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Upgrades for Mak 127 (diagonal and eyepiece)


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I recently bought a Skywatcher 127 (Maksutov, FL=1500 mm, AP=127 mm). I got it since 1) it's small, and 2) watching planets sounds like fun. :) First I thought that I would try prime focus photography with it, but after looking at the moon and Jupiter using the kit eyepieces, I realised how cool direct observation is. :)

I'm new to astronomy, but not completely new to optics (I worked for a company building lasers some 10 years ago). I do like the physics part of this hobby (i.e. the math, and the actual hardware, so to speak :) ).

I have signed up to the local astronomy club, and have been to my first meeting there, and got a peek at Jupiter, Venus and Mars through their Celestron 11" Cassegrain. That was cool, although I was surprised at the amount of scatter their 'scope had (the 'scope's corrector lens was really dirty, but maybe the atmosphere was the culprit; I don't know).

I hope to go to a local "star party" when/if such an event is held. Otherwise, I might have a mini-star-party with some friends. Either way, I'd like to make the most out of it, so I've been thinking of upgrades for the €19 Skywatcher "SUPER RK" (Kellner) eyepieces and the €25 Teleskop Service diagonal mirror that came with the telescope. I did not get any manual describing this equipment, but found what has to be the same things here: mirror, SUPER RK 10 mm, SUPER RK 25 mm.

I read Al Nagler's Choosing an Eyepiece - Step by Step article (available as PDF from televue.com -> Eyepieces -> Advice -> Choosing Eyepieces (Advanced)). The advice to get one eyepiece to maximize (true) field of view felt sound, so I started there.

The maximum TFOV allowed by any telescope is (field stop)/(focal length) (source). (This is in radians; multiply by 180/π for degrees.) For 1.25" eyepieces, the maximal field stop is about 27.1 mm, which gives 27.1/1500*180/π ≈ 1.04° for the Skywatcher 127.

The apparent field of view (AFOV) is simply TFOV*magnification. That, and a lot of forum reading to find good value eyepieces, gave me the following candidates (here, ER is eye relief):

* €49: Vixen NPL 30 mm (AFOV=50°, ER=24 mm): Mag=50, TFOV=1.00°

* €89: Celestron X-Cel LX 25 mm (AFOV=60°, ER=16 mm): Mag=60, TFOV=1.00°

* €159: Explore Scientific 24 mm (AFOV=68°, ER=18.4 mm): Mag=63, TFOV=1.09°

The Vixen NPL 30 mm seems to be of high quality, and the price is nice, but since this is supposed to be an "as wide a field as possible" eyepice, I think I will be disappointed by the small AFOV.

The Celestron's build quality seems a bit questionable (apparently the eye cups gets hard and uncomfortable in cold weather, and sometimes comes loose?). I also seem to remember that optically, even though they are good value for the money, they had some things left to wish for? (But annoyingly, I cannot find where I read this right now. I believe my thinking was that €89 is too much to pay for something that might "get in the way".)

The ES68 24 mm seems to be a "keeper", I really haven't read anything bad about it. Also, if I understand correctly, the larger magnification should give better contrast thanks to a darker image of the sky. It's expensive, but I do have the money for this thing, and after all of the research I've done, I think I've earnt it. :) The question is, is it a sane eyepice to get? Does it matter that its field stop is a bit bigger than I will be able to use?

And much more importantly: are there any nice objects to see with a FOV of 1°, using an aperture of 127 mm, that will make this thing worth its price? If so, please give suggestions! :)

I then realised that, if I get a high quality, expensive eyepiece weighing in at 329 g, I will need something more substantial than the mirror that came with the telescope to hold it. A bit of googling quickly found William Paolini's Mirror-Prism-Dielectric Diagonal Comparison article, where he strongly favours prisms over mirrors, especially for planetary observation. And a lot of forum posts discussing the results (mostly at Cloudy nights). The forum consensus(es?) seem(s) to be that the Baader Zeiss T2 prism is pretty much the best there is (both optically and build quality-wise), but this thing costs more than I'm ready to spend. However, I'm prepared to spend enough to get the Baader T2 non-Zeiss prism, which apparently has got the same build quality. Unfortunately I haven't been able to find anyone directly comparing the views between the two, but people with the non-Zeiss version seems to be happy with it.

