A little bit of first light with the 8mm TV Radian.

[AlexB67]

So after a long time of poor weather, the sky decided to play ball. though a full moon and fairly average seeing to begin with, I finally got to have my first look through the TV Radian 8mm and also put it up against the 8mm BST starguider in the f4.7 10 inch Dob. 

I spent about 3 hours on saturn, while 150x is a bit on the low side, it still gives a nice view of the planet and it is enough to discern some of the finer contrast details around the globe form equator to the polar region that shows so nicely at the moment with the way the planet is tilted. For ring details so far I have found higher mags a bit more desirable to offer up its beauty under good seeing when possible.

First of all, very much like its brother the 6mm the 8mm is a bit shorter, a solidly build eyepiece and does away with the 7/4 design versus a 6/4 arrangement, the second hand 8mm I recently purchased looked pretty much new I get the impression, the instadjust is quite a bit stiffer compared to the 6mm, again, and the optics sparkling clean, probably due to lack of use.

On with the views with a well cooled scope, fully shrouded and light shield for the bright moon  Saturn showed up nicely with its moons, I did not have any guides with me so their names elude me right now, just to note them for comparison sake. There was a bit of swapping going on given both the 8mm BST and 8mm Radian equal time. Seeing was a bit up and down but there were some good moments, though nothing like what I experienced a few weeks ago on Saturn/Mars, luckily 150x is not that high a magnification, so views were still reasonably clear and crisp lot of the time.

So on with the good and the bad. Probably influenced by the bright nearby moon and unwanted light coming into the scope to some degree, the sky background darkness in the Radian and BST were very close on axis, but the sky background darkness in the Radian was more uniform across the FOV, the BST on the other hand suffered a bit more from brightening near the outer edges closer to the field stop. 

The moons stood about equally in brightness and sharpness, contrast variation  and sharpness from the equator to the poles were very similar overall.

Drifting across the view: Comparing the views nudging from on axis to somewhere closer the field stop the radian was a bit better in this regard in retaining detail, also less distortion of the planet as the BST does seem  to have a bit more noticeable pincushion distortion near the edges it seems , this was quite difficult to test though with seeing a bit up and down and times, but at least that is my impression. 

In the BST the sweet spot works quite well up to at least halfway to the field stop. I should say that generally I am a bit of a nudger anyway, and tend to really view planets on axis as much as possible, the sweet spot is there in all eyepieces, though the pentaxes and TVs are better in this regard, I believe coma is a contributing factor in smearing out contrast and therefore resulting in a slight loss in planetary detail.

One day I will be able to compare some of my eyewear  with a coma corrector and will steal Daniel's paracorr at Dobfest 2 when he is looking the other way     ( There goes my invite out of the window )

On axis, I felt if anything the BST had a slight edge with the views being a very slight bit crisper and contrast slightly easier to see,  very close, but after many hours at the eyepiece  I felt the starguider at minimum was at least the equal of the radian if not slightly edging it. Not quite what I was expecting I must admit, but the sweet spot on axis  was proving to be quite impressive in the BST.

All in all, I feel neither the BST nor the Radian has that real biting point when you know you are in optimal focus, which I can really feel with the BGO and pentax.  The Radian and BST compared to the company of the BGO and pentaxes, regardless of  the magnification differences got that real sharpness to them and a sweet spot that the 8m Radian and 8mm BST lack a little bit, both the 8mm BST and 8mm Radian are that bit softer overall I would say.

I also tried the 7mm XW, 6mm Radian, 5mm BGO, it was getting around 2 - 3 AM and some lovely seeing despite the planet being somewhat lower down at this point. When seeing allows, something around 200 - 240 works really nicely on Saturn, the BGO offered some lovely clear views and contrast, as it always does, the 6mm Radian with it slight tinted version of the planet also looked lovely, and the pentax 7mm was fabulous for subtle contrast details around the globe and that ultimate crispness is right there telling you

look through me, not at me

it is literally like the sound you would hear when putting your teeth into a nice  bag of crunchy crisps

For the finale. Transparency must have been very good, the big moon did not stop me easily seeing the diamond shape of Lyra where the sky seemed nice and dark, so a quick squirt on the DOB mount looking through the finder and the ring (M57) was easily found.  Again both the Radian and BST provided very similar views, though it should be said darker skies will provide a much better test bed. I felt the Radian edged it by a smidgeon in terms of how the ring showed itself, but more on that to come under darker skies, when double stars brighter galaxy details will be tested out. 

