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Larger medium quality refractors - where to now.

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#1 Tropobob

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Posted 12 July 2018 - 06:57 PM

I looked at Menzel 2 in Norma, which is a  very faint planetary nebula with my 8" Edge SCT a few nights ago.  Though I was pleased to see it , I was frustrated by the lack of clarity when compared to my refractors. There was too much 'white noise' from other objects. It was like having a sheet of plastic over the front and yes, it is properly aligned.  

 

Maybe I should have used my 140mm Vixen, which has more clarity, but less light gathering power. 

 

I know people will say get a larger Dob to satisfy my aperture fever.  Fact is that I had a 12" Dob for years, but after a combination of ageing and discovering the joys of refactors, I sold it off. I also came to dislike 'mirror imaging' the views from each instrument and found this to impede the flow of my viewings.  I brought the SCT to be my light bucket, but as said, its clarity pales in comparison with a quality refractor.  

 

I notice in comment about the new skywatcher 6inch ED refractor, some are already calling for a 7" F9.  It makes me wonder about the future of medium quality refractors. 

 

There are two other paths that future ED refractors that future designs may take, instead of just scaling up.  

 

Remember the folder Unitrons?  Perhaps a large, folded design might make handling, storage and transporting much more feasible to the likes of me.  

Or are we simply awaiting a design with a builtin reducer like the Vixen 140mm or like some of the TeleVue designs?  Maybe there are other paths that I have not thought off. 

 

I will never have a 8" refractor by just scaling up the current offerings. However, I look forward to what may come forth after some innovation.

 

Your opinions please...

 

 


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#2 coopman

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Posted 12 July 2018 - 07:11 PM

I believe that ES is also working on a line of larger triplet refractors. 

I wonder how much the "folding" of the light path may have degraded the resultant images provided by such scopes?  And how difficult it would be to mass produce these folded light path refractors today?....And could anybody afford them?   



#3 Steve Cox

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Posted 12 July 2018 - 07:11 PM

Don't know how much you want to pay or how much weight you're willing to deal with, but there is this option - the Zerochromat.


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#4 havasman

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Posted 12 July 2018 - 07:23 PM

And I think D&G are still out there.  http://www.dgoptical.../refractor.htm 


Edited by havasman, 13 July 2018 - 01:02 AM.


#5 mogur

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Posted 12 July 2018 - 07:43 PM

Don't know how much you want to pay or how much weight you're willing to deal with, but there is this option - the Zerochromat.

Does anyone actually have one of these? They seem like a fabulous lower-cost option for someone who wants a large (8" or larger) refractor. At least on paper anyway. After purchase collimation must be near impossible with all the internal elements though!



#6 Steve Cox

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Posted 12 July 2018 - 07:49 PM

Yeah, got no clue on that Mogur, but have been curious and waiting to see if anyone here owns one and willing to give it a fair shakedown, along with a writeup here.



#7 starman876

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Posted 12 July 2018 - 08:20 PM

Don't know how much you want to pay or how much weight you're willing to deal with, but there is this option - the Zerochromat.

That is a really interesting scope.  



#8 gezak22

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Posted 12 July 2018 - 08:23 PM

I thought folded telescopes such as the Zerochromat, while controlling CA well, displayed lots of higher order aberrations.

 

 

... I brought the SCT to be my light bucket, but as said, its clarity pales in comparison with a quality refractor ...

How do you define clarity? Is it contrast, image brightness, star sizes, or something else entirely? Also, are you comparing a refractor to an SCT at the same focal length and same magnification? Because if not, then the comparison is not very fair.



#9 Tropobob

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Posted 13 July 2018 - 12:55 AM

Don't know how much you want to pay or how much weight you're willing to deal with, but there is this option - the Zerochromat.

Thanks Steve,

 

I had no idea of these - maybe the future is here already.

 

I need to find out more, but the 8" is tempting. 



#10 mogur

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Posted 13 July 2018 - 09:55 AM

That's the problem as I see it. Where does one find more information, preferably from actual owners. There's not much on the website except for the empirical data of weight, length, etc. Hardly any pictures even. It's kind of "Buy it you'll like it".



#11 db2005

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Posted 13 July 2018 - 10:07 AM

Yeah, refractors do tend to become very unmanageable in larger sizes bawling.gif. Am I right to assume that such a scope you are looking for, say 8-10" aperture, would be permanently mounted? If not, if this would be used as a portable scope, its massive objective lens would need serious time to acclimatize, thus negating one of the  advantages of refractors, which is fast cool-down.

