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why no 4 inch f6 fpl53 doublets?

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#1 jag767

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Posted 24 January 2014 - 08:01 PM

Title kinda asks the question. If a 120mm can have acceptable correction at f7.5 with fpl53 glass, why arent there any f6 or so 4 inch fpl53 refractors out there? It would really fit well in the skywatcher line IMO.

#2 jrbarnett

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Posted 24 January 2014 - 09:20 PM

To be equivalent, a 4-incher would need to be ~f/6.3.

You can get a near perfectly color corrected f/6.5 4" FPL-53 triplet for around $1700. Could you sell a similar focal ratio and aperture doublet for enough to both (a) make a profit and (b) attract business away from the better color corrected triplet?

My guess is that there's not a great business case for it. If I wanted an easy mounting 4" doublet today, I'd go with the new Tak FC100D. It's featherweight and slow enough to offer a reasonably flat field and perform well with any eyepiece design.

Regards,

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#3 Djarum

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Posted 24 January 2014 - 09:33 PM

Id like to see a fpl53 f6 110mm doublet.

#4 The Mighty Mo

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Posted 24 January 2014 - 09:44 PM

About the closest I know of you guys are asking for is the Lunt f/7 102ED, but I don't know what the ED element is.

#5 jag767

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Posted 24 January 2014 - 09:45 PM

Oh absolutely there are solutions in the triplet arena, but here's my thought process:

Look how many f9 ed100's sell and have sold. Adding the versatility of a much wider field has to be worth something to more than just me or those faster triplets wouldnt exist. I guess the question is would it cost more to make it at lets say f6.5 to satisfy proper correction than at f9? If so how much more? I just see this is as a great fit in the skywatcher line since they seem to be a great value per dollar option with fpl53 doublets, maybe they could make it work?

Would anyone else have interest in such an optical tube?

#6 skullpin

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Posted 25 January 2014 - 04:13 AM

Borg has a 5" f/6 FPL-53 doublet.

Keith

#7 Jon Isaacs

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Posted 25 January 2014 - 06:55 AM

About the closest I know of you guys are asking for is the Lunt f/7 102ED, but I don't know what the ED element is.


I would be the Chinese version of FPL-51.

I had written FPL-53 but that was a mistake I made typing on my cell phone.

This topic comes up every so often, I would like to see a 100mm F/7 from Skywatcher with an FPL-53 element. This has been discussed a few times. Not so long ago, Skyward Eyes, (Kevin Legore) who is listed as a Skywatcher Vendor, said he would pass it along.

Having owned the AT-102ED, F/7 makes a reasonably compact 4 inch..

Jon

#8 jag767

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Posted 25 January 2014 - 07:05 AM

About the closest I know of you guys are asking for is the Lunt f/7 102ED, but I don't know what the ED element is.


I would be the Chinese version of FPL-53.

This topic comes up every so often, I would like to see a 100mm F/7 from Skywatcher with an FPL-53 element. This has been discussed a few times. Not so long ago, Skyward Eyes, (Kevin Legore) who is listed as a Skywatcher Vendor, said he would pass it along.

Having owned the AT-102ED, F/7 makes a reasonably compact 4 inch..

Jon


I would be fine with at the slowest f7, especially if it could be priced right around the f9 variant. I would be interested to hear Kevin weigh in on this, maybe shed a little light as to the possibility that it could happen :question:

#9 Jon Isaacs

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Posted 25 January 2014 - 07:21 AM

I would be fine with at the slowest f7, especially if it could be priced right around the f9 variant. I would be interested to hear Kevin weigh in on this, maybe shed a little light as to the possibility that it could happen



I think you would have to expect it to be priced somewhat higher than the F/9 version as the objective would be more difficult to make.. Say $900 in standard Skywatcher trim with the 2 inch diagonal and everything. I would like to see a sliding dew shield too.

Jon

#10 photiost

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Posted 25 January 2014 - 07:36 AM


I would be fine with at the slowest f7, especially if it could be priced right around the f9 variant. I would be interested to hear Kevin weigh in on this, maybe shed a little light as to the possibility that it could happen



I think you would have to expect it to be priced somewhat higher than the F/9 version as the objective would be more difficult to make.. Say $900 in standard Skywatcher trim with the 2 inch diagonal and everything. I would like to see a sliding dew shield too.

Jon


I would definitely be interested.

:cool:

#11 Jon Isaacs

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Posted 25 January 2014 - 07:48 AM


I would be fine with at the slowest f7, especially if it could be priced right around the f9 variant. I would be interested to hear Kevin weigh in on this, maybe shed a little light as to the possibility that it could happen



I think you would have to expect it to be priced somewhat higher than the F/9 version as the objective would be more difficult to make.. Say $900 in standard Skywatcher trim with the 2 inch diagonal and everything. I would like to see a sliding dew shield too.

Jon


I would definitely be interested.

:cool:


I personally think it would be a killer, not only out under the night sky but also in the marketplace..