On with the ring, I also tried the pentax XWm which shows a slightly greater amount of sky, aside from the mag drop, 8 to 7mm, it  a nice example where even a drop form 170x to 150x ( 8mm to 7mm ) the differences can be easily seen, though the pentax background was a tad darker, the ring was also ever so slightly dimmed, the slight reduced size of the ring and therefore increased apparent brightness of the ring was nice to see in the 8mm eyepieces, though I still felt overall the pentax showed it best in this category.  At lower mag the 10.5 mm pentax gave a beautiful contrast laden version of the ring with best hints of subtle amounta of colour, even if  the moon did its best to destroy it.  

As an aside when I had the smaller 5 inch scope out a couple of weeks ago looking at the ring, the pentax was outstanding on this target under dark skies from a better site,  I did not have the 8mm Radian at the time, but clearly the pentax was edging the 8mm BST by a bit in terms of contrast and clarity, while retaining almost a much apparent brightness as it did in the 8mm BST. In the bigger scope the early indicators are very hard to judge with the moon as it was anyway, so more on that to come.

Only early thoughts to be solidified in time, but my initial impression is that I am finding the 8mm  Radian a fine eyepiece so far, however, I wouldn't be lying in saying that feeling slightly underwhelmed would be an incorrect description, but much work to be done.

As much as I do love the 6mm Radian for Jupiter and Saturn so far in the time I owned it, the 8mm Radian has not left me with that same strong feeling in that regard.  In terms  of a pecking order I would say the it is not a pentax XW, FOV aside, in terms of clarity, sharpness and contrast. As much as it may be a personal thing and subjective in many ways, the 8mm Radian feels closer in performance overall to the 8mm BST to me, with the pentax XW in sort of slightly different  class in terms of optical quality I feel as the nearest magnification contender.    

As I said and should stress, early days, not a definite review.  In time my  views my well change a bit, but in terms of upgrades since I got a 5m BGO, 6mm Radian, 7mm pentax XW this has probably been the least of what seems like a step up in terms of making an impression on me.

For now both the 8mm BST and 8mm Radian will be staying in the case for more testing. If I really feel  I do need them, part of the idea was I could use the 8mm with a focal extender to give me 4m for the moon and some other things, ( to be tested put with current barlow)  but around that exit pupil and FOV that the pentax XW provides it has the current 8mm 60 degree eyepieces covered pretty much. 

Thanks for reading if you got this far 

[cotterless45]

Neat, it's not easy trying to fit observing in with these short nights, especially with Moon. I found a very stable and clear Saturn at x200-x300. The rings are very open , nearly pole to pole, what a view !

Nick.

[John]

Interesting report Alex. I've been doing a similar comparison with my shorter focal length eyepieces over the past months. I have the 4mm and 3mm Radian's sandwiched between the 5mm and 3.5mm Pentax XW's and its been interesting seeing the effects of switching between the 2 types. I had a Nagler 3-6 zoom in the mix for a while too just to add to the fun / confusion.

It think you are right not to jump to conclusions quickly on these eyepieces. In some cases I feel that two eyepiece types can both have their strengths and weaknesses depending on the type of object being viewed so can both earn a place in the eyepiece case - unless one has to ultimately go to pay for the other of course !

Apart from the cost I have to admit that it's hard to find a weakness in the Pentax XW's though - they seem to deliver really well whatever is being viewed 

[Paul73]

Good unbiased write up Alex.

It has taken me 3 or 4 months to start to appreciate my BST 8mm. So it may be that the charmes of your Radian will grow n you.

