGE Pro 1400, which I purchased in 2010, gives the CO values as 4.5 " (114mm); 10% by area; 32% by diameter.



#10 roadi

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Posted 06 July 2017 - 12:10 AM

Mewlon 210: (former)   CO 70mm = 33% ( Secondary baffle diam. )  spidervanes not included (yet about 1%)


Edited by roadi, 06 July 2017 - 03:09 AM.


#11 jjack's

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Posted 06 July 2017 - 02:49 AM

Remember : obstruction is given by the diameter of the secondary baffle. not by the secondary Mirror.

It is difficult to measure the larger part of the conical baffle on a maksutov.

On my Vixen VC 200L : secondary baffle = 85mm. 42,5% spidervanes not included.


Edited by jjack's, 06 July 2017 - 02:49 AM.


#12 luxo II

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Posted 06 July 2017 - 05:20 AM

Santel MK91, D=228mm, F=3100mm, CO = 28%. This is a Rumak, f/13 with separate secondary mirror.

Skywatcher D=180mm, F= 2700mm, CO=30%. This uses the classic Gregory f/15 design but given the image quality (essentially perfect) for this aperture I suspect SW are aspherising one surface to suit.

Both by means of the torch test ie actual CO, not secondary diameter.

Someone with a TEC 8" or 10" f/20 mak ?

Edited by luxo II, 06 July 2017 - 07:50 AM.

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#13 Cotts

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Posted 07 July 2017 - 08:19 AM

Ceravolo HD 145 Mak Newt 145mm f/6 ---- 17%  No spider vanes either....

 

For comparison, my Lockwood/Teeter 12.5" f/6.5 has a 16% central obstruction. With spider vanes.....

 

My two 'refractors'.......smirk.gif

 

My Skywatcher 180mm is 30% as reported upthread....

 

Dave



#14 vahe

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Posted 07 July 2017 - 11:36 AM

Someone with a TEC 8" or 10" f/20 mak ?

I have both 200/20 and 250/20 TEC Maks, both have 22% co.

I also have TEC6, this one has 29.6% co.

 

Vahe


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#15 Phil Barker

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Posted 07 July 2017 - 02:59 PM

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%

I measured my faster compatible c11 as 35.7% on the inside of the baffle which was exactly 100mm!!!



#16 TG

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Posted 07 July 2017 - 05:34 PM

 

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%

I measured my faster compatible c11 as 35.7% on the inside of the baffle which was exactly 100mm!!!

 

Phil, did you mean "outside"? Inside dia will be a few mm smaller than the obstruction.



#17 TG

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Posted 07 July 2017 - 05:38 PM

Parks/JSO 4-inch "Jovian-4"

 

Vintage unknown, probably from the 80s. CO 42mm (42%).



#18 TG

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Posted 07 July 2017 - 06:24 PM

C14 HD 2014 113mm (31.7%). Looks like the C14 Fastar secondary size has been stable for over a decade.

#19 Phil Barker

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Posted 07 July 2017 - 08:39 PM

 

 

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%

I measured my faster compatible c11 as 35.7% on the inside of the baffle which was exactly 100mm!!!

 

Phil, did you mean "outside"? Inside dia will be a few mm smaller than the obstruction.

 

i mean the diameter of the secondary baffle.  



#20 GlennLeDrew

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Posted 08 July 2017 - 08:14 AM

Phil,

Or more specifically, you probably mean, "The inside end of the outside of the secondary baffle." ;)

 

Does this baffle have any taper, or is it cylindrical?

 

--------

 

Measuring the CO for a Mak is more reliably done with the "flashlight" test for aperture; actually, a green laser--expanded of beam if necessary--is better. The thick meniscus refracts the light path, and so the effective obstruction is a bit smaller than the physical diameter.


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#21 chuckscap

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Posted 08 July 2017 - 09:32 AM

 

Someone with a TEC 8" or 10" f/20 mak ?

I have both 200/20 and 250/20 TEC Maks, both have 22% co.

I also have TEC6, this one has 29.6% co.

 

Vahe

 

I have a TEC 7 f/15 Mak, just under 25%


Edited by chuckscap, 08 July 2017 - 09:33 AM.


#22 BWAZ

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Posted 08 July 2017 - 11:13 AM

 

 

 

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%

I measured my faster compatible c11 as 35.7% on the inside of the baffle which was exactly 100mm!!!

 

Phil, did you mean "outside"? Inside dia will be a few mm smaller than the obstruction.

 

i mean the diameter of the secondary baffle.  

 

Since I took my C11HD apart already, I measured the OD of the secondary baffle and it was 100.8mm, and the locking ring on the front surface of the primary mirror is 98.9mm in diamater, just to be more cautious. So the CO of C11HD (Fastar compatible) is indeed 36%. 


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#23 csauer52

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Posted 08 July 2017 - 02:05 PM

M14" f8 = 14.1%



#24 Phil Barker

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Posted 08 July 2017 - 04:46 PM

 

 

 

 

TG, it's an interesting topic as always wink.gif

 

I did the measurements on some of the SCTs I've owned, the numbers could be off by +/- 0.5%

 

C6: 37%

C8: 34%, depending on the vintage

C9: 36%

C11: Fastar compatible: 32%

C14 (non Fastar compatible, new style tube with rear vents and curved back plate), 31.7%

 

M8 f10 ACF: 37%

M10 f8 ACF: 49%

M12 f10 ACF: 34%

I measured my faster compatible c11 as 35.7% on the inside of the baffle which was exactly 100mm!!!

 

Phil, did you mean "outside"? Inside dia will be a few mm smaller than the obstruction.

 

i mean the diameter of the secondary baffle.  

 

Since I took my C11HD apart already, I measured the OD of the secondary baffle and it was 100.8mm, and the locking ring on the front surface of the primary mirror is 98.9mm in diamater, just to be more cautious. So the CO of C11HD (Fastar compatible) is indeed 36%. 

 

Yes its more % wise than a c8.  Its the same as the 9.25 inch or is that also above what is claimed???

 

I have a sneaky suspicion my intes Micro 10 inch Mak is similar although in the case of a mak the light converges out from the meniscus.

 

Haven't measured it and it would not be easy to do so i have no intention of removing the meniscus.  

 

I sold my 11 so thanks for backing me up on this.  It was a good scope very happy with it the intes micro mak is  better so i sold the c11 but it was no lemon.



#25 Cotts

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Posted 08 July 2017 - 05:16 PM

M14" f8 = 14.1%

By area, yes.  By diameter, which is what we are all using for comparison here and what is generally quoted around the hobby the 14" Meade f/8 ACF is probably in the 35%-45% range.    

 

Dave


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