What refractors do best !

[John]

How many times have I observed the wonderful triple star Iota in Cassiopeia over the past, say, 15 years ?

Probably almost every time that I observe. The constellation is always above the horizon in the UK - one of 5 such constellations.

I first observed Iota when I got my first ED refractor, a Skywatcher ED100, which was just over 15 years ago now. Initially I found splitting the tighter pair of stars quite difficult but, back then, the highest power eyepiece I had was 166x and my experience in observing was limited.

Since then I have observed the triple star with many different instruments and split it many times. Sometimes the seeing has been mediocre or downright poor so the definition of the 3 stars has left a lot to be desired.

While obstructed scopes ie: newtonians, cassegrains etc split close multiple stars pretty well, to me it is the unobstructed refractor that produces the most satisfying views of these stellar treasures.

Last night it was my 130mm triplet refractors turn. This instrument is quite probably the best that I've owned or observed with in terms of pure optical quality. It has a LZOS (Russian) objective which have a superb reputation for both control of false colour and overall optical accuracy.

The fine objective lens and excellent construction of the scope enable it, under decent seeing conditions, to use magnifications that I had hitherto not experienced. The scope has a focal length of 1200mm (F/9.2). Last night, for tight double stars, my Nagler 2mm-4mm zoom eyepiece went straight into the diagonal and stayed there with 300x being the starting point for observing.

Naturally, very early in my session I turned the scope onto Iota Cassiopeia and the view was truly breathtaking. Moving the zoom eyepiece onto the 3mm setting boosted the image scale. 400x (nearly 80x per inch of aperture) and the 3 star system was really sharply defined. At this magnification the 2.7 arc seconds between the closer pair of stars seems quite a wide gap. It is actually a touch larger than Neptune's apparent diameter currently so the distant gas giant could fit between that pair of stars !

Even the 2mm zoom setting, for a dizzying 600x magnification, did not overpower the definition but 400x did provide the optimum balance of crispness, virtually no light scatter and the impression of a trio of tiny beads on a black velvet background. Just why I love using refractors on such targets.

I made a rough sketch (very rough) and this morning played around with some software to produce what I think is a decent representation of that view last night. It's not as good as the real thing of course - being at the eyepiece end of a large, long refractor on a warmish night with one of the finest binary stars in view takes some beating  

Of course there were many other targets last night including Saturn and Jupiter with the Io shadow transit but it was Iota in Cassiopeia that was in my mind as I drifted off to sleep last night

 

 

Edited August 29, 2021 by John

[wookie1965]

Iota Cassiopeiae and Zeta Cancri (Tegmine) are my absolutely favourite triples with these you can tell at once how good seeing and transparency is. Most importantly you can see how good your optics are A good 4" refractor given seeing and transparency will split both these objects.

I totally agree with you John both my four inch's have split it and my five inch, the view was much clearer in the 5" though. 

Paul

Edited August 29, 2021 by wookie1965

[Stardaze]

I'll add that to the list John. But you're not helping the 'Frac itch' with these comments 😀

[lunator]

Hi John, note Cass is a fantastic sight. The only frac is my little ST80 and it might struggle with the close pair. I will give it a go sometime.

I do like the view in my 8" f6 newt

cheers

Ian

 

[wookie1965]

Just a quick one what mount have you got that 130mm on please.

[ShrewView]

One to add to my list too. Thanks

[callisto]

Thanks for sharing John...Think I'll stretch my 127mm Frac's legs and give it a bash 

 

Mark

[Pixies]

Was observing Iota Cas on Thursday night, but with the 8" dob. Seeing was OK but the view has been better in the past. I might give the  old secondary collimation a check soon. I love  the colour differences.

I have no chance of splitting it with the ST80, the magnification just isn't there. But have yet to try it with the Vixen 80. The Rayleigh limit of an 80mm aperture is 1.75  arc seconds, so it should be possible, shouldn't it?

[John]

2 hours ago, wookie1965 said:

Just a quick one what mount have you got that 130mm on please.

It is a T-Rex heavy duty alt-azimuth. It's been out of production now for a few years and you don't see many around.

 

[John]

56 minutes ago, Pixies said:

Was observing Iota Cas on Thursday night, but with the 8" dob. Seeing was OK but the view has been better in the past. I might give the  old secondary collimation a check soon. I love  the colour differences.

I have no chance of splitting it with the ST80, the magnification just isn't there. But have yet to try it with the Vixen 80. The Rayleigh limit of an 80mm aperture is 1.75  arc seconds, so it should be possible, shouldn't it?

I think it should be possible with a decent 80mm scope. I just about managed it with my ED120 stopped down to 52mm (as an experiment) back in May. The component stars were very dim though:

https://stargazerslounge.com/topic/377032-trying-to-split-izar-with-66mm/?do=findComment&comment=4085866

 

[JeremyS]

Super report, John 👍🏻

[Knighty2112]

Nice report John. Can’t remember looking at this one, but anyway I’ll add it to me to do doubles list on the next opportunity. 

