73 replies to this topic

[peleuba]

 I read the following “To be sure, its likely this telescope will produce better images than an 8” SCT. Admittedly, that is a rather low performance bar to exceed. “. I’m ok with the first sentence but hey hey hey, the second?

 

I am certainly open to criticism and further discussion but I am not not sure there is much to argue with as most SCT's have barely ¼ wave optics and all have very rough corrector plates.  The modern SCT, like the Askar refractors, is made to a price point.  Once the optics reach the diffraction limited threshold, work stops.  There is no attempt to eek any additional performance via tweeking or extended polishing and figuring in an SCT.  The selling price does not support this extra work.   

Edited by peleuba, 10 January 2025 - 12:07 PM.

[ZX12]

I bought what might have been the first Askar 203 in the U.S. back in September last year, and had it for about three weeks before sending it back to the distributor.

 

It appeared to have an optical issue which to me looked like spherical aberration. When looking at a star, a series of concentric rings radiated out from the Airy Disk.

As you focused the star to a fine point at high power the Airy Disk would shrink down to a smaller than typical size for the aperture and the rings would grow in size. Splitting a binary star less than 2" was impossible due to the interference of the ring pattern. 

 

Looking at a planet, the 203 would not come to perfect focus. I could see a relatively sharp image superimposed over another less sharp image. It was a subtle almost ghost like effect, and clearly not correct.

 

Objects like M42 look spectacular, but resolving the Trapezium down to the E and F stars which the 185 does with ease, left the 203 struggling due to the ring pattern around each of the four main components.

 

The intra focal pattern looked okay, although you could just see what appeared to be a central zone. At the extra focal position, the zone was bright and grew in size as focus moved out before dispersing into the rest of the fainter rings.

 

The Askar 185 was along side during my viewing sessions and it easily outperformed the 203 in sharpness. The ability to see fine stars in M13 at low to mid power with the 185 is something the 203 should have been more than capable of, but the 185 was superior due to the lack of perfect focus in the 203. 

 

The 203 is quite a beast compared to the 185. Much heavier feeling than the actual difference, with more front bias making it awkward to mount. A permanent mount in an observatory would be needed to get the most out of this size refractor.

 

Fit and finish of the 203 is excellent overall, and with the collapsible draw tube it's very compact for an 8" refractor. The 203 didn't appear to have any thermal issues with the lens as the optical aberration did not change regardless of temperatures.

 

I took some deep sky photos with it and they didn't look too bad compared to the view through the eyepiece (stars appeared slightly more bloated than the 185), but I bought the 203 more for visual use.

 

After contacting Askar with the issue they asked for photos of the intra and extra focal pattern, and they subsequently handled the return with help from the distributor very professionally.

I would say their customer service is top notch, especially in handling a scope of this size. 

 

It's difficult to understand how a scope like this is not just tested photographically, but also visually as it's likely that a large percentage of buyers would use it for that purpose.

 

There is certainly a lot of potential for the 203 to be a great scope, and I'm sure once the issue gets sorted out the scope will get into regular production.

 

I'm guessing they are still working on issues with lens polishing that looks to be creating a central zone, but maybe some of the people here on CN might understand more about what I am describing optically.

 

Mike

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Edited by ZX12, 11 January 2025 - 10:06 PM.

[CHASLX200]

I will pass.

[denis0007dl]

I bought what might have been the first Askar 203 in the U.S. back in September last year, and had it for about three weeks before sending it back to the distributor.

 

It appeared to have an optical issue which to me looked like spherical aberration. When looking at a star, a series of concentric rings radiated out from the Airy Disk.

As you focused the star to a fine point at high power the Airy Disk would shrink down to a smaller than typical size for the aperture and the rings would grow in size. Splitting a binary star less than 2" was impossible due to the interference of the ring pattern. 

 

Looking at a planet, the 203 would not come to perfect focus. I could see a relatively sharp image superimposed over another less sharp image. It was a subtle almost ghost like effect, and clearly not correct.

 

Objects like M42 look spectacular, but resolving the Trapezium down to the E and F stars which the 185 does with ease, left the 203 struggling due to the ring pattern around each of the four main components.

