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FPL-51, FPL-53, FCD-100 question

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#1 lwhagood

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Posted 01 July 2017 - 12:29 PM

Hello,

   I'm pretty much a noob to astronomy, I've had a few inexpensive scopes in the past but plan to give it another go now that I have the means to get some relatively good equipment. I decided I wanted as large of an apochromatic triplet as I could get for under five kilobucks. I picked the 130mm apo currently offered by Stellarvue and I sent Vic a $500 deposit to get my name on the list for the next batch . Then I noticed that the specs page for all of the apo scopes on SV's website list the ED glass type as FPL-53, and their quad astrograph uses FCD-100, both glass types have an Abbe number of 95. The specs on the 130 just say "ED center element" searching through some forums I discovered this is FPL-51, which has an Abbe number of like 82 and everyone seems to agree that scopes with FPL-53 or FCD-100 are noticably better than those with FPL-51. So now this scope, that I am about to pay an additional $4200 for (scope flattener, FT focuser, diagonal and hard case) is gonna be worse than the new ES-127 carbon fiber with FCD-100 which costs about $1500 less! And maybe the next batch of SV 130's will have FCD-100 like their quad does. What should I do??! I'm freaking out!! 

Thank you for any advice!

-Larry



#2 HarryRik9

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Posted 01 July 2017 - 12:58 PM

Larry, I think this is the wrong forum for this question. I think you ought to go to this forum:https://groups.yahoo...Stellarvue/info

 

Your question was confusing to me since there are different versions of the scope. Which one are you talking about? I think the question you are asking ought to be sent to Vic or Dan at Stellarvue. 


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#3 mistateo

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Posted 01 July 2017 - 01:13 PM

Agree with Harry.  Vic will help you find the scope you want.  You can also get an optics test report on any scope you buy.


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#4 lwhagood

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Posted 01 July 2017 - 01:22 PM

Okay thank you!! I'll email Vic.
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#5 bobzeq25

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Posted 01 July 2017 - 01:22 PM

Hello,

   I'm pretty much a noob to astronomy, I've had a few inexpensive scopes in the past but plan to give it another go now that I have the means to get some relatively good equipment. I decided I wanted as large of an apochromatic triplet as I could get for under five kilobucks. I picked the 130mm apo currently offered by Stellarvue and I sent Vic a $500 deposit to get my name on the list for the next batch . Then I noticed that the specs page for all of the apo scopes on SV's website list the ED glass type as FPL-53, and their quad astrograph uses FCD-100, both glass types have an Abbe number of 95. The specs on the 130 just say "ED center element" searching through some forums I discovered this is FPL-51, which has an Abbe number of like 82 and everyone seems to agree that scopes with FPL-53 or FCD-100 are noticably better than those with FPL-51. So now this scope, that I am about to pay an additional $4200 for (scope flattener, FT focuser, diagonal and hard case) is gonna be worse than the new ES-127 carbon fiber with FCD-100 which costs about $1500 less! And maybe the next batch of SV 130's will have FCD-100 like their quad does. What should I do??! I'm freaking out!! 

Thank you for any advice!

-Larry

Advice.  Don't freak out.  As someone suggested, talk to Stellarvue about what might be the right scope for you.

 

And understand that all FPL-53 lenses are not better than all FPL-51 lenses, lens design counts.  And, there's more to a good scope than the lens, in particular, if you're thinking about imaging, the focuser is important.

 

Also, if you're going to mostly be imaging, aperture counts less than you might think.  The choice between a bigger scope, and a better smaller one, is a frequent dilemma for imagers.


Edited by bobzeq25, 01 July 2017 - 01:25 PM.


#6 jeremiah2229

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Posted 01 July 2017 - 03:32 PM

I use the SV130EDT here, an older model with "equivalent FPL-51" as are most of the Chinese triplets are that do not specifically state FPL this or that. As bobzeq25 shared the cell design is where it all begins. My sample is just fine visually, no complaints at all. Will it produce an image as good as a TOA/A-P/TEC? I have no idea. Will a TOA/A-P/TEC leave it in the dust? Absolutely not. The glass is smooth, the in focus images are as good as any of my now/or was FPL-53/Fluorite and the images before/after focus are text book. Don't get caught up on advertizing hype, just enjoy what you are blessed to have.

