Evaluation of CA on new (used) TS Optics 130 F7 Apo (FPL53) - Forums

Topic starter

Sep 3, 2022

I have been using reflectors for many years and therefore I am new to the look of data for an APO.

Therefore I would be very gratefull if someone with expertise on refractors would give me their view on what they see in these two images wich are OSC data from the ASI294MC Pro with just a IR cut filter. The data was processed in Astro Pixel Processor.

Image 1, only background calibrated: https://www.astrobin.com/lx6mo8/
Image 2, background calibrated and star calibrated: https://www.astrobin.com/3dnaoi/

Clear skies :-) Steen.

Lynn K

Sep 3, 2022

Hi Steen, I am not an optical designer and never ground my own mirror or lens, but have used refractors for astro imaging fo years. I have owned acrochromatic doublest for visual. My first imaging refractor was a WO Megrez 80II triplet. My second was a Astro Tech AT110ED (FPL51 galss). I upgraded to a TMB130SS with FPL53 glass. I saw no increase in resolution from the 110mm to 130mm, but did see a decrease in Color aberations due to the FPL53 glass. The TMB had pitched optics. So, I know waht that looks like. I was able to correct that. I now own a Takahashi FSQ106ED four element F5 and a Astro Physics AP130GTX triplet (FPL53).

I have a Vixen 150mm f5 reflector for visual. I have imaged through Celestron SCTs 8", 9.25" and 11". I have a EDge 8, but only do visual with it.

I'm a mono filtered imager using mostly narrow band, and only recently moved to CMOS. I do have an older OSC CCD camera, but have used it very little.

Your image looks fairly typical to me. I see no CA around the stars. There is a good amount of "glow" around the blue stars. They are hotter and brighter. The glow is caused by a measureble amount of light not going into the airy disk, but ending up in the outer defraction rings. As you know, this will put photons in the sorrounding pixels. As the image is stretched, those surrounding pixels will become lighter.

Better refractor optics will put more of the light in to the airy disk and less into the surrounding pixels. I suppose filters and pixel size can affect this as well. Focus is also a big issue with the smallness/sharpness of the stars.

There is a very very slight bit of CA on the outer edge stars caused by coma. I think very aceptable.

My solution to star size and color is to eliminate them from processing with Star ExTerminator, and then use stars from short RGB subs.

That's my thoughts. I hope it helps some.

Lynn K.

Helpful

andrea tasselli

Frequent contributor

Sep 3, 2022

Looking at both I'd say you have some CA, violet in the main. Doesn't look like is coming for a fully corrected APO, more like a ED. I'd want to use a minus-violet filter ahead of the camera, better still the Baader Semi-APO.

Steen Knarberg

Topic starter

Sep 3, 2022

Thanks Andrea, that's what I notice also, though not being an expert on refractors.
What's a bit odd is that this scope has a couple of good reviews which says it's free of CA.

I'll have a talk with TS about this.

Thanks for your valuable input 😃

Björn Arnold

Sep 3, 2022

Hi Steen,

For a triplet with FPL55 glass, I would expect much less chromatic aberration.
In addition, did you use a corrector (flattener/reducer)?

Björn

Well Written Insightful Respectful Concise

Steen Knarberg

Topic starter

Sep 3, 2022

Hi Bjørn

It's FPL53 glass.

But it turned out that I have probably gotten the white balance a bit of by assuming that dark areas around the Nebulae was not Nebulae, which it is. That threw the balance of in blue direction.
I have just examined the raw OSC fits files which shows stars of all colors, also what looks to be neutral ones.
Right now I'm shooting some Optolong L-extreme OSC which looks rather promising.

I'll post those.

Thanks and clear skies
Steen

Steen Knarberg

Topic starter

Sep 3, 2022

Lynn K:
Hi Steen, I am not an optical designer and never ground my own mirror or lens, but have used refractors for astro imaging fo years. I have owned acrochromatic doublest for visual. My first imaging refractor was a WO Megrez 80II triplet. My second was a Astro Tech AT110ED (FPL51 galss). I upgraded to a TMB130SS with FPL53 glass. I saw no increase in resolution from the 110mm to 130mm, but did see a decrease in Color aberations due to the FPL53 glass. The TMB had pitched optics. So, I know waht that looks like. I was able to correct that. I now own a Takahashi FSQ106ED four element F5 and a Astro Physics AP130GTX triplet (FPL53).

I have a Vixen 150mm f5 reflector for visual. I have imaged through Celestron SCTs 8", 9.25" and 11". I have a EDge 8, but only do visual with it.

I'm a mono filtered imager using mostly narrow band, and only recently moved to CMOS. I do have an older OSC CCD camera, but have used it very little.

Your image looks fairly typical to me. I see no CA around the stars. There is a good amount of "glow" around the blue stars. They are hotter and brighter. The glow is caused by a measureble amount of light not going into the airy disk, but ending up in the outer defraction rings. As you know, this will put photons in the sorrounding pixels. As the image is stretched, those surrounding pixels will become lighter.