I had my 6mm Vixen SLV side by side with the BST 8mm last night and the Vixen performed better on the planets in pretty mucky seeing !! But, it is twice the price.

Paul

[AlexB67]

Thanks Paul, last night was a it better, so both the Radian and BST were giving some nicer views for longer periods where I got to the point that on axis at least the BST can really compete with the Radian, but the Radian was at least as good in that area.  Due to longer periods of good seeing that more useable FOV in the Radian did begin to show a bit more clearly though, but it Is much more subtle compared to when I upgraded my cheap skywatcher 6mm UWA to the Radian where the differences were just very clear to see.

To get a better feeling of it though I need the moon to go away, and try some different targets, that will give a much better idea.  Still it has that feeling of beginning to grow on me. Shame jupiter is out now for me with my trees in my backyard since at that mag saturn is quite a difficult test case I feel with the moon as well right now. I just have a feeling that in time that Radian is going to shine a bit more when I get a bit more of a feel for it on a range of targets. 

As John said above, not only does it need time and targets as well, sometimes the same two eyepieces swap in term of preference on a different nights. 

Last night I was in the BGO ortho mood to finish up the session, that eyepiece just keep impressing me, delightful views at 240x  compare that to the pentax 10.5mm with and my  cheap 2x barlow   which gives a very similar magnification and you can really tell there is more glass there, darker views, not quite as contrasty and clear, still works remarkably well though that combo since the cheap barlow will almost certainly be limiting it somewhat. 

[Paul73]

Indeed. I can't see the point in putting extra glass in the way. There is a 10mm Radian on AstroBuy&Sell at the moment.

A Radian vs Pentax head to head should be a crowd pleaser and it would look good next to your 6 and 8mm's.

I point this out purely as revenge for your introduction of the Ethos angle into one of my threads the other day. I am now actively looking out for a Delos of that mm to satisfy the craving.....

Paul

[AlexB67]

Indeed. I can't see the point in putting extra glass in the way. There is a 10mm Radian on AstroBuy&Sell at the moment.

A Radian vs Pentax head to head should be a crowd pleaser and it would look good next to your 6 and 8mm's.

I point this out purely as revenge for your introduction of the Ethos angle into one of my threads the other day. I am now actively looking out for a Delos of that mm to satisfy the craving.....

Paul

After trying to push the ethos I deserve it   I saw that Radian 10mm I think this one 

http://www.astrobuysell.com/uk/propview.php?view=79429

A little costly IMO, but I love the pentax XL 10.5 anyway which has 65 degrees FOV I got for less ( around 110 or something I recall) so that wont going anywhere    I think that sort of 100 pounds bracket the Radians  often go for is a nice grab.  Sometimes an  XW can be got for 150 - 170 as well. If you are looking for a 10mm  and see It for that sort of cash grab it I would say, since the Delos are often a tad more.

If buying new, well they are pretty much the same cost and will be a matter of preference, it is generally agreed they are a very close performance wise, some will prefer one some the other.  this is an eyepiece focal length you will really enjoy in your scope, the 10.5 XL is my most commonly used work horse.

[alan potts]

Very nice and well writen report Alex, I have never seen the 8mm Radian, it seems that is was one that got stopped a long time ago with the 12mm. I can remember 4 years ago the Telescope House site made no mention of either, suggesting to me they had been pulled. 

Alan.

[michael.h.f.wilkinson]

Interesting review. I found similar distinctions between the LV 7 and 9mm I owned, and Radian 8 and 10mm. In the centre the cheaper LVs were essentially the equal of the Radian, or maybe a gnats whisker behind. Towards the edges the Radian was clearly better (and it had a bigger FOV). The XWs are definitely better, and definite keepers for me. If you can get hold of a Pentax XF8.5: try it. It knocked the Radian 8 out of my line up. Again, the differences were small, but they were there. XFs are not reall 60 deg XWs, but the 8.5 comes close. I now use the Delos 8mm to fill the gap between the XW7 and XW10, and the XF is used mainly for solar work.