Opinions - New Askar 103mm APO triplet

[Elp]

Just been uploaded to FLO:

https://www.firstlightoptics.com/askar-telescopes/askar-103-apo-triplet-refractor.html

Looking for opinions, mainly for AP use on all around targets.

[Stuart1971]

Looks a very nice scope, and a good spec for the cost…but the only real way to know is for some real world reviews…

I bought a Takahashi FSQ85 and thought it would be superb, and ended up selling to buy an Esprit 100, due to the Tak being really poor with astigmatism due to me using a modern small pixel camera, QHY268m, it was superb with my old CCD cameras with massive pixels….it’s an issue with them for sure, and to try and cure it they bought out another flattener for it, which is not included in the package, so with this Petzval design 4 element scope, to image, you have to use 2, yes 2 flatteners together, the one built into the scope and another on the back, it’s ridiculous TBH…

But this one being a new design should be fine on that front…it does seem a really good buy on paper for sure…with good spot diagrams, .If you do get it, keep us informed how you get on…

[Stuart1971]

One thing I will add, is that it’s a lot cheaper than the rest of the Askar range, so am guessing that will be for a reason…probably the glass….👍🏻

[Elp]

Always dubious when they don't declare it.

[Louis D]

2 hours ago, Stuart1971 said:

One thing I will add, is that it’s a lot cheaper than the rest of the Askar range, so am guessing that will be for a reason…probably the glass….👍🏻

 

2 hours ago, Elp said:

Always dubious when they don't declare it.

That just means it is FPL-51 equivalent glass when the term "ED element/glass" is used.  Generally figure an FPL-51 triplet will have about the same amount of chromatism visually as an FPL-53 doublet, but with longer cool down time.  I'm not sure how they would compare for astrophotography.  For visual, I would go for an FPL-53 doublet to save weight and cool down time.

[Elp]

My current z61 is an FPL53 doublet, it's been fantastic for both visual and photography. I'm led to believe a triplet will be better but one with good glass especially at this aperture. Seen a few fpl53 or equivalent doublets which are also in mind, namely the TS/Altair 102mm F7 (also comes from others). Either that, or an FPL53/55 triplet but at 90mm.

[Vash]

To me, this scope becomes very interesting when considering the matched reducers. 

The 0.6x takes it to f/4 and you still get an image circle large enough for an aps-c sensor. 

I do not think there is currently any 100mm doublet or triplet that can do f/4 at a comparable price. (please tell me if I am wrong!) 

Looking forward to seeing some reviews /pictures

[Elp]

I'd be surprised if it can do 0.6x well. I do f3.8 with my Z61, still haven't managed to remove the edge distorted stars with a 183 sensor.

[Adam J]

10 hours ago, Elp said:

Just been uploaded to FLO:

https://www.firstlightoptics.com/askar-telescopes/askar-103-apo-triplet-refractor.html

Looking for opinions, mainly for AP use on all around targets.

It will likely have some bloat in the blue and not be what I would consider a true apo but it should be manageable with blue filters cutting at 420-430nm or higher and or UV/IR like a Astronomic L3 or Baader UV/IR. But once you do that I am sure it's going to be great for the money. The reason I conclude that is hidden in the spot diagram. Askar normal generate the blue line at 430nm but for some 'inexplicable' reason the choose to specify it at 440nm for this scope, that says it all to me it's not a true APO but it's good for it's price. 

Adam

Edited August 3, 2023 by Adam J

[ollypenrice]

I don't know how much blue bloat it will have but that can be minimized in post processing.  I do see that it has a  rack and pinion focuser and slipped focus from a Crayford cannot be fixed in post processing...

I know that lots of words are devoted to glass type but I would rather see them devoted to collimation, field curvature and... the focuser.

Olly

[bosun21]

I’m happy to stick with my Starfield 102 doublet which has FPL53 and Lanthanum lenses. It also has a 2.5” fully rotatable R&P focuser. The objective is also a weather compensated cell so no pinched optics. Visually I can’t see any CA even at high magnification. Great price as well.

[Space Hopper]

Looks like a nice scope, at a good price point. Compare that to the 107mm PHQ at nearly 3x the price. What gives....???

The option to remove the small section of the tube is good for binoviewers / imagers etc.

 

[Vash]

2 hours ago, Adam J said:

Askar normal generate the blue line at 430nm but for some 'inexplicable' reason the choose to specify it at 440nm for this scope, that says it all to me it's not a true APO but it's good for it's price. 

Adam

Very good spot, the devil is always in the details! 

I eagerly await reviews! 

