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Equipment Discussions >> Refractors

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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6078651 - 09/13/13 12:27 PM

If cost is a stumbling block and you wish to take black and white photos (not necessarily mono) you can use a light yellow or violet minus filter on the achro and get some nice shots. Doing this you will be taking black and white photos in red and green light and will not have blue/violet bloat around the brighter stars.

Using such a filter for visual just depends on your tolerance for a slightly dimmed yellow cast on all views.

Gale


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Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Apochromatic or Achromatic does it really matter? new [Re: gdd]
      #6078810 - 09/13/13 02:01 PM

For astrophotography the best results with an achro are obtained by stacking a Baader Fringe filter with their Skyglow filter. You'll get white stars with no yellow cast or purple halos. This combo really works nicely on the moon and Jupiter too for visual.

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PeterR280
Pooh-Bah
*****

Reged: 05/27/13

Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6078821 - 09/13/13 02:08 PM

I think you still get a greenish tint with both filters. You can always correct the color in photoshop if there is a tint.

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #6078859 - 09/13/13 02:36 PM

Here's why it matters. No, it's not about chromatic aberration, or field of view, or anything else achromat and apochromat fans tend to argue about. Apochromats are better because of *economics*. Wha?

Yeah, that's right. The economics of making and selling apochromats favor superior quality. While it's true that low dispersion glasses cost more than traditional optical glasses, but this is greatly over-emphasized. Increased glass costs are only a small component of the increased relative cost of an apochromat over a similar achromat. Instead, because apochromats (fairly or not) are in higher demand. This means that manufacturers and dealers of such designs enjoy much larger per unit margins. With a larger margin to play with, there's more money available to spend on materials and workmanship quality. No one can afford to put $800 worth of glass working labor into an achromat that sells for $600. A similar aperture apochromat that sells instead for $1700, could indeed - economically - receive $800 in materials and workmanship investment.

As a result, apochromats today tend to be better quality than like aperture achromats.

Quality is king. Optical quality helps you beat the seeing. Helps reveal fine detail. It's well established that the difference between a 1/8 wave optic and 1/4 wave optic is quite detectable visually at the eyepiece.



- Jim


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PeterR280
Pooh-Bah
*****

Reged: 05/27/13

Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079006 - 09/13/13 04:07 PM

From what I am reading, FPL-53 glass raw material cost could be over $400 for a 4" blank.

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Bonco
Post Laureate
*****

Reged: 04/17/06

Loc: Florida
Re: Apochromatic or Achromatic does it really matter? new [Re: ken svp120]
      #6079053 - 09/13/13 04:37 PM Attachment (23 downloads)

Quote:

I'm going to add my two cents by saying that a long achro might well be corrected as well as an apo but that the nice compact package of a modern apo makes such scope truly portable...you can take it to whatever dark skies you wish with very little transport worries and get phenomenal optical performance. Or, if permanently mounted, you can put it in a smaller facility. Yes, an apchromat definitely matters for more than one reason. Can you attain the same performance from an achromat...probably...but with the same functionality? I don't think so.




Here's a picture that illustrates your point. Televue 4 inch f/5 next to Antares 4 inch f/15. Both great telescopes and offer the best of both worlds. Wide field views in the f/5 are stunning. High power double star views in the f/15 are amazing. Take your pick, or buy both. Bill


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Kunama
professor emeritus


Reged: 10/22/12

Re: Apochromatic or Achromatic does it really matter? new [Re: Bonco]
      #6079102 - 09/13/13 05:12 PM

Very nice comparison Bonco !
Here is my version:
Istar Perseus AT150mm F10 on c1865 Gaunt Mount versus Takahashi TSA120 F7.5 on Vixen GPDII



oh by the way Jim, I think you got the info the wrong way around:

"Instead, because apochromats (fairly or not) are in higher demand. This means that manufacturers and dealers of such designs enjoy much larger per unit margins. With a larger margin to play with, there's more money available to spend on materials and workmanship quality."

I think the demand was a result of the high quality, not the cause of it !

In all seriousness, when it comes to visual on nebulae and other faint objects, APERTURE RULES !!! Go for an Istar Perseus AT150, one of the nicest modern achromats I have seen.


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Mark Costello
Post Laureate
*****

Reged: 03/08/05

Loc: Matthews, NC, USA
Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079110 - 09/13/13 05:28 PM

Based on what I seen it can do, I'm of the opinion that my achromat can perform to its design limits as well as any aprochromat can perform to its design limit. This may be true of a lot of achromats out there.

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VNA
member


Reged: 11/13/09

Loc: 37.893 N, 122.124 W
Re: Apochromatic or Achromatic does it really matter? new [Re: Mark Costello]
      #6079116 - 09/13/13 05:36 PM

Apochromatic or Achromatic does it really matter?

Yes it matters a great deal in the pocket book!

No one has really answered it other than proclaiming virtues of one or the other!

Is it worth 10 times more than an achromatic?

Is the view 10 times better?

