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Old 30-08-2019, 01:47 PM
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New Scope CFF 105 F6 with .993 strehl!

I just received my CFF 105mm F6 APO oiled triplet with FPL55 glass.
It has a 3.2 inch Feathertouch rotating Focuser with microfocuser.

The most amazing part is the test report on the optics. .993 strehl! I have never heard of a strehl that high before in a scope. I am wondering if its in part a result of using the FPL55 glass which is the same performance as FPL53 but better polishing qualities.

The scope is super well made with flocked interior of the dewshield and a nice sliding and locking dewshield, pearly white paint and the scope comes with a handle, rings and dovetail plate plus a mounting point for the finder scope.

I got a field flattener designed to cover a 16803 sensor. I only now need an adapter from the flattener to the FLI cameras. Later I'll get a Starlight Feather touch focuser electronic focus unit.

It comes with a soft case. I used to have a TEC110 F5.6 fluorite and it had a TEC made lightweight focuser which was too light weight for FLI cams. I think this scope will surpass the TEC, time will tell. Its an alternative to FSQ scopes (I have had an FSQ106N and an FSQ106EDX111 both good but I wanted something different).

Photos later.

First light is likely to be using a full frame mirrorless if I can find some attaching adapters.

Very excited.

Greg.
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Last edited by gregbradley; 30-08-2019 at 06:37 PM.
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Old 30-08-2019, 03:39 PM
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Re CFF

Pics soon? Phenomenal strehl
Bigjoe
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Old 30-08-2019, 03:56 PM
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Fantastic news Greg - congratulations!

My unit of 105 has only 0.990 Strehl in green - I must have gotten a substandard unit

Looking forward to reading about your impressions with the scope in the field. Are you going to look at the stars through the glass before attaching a camera?

Echoing Joe, pics would be nice
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Old 30-08-2019, 05:09 PM
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Quote:
Originally Posted by gregbradley View Post
I just received my CFF 105mm F6 APO oiled triplet with FPL55 glass.
It has a 3.2 inch Feathertouch rotating Focuser with microfocuser.

The most amazing part is the test report on the optics. .993 strehl! I have never heard of a strehl that high before in a scope. I am wondering if its in part a result of using the FPL55 glass which is the same performance as FPL53 but better polishing qualities.

The scope is super well made with flocked interior of the dewshield and a nice sliding and locking dewshield, pearly white paint and the scope comes with a handle, rings and dovetail plate plus a mounting point for the finder scope.

I got a field flattener designed to cover a 16803 sensor. I only now need an adapter from the flattener to the FLI cameras. Later I'll get a Starlight Feather touch focuser electronic focus unit.

It comes with a soft case. I used to have a TEC110 F5.6 fluorite and it had a TEC made lightweight focuser which was too light weight for FLI cams. I think this scope will surpass the TEC, time will tell. Its an alternative to FSQ scopes (I have had an FSQ106N and an FSQ106EDX111 both good but I wanted something different).

Photos later.

First light is likely to be using a full frame mirrorless if I can find some attaching adapters.

Very excited.

Greg.
Hi Greg,
Congrats on your new scope - CFF was the other brand I was considering when I bought the APM 152/1200 F7.9 LZOS which also has a certificated massive Strehl (I am sure it's the same, from memory). CFF scopes look great.

Just one question: With a CCD like the FLI 16803, how can your scope produce an image circle sufficient to cover the big square sensor? (Or do I have my facts wrong here? ) I bought a massive, dedicated WO Reducer /Flattener for my WO Gt 102, (though why did I buy a reducer when it's f6.9 anyway?)and have been informed that I can't use full frame sensor cameras with it as I will get vignetting (caused by the reducer rather than the flattener optics). Is this likely? No wonder I am still undecided about a OSC camera (goodbye QHY367C?)Maybe an APSC sensor only.

Wishing you many happy hours and clear skies with your new high quality scope!

