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Askar FRA600 Quintuplet Astrograph initial impressions + unboxing

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#26 coinboy1

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Posted 27 February 2021 - 05:41 PM

Thanks for the star test, your sample does seem to be suffering some spherical abberation. I will test the scope out in DPAC against my 1/20th wave zerodur flat to test for spherical aberration.

#27 maxmir

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Posted 27 February 2021 - 06:41 PM

Thanks for the star test, your sample does seem to be suffering some spherical abberation. I will test the scope out in DPAC against my 1/20th wave zerodur flat to test for spherical aberration.

I know I am at 1.125 on either side of focus.

 

This is 0.4 wave low order spherical aberration undercorrected  simulated with Aberrator V3.

Very close to what I see.

 

I may have to return this one.

 

 

What is DPAC ?

 

Thanks

 

Max

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Edited by maxmir, 27 February 2021 - 06:45 PM.


#28 coinboy1

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Posted 27 February 2021 - 07:00 PM

DPAC is double pass auto collimation (an optical bench test). Before you return it I would determine whether your happy with its results as an astrograph. It doesnt have to be a perfect visual scope to make a good astrograph but I understand that .4 wave seems too much spherical aberration. Have you tried a Ronchi eyepiece against a star visually?

#29 coinboy1

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Posted 27 February 2021 - 07:00 PM

DPAC is double pass auto collimation (an optical bench test). Before you return it I would determine whether your happy with its results as an astrograph. It doesnt have to be a perfect visual scope to make a good astrograph but I understand that .4 wave seems too much spherical aberration. Have you tried a Ronchi eyepiece against a star visually?

#30 maxmir

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Posted 27 February 2021 - 09:57 PM

DPAC is double pass auto collimation (an optical bench test). Before you return it I would determine whether your happy with its results as an astrograph. It doesnt have to be a perfect visual scope to make a good astrograph but I understand that .4 wave seems too much spherical aberration. Have you tried a Ronchi eyepiece against a star visually?

I don't own a Ronchi grading right now.  I might pick one up.

Certainly not a star test expert. I could be well off on my 0.3-0.4 wave error estimate.

It hard to know what is acceptable yet.

A 0.25 wave error should still be fine for most of us

I have seen much worse.

 

My seeing has been below average so it been hard to judge.

 

The image I posted it the best to date.

Have not been able to get the corners to snap in yet.

 

I hope your and other scopes will serve for comparison.


Edited by maxmir, 27 February 2021 - 10:02 PM.


#31 Sponge

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Posted 02 March 2021 - 04:57 PM

Hi, I'm very interested in this scope; did you manage to get any tests done under the stars / on the bench?

Cheers
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#32 maxmir

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Posted 02 March 2021 - 08:08 PM

No more tests here recently.

It would be nice to have other reports.



#33 RogeZ

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Posted 02 March 2021 - 09:40 PM

My initial tests show the scope has better star shapes than the FRA400 with the 6200MM in Ha. I need to get some clear skies and get an actual image :)

#34 StephenW

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Posted 02 March 2021 - 09:44 PM

Hey Roger - do you have comparative images?   Would love to see how both the 400 and 600 look on the 6200. 



#35 Sponge

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Posted 03 March 2021 - 02:57 AM

Hi guys, are any of you using an autofocuser with this scope?

If yes, which one and how are you attaching it?

I have a Sesto Senso 2 so am interested to know if it would be compatible with this scope.

#36 coinboy1

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Posted 03 March 2021 - 10:41 AM

I heard the ZWO EAF is a perfect fit for the scope. Sorry for my lack of testing on this scope. I have been away for work during the week and weekends seem to be cloudy or busy (I have 3 little kids at home). Will try to setup DPAC soon and report back. -Tony

#37 alfogator

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Posted 03 March 2021 - 11:49 AM

Yes, I installed the EAF and it fits very well on it. Installing it is a two minutes job.



#38 coinboy1

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Posted 07 March 2021 - 07:56 AM

Askar FRA 600mm Review

 

I finally got around to testing out the Askar FRA 600 last night. After a month of cold and cloudy weather (and busy life), I got the telescope mounted and ran it through its paces. It was a clear and cool evening (not too cold) and the seeing was very good.

 

Overall I feel the telescope optically is “good” and mechanically it is “excellent”. It is marketed as an astrograph and I do believe it is a good astrograph but I can say this scope is NOT an outstanding visual performer.

Now that is out of the way I will explain why:

 

I have tested many telescopes out before so I am familiar with the star test and also have tested this scope with a Ronchi screen. I know how to interpret the results seen at bright stars based on the book “Star Testing Astronomical Telescopes” by H.R. Suiter and years of telescope mirror making experience. I once owned a “visually perfect” Vixen Fluorite doublet 90mm F/10 so I know what color purity looks like at the eyepiece.