 

The intra focal pattern looked okay, although you could just see what appeared to be a central zone. At the extra focal position, the zone was bright and grew in size as focus moved out before dispersing into the rest of the fainter rings.

 

The Askar 185 was along side during my viewing sessions and it easily outperformed the 203 in sharpness. The ability to see fine stars in M13 at low to mid power with the 185 is something the 203 should have been more than capable of, but the 185 was superior due to the lack of perfect focus in the 203. 

 

The 203 is quite a beast compared to the 185. Much heavier feeling than the actual difference, with more front bias making it awkward to mount. A permanent mount in an observatory would be needed to get the most out of this size refractor.

 

Fit and finish of the 203 is excellent overall, and with the collapsible draw tube it's very compact for an 8" refractor. The 203 didn't appear to have any thermal issues with the lens as the optical aberration did not change regardless of temperatures.

 

I took some deep sky photos with it and they didn't look too bad compared to the view through the eyepiece (stars appeared slightly more bloated than the 185), but I bought the 203 more for visual use.

 

After contacting Askar with the issue they asked for photos of the intra and extra focal pattern, and they subsequently handled the return with help from the distributor very professionally.

I would say their customer service is top notch, especially in handling a scope of this size. 

 

It's difficult to understand how a scope like this is not just tested photographically, but also visually as it likely that a large percentage of buyers would use it for that purpose.

 

There is certainly a lot of potential for the 203 to be a great scope, and I'm sure once the issue gets sorted out the scope will get into regular production.

 

I'm guessing they are still working on sorting out some issues with lens polishing that looks to be creating a central zone, but maybe some of the people here on CN might understand more about what I am describing optically.

 

Mike

Hi Mike,

 

thanxs for input.

 

Seems so far 185mm model is better than larger brother.

[Traveler]

Yesterday i saw an Askar 203 live. Although big, not a beast imo...

[Kim2010]

"Objects like M42 look spectacular, but resolving the Trapezium down to the E and F stars which the 185 does with ease, left the 203 struggling due to the ring pattern around each of the four main components."

 

Wait, isn't the E and F stars supposed to easy with an 8"? My C8 SCT easily reveals E and F.

[Astrojensen]

"Objects like M42 look spectacular, but resolving the Trapezium down to the E and F stars which the 185 does with ease, left the 203 struggling due to the ring pattern around each of the four main components."

 

Wait, isn't the E and F stars supposed to easy with an 8"? My C8 SCT easily reveals E and F.

That was exactly the point he was making. 

 

To me it sounded like the scope had excessive undercorrection, combined with some spherochromatism. Completely unacceptable in any scope, regardless of price. 

 

 

Clear skies!

Thomas, Denmark

[CHASLX200]

Yesterday i saw an Askar 203 live. Although big, not a beast imo...

Needs to be F/10 for my taste.  

[CHASLX200]

"Objects like M42 look spectacular, but resolving the Trapezium down to the E and F stars which the 185 does with ease, left the 203 struggling due to the ring pattern around each of the four main components."

 

Wait, isn't the E and F stars supposed to easy with an 8"? My C8 SCT easily reveals E and F.

I never see em in a 8". I had seen them back in the 80's with a big Dob. But until i had my 18" Obsession they popped out and stabbed my eye they were so easy to see.

 

But out of mind out of site as i never think to look for E and F as most deep sky objects i just take a fast peek at and move on.    I am gonna make it a plan to look for them on a good seeing nite.  I only have 2 8" scopes as of now. I really want a big gun fract.

Edited by CHASLX200, 12 January 2025 - 06:39 AM.

[Josef1968]

Hello!

 

With star test!

 

https://www.youtube....ObservarelCielo

[Dave Novoselsky]

Well 203mm is 8 inches and 185mm is 7 inches.

Thanks, I needed the help, I’m math challenged 

[denis0007dl]

Hello!

 

With star test!

 

https://www.youtube....ObservarelCielo

Excellent startest IMO, considering price of scope and its size.

[Bearcub]

Thanks for posting this. I ordered the 185 APO in December. It's arriving tomorrow. I'll be doing a star test tomorrow night if the SoCal winds calm down before then.  