Cheers,
Richard
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Old 30-08-2019, 05:35 PM
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Quote:
Originally Posted by gregbradley View Post
I just received my CFF 105mm F6 APO oiled triplet with FPL55 glass.
It has a 3.2 inch Feathertouch rotating Focuser with microfocuser.

The most amazing part is the test report on the optics. .993 strehl! I have never heard of a strehl that high before in a scope. I am wondering if its in part a result of using the FPL55 glass which is the same performance as FPL53 but better polishing qualities.

The scope is super well made with flocked interior of the dewshield and a nice sliding and locking dewshield, pearly white paint and the scope comes with a handle, rings and dovetail plate plus a mounting point for the finder scope.

I got a field flattener designed to cover a 16803 sensor. I only now need an adapter from the flattener to the FLI cameras. Later I'll get a Starlight Feather touch focuser electronic focus unit.

It comes with a soft case. I used to have a TEC110 F5.6 fluorite and it had a TEC made lightweight focuser which was too light weight for FLI cams. I think this scope will surpass the TEC, time will tell. Its an alternative to FSQ scopes (I have had an FSQ106N and an FSQ106EDX111 both good but I wanted something different).

Photos later.

First light is likely to be using a full frame mirrorless if I can find some attaching adapters.

Very excited.

Greg.
Unfortunately we don't all live in a laboratory and in the real world no one ever would see any difference between 53 and 55 glass, Im happy with my humble Skywatcher Strehl reading 94%

I didn't go for oil spaced due to the problems with solar observing and imaging


NICE scope though enjoy it


.
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Old 30-08-2019, 05:44 PM
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Quote:
Originally Posted by Decimus View Post
Hi Greg,
Congrats on your new scope - CFF was the other brand I was considering when I bought the APM 152/1200 F7.9 LZOS which also has a certificated massive Strehl (I am sure it's the same, from memory). CFF scopes look great.

Just one question: With a CCD like the FLI 16803, how can your scope produce an image circle sufficient to cover the big square sensor? (Or do I have my facts wrong here? ) I bought a massive, dedicated WO Reducer /Flattener for my WO Gt 102, (though why did I buy a reducer when it's f6.9 anyway?)and have been informed that I can't use full frame sensor cameras with it as I will get vignetting (caused by the reducer rather than the flattener optics). Is this likely? No wonder I am still undecided about a OSC camera (goodbye QHY367C?)Maybe an APSC sensor only.

Wishing you many happy hours and clear skies with your new high quality scope!

Cheers,
Richard
I have the same scope (but not such large CCD), and the corrector’s lens has 80mm diameter, so vignetting should be correctable with flats I think. WO 68III flattener has 50mm lens. Greg will let us know anyway when he gets a chance to put his new baby through it’s paces.

Last edited by Slawomir; 30-08-2019 at 05:59 PM. Reason: Typing error
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Old 30-08-2019, 06:39 PM
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Quote:
Originally Posted by Decimus View Post
Hi Greg,
Congrats on your new scope - CFF was the other brand I was considering when I bought the APM 152/1200 F7.9 LZOS which also has a certificated massive Strehl (I am sure it's the same, from memory). CFF scopes look great.

Just one question: With a CCD like the FLI 16803, how can your scope produce an image circle sufficient to cover the big square sensor? (Or do I have my facts wrong here? ) I bought a massive, dedicated WO Reducer /Flattener for my WO Gt 102, (though why did I buy a reducer when it's f6.9 anyway?)and have been informed that I can't use full frame sensor cameras with it as I will get vignetting (caused by the reducer rather than the flattener optics). Is this likely? No wonder I am still undecided about a OSC camera (goodbye QHY367C?)Maybe an APSC sensor only.

Wishing you many happy hours and clear skies with your new high quality scope!

Cheers,
Richard
The only reducer I have seen work on a 16803 without aberrations in the corners is the AstroPhysics TCC which is an expensive accessory.

