FPL55 Glass Query

[PembrokeSteve]

Hi,

Noticed this evening that German Retailer TSOptics have a new APO with what appears to be something different, in that it has FPL55 glass.

“TS Optics CF-APO 90mm f.6 FPL55 Triplet”

Does anyone know is FPL55 equal, to or better than FPL53.

Most interested to find out what is known about FPL55, and will it eventually replace FPL53.

Regards

Steve

[johninderby]

Found this quote.

FPL55 is a newer glass than FPL53 and is supposed to supersede it. It is supposedly cheaper and easier to work than FPL53 but maybe not quite as good.

https://www.ohara-gmbh.com/fileadmin/user_upload/export-data/pdf/product_datasheets/S-FPL55_English_.pdf

Edited October 23, 2020 by johninderby

[John]

It's somewhere between FPL-51 and FPL-53 in terms of potential for CA control but remember that the glass used in the mating element plus the figure and polish of the lenses is equally important.

 

[Adam J]

56 minutes ago, PembrokeSteve said:

Hi,

Noticed this evening that German Retailer TSOptics have a new APO with what appears to be something different, in that it has FPL55 glass.

“TS Optics CF-APO 90mm f.6 FPL55 Triplet”

Does anyone know is FPL55 equal, to or better than FPL53.

Most interested to find out what is known about FPL55, and will it eventually replace FPL53.

Regards

Steve

It's almost the same as fpl53 not quite as good in terms of dispersion. But overall I would say it's better glass as it is harder and easier to grind resulting in better figure on average and a high performance lens. 

Having said that though I am not overly in Impressed with the optical report they show it's got a significant central zone showing. 

Edited October 23, 2020 by Adam J

[billhinge]

If you don't like FPL55 there is still LZOS OK-4 glass afaik

[Louis D]

Hmmm.  This scope seems to have replaced the TS-Optics Photoline 90mm f/6,5 Triplet FPL-53 APO.  Searches for it redirect to this new scope.

vs.

The new one is about 50 Euros more, slightly faster, no removable segments, has a flimsier looking focus knob, comes with a carrying handle, appears to use collets instead of compression rings, and substitutes FPL-55 for FPL-53 glass.  It would be interesting to compare test reports and actual images taken with both.

I have the older version.  It's quite nice, though I don't know where they get the 6kg load capacity of the focuser from.  When I load up mine with a 2" GSO dielectric diagonal and 17mm ES-92 (not even 3kg combined) and point it near zenith, it wants to unwind.  I have to tighten up the two focus tensioners (one on the pinion, one on the tube).  Perhaps they're referring to deflection?

I still don't know why focuser manufacturers they don't use a system similar to the Manfrotto geared central column.  The crank axle comes in nearly perpendicular to the rack and is completely impervious to having thrust driven backward through it:

I'm guessing they use a worm gear arrangement.  Perhaps there would be too much slop for a fine focuser?  I don't know about others, but I almost always approach best focus from only one side (that being the lifting side) anyway.  If I overshoot, I tend to come back to the other side and creep up more carefully.

Once you're at the right height with the tripod crank, you just snug down the column lock which pushes the two flat sides of the column against two bearing pads to prevent any play in the system.  Something similar would appear to be applicable to focusers.

Edited October 23, 2020 by Louis D

[Louis D]

According to this chart from Ohara, FPL-55 is much closer to FPL-53 than it is to FPL-51:

If it is easier to work with and cheaper than FPL-53, then it probably is a win-win all around.

[GazOC]

On 23/10/2020 at 01:54, John said:

It's somewhere between FPL-51 and FPL-53 in terms of potential for CA control but remember that the glass used in the mating element plus the figure and polish of the lenses is equally important.

 

Not much chance of forgetting it, John. You can pretty much guarantee that someone will make that comment every time a thread is started about glass types 😉

[Adam J]

On 24/10/2020 at 07:36, GazOC said:

Not much chance of forgetting it, John. You can pretty much guarantee that someone will make that comment every time a thread is started about glass types 😉

Yeah an it would have to be a poor fpl53 design before it was outperformed by a fpl51 scope. In practice I have never seen it happen.

[Louis D]

2 hours ago, Adam J said:

Yeah an it would have to be a poor fpl53 design before it was outperformed by a fpl51 scope. In practice I have never seen it happen.

Some of the FPL-51 triplets rival FPL-53 doublets.

[Adam J]

4 minutes ago, Louis D said:

Some of the FPL-51 triplets rival FPL-53 doublets.

Hardly a like for like comparison. 

[Louis D]

51 minutes ago, Adam J said:

Hardly a like for like comparison. 