Better refractor optics will put more of the light in to the airy disk and less into the surrounding pixels. I suppose filters and pixel size can affect this as well. Focus is also a big issue with the smallness/sharpness of the stars.

There is a very very slight bit of CA on the outer edge stars caused by coma. I think very aceptable.

My solution to star size and color is to eliminate them from processing with Star ExTerminator, and then use stars from short RGB subs.

That's my thoughts. I hope it helps some.

Lynn K.

Hi Lynn

Thanks for your very helpful and valuable input on this.

I have come to the same conclusion after studying the raw subs. As I wrote to Bjørn the white balance was thrown a bit of by the nebulousity which made the stars look more blue. And you're right, there are a lot af very hot stars in that field.

I think the scope is a keeper and thanks again for taking your time.

Clear skies
Steen

Respectful Supportive

Lynn K

Sep 4, 2022 · Edited: Sep 4, 2022

Steen, that makes sence to me. It just looked more of a processing issue than an optical issue to me. I have had refractors that were not fully alpochromatic and there was a small tight blue area around all stars. Not just creating a bloaded blue area around the blue stars. I can get a similar looking effect when tring to layer in OIII as a blue channel. The OIII stars are larger than the Ha and can overwhelm the star. Star ExTerminator has solved that issue for me.

Lynn K.

Steen Knarberg

Topic starter

Sep 4, 2022

Exactly! Thanks again Lynn, I appreciate it very much :-)

Steen K.

andrea tasselli

Frequent contributor

Sep 4, 2022

I wonder if it is this one:

https://www.teleskop-express.de/shop/product_info.php/info/p6679_TS-Optics-PHOTOLINE-130-mm-f-7-FPL53-Triplet-APO-Refractor.html

I'd like to keep a tab on those ones not up to their hype.

Steen Knarberg

Topic starter

Sep 4, 2022

It is, but I think I got things wrong with the white balance because of the nebulousity stretching further than I imagined.

After examining the raw data it actually looks quite ok and to my eyes very sharp. I shot some duo band yesterday which looks fantastic.

/ Steen K 😊

andrea tasselli

Frequent contributor

Sep 4, 2022 · Edited: Sep 4, 2022

Steen Knarberg:
It is, but I think I got things wrong with the white balance because of the nebulousity stretching further than I imagined.

The white balance has got nothing to do with it, your h-g lines are off with respect to the the average RGB position and that shows as a violet halo around bright stars (white to off blue). I've seen worse but that was for ED doublets, not supposedly well-corrected FPL53 APO triplets.

Mind you, if you're happy with it then it is all cool.

Insightful Concise

Rafał Szwejkowski

IOTD Staff

Sep 4, 2022

These come with a lot of CA. It's not a collimation issue or particular one tube. Hence their attractive price, but if they were good, would they be so cheap?

andrea tasselli

Frequent contributor

Sep 4, 2022

Just to put in prospective a Takahashi TOA 130NS with the craddle is upwards of 6000 euro, i.e. 3 times as much as the TS ones.

Steen Knarberg

Topic starter

Sep 4, 2022

I have now shot images of a star on the inside and outside of focus, see below. Could

andrea tasselli:
Steen Knarberg:
It is, but I think I got things wrong with the white balance because of the nebulousity stretching further than I imagined.

The white balance has got nothing to do with it, your h-g lines are off with respect to the the average RGB position and that shows as a violet halo around bright stars (white to off blue). I've seen worse but that was for ED doublets, not supposedly well-corrected FPL53 APO triplets.

Mind you, if you're happy with it then it is all cool.

Hi Andrea

Would you take a look at these two images of inside/outside focus and give med your thoughts?

Inside focus

Outside

Cheers, Steen K

Steen Knarberg

Topic starter

Sep 4, 2022

Lynn K:
Steen, that makes sence to me. It just looked more of a processing issue than an optical issue to me. I have had refractors that were not fully alpochromatic and there was a small tight blue area around all stars. Not just creating a bloaded blue area around the blue stars. I can get a similar looking effect when tring to layer in OIII as a blue channel. The OIII stars are larger than the Ha and can overwhelm the star. Star ExTerminator has solved that issue for me.

Lynn K.

Hi Lynn

Could I ask you to have a look at the startests I just posted in this thread and give me your thoughts, please?

/ Steen K

andrea tasselli

Frequent contributor

Sep 4, 2022

Steen Knarberg:
I have now shot images of a star on the inside and outside of focus, see below. Could
andrea tasselli:
Steen Knarberg:
It is, but I think I got things wrong with the white balance because of the nebulousity stretching further than I imagined.

The white balance has got nothing to do with it, your h-g lines are off with respect to the the average RGB position and that shows as a violet halo around bright stars (white to off blue). I've seen worse but that was for ED doublets, not supposedly well-corrected FPL53 APO triplets.

Mind you, if you're happy with it then it is all cool.

Hi Andrea

Would you take a look at these two images of inside/outside focus and give med your thoughts?

