More doubles in Aquila and magnification issues

[Johnny81]

24/09/2024

Had a couple of hours of relatively clear spells with the odd patch of cloud - so I decided to try a few of the dimmer Struve doubles in Aquila...

This was a test for my 127mm Mak, purposely selecting slightly dimmer stars in a relatively close area of sky.

STF 2389: with a secondary listed at magnitude 11.88 I held no hopes on this one... but something was jutting out but there is a wide 31.8" separation... this must have been my eyes playing tricks

STF 2396: 11th mag secondary and 82'' separation - couldn't see a thing even using averted vision. Any star near or at 11th mag seems nearly invisible from my location

STF 2402: 8.94 mag primary and a 9th mag secondary invisible at a 1.4'' separation - seemed impossible whilst trying at x187. 

STF 2404: A nice close pair of 3.61 separation - yellow primary but couldn't note the colour of the companion. 

STF 2408: A 2'' separation doesn't seem like too much trouble for the Mak but the pair are dim at 8 and 9th magnitudes to see anything meaningful.

STF 2428: Faint secondary of mag 10.31 with a separation of 7'' popping with averted vision. PA approx. 280°. Star right next to ε Aquilae. 

STF 2442: Widish pair at 10'' with an approx. PA: 200°. Yellow primary. Located in a pretty area of the sky above ε Aquilae.

STF 2464: Couldn't split these at all - the Mak and my eyes are struggling with dimmer stars at 1.5 mag difference and a super tight 1.16'' separation (needs much more power!).

STF 2468: 8.80 mag primary and 9.66 mag, over 7'' separation with the companion at approx. PA: 240°. This one wasn't too much of an issue. 

STF 2471: No split on this one - 7.4 and 10.64 magnitudes at a separation of 8.5'' should be doable... 

STF 2489: Close dim companion at approx. PA: 330° with a mag difference of 3.63 - quite the comparison from the much brighter blue/white primary. A nice double, best of the evening. 

STF 2506: Faint companion at mag 10.46 with decent 17'' separation which required some averted vision to see. PA approx. 330°

STF 2518: Nope - no split, secondary invisible at 5'' separation (8.24 and 10.48 pair)

STF 2520: 9th and 10th mag pair at 1.8'' couldn't resolve at x187. 

Many failed splits seems a case of biting off more than I can chew but a good test of limitations. The resolving power of a 5'' scope on dim stars/pairs is a struggle, taking into account light pollution and seeing. I don't think it helps Aquila getting a little low now either (although I stayed mainly in the northern regions). Time for a bigger scope or darker skies?  I felt I just couldn't 'get in there' enough with a few of these. I could try going above x187 power but it just gets a bit horrid and more magnification doesn't seem to help at times.

Edited September 26 by Johnny81

[wookie1965]

Yes in my Bortle 6 sky anything with a mag greater than 9 is very difficult especially with a bright primary. 

[lunator]

The sky brightness will definitely be a factor although if the seeing is good then it always helps.

Hopefully a better night will give you a chance to split these.

Cheers 

Ian

[Mr Spock]

My 100mm is limited to 10.0 in my LP. I've arranged all my doubles charts to suit; I don't list doubles where the secondary is below 10.

Close pairs can be split if they are fairly even and seeing is good and you have high quality optics. The above scope has split 1.2" on a good night.

I have a 6" CC which gives me nothing extra over this scope both in terms of resolution and magnitude.

[Johnny81]

I will certainly go back to a couple of these - perhaps try my 120 refractor and perhaps see if a barlow might help (I never use them). The light pollution to the South is especially horrendous from slightly outer (wouldn't call it suburban) Northampton. One other thing I will try is trying a bit later in the evening - mindful of a dipping Aquila. As we all know - some nights are better than others. 

1 hour ago, Mr Spock said:

My 100mm is limited to 10.0 in my LP. I've arranged all my doubles charts to suit; I don't list doubles where the secondary is below 10.

Indeed - I have a full list of the STF catalogues for each constellation on a spreadsheet and many are highlighted in red.... Surprising as Fredrich Von Struve was seeing these 200 years ago!  Although I would guess separations have changed in a few systems since then and he was using a 9'' refracting telescope according to Wikipedia (no light pollution either).  

 

Edited September 27 by Johnny81

[Johnny81]

Had a much better evening yesterday (27/09/2024) - seen 20 more doubles in Aquila with only 3 or 4 not split (or invisible secondary). I won't list them all but STF 2613 was the highlight (the rest were mainly averted vision jobs). 

