FPL-53 v 51 refractor

[bosun21]

I am looking at buying my first decent refractor and was wondering what the actual difference is between the two glass types. I have a 120/1000 Evostar at present which I use with the Baader semi apo filter for any CA that crops up . What is the actual viewing difference between buying a FPL53 as opposed to a FPL51 refractor. I’m looking at around f7. The price points towards the 53 being superior to the 51, but does it merit almost 2 x the cost?

[Mr Spock]

My 102mm FPL53 and Lanthanum has no false colour at all, either in focus, or inside/outside focus. It also has good SA correction. This means it will support high powers without turning to mush.

[Franklin]

As @Mr Spock says, the 53 is better, especially at f/7. I had a refractor with 51 glass which was very good indeed but it was also f/11 which would have made the difference. Still, if you're not imaging then the 51 will be a big improvement over the crown and flint in your 120 achro.

[Mr Spock]

I recently compared my Helios 120/1000 (same as Skywatcher) and it wasn't even close. The 102 spanks it in all departments.

[Deadlake]

FPL53 is better, the main difference between brands will be: 

• Lens fabrication 
• Melt variability 

Usually as far as lens fabrication you get was you pay for, more time to produce a smoother higher Strehl lens. However melt variability means the fabricator tales this into account and adjusts the lens accordingly.

I do not know your budget but TS has some Japanese made FPL53 APO’s which are very close or similar to AP/LZOS quality when placed on an optical bench, but better value. Same time I’d expect lens quality to be consistent due to Japanese manufacturers but at present it is an unknown quantity.

Edited July 22, 2022 by Deadlake

[Knighty2112]

I have an Altair Astro Starwave ASCENT 80ED F7 Refractor with fpl51 ED glass which punches well above its weight when the seeing is good. I also have their Starwave ASCENT 102ED F11 Refractor that does very well too, but although ED glass I am not sure if its fpl51. The 80ED has a very good price point for fpl51 glass. I’m sure fpl53 scopes do even better but  I guess the answer for most is then how deep do you want your pockets to be?  

[bosun21]

2 hours ago, Mr Spock said:

My 102mm FPL53 and Lanthanum has no false colour at all, either in focus, or inside/outside focus. It also has good SA correction. This means it will support high powers without turning to mush.

I am pretty sure that I’m looking at the same telescope. It was between the 102mm Starfield, which has O’Hara FPL53 and Lanthanum f7 £900 ,or an Altair Starwave 102ED , f7 FPL51 at £495. Due to the considerable difference in price I just wanted to check that the FPL53 was worth it. I am really impressed with the fact that you found no CA to speak of. I’ve put one in my cart at FLO. Thanks all

   Ian 

[bosun21]

It was actually @Mr Spock who drew my attention to the Starfield 102 in an older post where he was using high magnification on doubles with no obvious CA. It’s almost double the price of the 102 with FPL51 glass, but it’s the age old saying of you get what you pay for. 

[A Scanner_darkly]

The '51 glass will require a longer Focal ratio to give an equivalence to the superiour glass holding aperture the same.

My F/9 4"  coupled with '53 glass (and the long time they have fabricated the tube) has revealed an absolutely astonishing figure, (in the seeing necessary to determine that) with nary one or ANY other perceptible aberrations visible but it took multiple, excessively multiple times, of witnessing truly euphoric images that I now call 'etched fluidity' finally acknowledging what the scope was saying to me all along and know the loudest tell of all is the 'snap-to' when focusing.

When SA & CA are very near zero the snap can almost be  heard !!

 

Finally one night in deep lunar exploration at near 300X, in magnificent conditions, examining the Alpine Valley rille in minutest detail for about one glorious hour I succumbed and finally really LISTENED to it.

It was a Simply Insane LRO type lateral burn obervation, slewing at 2X siderial, up and down its entire length, in such mind blowing detail that this single observation cemented a new ocular plan, sinking the minimallist one, the cheap one,  for a MUCH MORE impressive and (VERY) costly set of nine (9) instead of two (2) eyepieces costing a few $ into a new one (@3.3K$!!!), that this pensioner could not really afford, but when you are PRESENTED with a CLEAN wavefront you MUST modify your approach to buying eyepieces as every scope will have a unique function, from ~1/4 -1/20 wave and all points between, it takes a lot of TIME to properly assess an apo telescope unless you have much better conditions than I.

I eventually went with consensus opinion when I finally bought and am very gratified by my choice of a Evostar 4incher F/9 (purchased in 2019.)

Its a glorious tube and worthy of a deep investment in all aspects, H-a especially, (eventually), but the initial plan was just Barlow, widest t.f.o.v. and zoom.

 

I'm sure you'll make good choices bosun21 just research till your sick then go with your gut instinct.

 

* An F/11 and '51 glass would be AMAZING !!!

 

Clear and steady skies

[Franklin]

6 minutes ago, A Scanner_darkly said:

An F/11 and '51 glass would be AMAZING

The Altair Ascent and TS 102ED f/11 are amazing scopes, quite long and need a beefy mount but the definition they give is superb and all with 51 glass. For around £750 new it's a great buy and they come with a split tube, so bino friendly and a dual speed focuser. What's not to like?

