Many of us using the Baby-Q have seen the so-called inverted lighthouse or hourglass effect on some bright stars. I discussed this with Adam Block on his forum and asked if he had a suggestion as to how to repair it. He made a short video (on his Adam Block Studios website) demonstrating it using clone stamp and it works pretty well. Here I fixed the star Tejat Posterior (Mu Geminorum) using a clone stamp technique. Basically, you open up two versions of the image and rotate one 90 degrees. Then center your pointer in the middle of the star on the rotated image and then move over to the image you are going to correct and click dead in the center. Then carefully flare out from the center outwards to fill in the gap of light on one side and then rotate the first image again to the opposite side and do the same on your final image. It is hard to explain this as the videos demonstrates it so easily, but once you try it, you will figure it out quickly enough.
Inverted lighthouse effect
Fixed using a clone stamp approach. Note the correct color is also coming out.
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Nice fix! This should also help with Rokinons that produce this effect.
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It is a good fix visually, but using clonestamp to fix anything rubs me off the wrong way. I know we use false color, enhance the image with deconvolution, process stars and background separately and stretch an image. But the one thing I feel I need to draw the line at when post processing an image is messing with the actual structure of the image / pixels by copying one part of the image onto another part, or creating objects that do not exist, like stars and nebulae. The only time I may use clonestamp is if I have a completely neutral background without any structure that needs to be fixed (dust mote in an empty region when stars are removed, or some neutral background errors).
For example in your image you can clearly see that you created stars that do not actually exist in the hourglass area that you were filling by copying it from the non affected region. I just don't know if it is worth the fix to create non existent stars in the final result. Would rather just keep the artifact if that is the only solution.
Just my personal preference, of course everyone has other tolerances.
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Ashraf AbuSara:
It is a good fix visually, but using clonestamp to fix anything rubs me off the wrong way. I know we use false color, enhance the image with deconvolution, process stars and background separately and stretch an image. But the one thing I feel I need to draw the line at when post processing an image is messing with the actual structure of the image / pixels by copying one part of the image onto another part, or creating objects that do not exist, like stars and nebulae. The only time I may use clonestamp is if I have a completely neutral background without any structure that needs to be fixed (dust mote in an empty region when stars are removed, or some neutral background errors).
For example in your image you can clearly see that you created stars that do not actually exist in the hourglass area that you were filling by copying it from the non affected region. I just don't know if it is worth the fix to create non existent stars in the final result. Would rather just keep the artifact if that is the only solution.
Just my personal preference, of course everyone has other tolerances.
Well, yes, of course, we all have our tolerances on how we "doctor" up our images. I never even liked false colorization but NB is better for where I live vs. RGB. However, to your valid point: 1) this is weak fix if those funny stars annoy you; I am still up in the air about it but I found this an intriguing easy fix; 2) the extra stars (I only see two but maybe your eyesight is better than mine) could have been avoided if I was a bit more careful. Adam specifically pointed this out as a possibility if you are not careful when using the tool. It can be avoided by making sure you do not touch any stars from the image you are copying from. So, I need to get better at this; and 3) for me, I see this less an issue on these very wide fields as the focus is almost always on the large area of nebulosity. I would never even think of something like this using a scope on closeup images. Like you, just my personal preference.
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While it may be a good fix, I think the real question is why it's happening in the first place. I had an FSQ 85ED and never had this issue, if it's the EDX version, Tak didn't do it any favors by changing the optics.
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Well- folks with both the ED and EDX versions have said they see these on random bright stars. And the reason for this is due to diffraction and is intrinsic to the Petzval design- according to Takahashi America. So, why some get these, and others do not, is a mystery to me. I have gotten just one bright star display this effect on an object, and yet, someone else taking the same object, is showing two or more stars with the inverted lighthouse effect.
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For what it's worth, I have these artifacts on bright stars near the edge of the field with my Epsilon160ed.
What's the common culprit between a rokinon 135, an FSQ, and an Epsilon?
