The BST starguider/explorer 8mm and TV Radian 8mm

[AlexB67]

Hello,

Not that I am going to claim I can provide a definitive answer, but I happened to have been in the possession of a 8mm TV Radian and a 8mm BST starguider recently, there doesn't seem to be much in terms review material against a high quality eyeiece such as the TV Radian, perhaps this will help some of you a little bit.

I forwarn this is not a thorough review in the Alan Potts or John style, for that I would need more time over a period of weeks. Nevertheless having been blessed with some clear nights I managed to take out the eyepieces side by side for 5 nights total, sessions of 3 - 4 hours each, one on a better site away from light pollution.

The skywatcher f4.7 10 inch Dobsonian was used throughout.

Rather than a review in the style of going through target by target I'll try and keep it brief, suffice it to say I covered quite a few doubles, some planetary nebulae, globulars and galaxies and revisiting them on each night. So far anyway, my feeling is that in a lot of ways the 2 eyepieces are very close in performance in a lot of areas, however both have some strenghts and weaknesses. I looked for particular characteristics, such as optical correction, scatter, things like ghosting, internal reflections etc and colour rendition, contrast etc. etc.

My albeit arguably tentative conclusion after 5 sessions, it seems to me the radian is the slightly better eyepiece in most areas, that being said I'll mention two things where the biggest differences were noted and where I feel each eyepiece excels more in particular.

Off axis performance: The Radian is noticably better in this regard, it should be noted however that the BST range is rated for f/5 scopes and I am using it in a f/4.7 ( though I know what the views look like in the Heritage130p at f/5 where I still feel it suffers too) . The Radian is advertised being suitable for scopes as fast as f/4, so this result is to be expected. Planetary performance dropoff off axis axis could be noticed in the BST, however even in the f/4.7 the BST does quite well if you keep the target fairly central you'll have no problem.

During several drift tests on a brighter stars again the difference became quite obvious. I shoud mention I do not own a coma corrector, and while the tell tale signs of coma could be seen on the outer parts of the FOV, in the Radian it appeared to be prety much the only thing affecting the view as the dominant and standout abberation overall. The BST starguider however star shapes and sharpness dropped off noticeably more approaching the edges of the field stop. On my darker site visit with lots of nice bright stars the differences became even more apparent, though on faint stars you will not notice it nearly as much.

Overall the Radian is the winner here.  A bit of Brazil verus England football here I am afraid, expect a bit of a drubbing (if you really look for it ).

Transmission/rendition of colour: A few days ago, I wote some preliminary report of my experiences with this, and over this period I found my opinion to change little in aspect, though on the dark site visit I found it to matter less, there is so much more contrast on these targets with respect to the background and are that much more impressive, that being said, the issue  could be seen. 

One of the weaknesses with the Radians are the rather low transmission, in particularly in the shorter wavelenghts in the blue and green.  I found in tests elsewhere ( albeit the data I have is quite old and perhaps outdated ) that transmssion can drop below 90%, even as low as around 85% on some of the Radians at these wavelenghts. While I highly doubt I can visibly detect a few percent difference in tansmission, perhaps around 10 % becomes more noticeable, this would translate to about a greater than > 0.1 stellar magnitude difference ( according to my magnitude calculator ).

Whatever the case, whatever the theory, I'll go with the outcome of what my eyes tell me and that tells me colour rendition in the Radian to me does not seem as good as the BST starguider, depending on target it may appear to be next to not noticeable to actually becoming rather quite noticeable.

I'll cover some cases:

In a specific test I observed a double in Hercules ( sorry my notes are on my other computer ) but the main charactersitics of this double is that one has a very sublte blue tint with a B-V index close to zero, it was actualy the BST that gave me the hint of this color best, in the radian the B component apeared more desaturated. Both eyepieces gave a very nice clean split of izar for exmaple at 150, but the colour differece seemed that little bit more muted in the Radian and appeared a tiny bit more vibrant in the BST.

Planetary performance I had the privilige to say a final goodbey to Juipiter, and while I only got about half an hour on it I can only say this very tentatively, my preference leaned towards the Radian as it appeared that little bit sharper to me, and there is quite a bit of contrast on Jupiter anyway, however when came to more subtle colour contrast variations on Saturn, on axis at least I felt the BST again edged over the Radian, it was rather noticeable how the variation in subtle contrast in colour variation from equator to pole was that bit more vibrant.

Mars was barely tested over this period, I did look at it but it involved using a barlow and that would negate any fair test.

