Askar 107phq for Cal H/K?

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sywong2000
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Askar 107phq for Cal H/K?

Post by sywong2000 »

Hi everyeone

While browsing around and looking for a possible ~100mm aperature scope for solar works... I've found Askar 107PHQ.... It's advertised as air-spaced quadruplet for astrograph use with internal flattener...

The spot diagram is what caught my attention: it seems the scope does pretty well < 430nm. I was trying to get a scope for Calcium H/K imaging use so this looks pretty attractive. At the Ha range it seems to be good as well. I'm not sure if I'm right, but after comparing the spot diagram between Tak TOA and Askar ones, they seemed to perform similar. In terms of aperture of course the 130 or 150 is a better choice. However for my case, I don't have a stationary observatory so transportation is also something I have to consider.

Just see if anyone may have any idea of how it performs for solar works..
you can see the spec and spot diagram here
https://www.firstlightoptics.com/askar- ... graph.html


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Re: Askar 107phq for Cal H/K?

Post by RomanH »

Askar 107PHQ is on my "thinking about" list :D. It looks like super astrophoto machine with big corrected field. I already have Askar 90/500mm which I stopped to 82mm for perfect pinpoint stars. Stars are perfect from center do the edge even with big sensor of Fujifilm GFX 50S I use with it. I tried it few times also with Daystar Quark Ha with very good results. The 155mm APO is different beast, but its also big/long and heavy. Here is one image from Askar 90/500mm (stopped to 82mm). More info and resolution on https://astrofotky.cz/gallery.php?show= ... 237643.jpg. You can expect much better result with good seeing due to bigger aperture and native f7 (works better with Quark).

Image
Last edited by RomanH on Mon May 23, 2022 11:44 am, edited 1 time in total.


sywong2000
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Re: Askar 107phq for Cal H/K?

Post by sywong2000 »

after more readings on the spot diagram I think TOA still win - Tak uses a 100um area while the Askar uses a 200um area. Yet the Askar still being attractive...


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Re: Askar 107phq for Cal H/K?

Post by Bastelhannes »

sywong2000 wrote: Mon May 23, 2022 10:01 am after more readings on the spot diagram I think TOA still win - Tak uses a 100um area while the Askar uses a 200um area. Yet the Askar still being attractive...
Hm.. I did not understand anything. What does it mean? Sorry, if I sound to dumb...


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Re: Askar 107phq for Cal H/K?

Post by RomanH »

He means those "boxes" where the spot is drawed. Someone use bigger box to look spot dot smaller and so more attractive. You can still check the number values - RMS radius between 3-5um is pretty good value on par with LZOS telescopes ... I think that those new Askar telescopes (green) are very good and very close to LZOS/Tak or similar high quality brands. In one comparison of astrophotos I saw that 107mm gave better/sharper stars than SW Esprit 120mm.


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Re: Askar 107phq for Cal H/K?

Post by sywong2000 »

RomanH wrote: Mon May 23, 2022 10:26 am He means those "boxes" where the spot is drawed. Someone use bigger box to look spot dot smaller and so more attractive. You can still check the number values - RMS radius between 3-5um is pretty good value on par with LZOS telescopes ... I think that those new Askar telescopes (green) are very good and very close to LZOS/Tak or similar high quality brands. In one comparison of astrophotos I saw that 107mm gave better/sharper stars than SW Esprit 120mm.
Roman, thank you. Yes I saw your results with the 90mm and the 107 seemed to be in another series, and the F/7 would be better for the Daystar Quark.


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Re: Askar 107phq for Cal H/K?

Post by christian viladrich »

Just for the record, here are the spot diagrams calculated at 393 nm by Takahashi for the TOA 150 :

http://astrosurf.com/viladrich/astro/in ... ka-TOA.htm

Basically, it is diffraction limited to 5 mm from the optical axis when used at the prime focus.
With the 67 field flattener, the diffraction limited field is much wider. More than 30 mm diameter. I have to give it a try some day. Still on my to do list ...

At the bottom of the same page, I also included some OSLO simulations of the TOA 130 based on an approximate model.


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Re: Askar 107phq for Cal H/K?

Post by sywong2000 »

Christian,

Great info, thank you. When I look at the longtitudinal abberation I still see the Askar 107 beats most of the APO's average from the apo sample page, especially in the UV range. Probably due to that they have the flattener accounted for already. TOA is of course superb.

I see Askar also planning to have a 0.7x reducer for the 107. I am no expert on optics, but I didn't much find a scope that comes with built-in flattener and then an external reducer. Usually they're both externally available and changable for different uses. So I wonder what's the optic performances it will be, with the reducer in place. As a user, I'd I say I'll pretty much enjoy using the same scope for both solar works and deepsky imaging, given both setup having a good optical performances. But this seemed a little bit too magical to happen :D

Stephen


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Re: Askar 107phq for Cal H/K?

Post by marktownley »

It's spherical aberration you want to be considering for CaK work.

Stop the Askar 107 down to 70mm and it will be wonderful, there are numerous 100mm f10 achros out there that I suspect would win hands down comparing to the Askar full aperture...

Just my thoughts...


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Re: Askar 107phq for Cal H/K?

Post by sywong2000 »

Mark,

Thanks for your comments. Yes I do see posts saying any stopping most 100mm acrhomatic scope would acheive good results. SAFIX was mentioned but I'm afraid they're not available except in the 2nd-hand markets. The UV range is a very specific bandwidth and appearing not many commercial scope would design to handle in such spectrum. Guess very limited areas of interests: solar or Venus imaging I can think of.

I got a Tak 1.7x extender, and I realized I can make a F/12 system together with the 76mm objective unit. I recalled there's a review of this configuration in scopeviews.co.uk - I read the review again and seeing that the violet bloat seemed to be pretty well controlled, and this sounds positive. So I better experiment with it when the CaH arrives before considering making further investments. Cheers

Stephen


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Re: Askar 107phq for Cal H/K?

Post by sywong2000 »

I finally go for the 107phq, as there was a discount from a vendor. The scope has arrived. But weather forecast saying here in Hong Kong will be rainy for the next ten days :(. Scope is pretty well-built and with everything I need (the scope mounting bracket, a handle, vixen dovetail, an a few imaging adapter rings). All I need is to add a 2 inch extension around 40mm, and it focuses well with both a televue 4x or 2.5x, and a Daystar Quark filter configuration. I'm waiting for the Ha ERF still, while prep-ing the mount with a 80mm UV/IR GRB3 as the front ERF. I'm still finding a blue glass as the ERF for Cal H/K...

I'll post first lights once the weather gets better.


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Re: Askar 107phq for Cal H/K?

Post by RomanH »

Congratulations to a new wonderfull telescope. Can't wait for your tests/reviews. As for the Blue ERF filter - Baader Blue filter works for me (bought here: https://www.teleskop-express.de/shop/pr ... nfo/p13870). - I ordered 1.25" since only that was in stock, but works great as an internal ERF in my 155mm APO.


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Re: Askar 107phq for Cal H/K?

Post by marktownley »

RomanH wrote: Thu Jun 16, 2022 6:22 pm I ordered 1.25" since only that was in stock, but works great as an internal ERF in my 155mm APO.
I'd be careful with this, you'll end up cracking it.


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Re: Askar 107phq for Cal H/K?

Post by RomanH »

I know, its not ideal solution. I usually do 5-7 minutes video recording and then I cover the telescope lens. Ideal would be front ERF for Ha and CaK (which I am saving for).


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