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This is aperture vignetting and here is a nice explanation and demonstration:
https://stargazerslounge.com/topic/275921-star-shape-artifacts-black-wedges/
It is just a matter of geometry and can happen with fast systems and large sensors. If any obstructions (lens edges, field stops, baffles are in the way) the photosites at the edges of a sensor will partially "see" the objective lens.
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Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
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Hope this helps but if you go that road, put in someone's hands who knows what they are doing it:
https://interferometrie.blogspot.com/2014/08/esprit-tuning-how-we-finetune-esprit80.html?m=1
Regards,
Cesar
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I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
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Tyrel Smith:
I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
AstroShed:
Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
First I read about these two explanations (dew cap and rubber rings). I can't see any gap in the rings on mine (actually, I can't really make out any rubber rings, really). If the dew cap was undersized, that would be a major blunder. When I get mine out the next time, that will be easy to check.
I have to disagree with Stewart William. Takahashi publishes their optical design specs, so it's easy to check if they fit your quality requirements. The FSQ-85 without the flattener is slightly better in field correction but has much better on-axis sharpness than the usual FPL-53 triplets with a 0.8x reducer/flattener or the so-called "flat-field astrographs" that are currently flooding the market. The off-axis aberrations are more visible because these other designs introduce spherical aberration which leads to big but round stars. The 1.01x flattener fixes these off-axis aberrations in the FSQ and makes the scope far better corrected than the usual fare: Excellent to APS-C and quite good to full frame even with small pixel cameras.
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Torben van Hees:
Tyrel Smith:
I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
AstroShed:
Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
First I read about these two explanations (dew cap and rubber rings). I can't see any gap in the rings on mine (actually, I can't really make out any rubber rings, really). If the dew cap was undersized, that would be a major blunder. When I get mine out the next time, that will be easy to check.
I have to disagree with Stewart William. Takahashi publishes their optical design specs, so it's easy to check if they fit your quality requirements. The FSQ-85 without the flattener is slightly better in field correction but has much better on-axis sharpness than the usual FPL-53 triplets with a 0.8x reducer/flattener or the so-called "flat-field astrographs" that are currently flooding the market. The off-axis aberrations are more visible because these other designs introduce spherical aberration which leads to big but round stars. The 1.01x flattener fixes these off-axis aberrations in the FSQ and makes the scope far better corrected than the usual fare: Excellent to APS-C and quite good to full frame even with small pixel cameras.
Well you are entitled to your opinion, but how many other scopes are out there that require 2 flatteners to work, I will tell you none, I swapped my FSQ85 for an Esprit 100 and the difference is huge, the Esprit being far better and corrected than the tak ever was, with or without the second flattener, and if you are happy with stars like this in the corner of your images with a modern small pixel camera, then good luck |
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AstroShed:
Torben van Hees:
Tyrel Smith:
I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
AstroShed:
Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
First I read about these two explanations (dew cap and rubber rings). I can't see any gap in the rings on mine (actually, I can't really make out any rubber rings, really). If the dew cap was undersized, that would be a major blunder. When I get mine out the next time, that will be easy to check.
I have to disagree with Stewart William. Takahashi publishes their optical design specs, so it's easy to check if they fit your quality requirements. The FSQ-85 without the flattener is slightly better in field correction but has much better on-axis sharpness than the usual FPL-53 triplets with a 0.8x reducer/flattener or the so-called "flat-field astrographs" that are currently flooding the market. The off-axis aberrations are more visible because these other designs introduce spherical aberration which leads to big but round stars. The 1.01x flattener fixes these off-axis aberrations in the FSQ and makes the scope far better corrected than the usual fare: Excellent to APS-C and quite good to full frame even with small pixel cameras.
Well you are entitled to your opinion, but how many other scopes are out there that require 2 flatteners to work, I will tell you none, I swapped my FSQ85 for an Esprit 100 and the difference is huge, the Esprit being far better and corrected than the tak ever was, with or without the second flattener, and if you are happy with stars like this in the corner of your images with a modern small pixel camera, then good luck
This doesn’t meet specs, with or without the flattner (well, it might just barely if it‘s an IMX455 without the flattener - but the Esprit isn‘t better with that sensor). The thing to know is that the FSQ, like other Petzvals, is both susceptible and sensitive to decollimation of its lenses. This seems to happen not infrequently during shipping - and I agree that’s a point Tak needs to address. The first one I got was as bad as the image you show. The second one is perfect with the flattener (better than my optimised Esprit 100, which isn’t a slouch) and very good without.
