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vlaiv

Yet another Mak 102 vs Mak 127 thread - with a twist.

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Christmas presents time ... :D

Nothing like "surprising" oneself with another piece of astro kit, right?

Thread title pretty much says it all, need some swaying one way or another, but as mentioned - there is a twist to this story.

It will be AZGti mounted scope and its primary use is as testing rig (or rather purchasing excuse? :D ). I'm strongly motivated to write EEVA software and feel that one of these might be perfect platform to test it out. In part this decision is driven by the fact that many people look for affordable scope that will do it all - do some planetary viewing, some planetary imaging, some DSO viewing, some "DSO imaging" - or as they frequently put it - "Would like to record what they saw in an image".

Many will tell that such a slow scope is not suited for EEVA purpose, but I intend to trial it specific "configuration" - Eyepiece + suitable lens + small sensor CMOS camera (can be used for both planetary and EEVA). I concluded that it is possible good combination for doing this and would need to try it out.

Secondary role of the scope will be of course some quick viewing, probably mostly Moon gazing and sometimes quick peek at DSOs (those that are within reach in my LP for the time being). Sort of grab&go setup that does not require extensive preparation/setup time and is suitable for "off the balcony" use.

I'll list my so far pros/cons list and some technical question people might be able to answer (owners and former owners of said scopes).

102 pros:

- I really like compact format and light weight of this scope

- Slightly slower - which means easier on the EPs and probably less optical issues for Mak (Gregory type). Smaller secondary? Does this impact baffling / any stray light issues?

- Potentially choice for more people looking for above mentioned type of scope due to slightly smaller cost (not issue for me, but could be issue for some)

- Focal length of 1300mm - I think I would feel less "boxed in" because it is very close to FL of scope I regularly use to observe - 200/1200 dob

- Latest version has "groove" at front of the scope (probably to fit cover) - which can be used to fit dew/stray light shield as well?

102 cons:

- I have slight feeling that mechanically this version is not the same as 127 - design more for the "masses" and aimed at being affordable. At some point 127 was marketed as "Black Diamond" if I'm not mistaken along with 150 and 180 versions - which gave impression that these three were higher class instruments (not only by aperture and price) than 90 and 102 which were sort of beginner scopes?

- For visual it will have lower resolution and light grasp vs 127

127 pros:

- Obviously aperture, both in terms of planetary performance but also for DSO / EEVA

- Possibly mechanically better instrument?

- Possibly better optically?

127 cons:

(should I even write those or we can just "invert" pros for 102? :D )

- bulkier / heavier - mind you I plan to use it on AZGti - with eyepiece, ep projection adapter, cooled ASI camera (178mmc) and small lens - I have sense it will all build up towards 4kg+ rather quickly. But there is also issue of size - I just love how 102 looks as small (but capable) instrument.

- cool down issues?

- I feel that 1500mm FL will be a bit too much for grab&go / general purpose scope

That would be about it I think - maybe I'll remember something later as well.

I'm also interested in couple of technical characteristics of said scopes, so I would be grateful to owners if they can provide such data.

- for both scopes, do you know what is fully illuminated circle on both (would need that to calculate usable TFOV for EEVA, and proper combination of Eyepiece / lens). I always assumed that both scopes would illuminate 1.25" field (so up to about 28-30mm) but I'm not quite sure - this might not be full illumination and there could be some vignetting. I've read somewhere that back openings are quite smaller than this?

- I'm not interested in working aperture of scopes - I know that it's a bit less than one would believe from scope designation (102mm and 127mm), but it does not really matter - I accept that as design limitation (need for larger secondary and some baffling inside), but would like to know if there is stray light in the field at "close" focus position - or rather when one sights down the tube on EP side - can you see past / to the side of central obstruction and if so - at what distance to T2 thread (end of scope in literal sense). If you check this - move eye to edge rather than keep it on axis to check for gap

- Of course, in context of what is written above - any difference that you feel could sway me one way or another.

