Planetary observing with an 8 inch SCT

[Umar Ahmad]

Dear Users,

I have recently bought a Celestron CPC 800 8 inch SCT (Focal Length: 2,032mm, Focal Ratio: f/10). I have managed to get somewhat pleasing views of Venus, Mars and Uranus over the last couple of weeks using the supplied eyepiece and others I had lying around, from my previous scopes:

1. 40mm Plossl (50.8x) - came with the CPC 800
2. 20mm erecting Plossl (101.6x) - came with my first telescope - a 127mm reflector
3. 6mm Vixen NLV (338.6x) – This was bought for my old 300mm Dob

However, the 40mm (50x) and 20mm (100x) eyepieces gave too small a view and the 6mm Vixen, bought for my previous telescope, seems to be too overpowered for my new scope.

I am now hoping to get some eyepieces better suited to planetary viewing (and what little deep sky I can under heavy light pollution) through my new 8 inch SCT. 

I have fairly bad astigmatism so would prefer longer eye relief.

Could anyone recommend what combinations of eyepieces/barlows I should look to invest in?

Has anyone got any experience of zoom eyepieces? Are these an option?

Based on what I've heard so far, the ability to have 150-190x and approx 250x are two good magnifications? Based on this, I'm looking at perhaps an 8mm (254x) and 13mm (156x) Vixen LVW?

Would be great to hear from anyone who views the planets or has had any experience with these type of scopes or equipment?

 

Kind Regards,

 

Umar Ahmad

[michael.h.f.wilkinson]

I have the Celestron GP-C8 (essentially same optics but on a Vixen Great Polaris EQ mount). I find that EPs between 10 and 7mm find most use in planetary observation. The 10mm in particular gets used a lot, whether it was the old Plossl I had, or the later Radian, or now the Pentax XW, more than the 8mm (Radian first, now Delos) or the 7mm (Vixen LV in the past, now Pentax XW). I would also suggest fairly closely spaced focal lengths, to tune the magnification to the conditions. I would certainly consider the Vixen SLV range. I have the 5 and 15mm, and they are great performers. Excellent eye relief. A set consisting of the SLV 9 and 10mm, possibly extended with an LVW 8 would be very nice.

 

[ronin]

For a more budget eyepiece the 8mm and 13mm you give fall close to the BST Starguider which come in at 8mm and 12mm.

Suspect someone here will have this combination and so may be able to offer direct experience of the supplied performance.

[Umar Ahmad]

Dear michael.h.f.wilkinson and ronin,

 

Thank you so much for your advice.

 

I am leaning towards the Vixen SLV 9mm and 10mm, and then possibly the LVW 8mm, depending on how much I will have left over after budgeting for a deep sky eyepiece. The SLV's are on sale at cut price at First Light Optics. I'll also look into the BST Starguider 8mm. 

 

Anymore advice from anyone would be greatly appreciated!

 

Umar

[Peter Drew]

I have a Celestron 8SE which I keep in Tenerife. Due in a large part to the location it has given me wonderful lunar and planetary views. I use either a Leica zoom or binovierwers and plossl eyepieces. I find 150x-200x the most usable range on the average but the Moon and Mars usually respond well to double that. For UK viewing I think  8mm 10mm and 12mm would be a good choice, they would Barlow well for use on exceptional nights.  

[YKSE]

Like Peter, I do planatary mostly with binoviewer in C8, because it takes higher mag, less scatter and virtually no floater when exit pupils are close to 0.5mm. My  top preference for planetary eyepiece is low scatter light, i.e. the smaller and the fainter of bright patch around a bright star, the better.

Of your three choices, I've only had 8mm BST, the scatter light was too much to my taste, so it went a new home. Of the reviews I've read, SLVs seem to be the best ones, with its Abbe-ortho-like low scatter light.

[alanjgreen]

When I had a cpc800, I used a baader mk3 zoom eyepiece. It worked well and helped me find the focal lengths that worked for me. I would recommend it. BUT EYE RELIEF OF 13-15mm MAY RULE IT OUT FOR YOU  

- it has optional 2.25x Barlow. I didn't use that much so I would recommend that you skip that, you could add it later but it is too powerful for a 2000mm focal length scope!