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Based on above information I Think I will stick to another refractor design (I had my eye on the FSQ-85 EDX ,do I roll the dice hoping I get a good version after it is shipped); may the skies clear for all us imagers.
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Based on above information I Think I will stick to another refractor design (I had my eye on the FSQ-85 EDX ,do I roll the dice hoping I get a good version after it is shipped); may the skies clear for all us imagers.
Yes, that‘s a danger with all Petzvals - and the FSQs can only be fixed in Japan.
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I purchased my FSQ-85 last Summer to compliment the FOV of my TOA-130. Last month I acquired the new .73X reducer for the FSQ. I absolutely love the light frames produced with that setup….except for the inverse lighthouse effect on the bright stars. I read the above post about Adam Blocks cloning fix but couldn’t find the video on his webpage -guessing you have to subscribe to watch it?
I began playing with PhotoShop, I have both PixInsight and Photoshop on my processing Computer. I came across the fairly new PS Generative Fill layer which is AI based and apparently is an update to the content aware fill layer. I simply did a quick selection of the Lighthouse effect area on the bright stars then clicked on the Generate tab. It gave me three AI choices that it came up with to correct the star “defect”. And if none of those three choices are what you want then you simply click the tab again and it gives you three more choices. You can do this repeatedly until you get the exact correction. It is very quick and simple to do and gives excellent results. If you have PS and have not tried this to fix the stars showing the inverse Lighthouse effect I highly recommend you give it a try.
Bob
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Bob Masters:
PS Generative Fill layer
Just tried this, very cool and works great. Thanks for the heads-up. Didn't know they added this. Did take a minute to find where and how to use it.
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Bob Lockwood,
I was totally unaware of the capabilities of this in Photoshop and stumbled across it by accident. After my earlier post I started looking at YouTube videos of the Photoshop Generate Fill tool. It does a heck of a lot more than I realized after watching some of those videos. A little scary about its power to produce a totally “fake” picture. I had wondered about the delay when you click on the generate tab. One of the videos explained that it actually goes into the cloud to the mainframe computers at Adobe. I guess it must take a lot of processing power. Will be interesting to see future applications to Astrophotography.
Bob
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AstroShed:
Torben van Hees:
Tyrel Smith:
I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
AstroShed:
Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
First I read about these two explanations (dew cap and rubber rings). I can't see any gap in the rings on mine (actually, I can't really make out any rubber rings, really). If the dew cap was undersized, that would be a major blunder. When I get mine out the next time, that will be easy to check.
I have to disagree with Stewart William. Takahashi publishes their optical design specs, so it's easy to check if they fit your quality requirements. The FSQ-85 without the flattener is slightly better in field correction but has much better on-axis sharpness than the usual FPL-53 triplets with a 0.8x reducer/flattener or the so-called "flat-field astrographs" that are currently flooding the market. The off-axis aberrations are more visible because these other designs introduce spherical aberration which leads to big but round stars. The 1.01x flattener fixes these off-axis aberrations in the FSQ and makes the scope far better corrected than the usual fare: Excellent to APS-C and quite good to full frame even with small pixel cameras.
Well you are entitled to your opinion, but how many other scopes are out there that require 2 flatteners to work, I will tell you none, I swapped my FSQ85 for an Esprit 100 and the difference is huge, the Esprit being far better and corrected than the tak ever was, with or without the second flattener, and if you are happy with stars like this in the corner of your images with a modern small pixel camera, then good luck
This looks like a collimation issue. I had a FSQ-106EDX3 that developed a collimation problem and stars looked exactly like this on the edge of the frame. I sent it to Tak USA and they recollimated it and it was fine afterwards. Nice round stars.