Inside focus

Outside

Cheers, Steen K

Hi Steen,

Hard to say as it is very out of focus. And won't say much about CA anyway. I expect around lambda/4 from the difference between intra and extra-focal images, but this a more a gut-deeling than a precise evaluation. To be able to say more I'd need the out-of-focus images to show few diffraction rings, 4-6 I'd say.

Steen Knarberg

Topic starter

Sep 4, 2022

andrea tasselli:
Steen Knarberg:
I have now shot images of a star on the inside and outside of focus, see below. Could
andrea tasselli:
Steen Knarberg:
It is, but I think I got things wrong with the white balance because of the nebulousity stretching further than I imagined.

The white balance has got nothing to do with it, your h-g lines are off with respect to the the average RGB position and that shows as a violet halo around bright stars (white to off blue). I've seen worse but that was for ED doublets, not supposedly well-corrected FPL53 APO triplets.

Mind you, if you're happy with it then it is all cool.

Hi Andrea

Would you take a look at these two images of inside/outside focus and give med your thoughts?

Inside focus

Outside

Cheers, Steen K

Hi Steen,

Hard to say as it is very out of focus. And won't say much about CA anyway. I expect around lambda/4 from the difference between intra and extra-focal images, but this a more a gut-deeling than a precise evaluation. To be able to say more I'd need the out-of-focus images to show few diffraction rings, 4-6 I'd say.

Hi Andrea

I seem to have dificulties getting the rings very clearly defined no matter what focus I set. But this is much less defocussed. Can you make something of it?

Thanks, Steen K

Pete Bouras

Sep 4, 2022 · Edited: Sep 5, 2022

Lynn K:
Hi Steen,...

The TMB had pitched optics. So, I know what that looks like. I was able to correct that. ...

Lynn K.

Hi Lynn,

As a TMB130SS owner, I would like to know what are pitched (or perhaps pinched?) optics, and what was the symptom you were able to correct?

CS
Pete

andrea tasselli

Frequent contributor

Sep 4, 2022

Hi Steen,

I'm afraid not much, except the optics look pretty smooth and no major aberration to report. You'd normally get those rings with 3-4 lambda of defocus, which is between 0.6-0.8 mm for your scope. These is typically seen at high magnifcations, so probably the 294 isn't a good starting point. Have you got a planetary camera with small pixel pitch, the smaller the better? As an alternative, a 2" barlow (assuming of good make).

Helpful Concise

Lynn K

Sep 5, 2022

Hi Steen, Sorry but I can't tell much from those two images. i can say is there is a little mode light put into the outer defraction ring in the outside focus. But I would expect that. But my understanding is that is meassuring spherical aberation not chromatic. I am not an optical designer or amateur mirror/lens maker. My experience only comes from doing astrophotography over the years.

I would think the best test would simply be a stacked un processed image of stars of different magnitide. There may be some cromatic aberation, but exceptable for the scope manufacturung level. I have discovere the only bargains with regard to astro equipment is a good used price.

If you are happy with the new processed star results, then all may be well.

Lynn K.

Lynn K

Sep 5, 2022

Hi Pete, I bought the TMS130SS after Tomas M. Back had passed away. I never got a clear answer where the optics were manufactured. Astronomics said "they thoufgt Japan, but not sure".

I started to notice some images had odd shaped stars with a pertruding point off one side. I considered many culprits such as focal reducer/tracking etc. I then noticed that it was only the images done in very cold weather that the problem occured. That's when I concluded that the issue may be caused by pinched optics. I called Astronomics which had marketed that scope. They informed me that they no longer did scope matainence, but that it could be pinched optics. They said the rear retainer ring (holding in the optics) should only be finger tight. I removed the lens cell and with a special spanner wrench, I had to put my whole body weight to losed it, WAY OVER tightened. As if it was over tightened in a very warm climit.

Pinched optics will create a diamond shaped star, which can look oval when blured by atmosphere and processing. Mine pertruded more to one side which gave them a kind of odd apentage.

Loosening the retainer ring corrected the odd star shap issue, BUT during the process, I stupidly forgot that the front lens element pertruds beyone the lens cell, and while the lens was face down I put a 1/4" strach in the center of the lens. Very, Very upsetting. On a good note; Al Naglar of Televue once told me (when I was commenting on a strach on a filter I had) that he could place a broken tooth pick in my filter, and I would no be able to see it. Because it would be so out of focus. So any stratch on my filer was insignificant. For visual, anyway. Im have concluded the same for the TMB, when considering the secondary holder of reflector and cadioptic scopes is much more extream.

However the TMB mostly sets in it's case doday. I have aquired a AP130GTX that I use now.

Lynn K.

Helpful Insightful Respectful Engaging

Pete Bouras

Sep 5, 2022

Lynn,

Thanks for the info. It seems my TMB has escaped that issue.
I think I read somewhere in Asia (Philippines?) for the optics made to Thomas' specifications.

Clear Skies,
Pete

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