8” SCT eyepieces for the Moon

[DeanCJ]

Hi everyone, hope someone can help.

Six weeks ago I purchased a mint used Celestron 8se. 
Last night was the first time I have been able to give it some use and I set up nice and early, hoping to catch Venus around dusk. 
Once darkness fell I checked and double checked the collimation which looked pretty much perfect, so I spent a good couple of hours on the Moon which for me, as it is almost full, I find it kind of flat due to the lack of shadows. I have a Mak 127 so am reasonably used to high power lunar views, but the 8se is definitely in another league. I started with my new 12, 10, and 9mm Vixen SLV eyepieces which probably gave me the sharpest views I have had to date, l bought these hoping that they would be just about right for planetary viewing. I also have an 8mm BST Starguider and 7, 6, and 5mm Skywatcher 58 degree planetary eyepieces, which I tend to use in my little Startravel 102, this gave me approximately 170x to a shocking 400x I even,out of curiosity, barlowed the 8mm BST to give a ludicrous 500x, although the view was pretty good there didn’t seem to be anything to gained by trying this. I must add though, my 2x Barlow is only the cheep, kit supplied one, not a high end quality item. I had been told that the UK skies tend to limit the 8se to around 8mm / 250x but I did find the Moon took quite a bit more.

I did read somewhere, I think on CN,  that our US cousins have been using powers well in excess of 500x which I am finding hard to get my head around.

So, after this rather long winded post, I am really wanting to ask all you 8” SCT owners, what range of high power eyepieces you use for lunar-only viewing ?

Cheers in advance,

Dean.

 

[cloudsweeper]

Dean - the Moon is generally good in the x150 - x250 range, then the view can get unstable, although I have had moments operating at over x400.  I use a combination of Celestron XCel LXs, Explore Scientific 82s, Baader Hyperions, and others (see signature).  Plossls are very good at lower mags where their eye relief is not too small.

At high mags tracking can be a problem (especially when the field of view is very small), but the GoTo 8SE takes that particular worry away with its tracking capability. 

Nice 'scope, have fun!

Doug.

[BGazing]

The highest I used was once 265x (8mm Baader Zoom in 1.25 BBHS). Seeing was perfect. C8 was cooled with Lymax and there were no internal thermals. Collimation was spot on.  Back then I did not have 7mm T6 yet, would have been interesting to try. The Moon was relatively low but the seeing was great for what we usually have here. 

 

[MartinHiggins]

Hi Dean,

I've got a Celestron C8 which I use with a Williams bino and Starguider 25mm eyepieces which I find are a big improvement over the 20mm ones supplied with the Williams. I think I get about 89x mag. which gives enough detail and field of view to keep me interested but I'm thinking of getting a decent Barlow to up the mag. a bit.

Cheers

Martin

[DeanCJ]

Thanks for the quick reply’s everyone. It looks like the 8mm / 250x advice I have been given is about right although I may look at upgrading a couple of eyepieces, its a shame Vixen don’t do the SLV range around the 8 and 7mm size.

 I really enjoy looking at the Moon, there is always something new to find. My wife and I love mount Marilyn, we were so excited when we found it. If you don’t know, Jim Lovell on Apollo 8 named it after his wife, and just recently the IAU officially recognised the name. They were married in 1952 and as far as I know are still alive today, How romantic !!

 

[John]

Some of my best ever views of Saturn came with an older C8 that I used to have. On one memorable Summer evening Saturn was high in the sky (unlike now ) and the views of Saturn using a Tele Vue plossl 8mm (250x) were truly breathtaking and steady as a rock.

It is worth having something that can take you a bit higher than that though, for periods of really good seeing on a suitable target. Something around 7mm (285x) or even 6.5mm (308x) would be good. The Baader Morpheus 6.5mm would be a very nice tool for such use I reckon. The Pentax XW 7mm is also rather nice

 

 

[paul mc c]

I will never forget one view i had of Saturn when i had an 8" Meade sct,the eyepiece i used was a 7mm TS planetary,with the blue band,this eyepiece was the perfect one for me.

[DeanCJ]

2 hours ago, paul mc c said:

I will never forget one view i had of Saturn when i had an 8" Meade sct,the eyepiece i used was a 7mm TS planetary,with the blue band,this eyepiece was the perfect one for me.

