127mm ED Triplet for $1199 at VTI Optics

[wulfgar]

Originally Posted by Profiler

Another point for some perspective as to why these generic 127 models are becoming much cheaper is that a new design is now on the horizon - the first examples/incarnation being under the badge of 'Meade 6000 series' refractors (these 127's being examples of the previous Meade 5000 series). Examples of the 6000 series can be found on the Bintel site.

I could hazard a guess that the glass merchants are getting rid of their stocks of FPL-51 and its equivalents. So the Scope uses the advertising point of "ED" triplet obscuring the fact that it is a very ordinary type of ED.

[casstony]

FPL51 is still a very useful glass type and I doubt it will be disappearing anytime soon. FPL53 allows the same performance as FPL51 (both with apropriate mating elements) at a shorter focal length. A lot of factors contribute to making a good refractor including cost and availability of ED glass types and mating elements, care taken with grinding and polishing and stability of the lens cell.

[MortonH]

Originally Posted by casstony

FPL51 is still a very useful glass type and I doubt it will be disappearing anytime soon. FPL53 allows the same performance as FPL51 (both with apropriate mating elements) at a shorter focal length. A lot of factors contribute to making a good refractor including cost and availability of ED glass types and mating elements, care taken with grinding and polishing and stability of the lens cell.

Vic Maris at Stellarvue has said many times that the mating element is just as important as the "headline" element of FPL-53, FPL-51 or whatever. It's also dependent on how well put together they are. I've seen this myself with my SV110ED which has less colour error than a William Optics 80ED of the same focal ratio and both using FPL-51. All other things being equal, the Stellarvue should show more colour since it has a larger aperture, but it does not. Hence all other things are not equal, and one of those things is the additional effort Stellarvue puts in to get the lens "as good as it can be" in Vic's own words.

In terms of getting rid of FPL-51 stocks, I've read that the price of Japanese "FPL" glass has increased significantly and therefore it's only getting more and more likely that the cheaper scopes will be using FCD1 or FK61 or other Chinese equivalents, which may or may not match FPL for colour correction, homogeneity or any other characteristic you care to mention.

[Larryp (Laurie)]

Originally Posted by MortonH

In terms of getting rid of FPL-51 stocks, I've read that the price of Japanese "FPL" glass has increased significantly and therefore it's only getting more and more likely that the cheaper scopes will be using FCD1 or FK61 or other Chinese equivalents, which may or may not match FPL for colour correction, homogeneity or any other characteristic you care to mention.

What you say about Stellarview lens is quite true, My Nitehawk 80mm f7 doublet shows no visible colour error using FPL51

[Profiler (Profiler)]

I only briefly looked at the new scopes some weeks ago and from what I remember everyone is generally correct that these new models (e.g. Meade 6000 series) are using a different type of glass from the previous generation (eg the 127mm $1,200 badged HiOptics) and they feature an improved larger focuser. No comment from me on what is the actual quality/performance of any of these different design features but to get a general impression for comparison purposes between the two generations specs and marketing blurbs for the Meade 6000 refractors are available on various websites.

[MortonH]

Are the new Meade scopes actually in the wild yet? Couldn't find any reviews of them.

[wulfgar]

Originally Posted by casstony

FPL51 is still a very useful glass type and I doubt it will be disappearing anytime soon. FPL53 allows the same performance as FPL51 (both with apropriate mating elements) at a shorter focal length. A lot of factors contribute to making a good refractor including cost and availability of ED glass types and mating elements, care taken with grinding and polishing and stability of the lens cell.

That's precisely the issue. In theory an apochromat can be made from ordinary glass, but the curvatures of the element figures becomes something wicked. This in the past limited practical apochromats to very long focal lengths.
Generation one style ED enabled practical shorter designs in both true apo triplets and "semi-apo" doublets, but F7.5 is very short and more the province of the later generation ED's.
Chromatic aberration isn't the only issue with a refractor and these short focal lengths that are popular for imaging face increasing other problems that the old F15 standard for achromats never had to deal with.
But the introduction a third element risks the loss of more contrast due to scattered light which is perhaps part of the reason that "semi-apo" doublets remain popular.
I tried my old Vixen 102 triplet fluorite against a friends later doublet version. Racked slightly in and out of focus the triplet remains dead white while the doublet shows color. Is it decided then? No, even though the doublet showed some color, the doublet had better contrast in other ways with a blacker sky background. I can assume the extra element also means more scattered light. You gain some to lose some, everything comes with a price. I assume that greater curvatures on the elements of fast telescopes, will scatter some more light as well.
It looks to me like these cheaper 5" triplets are trying to cash in on the reputation of high end imaging products like the Tak's.

[casstony]

The ED127 comes with a bit more CA and Spherochromatism than than a similar spec FPL53 scope, but in the end it still produces a decent image at a low price. Even my Megrez 88 works fairly well and it's a very fast FPL51 doublet - much closer to an apo than an achro.

