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Meade 7" Maksutov

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#51 dweller25

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Posted 01 January 2018 - 12:00 PM

Hi David,

 

nice - thanks for sharing! is it a 715 or 703? 

 

Thought about one of these too as actually there´s one of each offered on the "local") used market - but prices are "a little bit" higher for these - the 703 is at 1.500 EUR (old version without fans!) and the 715 at 1.990,- when this Meade came up for sale it seems to be a bargain and I´m very happy the optics is a good one smile.gif

 

cs

Chris

Hello Chris,

It's a 715 - I really like it and like yours it has active cooling which makes a huge difference to thermal management.

Mine is a little lighter than your at 7kgs including finder - I guess your tube rings weigh around 2kgs ??

Best regards

David


Edited by dweller25, 01 January 2018 - 12:02 PM.


#52 donadani

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Posted 01 January 2018 - 02:24 PM

Hi David,

 

rings together with that massiv rail is point 1,8kg - so scope only with finder 7,2kg.

 

cs

Chris



#53 Asbytec

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Posted 01 January 2018 - 07:52 PM

"2. the scope really needs its time to cool properly to show it´s great optics (took it out about 1,5h before watching without using the fans)"

 

I use a frozen medical gel pack laid along the top of the OTA and overlapping the primary mirror end (the culprit) for about 30 minutes prior to set up or when the gel pack is spent. The OTA is cool to the touch as if it had been sitting out all night and star images are 'perfect' right out the door.

 

It works perfectly for modest temperature differentials, and my guess is a gel pack (of reasonable size) will give you scope a good head start in cooler weather. Then maybe a fan can take it the rest of the way toward ambient in less time.  The gel pack does an excellent job of dampening internal heat and it's cooling properties are more efficient than air.

 

They are cheap, try one and see how it works for you to reduce full cool down time. I have not seen a heat plume in years, my Mak is always ready to go right out the door (in our climate.) 


Edited by Asbytec, 01 January 2018 - 07:54 PM.

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#54 Peter Besenbruch

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Posted 02 January 2018 - 01:21 AM

Every surface in a Gregory mak is spherical. This means that they are particularly easy to machine-fabricate well. I would guess this has a lot to do with why they're so inexpensive (in small apertures) and good these days.

Some of the really fancy maks diverge from this and have some non-spherical surfaces (the AP and the Questar, I hear) and thus have better correction. But they have enough money put into them to hand-figure those surfaces well.

Then the 7" Maks are not a Gregory design. Actually, they are, but to get as short as f15, you need one non-spherical surface. Meades use elliptical primaries. I don't know what Skywatcher does, but I suspect it's something similar. Gregory allowed for that, because the f23 required for all spherical surfaces is a bit long.


Edited by Peter Besenbruch, 02 January 2018 - 01:25 AM.


#55 freestar8n

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Posted 02 January 2018 - 03:04 AM

I prefer the term, "spot Maksutov" because Gregory did not invent that idea.  It dates back to Maksutov's original work - but it didn't really gather interest until Gregory promoted it with two specific versions: 6" f/15 and 23 in 1957.

 

"Maksutov" covers all designs that have that steep meniscus in front to magically correct for spherical aberration without adding much color - and that includes Newtonians, Cassegrains with spot on the secondary, Cassegrain with separate secondary - etc.  And "Maksutov" doesn't need to imply spherical surfaces - but he did promote an advantage of the design as having spherical surfaces - but in reality that didn't make them easy to make - or make well.  That's why they tend to cost more - especially the good ones.  They are in a class of design that relies on final checks of the assembled system to allow final corrections to make sure it works well - and both Maksutov and Gregory describe the importance of final figuring with an autocollimator.

 

The need for asphere depends on the operating f/ratio, the speed of the primary (and length of the tube), the thickness of the meniscus, and the aperture size.  

 

If you see a current spot Maksutov offering that is 6" or larger and below f/15 and in a relatively compact tube - and it isn't optically horrible - then it probably involves an asphere as part of the design.  The smaller ones may also involve an asphere, but it is easier to be diffraction limited when the aperture is smaller.  They may also not be operating at either the stated aperture or f/ratio.

 

Frank


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#56 Asbytec

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Posted 02 January 2018 - 08:14 AM

They may also not be operating at either the stated aperture or f/ratio.

 

That's a fact. I did rather extensive star drift testing and measuring the size of the lunar image on the focal plane trying to determine the focal ratio. I got values between f/15 using the star drift method with only approximate data on field stop and f/13 using data on the moon's diameter.

 

I went with f/13 as it seemed the most reliable measure with the least uncertainty and at f/15 which meant I was observing Jove at 281x and Mars at well over 400x. That didn't feel right. They are not f/12 at the normal diagonal placement and at focus of normal eyepieces and a 2x Barlow (both before and after the diagonal.) Others have done calculations and attained similar results.



#57 divers

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Posted 03 January 2018 - 04:40 PM

Here is a picture of mine...love it with my binoviewers. With UHTC  and supercharged it is a real nice scope.

Attached Thumbnails

  • BB761715-4E24-49BD-A3DC-EEB22C952F63.JPG

Edited by divers, 03 January 2018 - 04:43 PM.

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#58 jgraham

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Posted 06 January 2018 - 09:50 PM

+1 on the binoviewers. I use mine with my Mak 7 for lunar and planetary viewing. Wonderful!


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#59 contrailmaker

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Posted 07 January 2018 - 09:39 AM

+2 on the binoviewers. For me, there is no way to go back to mono viewing for solar system objects.

 

CM



#60 divers

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Posted 08 January 2018 - 04:11 PM

Rather than starting a new thread on this Mak - thought I would just ask this question here.  I had a crazy idea to remove the finder scope on my scope and replace with something in the 60 - 70 mm wide field refractor.  Anyone done this?  Can the fork mount support the extra weight?

 

Thanks!



#61 Starman27

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Posted 08 January 2018 - 06:39 PM

I believe that the fork mount on my &' LX200 is the same one used for the Meade 8' SCT. I have a top and bottom Losmandy bar for my Mak and it worked fine. I haven't mounted a scope. The telescope is now resting as the pier is being used by a TAK FS128.


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