This is a flattener. Time will tell if it covers the 16803 but I believe it was specified to just make the circle of the 16803.

The large Riccardi reducer I believe has a large enough corrected circle for a full frame sensor.

Flatteners are easier to make it seems than reducers.

Greg.

Last edited by gregbradley; 30-08-2019 at 06:55 PM.
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Old 30-08-2019, 07:30 PM
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Congrats. Looks to be a superb instrument.
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Old 30-08-2019, 08:52 PM
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Quote:
Originally Posted by gregbradley View Post
I just received my CFF 105mm F6 APO oiled triplet with FPL55 glass.
It has a 3.2 inch Feathertouch rotating Focuser with microfocuser.

The most amazing part is the test report on the optics. .993 strehl! I have never heard of a strehl that high before in a scope. I am wondering if its in part a result of using the FPL55 glass which is the same performance as FPL53 but better polishing qualities.

The scope is super well made with flocked interior of the dewshield and a nice sliding and locking dewshield, pearly white paint and the scope comes with a handle, rings and dovetail plate plus a mounting point for the finder scope.

I got a field flattener designed to cover a 16803 sensor. I only now need an adapter from the flattener to the FLI cameras. Later I'll get a Starlight Feather touch focuser electronic focus unit.

It comes with a soft case. I used to have a TEC110 F5.6 fluorite and it had a TEC made lightweight focuser which was too light weight for FLI cams. I think this scope will surpass the TEC, time will tell. Its an alternative to FSQ scopes (I have had an FSQ106N and an FSQ106EDX111 both good but I wanted something different).

Photos later.

First light is likely to be using a full frame mirrorless if I can find some attaching adapters.

Very excited.

Greg.
I'm sure it's a lovely scope, but I have to say that test report is pretty strange. "Mirror roc" is 630mm - firstly it's not a mirror And secondly, the ROC is twice the focal length in any case. This must be misprinted? The P-V surface error is supposedly 1/8 wave but the strehl is 0.993? VERY optimistic prediction. And the actual surface doesn't lie either, with there being a pretty big turned down edge. I'd be interested to see an actual star test though! Congrats on your purchase!
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Old 30-08-2019, 09:37 PM
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Originally Posted by Lognic04 View Post
I'm sure it's a lovely scope, but I have to say that test report is pretty strange. "Mirror roc" is 630mm - firstly it's not a mirror And secondly, the ROC is twice the focal length in any case. This must be misprinted? The P-V surface error is supposedly 1/8 wave but the strehl is 0.993? VERY optimistic prediction. And the actual surface doesn't lie either, with there being a pretty big turned down edge. I'd be interested to see an actual star test though! Congrats on your purchase!
Well spotted Logan with the mirror. However, I would argue that for a lens made of glass with refractive index of 1.5, the RoC = exactly focal length - it is not a mirror after all. Also, if we use the stated rms to calculate Strehl with well known formula, we will arrive at about 0.993. PV error of 1/8.8 is pretty good for a lens I would say. Not sure where do you see big turned down edge either
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Old 30-08-2019, 11:13 PM
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Good point Logan, and it has me scratching my head as to what was actually measured/calculated.

P-V 1/8.8 does not correlate with Strehl 0.993, no way, something wrong there IMHO. Also “surface error” is meaningless (a refractor objective has 4, 6 or more surfaces) - wavefront is what it’s really measuring - which suggests the software was written for testing mirrors - in which case the wavefront error is exactly double the “surface error” plotted on the graph at the bottom. If that’s the case the P-V wavefront error is more like 1/4 and RNS 1/10, which are still both entirely respectable.

Conversely when testing lenses the refractive index matters when calculating surface errors ... but then the P-V value is way off for the contours shown.

The contours do suggest the outer 3mm has a turned edge, but whether its worth masking off is another matter (its minor and I would not - aperture counts).