Thanks

 

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To throw something else into the mix there is the Bresser 127 mak which is actally 127mm aperture not the 118. / 119 mm  actual aperture of the Skywatcher. Slightly longer focal length as well. I’ve had a couple of the Skywatcher 127 maks which were very good but the Bresser performs a bit better optically probably because of the longer fl and bigger actual aperture. The Bresser tube has micro baffles machined into the inner surface instead of the paint on a smooth surface of the Skywatcher. The Bresser has an SCT fitting.

The downside is the Bresser is more expensive than the Skywatcher however just performs that bit better. 

 

Edited by johninderby
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Worth noting perhaps that the 127 is actually the faster of the two OTAs, though there's not a huge amount in it.

I have an old blue Skywatcher 127 Mak and do occasionally look down the baffle tube to line up on the Moon (when I forgot to fit a finder :)  It's definitely possible to see the light from the Moon on the sides of the baffle tube near the corrector end, but I don't recall being able to see it the Moon directly past the secondary at all.  I can't check that at the moment though.

Not sure what the fully-illuminated field size is, but I've not noticed any vignetting on full disc lunar images using a DSLR when the disc covers pretty much the entire height of the frame, so I guess it must be at least 15mm.

From memory the optical path is a clear 1.25" -- I used to put barlows and cameras directly into the visual back without a problem.  Forgive me for not checking at the moment, but I don't want to go out to the observatory in the pouring rain :D

For the money I have been very happy with it for viewing/imaging lunar/solar/planetary and globs, but anything diffuse really isn't in its comfort zone.

James

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35 minutes ago, johninderby said:

To throw something else into the mix there is the Bresser 127 mak which is actally 127mm aperture not the 118. / 119 mm  actual aperture of the Skywatcher. Slightly longer focal length as well. I’ve had a couple of the Skywatcher 127 maks which were very good but the Bresser performs a bit better optically probably because of the longer fl and bigger actual aperture. The Bresser tube has micro baffles machined into the inner surface instead of the paint on a smooth surface of the Skywatcher. The Bresser has an SCT fitting.

The downside is the Bresser is more expensive than the Skywatcher however just performs that bit better. 

At one point I did actually consider Bresser maks, but given pro/con lists above you can see that it is not quite suitable for my needs.

- It's slightly heavier than Mak 127 (which is already where I don't feel comfortable on mount quoted at 5kg carry capacity)

- It has very long focal length - something I would not fancy for visual as well as for primary use - EEVA (small TFOV capability)

I did look at 102 version from Bresser - but there is also issue of getting one. FLO and TS don't stock 102mm OTAs, and Bresser does not ship to my country for some reason.

If I were looking for scope that is primary visual and meant for Moon and planets - I would probably go with classical Cassegrain from TS (either 6" or 8"). Scope I'm after now has different primary role.

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39 minutes ago, JamesF said:

Worth noting perhaps that the 127 is actually the faster of the two OTAs, though there's not a huge amount in it.

I have an old blue Skywatcher 127 Mak and do occasionally look down the baffle tube to line up on the Moon (when I forgot to fit a finder :) It's definitely possible to see the light from the Moon on the sides of the baffle tube near the corrector end, but I don't recall being able to see it the Moon directly past the secondary at all.  I can't check that at the moment though.

Not sure what the fully-illuminated field size is, but I've not noticed any vignetting on full disc lunar images using a DSLR when the disc covers pretty much the entire height of the frame, so I guess it must be at least 15mm.

From memory the optical path is a clear 1.25" -- I used to put barlows and cameras directly into the visual back without a problem.  Forgive me for not checking at the moment, but I don't want to go out to the observatory in the pouring rain :D

For the money I have been very happy with it for viewing/imaging lunar/solar/planetary and globs, but anything diffuse really isn't in its comfort zone.

James

Don't worry about not checking straight away, I'm in no hurry with this.

If you manage to find the time and it's not too much trouble for you - just take a look at daylight - as long as you can't see sky past the secondary - that should be ok. Odd reflection on baffle tube is ok - that is what it is there for.

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7 minutes ago, vlaiv said:

Don't worry about not checking straight away, I'm in no hurry with this.

If you manage to find the time and it's not too much trouble for you - just take a look at daylight - as long as you can't see sky past the secondary - that should be ok. Odd reflection on baffle tube is ok - that is what it is there for.

