Higher magnification required for f/5

[astronoam]

Hi guys,

I have two f/5 scopes - a SkyWatcher 120ST (120/600 Achromat) and Orion SpaceProbe 130ST (130/650 Newtonian). 

I'm looking to get the best possible view for planets, especially for the SkyWatcher which I use more often even though the Newtonian is a better fit for the task but less portable.  I'm quite happy with the view of Jupiter and Saturn using my 6mm Zhumell Z EP or 6mm Ortho EP however I want more power without a Barlow.  I wear glasses that corrects astigmatism but must take them off to read and lately I found out that it is more comfortable for me to use the scope without them?! (I can't really explain this, maybe the astigmatism is not noticeable on higher magnifications?).

I'm currently considering getting one of these:

1. Explore Scientific 52 series, 4.5mm - I know this company has very good products however I read mixed opinions on the 3mm, probably some QC issue.

2. BST StarGuider 3.2mm - this series is highly appraised on the forum but maybe this is too much? (0.64mm exit pupil)?

3. TMB Planetary clone 4mm - probably the best value for money (~20 pounds)

I understand that with a 5mm I get 1mm exit pupil which is recommended but this only gives me 120x magnification and I hope for more...

 

Which one will you recommend?  I don't have a chance to try before buying.

 

Thanks in advance

[Carbon Brush]

I'm no expert on this but here is my limited understanding....

At any magnification, astigmatism is an issue.
But, as exit pupil size reduces, the problems caused by astigmatism reduce.
Unfortunately a tiny exit pupil introduces other problems.

If high magnification planetary views are really what you want, then go for a longer focal length scope of a similar diameter.
If you are happy with a newt, that will give you most light gather & magnification for your ££ spent.
Having said that, CA in a long FL scope is less of an issue.

This will give you higher magnification and allow you to consider the need for other eyepieces.

Another thought is dealing with astigmatism either by a contact lens, or a TV dioprix, or simlar approach.
The dioptrix will only fit certain eyepieces so can be a big cost of ownership!

Not exactly the answer you asked for. But a different approach.

David.

[astronoam]

Thanks for the info, currently I'm not looking for another scope... maybe in the future.

Any advice on which EP is more appropriate?  I can manage with or without the glasses.

 

Thanks

[Louis D]

If you have deep pockets, a 3-6mm Televue Nagler Zoom would be ideal so you could dial in the highest usable power for the conditions.  Alternatively, @John recommends a 7.2mm-21.5mm zoom with the Baader Q-Turret barlow.  I have a similar 7.2mm-21.5mm zoom, and it is indeed quite sharp even without a barlow f/6.  Look for my zoom's images in my eyepiece FOV postings from last night in the 6.5mm to 8mm, 12mm to 12.5mm, and 18mm to 22mm sections.  With a barlow in your f/5, it would be operating at f/10, so this might be a good budget option.

[BGazing]

Your scopes are somewhat limited at how far you want to push their magnification. Achromat will show color and those little newts with spherical primaries peter out over 150x.

I'd reccomend something around 4mm at most. Those scopes are not taking high magnification that well, IMO.

[RT65CB-SWL]

Hi @astronoam and welcome to SGL. 

Unfortunately the two major gas giants, i.e. Jupiter & Saturn are low down for Northern latitudes for a few years more, so views are far from perfect. 

I too am no expert on this, but here is my view/opinion. I once said to myself, years ago, I would never purchase a zoom eyepiece [the TeleVue Nagler 3-6mm zoom was an exception] I did purchase a 'cheap' 7-21mm zoom from AstroBoot. Many zoom eyepieces, the AFOV tends to get narrower with higher magnifications at shorter focal lengths. However, for 'grab & go' or to experiment different with focal lengths, they give you an idea of what a fixed e/p length can deliver magnification wise before purchasing a 'fixed' length e/p.

 <--- my 'cheap' 7-21mm zoom.

 <--- the TeleVue Nagler zoom.

Edited October 5, 2019 by Philip R

[astronoam]

7 minutes ago, Philip R said:

Hi @astronoam and welcome to SGL. 

Unfortunately the two major gas giants, i.e. Jupiter & Saturn are low down for Northern latitudes for a few years more, so views are far from perfect. 