In any case it appears quite good if the measurements are to be believed, and for imaging, anything above 0.93 I'd defy anyone to tell the difference because so much depends on the seeing on the night and other factors such as flatteners, reducers and filters all of which may not be so good - and all of which contribute to the end result at the focal plane. It all comes down to the end result.

Visually you might - and only maybe - spot a difference visually side-by-side with say an AP130GTX on a night with 10/10 seeing.

Last edited by Wavytone; 31-08-2019 at 12:19 AM.
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Old 31-08-2019, 04:14 AM
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Nick - there are only two surfaces to consider in an oil-spaces triplet

Did you even read Greg’s opening post?

Last edited by Slawomir; 31-08-2019 at 04:38 AM.
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Old 31-08-2019, 05:54 AM
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There has been an ongoing war between German optician Rohr and Catalin of CFF for many years. Owners have sent Rohr their CFF optics and Rohr test results are not agreeable to those CFF releases. Rohr gives results in full-spectrum poly-Strehl, whereas CFF only gives out green Strehl - and they are QUITE different. The war still continues...
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Old 31-08-2019, 06:00 AM
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Both Roland and Yuri wrote that Rohrís methodology is flawed and his knowledge lacking.

Last edited by Slawomir; 31-08-2019 at 07:28 AM.
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Old 31-08-2019, 06:36 AM
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And the war continues

Regardless of the report I’m sure you’ll have a very nice little refractor there Greg
I’m interested in seeing how it’ll tackle a 16803.
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Old 31-08-2019, 09:55 AM
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Enjoy the new toy.
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Old 31-08-2019, 10:38 AM
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I have in my possession a lovely hand-written letter from Roland Christen regarding optical testing and quality.

BTW this is not intended to rain on Greg's parade, as I am sure the CFF scope will serve him well.... this is just to give some background information on optical testing.

AP typically deliver PV 1/10th to 1/16th wave optics. Most of this comes from a slight lack of homogeneity in the glass itself. Their Strehl cut-off of 98.4% or better....however...Strehl can be a little useless without enough data points.

AP use a super-smooth polishing technique to get the RMS figure down to 1/50th of a wave (or better!) , plus sample hundreds of data points in 5-8 orientations to produce a Strehl number they can rely upon.

As to what CFF do, I cannot say. 1/8th wave does seem a little high for such a superb Strehl number, but I am confident Greg's considerable experience with quite a few top-shelf telescopes, will quickly reveal the CFF's quality is real (or not) within a few imaging sessions.
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Old 31-08-2019, 12:27 PM
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Test reports can easily lead to disagreement with methods etc. I was not buying it on the basis of a Strehl ratio. I was buying it because Suavi's images are super sharp and show an exceptional level of detail that even a larger high end telescope does not show much more at all. I judge the results not the test reports. They should match up. Suavi's images match up with the results I would expect from a top end AstroPhysics scope. Also these CFF scopes have a 1 year waiting list which tells you something about their quality as well.
I don't know that AP are making anymore APOs apart from the 92mm F6. I wouldn't bank on it. Roland stopped making the RHA astrograph I believe.

TEC also judge strehl from the green. That's for visual people. Imagers are probably more interested in the blue and the red where false colour lives. I was surprised to see the TEC180FL was weak in the red for example although I can't say I noticed that when imaging with it. But I did notice Tak TOA150 images always seemed to get a tad more detail from the same scenes. Its a shame Tak does not make a TOA 110. They probably don't want to overlap against the FSQ which is there best seller.

The alternative scope was a Tak FSQ106EDX iv. They are in short supply and are a touch more expensive. I have had an FSQ106N and an 106 EDX iii before with the reducer and its an amazing scope but just wanted something different. Mainly to replace the lovely TEC110 F5.6 fluorite oil spaced triplet.