Pi Aql was slightly elongated, nowhere near split and seeing was a bit all over the place so no chance at x200 this time. 

The sky was a tad better even though my hands were numb from the cold by 10:30pm. 

STF 2596 and STF 2616 up on the border with Sagitta were an absolute pain but there was something there on each at x200 - but only when the seeing played ball which wasn't often and time was spent just eyeballing and digging in with my right eye...

I didn't like Barlowing - I only have the stock Skywatcher x2 Barlow and it just darkens too much and any contrast is just zapped away. Me thinks I need a couple of better optics even though the Mak is a slow F12, I just don't think you can get away with poor optics on tighter/dimmer doubles. 

[John]

Nice report - Aquila is an interesting part of the sky 🙂

I'm a little surprised you did not split Pi Aql, assuming your mak is a 127mm (120mm working aperture) ?

I can get it with my 85mm refractor and upwards, unless the seeing is pretty poor. 

 

[Johnny81]

17 minutes ago, John said:

Nice report - Aquila is an interesting part of the sky 🙂

I'm a little surprised you did not split Pi Aql, assuming your mak is a 127mm (120mm working aperture) ?

I can get it with my 85mm refractor and upwards, unless the seeing is pretty poor. 

 

Yes 127mm Mak. Might have to break out my refractor when the clouds clear off.

My Mak might need a little tweak in collimation but it isn't bad at all (still holding on after 9 years!) - I think it's just one of those doubles that needs the seeing to play ball to get a clean split. 

[Zermelo]

Out of interest, which EPs were you using?

I've split Pi Aql a couple of times with my Skymax 127, though it wasn't the easiest. It's tight enough that the secondary sits in the diffraction ring of the primary. If there's a bit of wobble in the seeing, and especially if the collimation isn't perfect (mine isn't), it can "hide". I find that scatter from the optics can also hinder a definitive sighting on these tight ones. My splits were with an ES 82° 6.7mm and a BST Starguider 5mm, both of which were not too bad for scatter whereas, for example, my Nirvana 4mm often looked a bit mushy.

[Johnny81]

9 hours ago, Zermelo said:

Out of interest, which EPs were you using?

I've split Pi Aql a couple of times with my Skymax 127, though it wasn't the easiest. It's tight enough that the secondary sits in the diffraction ring of the primary. If there's a bit of wobble in the seeing, and especially if the collimation isn't perfect (mine isn't), it can "hide". I find that scatter from the optics can also hinder a definitive sighting on these tight ones. My splits were with an ES 82° 6.7mm and a BST Starguider 5mm, both of which were not too bad for scatter whereas, for example, my Nirvana 4mm often looked a bit mushy.

Nothing mega, just Celestron Omni Plossls 40mm, 15mm, 9mm and an 8mm BST starguider (and the stock 25/10mm). 

Above x200 the image seems to deteriorate too much in my mak. 

Edited September 29 by Johnny81

[Mr Spock]

I recently split πAql with the 100mm at x185. It should be relatively easy in good seeing conditions. It does help if your scope doesn't have much in the way of diffraction rings though as they can interfere with each other at that sort of separation (1.4").
I saw two round blobs close together - very nice.

[Johnny81]

37 minutes ago, Mr Spock said:

I recently split πAql with the 100mm at x185. It should be relatively easy in good seeing conditions. It does help if your scope doesn't have much in the way of diffraction rings though as they can interfere with each other at that sort of separation (1.4").
I saw two round blobs close together - very nice.

Well last couple of  times I was observing I noticed half or partial diffraction...(I was meaning to start a new topic on this). The bottom or southern side of the star diffraction ring is fainter than the rest. But my collimation isn't too bad to my eye. Not sure what's going on here. 

[Mr Spock]

1 hour ago, Johnny81 said:

The bottom or southern side of the star diffraction ring is fainter than the rest. But my collimation isn't too bad to my eye. Not sure what's going on here. 

Adjust collimation until it's even. 

[John]

Pi Aquilae is one of my favourite doubles. I was pleased to be able to split it with my 85mm refractor, it's close to the limit for that aperture. Somewhere between the Dawes and Rayleigh limits for an 85mm aperture. I think Pi Aql is around 1.4 arc seconds separation ?