 

 

Peace...


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#7 Jon Isaacs

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Posted 02 July 2017 - 07:05 AM

Advice.  Don't freak out.  As someone suggested, talk to Stellarvue about what might be the right scope for you.

And understand that all FPL-53 lenses are not better than all FPL-51 lenses, lens design counts.  And, there's more to a good scope than the lens, in particular, if you're thinking about imaging, the focuser is important.

Also, if you're going to mostly be imaging, aperture counts less than you might think.  The choice between a bigger scope, and a better smaller one, is a frequent dilemma for imagers.

Lens design does count as does the execution of the design.  But these are lenses manufactured in a Asian factory and one cannot ignore the advantages of FPL-53, it's not hyperbole... 

 

Jon


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#8 AtmosFearIC

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Posted 02 July 2017 - 07:40 AM

A good FPL-51 will beat a poorly executed FPL-53 every time. FPL-53 allows for faster scopes to be made with good colour correction. For instance, you can build a F/5-6 with FPL-53 but you may not want to go faster than F/7 with FPL-51.

#9 Jon_Doh

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Posted 02 July 2017 - 08:01 AM

I like the TS Photoline 130 with FPL-53 glass.  It's well made and gets good reviews. It has a good focuser, but you can upgrade to larger focusers for a reasonable cost.  The starting model is less than two grand including shipping.



#10 Max Power

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Posted 02 July 2017 - 08:13 AM

I have 3 fpl-53 triples that are keepers forever: 90, 107, 130mm's. All from Asia. The other 35 fracs of other glass types got sold.

Mite dabble in a fluorite double, come on APM build it.

#11 Nippon

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Posted 03 July 2017 - 09:07 PM

I know how you feel because I ordered a CPO SV 115T from Stellarvue and after the fact realized it did not specify FPL53 as one of the elements in the objective. But like you searched on the internet for reviews and opinions. Most said it was good but some suggested that Stellarvue was not being transparent with some of their offerings. I decided to trust Stellarvue's reputation. So far after having it about a month it appears to be very good optically. I have compared it to my Vixen 103 FPL 53 doublet and my Stellarvue 80mm ST FPL 53 triplet and the 115 appears to be just as color free as either of my FPL 53 scopes. Summer in Florida is not observing friendly. It is cloudy most nights and by chance if it is clear the air is really saturated with moisture not to mention it's hot. So I have not had a chance to use the 115 as much as I'd like but one evening that was okay seeing wise I was looking at the Moon with it and paying attention to the limb for any color error. I did not see any color but what I did see was the most stark contrast of bright Moon to black sky at the limb I have ever seen. There was no fading of white to gray to black. The moon was super bright white and the sky was pitch black. I should also mention that when I first received the SV 115T it was out of collimation. I emailed Vic. He replied almost immediately, expressed surprise and told me to send it back. It was back in about 12 days, perfectly collimated and Vic gave me a brand new 2" diagonal for my trouble. In other words they were great when there was a problem and taking care of this customer. It is about more than "FPL53." Lens design, mating elements all count. LOMO lenses are highly regarded and use OK4 glass that I believe has an Abbe number somewhere between FPL 51 and FPL 52. So as someone who has just recently experienced the exact same anxiety you are feeling. My story had a very happy ending:)  


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#12 Jon Isaacs

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Posted 05 July 2017 - 06:18 AM

It is about more than "FPL53." Lens design, mating elements all count. LOMO lenses are highly regarded and use OK4 glass that I believe has an Abbe number somewhere between FPL 51 and FPL 52.

 

 

OK-4 is much closer to FPL-53 than it is to FPL-51.  it's about halfway between FPL-52 and FPL-53..

 

Most said it was good but some suggested that Stellarvue was not being transparent with some of their offerings.

 

 

 

StellarVue seems to mention it when the objective uses FPL-53. In general they won't tell say what it uses if it's not FPL-53.  That's how you can tell.

