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07/12/2021. More short tube shenanigans and new kit to test on M42



More than two months after my last session, I managed to get out again for a short time (just over an hour) on M42 and the surrounding area.

It's the first time this year I've looked at Orion and the first time ever with the ST80 - I didn't have the time last night to get the dob out and let it cool so I grabbed and gonned!

It was windy and 20% cloud cover when I went out, so I didn't have great expectations as to transparency or seeing but with the low magnifications of the ST80 this is less of an issue anyway. It was 4 degrees so fairly chilly.

I was running the AzGti on a new power source - a usb powerpack and a 9V or 12V step up voltage converter  based on the LM2577 chip:


Maximum load is 800mA for this chip (not sure whether on the 12V or 5V side)  - I did some load tests to check and logged load during my session.

Here's power utilization with a phone connected to the on board WiFI and the unit tracking:


And here's the power during a maximum speed two axis movement:


The usb power meter showed peak current was 650mA during the session (probably when I leaned on the telescope or something) so it looks like it will be fine. It powered the mount happily for the hour and was still showing 99% battery remaining, which is promising although probably inaccurate but not bad for 20 odd quid all in.

I'm going to 3D print a holder for the battery so it slots into the battery compartment of the AzGti so the unit is completely self contained. 

During the session I used the following eyepieces, the two middle ones being new UFF ones by SVbony from Amazon I got during Black Friday - I got these because I liked the Altair UFF 24mm so much:


Initial impressions (I'm neither experienced enough or knowledgeable enough for a review!) are that the 18mm in particular is very much more of the same - lovely sharp stars across lots of the field that soften progressively towards the edge with the ST80 (curved field?) with loads of contrast.

The 10mm seemed to have a smaller sharp spot, but a similar amount of contrast - it darkened the sky over London nicely to allow the nebulosity of M42 to show up far more clearly than through the 24mm or the 18mm and the teeny, tiny trapezium (at 40x magnification) shone out beautifully.  

All three eyepieces are fairly picky when it comes to eye position being central, and I noticed a few times it was easy to get under the eye relief of the 18mm in the same way as the 24mm so it takes a bit of practice to see the field stop consistently - less so with the 10mm. None of the eyepieces are parfocal to me.

Overall I'm really pleased - I hope the 18mm and 10mm barlow as well as the 24mm (didn't get a chance to test last night) and work well in my dob - I'm on the way to being able to retire my cheapy zoom! Seriously temped to get a better barlow (any recommendations?) and the 15mm Altair model would be after that to give me 24, 18, 15, 12, 10, 9, 7.5, 5 and 4 with my Nirvana. I'd only really want a 6mm then probably?

On to the last new bit of kit (to me!) an old black t-shirt. I used it as a shroud to see how I would get on with a proper one.  I liked it but I'd need a thicker one (I could see light through the fabric which was distracting) . One unexpected upside was that it was lovely and warm in there, and my 4mm Nirvana that I normally avoid using as it mists up so readily steadfastly refused to mist up! I used it to chase the E and F stars of the Trap - no luck on either but the nebulosity showed up really well under the shroud even at 100x magnification.  Not sure whether to make my own or buy one.

So a short, packed session on just one target - lots to take in and think about for the future and quite frankly it was great to get out there again, however fleetingly! 






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Nice result. I've used the black T-shirt shroud before. It does keep your head warmer!

To confirm it's field curvature, adjust the focus slightly. If you can get the outer stars in focus, with the centre now out of focus, it's field curvature.

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On 11/12/2021 at 11:01, Pixies said:

Nice result. I've used the black T-shirt shroud before. It does keep your head warmer!

To confirm it's field curvature, adjust the focus slightly. If you can get the outer stars in focus, with the centre now out of focus, it's field curvature.

Ah ha! Yes - as I adjusted focus a "ring of sharpness" moved outwards or inwards from the centre. So field curvature then.

It's SO different to the dob - there the stars stay sharper (but not sharp sharp!) towards the edge but obviously get more comet shaped...

Love the way the stars in the ST80 "pop" in and out of focus!

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