 

The closest I can think of that is readily available on the market is one of the larger Maksutov-Cassegrain scopes, but they are rarely seen above 7" (SW Skymax 180), and they are slow. They reportedly offer almost APO-like views and they don't break the bank. Intes Micro have also made some 8" versions but the sad rumour is that Intes aren't making more scopes.

 

I am a bit surprised that you are unsatisfied with the views through the EdgeHD C8... are you sure the poor results aren't just the effect of larger aperture and seeing effects which just aren't as pronounced in smaller aperture refractors? EdgeHD owners mostly seem to be praising their scopes, so personally I'd give it another go to see if you can verify that cause of inferior views isn't caused by a problem with the diagonal, eyepieces, insufficient protection against stray light, etc.


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#12 Tropobob

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Posted 13 July 2018 - 06:44 PM

Thinking about it overnight, I have never been an earlier adopter of new technology, so I like to see something that is well proven before I buy it. The Zerochormat was an interesting design though and very light for its size. 

 

Regarding the SCT, I  used a 2" Takahashi diagonal and a 35mm Panoptic for low power views, so with these items and the low magnification, I really did expect better images from the SCT.  It reminded me of some the achromatic scopes when a lower quality lens is used. 

 

When I obtain another clear night, I will do a direct comparison between the SCT and some of my quality refractors and report the results. 



#13 Tyson M

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Posted 13 July 2018 - 07:58 PM

Assuming you're all collimated well, the 8" Edge can be a perfect scope for many. Tons sing their praises. 

 

Over 6" refractor land means fast achro to me. Like Istar. Still big scopes. They don't scale well as you mentioned. 

 

If your observing planetary nebula , you want focal length. I would look towards to the Takahashi Mewlon series of scopes.



#14 gezak22

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Posted 13 July 2018 - 09:10 PM

Chiming in on SCTs. I terribly misidentified tube currents in my 11" Edge as astigmatism. But once I realized my mistake, all other outings have been just fine. No issues with lousy images or anything. Then again, not all SCTs are created equally. I highly recommend these two articles.

 

An SCT can be a very capable tool, far more compact than a refractor and at a much lower cost, without prohibitive compromises in my opinion.


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#15 Scott Horstman

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Posted 13 July 2018 - 09:16 PM

I looked at Menzel 2 in Norma, which is a  very faint planetary nebula with my 8" Edge SCT a few nights ago.  Though I was pleased to see it , I was frustrated by the lack of clarity when compared to my refractors. There was too much 'white noise' from other objects. It was like having a sheet of plastic over the front and yes, it is properly aligned.  

 

Maybe I should have used my 140mm Vixen, which has more clarity, but less light gathering power. 

 

Could have been Sky quality? Aperture rules but aperture will also increase lousy seeing. 



#16 Tropobob

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Posted 13 July 2018 - 11:57 PM

Could have been Sky quality? Aperture rules but aperture will also increase lousy seeing. 

True. In general, I think my skies may be a little below average. 

 

 I don't use the SCT much, only twice this year but I was generally satisfied with it till I brought a number of quality refractors.

 

The nights on which the SCT was used had cool temperatures by local conditions, although in both instances the scope was set up just after sunset. However, on reflection, it would not be a total surprise if internal air currents were partly to blame.  

 

The issue of scaling telescopes has a lot to answer for.  The smaller scopes cost less and perform well, then when I go larger, well costs increase, I use them less and they often do not perform as well as expected. Its a real case of diminishing returns for my money when pursuing better views! 



#17 Tropobob

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Posted 14 July 2018 - 08:31 PM

... Regarding the SCT, I  used a 2" Takahashi diagonal and a 35mm Panoptic for low power views, so with these items and the low magnification, I really did expect better images from the SCT.  It reminded me of some the achromatic scopes when a lower quality lens is used. 

 

When I obtain another clear night, I will do a direct comparison between the SCT and some of my quality refractors and report the results. 

I did that direct comparison last night, which by local standards was a very good night. 

 

On Menzel 2, the SCT performed best, and its performance was better than the evening in Post 1.

 

I did see Menzel 2 with my Meade ED 127mm F9. Its performance at high power was not as crisp as I expected, although it would have been sufficient to find Menzel 2, if I had not already done so. 

 

So, my apologies to the SCT Edge HD, all its fans and indeed their sellers who have to put up with many 'unfair' opinions, even from experienced observers, such as myself. 

 

Overall, this has been a good example of how problems multiply with scale. Its no wonder that the humble 6" F8 Newtonian was so beloved for some many years.    




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