(Law of diminishing returns)


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PeterR280
Pooh-Bah
*****

Reged: 05/27/13

Re: Apochromatic or Achromatic does it really matter? new [Re: VNA]
      #6079125 - 09/13/13 05:42 PM

The same can be said about size. Looka at the price differential between 100, 130, 150 and 175 mm. The resolution improvement is linear. Light gatherin does increase with the square of aperture. Cost seems to be logarithmic.

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Apochromatic or Achromatic does it really matter? new [Re: VNA]
      #6079135 - 09/13/13 05:47 PM

Quote:

Apochromatic or Achromatic does it really matter?

Yes it matters a great deal in the pocket book!

No one has really answered it other than proclaiming virtues of one or the other!

Is it worth 10 times more than an achromatic?

Is the view 10 times better?

(Law of diminishing returns)




Your eyes are free. There is not telescope that can be justified in terms of how much better the view is. If one is looking for performance per dollar, a mirror is the way to go...

Jon


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Kunama
professor emeritus


Reged: 10/22/12

Re: Apochromatic or Achromatic does it really matter? [Re: VNA]
      #6079184 - 09/13/13 06:20 PM

Quote:

Apochromatic or Achromatic does it really matter?
Yes it matters a great deal in the pocket book!
No one has really answered it other than proclaiming virtues of one or the other!
Is it worth 10 times more than an achromatic?
Is the view 10 times better?
(Law of diminishing returns)




Of course the view is not 10x better, in fact on some targets there is almost no difference in the view, but then you point the scope at a bright cluster, Saturn, Jupiter or the Moon and you see the difference.

If the difference is worth the extra $$$ depends on the individual.

Like anything else, to get a small improvement in performance you have to spend quite a bit more.


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Apochromatic or Achromatic does it really matter? new [Re: PeterR280]
      #6079609 - 09/13/13 11:25 PM

I doubt it given that Synta was selling complete 4" FPL-53 doublets for $450 under several different brands (Sky Watcher and Celestron). Of course, Ohara blanks come in different quality levels too, at widely varied costs.

Regards,

Jim


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Mike Clemens
Frozen to Eyepiece
*****

Reged: 11/26/05

Loc: Alaska, USA
Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079769 - 09/14/13 03:10 AM

When I first started, I owned a 6" achromat and then picked up a 4" APO. I almost never looked through the achromat again. The APO view was so insanely aesthetic in comparison.

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Maurice
member


Reged: 04/19/07

Loc: Netherlands
Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6079811 - 09/14/13 04:40 AM

Thanks again for all the help gentlemen, this forum is really great!
Thanks to all your input I will be able to make a better choice.

To answer some of your questions: my current setup is a 80mm WO Zenithstar II ED mounted on a Voyager alt/az. I'm not into AP, but I do sketch the objects that I'm looking at, hence my wish for an alt/az with tracking ability. This little scope performs beautifully on the moon and star clusters, especially in combination with my UWAN16 eyepiece.

This shorttube however is not that useful on planets and nabulae due to the small aperture and short focal length. That's why I'm looking for a second scope, not to replace the shorttube but as an addition to it.

All your input makes me wondering, is the best addition to the shorttube not simply a "slow" refractor with an larger objective? So instead of the 152/900mm it looks to me I'm better off with for instance a 130/1200mm scope. The larger focal length also helps in reducing CA.

As an example my 80mm next to this one: http://www.teleskop-express.de/shop/product_info.php/info/p680_ELITE-127-Refr...

Makes sense or is the 120/900 ED a better option (regardless the price)?


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6080061 - 09/14/13 09:47 AM

Quote:

All your input makes me wondering, is the best addition to the shorttube not simply a "slow" refractor with an larger objective? So instead of the 152/900mm it looks to me I'm better off with for instance a 130/1200mm scope. The larger focal length also helps in reducing CA.





Adding an AP CCDT67 reducer would convert the 130/1200mm to a 130/800mm.

Gale


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Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Apochromatic or Achromatic does it really matter? new [Re: gdd]
      #6080133 - 09/14/13 10:32 AM

There have been some folks who have tested an AR152 against the smaller aperture 127ED and reported that the smaller scope put up better views even on dimmer deep space subjects. I suspect this is due to the superior optics and the way the light is focused. This is something Jim may know about and can comment on.

I'm Just a former dumb football player and all this physics stuff goes over my head. But give me a receiver coming out of a crossing pattern on a single four wideout spread and I'll stuff him


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Mike4242
Pooh-Bah


Reged: 11/02/11

Loc: Memphis, TN
Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6080160 - 09/14/13 10:51 AM

I think this might be the review you had in mind:

http://www.cloudynights.com/ubbthreads/showflat.php/Number/5369924


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Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080334 - 09/14/13 12:43 PM

Yes that is the review. DrWho posted it on another forum too. What is your take on this Mike? Have you had a chance to compare the achro with an apo? I'm wondering after your post about the difference the filter made on M13 whether the views between the 127ED and AR152 might not be closer.

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Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Apochromatic or Achromatic does it really matter? *DELETED* new [Re: Mike4242]
      #6080336 - 09/14/13 12:43 PM

Post deleted by Jon_Doh

Duplicate

Edited by Jon_Doh (09/14/13 02:21 PM)


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