Edited August 29, 2021 by Knighty2112

[John]

6 minutes ago, Knighty2112 said:

Nice report John. Can’t remember looking at this one, but anyway I’ll add it to me to do doubles list on the next opportunity. 

It's quite an easy one to find:

 

[IB20]

Great report. I must admit it’s not a target I have observed yet but sounds like a nice test for the Starbase 80! Cassiopeia is obscured during my regular viewing times a few months of the year but it has emerged recently. I will give it a go during my next opportunity. 

It is great when something observed that night sticks in your mind. Liking this new target digital simulation you are doing recently too, John. 👍🏻

[John]

I've just been looking at Iota Cass with my 100mm refractor. At 300x the view was pretty much the same as with the 130mm except the stars were slightly dimmer and the airy disks a touch larger.

Very attractive triple.

[IB20]

First view of Iota Cass this evening through the 8” dob. A really nice triple system. The brighter larger primary displayed some unevenness in the diffraction ring suggesting the seeing might not have been as good as the previous night but the close secondary and tertiary star showing lovely airy discs at 240x. A great target. 👍🏻

Edited September 8, 2021 by IB20

[dweller25]

Great report John, refractors are my favourite design 🙂

[F15Rules]

Well, it took a couple of weeks to get the chance, but I finally got out last night with Iota Cassiopeiae on a short list to view.

I'll report on the session separately as this is John's Iota thread..

Iota was the final object I viewed, and wow, talk about saving the best til last! Seeing was pretty good last night, although at the time of viewing Iota, there was a heavy dew forming and transparency wasn't the best.

You can see the dew on the scopes' tube, but fortunately the objective stayed clear.. (the scope was pointing at Iota in the shot).

I found the system very easily (thank goodness for RACI finders!) and used the following eyepieces over the next half hour:

Vixen LV 5mm, Vixen LV 10mm, Carton zoom 7-21x, Vixen LV 8-24 zoom, Morpheus 9mm. I also used a Baader Hyperion zoom 2.25X with some of the above.

I found that the best image was with the Morpheus 9mm combined with the 2.25x zoom. The image I saw was very like John's one above, but this was at 260x.. a single faint and rather steady diffraction ring was around the primary, with both the closer and farthest companions being tiny but well defined points. Just beautiful!

I did get up to 468x ( Vixen 5mm with Baader 2.25x), and the system was quite viewable: however, the "less is more" mantra really was true last night, and 260x gave a wonderful view.

Thanks again John for your original report ☺️!

Dave

 

Edited September 17, 2021 by F15Rules
Photos added

[JeremyS]

3 hours ago, F15Rules said:

Well, it took a couple of weeks to get the chance, but I finally got out last night with Iota Cassiopeiae on a short list to view.

I'll report on the session separately as this is John's Iota thread..

Iota was the final object I viewed, and wow, talk about saving the best til last! Seeing was pretty good last night, although at the time of viewing Iota, there was a heavy dew forming and transparency wasn't the best.

You can see the dew on the scopes' tube, but fortunately the objective stayed clear.. (the scope was pointing at Iota in the shot).

I found the system very easily (thank goodness for RACI finders!) and used the following eyepieces over the next half hour:

Vixen LV 5mm, Vixen LV 10mm, Carton zoom 7-21x, Vixen LV 8-24 zoom, Morpheus 9mm. I also used a Baader Hyperion zoom 2.25X with some of the above.

I found that the best image was with the Morpheus 9mm combined with the 2.25x zoom. The image I saw was very like John's one above, but this was at 260x.. a single faint and rather steady diffraction ring was around the primary, with both the closer and farthest companions being tiny but well defined points. Just beautiful!

I did get up to 468x ( Vixen 5mm with Baader 2.25x), and the system was quite viewable: however, the "less is more" mantra really was true last night, and 260x gave a wonderful view.

Thanks again John for your original report ☺️!

Dave

 

Good to hear about your session Dave. Seeing has been very stable the last few nights 

[F15Rules]

Thanks Jeremy,

It was lovely to get outside with a clear sky again. Getting quite excited about the forthcoming winter season..I just hope we get some better skies than last winter..

Dave

[Highburymark]

Spurred on by this thread, I also checked Iota Cassiopeiae last night. What a beautiful sight. Used TSA-120 with TOE 3.3mm, Delite 3mm and TOE 2.5mm to go up to 360x. 

[Xgaze]

Nice report John.

I particularly love the way you mention "drifting off to sleep..." I totally relate to this, I really enjoy falling asleep with my head full of the wonder's of space, mostly meditating on one object in particular. The next morning that image is still strong in my recollection spurring me on to the next session.

Regards,

T