 

Jon


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#13 Ken Sturrock

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Posted 06 July 2017 - 01:55 AM

Interesting about the SVQ. It may be a recent lens change as mine allegedly has FPL-53.

 

Having said that, obsessing over the composition of a single lens element alone is simplistic. Sure, the glass matters, but we also tend to reduce a system to a single number with no context, be that number horsepower, calories, watts or square footage. It doesn't usually tell the whole story.

 

I will say that my (maybe) FPL-53 SVQ is just as color free as my older OK-4 triplets (each with different focal ratios) are. 


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#14 mikeDnight

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Posted 06 July 2017 - 03:14 AM

Hello,

   I'm pretty much a noob to astronomy, I've had a few inexpensive scopes in the past but plan to give it another go now that I have the means to get some relatively good equipment. I decided I wanted as large of an apochromatic triplet as I could get for under five kilobucks. I picked the 130mm apo currently offered by Stellarvue and I sent Vic a $500 deposit to get my name on the list for the next batch . Then I noticed that the specs page for all of the apo scopes on SV's website list the ED glass type as FPL-53, and their quad astrograph uses FCD-100, both glass types have an Abbe number of 95. The specs on the 130 just say "ED center element" searching through some forums I discovered this is FPL-51, which has an Abbe number of like 82 and everyone seems to agree that scopes with FPL-53 or FCD-100 are noticably better than those with FPL-51. So now this scope, that I am about to pay an additional $4200 for (scope flattener, FT focuser, diagonal and hard case) is gonna be worse than the new ES-127 carbon fiber with FCD-100 which costs about $1500 less! And maybe the next batch of SV 130's will have FCD-100 like their quad does. What should I do??! I'm freaking out!! 

Thank you for any advice!

-Larry

Hi Larry,

 

A few years ago I had chance to compare a SW 120ED doublet, which uses FPL53, with a friend's Meade 127 FPL51 triplet over an extended period. The 120ED is a very good visual scope showing very little CA either side of focus and essentially none in focus. The Meade 127 using FPL51 was an amazingly good scope optically, with zero CA visible at any time. It's images were razor sharp and its colours true, and as a visual scope it was flawless. I'm only mentioning this as what appears to be an inferior scope due to glass type choices, isn't always so. The mating elements along with the quality of figure are just as important as the FPL53 vs FPL51 debate.

There's a lot of debate about the advantages of one glass type or design over another, and graphs, Abbe numbers and Strehl ratios, though going some way to revealing a Scopes potential, tell only part of the story. Some scope manufacturers provide certificates with their instruments but the greatest variable, the observer, is uncertifiable, though some should be!

If you'd feel happier going for the ES 127 and saving yourself a small fortune in the process, then that's the way to go. If you're happy with Stellarvue and their reputation for delivering high end instruments, then may be the extra money will be well spent.

Go with your heart as well as your head! 

 

Mike



#15 lwhagood

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Posted 06 July 2017 - 03:37 AM

Thank you for all the replies. I emailed Vic explaining my concerns, he replied with a very lengthy infomative response that put me at ease. Basically he repeated what has been said here. He did say that the center element is NOT FPL-51 bud did not elaborate. He assured me that I would be getting as perfect an instrument as Stellarvue could provide for the money I'm spending. And givin their reputation, thats good enough fo me. It's set to ship at the end of august. I can't wait!!
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#16 jring

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Posted 06 July 2017 - 01:41 PM

Thank you for all the replies. I emailed Vic explaining my concerns, he replied with a very lengthy infomative response that put me at ease. Basically he repeated what has been said here. He did say that the center element is NOT FPL-51 bud did not elaborate. He assured me that I would be getting as perfect an instrument as Stellarvue could provide for the money I'm spending. And givin their reputation, thats good enough fo me. It's set to ship at the end of august. I can't wait!!


Hi,

it's most probably some chinese FPL-51 alternative. In a triplet at f7 you're going to be fine.