Jon

#12 jag767

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Posted 25 January 2014 - 08:07 AM


I would be fine with at the slowest f7, especially if it could be priced right around the f9 variant. I would be interested to hear Kevin weigh in on this, maybe shed a little light as to the possibility that it could happen



I think you would have to expect it to be priced somewhat higher than the F/9 version as the objective would be more difficult to make.. Say $900 in standard Skywatcher trim with the 2 inch diagonal and everything. I would like to see a sliding dew shield too.

Jon


I would definitely be interested.

:cool:


I personally think it would be a killer, not only out under the night sky but also in the marketplace..

Jon


If it had a sliding dew shield and compression fitting instead of just set screws for the diagonal I could get on board with a price around there, maybe a tad lower. And I also think they would have a hard time keeping it in stock!

#13 Kon Dealer

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Posted 25 January 2014 - 08:20 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.

#14 jag767

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Posted 25 January 2014 - 09:25 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount

#15 Vondragonnoggin

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Posted 25 January 2014 - 09:56 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount


I know which one you are referring to. Not a fan of red scopes either, but attractive price and looks to be a great visual scope. I like F/6.

Christmas knocked me out of the buyers market. Still waiting on a tripod and a 6" F/5, so I'll have to wait for tax return to look for g n g doublet like this.

There are places that will wrap it in black carbon fiber covering....

#16 jag767

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Posted 25 January 2014 - 10:30 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount


I know which one you are referring to. Not a fan of red scopes either, but attractive price and looks to be a great visual scope. I like F/6.

Christmas knocked me out of the buyers market. Still waiting on a tripod and a 6" F/5, so I'll have to wait for tax return to look for g n g doublet like this.

There are places that will wrap it in black carbon fiber covering....


I think I will pass on it, really want to see if we can get someone to pick up on building this to spec for us. I love my ed100, I just want it at f6.5/f7. same light weight, same glass, and shorter! The weight of the f9 is so light it can go on any mount, but the length of the moment arms kills it! if it werent for that I could even put it on my skyprodigy without a problem.

#17 Kon Dealer

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Posted 25 January 2014 - 10:42 AM

There is this 100mm, f/6 and according to the vendor FPL53;
http://www.telescope...tic_Refracto...
and this;
http://www.ebay.com/...ar-Power-Aus...

PS I have the smoke grey OTA :)

#18 jag767

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Posted 25 January 2014 - 10:46 AM

There is this 100mm, f/6 and according to the vendor FPL53;
http://www.telescope...tic_Refracto...
and this;
http://www.ebay.com/...ar-Power-Aus...

PS I have the smoke grey OTA :)


Post some pictures!

now if only those were sold in the US!

#19 The Mighty Mo

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Posted 25 January 2014 - 10:56 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount


I know which one you are referring to. Not a fan of red scopes either, but attractive price and looks to be a great visual scope. I like F/6.

Christmas knocked me out of the buyers market. Still waiting on a tripod and a 6" F/5, so I'll have to wait for tax return to look for g n g doublet like this.

There are places that will wrap it in black carbon fiber covering....


I think I will pass on it, really want to see if we can get someone to pick up on building this to spec for us. I love my ed100, I just want it at f6.5/f7. same light weight, same glass, and shorter! The weight of the f9 is so light it can go on any mount, but the length of the moment arms kills it! if it werent for that I could even put it on my skyprodigy without a problem.


Okay, I'm confused. You've been presented with two options here, both of which meet your wishes, yet you say you'll pass. The Lunt 102ED f/7 is everything you say you want. And the Kson 102 f/6 scope is also available in black, checkout the SmartAstronomy website.

Bit of past history, there have been many manufacturers, AT, Stellarvue, Orion, and others, who carried the exact same 102ED f/7 as the Lunt, and even 110ED's, under their name brand for quite a few years. But there wasn't enough of a market for them to continue carrying them, so they discontinued the lines. I doubt you're going to "will" any manufacturer or reseller to reintroduce them to a dry market just by bringing it up here on CN.

#20 jag767

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Posted 25 January 2014 - 11:03 AM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount


I know which one you are referring to. Not a fan of red scopes either, but attractive price and looks to be a great visual scope. I like F/6.

Christmas knocked me out of the buyers market. Still waiting on a tripod and a 6" F/5, so I'll have to wait for tax return to look for g n g doublet like this.

There are places that will wrap it in black carbon fiber covering....


I think I will pass on it, really want to see if we can get someone to pick up on building this to spec for us. I love my ed100, I just want it at f6.5/f7. same light weight, same glass, and shorter! The weight of the f9 is so light it can go on any mount, but the length of the moment arms kills it! if it werent for that I could even put it on my skyprodigy without a problem.


Okay, I'm confused. You've been presented with two options here, both of which meet your wishes, yet you say you'll pass. The Lunt 102ED f/7 is everything you say you want. And the Kson 102 f/6 scope is also available in black, checkout the SmartAstronomy website.