When it comes to higher-magnification eyepieces, I don't feel confident enough to go out and buy anything yet. I'm not sure what magnifications I will want, and I'm also not sure about the types I want (e.g., FOV may not be important for planetary observation, but eye relief may be). Maybe I will be able to try other people's eyepieces at some get-together. I might also get an opportunity to appreciate the difference in quality between the SUPER 10 and the ES68 24. (And if I don't see a difference, then I probably shouldn't buy any more such expensive equipment! :))

What do you think, should I go ahead with the quite substantial purchase of the ES68 and the Baader T2, or am I missing something? (BTW, I'm also thinking of throwing in some AstroSolar ND5.0 film for solar observation. Looking at the sun seems cool! ;))

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First off, you might be better off asking someone else who's got a bit more experience (both of this and of other 'scopes).

With that said, to me the build quality feels very nice and sturdy. The focusing knob could be a bit larger, and its feel is not completely even, but there is almost no focus shift/backlash when changing directions, so it's easy to go back and forth to find the best focus. The people at my local star club seemed to regard it as a nice telescope.

All in all, so far I like it, but then I have no previous experience, and I've only used it a couple of times. I also don't know how it will behave in cold and/or moist weather.

The accessories that came with my model (diagonal and eyepieces) have got a decidedly plastic/cheap feel about them though. Also, I only got the optical tube assembly (no mount), so I cannot comment on that.

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I also calculated the exit pupil (EP) with the different eyepieces above:

* €49: Vixen NPL 30 mm (AFOV=50°, ER=24 mm): Mag=50, TFOV=1.00°, EP=2.54 mm
* €89: Celestron X-Cel LX 25 mm (AFOV=60°, ER=16 mm): Mag=60, TFOV=1.00°, EP=2.12 mm
* €159: Explore Scientific 24 mm (AFOV=68°, ER=18.4 mm): Mag=63, TFOV=1.09°, EP=2.03 mm

(Is there any way to edit one's posts? I cannot find an Edit button...)

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I have been trying to answer my own question - are there any nice objects to see with a FOV of 1°, using an aperture of 127 mm, that will make the ES68 24 mm worth its price?

The excellent What can i expect to see article by forum member Qualia has been really helpful, as has this this field of view calculator.

First, Qualia's article made me realize that I pretty much will be limited to the moon and the sun with the 24 mm eyepice. If I get to some really dark place I might also be able to see/detect some of the brighter DSOs in the form of "grey fuzzies".

So maybe I would be better off using the supplied 25 mm eyepiece for full views of the moon and the sun, and instead start off with a better shorter focal length eyepiece, to replace (the apparently quite bad) "SUPER 10" that came with the scope? This I reckon would let me see greater details of sunspots, better surface detail on the moon, as well as give me useful views of Jupiter and Saturn.

But, what focal length to choose? In the ES82 series, there's one 11 mm and one 8.8 mm:

* €149: Explore Scientific 11 mm (AFOV=82°, ER=15.6 mm): Mag=136, TFOV=0.60°, EP=0.93

* €149: Explore Scientific 8.8 mm (AFOV=82°, ER=15.6 mm): Mag=170, TFOV=0.48°, EP=0.75

To get an idea of the apparent size of the planets as seen using these different eyepieces, I used the FOV calculator above. However, the calculator compresses the field of view of the eyepieces into an on-screen disc that is very much smaller than the actual apparent field of view of the eyepieces. This might be useful for figuring out how much of a larger DSO that will fit into an eyepiece, but it's not useful to get an idea of how a planet would look. Intead, I calculated the actual field of view of the calculator's disc:

* The width of the disc on my monitor: 117 mm.

* The distance from the screen to my eyes: about 700 mm.

The FOV of the disc is then (somewhat simplified) arctan(117/700), or approximately 10°. Entering that number in the "Apparent FOV" box, the planets should appear about the same in size as they would in the eyepiece.

... which didn't really help me a lot. The difference between 11 mm and 8.8 mm, on-screen, is not huge for Jupiter, but I'm starting to understand the craving for many different focal length eyepieces. Maybe I should go for something like both 14 mm and 8.8 mm? But boy, this is getting expensive! And I can see myself quickly realising that one of them gives better views, generally, and not use the other much. At the same time, I don't want to end up buying a lot of lower quality eyepieces just to find out which magnification is my favourite - especially since the favourite magnification could change with higher quality eyepieces!