[WolfieGlos]

11 hours ago, bosun21 said:

I’m happy to stick with my Starfield 102 doublet which has FPL53 and Lanthanum lenses. It also has a 2.5” fully rotatable R&P focuser. The objective is also a weather compensated cell so no pinched optics. Visually I can’t see any CA even at high magnification. Great price as well.

Couldn't agree more, since purchasing mine a few months back I'm still very happy with it. Even with the cost of the adjustable reducer (that I purchased), it's also cheaper than the Askar.

[Vash]

3 hours ago, WolfieGlos said:

Couldn't agree more, since purchasing mine a few months back I'm still very happy with it. Even with the cost of the adjustable reducer (that I purchased), it's also cheaper than the Askar.

The starfield does look like a great scope but f/4 is a whole stop faster. That means half the exposure time for the same noise level. A 2 night imaging run becomes a 1 night sesion. 

Given the UK weather this year, that excites me! I currently image with a few scopes at f5.5 to f6.6 but I am after something faster. 

[gorann]

Will be interesting to see a review of it. It is half the price of an Esprit 100 so a very tempting price. Presumably this is partly because cheaper ED glass like FCD1 or FPL51 is used. My first refractors were an ES127 and an ES80, both with the cheaper FCD1 (similar to FPL51). They got me addicted to imaging even if they gave blue ringed stars. I assumed that stars looked like that until I got the Esprits I now have.

[Elp]

I'm erring towards a TS triplet 90, or the SM 90 in this case. Don't think I'd notice much in the 10mm difference in aperture, the longer focal length of the 100 however would be nice for framing choice options.

[Elp]

The below diagram is just an indication, but I wouldn't expect a triplet to focus wavelengths of light like this:

[Louis D]

4 hours ago, Elp said:

The below diagram is just an indication, but I wouldn't expect a triplet to focus wavelengths of light like this:

Maybe it's trying to show something else like focus flatness across the field at all frequencies?  I'm really not sure what it's trying to show.  Perhaps @vlaiv might know?

[Elp]

I suspect it's the focal point of the main visible colours of light, looking at this it'll suffer purple star bloat one side and blue the other so will have colour fringing. It doesn't seem to match the spot diagrams from my view.

[vlaiv]

5 hours ago, Elp said:

The below diagram is just an indication, but I wouldn't expect a triplet to focus wavelengths of light like this:

As far as I can tell - that diagram shows lateral chromatic aberration - although scale is really exaggerated.

Here is comparison of two types of chromatic aberration:

and associated ray trace diagrams:

This is longitudinal - or one that we are more familiar with, when different colors have different focal length and converge at different points along the optical axis

Lateral behaves like this:

All wavelengths of light are focused in same place along the optical axis (at focal plane), but at different distances from center of the optical plane.

You need complex optical system to produce lateral chromatic aberration - like telescope + eyepiece (especially wide AFOV eyepieces exhibit this) or camera lens with multiple elements (7+) which correct other aberrations but introduce this one.

[licho52]

On 04/08/2023 at 00:01, Vash said:

Very good spot, the devil is always in the details! 

I eagerly await reviews! 

The reviews will come from either people who have bought it already (they will love it and gush) or YouTuber Reviewers who get this stuff from Sharpstar to review (they will love it and gush).  But yeah, it will be fun to watch them do flips trying to hide any glaring problems..

[GTom]

5 hours ago, vlaiv said:

You need complex optical system to produce lateral chromatic aberration - like telescope + eyepiece (especially wide AFOV eyepieces exhibit this) or camera lens with multiple elements (7+) which correct other aberrations but introduce this one.

I am afraid a doublet-triplet apo + reducer setup may already qualify for that "complex system" title. Can't recall which scope but I do remember seeing LA-CA on apo+reducer system (radial pattern, blue out red "in").

[Elp]

There's two images on their website which don't look too bad especially the one with the x0.6 reducer. But who knows the real performance until it's released.

[vlaiv]

2 minutes ago, Elp said:

There's two images on their website which don't look too bad especially the one with the x0.6 reducer. But who knows the real performance until it's released.

There are spot diagrams published for all combinations - with x1 flattener, x0.8 reducer and x0.6 reducer.

Here we have RMS radius of spot diagram. With focal length of 700mm and reduction of 0.6 - that turns out to be 420mm of effective focal length.

6um RMS spot size is equal to 3" at 420mm - so that is quite low resolution.

If we were to calculate effective aperture it would be

3" RMS radius spot size is equivalent to 3" * 2.355 = 7.065" FWHM which is in turn equal to 2.44 * 7.065" / 1.025 = 16.82" airy disk diameter

That is the same as 16.46mm aperture scope. Like I said - not much of a resolving potential.