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Chromatic Aberration Reducing Filters?

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#26 Sarkikos

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Posted 19 October 2014 - 10:37 AM

The C80 ED from AWB is well worth the cost/aperture ratio at $349.

 

Mike



#27 Sarkikos

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Posted 19 October 2014 - 10:43 AM

You will would have to try them and see.  A #8 cuts ~50-60% of the purple CA whereas the 495 LP cuts 100% of  the purple CA. With an ED  scope I would think the #8 LY would be sufficient. 

 

So far I don't see that my C80 ED requires any CA filter, whether for planet/lunar, double stars or DSO.  

 

I have a 2" Baader SemiAPO filter.  At the suggestion of a poster in another thread, I tried the SemiAPO on the 80mm ED.  It did not improve the view.  For the Moon, it made the image a bit dimmer and "muddier" looking, with a yellowish tinge.  But it did not improve the contrast or allow me to see fine detail such as rilles any easier. The image was better without the filter.

 

Mike



#28 JustaBoy

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Posted 19 October 2014 - 10:58 AM

Hi Mike,

 

What do you have your C-80 ED mounted on? - Seems like it would be a great G&G with the appropriate mounting. 

 

 

Thanks,



#29 Sarkikos

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Posted 19 October 2014 - 11:05 AM

I already had a 501HDV head and a Bogen tripod.  The C80 ED works very well on this setup, an excellent grab-n-go combo.  I especially like being able to direct the scope by a panhandle.  But it might not be cost effective to buy a beefy photo head specifically to use with a small telescope.  Such heads mount the scope directly on top, which isn't ideal.  Mounting a telescope on the side of the head is better.

 

If I didn't already have the 501HDV, I'd probably buy something like the UA DwarStar.  But I'd make sure I could get a panhandle for it.  Moving a scope by tugging on the OTA - or worse, by grabbing the diagonal - is not very ergonomically comfortable or precise.  Even for my Newts, I attach a little knob to move the OTA.  IME, a panhandle on an alt-az is ideal for moving and aiming small scopes, better than slo-mo knobs.  Unless you want to acquire a goto with tracking.

 

A DwarfStar with panhandle is on my short list of things to buy for astronomy.  It should work well with my C80 ED and my C5.

 

Mike


Edited by Sarkikos, 19 October 2014 - 11:08 AM.


#30 Cometeer

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Posted 19 October 2014 - 11:14 AM

 

You will would have to try them and see.  A #8 cuts ~50-60% of the purple CA whereas the 495 LP cuts 100% of  the purple CA. With an ED  scope I would think the #8 LY would be sufficient. 

 

So far I don't see that my C80 ED requires any CA filter, whether for planet/lunar, double stars or DSO.  

 

I have a 2" Baader SemiAPO filter.  At the suggestion of a poster in another thread, I tried the SemiAPO on the 80mm ED.  It did not improve the view.  For the Moon, it made the image a bit dimmer and "muddier" looking, with a yellowish tinge.  But it did not improve the contrast or allow me to see fine detail such as rilles any easier. The image was better without the filter.

 

Mike

 

 

I was thinking of going with a  C80, but then I'd need to buy a tripod for it which defeated my purpose of an ultra portable scope. I mount my AT72ED on sturdy camera tripod that I have at home, but the tripod cannot properly support a C80. The AT72 has virtually no CA i can see except when I roll my eyeball around, I can see a little purple around the moon. It may not be as good as a C80 (different glass elements used), but it suits my needs fine.


Edited by astronomylife, 19 October 2014 - 11:15 AM.


#31 Sarkikos

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Posted 19 October 2014 - 11:16 AM

You might be able to mount the C80 ED on your photo tripod, depending on how sturdy it is and what kind of head it has.  A 501HDV on Bogen tripod carries my C80 ED very well indeed.

 

Mike



#32 Sarkikos

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Posted 19 October 2014 - 11:23 AM

I should have mentioned how I attach the C80 ED to the 501HDV.  The 501HDV has a quick-release plate with a 1/4-20 bolt.  I bought a dovetail shoe with 1/4-20 hole from ScopeStuff.  I attach this shoe to the quick-release plate, allowing me to mount the C80 ED to the 501HDV  You should be able to do this with any photo tripod with a 1/4-20 bolt.  But I would make sure the head and tripod have the capacity to handle the C80 ED.

 

http://www.scopestuff.com/ss_ds13.htm

 

Mike



#33 russell23

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Posted 19 October 2014 - 11:48 AM

The C80 ED from AWB is well worth the cost/aperture ratio at $349.