I too am no expert on this, but here is my view/opinion. I once said to myself, years ago, I would never purchase a zoom eyepiece [the TeleVue Nagler 3-6mm zoom was an exception] I did purchase a 'cheap' 7-21mm zoom from AstroBoot. Many zoom eyepieces, the AFOV tends to get narrower with higher magnifications at shorter focal lengths. However, for 'grab & go' or to experiment different with focal lengths, they give you an idea of what a fixed e/p length can deliver magnification wise before purchasing a 'fixed' length e/p.

 <--- my 'cheap' 7-21mm zoom

 <--- the TeleVue Nagler zoom.

 

Thanks @Philip R , @Louis D

I believe the TV zoom is a good solution, however it's *very* expensive!

I already have two nice 6mm EPs that I use for this task, I feel that adding just a little more power will be fine. Considering what I read before including @BGazing's comment to limit power to 4mm I will either get the ES 52 4.5mm or the TMB planetary 4mm (they also have a 4.5mm).

Which one you think will do better in my humble f/5 scopes? 

I know that Explore Scientific gained themselves a good reputation and the 52 series is quite affordable but their reviews is a mixed bag...

On the other hand the TMB clones are only 20£...

[iPeace]

23 hours ago, astronoam said:

I understand that with a 5mm I get 1mm exit pupil which is recommended but this only gives me 120x magnification and I hope for more...

I often find that 120x is most pleasing for Jupiter and Saturn. The view is great, and I always try more magnification, but most often I'll return to 120x to enjoy that less-magnified, but nicer, view.

So based on my own experience, I'd suggest getting a 5mm first. That will make you happy and wanting even more...and when you eventually try something below 5mm, you may well find that you're glad you have the 5mm to fall back on most nights.

[JTEC]

Could I ask why you are ruling out the Barlow option?  Barlows have a number of advantages not the least of which is to allow the use of longer focal length eyepieces which, generally speaking, are going to be more comfortable to use than, for example, shorter orthos than the ones you have. 

[astronoam]

1 hour ago, JTEC said:

Could I ask why you are ruling out the Barlow option?  Barlows have a number of advantages not the least of which is to allow the use of longer focal length eyepieces which, generally speaking, are going to be more comfortable to use than, for example, shorter orthos than the ones you have. 

The 6mm that I have is quite weighty and also didn't work very well with the Barlow.

I also have a Meade UWA 8.8 but didn't try with a Barlow yet, I'm afraid that together with the bulky Barlow it will make my scope even less steady, but I'll try it soon.  I also find it less comfortable to switch between EPs, which I do quite often.

One thing I do consider it to thread the Barlow to the back of the diagonal, this way it might be less noticeable, WDYT?

I'm quite surprised no one here recommends the ES 52?! 🙄

Edited October 5, 2019 by astronoam

[mark81]

I've always found the BST EPs to work well with my ST80 (f5) but if you go for the 3.2mm you've got a very high mag EP that you with the scopes you've got, you might not use that often... I would go for a 6-7mm that is light enough to Barlow which I guess will get more use.  For high power on my ST80, I use the SW UWA 6mm and to be honest I prefer viewing Jupiter and Saturn at slightly lower power...

[Timebandit]

 

 

Hi

Don't get into the trap of magnification is everything on planets. You are far better off on using a magnification that is slightly lower, that gives you a clear sharp view. Than pushing your magnification as high possible, and getting a softer view. Planetary IMO is getting the sharpest view possible, and not the highest magnification possible.

 

[John]

This is a combination that I use for high power observing a lot at the moment (photo below). It's a 21.5mm - 7.2mm zoom and a Baader 2.25x barlow. I got both for around £100.00. When used together you get the equivilent of a 9.5mm - 3.2mm zoom eyepiece and the optical performance is pretty good.

My other high power eyepieces are Pentax XW's and a Nagler 2-4mm zoom and the above combo, though a lot less expensive, gets a lot of use despite the more exotic stuff in the eyepiece case next to it

The zoom facility allows you to instantly try a little more or a little less power to see what works best with the seeing conditions and target. The zoom is also pretty decent when used without the barlow although the field of view at 21.5mm is a little limited in common with most zooms.