- although it is nice that you can screw the Barlow directly into the zoom to convert it to a power zoom. 

The baader zoom is soft at the 24mm end, so i needed a separate low power eyepiece.

i used a baader 36mm aspheric (2" eyepiece) for low power, it worked really well and I liked it a lot.

the baader zoom is excellent from 20mm - 8mm for sure.

once I tried the zoom a few times, I found that I liked 17mm, 14mm and 10mm, below 10 was too much.

Also note that baader are bringing out a new mk4 version soon (see sponsors announcements section)

 

Alan

[Timebandit]

2 hours ago, Umar Ahmad said:

Dear michael.h.f.wilkinson and ronin,

 

Thank you so much for your advice.

 

I am leaning towards the Vixen SLV 9mm and 10mm, and then possibly the LVW 8mm, depending on how much I will have left over after budgeting for a deep sky eyepiece. The SLV's are on sale at cut price at First Light Optics. I'll also look into the BST Starguider 8mm. 

 

Anymore advice from anyone would be greatly appreciated!

 

Umar

 

Hi welcome to SGL 

I would say the Vixen would be a great choice for you. I have had a few Vixen and found them capable eyepieces and do not cost a fortune. The SLV should be a great eyepiece especially if they are on sale at FLO. I have the predecessor to the SLV which was the NLV . I have found this eyepiece very nice to use as it has great eye relief, fov is fine for planetary views. But the optical quality was absolutely great . Certainly an eyepiece which I thought was a great buy , therefore the SLV would be a very good choice IMO. The LVW from reports is certainly no light weight with its capability, with more fov and the optical quality is supposed to be top notch.

I hope the above helps☺     

[alanjgreen]

Umar,

probably not the best plan to get lots of eyepieces just 1mm apart.

10mm in your scope gives 200x

9mm in your scope gives 222x

8mm gives 250x

Jumps of 50x are very worthwhile, but a small jump of x22 will be hardly noticeable at the eyepiece.

so, buying a 10 and 8 would make more sense. Skip the 9mm would be my advice.

 

Alan

[Umar Ahmad]

Dear all,

 

Thank you so much for helping me decide!

 

The Mark 4 Baader Hyperion zoom does look very tempting, but unfortunately the eye relief seems inadequate, which is a shame.

 

It looks like 10mm (200x) and 8mm (250x) would go well together then.

 

I just came across the Baader Hyperion range and initially they looked promising - 20mm eye relief, 68* FOV and at £99 each, would be cheaper than a 10mm Vixen SLV and 8mm LVW. However, two downsides I read in a review were that:

1. The Hyperions had more noticeable astigmatism near the edges in fast scopes - probably not much of a problem for me then?

2. The LVW had less light scatter than the Hyperions when viewing the moon and planets

https://www.firstlightoptics.com/blog/vixen-lvw-vs-baader-hyperion-review.html

 

I didn't know that light scatter was a consideration when planetary viewing, so thanks for pointing this out! I guess I'll go for the two Vixen eyepieces then?

 

Thanks again to all,

 

Umar

[Dave In Vermont]

You might also be interested in the following thread here in SGL:

It can help assure you that your telescope is working correctly as regards the size of things out there through your 8" SCT (a fine instrument!). No telescope will match the views of photographs in magazines from the Hubble Space Telescope - unfortunately. But you can do quite well.

Enjoy!

Dave

[YKSE]

6 hours ago, Umar Ahmad said:

The Mark 4 Baader Hyperion zoom does look very tempting, but unfortunately the eye relief seems inadequate, which is a shame.

I have Mark III zoom, and wear glasses, the eye relief is good enough me, no problem seeing the field stop in any settings (around 16mm was eye relief shortest).

If the Mark IV zoom is in your consideration, I'd second Alan's recommendation, the zoom give very flexible tuning for the seeing conditions, the improvement ergonomy and weight is very good if you later decide to go binoviewing, the zoom is handy too when you do alignment.

[alanjgreen]

Umar,

Your choices would give 6,8,10,20,40 as your focal lengths.

why not consider buying a 14 (x150) or 15mm, 150x is a great magnification level and a big hole in your list.

