60mm Imaging Refractor Advice

[pjspur]

Hi. I hope someone can help as this is starting to drive me mad!

I am looking for a really wide field DSO imaging refractor that can give a focal length in the range of 250-300mm for (I am set on a refractor rather than camera lens as I will use it as a travel scope for visual as well). I will be using a Cannon 450D (on an EQ6 mount) and have (sort of!) narrowed it down to the following:

- Tak FS-60CB with the reducer and micro focuser upgrade

- Mini Borg 60 Astrograph

They both look fantastic but I am having problems seperating them. Does anyone have any experience/comparisons they can share that might help decide between them, or are they too close to call?

Two specific questions I have not been able to find an answer to are:

- How good is the focuser on the mini Borg Astrograh?

- Is there much difference in the optics between them?

Just to confuse things, I could up the FL to around 350 opening up a range of other alternatives (some much cheaper), for example:

- TV60is (this is in the same price bracket as the Tak and Borg)

- Megrez 72 with a reduce/flattener (would work out about half the price I think)

This opens up another question - are the Tak/Borg/TV options really worth the doubling of the cost over a Megrez 72 (or an Equinox 66 with nice focuser upgrade and reducer for 2/3 the cost of the Tak)? I understand there would be a difference in the quality of the optics, but should I expect to see a really significant difference in the image quality betweem the Tak and the M 72 for example?

Its all subjective I guess (particualrly whether or not its worth the extra £), but any thoughts or advice is more than welcome (and will stop my wife from killing me if I mention this to her once more )

Many thanks,

Paul.

[david o]

Hi Paul, first up... a belated welcome to SGL

This may well be a case of the law of diminishing returns - smaller and smaller improvements at increasingly higher prices.

At the end of the day it all boils down to how good is "good enough" for you.

Just my two penn'orth

[kniclander]

I don't know the answer to your question but I congratulate you on your first post after 18 months of membership

Hope you find the answers.

[pjspur]

Thanks to you both for the welcome, and to David o for the input.

I think its safe to say I am not one to rush into things given my posting record so far (has it really been 18 months? - thats scary!) I hope I can eventually contribute something to pay back some of the hugely valuable information I have gained from the forum in the past.

[ollypenrice]

Personally I think the Tak FS60 is a disappointing imaging scope. It seems to give blue bloat on some stars and for the price should do better. I don't know the Borg at first hand but images look good.

If you are up for buying the TeleVue 60is than that would be my choice.

Just to confuse matters, a Cannon Prime L lens and modest 80mm refractor as well might work out cheaper...

Olly

[swag72]

If you want approx 250-300mm of focal length then how about no scope and just a telephoto lens? Canon do an excellent 300mm lens at f/4 that is their L version, so their best quality. You can pick these up second hand for around the £500 I would expect now. There are non IS versions that are cheaper, and as you are going to mount it, you don't need IS anyway. Of you wanted longer FL you could then add a 1.4x or 2x teleconverter to get 420mm and 600mm respectively.

[Stu]

I think there's a William Optics SD66 for sale on SGL which might do the trick. 388mm f/l but I've heard they make good imaging scopes. I love mine for portable visual use. Sure Olly can confirm whether it's any good for imaging

Stu

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[ollypenrice]

Mine's a ZS66 which I don't think is the same as the SD but WO are so confusing. It isn't a bad scope for imaging if you have the flattener. I started out with my 66 and shouldn't compare it with the expensive stuff I use now, so maybe 'not bad' was a bit harsh!

Olly

[Stu]

I think there's a petzval (no idea what that means) which is semi apo, and the SD which is an apo. Very good scope for the price but then I've not looked through anything better at this aperture.

Stu

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[pjspur]

Thanks to all for their advice. I have done some thinking and have slightly changed direction based on the feedback. I can get hold of some 50, 135 and 200 L Canon lenses as loaners so I will use these to see what I can manage in terms of starfields and Milkyway images. For now I will miss out the 200-400 FL range and see what I get from the lenses before deciding if I need to fill that gap or not.

So, the plan now is to look to get something in the 500-600mm FL range (my C80ED met with a rather untimely end at the hands of my 2 year old son ). The TS 80 and 90 Triplets both look very appealing (AMT are selling a version of the TS90 with a 2.5" Moonlite focuser that I am having a hard time ignoring )

I guess this probably needs a new post, but does anyone have any oinions on these two scopes and what impact the longer 600mm FL of the 90mm scope might have compared to the 480mm FL for the 80mm scope in reality? Is there really an appreciable difference in FoV, stability etc that would make one a clear winner for imaging large to medium sized DSO targets? (Or, as is more likely, am I splitting hairs!?)

Cheers,

Paul

[ollypenrice]

You can model focal lengths and chip sizes against the sky on the free CCD calc download. I do this in SkyMap Pro because I have it. It is essential in preparing an image and choosing a FL for it.

Using camera lenses is all about focus. Make sure you have a way of getting it absloutely right because the focal depth is in microns.

BTW, someone sent me a first light from their new FS60 and it was petty good.

A Petzval is a 4 element design, two front and two rear, originally designed as a portrait lens and used by the pioneers like Barnard. It is the basis of the Takahashi FSQ series.

Olly