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Mark Petersen:
AstroShed:
Torben van Hees:
Tyrel Smith:
I received a note from Tak America recently that addressed this. They claimed that they have recently learned that shooting with the dew shield retracted seems to eliminate these dark wedges. I haven’t owned the scope in years so can’t confirm. I also had heard the aperture vignetting explanation, which seems legit.
AstroShed:
Tak are a law unto themselve, I had the 85 and it was dire in all respects, and it’s the only scope in the world that I know of where you have to now use 2 flatteners with it….absolute joke, we buy a premium Petzval 4 element design to get away from back focus issues, then because of the poor optics and the fact they can’t cope with modern small pixel cameras, they decide to add another flattener with a dedicated 56.2mm back focus into the mix, well at least they supply it with the scope now, they didn’t when I got mine
The lighthouse beam effect is caused by a rubber seal on the front element that goes around the glass, and if you are lucky you get one that fits, if not like most of them you get one with a tiny gap between the two ends of the rubber, as they don’t meet, this causes the effect….also if it’s fine when you get the scope, over time the rubber shrinks back and causes the issue.
poor QC from a premium manufacturer, I will never buy another one…☹️
First I read about these two explanations (dew cap and rubber rings). I can't see any gap in the rings on mine (actually, I can't really make out any rubber rings, really). If the dew cap was undersized, that would be a major blunder. When I get mine out the next time, that will be easy to check.
I have to disagree with Stewart William. Takahashi publishes their optical design specs, so it's easy to check if they fit your quality requirements. The FSQ-85 without the flattener is slightly better in field correction but has much better on-axis sharpness than the usual FPL-53 triplets with a 0.8x reducer/flattener or the so-called "flat-field astrographs" that are currently flooding the market. The off-axis aberrations are more visible because these other designs introduce spherical aberration which leads to big but round stars. The 1.01x flattener fixes these off-axis aberrations in the FSQ and makes the scope far better corrected than the usual fare: Excellent to APS-C and quite good to full frame even with small pixel cameras.
Well you are entitled to your opinion, but how many other scopes are out there that require 2 flatteners to work, I will tell you none, I swapped my FSQ85 for an Esprit 100 and the difference is huge, the Esprit being far better and corrected than the tak ever was, with or without the second flattener, and if you are happy with stars like this in the corner of your images with a modern small pixel camera, then good luck
This looks like a collimation issue. I had a FSQ-106EDX3 that developed a collimation problem and stars looked exactly like this on the edge of the frame. I sent it to Tak USA and they recollimated it and it was fine afterwards. Nice round stars.
The FSQ 85 does 'suffer' aperture vignetting, often known as cat eye bokeh for lens users or inverse dark lighthouse beams for the rest of us. Its a part of the design.
It does not happen because of a gap in the rubber seal anywhere inside the scope. Retracting the dew shield is one way to test, I will be curious if there is a benefit since the field stop is close to the third lens (1st of the two back doublet correctors). But I am going to try it out on a couple of extremely defocused star fields to see how (if) the edge stars change in almond/cat eye shape as the dew shield is extended - just for fun.
In 9um pixel cameras, issues were hidden a little more, but it shows more readily when sensors are large, pixels are small and especially when they are backlit, since it is a planar surface where light hits and diffraction from microlenses (the classic short stubby newtonian-like spikes from the older ccds) are not there to cover the effect.
But, the astigmatism in the above image is absolutely a collimation problem in that Tak. You can 'hide' it with 9 um pixels, but I can get absolutely perfectly round stars on the imx 571 with 1.01x flattener and also with the 5.94 um imx 410 full frame also with the flattener. They are the best color corrected stars of any refractor I have used, but the aperture vignetting is annoying, must admit.
Modern petzvals liek the askars are not formal petzvals anyway, but an optical design to flatten the field. I like them scopes also. True that they also use SA to balance on-axis sharpness with flatness across the field. The FRA300 is one of the best examples where this balance is really good, but its color correction does not come close to the FSQ 85. I have both, and how much it bothers anyone is in the weeds, personal preference stuff really in my opinion. The PHQ line take an approach using SA and flat fielding, with lower curvature to slow the system down and deal with lateral CA and star size a bit better, but its the easier route to do this.