Joachim

#17 John Huntley

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Posted 06 July 2017 - 01:46 PM

 

Hello,

   I'm pretty much a noob to astronomy, I've had a few inexpensive scopes in the past but plan to give it another go now that I have the means to get some relatively good equipment. I decided I wanted as large of an apochromatic triplet as I could get for under five kilobucks. I picked the 130mm apo currently offered by Stellarvue and I sent Vic a $500 deposit to get my name on the list for the next batch . Then I noticed that the specs page for all of the apo scopes on SV's website list the ED glass type as FPL-53, and their quad astrograph uses FCD-100, both glass types have an Abbe number of 95. The specs on the 130 just say "ED center element" searching through some forums I discovered this is FPL-51, which has an Abbe number of like 82 and everyone seems to agree that scopes with FPL-53 or FCD-100 are noticably better than those with FPL-51. So now this scope, that I am about to pay an additional $4200 for (scope flattener, FT focuser, diagonal and hard case) is gonna be worse than the new ES-127 carbon fiber with FCD-100 which costs about $1500 less! And maybe the next batch of SV 130's will have FCD-100 like their quad does. What should I do??! I'm freaking out!! 

Thank you for any advice!

-Larry

Hi Larry,

 

A few years ago I had chance to compare a SW 120ED doublet, which uses FPL53, with a friend's Meade 127 FPL51 triplet over an extended period. The 120ED is a very good visual scope showing very little CA either side of focus and essentially none in focus. The Meade 127 using FPL51 was an amazingly good scope optically, with zero CA visible at any time. It's images were razor sharp and its colours true, and as a visual scope it was flawless. I'm only mentioning this as what appears to be an inferior scope due to glass type choices, isn't always so. The mating elements along with the quality of figure are just as important as the FPL53 vs FPL51 debate.

There's a lot of debate about the advantages of one glass type or design over another, and graphs, Abbe numbers and Strehl ratios, though going some way to revealing a Scopes potential, tell only part of the story. Some scope manufacturers provide certificates with their instruments but the greatest variable, the observer, is uncertifiable, though some should be!

If you'd feel happier going for the ES 127 and saving yourself a small fortune in the process, then that's the way to go. If you're happy with Stellarvue and their reputation for delivering high end instruments, then may be the extra money will be well spent.

Go with your heart as well as your head! 

 

Mike

 

Interesting Mike.

 

A few years back I had the opportunity to do the same comparison - My ED120 alongside a mates Meade 127 triplet for 3 clear nights. Both great scopes but in this case the Meade triplet was showing more CA than the ED120 around bright targets at focus.

 

Other than that there was little difference between them. The ED120 cooled more quickly and was quite a bit lighter and less bulky, both of which are quite important assets to me smile.gif



#18 Ken Sturrock

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Posted 06 July 2017 - 02:01 PM

Hi,

it's most probably some chinese FPL-51 alternative. In a triplet at f7 you're going to be fine.

Joachim

FCD-100 appears to be more of an FPL-53 alternative (versus FPL-51) by a different Japanese company. Particular runs may, of course, vary.



#19 jeremiah2229

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Posted 06 July 2017 - 02:15 PM

Thank you for all the replies. I emailed Vic explaining my concerns, he replied with a very lengthy infomative response that put me at ease. Basically he repeated what has been said here. He did say that the center element is NOT FPL-51 bud did not elaborate. He assured me that I would be getting as perfect an instrument as Stellarvue could provide for the money I'm spending. And givin their reputation, thats good enough fo me. It's set to ship at the end of august. I can't wait!!

It's nose heavy... the FT option helps with the ballast as does a RACI riding the FT.  ;)

 

Have fun and enjoy...



#20 Jared

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Posted 06 July 2017 - 03:49 PM

At f/7, it's almost certainly using an FPL-51 analog such as FCD-1 or H-FK61.  They are equivalent to FPL-51.  Basically, for a 130mm class telescope, the use of FPL-51 or equivalent will limit you to a focal ratio of f/7 or so if you want good color correction.  It is certainly possible to create a visually "color free" FPL-51/FCD-1/H-FK61 based telescope, so no issue there.  And there is nothing intrinsically "lower quality" about FPL-51 or its analogs.  You just can't make as fast a scope with it for a given color correction.