 

Mike

 

Mike,

 

I never said any particular scope (APO or achro) was or was not worth the cost for its aperture.  What I said is that the cost per aperture is a factor sometimes when there is a specific aperture goal in mind.   If you want a 6" refractor and have $1000 to spend, then an achromat is an option, but an APO is not.  That is all I meant.  I was agree with you.  Green is the overall best way to fix the problem with achromat CA, but not everyone has the $$ for the APO and still meet the aperture goal for their refractor purchase.  And News/Cats can be left out of this because some people like the attributes of refractors. 

 

Dave



#34 russell23

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Posted 19 October 2014 - 11:53 AM

 

You will would have to try them and see.  A #8 cuts ~50-60% of the purple CA whereas the 495 LP cuts 100% of  the purple CA. With an ED  scope I would think the #8 LY would be sufficient. 

 

So far I don't see that my C80 ED requires any CA filter, whether for planet/lunar, double stars or DSO.  

 

I have a 2" Baader SemiAPO filter.  At the suggestion of a poster in another thread, I tried the SemiAPO on the 80mm ED.  It did not improve the view.  For the Moon, it made the image a bit dimmer and "muddier" looking, with a yellowish tinge.  But it did not improve the contrast or allow me to see fine detail such as rilles any easier. The image was better without the filter.

 

Mike

 

 

Mike,

 

The OP has an ED scope and sees some CA that he is looking to eliminate - that was the purpose of this thread.  I had a Vixen 80EDSf scope myself last fall and did not see any problems with CA.  My point in this quote above was that if the OP feels there is some CA he wants to eliminate, then the #8 light yellow would be sufficient for that purpose I would think.  The 495 LP would seem to be overkill.

 

I agree about the Semi-APO filter - for an achromat too.  The Semi-APO dims the image needlessly while offering no additional CA reduction beyond a #8 LY or a Baader Fringe Killer.  Some people love the semi-APO and that is great for them.  I did not like it that much myself. 

 

Dave



#35 Cometeer

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Posted 19 October 2014 - 11:56 AM

Thanks Dave, I'll go with a  #8 yellow filter. A 2" filter is 49mm right?



#36 Sarkikos

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Posted 19 October 2014 - 12:10 PM

 

The C80 ED from AWB is well worth the cost/aperture ratio at $349.

 

Mike

 

Mike,

 

I never said any particular scope (APO or achro) was or was not worth the cost for its aperture.  What I said is that the cost per aperture is a factor sometimes when there is a specific aperture goal in mind.   If you want a 6" refractor and have $1000 to spend, then an achromat is an option, but an APO is not.  That is all I meant.  I was agree with you.  Green is the overall best way to fix the problem with achromat CA, but not everyone has the $$ for the APO and still meet the aperture goal for their refractor purchase.  And News/Cats can be left out of this because some people like the attributes of refractors. 

 

Dave

 

 

Personally, I don't think I've ever wanted a 6" achromat more than about 15 minutes.  After some thought, I soon recall the weight, the long unwieldy tube, the difficulty of mounting, the long range in eyepiece height, the surfeit of easy portability, the surplus of bothersome CA and the fact that after all, it is only a 6" aperture.  A 6" APO would have all those disadvantages, except for the CA, and with the additional disadvantage of a very hefty price tag. No 6" refractor for me, thank you very much! :grin:

 

After considering all the pros and cons, I think that $349 for an 80mm ED is a very good deal!

 

:grin:

Mike


Edited by Sarkikos, 19 October 2014 - 12:11 PM.


#37 mogur

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Posted 19 October 2014 - 12:59 PM

 

 

 

Personally, I don't think I've ever wanted a 6" achromat more than about 15 minutes.  

 

 

Yeah, to each his own. That's kind of the way I feel about an 80mm. I guess they're OK for low power wide field, but then why spend the extra $ for an apo? I find them too dim for planets when you try to push the power up. I feel they're pretty much an AP tool and that's it. That's where they really shine.



#38 russell23

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Posted 19 October 2014 - 01:03 PM

 

 

The C80 ED from AWB is well worth the cost/aperture ratio at $349.

 

Mike

 

Mike,

 

I never said any particular scope (APO or achro) was or was not worth the cost for its aperture.  What I said is that the cost per aperture is a factor sometimes when there is a specific aperture goal in mind.   If you want a 6" refractor and have $1000 to spend, then an achromat is an option, but an APO is not.  That is all I meant.  I was agree with you.  Green is the overall best way to fix the problem with achromat CA, but not everyone has the $$ for the APO and still meet the aperture goal for their refractor purchase.  And News/Cats can be left out of this because some people like the attributes of refractors. 