The main issue with that scope was the lightweight focuser, it really needed a heavy duty Feathertouch. What I liked about the TEC over the FSQ was the better colour transmission of the fluorite lens. The Tak is not as "colourful". I mentioned this to someone once and he tested his as I thought perhaps the shift to a different type of lens coating created a slight colour bias in the FSQ106ED series. His testing led to the conclusion the black internal tube paint on the FSQ does create a slight green bias which is what I was seeing in a lot of FSQ106ED images. I haven't noticed it in any of Mike's images so I wonder if Tak adjusted their coatings or internal paint or not. The FSQ has the large 88mm corrected imaging circle, has a wonderful flat field. Its weak points mechanically are the poor focuser, the poor focuser lock, the weak microfocuser, the focus shift with temperature shifts due to the large air space. Nothing is perfect and the imaging capabilities are the main thing, the focuser issues perhaps are now fixed - not sure, hence the EDX iv the earlier 3 had issues with heavy imaging trains although the EDX iii I had was perfect.

There are many nice FPL53 triplet scopes offered these days - a lot are reasonably priced compared to years ago when I was first getting high end scopes.
But as usual you pay a lot more for that last 10% of performance. Its the same with cars and everything else.

So I will be comparing it to the 2 FSQ's I have had, the TEC110 F5.6 fluorite triplet, the TEC 180FL and an AP140 F7.5.

Also I bet if I asked Roland Christen, an AP quad TCC could probably work on this scope or perhaps his flattener for the Traveller if they still make them. The alternative is the Riccardi reducer.

Greg
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Old 31-08-2019, 12:37 PM
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Quote:
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I have in my possession a lovely hand-written letter from Roland Christen regarding optical testing and quality.

AP typically deliver PV 1/10th to 1/16th wave optics. Most of this comes from a slight lack of homogeneity in the glass itself. Their Strehl cut-off of 98.4% or better....however...Strehl can be a little useless without enough data points.

AP use a super-smooth polishing technique to get the RMS figure down to 1/50th of a wave (or better!) , plus sample hundreds of data points in 5-8 orientations to produce a Strehl number they can rely upon.
sigh...Obvious marketing jargon from AP - people love the term "super smooth polishing", look at zambuto for example. Once the pitch lap is on and conformed, there is no such thing as "super smooth polishing" It comes down to technique.



I highly doubt AP stops figuring because of errors in the glass - It is more likely that they recognize that no one will notice or care that the optic is better than 1/10 wave. But to let an optic slip that badly as the wavefront shows... I'm confused. A massive TDE like that is a rookie mistake - if that wasn't there, sure the lens would be great, but that is sure to produce a visible issue at higher powers. As the scope is used for imaging though, it will do the job nicely.


That's just my (most likely controversial) opinion, from someone tho has made a few optics and used an interferometer.
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Old 31-08-2019, 12:46 PM
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Not sure what people are referring to when they say the lens has a turned down edge. Is it the graph that shows the line falling heavily just before the edges of the graph?

Visually there is turned down edge. Of course the lens sits in a cell several mm so any far edge is not even exposed to light. So no issue.
It looks no different to any other high scope I have had like Taks, AP and TEC's. In fact it looks superb and the coatings are very even and a lovely bluish colour. Like an AP.

Oil spaced triplets only have 2 air to glass surfaces which is why they do them this way. They also cool down faster and are less prone to focus shift from temp drops as a large air spaced scope does. Its interesting AP have only done an air spaced triplet once that I know of - the AP160 and I have heard it wasn't as good a scope as the AP155 due to these issues of cooldown and temp focus shift etc. The 130GTX has 1 air space so it must give an extra element of improvement to bother.

TEC only make oil spaced triplets.

A turned down edge refers more to mirrors where depending on how the mirror is mounted the mirrored light surface goes all the way to the edge so a turned down edge would require masking as there is no lens cell to cover that edge and it can lead to a weakness in the image.

Anyway all this is hypothetical and the proof of the pudding will be in the imaging. The camera is a known quantity for me.

Greg.
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