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SW 127 Mak OTA with 2" focuser


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Having just submitted an unsuccessful bid on ebay today for a 127 OTA and seen the level of interest and the price paid I'm drawn to the reluctant conclusion that if I really, really want one of these highly-rated OTAs the stakes have to be raised.  In Europe, at a comparable price (including shipping) to the standard model, there is a version available with a 2" focuser (quaintly described in the English version of the website as a 2" spectacle lift).  I've just asked FLO if this is available in UK but wonder what the optical advantage would be, apart from the obvious joy to be exhibited by my 2" EPs at being brought out of the back of the cupboard once more to gaze at the moon.  With this version SW even throw in a 2" EP,  which may - of course -  be of the usual low quality of "kit" EPs but seems to be an indication of some confidence in the system.  Any obvious disadvantages apart from added weight?

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I do wonder what the point of using 2 inch eyepieces in a 120mm aperture F/12 scope actually is so I will be watching the replies to this with interest :smiley:

There seem to be quite a few for sale over here at any one time but all 1.25 inch visual back.

 

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The problem with using a 2” crayfotd on a Skymax127 is it fouls the stock focuser knob. Usual way to get around this is to remove the knob and put a bit of pvc tubing over the focuser shaft.

Wonder what sort of focuser this French dealer is using?

I have experimented with using 2” eyepieces with a Skymax127 and by using a 30mm 70 degree eyepiece you do get a bit wider fov but not a lot more.

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I don't think the Mak can give much more than a 1 degree FOV no matter what eyepiece is put in it due to size of the hole in the back of the mirror

 

Unless there's a  specific reason to use a 2 inch setup, such as a Crayford focuser or 2 inch eyepieces you'd like to be able to use, there's not a great deal to be gained 

Edited by GazOC
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It's a Polish company which I have used before.  The exchange rate, sterling against the zloty, is usually favourable.  As far as I can see the focuser is the standard Mak focuser where the mirror moves, not a Crayford.  I'm using a Celestron 4se tube at present which I have modified to fit on a Skywatcher AZ-GTI mount and though it's really pretty good for lunar observing I would like something better,  I understand, and have found from my own experience, that ordinary 1.25 plossls give excellent results with the 4se but I do have 2" EPs  which I use with my PhotoLine refractor.  If there is no real benefit to be had then, so be it.  Thanks for the responses

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  • 2 weeks later...
1 hour ago, nfotis said:

It's my impression that from Skymax 150 and above you get 2" eyepieces.

Why not go for the Skymax 150 instead of the 127? Or even the 180? 🙂

N.F.

 

Thanks.  I was the very happy purchaser of an Omegon 127 Mak from an SGL member a week or so ago.  This will take a 2" diagonal so I'm happy to draw a line under this now.

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The Omegon 127 mak is a bit heavier than the Skymax (3.5kg vs 3.0 kg) and is an actual 127mm aperture unlike the Skymax that is 118 or 119mm actual aperture and the Omegon is f/15. Just a bit  better performer on lunar / planetary than the Skymax due to it’s full apeture and longer focal length.

Edited by johninderby
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Erm, I thought that the Skymax 127 and 150 are rated at f/12?

I have read many coflicting stories about the aperture/secondary, it seems that there were different models.

Some claim a smaller aperture, some claim the correct aperture, give or take one mm, etc.

 

N.F.

 

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Are the gold 150mm Maks not full aperture but have oversized mirrors in the later black diamond models?

I only ask as this was supposed to be the case with the 180mm model and, from the model I measured, the gold model also had an oversized primary the same size as the black diamond version 

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I'm very sceptical of the baffle tube being the problem, it's very carefully tapered in width from top to bottom 

That's not to say it can't be wrong, just that the designers have given that part a fair bit of time and effort 

 

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I've been using 2" visual backs on my Synta 127 Maks and haven't noticed any vignetting, just weird oval reflections as bright stars pass the edge of the rear baffle tube/port.  The TFOV isn't a little wider, it's a lot wider with a 40mm Meade SWA than with a 24mm APM UFF.  1.7 degrees is noticeably wider than 1.0 degrees to me at least.  It's like a breath of fresh air to be able to see more of the context around objects.  I might be off on the actual degrees since using a 2" visual back and diagonal extends the focal length somewhat, but the 70% increase in TFOV remains regardless.

As far as fitting a Crayford focuser to a 127 Mak, I wouldn't bother.  Neither of my 127 Maks has any mirror slop or focus backlash, and fine focusing is quite easy with the supplied focuser knob.  The 2" visual backs barely fit back there, so I don't know how you'd get a Crayford focuser to fit.  That, and you be extending your focal length even further than by just using a 2" diagonal versus a 1.25" diagonal.

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I composited together the max field of view in a Synta 127 Mak with a 1.25" eyepiece and with a 2" eyepiece, both while using a 2" visual back and 2" diagonal.  While some may disagree with me, I think it's pretty clear that there's a lot more true field of view available in a 127 Mak with very little vignetting when using 2" eyepieces.  By sampling luminosity center and at 85% to the edge in the 40mm image, it appears there's 65% of the center brightness available there which isn't bad at all visually at night.

220226258_Max127MakTFOVComparison.thumb.jpg.fa1c73bddd25963f5af583532ef1f858.jpg

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2 hours ago, johninderby said:

Simple fit a 1.25” crayford.

Never found extending the focal length of a mak to be any problem.

 

65F87CA7-9C54-4C8B-BA73-61A0BCE8FB3E.jpeg

Would you mind explaining to me how that focuser fits on a Mak please John, I can’t seem to picture how it would work.

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17 minutes ago, johninderby said:

Fitted to an Omegon 127 Mak. On a SW needs a short SCT extension.

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Thank you very much for explanation John, I was wrongly thinking it replaced the existing focuser. Am I right in thinking the replacement focuser works independently of the original one ?

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1 minute ago, banjaxed said:

Thank you very much for explanation John, I was wrongly thinking it replaced the existing focuser. Am I right in thinking the replacement focuser works independently of the original one ?

Yes the original focuser isn’t changed. Focus using the stock knob then leave it alone and just use the crayford.

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5 minutes ago, johninderby said:

Yes the original focuser isn’t changed. Focus using the stock knob then leave it alone and just use the crayford.

Now I understand, I was thinking you had to replace the existing one which didn’t seem an option. Thanks again for your explanation.

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18 hours ago, Louis D said:

I composited together the max field of view in a Synta 127 Mak with a 1.25" eyepiece and with a 2" eyepiece, both while using a 2" visual back and 2" diagonal.  While some may disagree with me, I think it's pretty clear that there's a lot more true field of view available in a 127 Mak with very little vignetting when using 2" eyepieces.  By sampling luminosity center and at 85% to the edge in the 40mm image, it appears there's 65% of the center brightness available there which isn't bad at all visually at night.

 

Having started this thread I've been interested to see how it's developed, especially since I bought the Omegon from John!  I'm still awaiting delivery of a 2" visual back but as soon as that arrives I'll hope to make a comparison of lunar views using a 25mm ES 2" and a 27mm 1.25" Orbinar flat field.  Not a direct comparison but close enough, maybe.  As John has said in other posts, the Omegon is a true 127mm so vignetting should, I imagine, be even less noticeable using the 2" but I certainly hope my ancient eyes will get added benefit from a 2" option.  I asked the question originally because the Skywatcher 127 is available with a 2" option in Europe,  (and I believe Canada) at minimal extra cost, but not in UK.  FLO, at my request, were asking the importers why it was not on offer to UK buyers but I've had no response.  It's irrelevant now anyway since I'm delighted with the Omegon.

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