Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

Skywatcher Dual Speed Crayford Focuser for SCTs


MickyWay
 Share

Recommended Posts

The Celestron 8inch SCT is a good all round telescope, especially for planetary imaging.

Focusing for observing and deep sky imaging using a DSLR is well served by the mirror

focusing knob, which is smooth in operation, and allows for accurate focusing under normal

circumstances. However, when imaging with a webcam at long focal lengths, the dreaded

mirror shift can make focusing very frustrating. As soon as near focus is reached, a tweak in

the opposite direction can send the image off the screen, and at f40 plus, finding the target

again can be difficult.

So, I decided to invest in a Crayford focuser, which attaches to the ‘Visual Back’ of the SCT

and would eliminate the effect of mirror shift and offer accurate focusing. After much searching

and investigation I decided on the Skywatcher Dual Speed Focuser for SCTs.

On opening the box, first impressions were, it’s big (!) and beautifully made. Real quality at a

reasonable price. Fitting the focuser to the ‘scope is very easy. The large knurled ring nut picks up

the thread easily, and despite it’s weight, fits very securely to the back of the ‘scope. Loosening

the nut allows the unit to be turned to any position. To adjust the rotation friction, there are three

recessed set screws around the perimeter. The focuser takes 1.25 and 2 inch accessories, which

are secured by large, single knurled screws. The focussing mechanism itself is very smooth in

operation, and the dual speed function is very usable.

Initially, on loading the focuser with 2 inch diagonal, filter wheel and camera, I was dismayed in

seeing the whole lot sliding to the end stops. A quick phone call to Steve at FLO solved this

(thanks Steve). The friction of the focuser can be adjusted by turning the recessed

Allen screw located in the centre between the focusing knobs.

Once the object is focused, the knobs can be disabled, effectively locking the mechanism, by

means of a large knurled knob on the base (immediately below the friction Allen screw).

In summary, my initial fears of whether the extra weight of focuser, diagonal , camera etc.

would be a problem were unfounded. The SCT back is built like a tank, and I cannot detect any

flexing at all. Providing all knurled screws are tight, and the tube is balanced carefully, then all

will be well. My EQ6 just carries on as if nothing has changed. The focuser works very well.

No more image shifting, apart from the wobbling when touching the knobs, which dies down

very quickly, and the image returns to the centre. Nice. Highly recommended.

See also johninderby's excellent review Feb 2009 on the Low Profile version for Newtonians.

Regards,

post-16403-133877437393_thumb.jpg

Link to comment
Share on other sites

Agreed. This seems to be a really good bit of kit for the price. I bought one second hand from an SGL post. Unlike you with your Celestron I found that my Meade SCT main mirror focuser was hopeless for imaging of any kind and inconclusive in viual as well TBH. Now sorted.

One thing to remember, though, when using a reducer is to set the crayford to the right chip distance, focus with the mirror as closely as you can, then use the Crayford as sparingly as possible to fine focus. That way you don't end up miles out on chip distance.

On the very posh Moonlite you can insert the reducer in the draw tube so the chip distance never changes.

Olly

Edited by ollypenrice
Link to comment
Share on other sites

Hi Olly,

Thanks for the advice. It can be a problem finding the target at the best of times.

I plan to use the reticule on the focuser to maybe help in this sort of situation.

Changing the subect, I notice you have the ZS66 in your equipment list. I'm considering the Megrez 72 as my next scope. As you know the 66 is no longer available. How have you found the 66?

Regards,

Link to comment
Share on other sites

Hi,

It is hard not to love the ZS66. It is tiny, very pretty and can deliver quite nice images at an affordable price. Build quality is fairly good but not, maybe, quite as good as WO make it look. I don't mean to be catty but they do make their stuff look Rolls Royce when it is not quite that! But then, they don't charge Rolls Royce prices so fair's fair.

I would criticize 1) The overly short main tube meaning too much draw tube extended, leading to the risk of sag. Rob Hodgkinson has had a new longer tube made for one of his WOs. 2) Only just enough tension on the focuser to hold fairly normal camera setups and not enough for heavy ones. 3) Huge field curvature making the flattener an imaging 'must.'

So it's not perfect but it's not for sale either and is bound to suffer in my estimation since the other way I can image at about 330mm is with a Takahashi FSQ. (For an extra £2700.) Say no more.

You don't fancy a SW ED80? Of small, affordable refractors that would probably be my choice.

Olly

Link to comment
Share on other sites

Hi,

It is hard not to love the ZS66. It is tiny, very pretty and can deliver quite nice images at an affordable price. Build quality is fairly good but not, maybe, quite as good as WO make it look. I don't mean to be catty but they do make their stuff look Rolls Royce when it is not quite that! But then, they don't charge Rolls Royce prices so fair's fair.

Olly

I had a ZS66 and the only real complaint I ever had about it was the focuser. Both because it's only a 1.6" one, and also it isn't exactly heavy duty. The Megerz 72 has a nice 2" focuser and decent optics. You might also consider the ZenithStar 70 or the Ian King Imaging IKI70 ED. Optics are very close to the Megrez 72 in quality, but they are cheaper but still have a 2" focuser.

It's a pity WO doesn't put better focusers on some of their scopes. When I got my FLT98 DDG Alu Tube a few months ago the actual OTA and the Russian optics were top class in quality, but the focuser was unfortunately not up to the same standard and badly let the scope down. However that was well and truly cured with the addition of a Feather Touch R&P focuser. Now the scope's an absolute delight to use.

Link to comment
Share on other sites

Hi Olly and John,

I went to see Ian King today, what a nice guy, and he was very helpful in helping me make an informed choice. If you disregard the 'bling' factor in choosing, (not only in astro equipment),

it comes down to affordability alongside performance. I had a short list:

IKI70mm, INED70, Stellavue SV70ED and the WO Megrez 72.

The first three are virtually identical, apart from cosmetics and price. The Stellavue was £140 dearer than Ian King's IKI70!

After weighing the up the pros and cons, I decided on the Megrez72. With a bit of discount, it work out cheaper than the INED70 (at £324 del) and about the same as the IKI70.

As for performance, I have no idea at the moment, but if the consensus of opinion on the forums are to be believed, then I have made a good choice.

Ian did say that a field flattener is almost a must for imaging, and although WO recommend their 'dedicated' flattener, it requires very careful spacing (to within 1mm) to achieve optimal performance.

I think this probably applies to most optical add-on's.

The advice and suggestions you guy's have given me is really appreciated, and I welcome any more suggestions you may have.

Kind Regards,

Link to comment
Share on other sites

Hi

I think that you've made the right choice. The Megrez 72 has that little edge over the 70mm ones in optical quality. Very compact scope but surprisingly heavy.

Ian is one of the best people in the business. I've bought a number of things off him and he's always given excellent service and good advice every time.

John

Edited by johninderby
Link to comment
Share on other sites

Thanks, John, nice to have some reassurance.

I've only managed to do some terrestrial imaging so far, but what I'm seeing

is very good. Contrast is excellent, and sharpness in the central part of the image

looks more than acceptable. This was using a DSLR and a DMK21.

Pity M45 is disappearing fast over the horizon !

All the Best,

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.