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Maksutov-Gregory Aspherized ZEN D=200mm F/15

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#1 astromazzo

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Posted 03 May 2024 - 11:10 PM

This Maksutov by Zen Romano (Costruzioni Ottiche - Made in Italy) has a fine focus, with no focus shift but a bit backlash. Excellent centric, no zonal defects, no irregularities of the image point in the central peak of Airy.
From the overall image in focus it is estimated a correction to no less than lambda / 8 (therefore very good in truth), but I would say very high for this type of instrument and artisan typology!
The spherical with intra and extra images is practically not evident and there are no distortions or defects, zonal, neither obvious, nor light. Neither is there criticality due to tensioning or forcing given by placing in the cell or by the meniscus and primary support systems. as evident zonal defects.
Once acclimatized (it will take at least 60-90 min. For 20 ° delta as is typical) it works well thanks to the right dimensions and spacing of diameters and thicknesses/masses of mechanical intubation elements.
Yield at high magnifications Romano Zen gives by default a focal length of 2800 mm, the lens is valid (attention .. with commercial instruments I rarely exceed 250-300x - unless it is AP or Taka or similar - so you get a maximum of one "vote "of 5 or 6 as an overall rating on a scale of 1 to 10, while here I would give it an 8). It is a true "planet killer" !

Primary Miror: 205 mm
Meniscus: 190
Focal lenght: 2691
Obstruction: 21%
dovetail: Losmandy type
Weight: 9.5 kg
Tube lenght: 500 mm

 

Incuded: aluminum caps ,  Losmandy bar, 2" eyepiece holder and it get a classic SC thread so you
attach a lot of accessories, top handle, finder 90° straightened.
Collimation performed on the optical bench, perfectly successful and stays for a long time.
Shipping:  I ship safely in very sturdy and floating packaging.

Price:  2050€  shipping comprensive

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#2 Redbetter

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Posted 04 May 2024 - 01:05 AM

Something is off with the specs in a couple of ways:

If the meniscus is 190mm, then it is a 190mm aperture at most.  (This appears to be the same OTA as in the following Astromart listing, link.) With the Maks the primary has to be larger than the meniscus diameter or it will be operating at a reduced aperture (because the meniscus rays diverge.).  The Synta 127mm Maks actually operate somewhere around 118-120mm for this reason, despite have a 127mm meniscus.

 

I am wondering how the focal length was determined?  2691 sounds short.  It will be dependent on the focal plane position for this moving primary focus system, so one would assume the focal length would be some nominal value associated with a diagonal (perhaps 2" since it is configured for 2"?)  The scope would be f/13.5 with the 2691mm focal length listed if 200mm aperture was assumed, or f/14.2 based on the 190mm meniscus. The Astromart listing says 2800 with 190mm meniscus for f/15 (nominal, since that would calculate out to 14.7).



#3 astromazzo

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Posted 04 May 2024 - 02:03 AM

Maksutov-Gregory:

Designed for the first time by John Gregory in 1957 and then industrially produced as Questar, the Maksutov-Gregory consists of a cassegrain in which the function of secondary mirror is performed by the central part of the appropriately aluminised Maksutov corrector meniscus.
For diameters greater than 150 mm one of the surfaces is slightly asphericized to correct the zonal sphericity characteristic of Maksutov correctors.

The residual chromatism introduced by the meniscus lens is very low, lower than that of an equivalent Schmidt plate; furthermore, given that the two radii of curvature are different, the reflection that returns inside the tube is not refocused, as for the Schmidt- cassegrain, in the vicinity of the fire, but disperses over a very large area. This results in greater contrast in planetary images.

Our company was the first to introduce these instruments in Italy.

 

MENISCO 190 SPECCHIO 205 FOCALE 2800

 

 http://lnx.costruzio...ttici&Itemid=30




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