First light with a giant refurbished AR-152s

[badhex]

Hello all,

Reasonably clear skies and my so far busy first few months back in the UK aligned such that I was finally able to have a first quick observation from my new flat, and a very belated sort of first light for my previously (8 years ago!) refurbished Bresser AR-152S. Perhaps an ambitious choice with so many new variables to contend with!

I set up on my balcony as lugging a huge frac and mount downstairs to some as yet undiscovered good observing spot was not on my agenda! Sadly it is a very obstructed (trees) view from the balcony, and near a busy road with streetlights, so will need to find a better spot in future. I also made a judgement error in how low to the ground I would need to be when the frac was pointing to much of the available sky, which proved to be very uncomfortable!

This is the first real test under the stars for this scope since it was lobbed down the stairs (well, it certainly looked like it) by some previous and dastardly persons unknown, and subsequently repaired by me. I was honestly not expecting great results since daytime tests show a lot of CA, and higher mags seemed very difficult to dial focus in. Additionally, I made the repairs a long time ago and have learnt a lot about observing and telescope optics in general since then.

All of this said, as the first photons from the stars hit my eyes via the 35mm ED it seemed surprisingly okay! I couldn’t detect any hugely obvious CA when focused, and it seemed to be a consistent image across the field of view. My first target was M13 which was decently placed and not so high up that I couldn’t view it without doing the limbo, and was clearly visible despite the LP greying out the background with such a large exit pupil. I switched up through the 17.5mm Morpheus and toe the Pentax XW 10mm, but started to see more issues as I increased magnification, mainly in not being able to fully focus properly. M13 was clear visible, but somewhat indistinct and lacked that lovely snap-in of focus that I have come to expect from my other refractors. Thin cloud cover was potentially causing some of this, but I strongly suspect collimation of the main lens cell to be the issue here.

After a bit of poking around, I switched targets to Lyra and the ring, which were somewhat higher up than my back enjoyed. Poor planning on mount height aside, star field at lower powers looked pretty good (for Bortle 7) and Lyra is a particularly enjoyable part of the sky for me from that perspective. I panned around for a bit then searched out the ring. After locating, I again started switching up magnification to find a happy medium. Again I found the same thing, but somehow less pronounced than with M13. Things got worse as magnification increased, and although I did find that it could support the Pentax 10mm at 77x, the ring was decidedly more smudgy and indistinct than it should be. I spent some more time experimenting with focus, different EPs and so on, but eventually called it a night since this was only a supposed to be a short testing session anyway.

Not a fantastic outcome, but certainly not the worst; “not great, not terrible” as the man said.

I looks forward to getting better opportunities, but will start by checking over all optical and mechanical aspects of the scope to see if anything obvious presents itself. Once I have funds again I will avail myself of Suiter’s star testing book and do more methodical testing, and hopefully, bring the scope back to better condition.

Thanks for reading!

[westmarch]

Thanks for the report. Good Luck with the next test. What sort of damage had you found and how did you try to fix it?

John

[John]

Interesting report 👍

I think I would be checking the collimation of the scope as an early measure.

I think the objective cell on those can be collimated.

 

[badhex]

37 minutes ago, westmarch said:

Thanks for the report. Good Luck with the next test. What sort of damage had you found and how did you try to fix it?

John

There are a couple of very old threads on this, linked below if you fancy reading them!

 

[badhex]

30 minutes ago, John said:

Interesting report 👍

I think I would be checking the collimation of the scope as an early measure.

I think the objective cell on those can be collimated.

 

Cheers John. Absolutely, and will be the first to admit I've never collimated a frac and although I understand the general principle, it seems like a terrifying task! I had a crack at it at the time of repair, but it was likely not a very good job! 

[westmarch]

Blimey!  What a job you undertook and hats off for attempting it. 

John

[John]

24 minutes ago, badhex said:

Cheers John. Absolutely, and will be the first to admit I've never collimated a frac and although I understand the general principle, it seems like a terrifying task! I had a crack at it at the time of repair, but it was likely not a very good job! 

I've found the most useful tools are a collimated laser collimator, which is used to check that the focuser optical axis co-incides with that of the objective, and a cheshire eyepiece to check for objective tilt.

The 1st phase involves putting the laser collimator in the drawtube (no diagonal) and seeing where the laser exits the objective lens. It should be pretty much dead centre. If it is not, the focuser needs to be tilted slightly to get that laser in the centre of the objective.

The 2nd phase needs uses the cheshire eyepiece. Again with no diagonal, put the cheshire in the drawtube, illuminate the 45 degree angle face of the collimator and look through the collimator. Ideally you should see 2-3 circular reflections of the collimator face reflected back from the rear of the objective and they should be pretty much on top of each other. If they are separated, the tilt of the objective needs adjustment.

In this image the cheshire is being used to detect focuser tilt or objective tilt. If you use the laser to check / adjust focuser tilt first, you have eliminated that so it is just objective tilt that you are testing for with the cheshire:

Edited August 18, 2023 by John

[JeremyS]

You do seem to have quite a few projects on the go, Joe!
Interesting read 👍🏻

[badhex]

51 minutes ago, John said:

I've found the most useful tools are a collimated laser collimator, which is used to check that the focuser optical axis co-incides with that of the objective, and a cheshire eyepiece to check for objective tilt.

The 1st phase involves putting the laser collimator in the drawtube (no diagonal) and seeing where the laser exits the objective lens. It should be pretty much dead centre. If it is not, the focuser needs to be tilted slightly to get that laser in the centre of the objective.

The 2nd phase needs uses the cheshire eyepiece. Again with no diagonal, put the cheshire in the drawtube, illuminate the 45 degree angle face of the collimator and look through the collimator. Ideally you should see 2-3 circular reflections of the collimator face reflected back from the rear of the objective and they should be pretty much on top of each other. If they are separated, the tilt of the objective needs adjustment.

In this image the cheshire is being used to detect focuser tilt or objective tilt. If you use the laser to check / adjust focuser tilt first, you have eliminated that so it is just objective tilt that you are testing for with the cheshire:

Thanks John, this is super helpful! I actually think in my old bits box from storage I have a laser collimator, I'm still yet to go through it properly. It's amazing what you forget in 8 years! I have the added concern of whether the two halves of the objective are aligned properly with each other, though I hope they should be okay having re-read what I did back in the day. Very glad I posted about it on SGL at the time as something to refer back to! 

This being a pseudo petzval I'm also going to need to check and make sure the rear lens cell is aligned correctly, as I recall there is no collimation possible with it. 

[badhex]

1 hour ago, westmarch said:

Blimey!  What a job you undertook and hats off for attempting it. 

John

Thanks! Perhaps I bit off more than I could chew but I like a challenge! 

Edited August 18, 2023 by badhex

[badhex]

43 minutes ago, JeremyS said:

You do seem to have quite a few projects on the go, Joe!
Interesting read 👍🏻

Haha thanks, I have certainly been known to have a few things on the go at once 😂