[Mr Spock]

2 hours ago, bosun21 said:

I’ve put one in my cart at FLO.

👍 You won't be disappointed. 

[Adam J]

On 22/07/2022 at 18:15, bosun21 said:

I am looking at buying my first decent refractor and was wondering what the actual difference is between the two glass types. I have a 120/1000 Evostar at present which I use with the Baader semi apo filter for any CA that crops up . What is the actual viewing difference between buying a FPL53 as opposed to a FPL51 refractor. I’m looking at around f7. The price points towards the 53 being superior to the 51, but does it merit almost 2 x the cost?

The TS115mm triplet FPL-51 is a great scope to consider as its better than either doublet option you mention above. 

[Zeta Reticulan]

All of my ED doublets have FPL-53 glass except for the SW 72ED DS Pro Evostar. 

I'm strictly visual so a doublet's fine for my needs. The 72ED can show a small amount of CA, although it is very well corrected. The others (Altair Starwave 102mm, SW 80ED DS Pro, Altair 60 EDF) don't. I don't know what type of glass is utilised in the 72ED (it has a Schott crown). If a small amount of CA doesn't bother you FPL-51 (or an equivalent) should be fine. I can tell the difference though. It's noticeable when comparing the 60 EDF (above) with the slightly larger 72ED. 

[bosun21]

2 hours ago, Adam J said:

The TS115mm triplet FPL-51 is a great scope to consider as its better than either doublet option you mention above. 

I was looking at this scope as well, however another £300 pounds over the Starfield 102 for visual astronomy is stretching it a little for me.

[Louis D]

On 22/07/2022 at 17:05, Franklin said:

The Altair Ascent and TS 102ED f/11 are amazing scopes, quite long and need a beefy mount but the definition they give is superb and all with 51 glass. For around £750 new it's a great buy and they come with a split tube, so bino friendly and a dual speed focuser. What's not to like?

I guess it depends if you already have a beefy mount.  If you need to spend an additional $800 or more on a beefier mount, then you could apply that toward a shorter FPL-53 doublet or triplet of the same aperture.

[badhex]

+1 here for the Starfield. I have the TS-Optics version which is exactly the same optics and build, except for the cosmetics. It's a great scope, very lightweight and I can also vouch for the lack of CA even at very high powers. I had it at 397x on the moon as a completely over the top test, and to my surprise it was still super sharp with no CA. The below was taken just with a phone. 

[KP82]

On 24/07/2022 at 22:20, bosun21 said:

I was looking at this scope as well, however another £300 pounds over the Starfield 102 for visual astronomy is stretching it a little for me.

If you were going for the 115 triplet, make sure your mount can handle it as it's significantly more hefty than the 102 doublets.

[badhex]

32 minutes ago, KP82 said:

If you were going for the 115 triplet, make sure your mount can handle it as it's significantly more hefty than the 102 doublets.

I was actually going to ask - @bosun21what mount and tripod do you intend to use your potential new purchase with? 

[bosun21]

21 minutes ago, badhex said:

I was actually going to ask - @bosun21what mount and tripod do you intend to use your potential new purchase with? 

I’m going to mount the more than likely Starfield 102 on a new EQ5 pro go to mount which i already have for visual 

Edited July 26, 2022 by bosun21
Spelling error

[bosun21]

I already have an Evostar 120/1000 mounted on a brand new EQ5 pro go to mount. I am intending in simply swapping the scopes over 

[badhex]

1 hour ago, bosun21 said:

I’m going to mount the more than likely Starfield 102 on a new EQ5 pro go to mount which i already have for visual 

Great choice on both fronts, the EQ5 should have no problems with the Starfield at all. I initially got a Skytee-2 and used the EQ6 tripod which is a super rock solid combo, but as I have to traverse 2 flights of stairs to observe it's a bit of a pain lugging all that weight. I have been using a Gitzo 5 series and Scopetech mount zero which is rated for much lower capacity overall than an EQ5 so you should golden. 

Assuming you go for the Starfield I echo @Mr Spock in saying you will not be disappointed. In fact, much like you I was also inspired by his posts on the Starfield! Another inspiration for me was @John pointing out that with this size of scope you can go from 4° TFOV at one end to 200x at the other merely with the switch of an eyepiece 🙂

[Louis D]

2 hours ago, badhex said:

with this size of scope you can go from 4° TFOV at one end to 200x at the other merely with the switch of an eyepiece

Another advantage of short, fast fracs over long slow versions.  Of course, cost skyrockets to make them as color free.

[Davesellars]

I can attest to the quality of the Starfield.  It's been nothing but excellent on DSOs, lunar and planetary (Saturn).   As mentioned previously, it's very capable with pushing the power without sharpness breaking down (as long as conditions allow).

 

[Carl Au]

I have had the Altair Astro 102 ED-R FPL 53 version for the last 2 years, currently it is my only scope and that’s something which is unlikely to change. I think it’s excellent value for money, built to a very high standard with excellent optics, what is not to like? I don’t see any CA at all to be honest. If anything happened to my scope, I would buy another