 

You mentioned that you were getting the upgraded version with the feather touch focuser and the flattener.  Do you plan on imaging with the telescope?  Or will your use be primarily visual?  If visual, you don't really need the flattener but the FT focuser is still a nice upgrade.  Plus, it's not a bad idea to get the appropriate flattener with the telescope since matched flatteners can be hard to find at a later date if you eventually decide to try out imaging or if you want to resell the telescope and the acquiring party happens to be an imager.  In other words, no problem buying the flattener now if if you don't have immediate plans to image.

 

If you are planning on using the scope exclusively for imaging, I might give some thought to swapping out your 130mm for the Stellarvue SVQ100.  You'd be trading some aperture for better color correction.  While I wouldn't make that trade for a mixed use telescope, for pure imaging it might be a better choice.  Better still would be the 130mm f/5 sextuplet, but that's a lot more money than you were planning on spending.

 

Again, for visual or mixed use, nothing wrong with the scope you ordered. FPL-51 and its analogs do just fine.  For purely astrophotographic use, I'd recommend the 4", downgrading size but getting the scope with the better color correction, the designed-in flattener, and the larger imaging circle.


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#21 lwhagood

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Posted 06 July 2017 - 04:47 PM

At f/7, it's almost certainly using an FPL-51 analog such as FCD-1 or H-FK61.  They are equivalent to FPL-51.  Basically, for a 130mm class telescope, the use of FPL-51 or equivalent will limit you to a focal ratio of f/7 or so if you want good color correction.  It is certainly possible to create a visually "color free" FPL-51/FCD-1/H-FK61 based telescope, so no issue there.  And there is nothing intrinsically "lower quality" about FPL-51 or its analogs.  You just can't make as fast a scope with it for a given color correction.

 

You mentioned that you were getting the upgraded version with the feather touch focuser and the flattener.  Do you plan on imaging with the telescope?  Or will your use be primarily visual?  If visual, you don't really need the flattener but the FT focuser is still a nice upgrade.  Plus, it's not a bad idea to get the appropriate flattener with the telescope since matched flatteners can be hard to find at a later date if you eventually decide to try out imaging or if you want to resell the telescope and the acquiring party happens to be an imager.  In other words, no problem buying the flattener now if if you don't have immediate plans to image.

 

If you are planning on using the scope exclusively for imaging, I might give some thought to swapping out your 130mm for the Stellarvue SVQ100.  You'd be trading some aperture for better color correction.  While I wouldn't make that trade for a mixed use telescope, for pure imaging it might be a better choice.  Better still would be the 130mm f/5 sextuplet, but that's a lot more money than you were planning on spending.

 

Again, for visual or mixed use, nothing wrong with the scope you ordered. FPL-51 and its analogs do just fine.  For purely astrophotographic use, I'd recommend the 4", downgrading size but getting the scope with the better color correction, the designed-in flattener, and the larger imaging circle.

It will be mixed use and he said the flattener will be matched to the scope. This brings it to f/5, will that be too fast for the 51 equivalent objective or does it not matter since the light cone is f/7 between the objective and the flattener? (sorry if this is a dumb question or worded wrong) I've never imaged before but plan to get started with this scope and the ZWO ASI1600MM Cool camera, ZWO OAG and one of their cheaper monochrome cams as a guider. All on a CEM-60 mount.  I thought about getting the Quad, but on their page it says even though it can be used visually with an adapter, the views are not as good as the other apos. Not sure why this would be the case but that statement scared me off. Vic did say that Ohara only offers the FCD-100 in pressings and he does not like to use pressings in his visual instruments. 



#22 lwhagood

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Posted 07 July 2017 - 02:37 AM

Dangit I meant Hoya, not Ohara.

#23 Jon Isaacs

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Posted 07 July 2017 - 08:53 AM

 

Hi,

it's most probably some chinese FPL-51 alternative. In a triplet at f7 you're going to be fine.

Joachim

FCD-100 appears to be more of an FPL-53 alternative (versus FPL-51) by a different Japanese company. Particular runs may, of course, vary.