One specific question then: If you had to choose one eyepiece for viewing the planets, as well as details of the moon and the sun, using an f=1500mm, D=f/11.8 telescope, with a price cap of €160, which one would you choose, and why?

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I guess I will continue my monologue... :)

These two reviewers both seem to use 150x-260x when observing the planets with the 127 mm Maksutov. This guy chose the 8.8 mm, 14 mm, and 28 mm Explore Scientific eyepieces for his 127 mm Maksutov, and seems most happy with planetary views with the 8.8 mm (170x). This last article is a really nice report on the combination of Explore Scientific eyepieces and the 127 mm Maksutov, BTW.

So I think I'll go with the 8.8 mm. Maybe sleep on it until tomorrow though.

Then again, this site very convincingly calculates optimal exit pupil (for maximum resolution) to 1 mm, which corresponds very well to the 11 mm ES82 (EP=0.93 mm, 7 % higher magnification than max resolvable). But they also say it's easier to see all of the detail if one increase the magnification - up to 50 % higher - "before the blurring (not to mention the image darkening) becomes objectionable". This would correspond to an exit pupil of 0.67 mm, which still is below that of the 8.8 mm ES82 (EP=0.75 mm, 34 % higher magnification than max resolvable).

*sigh* :undecided::icon_rolleyes::icon_question::help:

Will I prefer a sharper-looking, brighter image, or one where it's easier to see the maximum amount of detail? :dontknow:

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As regards the diagonal, I see this is for a 1.25" focuser. So being limited to 1.25", I'd suggest one of two dielectric 99% reflectivity diagonal in 1.25" format: William Optics, or GSO Dielectric.

Here's the W.O. 1.25" Dielectric:

http://www.firstlightoptics.com/diagonals/william-optics-125-dura-bright-dielectric-diagonal.html

And the GSO - which are called Revelation on your side of the pond at present:

http://www.scopesnskies.com/prod/Revelation/astronomy%20-accessories/mirror-star-diagonal/125dielectric.html

A person I know over in Israel wrote to WO and got a personal response from William. They exchanged several emails in short order, and William gave him a discount and sent along several other things my friend needed for free! Nice guy! And he says the optics are exquisite!

And I have the GSO, and the same holds true for the optical quality. You'd be making the correct choice if you tossed a coin in the air and called it!

As a very slow F/11.81, I doubt it's a good choice for getting really wide-field views. I'd be looking to push the magnification up on objects like planets instead. But that's me. It looks like a really nice scope! Maksutov's have been calling to me as of late. I'll likely crack and get one soon enough! :eek::p

Clear & Dark, Sharp Skies,

Dave

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How do you rate the scope? I am considering the celestron nexstar 127SLT

If you're after wide field views, it's not the scope to choose.  For planetary/lunar/solar and targets such as bright globular clusters and planetary nebulae it's a nice little scope for the money.  You can probably get a larger dob for a similar price and that's something to consider, but the other side of the coin is that I can take my 127 Mak on holiday with us and it doesn't need much space in the car.  Mine has been with us to France for the last three or four years.

It's also great for lunar and solar imaging with a DSLR as well as planetary imaging with a suitable high frame rate camera, though being able to bodge a motorised focuser for it helps enormously.  If you're a real masochist you can put it on a decent EQ mount and have a go and longer exposures for those globs and planetary nebulae.

James

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Bitnik,

Keep on the excellent research work, that exit pupil link is a very good guide, having a general understanding is fundation to make well-judged decisions.

I don't think you need to hurry in buying new eyepieces, there're excellent Messier objects to start with the stock eyepieces and diagonal. M35/36/37/38 in early evening, M3/53/5/13/92/57 in late evening.

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you sound like a Professor of Optics....

I changed my diagonal to one which shows th object exactly as you see it....that is, the left is left and right is right. I did not like thinking of the Moon as as being sideways inverted.  I also bought the Hyperion click zoom Mark 111 (8 to 24 mm ) and tend to use the lower  magnifications as they produce the best clarity. I find it is really easy not to have to change eyepieces.