 

Star test using Arcturus and Regulus- some spurious color inside and outside of focus. Mostly color free @ critical focus. Airy Disc easily seen at 110x. Not quite “snap focus” due to colors not coming to focus at the peak focus point. There is certainly a point where the color balances to being “almost color free” at critical focus. No hints of astigmatism. Very concentric rings but definitely not identical inside/outside of focus. Star test reveals undercorrection and some false color.

 

Equivalent to many FPL51 ED doublets in color correction. I have seen many apochromats with more superior color correction and fluorite doublets with far superior color correction. I would say the color correction is not good for having a triplet lens up front with two “ED” elements (of unknown type). Compared to my Vixen Fluorite doublet, the color correction of this scope is not great. I have seen views with other triplets and this one does not rank high among the list I have seen. It's pretty close to an old AT102ED I once owned in color correction. Compared to a Takahashi FSQ106 I once owned, the FSQ had much better color correction and correction for spherical aberration. Optically the FSQ106 wins hands down.

 

Ronchi screen @ Arcturus and Regulus. Smoothly undercorrected approx ¼ to ⅙ wave. No zones. Very smooth ronchi lines. Very slight inward bowing inside of focus, very slight outward bowing outside of focus.

I would say the scope is not designed for optimal visual color correction, but is designed as an astrograph where the color is mostly color free at focus. 

 

Okay with optics out of the way (for now) let's go into the mechanics:

 

Mechanically this scope is excellent. One of the best experiences of any scope I have ever owned mechanically. Giant 4.3” focuser was a dream. Buttery smooth R&P with fine focus was a pleasure to use. Even better than a 3” Feathertouch R&P I once owned. I have owned 2.5” and 2” moonlites and this beats them too. The giant 4” focuser on an FSQ106 was never my favorite focuser, and the Askar FRA600 beats the FSQ106 focuser in every way.

 

The buttery smooth rotator was a joy when I had my FujiFilm XT3 camera attached to it. No hint of image shift and locked down nicely. Using the included adapters, I was easily able to get it to focus and there should be no problem with other cameras or DSLRs.

 

The dew shield slid down smoothly with just some drag (but not too much). I would feel confident the sliding dew shield would never get too loose over time either. The beautifully machined dew shield cover also slid on with some drag. Tighter fitting than some scopes but this is a good thing, since you won't worry about it falling off and getting damaged.

 

The handle was a pleasure to use when mounting the scope. It is very ergonomic and I really like the tube ring/handle system. The “D” dovetail had no problems mounting to my “D” saddle.

 

Closing thoughts:

This scope mechanically is everything I could ask for in an astrograph. Optically it definitely has some shortcomings. I would not recommend this scope for critical visual observers but it does provide pleasing views with a wide angle eyepiece. It is a Petzval flat field so the stars are round across the field when paired with a decent eyepiece. You don't always get that with other scopes.

 

Compared to my Takahashi FSQ106 I once owned, I would say the FSQ106 optically is far superior. Mechanically, the Askar FRA600 is a better scope. This scope is marketed as an astrograph so its main selling point is the large flat field 66mm diameter image circle. At $2599, it is less than half the cost of a new FSQ106. You would still have to buy tube rings, dovetail, adapters, and a case with an FSQ so I would actually say this scope is about ⅓ the cost of a new FSQ106 setup when it's all said and done. However, the FSQ will probably have much better optics….

 

I am going to post some pictures of my test shots soon, I will also go deeper into the analysis of the spot diagrams vs the FSQ106 and my thoughts on the optics of this scope. 


Edited by coinboy1, 07 March 2021 - 08:00 AM.

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#39 coinboy1

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Posted 07 March 2021 - 09:06 AM

Single 30 sec sub, stretched. Attached aberration inspection 1:1 image scale, across an APS-C sensor. Obviously I am missing out on a lot of real estate. Stars are mostly round across the field. Slight elongation of right side of field. Could be image sensor tilt or my camera adapter? Chromatic aberration is well controlled @ critical focus. 

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#40 maxmir

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Posted 07 March 2021 - 10:09 AM

I had a Tak FSQ 106N the figure on it was spot on. I even put it on a planet at 150x and it performed nicely.

If it was the newer ED model, I would still have it. The FSQ 106N was designed for film.  The chromatic aberration is much lower on the FSQ106ED.

 

That said, I agree with your assessment so far. I wish you had a full frame test. I missed a chance to do some imaging last night.

Looks like a front is coming in tonight.

 

Here is a full frame aberration test with seeing 4/10 from 2/23.

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#41 maxmir

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Posted 07 March 2021 - 10:16 AM

Note:

To compare Tony's test with mine use the top and bottom of the center column.

