Askar FRA 300 & OAG First Light!

[Ouroboros]

Took delivery of an Askar FRA 300 telescope and OAG last week. I’ve had a humdinger of a cold the last four days but decided tonight I just had to try it out before the weather deteriorated in the south as forecast. The skies were misty which didn’t really matter for some tests.

Here’s a couple of single subs - 120s and 300s respectively. The stars look pretty round right across the field, although towards the corners there is clear evidence of chromatic aberration.   This surprises me a little because the ASI2600 is an APS-C sensor and the 300 is supposed to be designed for full frame cameras. I want to analyse the images properly in Pixinsight. These are just screen shots.  Any thoughts on the quality of the stars anyone?

Zoomed into a corner ….

 

I found the Askar OAG quite easy to set up. And the guiding seems quite good. I was a tad surprised how elliptical the guide stars looked. More like a streak. Is that normal for OAGs?

[pipnina]

The effect seems exceptionally minimal- but weirdly I have seen something similar in a reflector image (no corrector lens, no filters!)

It could be anything from the atmosphere, to light scattering in the dichroic anti-reflective coating (???) maybe even light being bent as it moves through the camera's AR glass window. I have no idea!

To my mind this looks totally acceptable, and I thought I was a fussy one! I think you have a spectacular piece of kit!

Sorry if that sounds aggressive, it's not meant to be. I'm just dismayed at how these tiny tiny little problems appear in sometimes the least likely places. And also amazed at how well this hobby turns us into pixel-peepers haha

[Ouroboros]

@pipnina Yes, I’m pleased with what I see, but then I don’t have the experience to know whether it is what I should expect.  That’s why I would appreciate comment from experienced ‘opticians’.  I also don’t really know what to measure. 

[Ouroboros]

As for my elongated guide stars, a quick google this morning suggest this is quite a common observation with OAGs.  I understand it is due to picking off stars at the edge of the image field where distortion will be most apparent. I didn’t adjust the position of the prism when putting the set up together. I just checked the prism wasn’t vignetting the main image in daylight. Regardless of stretched stars the guiding looks good to me, and I haven’t even fiddled with any of the settings.