Celestron build is very good and I don't see many complaints on this forum.

In Sweden you may well be blessed with dark skies and  fancy optics are no subsitute fot that...

PS

I do think a good finderscope is really helpful.

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Dave, thanks for the diagonal suggestions! I'm sure most diagonals in this price segment are very nice, but did you read William (Bill) Paolini's article Mirror vs. Dielectric vs Prism Diagonal Comparison? He quite strongly favours prisms for planetary observation, and most comments (particularly at cloudynights) seem to agree.

More importantly, I think the T2 threads of the Baader prism will be much more stable on my telescope than a normal 1.25" connection:

The Maksutov actually does not have an external focuser - focusing is done by moving the primary mirror (and thus adjusting the telescope's focal length until focus is reached). There's a metal adaptor on the scope: a nut that mates with the telescope's ~45 mm thread and holds a tube with an male T2/female 37 mm-ish thread combo on the back end. The tube's inside diameter is 32 mm and it's got two thumb screws to hold 1,25" accessories - but no compression rings. It should be possible to securely screw the Baader T2 prism onto the tube, and adjust the rotation during use by loosening the nut that holds the adaptor tube.

I'm still trying to figure this out, but I don't think the achievable FOV is related to focal ratio per se, but rather to focal length? E.g., a f=1600 mm/D=250 mm scope has a focal ratio of 6.4, but would still have a smaller maximal FOV of 0.97° than the f=1500 mm/D=127 mm Maksutov's 1.04° (assuming they both used 1.25" eyepieces with a maximum field stop of 27.1 mm). TFOV=(field stop)/(focal length)*180/pi degrees.

But yes, it's a long focal length scope, so not suited to wide fields. Unfortunately, it's also got a relatively small aperture, so it's not really suited for high magnification either. I think, if I were to get seriously hooked on this hobby, and space/portability was not an issue, I'd get something like the above D=250 mm scope. It would be much better suited to higher (but still usable) magnifications, with regards both to image brightness and to exit pupil size (the later affecting the eye's ability to resolve detail).

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impactcrater, yes, maybe I went a little bit overboard on this. :) But I think it feels great to understand things, and math is a very good tool for that!

I've read a lot of good about the Hyperion 8-24 mm Mark III Zoom. It would be nice to try one sometime!

In summertime, the nights in Sweden never get real dark - we're too far north for that. On the other hand, most of the day feels very dark during the winter. :rolleyes: You do need to get an hour's drive outside the largest cities though, to escape most of the sky glow.

I got a red-dot sight with the scope, and thought I will give that a chance before looking at finderscopes. I did really like the finderscope on the star club's telescope though.

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Bitnick,

I observed these Messiers with 130P when I hade it for two years ago, in addition to some 40 more Messiers, in my backyard. Nowadays I'm using C8 mostly for hunting fainter NGC objects,I use these bright Messiers for checking alignment precision as I did last night.

Print out a map of Messiers as in Wiki is easy way to quickly locate what are avaible DSO.

For these bright open clusters and globulae, you can use the 25mm for locating them, then 10mm for closer look, stars can take higher mags.

A RACI(Right Angle Corrected Image) finder should be a good alternative if you have difficulty finding object with the red dot finder.

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YKSE, thanks for the Wiki link and info! Those Messiers will go on my list for sure!

Anyway, I've decided to stay near the comfort zone of the telescope and go with the 11 mm eyepiece (136x, 0.93 mm exit pupil). Why? Because I think I will prefer a sharper, brighter image over a somewhat more magnified one.

As I understand it, between 3 and 2 mm exit pupil, the eye has the best chance of resolving the most detail optically (disregarding the brain). This is limited by eye lens aberrations (>3 mm) and eye lens diffraction (<2 mm). At 1 mm we reach the maximum, diffraction-limited resolving power of the telescope. But even below this, out fantastic image-processing brain can manage to squeeze out a bit more detail, down to about 0.67 mm exit pupil - after that, the image just gets too dim and blurry even for the brain to do its work. (All this is my interpretation of The Exit Pupil and Scope Performance article.)