 

Dave

 

 

Personally, I don't think I've ever wanted a 6" achromat more than about 15 minutes.  After some thought, I soon recall the weight, the long unwieldy tube, the difficulty of mounting, the long range in eyepiece height, the surfeit of easy portability, the surplus of bothersome CA and the fact that after all, it is only a 6" aperture.  A 6" APO would have all those disadvantages, except for the CA, and with the additional disadvantage of a very hefty price tag. No 6" refractor for me, thank you very much! :grin:

 

After considering all the pros and cons, I think that $349 for an 80mm ED is a very good deal!

 

:grin:

Mike

 

 

My 5.5" refractor rides on a Vixen Super-Polaris mount - with the only mount upgrade being better tripod legs.  There are some vibrations, but very portable.  I can pick up the entire assembly and carry it round my back yard.

 

Dave



#39 Sarkikos

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Posted 19 October 2014 - 03:14 PM

 

My 5.5" refractor rides on a Vixen Super-Polaris mount - with the only mount upgrade being better tripod legs.  There are some vibrations, but very portable.  I can pick up the entire assembly and carry it round my back yard.

 

Dave

 

 

Yes, but could you carry it mounted down a flight of a half-dozen steps and then walk it 300'?  That's what I would need to do for real grab-n-go.  Maybe I could break it down into at least two trips.  But if I did that, I might as well take out my 10" Dob.

 

On the other hand, the 10" Dob would take some time for cool-down during the colder months. That's why I'm considering about a 5" ED.

 

Mike


Edited by Sarkikos, 19 October 2014 - 03:17 PM.


#40 russell23

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Posted 19 October 2014 - 03:33 PM

 

 

My 5.5" refractor rides on a Vixen Super-Polaris mount - with the only mount upgrade being better tripod legs.  There are some vibrations, but very portable.  I can pick up the entire assembly and carry it round my back yard.

 

Dave

 

 

Yes, but could you carry it mounted down a flight of a half-dozen steps and then walk it 300'?  That's what I would need to do for real grab-n-go.  Maybe I could break down into at least two trips.  But if I did that, I might as well take out my 10" Dob.

 

Mike

 

Yes I could.  I've walked it down three steps and then 40' which is easy. Another 3 steps and 260 feet would not be a deal breaker but I'd definitely be a little tired at the end.  No doubt about that!   :) 

 

The most unwieldy part is getting in and out the door with the Vixen 140.   The SV80/9D is much easier getting through a doorway.  The difference in OTA weight between the two is about 8 pounds and not really a factor compared to the mount weight.

 

But that said the C80 ED is certainly much easier than the Vixen 140 on Superpolaris mount.  You can put it on a lighter mount such as a Porta II, it is shorter so the door is easier to get through, and you can have an eyepiece case in one hand which I cannot do if moving the Vixen 140 around my property.  So definitely if you routinely travel 300' that would be preferable to a 6" refractor.  

 

Dave



#41 Sarkikos

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Posted 19 October 2014 - 06:36 PM

 

 

 

 

Personally, I don't think I've ever wanted a 6" achromat more than about 15 minutes.  

 

 

Yeah, to each his own. That's kind of the way I feel about an 80mm. I guess they're OK for low power wide field, but then why spend the extra $ for an apo? I find them too dim for planets when you try to push the power up. I feel they're pretty much an AP tool and that's it. That's where they really shine.

 

 

Define "low power."  I've had the C80 ED up to 200x with the 3mm setting of my Nag 6-3 Zoom. That's 63x per inch. This was for double stars. I'm sure I could have gone higher with better seeing.  It is excellent viewing the Moon at this power as well. But for lunar at 0.4mm exit pupil, my eye floaters start aggravating me.  That's my problem, not the C80 ED's. 

 

Maybe you're thinking about an ST80, which is an f/5 achromat.  I agree that the ST80 is only good for low power wide field.  But the C80 ED is not an ST80.  True, you can get a new ST80 for only $119. Worth every penny. But a new C80 ED is available now for $349.  IMO, a much better deal.

 

I would never buy an "AP tool." I don't give a fig for AP. AP is a good view ruined. :grin:

 

Mike


Edited by Sarkikos, 19 October 2014 - 06:37 PM.


#42 mogur

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Posted 19 October 2014 - 10:03 PM

Ya for the moon and point sources like stars they're OK. I used to own a Celestron Onyx and I remember being quite disappointed at how dim Saturn looked at 150x. I guess my bad eyes have narrowed my choices. :(


Edited by mogur, 19 October 2014 - 10:06 PM.