This is 25mm field to compare with APS diagonal 


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#42 maxmir

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Posted 07 March 2021 - 10:22 AM

" The “D” dovetail had no problems mounting to my “D” saddle."

 

Mine was 1/8 less than 3" D standard.

It slides out on ADM, Losmandy, IOptron and paramount ME saddles.

I had to replace the dovetail.

 

Max



#43 alfogator

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Posted 07 March 2021 - 10:42 AM

" The “D” dovetail had no problems mounting to my “D” saddle."

 

Mine was 1/8 less than 3" D standard.

It slides out on ADM, Losmandy, IOptron and paramount ME saddles.

I had to replace the dovetail.

 

Max

The dovetail in mine is 73mm wide (same as yours), luckily my saddle (primaluce) is able to clamp on it.



#44 whwang

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Posted 07 March 2021 - 11:02 AM

Hi Max,

 

Based on your image and Tony's, I would say the 106N is a bit sharper. However, this doesn't take the pixel size into account.  I know Tony's pixel size is 3.76 um (Fuji X-T3).  How about yours?

 

Thanks.


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#45 coinboy1

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Posted 07 March 2021 - 11:21 AM

My old model was the original FSQ106 before the N model. Optics the same (fluorite elements), I agree with maxmir on his assessments. FSQ106ED probably far superior. The Askar FRA600 isn't bad for the price point but isn't perfect either. With larger pixels, it may be hard to tell the difference. 

 

Sorry about your dovetail issues, I never actually measured it, I just know it worked well on my iOptron iEQ45 "D" saddle. 



#46 maxmir

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Posted 07 March 2021 - 01:26 PM

Hi Max,

 

Based on your image and Tony's, I would say the 106N is a bit sharper. However, this doesn't take the pixel size into account.  I know Tony's pixel size is 3.76 um (Fuji X-T3).  How about yours?

 

Thanks.

ASI 6200 ~ 3.75um for me.

 

I have the Asker FRA400. This is a much better scope for FF

 

Max


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#47 coinboy1

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Posted 07 March 2021 - 03:07 PM

I had a Tak FSQ 106N the figure on it was spot on. I even put it on a planet at 150x and it performed nicely.

If it was the newer ED model, I would still have it. The FSQ 106N was designed for film.  The chromatic aberration is much lower on the FSQ106ED.

 

That said, I agree with your assessment so far. I wish you had a full frame test. I missed a chance to do some imaging last night.

Looks like a front is coming in tonight.

 

Here is a full frame aberration test with seeing 4/10 from 2/23.

Still a very good full frame sensor shot. Not sure many would pixel peep at the 1:1 scale to notice any major issues. 

 

 

ASI 6200 ~ 3.75um for me.

 

I have the Asker FRA400. This is a much better scope for FF

 

Max

Wow. I am surprised to hear this considering the FRA400 is less than half the cost of the FRA600. I think perhaps they went cheap with the ED elements of the design. However, I do think Askar marketed the fairly correctly because the spot diagrams do match what I see as far as chromatic aberration. I will touch on this in the below posts:



#48 maxmir

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Posted 07 March 2021 - 07:25 PM

I did not express my self well.

 

The FRA 600 is very much better for a full frame sensor.  

I would only recommend the Asker 400 for a APS sized frame.

 

Max


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#49 coinboy1

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Posted 07 March 2021 - 07:59 PM

I did not express my self well.

 

The FRA 600 is very much better for a full frame sensor.  

I would only recommend the Asker 400 for a APS sized frame.

 

Max

 

Ok whew glad to hear.



#50 coinboy1

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Posted 07 March 2021 - 08:17 PM

Attached below is the spot diagram for the FRA 600. What I see at the eyepiece is very similar to what I see on the spot. The blue spectrum blurs a bit more than the red band of the spectrum. Notice the scale of the spot diagram is 200 microns for the large box, and each tiny box represents 20 microns. Notice as the spots go off-axis the image deteriorates somewhat.

as-fra600-9s.jpg

Now here is the FSQ106ED spot diagram. Notice the scale of this spot diagram. It is 0.1mm or 100 microns. Notice the light focuses in a much tighter spot on-axis and off-axis it deteriorates quite a bit more.

FSQ-106ED_SD.jpg

 

Since focal lengths/ratios are close, I decided to scale the the Askar spot diagram next to the FSQ106ED and here is the result.

 

SpotsCompared.jpg

 

Obviously FSQ106ED is much sharper on-axis but not sure you could really tell on a camera sensor. There are a lot of factors involved such as seeing, size of pixels on camera, bayer array, etc. I think the Askar does a good job at producing round stars across the FOV but you can see the blue channel separates quite a bit compared to the red channel. This color shift could show up on images. 




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