Barlow / Powermate

[Shibby]

I really want a Televue 2x Barlow for imaging (having read they are good quality according to various threads on this forum). Please correct me if this is wrong or if there are alternatives?

I've been waiting quite a while for a second-hand one to show up, but so far I've managed to miss them all - they really get snapped up! However, I've seen a 2.5x Powermate for sale at £90... Is this a sensible alternative? The magnification is slightly higher so I suppose this would mean longer subs or less detail? Unless the quality is significantly better than the barlow, it's probably not worth it as I've seen new TV 2x Barlows at £80.

It's currently a test of will; I'll probably end up giving in and buying one new

[Merlin66]

I gather you're thinking of doing DSO imaging - you mention "subs"

Unless you have a fairly large scope and imaging small objects (galaxies) then normally adding a barlow is not recommended.

If you're doing Lunar/ Solar/ Planetary imaging then the Powermate is much better than a Barlow. - But I'd also suggest a webcam based camera ie DMK etc rather than a DSLR or CCD. Subs wouldn't be used or become an issue.

Ken

[Shibby]

Sorry, I should have explained further. Yes I'm talking about DSO imaging with a DSLR on a 130P Newtonian. The barlow is essential - the only way I can achieve focus - so that's why I'm after a good quality one.

[Merlin66]

A low profile focuser or move the main mirror up the tube to gain prime focus would be a far better choice.

That way you can also image wide field objects and get an overall better, wider, field of view.

Adding a barlow is the last option to consider, when all else fails!

[Keiran]

I have been doind DSO for only a short time, and in this time I have learnt alot... I was using a 2x barlow, I was having so much trouble capturing colour and detail.... I was then asked WHY? Why was i using a barlow?

Since then I have removes the barlow, and cropped an resized the image...

The results were far better I would take Kens advice!

How are you attaching the DSLR... have you got a T Thread on your focusser, because that is how I do it... If you are using a nose piece in to the 1 1/4" .... remove the nose, and remove the 1/4" for the adaptor... thats how i gain focus.

HTH

[Shibby]

Yeh I've tried screwing the camera directly onto the focuser with all eyepiece holders removed - the camera was not even close to focusing. Even with a barlow, the focuser is almost all the way in! This leads me to believe that a (pretty expensive) low-profile focuser might not even help. Moving the primary mirror might be an option I suppose, is this an easy thing to do? I've already moved it in as far as possible with the existing collimation screws.

But in the mean-time while I'm using a barlow, I think it's the Televue that will give best results...?

[russ]

How about instead of spending £90 on a barlow, spend the £90 on another scope. Something like a short tube refractor for the same money. No probs focusing, you can use 2" connection, so no vignetting. And a huge field of view. And won't tax the mount.

[Shibby]

You know Russ, you raise a very good point. I'm going to look into this; a tube for observing and a tube for imaging. Intriguing...

Would a £90 scope be up to scratch quality-wise for imaging?

[Shibby]

Also, if I did switch to a refractor, would I need to get a field flattener?

[russ]

A £90 scope would be a short tube Achro like the Skywatcher Startravel 80 or better still, the 102. An Apo like the ED80 or William Optics SD 66 would be better still but would double the price. And ultimately a field flattener would be needed for a large sensor camera but no point getting ahead of yourself. You'll get fine results straight off with the scopes.

[Keiran]

Just a little comment from me ...

With an achro scope you are seseptable to chromatic abraission... I have a Celestron 102, and you can clearly see this flaw, so surely the newt will be better for imaging, atleast until you can afford a APO...

Just my opinion, you will have to let me know if this is correct ?

[Merlin66]

Ab ED80 type scope gives good imaging results, but to be accurate still needs a reducer/ flattner....

Stick with the reflector, it has tremendous potentiial... you just need to address the prime focus position... the best and easiest way is to move the primary mirror up the tube by 40-50mm.

I don't know your particular scope so can't comment on degree of difficulty....

[Shibby]

Oh decisions, decisions! There's currently a large discussion going on in the Equipment Discussion forum about just this. I'm interested to see how that one plays out!

Personally, at the moment my interest lies in improving my DSO imaging. I have to wonder if the aperture of the Newtonian is best suited to this - provided I can acheive prime focus. And collimate properly...

So I think, for now (if I can work around the problems) I will stick with the reflector at least until I'm a bit more experienced, then maybe I'll save up for an APO as you suggest Keiran, or perhaps instead one of these??

Explorer-190MN DS-PRO Telescope (205)