TeleVue Radian + Barlow problems

[Jaxxxxx]

Hey guys

Had a clear night few days back so decided to go test my new Televue Radian which is a 10mm. Jupiter was overhead so in went the 10mm and wow what a result massive massive increase in almost all areas when viewing the planet, the disc was sharp and the bands where very much visible compared to the Plossl the Radian has replaced. Very happy!

Anyway decided to see how the Radian and Televue Barlow combination would work and all of a sudden very disappointed in what I saw. The planet as expected was double the magnification however just a blur with little to no detail visible which was disappointing to say the least.

I have read that Radians have some sort of Barlow already built in what is actually meant by this and for what purpose.

Does this inbuilt negative glass cause this issue I am facing with trying to use the Radian in a Barlow? In other words is the Radian designed to not be used in a Barlow!

I was going to get the 14 or 18mm Radian however if a Barlow is not an option I will have to spend the money on the 6mm instead to get the high power I need as the idea was to use the 10 in a Barlow to get 5mm

Hope you guys can help!

[russ.will]

I don't know what scope you're using, but it sounds like a bit optimistic with magnification versus UK skies. No amount of green lettering will clear that out of the way.

Russell

[Damo636]

I agree, most likely too high magnification for seeing conditions.

[Jaxxxxx]

Thanks for the responses!

I will try the high magnification on the moon when it next shows its face to just double make sure its not a Radian & Barlow combination problem. I prefer the idea of being a little optimistic on magnification vs an eyepiece limitation and also helps me answer the question of what Radian comes next!

Thanks

P.s the scope is only a small reflector 4.5" 900 focal length. I was set on a 10" Dob for the new scope next month but have decided to go with the Skywatcher Explorer 200P now

[John]

I have a feeling that the 180x magnification was just too much for the 4.5" newtonian, especially given less than ideal seeing conditions. So a combination of those two factors. Add the possibility of some mis-collimation of the scope and the odds go even more against getting a sharp image at 180x.

[Jaxxxxx]

You have put my mind at rest John. I was worried as mentioned above that the Radian and Barlow was the problem but now mentioned I believe its very much a limitation of the scope and the conditions!

Bring on the new scope

Further to this enlightenment I doubt I will be dropping below 10mm any time soon especially given that 90% of my viewing is from my garden which is not overly light polluted but nor is it anywhere near inky black....

I was thinking a 18mm TV Radian and a 32mm TV Plossl what do you think of the combination?

Cheers

[Doug]

Hi

Just like to say I agree with everything John said

But if I was you I would get the 10" dob looked through all dobs up to 20"

and the 10" is great the views will blow your mind if you could manage the 12 " even better clear skies

[Jaxxxxx]

I have long considered the 10" Dob and it was what I had my heart set on however after falling in love with EQ mounts simply for the fact that tracking is super easy I just can't get myself excited for the Dob mount anymore

That said EQ is far from perfect inc the back breaking and neck bending positions I sometimes find myself in the Dob does appeal and taking into consideration the bang for buck... Decisions decisions

[John]

Personally I don't like equatorial mounts. The tracking is nice but the angles the eyepiece and finder get to are awkward to say the least. Both my mounts are alt-azimuth now and the eyepiece and finder are always in a convenient place

I also found that I can carry the whole 10" setup (mount and scope) around the garden with an alt-az mount (which I need to do because of trees / neighbours houses, etc) but it's just too heavy to do this with a 10" equatorial setup.

You can get tracking and GOTO dobsonians now of course. Good enough for visual use at least.

[Jaxxxxx]

Do you not find that with lessor aFOV eyepieces such as Plossls and even the Radians at a modest 60 that you are forever messing around with chasing the object with the Dob mount to keep that object in the sweet spot?

Rather than a small twist of the slow motion and you are back on object?

[John]

Do you not find that with lessor aFOV eyepieces such as Plossls and even the Radians at a modest 60 that you are forever messing around with chasing the object with the Dob mount to keep that object in the sweet spot?

Rather than a small twist of the slow motion and you are back on object?

I really don't find it too much of a problem but I've been observing this way for years so I'm used to it. I've a few high power eyepieces with small fields of view (down to 30 degrees ) which concentrates the mind somewhat but, when I'm not in the mood for that, I have some 100 and 82 degree eyepieces too. I'm a bit of an "ocularholc" I'm afraid

[Moonshane]

the key to smooth manual (alt az) tracking is a well balanced tube and smooth axes both in altitude and azimuth. with these factors covered it becomes very easy indeed. I trend to put the object to the right of view (with an upside down newtonian view anyway) and let it drift across the field slowly. that way you get less shake and more time actually observing.

[Jaxxxxx]

I have to admit sometimes all I want to do is grab and go and a Dob would allow me to do this...

I have some large Oaks over hanging the garden so sometimes have to move the current scope about which knocks out the Polar alignment and have to re do so again another benefit of a Dob!

Humm looks like a 10" might be back on the cards again!

[swamp thing]

Hi

TBH a 10" Dob is the goldilocks of scopes.

Not too big, heavy and bulky that observing become a chore and set up times that make you wonder if a quick couple of hour session is worth setting up for.

Not to small that the views are disappointing. It will show very fine views of the Planets and deep sky starts to really show some stuff very well indeed.

A good 10"Dob is a scope for life, I will never part with mine. It's my grab n go set up.

Nothing wrong with an 8" but if I had one I'd always want a 10"

BTW if Dobs were hard to track with, I would have gone straight back to a power driven EQ mount, but I haven't, and don't think I ever will. Unless I succumb to the dark side (fat chance.)

Regards Steve

[newman]

Many Tele Vue eyepieces are combos of lots of elements, with a negative lens at the end tuned to fix exactly the sorts of aberrations those elements cause. Put simply, Imagine you have a positive lens on top and a negative on bottom that fixes it's problems. It's not exactly the same as having any old barlow at the bottom of the ep; this bit is often misunderstood and people start saying that since it has a built in barlow, you can't barlow it further. This is a fallacy - you can barlow it, provided you don't go over the limits of your scope and what the seeing allows. Many people use barlows / powermates with Radians, Naglers, etc..

[Jaxxxxx]

@swamp thing

Have to say the Dob is looking more and more favorable considering my lust for aperture!! Was out this evening for 4 hours and have to say more light gathering power would have been well received.

@newman

Thanks for the clarification on the Radian and Barlow combination. Was really happy to see clear skies this evening so had chance to use the Radian and Barlow on the moon with a 13% filter and was pleased with the results.