Yes, but you weren't very specific about "a poor fpl53 design before it was outperformed by a fpl51 scope".  Had you said "a poor fpl53 doublet/triplet before it was outperformed by a fpl51 doublet/triplet", then I wouldn't have made my point.

I brought it up because of the expense of FPL-53 has caused a lot of ED/APO designs to use FPL-51 triplets instead of FPL-53 doublets.  So, in that sense, it is a like for like comparison price-wise.

[TareqPhoto]

Reading this i feel like a foolish person to go with FPL-55, i should choose FPL-53 then, in this case then i have to choose my second scope to pair with my FPL-55 to be FPL-53, so both will do the job and i won't have issues using both together.

[Adam J]

8 hours ago, TareqPhoto said:

Reading this i feel like a foolish person to go with FPL-55, i should choose FPL-53 then, in this case then i have to choose my second scope to pair with my FPL-55 to be FPL-53, so both will do the job and i won't have issues using both together.

Dont know how you got that impression FPL-55 is great glass arguably better the FPL-53 because you are more likely to get a well figured lens and yet the despertion is so close to FPL53 that is would make not rea world difference.

[TareqPhoto]

On 03/11/2020 at 21:56, Adam J said:

Dont know how you got that impression FPL-55 is great glass arguably better the FPL-53 because you are more likely to get a well figured lens and yet the despertion is so close to FPL53 that is would make not rea world difference.

I really hope so that because even with FPL-53 scopes even being a triplet people keep looking for issues to analyze to death until it is 10000000% perfect, so i don't know if people care about the results or stars or performance or FPL55 vs. FPL53 or what exactly, but sounds i have to stop thinking about that and i just do imaging, i am not good at DSO so i won't just try to think that i have a high end scope although i look for one actually.

[John]

1 hour ago, TareqPhoto said:

I really hope so that because even with FPL-53 scopes even being a triplet people keep looking for issues to analyze to death until it is 10000000% perfect, so i don't know if people care about the results or stars or performance or FPL55 vs. FPL53 or what exactly, but sounds i have to stop thinking about that and i just do imaging, i am not good at DSO so i won't just try to think that i have a high end scope although i look for one actually.

I think you are right and this does get "analyzed to death" on forums. I would pay much more attention to feedback from owners on how specific scopes actually perform in the real world (which is far from perfect of course) in making your selection. Forums like this are very valuable for getting that feedback

 

[Deadlake]

1 hour ago, John said:

I think you are right and this does get "analyzed to death" on forums. I would pay much more attention to feedback from owners on how specific scopes actually perform in the real world (which is far from perfect of course) in making your selection. Forums like this are very valuable for getting that feedback

 

Agreed, a lot of unknowns about glass used even if it's cited by name, for example:

• Quality of glass from a batch
• Matting element used with ED element.

It's how it works in the field, however the above two can be implied by cost, no free lunches.

Edited November 5, 2020 by Deadlake

[Louis D]

4 hours ago, Deadlake said:

Agreed, a lot of unknowns about glass used even if it's cited by name, for example:

• Quality of glass from a batch
• Matting element used with ED element.

It's how it works in the field, however the above two can be implied by cost, no free lunches.

To add to that:

• Quality of lens polish
• Quality of lens coatings
• Quality of lens cell design and execution
• Quality of factory collimation and lens cell's ability to hold it
• Quality of stray light control (baffling, etc.)

[TareqPhoto]

And yet, i have to wait and see, sounds the telescope i ordered isn't in a hand of any yet, it is mentioned that it will be available by end of Jan next year, and sounds no one around got a hand on it for reviews, or maybe there is but couldn't find that review, so i just have to wait and see.

Some gave me the Abbe numbers of quality that those optics are giving, so between FPL53 and FPL55 it is very very minimal difference, it is like there is no different, FPL53 is about 94.93 and FPL55 is 94.66, it is very neglectable then.

[newbie alert]

On 26/10/2020 at 12:36, Adam J said:

Yeah an it would have to be a poor fpl53 design before it was outperformed by a fpl51 scope. In practice I have never seen it happen.

Dunno about that, a couple of friends have 127 triplets that I was shocked to learn that they have fpl51.. I've seen worst with fpl53 

[John]

1 hour ago, newbie alert said:

Dunno about that, a couple of friends have 127 triplets that I was shocked to learn that they have fpl51.. I've seen worst with fpl53 

Here is an example:

https://astromart.com/reviews-and-articles/reviews/telescopes/refractors/show/orion-120ed-vs-astro-tech-127edt

Both good scopes but the ED doublet did seem to show less CA than the triplet in this case.