The quad design of the FSQ 85, for me, gives the benefits of excellent CA, SA and aberration control for a fast aperture that is maybe matched but not beaten by any at that aperture of focal length, and the flat field for small chips, or APS-c with huge pixels is a bonus prize, but not why I bought one. The new flattener is just excellent and with a nicely collimated scope, works a treat and like my epsilon, its backfocus distance is much less of a guessing and trial game compared to generic flatteners. But, it all works out eventually and then the system is set.
Pity the example above has given a bad taste - its lenses were out of whack. for some, the need to be flat field out of the box up to APS-C minimum is a modern expectation, and I do agree that the Tak design could be updated - but the slow front doublet with a pair of correcting lenses is best used to correct aberrations for color and sharpness more so than a large flat field. Honestly don't know if there is a modified petzval design that can take the best of both worlds. The AP 110GTX needs a quad reducer to do something similar. The new VSD90ss look interesting, but it too has the aperture vignetting - field stops and where they end up etc.
I keep FSQ stars gently stretched as a broadband imager, where OSC imaging with modern sensors is the place where you get to see this effect the most and the stars are not narrowband-suppressed in size and intensity. All in all, I just love the look of the FSQ85, its my little scientific instrument (the new version, with the silver hardware). I have gawdy fast reflectors as workhorses, and see past the 'flaws' of the FSQ cause it just so nice of a lump of glass, cream enamel, and baby blue casting - silly I know...
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Spacetime Pictures:
For what it's worth, I have these artifacts on bright stars near the edge of the field with my Epsilon160ed.
What's the common culprit between a rokinon 135, an FSQ, and an Epsilon?
I've also seen it on the Epsilon 160Ed with the full frame sensors, and a little on the imx571. In both examples, a long dew shield was used and its geometry was not exactly circular and was tilted. That may not have been the reason, but the effect only comes from the closure of the aperture - to give defocues stars that look like cats eyes. I even saw it on my Intes MN56 Mak-Newt with an imx 571 as its secondary mirror is tiny, but the front meniscus is the field stop rather than the mirror, so far off axis stars were cat-eye shaped (when out of focus) and sure enough, inverse pair of dark beams on edge stars in focuse. I wonder where that happens in the epsilon if not the dew shield or the corrector?
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Colm O'Dwyer:
Spacetime Pictures:
For what it's worth, I have these artifacts on bright stars near the edge of the field with my Epsilon160ed.
What's the common culprit between a rokinon 135, an FSQ, and an Epsilon?
I've also seen it on the Epsilon 160Ed with the full frame sensors, and a little on the imx571. In both examples, a long dew shield was used and its geometry was not exactly circular and was tilted. That may not have been the reason, but the effect only comes from the closure of the aperture - to give defocues stars that look like cats eyes. I even saw it on my Intes MN56 Mak-Newt with an imx 571 as its secondary mirror is tiny, but the front meniscus is the field stop rather than the mirror, so far off axis stars were cat-eye shaped (when out of focus) and sure enough, inverse pair of dark beams on edge stars in focuse. I wonder where that happens in the epsilon if not the dew shield or the corrector?
Could be the too small secondary?
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I am supposed to have clear skies at my location this Friday night. Going to push in the dew shield on my FSQ 85 and see if that does make a difference with the inverse Lighthouse effect. I have seen the same effect when my dome has not synced properly and the scope field of view ends up partly blocked by the sides of the shutter. It would be nice if it is just a problem with the long dew shield being fully extended. The dew shield is quite long compared to the rest of the scope when comparing it to my other scopes, but I don’t know if that has any bearing. Just an observation. I will let everyone know the results of my test this Friday night.
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Keep us posted.
And please...send me some clear skies.
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12.64
2.71
7.12
6.08
4.07
11.14
1.81
0.00
2.41
4.40
0.90
0.90
0.00
3.31