I am looking for fpl53 which i think the only viable one present is $1500. also want it to be light (less than 8 pounds) and around the price of skywatchers f/9 100. not to say I'm picky, but I am :grin:

#21 Pete-LH

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Posted 25 January 2014 - 11:09 AM

I am extremely interested in the Borg series of telescopes. I recently bought a used 60ED and I'm thinking of upgrading. Apparently there was a 101ED f/6.3 (part of the 80 series which still includes the 71FL-my target, 77EDII and 89ED).

See the CN review here;
Borg 101ED

#22 The Mighty Mo

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Posted 25 January 2014 - 11:19 AM

FPL 51 or FPL 53, big deal. For visual use only, you're not going to see much difference, if any at all. And if your intent is for a widefield scope to leverage the benefit of the small size and shorter f/l, you won't see a difference.

Besides, I believe Jon above said that the ED element in the Lunt is FPL 53, or at least the Chinese equivalent (which is where ALL these scopes come from anyway). If you want a specialty scope made to your specifications, you'd better expect to pay, making that $1500 look attractive. Sorry, we haven't figured out a way to cheat basic economics and marketing in the hobby yet.

Now, all that said, I do appreciate your comment on the weight. Have you taken into consideration that a shorter scope, if even a pound or two heavier, is still a much more manageable scope by virtue of its shorter moment arm, which offsets the weight issue and makes it much easier to mount?

#23 jag767

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Posted 25 January 2014 - 11:31 AM

FPL 51 or FPL 53, big deal. For visual use only, you're not going to see much difference, if any at all. And if your intent is for a widefield scope to leverage the benefit of the small size and shorter f/l, you won't see a difference.

Besides, I believe Jon above said that the ED element in the Lunt is FPL 53, or at least the Chinese equivalent (which is where ALL these scopes come from anyway). If you want a specialty scope made to your specifications, you'd better expect to pay, making that $1500 look attractive. Sorry, we haven't figured out a way to cheat basic economics and marketing in the hobby yet.

Now, all that said, I do appreciate your comment on the weight. Have you taken into consideration that a shorter scope, if even a pound or two heavier, is still a much more manageable scope by virtue of its shorter moment arm, which offsets the weight issue and makes it much easier to mount?


To you not a big deal but for me it is. Pretty sure he said the equivalent of 51. there's nothing wrong with postulating a possible 'gap' in the market, and I'd bet if enough people said they wanted it low and behold it would be produced.

oh of course shorter and heavier would be easier I agree. For what my plans with the ota would be I really cant go heavier than 8lbs though. With the diagonal, rings, and some hefty ep's it will wind up over 12-13lbs, which is already pushing it for my intentions.

#24 Rich V.

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Posted 25 January 2014 - 12:19 PM

I would be the Chinese version of FPL-53.



I wasn't aware there was a Chinese equivalent of Ohara FPL 53; my understanding that the common 102mm f7 doublets marketed under numerous brands were using a Chinese FPL 51 equivalent like H-FK61.

Who makes this Chinese "FPL 53" glass? :confused:

Rich

#25 Kon Dealer

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Posted 25 January 2014 - 01:11 PM

If have a Kson 102mm f/6 which uses a FPL-51 doublet.
Yes there is a little CA on the brightest objects, but it is slight and not an issue for visual.
It is my "go to" scope most nights and I have a SE6 and SE8.
Main strengths are its compactness (20.5" with dewshield retracted) and weight (5.7lb) of the OTA. Has a great focuser too.
This link sings its praises;
http://www.astronomy...son-1026-c-r...

The happy owner (not me) reckons it's pretty good for AP as well.


Interesting. I found a display model red carbon fiber for 599. Only problem is I hate red :foreheadslap:

I would still rather have it in fpl53 and slightly longer for better correction, plus I love how the skywatcher ota's are so light and easy to mount


I know which one you are referring to. Not a fan of red scopes either, but attractive price and looks to be a great visual scope. I like F/6.

Christmas knocked me out of the buyers market. Still waiting on a tripod and a 6" F/5, so I'll have to wait for tax return to look for g n g doublet like this.

There are places that will wrap it in black carbon fiber covering....


I think I will pass on it, really want to see if we can get someone to pick up on building this to spec for us. I love my ed100, I just want it at f6.5/f7. same light weight, same glass, and shorter! The weight of the f9 is so light it can go on any mount, but the length of the moment arms kills it! if it werent for that I could even put it on my skyprodigy without a problem.


Okay, I'm confused. You've been presented with two options here, both of which meet your wishes, yet you say you'll pass. The Lunt 102ED f/7 is everything you say you want. And the Kson 102 f/6 scope is also available in black, checkout the SmartAstronomy website.


I am looking for fpl53 which i think the only viable one present is $1500. also want it to be light (less than 8 pounds) and around the price of skywatchers f/9 100. not to say I'm picky, but I am :grin:


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