Maksutov-Cassegrain Vs Schmidt-Cassegrain

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observer
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文章 observer » 週六 23 5月, 2009 10:08

MN 應該比 Mak-Cass/SCT 好, 但 Mak-Cass 是否比 SCT 好就似乎不是吧?

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willis
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文章 willis » 週六 23 5月, 2009 11:02

TONGKW 寫:6英吋 (150 mm) 以上的馬卡重過施卡好多,主要由於前面的彎月型透鏡好厚,最好放在天文台內用。
6英吋 以下馬卡與施卡長度及重量差不多,馬卡重過施卡些小,馬卡的焦比由 f/12至 f/20,施卡一般是 f/10,馬卡現時最細口徑大約是 65 mm,90 mm/100mm馬卡只售港幣壹仟多元,又輕便又矩身,最適合初學者。
但施卡現時最細口徑只係 127 mm (C5),沒有再細。
一般來說,馬卡的成像較施卡的銳利,尤其是高級的馬卡,可以比美高級ED折射鏡,馬牛 (Maksutov Newtonian )的成像就更加銳利同高級ED折射無差別。不過馬牛鏡筒好長,不易攜帶。
How come u have all these scopes! Anyway, thanks for sharing! I was told MN is very good! It is comparable with ED refractor. ABout the weight & length of MN. I think if we are comparing MN & refractor, for the same aperature, say 8". A MN is much much shorter & lighter than a 8" ED refractor.
Willis

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bingsze
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文章 bingsze » 週六 23 5月, 2009 21:59

I wonder anyone in HK have a big MN telescope, if it is 8" and the outcome is look like an ED refractor, it must be very attractive indeed.
But why not so many people talk about this?????

can anyone tell me about this!

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alget
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文章 alget » 週六 23 5月, 2009 22:18

重, 煩, 唔俾上巴士, anything else?

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Subaru
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文章 Subaru » 週六 23 5月, 2009 22:58

bingsze 寫:I wonder anyone in HK have a big MN telescope, if it is 8" and the outcome is look like an ED refractor, it must be very attractive indeed.
But why not so many people talk about this?????

can anyone tell me about this!
1. 8" Maksutov is very heavy
2. Collimating the MN is a bit tricky
3. Throughput of Maksutov is less efficient than Newtonian, APO & SCT, and the tone is a bit cool
4. Much higher cost compare to a Newtonian

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A/45
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文章 A/45 » 週六 23 5月, 2009 23:01

I once owned a MN56 and love the views, but it is considerably heavier than newts of the same class due to the front corrector, as well as it is Russian made means it's built like a tank and thus very heavy.
Except the collimation of the secondary is difficult to keep and the corrector had minor effects on image brightness, it's one of the sharpest scope I've seen.

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willis
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文章 willis » 週六 23 5月, 2009 23:11

bingsze 寫:I wonder anyone in HK have a big MN telescope, if it is 8" and the outcome is look like an ED refractor, it must be very attractive indeed.
But why not so many people talk about this?????

can anyone tell me about this!
It seems interesting! I would prefer to have a look at those MN scopes. Apart from the weight & size of MN, I found not many manufacturers produce MN. These two are what I found after a quick search.

Maxvision 152mm MN (6.1", RMB$7270)
http://www.hkastroequipment.com/fj01-35.html

Skywatcher 190mm MN (7.6" HK$9880)
http://www.astro.hk/84.html

These two MN have smaller aperature compared with C8, but more expensive than C8. [壓力] But I think their prices reflect part of the story. [鬼點子] If MN is just heavier & bulky, they cannot surive. I guess NM should have something good. May be this is what Tongkw said, as sharp as ED refractor... So any brother here got a MN, pls report or comment the performance of MN. Thanks![Good Job]

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willis
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文章 willis » 週六 23 5月, 2009 23:14

A/45 寫:I once owned a MN56 and love the views, but it is considerably heavier than newts of the same class due to the front corrector, as well as it is Russian made means it's built like a tank and thus very heavy.
Except the collimation of the secondary is difficult to keep and the corrector had minor effects on image brightness, it's one of the sharpest scope I've seen.
Hi A/45!
What is the aperature of ur MN? 56mm or 2.24" or..? As u mentioned it is sharpest scope u have seen. So how it compared with same aperature ED refractors?
Willis

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A/45
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文章 A/45 » 週六 23 5月, 2009 23:42

I don't think the 5" MN could exactly match a 5" APO in performance, probably comparable to a 4" APO.

