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Does the ES AR152 really have an aperture of 158mm?

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#1 jgroub

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Posted 17 July 2019 - 12:16 AM

So I just learned something interesting - that the Explore Scientific AR152 actually should be called the AR158.  The specs there list it as having a 158mm aperture. 

 

Is that really true?  If so, why would they call it the AR152 and not the AR158?  I mean, if ya got it, flaunt it, baby! 



#2 beggarly

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Posted 17 July 2019 - 12:53 AM

Focal Length  988mm
Focal Ratio  f/6.5

 

988/6.5=152

 

Tube? diameter  158mm


Edited by beggarly, 17 July 2019 - 12:56 AM.

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#3 Jon Isaacs

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Posted 17 July 2019 - 06:03 AM

https://explorescien...ublet-refractor

 

988mm/158mm = 6.25

 

I think Beggarly got it right.  158mm is the tube diameter, not the aperture.

 

Jon



#4 jgroub

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Posted 19 July 2019 - 03:00 PM

Yeah, but . . . 

 

I don't think you guys are right.  

 

If you look at that specs tab, it specifically says:

 

Tube length 

                           41"; 1041mm

w/dew shield 

 

Diameter            158mm

 

That 158mm is most definitely not the diameter of the dew shield.  We have the AR127 (the 5") out on the floor of the shop I work at here in Denver.  The dew shield measures 7 inches across = 178mm.  My AR152 is put away, or else I'd measure the dew shield on it, but it's around 8 inches.  

 

If you look at the specs tab for the AR127 - the 5" scope itself - it says at that same diameter part of the tab 130mm.  I don't think the tube itself could possible be just 3mm wider than the actual objective.  

 

 

In both cases, that's gotta be the diameter of the objective, no?  



#5 John Fitzgerald

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Posted 19 July 2019 - 04:48 PM

From the ES website:

 

Item Number DAR152065–01
Focal Length 988 mm
Focal Ratio f/6.5
Limiting Magnitude 13.4
Resolution .77 arcsec
Tube Length w/ Dew Shield 41"; 1041mm
Diameter 152 mm
Weight 2 3lb; 10.7 kg
Dovetail 45 mm Wide V-Block, Similar to Vixen Dovetail Style

 

It's a 152 mm achromat.


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#6 Sketcher

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Posted 19 July 2019 - 04:53 PM

I have a habit of checking clear apertures whenever I get a new telescope.  Going on (a three year old) memory, the clear aperture of my AR152 when it arrived was close enough to 152mm for me to accept 152mm as its clear aperture.  If it had been any other value, to the closest millimeter, I think I would have remembered.  For example, my 50mm Galileoscope has a clear aperture of 47mm.

 

The diameter of the OTA, as measured today, came out to about 156.3mm(+/-  0.5mm); but that number is based on the length of a strip of paper wrapped tightly around the tube (at one location only) divided by Pi.  So there's room for some additional error.  The paper strip had to be longer than the circumference of the OTA in order to fit around the OTA.

 

The dew shield has a fairly tight fit, so I didn't feel like removing it again.  I've removed it on at least three past occasions; probably to measure the clear aperture, to re-seat a rubber seal and clean the residue that the out-of-place seal had left on the objective, and to tweak the collimation.

 

Best guess:  ES's "158mm" number is for the OTA diameter.



#7 jgroub

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Posted 19 July 2019 - 05:07 PM

From the ES website:

 

Item Number DAR152065–01
Focal Length 988 mm
Focal Ratio f/6.5
Limiting Magnitude 13.4
Resolution .77 arcsec
Tube Length w/ Dew Shield 41"; 1041mm
Diameter 152 mm
Weight 2 3lb; 10.7 kg
Dovetail 45 mm Wide V-Block, Similar to Vixen Dovetail Style

 

It's a 152 mm achromat.

Yes, I sent the question directly into ES and they changed the figure today.  They agreed, they could not see anything on the scope that was 158mm, so they changed it to 152mm.  

 

Thanks, all!  




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