#43 Peter Besenbruch

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Posted 20 October 2014 - 01:56 PM

Here are a few unbiased :p observations:

 

A 6", f5 achromat isn't a good design. An optimized 6", f6 Newtonian would outperform it at both low and higher power. Using the rule of thumb that a top quality achromat should have a f-ratio of five times the diameter in inches, a 6" should be about f30.

 

Now there may be one or two people who claim that such a long telescope would be unwieldy, or too heavy. Bah! First, historically speaking, f30 isn't THAT long. Second, you can reduce the weight by employing an even earlier design. Behold! The f30 aerial achromat. Combining light weight with the reduced cost of the achromatic design, all you need is the country estate to put it on. ;)

 

As for the fancy glass type refractors, I agree with Dave. I may be able to afford a $6000-$20,000 tube assembly, but I would never spend it. Nor would I consider $4500-$7000 for a 5". That said, there is something of a battle going on in refractor land. I bought a 4.7" refractor tube assembly that included a 2" diagonal, two eyepieces, a decent finder, a case, and shipping for $1360. I bought a C80ED, like Mike, for $350. These instruments are good. For visual work they are all you need.

 

Going larger, Skywatcher produces a 6" triplet for $6000. For visual work, you can get a 6" Lunt, ED doublet for $4000. This is the instrument that went head to head with a 6" Takahashi in another thread. I wonder what a Chinese firm, like Synta would do with a 6", ED doublet, and what price it might go for?

 

The Chinese have begun to exert considerable downward pressure on fancy refractor prices. I think the 120mm size represents something of a sweet spot. It replaced a 6", f6 Parks Newtonian in my lineup. Does the refractor, gather more light? No. Does it do better on planets? Yes, I notice slightly better contrast. The 4.7" also does better on low power views, as it comes with a 2" focuser. The Parks was a little over half the cost of the Skywatcher 120ED, but came with lower quality, and fewer accessories. Had I designed a 6", f6 for good 2" focuser performance, I suspect the costs between it and the refractor would have been equal. That's when you know a design is viable.

 

As for the ED 6" sizes, their prices aren't there yet. A good 8", f6 or f7 Newtonian would match or beat the performance any 6" refractor.


Edited by Peter Besenbruch, 20 October 2014 - 02:03 PM.


#44 Cometeer

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Posted 01 November 2014 - 12:05 PM

I thought I'd post an update. I purchased a Hoya 85b filter and I can see little to a minuscule amount of CA. I also like the brownish tinge it applies. It was  great buy and I'd definitely recommend it.



#45 AR6

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Posted 01 November 2014 - 03:09 PM

I really like my 6" f/8 refractor, and I liked it even more once it was on a suitably large Atlas EQ-G mount, and with a decent 2 speed crayford focuser.   I've found with a Baader Semi-APO filter I get no noticeable CA on bright planetary or lunar targets, and I really appreciate the high contrast and sharp images it will offer.   For exmpel, last night I had great seeing and I could detect small 2 mile diameter craters like Thebit U, and it's something where I think the greater contrast produced in a refractor makes a difference that takes it beyond what you'd expect to see based only on the aperture compared to a reflector.  

 

I have the same opinion about the advantages of contrast with star clusters and  when it comes to nebulas, with the dimmer target and no need for a CA reducing filter, I think the increased contrast from the refractor makes up for the loss of a couple inches of aperture. 

 

Of course, I only have to haul the mount and tripod about 100' from garage to back yard (and I would not want to carry it much farther without breaking it down), and I added a handle to the OTA which makes carrying it a snap. 


Edited by AR6, 01 November 2014 - 03:10 PM.


#46 JustaBoy

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Posted 01 November 2014 - 03:34 PM

I have the Celestron and also have a 4" F/15 A. Yagers.

 

I never use a filter - I just ignore any false color, and so it really doesn't bother me.

 

Just think about the poor old guys having to use a 36" or 40" F/19 - Somehow they lived through it, or did they?

 

Still 'saving for my AP, but not sure that I will live long enough. - I did manage to put a 2.7" AP focuser on my 6" F/8, though:-)



#47 starcam

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Posted 01 November 2014 - 09:15 PM

I prefer the Baader Contrast Booster Filter, to decrease the ca in achromats, and it also increase contrast in apo's.

I have noticed ca correction with my carl zeiss jena ortho's in my wo 70 mm ed achromat.

And last but not least is the amici prisms are reported to decrease ca.


Edited by starcam, 02 November 2014 - 12:02 AM.



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