 

I wonder why Askar decided to offer a 203mm. It's only 20% more light than the 185. That's like offering at 100mm and a 109mm. A 210mm probably would have made more sense given they already have the 185. 

They most likely showing that they CAN produce 203mm and they probably testing how much % of sales goes for 185mm compared to 203mm.

 

Maybe in a couple years they will go for even larger apos after getting more experience with 203mm. If they would only stay stuck with 185mm and then go for lets say 225mm then thats a jump too high.

 

Thats my opinion

[Alan A.]

Hi,

 

Great posts, very informative.

 

Last year I was at the Grand Canyon Star Party and someone had a pair of Askar 185s set up as binocular telescopes.  The views were excellent,  and all the stars across the FOV looked very sharp - but I didn’t get to look at anything with high power.

 

Regarding this 203mm Askar scope and its Ronchi tests in DPAC, it should perform quite well visually, although not quite at the level of a Takahashi/TEC/AP.  Looking at the price you are getting, extremely high value per dollar.  Compare to a TOA-130 - almost the same price!

 

 

Alan

[Simoes Pedro]

"ouch"

[Psion]

Today, I finally took the Askar 203 mm under the night sky. Although it had been stored at a reasonable temperature of around 10°C, thermal stabilization was necessary, and I could see how the image gradually settled over time. There was a slight haze, so I didn't expect full contrast during testing. On Jupiter, when the seeing momentarily stabilized, I could see two main light brown bands and the orange Great Red Spot – using a magnification of 470x with the TV Zoom 3mm eyepiece. At this magnification, chromatic aberration was quite manageable; of course, it’s not zero, but even the TEC 140ED isn’t completely free of it.

 

For the Moon, the ideal magnification in terms of quality and contrast was 285x. The details in the craters and mountain ranges were quite decent. Sure, it's not the image quality of a TEC telescope, but it's not bad, especially considering that the TEC 140 today costs the same as the Askar 203 mm.

 

Mars was also a fantastic sight; the northern polar cap was shining brightly, and in the southern hemisphere, a dark region around Terra Sirenum was visible – again at 470x magnification. A dark band surrounding the cap was distinctly noticeable.

It’s clear that this telescope allows for high magnifications on planets, as it provides plenty of light and its decent aperture determines the resolution of details.

I should add that the manufacturer classifies this telescope as a photographic instrument rather than an observational specialist, but in my opinion, it is very usable for visual observation as well. The thermal stabilization to the final 2°C took about 5 hours. The telescope will need slight collimation – it’s a bit off, but nothing major.

 

For a moment, the haze cleared from the sky, so I attached the Zeiss Mark V binoviewer with TV 13mm eyepieces and a 2.6x multiplier, reaching a magnification of 284x. The contrasty view of the Moon was breathtaking. The view of Mars was also fantastic, revealing far more details than with one eye alone – almost like looking at a photograph. At times, the binoviewer even handled magnifications up to 480x, thanks to the ample light.

 

I think the Ronchi test is not great, but considering the price and expected quality, it's quite good. I was expecting a worse result.

 

Overall, I was very satisfied and thoroughly enjoyed this observation after a long time.

Attached Thumbnails

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Edited by Psion, 08 March 2025 - 01:26 AM.

[denis0007dl]

Today, I finally took the Askar 203 mm under the night sky. Although it had been stored at a reasonable temperature of around 10°C, thermal stabilization was necessary, and I could see how the image gradually settled over time. There was a slight haze, so I didn't expect full contrast during testing. On Jupiter, when the seeing momentarily stabilized, I could see two main light brown bands and the orange Great Red Spot – using a magnification of 470x with the TV Zoom 3mm eyepiece. At this magnification, chromatic aberration was quite manageable; of course, it’s not zero, but even the TEC 140ED isn’t completely free of it.

 

For the Moon, the ideal magnification in terms of quality and contrast was 285x. The details in the craters and mountain ranges were quite decent. Sure, it's not the image quality of a TEC telescope, but it's not bad, especially considering that the TEC 140 today costs the same as the Askar 203 mm.

 

Mars was also a fantastic sight; the northern polar cap was shining brightly, and in the southern hemisphere, a dark region around Terra Sirenum was visible – again at 470x magnification. A dark band surrounding the cap was distinctly noticeable.