I'll try to remember to do this when it stops raining and I can open up the observatory.  Looking at the weather forecast however, that might be several days away :(

James

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1 hour ago, vlaiv said:

If you manage to find the time and it's not too much trouble for you - just take a look at daylight - as long as you can't see sky past the secondary - that should be ok. Odd reflection on baffle tube is ok - that is what it is there for.

I've got a Mak 127. I can't look tomorrow becuase I'm running errands all day but Saturday looks to be clear and bright all day, so I can put the Mak through a testing :thumbright: Just let me know in simple terms what I'm looking out for :smile:

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I had thought I'd read a post that someone had damaged the azgti with the 127 mak in eq mode with camera, might have been on cloudy nights. I would hedge bets lower and say the 102 mak would give more room for better weight plus camera management.

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There is also an excellent thread on here showing images before and after adding a flocked tube liner into the baffle of sct and the 127 was included on the thread.

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My 2p worth - I'd probably go for the 102. As you've said, it's a very compact instrument, light and portable, and still quite capable. More aperture is always good, but it is at the cost of bulk (not that the 127 is exactly huge, but the planned mount is lightweight).

On quality, from experience with the 102 and the 150 Maks, Skywatcher can say what they like but mechanically and optically these two scopes are really very similar. There is not some kind of quantum leap in quality once you go above 102mm, just more light grasp (and the ability to use a 2 inch diagonal on the larger models). Optically, I'd say both are decent scopes, but not great - an f12 or f13 Gregory Mak is fast for that design - it will suffer residual spherical aberration, and it is obvious on both the 102 and 150 SkyMax at higher magnifications (c. x200). Neither will outperform a half decent Newt (including on planets or double stars) but there is not much of a loss and the ergonomics of these little scopes are fantastic. The slightly slower f ratio on the 102mm might actually play in its favour.

I have not checked the baffle tubes on these scopes but have never felt the need to, as I've never had an issue with stray light. That said, I have (like kappy-kat) heard good things about the advantages of flocking the baffle tube, and my one look through a C90 with internal flocking was very impressive, so maybe there is room for improvement there.

Vignetting should not be an issue with a small chip. At prime focus both scopes cover a whole Nikon DX (15.8 x 23.6 mm) chip. Light fall off towards the edges is easily corrected with flats.

Cheers,

Billy.

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9 hours ago, Rob Sellent said:

I've got a Mak 127. I can't look tomorrow becuase I'm running errands all day but Saturday looks to be clear and bright all day, so I can put the Mak through a testing :thumbright: Just let me know in simple terms what I'm looking out for :smile:

Test is fairly simple, and here is diagram "of my concerns":

image.png.bdfa1268c0f0a42c00452f29fccbe34c.png

These sort of scopes are made to be used with diagonal mirror, although they have extensive range of focus, I suppose that optimal focus is somewhere around 100mm or so behind the end of the scope (end of that receptacle with T2 thread - I would otherwise call it end of focuser, but focuser here is internal :D ).

In the configuration I plan to use it for EEVA, eyepiece will be quite a bit forward - it will be inserted in back tube directly (without diagonal). This is primarily because of weight / stiffness / balance issues - closer to tube - better (there will be EP projection adapter, small lens and camera hanging of the eyepiece).

My concern is that if focal plane is put too close to OTA, there could be light leak - light going directly past the secondary and down the main mirror central hole and onto the sensor. This would reduce contrast quite a bit, as most people doing that sort of thing probably live in LP areas (it's not a good thing even in dark skies).