I did some daylight-testing of the scope today, and found I couldn't really get the SUPER 10 eyepiece (0.85 mm exit pupil) into perfect focus; it was always a bit fuzzy. It was also quite dim. Now, this could just depend on lacking quality, but at least it showed me that I really don't like unsharp images.

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Binick,

Your interpretataion of exit pupil is much the same as mine, also my experience with f10 C8. Baader 31mm is my starting eyepiece for DSO hunting, for fainter and extended DSO, 40mm Aero takes the focuser, while for brighter DSO, I'll go down under 2mm exit pupil with zoom. Planetary too, even under 1mm. eyepieces produce lower then 1mm exit pupil are mostly for splitting double stars, and the Moon under good seeing.

10mm SUPER is judgeed by many not so good, the smaller exit pupil is not any help either, 11mm ES seems to me a very good choice.

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happy-kat: Some interesting details about the scope's adapter tube in that thread. Seems like the inner thread is not 37 mm but M36.4x1.0. Pretty weird. T2 is M42x0.75 BTW. Thanks!

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  • 3 years later...
6 hours ago, DS24 said:

Would this fit on the explore Scientific 127mm mak?  I'd like to be able to use 2in eyepeices. 

It would depend on the thread size of the rear port.  The Synta 127mm Maks (Orion, Celestron, Sky-Watcher) all have a smaller thread which can be adapted to the standard SCT thread with this adapter.  Since those are all f/12 scopes and the ES 127mm Mak is an f/15, it's not the same scope, so it might have a different rear port size.  You could measure the rear threads and see if they're M44.5 x 1.0.  If so, you could probably use that adapter.

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Hi @DS24 ss_smsa7.jpg.9b3846600093bd5ad94e585684588368.jpg<--- this is the adapter you are after. If you are from GB/UK, the SGL sponsor FLO sells them.

 

PIC011.JPG.d44aaf7659477cb4cf6a80da07ee9215.JPG<--- This is my 're-modded' Meade ETX105 with an ETX to SCT adapter fitted...

 

IMG_0385.JPG.63aa26dc64bb56b961a71d2dca61c605.JPG<--- before the ETX to SCT adapter was fitted...

 

PIC021.JPG.317e3ab5bc2a32848d576782c9caf3ab.JPG.4592fc6f2bbea546ef6fe542e1c067ae.JPG<--- and with an SCT star diagonal attached.

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Hi,

I have the 127 Maksutov from Sky-Watcher, shortly after buying this scope, i got myself a 2" visual back to replace the 1,25" and a 2" Primalucelab diagonal.

As for the eyepieces, i started of with the plösl-kit from Celestron, but the higher powered eyepieces were a pain to look trough, so i upgraded to Baader Hyperions, the nice thing about those is that they are modular if you get the 14 and 28mm Fine Tune Rings.

baader-hyperion-finetuning-ring-14-86f.thumb.jpg.9f1f9f0366ecffff046312743dd41249.jpg

As you can see, for example, the 21mm provided with the fine tune rings you get following focal lengts : 32,2mm / 21mm / 17,6mm / 15,5mm / 14mm and you can also put a Barlow in play.

I find those eyepieces  quite versatile and they are of good quality.

Do some reading about them, they are definatly worth considering in my opinion.

Good luck

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10 hours ago, Miguel1983 said:

Hi,

I have the 127 Maksutov from Sky-Watcher, shortly after buying this scope, i got myself a 2" visual back to replace the 1,25" and a 2" Primalucelab diagonal.

As for the eyepieces, i started of with the plösl-kit from Celestron, but the higher powered eyepieces were a pain to look trough, so i upgraded to Baader Hyperions, the nice thing about those is that they are modular if you get the 14 and 28mm Fine Tune Rings.

As you can see, for example, the 21mm provided with the fine tune rings you get following focal lengts : 32,2mm / 21mm / 17,6mm / 15,5mm / 14mm and you can also put a Barlow in play.

I find those eyepieces  quite versatile and they are of good quality.

Do some reading about them, they are definatly worth considering in my opinion.

Good luck

Do you actually thread these things in the dark?  I'd be afraid of dust getting into the eyepiece and of cross threading the threads.  I have enough trouble with barrel undercuts hanging up on compression rings in the dark that I wouldn't dare try threading and unthreading eyepieces in the dark.

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