[JTEC]

You said that the 6mm eyepieces don't work well with the Barlow - perhaps there’s a technical/optical reason for that but just as likely, imv, perhaps it’s because, with the equivalent of a 3mm eyepiece in there, you’re pushing the magnification too high with your scopes and conditions especially on those targets. I think timebandit has it right on this. And I think John’s idea of a zoom could be a really useful one and help you clarify just how far the mag can be pushed on different targets before quality begins to decline and extra ‘power’ becomes counterproductive. This would also help you determine whether a shorter focal length eyepiece is really what you need and, if so, how much shorter it’s reasonable to go. 

[Louis D]

4 hours ago, astronoam said:

I'm quite surprised no one here recommends the ES 52?! 

The ES-52 line was just introduced a few years ago, and they had a recall on the 3mm version, so there just haven't been a lot of reports about them so far.  This was the only one google could find.

I find the 4.5mm Meade 5000 HD-60 to be a decent performer.  It's not quite as good as their 6.5mm, but it's very close.  Here's a FOV image comparison I posted a couple of days back that includes the Meade, Paradigm, and a couple of Pentaxes.

[astronoam]

58 minutes ago, JTEC said:

You said that the 6mm eyepieces don't work well with the Barlow - perhaps there’s a technical/optical reason for that but just as likely, imv, perhaps it’s because, with the equivalent of a 3mm eyepiece in there, you’re pushing the magnification too high with your scopes and conditions especially on those targets. I think timebandit has it right on this. And I think John’s idea of a zoom could be a really useful one and help you clarify just how far the mag can be pushed on different targets before quality begins to decline and extra ‘power’ becomes counterproductive. This would also help you determine whether a shorter focal length eyepiece is really what you need and, if so, how much shorter it’s reasonable to go. 

The reason I believe I can push it further to 4mm is the view I got from this little thing that came with the 120ST that I bought 2nd hand:

Although nothing to be proud of, it was surprisingly better than the soft image I got the same night with the Zhumell 6mm + Celestron Omni Barlow.  This is why I believe a decent EP, let's say the ES 52 4.5mm will still work on this setup.

I understand a zoom + Barlow is a nice combination however I want to keep my setup lighter, I have a 6mm that I like very much and believe it is better than a zoom EP with a Barlow (I'm not talking about the expensive TV stuff...).

[JTEC]

Astronoam, why not put up a wanted ad for a decent s/h 4mm ortho then, such as the ones by Astro-Hutech? Or shorter if that is your intention? Afaik, there’s not really anything sharper that’s both affordable and available.  Good luck with your search.

 

 

[astronoam]

Thanks @JTEC , I'll update if I'll find something interesting.

[F15Rules]

Like others posting here, I think that x120 for your intended targets is the highest power I would recommend, given our current UK skies and weather (Jetstream), limitations of your scopes and, importantly the low positions of the planets.

That means that a decent 5mm eyepiece would be a good choice: be careful though, as some of the optically very good 5mms out there have very short eye relief - especially orthoscopics and plossls. This can make extended viewing sessions a bit uncomfortable, and an uncomfortable eye sees less than a comfortable one!

So, my recommendations for a high quality, comfortable, good value eyepiece would be one of the following: (used price estimates shown)

Vixen SLV 5mm (£60)

Vixen NLV or LV 5mm (older versions of the SLV, £40-50)

All the above have 20mm eye relief and are very comfortable to use.

Meade HD 5mm ( not common in the UK around £40-50, eye relief I think around 18-20mm)

Personally, I'd choose any of the Vixens above.

HTH☺👍

Dave

 

Edited October 6, 2019 by F15Rules

[Louis D]

16 hours ago, F15Rules said:

Meade HD 5mm

There is no Meade 5000 HD-60 5mm, only a 4.5mm and a 6.5mm.  There is a BST Starguider 5mm which is seemingly just as good.

[F15Rules]

10 hours ago, Louis D said:

There is no Meade 5000 HD-60 5mm, only a 4.5mm and a 6.5mm.  There is a BST Starguider 5mm which is seemingly just as good.

I stand corrected, it was the 4.5mm I meant, this would give x133 in the 120mm F5 refractor ☺