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Equipment Discussions >> Refractors

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Bonco
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Reged: 04/17/06

Loc: Florida
Re: Are achromats enjoying a come back? new [Re: astroneil]
      #5532807 - 11/21/12 06:51 PM

Quote:

Quote:

Quote:



Last night I had my 100mm F/6 achromat out in the back yard. The seeing was so so but it was giving me a nice clean split of the double-double. Later I tried to split delta Cygni but I just couldn't get it. I pulled out my 80mm F/7 FD and was able to get a nice clean split.

The right scope for the job...

Jon Isaacs




Congratulations Jon! You must be beside yourself for having finally split Delta Cygni with an 80mm 'scope (having posted negative findings in this aperture class several times in the past even in your excellent climate).

Delta Cygni is fairly easy in both my 80mm achromats (f/9 and f/11).

I used to own a 100mm f/6.5 achromat and my records show that this system was also easy to split from my less than idyllic vantage with this instrument.

http://www.cloudynights.com/item.php?item_id=1515

Elephants never forget.

Cheers,

Nelly.




Hmm, Last week I split Delta Cyg 3 nights in a row with my humble 75mm F/16 achro. Wasn't difficult either. I've routinely observed it with my 60mm f/15 Achro. Bill


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mikey cee
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Re: Are achromats enjoying a come back? new [Re: Bonco]
      #5532913 - 11/21/12 08:23 PM

Yessiree Bonco Delta Cygni is definitely kindergarten level. I too have split it in a 60mm Sears. I only look at it with my 10" when I'm bored and that's been getting more often than not lately. Mike

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7331Peg
Sirius Observer
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Reged: 09/01/08

Loc: North coast of Oregon
Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5533268 - 11/22/12 01:38 AM

Quote:



I don't know about other fast achromats but in my experience, there is enough chromatic aberration and general muck in the ones I have used that apochromats with their superior color correction and most likely the superior optics certainly are better performers on doubles, particularly when the seeing is sketchy.

Jon Isaacs




Not sure what the problem is down there in your neck of the woods, but it has nothing to do with achromat vs. apochromat. I've split Delta Cygni with achromatic apertures ranging from 60mm to 152mm more times than I can count.


John


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Jon Isaacs
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Re: Are achromats enjoying a come back? new [Re: 7331Peg]
      #5533384 - 11/22/12 05:30 AM

Quote:



Not sure what the problem is down there in your neck of the woods, but it has nothing to do with achromat vs. apochromat. I've split Delta Cygni with achromatic apertures ranging from 60mm to 152mm more times than I can count.




Done it with any 100mm F/5 or F/6 achromats?

Jon


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Are achromats enjoying a come back? new [Re: Joe Bergeron]
      #5533400 - 11/22/12 06:05 AM

Quote:

Jon, don't tell me you are a member of the worldwide anti-achromat conspiracy. Your contrary views suggest as much.




Joe:

I think of my views as realistic rather than contrary... In a thread like this one, I get a lot of flack. There's a lot of good scopes out there, most any scope I put my eye to provides enjoyable views. But honest evaluations require discussions of both the positive and negative aspects of the various designs. A few comments:

I own more achromats than apos. I own two of the Meade-Mizar 80mm F/11s that are essentially identical to the 80mm F/11 that someone was trying to sell for something close to $1000. They are good performers but I get better views with my 80mm F7 FPL-53 doublet.

I enjoy achromats, last night I spent with the 80mm F/5 which provides a 6 degree TFoV and the aforementioned 100mm F/6.. I also understand their limitations, the false color on Jupiter and the moon definitely affected the contrast. A fast achromat is no match for an apo at high magnifications and a slow achromat is no match for an apo in the widefield. That is just how it is.

In terms of performance, I like to think I play no favorites... In my world, refractors are small scopes, when the seeing is excellent, any refractor I would want to use is simply too small to really take advantage of it, half-arc second seeing needs at least a 10 inch and probably larger scope to do it justice. Rob's 10 inch would be a great scope but it's just too long and requires too large a mount to be portable. For such tasks, a larger Newtonian is my scope of choice, no problems with CA, easily mounted, well corrected at F/6, correctable at faster focal ratios...

The reason I mentioned Delta Cygni was simply that I have been unable to split it with the 100mm F/6 achromat, the optics seem quite reasonable, last night the seeing was adequate, at 150x and 225x I was seeing a clean image with stable diffraction rings but no companion.

And yes, delta Cygni is child's play, best suited for challenging smaller scopes. In a pedestrian 10 inch Newtonian, it's just a looker, not a challenge.