Planetary nebulae without a filter, I felt the sublte hints of blue showed just that tiny bit more clearly in the BST just edging the Radian again, the BST having that bit more spread around object like the cats eye and the lovely tiny PN in Hercules too, the NGC number eludes me right now. Globs and glaxies that apear largely black and white anyway, I noticed it much less, though still, looking for the faintest stars the BST was at least as good as the Radian.

The lateral colour issue, it is there and easy to see if you test for it on the moon, which I only did briefly, it is well known in the Radian line, but very little issue in the BST if at all that I could see however.

It may well be the case that some of my views will shift a little on some things, but at this stage I doubt it will change significantly and I have bit of a feel for both of these eyepieces in my case now, the 8mm BST I owned almost a year now.

On the whole right from the build quality to a lot of the other areas mentioned in the introduction but not covered in this report I feel the radian edges it over the BST. That being said having used a 5mm BGO, 6mm Radian, 7mm pentax XW and of course the 8mm BST and starguider I feel neither the BST nor the 8mm Radian are quite in the same level as the BGO for planets and doubles and moon for example, and not as good an allrounder as the pentax XW 7mm, ignoring FOV differences and comfort, but optically in giving the clear crips and the contrast rich views I like so much ( don't we all   ) That's just my opinion however, and besides those characteristics it perhaps has as much to do with preferences in eyepieces.

Wanting to purchase some other eyepieces, and letting go of some others finally for the first time the 8mm BST will be going in the classifieds over the coming days. I am not in the fortunate position of having lots of eyepieces like Joves, or John, who has half of the boxed eyepieces from FLO sitting in his basement

There is little point keeing 2 8mm eyepieces, and with the pentax XW 7mm it is debatable whether I really need the 8mm at all, thoughnice, as much for my own bit of eyepiece edification, and it has proven very useful.

My other plan to get a decent focal extender to give me a 4mm justisitfes keeping an 8mm. A 4mm ortho would be very tempting, though the very narow FOV and even tighter eyerelief over the 5mm I currently own however may be a step too far for me.

In conclusion, my overall feeling is that there is a lot to be commended for the BST starguider/explorer, especially given the cost. I woud say it is an excellent performer even in the fast Dob I own in this price range. Is an upgrade to a Radian worth it ? In the end it depends what you want from an eyepiece, I'll leave it up to you to decide.

To some degree personally my current feeling is for many that own a slower scope like the 8 inch Dobsonian that is so popular, there is a lot to be said for keeping the BST starguider in you case. In a lot of areas I felt these eyepieces were really rather quite close in on axis performance, but given the second hand price of the Radians are around the 100 pounds mark in the UK I think they are good value ( IMO). I am becoming a bit of stickler for wanting good optically corrected views however, and a faster Dob needs something like the TV to achieve this, the f/6 8 inch Dob much less so.

That being said in trading in my BST I feel I am letting go of something, In some ways I prefer the BST because of the main weakness in the Radian I described. To some observers such an issue may not matter much, but to me it does to some degree. I suppose we all have our own gripes/dislikes/preferences in eyepieces, and perhaps I am more sensitive and easily annoyed by some of the things I described, unfortunately for me the weakness in the Radian is something I do notice.

Having got used to the qualities of a pentax XW 7mm recently perhaps has shifted my expecations a bit, but I would not be surprised if I really wanted a 8mm in future I may be better served with the 8mm delos, even though I've never looked through one, I suspect the coatings and therefore colour transmission will be superior in this range.

Thanks for reading

　

　

　

[ronin]

I would have expected the Radian to have been the better since ultimately the comparision is a £190 eyepiece to a £50 eyepiece. The £190 is from Telescope House web site where the 2 Radians either side are £190 so it would seem fair to give that as the price.

http://www.telescopehouse.com/acatalog/TeleVue_Radians.html

Swap it round, one Radian at close to £200 or 4 BST's at close to £200. Lets ignore the £6.

Which £200 is the most useful for observing?

A single 8mm eyepiece or 4 eyepieces of say 5, 8, 15, 25?

Now that is a different aspect, but to many equally valid.

[YKSE]

Very good work alex, thanks for a very interesting read.

Overall the Radian is the winner here.  A bit of Brazil verus England football here I am afraid, expect a bit of a drubbing (if you really look for it ).

　

Nice comparison, I suppose there're still English fans calling themselvs Worldchampion

[Sandraj]

Very interesting read, thank you.