6 is too low for a 2000 focal length (ok for mars though), 333x

8 at x250 is the max really. X250 will be rarely used (I would put that on the wait list)

10 at x200 is good , I would add that

14 at x150 is great. A big hole in your list. Would be used regularly.

20 at x100 is great. Would be used regularly.

40 at x50 is great. Would be used regularly 

if I were you, I would be looking to add a 10 and a 14. Giving 50,100,150,200 and 333

add the x250 when funds allow. Planets are not in the sky at the moment either.

Hth,

Alan

[Umar Ahmad]

Dear Dave,

 

Thanks for the link!

 

YKSE,

 

That's really interesting. I was under the impression that eye relief less than about 18mm or so would be too uncomfortable for spectacle wearers. Evidently this isn't true then. I've noted down the Hyperion mark 4 zoom, and I think I will look into 2 of these coupled with a binoviewer at some point.

 

Alan,

 

I'd resigned myself to the shorter focal lengths as I can't seem to see any deep sky objects darker than the Orion Nebula and the brightest star clusters, even with a UHC filter. Wouldn't a 14mm only be used for deep sky viewing?

 

Thanks again to all!

 

Umar

[Stu]

Planetary observing at x150 to x250 is probably the most useful, often under x200 is best. That means eyepieces between 14mm and 8mm will be ideal. An 11mm would be very useful at x185 I think. Your scope has a long focal length so you don't need very short focal length eyepieces.

[alanjgreen]

As Stu says, over x250 is rarely used. You could just add one eyepiece and see how you get on with it.

if everyone thinks x200 is really useful, start with a 10mm or 11mm and see how you get on with that?

just avoid buying lots of eyepieces only 1mm apart.

[Umar Ahmad]

Dear Users,

I decided to go ahead with buying an 8mm Vixen LVW and 10mm SLV.  I ultimately decided starting with focal lengths on the shorter end of the 14 - 8mm range as I think my somewhat bad eyesight would prefer this.

I had also looked at the Tele Vue Panoptic and Pentax XW ranges, though these were out of my budget. (Maybe one day though!)

After I heard that a slow scope like mine would be more forgiving with eyepiece quality, I decided to research this point further and came across the Baader Hyperion range. This range was cheaper than the others and it became evident that their inferior edge of field performance would be mitigated by my f/10 scope. Ultimately I still went for the Vixens due to their better control of light scatter when observing brighter objects.

There hasn't been a cloudless night yet, but I can already notice that their build quality is far superior than the Plossl that came with the scope. One potential issue I do have is that the LVW is rather heavy. I hope it won't imbalance the scope or put any strain on the motors?

Thanks again,

Umar

[StarryEyed]

Umar.

You have made a good choice. From my own point of view I have a very strong astigmatism and in discussion with my optician I have learnt that my glasses should be 11mm from my eye and that the lens in my glasses expensive as they are do not have the same performance as the very best wide field lenses. This means that I would either tilt my head to compensate for this which would make things worse. Interestingly my optician suggested a 60 degree field of view. Next chance you get talk to your optician your glasses are a part of your telescope.

[alanjgreen]

8 hours ago, Umar Ahmad said:

One potential issue I do have is that the LVW is rather heavy. I hope it won't imbalance the scope or put any strain on the motors?

Umar, 

the cpc800 will have no problem with your new eyepieces! It is a well thought out scope.

The 8" mirror is not that heavy and therefore your tube is not too backheavy, compare it to a cpc1100 where the tube is very back heavy due to the weight of the mirror before you add anything.

the only time eyepiece weight can become an issue is if you add a crayford style focuser on the back which shifts all the weight away from the back and the effect of gravity is to double the weight... then you may be into balance bars etc

adding a dew shield to the front will counterbalance most eyepieces on the back.

the motors would become very noisy if balance is an issue, usually while trying to lift the front end of the scope so you would soon notice, however, adding a big eyepiece alone will not be enough to cause this.

just concentrate on trying out your new eyepieces  start with some globulars (m13, m92), they can take high power well & the moon will be up soon.

Alan

 

[LukeSkywatcher]

I have an 8" SCT also and find myself reaching for an 8mm EP most of the time when observing planets. I have an 8-24mm Hyperion zoom but i find the 8mm end of it slightly blurry, so i use my fixed focal length 8mm EP (Vixen NPL).