YMMV

Jon


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Mark Harry
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Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5533507 - 11/22/12 08:18 AM

I have one question about this-

-IF-,

Comparing a long achro where the relatively narrow field isn't a hindrance, how would the comparison work out against an apo? Would it be close as far as color error and contrast is concerned?
I don't have an apo, or an ED for comparisons, but I do have a smattering of achros.
M.


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Crayfordjon
Vendor - Zerochromat
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Reged: 06/17/09

Loc: UK
Re: Are achromats enjoying a come back? new [Re: Mark Harry]
      #5533723 - 11/22/12 10:48 AM

Its fashionable to have an apo, especially if it has a designer label. We live in the age of designer labelled goods. To have a 90mm apo by you know who means you have "arrived" into the ranks of the elite. Now the achro is definately and quaintly "retro" nobody uses them any more, so the recieved philosophy goes. In reality the apo only supresses the secondary colour, it is still not perfect, you have to use a reflecting scope for that, so what do we have left in the apo, tertiary colour aberration, but it is so small as not to be noticed. The achro is reletively cheap, does an excellent job and is quite good enough for general observing. I go for achros every time, I have looked through apos and say, so what!. When I was night assistant at the 28 inch refractor at the Old Royal Observatory at Greenwich, I used to look through the seven inch guide refractor bolted to the 28 inch tube, it was a Cook doublet, yes and achro, the colour correction is astoundingly good and images rival those seen through a reflector.

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astrogeezer41
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Re: Are achromats enjoying a come back? new [Re: Crayfordjon]
      #5534012 - 11/22/12 02:04 PM

I liked your post and its point. Although I am fascinated by the quest for state of the art perfection, and would love to
have a top line apo, I am quite happy with my four achromats and my 6"f/8 Planetary Newtonian.

Thanks for sharing your comments and experience,
Robert
SV80 Aplanat (f/7)
SV80/9D
SV102F11
Unitron 75,f/16
Homemade 6"f/8 Planetary Newtonian


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The Ardent
scholastic sledgehammer
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Reged: 10/24/08

Loc: Virginia
Re: Are achromats enjoying a come back? new [Re: Crayfordjon]
      #5534091 - 11/22/12 03:24 PM

Here in the US sometimes I look thru the BBC Sky at Night Magazine. All the ads and equipment reviews are for imported scopes. The are the same ones imported in the US sometimes with a different name.
My question is: What telescopes is the UK exporting? Where are your achromats and apos that are in high demand? Who are the UK lensmakers comparable to D&G?


Quote:

Its fashionable to have an apo, especially if it has a designer label.




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7331Peg
Sirius Observer
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Reged: 09/01/08

Loc: North coast of Oregon
Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5534726 - 11/23/12 01:37 AM

Quote:

Quote:



Not sure what the problem is down there in your neck of the woods, but it has nothing to do with achromat vs. apochromat. I've split Delta Cygni with achromatic apertures ranging from 60mm to 152mm more times than I can count.




Done it with any 100mm F/5 or F/6 achromats?

Jon




I got Delta Cygni with the old Stellarvue Nighthawk 80mm f/6 achro a few times, but I've never owned a 100mm f/5 or f/6. I can see where that could be a problem with those scopes, though.

Actually, I was thinking of your comment that you might have gotten Delta with one of your 80mm f/11's. There really shouldn't be a problem at that focal length, given cooperative seeing.


John


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Jon Isaacs
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Re: Are achromats enjoying a come back? new [Re: 7331Peg]
      #5534793 - 11/23/12 02:50 AM

Quote:

Actually, I was thinking of your comment that you might have gotten Delta with one of your 80mm f/11's. There really shouldn't be a problem at that focal length, given cooperative seeing.




I have split Delta Cygni a few times with my 80mm F/11s but it takes better seeing than it does in my 80mm F/7 apo.

Jon


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Jon Isaacs
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Re: Are achromats enjoying a come back? new [Re: Crayfordjon]
      #5534799 - 11/23/12 03:00 AM

Quote:

Its fashionable to have an apo, especially if it has a designer label.




I imagine there are those who choose their scopes based on fashion but I am certainly not one of them... I base my choices on what I see at the eyepiece and I assume that the rest of the members of this forum do likewise. To assume otherwise is disrespectful.

When it comes to a discussion between apochromats and achromats, costs somehow always seems to enter into the equation. Achromats are better deals, apochromats are better telescopes... I like them both.