With the ED120 it's somewhat easier unless conditions are poor.

 

Edited September 29 by John

[Johnny81]

2 hours ago, Mr Spock said:

Adjust collimation until it's even. 

If there is one thing that terrifies me more about anything else in this hobby - it is collimating a Maksutov telescope 😅

[Mr Spock]

1 hour ago, Johnny81 said:

it is collimating a Maksutov telescope

Easy - you only have three screws to worry about. Adjust one at a time until the diffraction ring becomes circular.

[Zermelo]

2 hours ago, Johnny81 said:

If there is one thing that terrifies me more about anything else in this hobby - it is collimating a Maksutov telescope 😅

I've had the link below on my todo list for a while.  The state of your 127 collimation sounds very like mine - not quite right, but not enough to inspire me to mess with it.

 

 

[Johnny81]

4 minutes ago, Zermelo said:

I've had the link below on my todo list for a while.  The state of your 127 collimation sounds very like mine - not quite right, but not enough to inspire me to mess with it.

 

 

Oh yes, I've watched Martin's video quite a few times. The central section of a defocussed star is only very slightly out on my mak, dipping slightly towards the bottom left (using a diagonal). I just don't know if it is enough to really start getting the Allen keys out... 

When I viewed Delta Cyg a couple of weeks ago during the period of good seeing, it was a lovely diffraction pattern with the secondary as a small dot within. So this tells me collimation isn't too bad. However, the missing or broken diffraction pattern i've been seeing lately is a slight concern. Although closer in seperation, I will give Pi Aql another go once we get a clear night...

If I choose to collimate - the plan is: Polaris>high power straight through scope (no diagonal)>defocus>slacken the large 3 screws very slightly>play carefully with the smaller screws starting where the off-center location is >keep checking/playing till centred>tighten larger screws back up (I presume you need to do this)>recheck. 

[Nik271]

Poor seeing or thermals can affect the diffraction pattern. My Mak is well collimated and I have split pi Aql in good seeing many times, it is a proper split with 120mm aperture: two balls of light with a harline of backness in between and a diffraction ring around each, like this:

 

However when seeing is poor I often tend to see disturbance in the diffraction ring, most commonly a trefoil pattern. Once scope is thermally stable this goes away.

 

By the way another challenging double in Aqula is 23 Aql STF2492, a close pair of very uneven stars. My 100mm refractor just split it in good seeing, so shoud be easier in the Mak.

[Zermelo]

21 minutes ago, Nik271 said:

I often tend to see disturbance in the diffraction ring, most commonly a trefoil pattern

I often see this with my Mak, but I've never understood why the diff ring splits into the threefold symmetry, but with no other distortions that I could see. I originally thought "pinched optics" (and of course the screws are set at 120°} but that didn't explain why it came and went? Is this a consequence of the design?

[Johnny81]

1 hour ago, Nik271 said:

Poor seeing or thermals can affect the diffraction pattern. My Mak is well collimated and I have split pi Aql in good seeing many times, it is a proper split with 120mm aperture: two balls of light with a harline of backness in between and a diffraction ring around each, like this:

 

However when seeing is poor I often tend to see disturbance in the diffraction ring, most commonly a trefoil pattern. Once scope is thermally stable this goes away.

 

By the way another challenging double in Aqula is 23 Aql STF2492, a close pair of very uneven stars. My 100mm refractor just split it in good seeing, so shoud be easier in the Mak.

I went back to Pi Aql tonight and was pretty easy in my 120mm Refractor at x133. The refractor is sharper than the mak but as we know, conditions come into play. 

Got 23 Aql in the Mak on the 20th Sept this year. I noted a faint companion nestled on-top of a much brighter yellowish primary. A difficult split. I'll see how the refractor gets on with this one on another night - pretty fatigued after tonight and I think we're due some cloud here for the foreseeable. 

I have taken the Mak to Orion Optics for some TLC, I tried to collimate it and the rubber O-ring popped out the back plate... I barely moved one of the screws...it could do with a service anyway. 

[Nik271]

12 hours ago, Zermelo said:

I often see this with my Mak, but I've never understood why the diff ring splits into the threefold symmetry, but with no other distortions that I could see. I originally thought "pinched optics" (and of course the screws are set at 120°} but that didn't explain why it came and went? Is this a consequence of the design?

The best explantion  have seen is that the corrector plate gets pinched by the metal tube which contracts faster than glass.