 

 

StellarVue seems to source their 130mm F/7 triplets from the same manufacturer that Orion, Meade, AstroTech etc use and those refractors are all based on the Chinese equivalent of FPL-51, FK-61.

 

If it had been FCD-100 or FPL-53, that would have been promoted.  

 

Jon


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#24 Jared

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Posted 07 July 2017 - 10:09 AM


At f/7, it's almost certainly using an FPL-51 analog such as FCD-1 or H-FK61. They are equivalent to FPL-51. Basically, for a 130mm class telescope, the use of FPL-51 or equivalent will limit you to a focal ratio of f/7 or so if you want good color correction. It is certainly possible to create a visually "color free" FPL-51/FCD-1/H-FK61 based telescope, so no issue there. And there is nothing intrinsically "lower quality" about FPL-51 or its analogs. You just can't make as fast a scope with it for a given color correction.

You mentioned that you were getting the upgraded version with the feather touch focuser and the flattener. Do you plan on imaging with the telescope? Or will your use be primarily visual? If visual, you don't really need the flattener but the FT focuser is still a nice upgrade. Plus, it's not a bad idea to get the appropriate flattener with the telescope since matched flatteners can be hard to find at a later date if you eventually decide to try out imaging or if you want to resell the telescope and the acquiring party happens to be an imager. In other words, no problem buying the flattener now if if you don't have immediate plans to image.

If you are planning on using the scope exclusively for imaging, I might give some thought to swapping out your 130mm for the Stellarvue SVQ100. You'd be trading some aperture for better color correction. While I wouldn't make that trade for a mixed use telescope, for pure imaging it might be a better choice. Better still would be the 130mm f/5 sextuplet, but that's a lot more money than you were planning on spending.

Again, for visual or mixed use, nothing wrong with the scope you ordered. FPL-51 and its analogs do just fine. For purely astrophotographic use, I'd recommend the 4", downgrading size but getting the scope with the better color correction, the designed-in flattener, and the larger imaging circle.

It will be mixed use and he said the flattener will be matched to the scope. This brings it to f/5, will that be too fast for the 51 equivalent objective or does it not matter since the light cone is f/7 between the objective and the flattener? (sorry if this is a dumb question or worded wrong) I've never imaged before but plan to get started with this scope and the ZWO ASI1600MM Cool camera, ZWO OAG and one of their cheaper monochrome cams as a guider. All on a CEM-60 mount. I thought about getting the Quad, but on their page it says even though it can be used visually with an adapter, the views are not as good as the other apos. Not sure why this would be the case but that statement scared me off. Vic did say that Ohara only offers the FCD-100 in pressings and he does not like to use pressings in his visual instruments.

You should be fine. The 1600 is not a very large chip, so no need for a larger imaging circle. The color may be slightly less than perfect when imaging (f/5 is pretty fast for an FPL-51 triplet), but as an imager just starting out I expect it will keep you happy for years. All scopes are compromises, and you need this one to be useful for both visual and photography. If you were to switch to the 4" quad you'd be giving up much more visually. The 130 is the better overall choice for the uses you are describing.

Honestly, I don't know of a reason the 4" would be "not as good" visually once you add appropriate adapters. Perhaps Vic is just referring to the fact that you would always have a field flattener in place, so there is more glass than you technically need? Not sure. Lots of planetary observers will pay extra and suffer through narrow fields of view and poor eye relief to get rid of an element or two in their eyepieces. It could be the same thing here. Or maybe Vic has found that some eyepieces don't work as well with a perfectly flat field--I suspect some wide field designs have some field flattening built in to the design in order to correct for mild field curvature in telescopes. I'm sure Vic has used his own scopes, though, so he would know.

#25 Ken Sturrock

Ken Sturrock

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Posted 07 July 2017 - 10:24 AM

StellarVue seems to source their 130mm F/7 triplets from the same manufacturer that Orion, Meade, AstroTech etc use and those refractors are all based on the Chinese equivalent of FPL-51, FK-61.
 
If it had been FCD-100 or FPL-53, that would have been promoted.  
 
Jon

Yes, Jon. In this case, I got my wires crossed in reference to the scope under discussion and the SVQ, so I suspect that you and jring are right.




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