[AlexB67]

I would have expected the Radian to have been the better since ultimately the comparision is a £190 eyepiece to a £50 eyepiece. The £190 is from Telescope House web site where the 2 Radians either side are £190 so it would seem fair to give that as the price.

http://www.telescopehouse.com/acatalog/TeleVue_Radians.html

Swap it round, one Radian at close to £200 or 4 BST's at close to £200. Lets ignore the £6.

Which £200 is the most useful for observing?

A single 8mm eyepiece or 4 eyepieces of say 5, 8, 15, 25?

Now that is a different aspect, but to many equally valid.

There I a lot minor things I did not mention Ronin. I feel overall scatter  is better, ghosting, reflections etc, less flaring on stars with respect to eye position, its all a lot of the smaller details. I pointed out two areas I felt quite strongly about where I felt they were rather noticeably different. Overall I think the Radian is the better eyepiece, and for me for a 100 pounds as they are now they are worth it second hand. Considering the radian new were around the 160 - 200 pounds mark I would agree that bang for buck the BST is the winner when bought new at that price, no wonder they are so popular 

[ronl]

A very good review and report, the outcome was probably a no brainer, but the BST Explorer 

seemed to do well, I use the BST's and find them to be very good, and the longer you have them 

you get used to some of the weaknesses, but for value I don't think  they can be beaten, the BST's

work well for most targets, and give me a comfortable view, they might not suit everyone but I am

very happy with all of them. Thank's again for the report, it's a very fair summery of both eyepieces.

[John]

Great report Alex, nicely balanced too 

There I a lot minor things I did not mention Ronin. I feel overall scatter  is better, ghosting, reflections etc, less flaring on stars with respect to eye position, its all a lot of the smaller details..... 

Personally I think the above are quite important details. The sort of issues that can make the difference between discerning a faint planetary moon close to the bright parent planet, seeing a vague planetary feature a little more clearly or splitting a close, unequal binary star for example. 

Even so the BST 8mm clearly has an awful lot to commend it, including a price which is very good for an eyepiece that behaves well even in fastish scopes.

[andyb505]

As a beginner, it is really good to be able to read reviews such as this. Thanks very much, very good.

Andrew

[AlexB67]

As a beginner, it is really good to be able to read reviews such as this. Thanks very much, very good.

Andrew

Thank you,  I have about a year experience myself, so I am a beginner too. 

Read around as much as you need about these eyepieces would be my best advice, opinions will always vary a bit, but often some common things will be pointed out by many and often agreed upon, in that case usually there is something in it.   If you read around enough you will end up making wise purchases I find, though as you get closer to the top end the smaller difference become more personal I feel  and harder to decide upon. I would say the BST provide the largest jump in upgrade from stock eyepieces in many performance areas for little money. That is not to say the premium eyepieces aren't better, but you pay a lot more money for incremental upgrades. Some may find it worth doing so, some not, I do so far.

I am very happy with the Radian eyepieces an upgrade over the BST in overall performance , for me it was worth the gain, in spite of the short coming I pointed out which may have given perhaps a slightly unbalanced feel to the report since I focused somewhat on a specific  example of the biggest feature in the Radian I did not like as much. In the overall scheme of things it is a relatively small issue I would say. 

If you are on a budget of around the 50 pounds mark,  especially in slower scopes the BSTs are a very good choice as overall performers, comfort, FOV and so on. If you want to spend a 100 or so the Radian is a very good choice second hand I think anyway, but around that sort of money there are other options too. Buying eyepieces can be a minefield if not careful, but there is lots of good info here if you take the time to find it.

[Singlin]

I am delighted with my 5,8 and 25mm BST's

I use the 5,and 8 with my F4 10" Quattro. Instead of the 25 I use an 18mm Celeston X Cel-lx.

I also have the Celeston Luminos 23 which is very favourable with the clients.

[Charic]

Very interesting, you just have to keep looking on the site for snippets like this........I have recently  compared the TV Plossl against the BST 8mm and for me, the eye relief and field of view win for me on the BST for my needs. Not  really so much a test, more just for the experience of trying out a Plossl. 

I'm not totally surprised by your review, as I am aware of another test, whereby a BST was inserted in the line-up,  and against those premium EPs ? ( especially being the cheapest EP in the test )  the BST drew favourable reports.

I could  possibly invest in a  6mm and 17.3mm Delos and a 35mm Panoptic, keeping to a three piece set up, if I went to a larger apertured,  faster ratioed telescope.

I did have the opportunity when building my  present system, to invest in TeleVue EPs, but I wanted a ' FULL SET' , so  from  suggestions and proposals from members at SGL, and my own my early research, I realised that TeleVue were  brand leaders, very good optics, very expensive,  but just not required for an f/6 Skyliner in my opinion at the time. Another 'SET'  I desired was the JAPAN made MEADE series 3000, EPs, but could not locate these individually at the time. 