Jon Isaacs


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Crayfordjon
Vendor - Zerochromat
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Reged: 06/17/09

Loc: UK
Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5534811 - 11/23/12 03:21 AM

Hi ICUCinVA. The reason why we are not exporting scopes from the UK is that the US have a stranglehold on telescope trade, There is one very good 21st Century hign tech advancement in telescope design, an APO of 200mm aperture at 1/10 the cost all ready for production, but it cannot get off the ground because the market is dominated by US products. The same goes for focusers, they are either Chinese mousetraps or US products.

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Astrojensen
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Re: Are achromats enjoying a come back? new [Re: Crayfordjon]
      #5534823 - 11/23/12 03:39 AM

Quote:

the US have a stranglehold on telescope trade... the market is dominated by US products.




Hmmm. Last time I checked, there were four major players in the apo refractor market: TEC, AP, APM and Takahashi. Two are US based and do their own optics, APM is located in Germany and use Russian or Chinese optics, and Takahashi is in Japan and do their own optics. APM and Takahashi outsell the two US based companies by a wide margin.

A US stranglehold on telescope trade? Come on...


Clear skies!
Thomas, Denmark


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astroneil
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Reged: 07/28/09

Loc: res publica caledoniae
Re: Are achromats enjoying a come back? new [Re: Jon Isaacs]
      #5534935 - 11/23/12 07:14 AM Attachment (17 downloads)

Quote:



I have split Delta Cygni a few times with my 80mm F/11s but it takes better seeing than it does in my 80mm F/7 apo.

Jon




That's simply not true in my experience. Indeed, there are several postings going back a few years now, from different people at different locations, which have reported the exact opposite.

Edited by astroneil (11/23/12 07:15 AM)


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Bob Abraham
sage


Reged: 05/17/05

Loc: Toronto, ON, Canada
Re: Are achromats enjoying a come back? new [Re: astroneil]
      #5535186 - 11/23/12 10:16 AM

I'm with Jon on this one. In my experience, given equal optical quality, and assuming thermal effects are not in play, focal ratio makes no difference to image stability and color error can be a bit distracting in an achromat in some cases. If cost doesn't enter into it and optical quality is good for both I'd personally rather have a well corrected apochromat than an achromat for pretty much any use.

Of course, the trick is that cost generally matters and its easier to make a high quality achromat, and a long tube can help with thermals sometimes so I can see why some people really like their achromats.

Bob


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Crayfordjon
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Reged: 06/17/09

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Re: Are achromats enjoying a come back? new [Re: Bob Abraham]
      #5535209 - 11/23/12 10:32 AM

I am aware that other countries make scopes but in the UK the scope trade is practically all US in origin, Need I tell what these brands are. Designer label syndrome again, if it aint either a wotsit or a doodad, then it aint any good, and these brands dominate. Same goes for focusers, but the problem here is that nobody is willing to compete with the US focusers, and this simple piece of engineering would not pose a problem for an enterprising entrepreneur.

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astroneil
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Re: Are achromats enjoying a come back? new [Re: Bob Abraham]
      #5535213 - 11/23/12 10:34 AM

Then ladies and gentlemen,

Let us have tests. Take a good 80mm f/11 and compare it to a a shorttube apochromat; the more complex the better.

Take them out at the same time; aim them at a tricky double star and observe the images.

Come back with reports. No cheating and let's form a consensus.


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Astrojensen
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Re: Are achromats enjoying a come back? new [Re: astroneil]
      #5535508 - 11/23/12 01:25 PM

Quote:

Then ladies and gentlemen,

Let us have tests. Take a good 80mm f/11 and compare it to a a shorttube apochromat; the more complex the better.

Take them out at the same time; aim them at a tricky double star and observe the images.

Come back with reports. No cheating and let's form a consensus.




History has a habit of repeating itself, right?


Clear skies!
Thomas, Denmark


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Sky Muse
sage


Reged: 10/26/12

Loc: De Soto County, MS
Re: Are achromats enjoying a come back? new [Re: Crayfordjon]
      #5535595 - 11/23/12 02:09 PM

I'd love another achromat, the Skylight 4" f/15 in particular, however while there are undoubtedly many apochromats marketed so fashionably, I consider, albeit few, that are above common marketing practices; Astro-Physics, for instance, and among mirrored arrangements, Questar. Another case in point, and perhaps even further removed, are the positively retroactive series of refractors from Takahashi...

http://www.google.com/imgres?q=takahashi+fs-102&start=508&um=1&hl...

Note its quaint, toy-like appearance, hearkening back to the days of Unitron and those achromats of other Japanese manufacturers, where many a generation whiled away the hours, gliding their hands over the textured fittings upon standing before them.

Alan


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