It’s clear that this telescope allows for high magnifications on planets, as it provides plenty of light and its decent aperture determines the resolution of details.

I should add that the manufacturer classifies this telescope as a photographic instrument rather than an observational specialist, but in my opinion, it is very usable for visual observation as well. The thermal stabilization to the final 2°C took about 5 hours. The telescope will need slight collimation – it’s a bit off, but nothing major.

 

For a moment, the haze cleared from the sky, so I attached the Zeiss Mark V binoviewer with TV 13mm eyepieces and a 2.6x multiplier, reaching a magnification of 284x. The contrasty view of the Moon was breathtaking. The view of Mars was also fantastic, revealing far more details than with one eye alone – almost like looking at a photograph. At times, the binoviewer even handled magnifications up to 480x, thanks to the ample light.

 

I think the Ronchi test is not great, but considering the price and expected quality, it's quite good. I was expecting a worse result.

 

Overall, I was very satisfied and thoroughly enjoyed this observation after a long time.

Thanxs for post!

 

Try remove GPC 2.6x when using Mark V, and use short focal eyepieces, and then check results.

 

I found 2.6x GPC to worsen image quality and to be worst from all Baader GPCs.

 

1.25x is best, then 1.7x is very good.

 

Also, try using mirror diagonal, and then switch to prism diagonal.

 

Results might suprise you positively.

 

With my Askar 185, I got fully colourfree image at 370x (even when defocussed on both sides!!!), using Nagler 3.5mm eyepieces, APO SS binoviewer, mirror diagonal, and NO GPC.

Edited by denis0007dl, 08 March 2025 - 03:17 AM.

[CHASLX200]

Jupiter better pop with life for a scope that is around 5k. I still say my 826 will beat it but need one to test.

[Psion]

Thanxs for post!

 

Try remove GPC 2.6x when using Mark V, and use short focal eyepieces, and then check results.

 

I found 2.6x GPC to worsen image quality and to be worst from all Baader GPCs.

 

1.25x is best, then 1.7x is very good.

 

Also, try using mirror diagonal, and then switch to prism diagonal.

 

Results might suprise you positively.

 

With my Askar 185, I got fully colourfree image at 370x (even when defocussed on both sides!!!), using Nagler 3.5mm eyepieces, APO SS binoviewer, mirror diagonal, and NO GPC.

Thank you! I plan to test the use of a prism, it can certainly help in less chromatic aberration. I have tried the GPC 2.6x and 1.7x and have not noticed a difference.

[SandyHouTex]

Today, I finally took the Askar 203 mm under the night sky. Although it had been stored at a reasonable temperature of around 10°C, thermal stabilization was necessary, and I could see how the image gradually settled over time. There was a slight haze, so I didn't expect full contrast during testing. On Jupiter, when the seeing momentarily stabilized, I could see two main light brown bands and the orange Great Red Spot – using a magnification of 470x with the TV Zoom 3mm eyepiece. At this magnification, chromatic aberration was quite manageable; of course, it’s not zero, but even the TEC 140ED isn’t completely free of it.

 

For the Moon, the ideal magnification in terms of quality and contrast was 285x. The details in the craters and mountain ranges were quite decent. Sure, it's not the image quality of a TEC telescope, but it's not bad, especially considering that the TEC 140 today costs the same as the Askar 203 mm.

 

Mars was also a fantastic sight; the northern polar cap was shining brightly, and in the southern hemisphere, a dark region around Terra Sirenum was visible – again at 470x magnification. A dark band surrounding the cap was distinctly noticeable.

It’s clear that this telescope allows for high magnifications on planets, as it provides plenty of light and its decent aperture determines the resolution of details.

I should add that the manufacturer classifies this telescope as a photographic instrument rather than an observational specialist, but in my opinion, it is very usable for visual observation as well. The thermal stabilization to the final 2°C took about 5 hours. The telescope will need slight collimation – it’s a bit off, but nothing major.

 

For a moment, the haze cleared from the sky, so I attached the Zeiss Mark V binoviewer with TV 13mm eyepieces and a 2.6x multiplier, reaching a magnification of 284x. The contrasty view of the Moon was breathtaking. The view of Mars was also fantastic, revealing far more details than with one eye alone – almost like looking at a photograph. At times, the binoviewer even handled magnifications up to 480x, thanks to the ample light.