Testing for this is quite easy - just point the scope at sky (of course be careful about the Sun) and place your eye at the end of back tube (you can't push your eyeball inside obviously :D, but place it fairly close - where eyepiece shoulder would be) and move it to the side so that secondary is not centered but to the side (bottom part of the image). If you see sky at the edge - bad, if not, and you only see secondary - good :D

I have couple of scopes that I could use to test this sort of eyepiece projection thing, but my idea was to do it on the scope that is not usually recommended for EEVA because it is too slow, and scope that could fit above role - being beginner scope that can pretty much do it all - visual and "taking some images" (in appropriate configuration). Of course it is also excuse to get another scope - one that I would use in sort of grab&go / lunar scope role. I planned to use Evostar 102 F/10 (not ED) in that role, but it does not quite fit it the way I expected - too large/heavy and a bit shaky on AZ-4 mount, so Evostar 102 will be for other things (solar work with herschel wedge and solar Ha with combo quark one day, maybe a bit of imaging - again trying to see if I can make usable imaging scope out of it with some tweaks - for those people that can't afford APO scopes for that).

For above reasons - I'm leaning towards Mak102 - it's lighter, it's more affordable to people and probably better suited for AzGti mount. One of more important things would be - what sort of TFOV each of those provide - I want one with larger TFOV. Normally, one with shorter FL will provide larger TFOV, but in this case, I'm not sure. Both scopes, according to reports online, have smaller back hole than is needed to fully illuminate 1.25" eyepiece. Given that and the fact that this exit hole might be smaller on Mak102, and that F/ratio of Mak102 is a bit slower - I can't really tell which scope would provide larger TFOV - One of the reasons I'm interested in illuminated field of both scopes.

 

 

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12 minutes ago, billyharris72 said:

Vignetting should not be an issue with a small chip. At prime focus both scopes cover a whole Nikon DX (15.8 x 23.6 mm) chip. Light fall off towards the edges is easily corrected with flats.

This is very useful info, thanks for that.

"Problem" is that I would not use small sensor at prime focus (too high sampling rate, too small TFOV), but rather in a sort of afocal arrangement. Eyepiece + lens would be used between scope and camera. This acts as sort of focal reducer, depending on focal lengths of eyepiece and lens (you can actually choose reduction factor).

For example, ASI178 has ~8.9mm diagonal. With 32mm plossl and 12mm lens - it would behave as ~23.7mm diagonal sensor - and vignetting there would certainly show (even field stop of EP would show depending on AFOV of eyepiece and angle of the lens). Fact that there is slight vignetting on 28.4mm diagonal sensor suggests that fully illuminated field has smaller diameter, but that scope can illuminate up to 28mm of field. I would certainly both use and recommend flats in this role. 32mm plossl (most likely to be used as projection EP) has 27mm field stop if I'm not mistaken.

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Just a small update.

I'm now at 95% confidence level that I'll go with Mak 102.

This is due to number of reasons:

- It turns out that I'll probably need to spend a bit more money on rig than I previously thought. Initial idea was to purchase AzGti + scope package, but it seems that scopes coming in this package don't have collimation screws unlike regular OTA versions - at least Mak 102. This can be seen on images of this scope, but it's also confirmed by Skywatcher rep over on CN in one thread. I would not want to get myself in situation where I can't collimate my scope and need to send it back. There is also concern about quality of scope if it's not the same as regular skymax OTA. I also figured that I want a bit more accessories with the scope - ES 82 6.7mm and quality 1.25" diagonal.

- Many people report that tripod coming with this package is rather poor in stability (probably to be expected from entry level scope/package), so purchasing only AzGti head and adapter to Eq5 class steel tripod seems like better option. I have spare tripod for this use (moved my HEQ5 on berlebach planet)

- I've came across image of back side of Mak 102 that is good enough to do rough measurement of rear baffle tube diameter. According to this rough measurement - it is about 23 mm in diameter. That would mean that there is some vignetting on 32mm plossl (field stop of 26-27mm), but it should not be more than 50% or so at the edges. It also means that Mak102 can provide larger TFOV in comparison to Mak127 (not by much, but still a bit larger).

image.png.56b1aa4efa2cb6fad970f48694342df9.png

This is Orion version, but I guess SW one can't be far off (if not exactly the same).

- I don't think that stray light will be a problem with these maks even on very close focus according to these images:

image.png.2b18d5e923cab8c939dc9ed93460983c.png

This is image of Mak127 - it looks like light is reaching about halfway down the baffle tube, so I think placing focus plane roughly 40mm away from end of baffle tube should not be impacted with stray light.

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