[casstony]

I got the scope out again last night but conditions were still ordinary with jetstream overhead. Looking closely I saw some astigmatism close to focus, then I put another scope on the mount and saw exactly the same pattern so I guess it's time to visit the optometrist again
Trapezium E was solidly visible at 100x with F coming in and out.

Note: I have to correct an earlier comment about the focuser not properly holding the diagonal; I used a Televue diagonal the first night and the safety undercut obviously doesn't mate well with the 127's compression ring since a William Optics bevelled diagonal nosepiece is held securely. The Hioptic supplied diagonal has the bevel as per WO and it appears to be of decent quality compared to a WO diagonal. The focuser is still not great but it is servicable for visual use.

[jjjnettie (Jeanette)]

Has anyone posted any images from this scope yet?

[mr bruess]

127mm ED Triplet looks like quite a bargain.

[gregbradley]

Nice post - thanks. I noticed my old Tak FS152 was stunning visually even compared to high triplets.
Also Yuri used FL51 in the now discontinued TEC160ED.

Greg.

Originally Posted by wulfgar

That's precisely the issue. In theory an apochromat can be made from ordinary glass, but the curvatures of the element figures becomes something wicked. This in the past limited practical apochromats to very long focal lengths.
Generation one style ED enabled practical shorter designs in both true apo triplets and "semi-apo" doublets, but F7.5 is very short and more the province of the later generation ED's.
Chromatic aberration isn't the only issue with a refractor and these short focal lengths that are popular for imaging face increasing other problems that the old F15 standard for achromats never had to deal with.
But the introduction a third element risks the loss of more contrast due to scattered light which is perhaps part of the reason that "semi-apo" doublets remain popular.
I tried my old Vixen 102 triplet fluorite against a friends later doublet version. Racked slightly in and out of focus the triplet remains dead white while the doublet shows color. Is it decided then? No, even though the doublet showed some color, the doublet had better contrast in other ways with a blacker sky background. I can assume the extra element also means more scattered light. You gain some to lose some, everything comes with a price. I assume that greater curvatures on the elements of fast telescopes, will scatter some more light as well.
It looks to me like these cheaper 5" triplets are trying to cash in on the reputation of high end imaging products like the Tak's.

[jjjnettie (Jeanette)]

Still waiting for mine to be sent.

[Tom Hancock (Tom)]

Ordered on the 28th Dec, just been told, mine ship out today.
Can't wait for it to arrives.

[jjjnettie (Jeanette)]

I ordered mine on the 30th. So maybe mine will be sent off tomorrow??

[wulfgar]

Originally Posted by gregbradley

Nice post - thanks. I noticed my old Tak FS152 was stunning visually even compared to high triplets.
Also Yuri used FL51 in the now discontinued TEC160ED.

Greg.

I was bit a doubter years ago, at the same time Barry Adcock was quite enthusiastic about the fluorite doublets when they first showed up. Technically only a Triplet can be an APO, however if the chromatic aberration remains at the Raleigh tolerance it could be termed a practical Apo. The amount of color aberration I saw in the Vixen doublet was hardly an issue.
I don't know why they are backtracking to triplets with the high end ed glass other than the shorter focal lengths are popular with imagers they are doing, require a triplet design to make the Raleigh tolerance. But these designs won't match the amount of general contrast that came with the fluorite doublets.

[Tom Hancock (Tom)]

My ED127 arrived a few days ago!
The scope look well made and appears to be of good quality.
I cannot compare with the TAKs as I have not used one before.
Pointed it at Jupiter and the Jewel Box last night and the view through it is crisp and sharp. I compare the view with my SW120 and the ED127 is the definite winner. perhaps it is not a fair comparison as the SW is not an apo.
Despite some comments on the forums, I found the focuser to be very usable but then I am only into visual observing and not into astrophotography.
So, overall, I am happy with my new acquisition. I will be looking at selling off my SW120.

[Wavytone]

Originally Posted by Tom Hancock

crisp and sharp

But... At high power - say around 200x on a bright star:
- can you clearly see the Airy disk and a nice set of diffraction rings ?
- when you defocus a little, is the appearance of the rings the same inside and outside focus ?
- is there a violet halo ?
- are the rings coloured ?

Secondly, does it cleanly resolve a close double star say 2-3 arc secs apart ?

Many of the short achromatic doublet refractors fail the first test - the star looks like a hard "knot" but no diffraction rings, or have a distinct violet halo.

[jjjnettie (Jeanette)]

My scope was delayed as the manufacturer ran out of focusers.
I now have a tracking number, and it's been sitting in a TNT depot in Sydney since yesterday morning.
waiting......waiting....waiting.... .

[Tom Hancock (Tom)]

Learning new things everyday!
Don't think, I can push it to 200x, as it is only 127mm aperture, which means under good condition, you are probably alright at 130x.
Had a look at the moon and Jupiter again last night. Jupiter at 100x show good details, the best I have seen so far,with no hint or visible purple or violet fringing even though Jupiter was very, very bright. The Moon at 50x also shown no visible purple or violet hue.