 

I think the Ronchi test is not great, but considering the price and expected quality, it's quite good. I was expecting a worse result.

 

Overall, I was very satisfied and thoroughly enjoyed this observation after a long time.

That's a beast of a scope, and very beautiful.  The Ronchi looks pretty good actually.  Congratulations.

[Psion]

Also, try using mirror diagonal, and then switch to prism diagonal.

I have tested the effect of the prism on the image of the telescope, but when compared with the mirror, both images appear to be the same.

[Psion]

I did a Ronchi test at home to get it centered, last time on the star it was off collimation. You can compare it to the old AP 178/F9 for example and TEC 160FL.

 

My explanation of the test is that the telescope is semi APO slightly overcorrected with slight spherical aberration.

.
https://www.cloudyni...re-ed-starfire/

.

https://www.cloudyni...2#entry13599345

 

 

Edited by Psion, 12 March 2025 - 01:44 PM.

[Psion]

Often people have trouble understanding Ronchi patterns so I tried the GPT 4.o chat, here is the result which matches my evaluation.

 

**Comparison of Ronchi Images Before and After Focus** 

We now have both images before focus ("IN") and after focus ("OUT"), which allows us to better assess the optical properties of the lens. 

### 1. Checking for Spherical Aberration 
- If the optics are perfectly corrected, the lines in the Ronchi test before and after focus should appear mirror-symmetrical. 
- Comparing both images, the lines do not appear perfectly symmetrical, indicating a slight spherical aberration. 
- The curvature of the lines is not extreme, meaning the spherical aberration is present but not a major issue. 

### 2. Chromatic Aberration 
- Visible color fringes (blue/orange) around the lines suggest some level of longitudinal chromatic aberration. 
- This is common even in APO triplets but should be minimal. 
- The color fringes appear both before and after focus, confirming a typical characteristic of chromatic aberration. 

### 3. Astigmatism 
- If astigmatism were present, we would see different line orientations before and after focus (e.g., crossed or deformed patterns). 
- Based on edge detection, no strong astigmatism is apparent, which is a good sign. 

### 4. Overcorrection 
- Comparing the before-focus (IN) and after-focus (OUT) images, the lines in the IN test appear to bend inward, while in the OUT test, they bend outward. 
- This confirms that the lens exhibits signs of overcorrection. 

✅ **Temperature Effects:** 
- APO triplet lenses can be sensitive to temperature changes. Overcorrection is common at lower temperatures when the glass and optical coatings contract at different rates. 
- If the telescope was tested in a cold environment, performance might improve under warmer conditions. 

✅ **Optical Adjustment:** 
- A slight change in lens spacing could optimize correction, but this is typically not done on factory-sealed lenses. 

✅ **Lens Type:** 
- Some fast refractors with short focal lengths may have slight overcorrection as a side effect of their design. 

### 5. Overall Optical Evaluation 
✅ The optical quality is very good, with only mild spherical aberration, which is acceptable. 
✅ Chromatic aberration is visible but within normal limits for a triplet APO of this size. 
✅ No significant astigmatism is observed, which is very positive. 
To achieve maximum performance, fine collimation or testing at different temperatures may be beneficial, as some optical aberrations change with temperature. 
**Result:** The lens is slightly overcorrected. 
Overall, the optics of this telescope are of good quality, suitable for both visual observation and astrophotography.

Edited by Psion, 13 March 2025 - 03:43 AM.

[davidc135]

I did a Ronchi test at home to get it centered, last time on the star it was off collimation. You can compare it to the old AP 178/F9 for example and TEC 160FL.

 

My explanation of the test is that the telescope is semi APO slightly overcorrected with slight spherical aberration.

.
https://www.cloudyni...re-ed-starfire/

.

https://www.cloudyni...2#entry13599345

 

Askar_IN-1.jpg

 

Askar_OUT-1.jpg

Is it not under-correction? Or over-correction but have the images been mis-labelled? 

 

David

Edited by davidc135, 13 March 2025 - 04:51 AM.

[Psion]

You're right, the optics are undercorrected, I am sorry.