Some detailed shots of my sold MN56 are at http://www.hkastroforum.net/viewtopic.php?t=10541
You'll see the secondary is held in place on the corrector lens by a retainer ring which I think will rotate easily and thus loose collimation.
Also, the internal baffles are remarkable which contributes to the high contrast.

The definitive Manufacturer of MN is Intes or Intes Micro, Russian made. You may search under Cloudy Nights with lots of reviews.

Another issue with the MNs is the limited back focus. The secondary is comparably small in order to achieve high contrast at the expense of back focus length. The MN56 (5 inch f/6) cannot reach focus with a DSLR with its stock focuser which already has a very low profile. Later they came up with a MN55 series at f/5 and allows a longer back focus for DSLR but I think this is a compromise which looses contrast.

It would be an excellent planetary scope but some people do take very good deep sky images with it.http://www.billionsandbillions.com/CCDGallery.html

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willis
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文章 willis » 週六 23 5月, 2009 23:56

A/45 寫:I don't think the 5" MN could exactly match a 5" APO in performance, probably comparable to a 4" APO.

Some detailed shots of my sold MN56 are at http://www.hkastroforum.net/viewtopic.php?t=10541
You'll see the secondary is held in place on the corrector lens by a retainer ring which I think will rotate easily and thus loose collimation.
Also, the internal baffles are remarkable which contributes to the high contrast.

The definitive Manufacturer of MN is Intes or Intes Micro, Russian made. You may search under Cloudy Nights with lots of reviews.

Another issue with the MNs is the limited back focus. The secondary is comparably small in order to achieve high contrast at the expense of back focus length. The MN56 (5 inch f/6) cannot reach focus with a DSLR with its stock focuser which already has a very low profile. Later they came up with a MN55 series at f/5 and allows a longer back focus for DSLR but I think this is a compromise which looses contrast.

It would be an excellent planetary scope but some people do take very good deep sky images with it.http://www.billionsandbillions.com/CCDGallery.html
A 5" MN can be compared with 4" APO! It sounds pretty good already. I just wonder how the two MNs I mentioned compared with a 5" or even 6" APO/ED or C8 or C9... It would be nice if I can have a try in PTC... [鬼點子]

PS* We started the discussion in MC & SC. But end up with MN. [好心情]

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Wah!!
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文章 Wah!! » 週日 24 5月, 2009 00:47

TONGKW 寫:....但施卡現時最細口徑只係 127 mm (C5),沒有再細。....
一手市場, 最細的應該係5".
二手市場, 最細的應該係4".
記得 Meade 同某間日本牌子, 都出過 4" SCT.

Chanlunlun
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文章 Chanlunlun » 週日 24 5月, 2009 09:13

bingsze 寫:I wonder anyone in HK have a big MN telescope, if it is 8" and the outcome is look like an ED refractor, it must be very attractive indeed.
But why not so many people talk about this?????

can anyone tell me about this!
Dear Mr. BingSze,

It is just because a Maksutov Newtonian cannot match the performance of a ED reflectror.

If it does we won't have so many ED refractors in Hong Kong. We have probably more AstroPhysics refractors here rather than Maksotov Newtonians.

Best regards
Chan Yuk Lun

CHYeung
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文章 CHYeung » 週日 24 5月, 2009 11:41

Dear Mr. Chan,

I agree that the MN cannot match the overall performance of a ED refractor. The MNs do not offer unvignetted field as wide as the Ed refractor because of the limited size of the secondary. However, a carefully made MN or MC with small secondary will match the on-axis performance of a ED refractor of similar size.

I also agree that there are more AP refractors than Maksotov Newtonians in Hong Kong but one of the the reason is the availability and price. A well made MN is not cheap though much cheaper than a ED refractor of similar aperture but MNs are much more expensive than a SCT or Newtonian of similar aperture. If you are going for deep-sky-object imaging, the MN's field of view is curved and the unvignetted field is much smaller than that of a ED refractor.

Best regards,
Yeung Chi-hung

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bingsze
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文章 bingsze » 週一 25 5月, 2009 10:26

weight !

this is the main concern for so many people in the forum, but I think some people who have thier own transport doesnt care to much about this.

but I do concern is the mount, if u need to buy a more expensive mount, the price performance ratio advantage will very soon disappeared.

In short, you can use the extra money to buy a lovely refractor of smaller aperture. am I correct?

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