When  my first BST arrived, the 8mm,   I just knew there and then, that the rest would  have to follow, and on the f/6 Skyliner, do I really need to spend a lot more on Eps,  and will they really give  me better results than I already have?

Sure the field of view could be slightly flatter at the extreme edges,  but off-axis is not a real problem for my needs, and i'm adept at tracking very smoothly, keeping the target central in whatever EP I'm using to frame my target. 

I expect that spending more on EP's for  faster scopes is an essential requirement, to get the best corrected final image, and I suspect this to be more of a requirement for manual scopes, especially at higher magnifications,  if your tracking is not so smooth.

My 8mm BST versus the  8mm Tele Vue Plossl,  was, in no way,  as detailed as your Radian / BST test,  I thankyou for the interesting report,  even though its taken me some Months to catch up with this thread?

[Charic]

........should have read MEADE 4000's ( out of time to edit?)

[cotterless45]

I'd definitely advise any beginner to stick to Bst or their equivalent Starguider.

For what you get , they are remarkable performers at that price point.

I've had some comparisons between the 12mm Bst and a 12mm Vixen NLV, the 25mm and a Celestron silver top and against the nearest Meade 4000.

The Bst produced the most comfortable and best views below f5, f6 and in refractors. I think under average observing conditions , which we mostly get here, that Bst is a super upgrade from stock supplied eps.

Nick.

[nightfisher]

Very good ep`s

at one time i had the full set, then went down the ortho road and slowly broke up the BST set, still have the superb 18 and 25mm and might be getting a 12 again

[YKSE]

I have recently  compared the TV Plossl against the BST 8mm and for me, the eye relief and field of view win for me on the BST for my needs. Not  really so much a test, more just for the experience of trying out a Plossl. 

You don't need spend any money at all to do this test, the info of eye relief and field of view can easily be get by reading.

[Charic]

.......agreed, but  measurements  as small as  1mm can have / make such a dramatic difference, to the final result,  so  hands on experience wins for me!

[Astro_Baby]

Great review, very thorough. Its always worth reading experiences as there is a world of difference between spec sheets and user experience IMHO.

[Charic]

Great review, very thorough. Its always worth reading experiences as there is a world of difference between spec sheets and user experience IMHO.

Some more valuable than others..........thanks for your collimating guides, they helped me get collimation sorted very quickly. Its a task I now enjoy, and from strip down to completion, I have no worries, and have great final results. 

[Charic]

........I too now own a Delos 8mm, since this thread started, and compared to the Starguider, its still an 8mm giving me 150x power with a slightly wider field of  view!

During my first test, I felt the Starguider gave me the brighter image, this was when looking at the Moon, however it was mentioned that the Delos may have better coatings, reducing some of the glare, yet I felt that It was brighter due to the wider field of view, seeing more light, my pupil closing right down,  due to the brightness.

My eyes are nowhere near as perfect as they used to be, I see what I see, rather than rely on the technical, its a visual experience.  I still could have purchased another 3 BSTs( if other focal lengths were available?) and had some change too? @John often mentions, there's a good second-hand market for premium EPs when they become available, they hold their prices should you wish to try the TeleVue  brand. That said, I've no worries that I will get some of my funds back should I move these EPs on!

Most would believe that the Delos should outperform the Starguider by a  standing mile, not so in my opinion, but I am only using an f/6 telescope  where eyepiece selection is not so critical. The only real advantage the Delos is providing me just now  is the extra 12°afov, everything else feels about the same?

On a much faster f/4 scope, I'll assume that the difference is more noticeable between the two  eyepieces, favouring the Delos, although it will be some time before I will experience this, as my intentions to get the 300P or a 250P have been delayed indefinately!

[John]

I think the differences between these eyepieces are very subtle Charic.

I've compared the views through an 8mm BST Starguider with my 8mm Ethos at the last SGL starparty and, aside from the FoV, there was not much difference in all honesty on the targets I was viewing on that occasion.

If you are looking for really clear and obvious differences I think you might be dissapointed.

For what it's worth the only times when I've noticed really large differences between eyepiece performance is comparing the stock 3-element types supplied with scopes with a nice quality eyepiece such as the Vixen SLV or something of that quality.

I suspect that the situation might be a little different if we owned really fast, large aperture scopes (ie: 16+ and F/4.5 or faster).

If you are looking for 3x the performance from an eyepiece that costs 3x as much, it's simply not going to be there.