I think the Skywatcher planetary eyepieces I have are similar to TS ones possibly a TMB clone I believe, so if you found the 7mm good I won’t rush to replace mine until I have had the opportunity to give it a good try. The eyepieces John has mentioned all seem to get very, very good reviews but unless I purchased second hand, it would require some serious saving up! I must admit though, I bought the Vixens having read John’s review of them and find them very good indeed, even in my f4.9 Startavel, and to be honest I am used to plossls so I don’t mind at all a 50 degree FOV, in fact I think FLO still have them on offer so might buy some more, my wife wouldn’t mind, as I did a quick comparison between the Skywatcher 9mm planetary and the 9mm Vixen, I didn’t tell her which one was which and it didn’t take her long at all to pick , in her opinion the best, which was, no surprise here,- the Vixen ! It’s hard to explain, but even the smallest  detail just seemed that bit sharper, a bit like comparing blu ray to 4k, both very good, but one just that little  bit better. Money well spent I think.

Once again thanks for your quick replies.

[michael.h.f.wilkinson]

My planetary and lunar line-up with my Celestron C8 consists of Pentax XW 5, 7, and 10 mm, with Tele-Vue Delos 6 and 8 mm to fill the gaps. The 10, 8, and 7 mm get used most. I also have a lightweight line-up for travel, consisting of Vixen SLV 5, 9, and 15mm, and these are superb, only compromising on field of view, not image quality. They are clearly a step above the TS Planetary EP I have used for outreach. 

[Space Hopper]

A binoviewer and some nice eyepiece pairs to take your observing to the next level.

 

[Mr Spock]

As a general rule x1 per mm gives you the best balance between detail retrieval and contrast loss on an SCT. Any less and you miss detail, any more and contrast reduces.

I'd increase that to x1.5 per mm for an apo refractor or Mak; both these types have better contrast than an SCT.

That isn't to say you can't go higher on nights of excellent seeing, but, the detail/contrast relationship still applies.

[DeanCJ]

4 hours ago, Space Hopper said:

A binoviewer and some nice eyepiece pairs to take your observing to the next level.

 

We have thought about binoviewers, but I am already close to the weight limit of our mount on both saddles (Meade lx65). Could be done if I removed 9x50 finder scope and changed the dialectric diagonal for the stock plastic kit item, as long as I am not one of the people who struggle to merge the images etc that might work, would probably look at second hand just in case.

[DeanCJ]

3 hours ago, Mr Spock said:

As a general rule x1 per mm gives you the best balance between detail retrieval and contrast loss on an SCT. Any less and you miss detail, any more and contrast reduces.

I'd increase that to x1.5 per mm for an apo refractor or Mak; both these types have better contrast than an SCT.

That isn't to say you can't go higher on nights of excellent seeing, but, the detail/contrast relationship still applies.

Thanks for the info, I have taken a screenshot. I did notice the Vixen 10+9 mm were really good and according to my maths that equals x1mm and x1.1mm respectively so a pretty good match.

[BGazing]

2 inch visual back and 2 inch dialectric diagonal add something between 200-300mm of focal length to C8, depending on the diagonal and whether you use 2 in or 1.25 in EP. Short fl EPs will almost invariably be towards the lower side, so your scope will operate at f/11 or close. 

8mm will land around 0.7mm exit pupil which, I believe, is the right spot to land for SCT highest power. The nights where more will be usable will not be that frequent.

 

edit: I see you use 1.25 visual back and diagonal, hopefully not stock diagonal.  In any event, you are at f/10, so perhaps a 9-7mm combo would be the right choice.

Edited March 8, 2020 by BGazing

[DeanCJ]

5 hours ago, BGazing said:

2 inch visual back and 2 inch dialectric diagonal add something between 200-300mm of focal length to C8, depending on the diagonal and whether you use 2 in or 1.25 in EP. Short fl EPs will almost invariably be towards the lower side, so your scope will operate at f/11 or close. 

8mm will land around 0.7mm exit pupil which, I believe, is the right spot to land for SCT highest power. The nights where more will be usable will not be that frequent.

 

edit: I see you use 1.25 visual back and diagonal, hopefully not stock diagonal.  In any event, you are at f/10, so perhaps a 9-7mm combo would be the right choice.

Stock diagonal on ST102 and dialectric diagonal on C8.

Once again a big thanks to everyone for your advice, I think the best way forward is to try my various high power eyepieces over a good few sessions and then look at upgrading the ones that work the best, with high quality brands such as John suggested. Unfortunately I work away from home so my time at the eyepiece is always limited, but I really am looking forward to putting the C8 through its paces, from what I have read there is a lot to look forward to as the year progresses.

[bomberbaz]

On 08/03/2020 at 08:09, Space Hopper said:

A binoviewer and some nice eyepiece pairs to take your observing to the next level.

 

I echo this sentiment, I love viewing the moon with my binoviewers, really does make a huge difference and I find it so comfortable to use.