Not overly impressed

[matt]

OK guys

FWIW

I'm going to post what I believe is my first and only criticism of an item I recently purchased which I thought would improve my set-up.

I've just recently bought and fitted a new GS 2" Crayford to my Skywatcher 8" f5 scope, replacing the R&P which came as standard.

Yes, the Crayford is smooth and "potentially" offers more precise focusing, but what's the point when I can't get a decent collimation with the ******* thing!!!!!

Here are my main gripes:

1: The single screw brass compression ring which secure the eyepieces.

But when I tighten it, it pushed the eyepiece or my collimation tools in the opposite direction, and you get a different result (through a Cheshire or laser) every time you tighten the ring depending on how tight you turn the screw. This offers little to no consistency and leaves the process open to image quality suffering through poor alignment.

Also, given such vaguaries in this area of the focuser's design, how can you ever be sure you've actually achieved a genuine collimation?

Why was there not a second screw on the opposite side to the only existing screw to provide a balance (and centering effect) in securing eyepieces, collimators and other accessories in the precise optical path?????

2: I also needed an extender to allow the tube to rack out far enough to acheive focus and outside focus. This extra piece of equipment only adds to the potential for all components to be out of optical "whack".

I was told (when this item was being "sold" to me over the phone) that it was a straight "plug and play", no adjustment or modification required.

Sure. The focuser only cost $150 ...

But that feels like something of an expensive mistake at the moment for an upgrade which came very highly recommended.

Sorry to whinge, but dammit... that feels better

Anyone got a higher quality Crayford kicking around in their kit they'd care to offload?

[janoskiss (Steve H)]

Don't be sorry Matt. I appreciate you sharing your experiences. I'm considering getting one of these focusers, precisely to avoid the sort of problems you are talking about. My rack&pinion is sags and flexes too much with heavy eyepieces. The Crayford on my ED80 is very basic but solid, and with the tension on, it does not shift even with heavy eyepieces or SLR cameras hanging off it.

[slice of heaven]

Originally Posted by matt

1: The single screw brass compression ring which secure the eyepieces.

But when I tighten it, it pushed the eyepiece or my collimation tools in the opposite direction, and you get a different result (through a Cheshire or laser) every time you tighten the ring depending on how tight you turn the screw. This offers little to no consistency and leaves the process open to image quality suffering through poor alignment.

Also, given such vaguaries in this area of the focuser's design, how can you ever be sure you've actually achieved a genuine collimation?

Whinge away, we don't mind.

Yep it's a downfall all right. I shimmed underneath the compression ring with a strip of plastic to take up the slack so the eps are a snug fit without using the screw to tighten....2 eps are very snug... but the sideways shift is gone.

Can't help with the extension though, that's a real problem without buying a new one or making an extension to fit under the baseplate.

[Starkler (Geoff)]

Sounds like your gripe is with the 1.25" adapter ?
My GS crayford has two screws on the brass compression fitting for 2 inch ep's.

Re drawtube travel , looky here.
http://www.iceinspace.com.au/forum/s...70&postcount=7

A few have fallen for this.

[slice of heaven]

Originally Posted by Starkler

Sounds like your gripe is with the 1.25" adapter ?
My GS crayford has two screws on the brass compression fitting for 2 inch ep's.

2??? Mine only has 1 on each size.... do the 2 screws stop the sideways movement?

[anthony2302749]

I just read the thread and it made me think. When you are making any changes to a Newtonian e.g. new focuser, it becomes much like a ATM project. You must consider what changes a modification may make to the optical axis. There is a program avaliable from the net called "Newt" which will give you some idea of what will happen when things are changed (follow the link).

http://home.att.net/~dale.keller/atm...t/newtsoft.htm

I can not comment on the GS Crayford, but I would assume that it either has a lower profile then the original R&P or that it does not have enough travel, additional if the scope was an f6 there may not be a problem with "draw tube travel". Maybe the point here is to consider the "draw tube travel" when selecting a new focuser Skywatcher 8" f5.

If the "brass compression ring" is similar to the JMI then all is required to secure the eyepiece is a gentle tweak of the screw, the eyepeice should not move. As GS is Taiwanese the manufactoring tolerances may not be as good as JMI so it maybe slightly large the 2" hence it pushed the eyepiece or collimation tools in the opposite direction. A probelm that can be fix but at additional cost.

Just my thoughts on the subject

Anthony

[matt]

Yep

Only one tightening screw per 1.25 and 2 inch brass compression rings.

What was really disappointing about this experience was the assurances I was given that this Crayford was straight forward "plug and play". I went to great lengths to make sure it was ready to go on my scope, out of the box.

I was (foolishly,as it turns out) comforted by the fact the same vendor actually sold my exact make and model of scope and assured me it was perfectly suited without any extra mods. I reckon that makes the problem of its lower profile almost unforgiveable. You'd think he'd be aware of the focusers specs?!??

Surely it's a sign of a good businessman to KNOW YOUR PRODUCT

By the way Anthony ...I think your comment about manufacturing tolerances is pretty spot on.



I'm going to see how a little "padding" of the 1.25 eyepiece holder goes in terms of limiting the amount of movement when tightening the compression screw.

But honestly, whatever happened to the days when you got and what you paid/asked for ... with no nasty surprises?

[anthony2302749]

Hi Matt

I know I should not be asking this question and you do not need to answer it, but who was the dealer?

Anthony

[matt]

Anthony

I don't think it's allowed on this site to "name names"???

Mike? Your stance on this?

[iceman (Mike)]

I'm quite sure I know who you're referring to - have you spoken with the dealer about your problems yet?

It's best to give the dealer the chance to help you fix the problem before naming them and bagging them.

One side of the story is a dangerous thing to take as word.

[matt]

Yep

Only about the lack of tube travel. To his credit he did send out the extender free of charge but it was still disappointing that it came to that at all.

I must say the individual in question was also quite dismissive when I expressed my frustrations over the phone. But that's a different issue altogether.

The problem with the compression ring I've only discovered today.

The Crayford I bought is apparently from a new line?

I would like to make it clear that my comments are in no way a personal attack, but an expression of frustration and moderate disbelief

[Starkler (Geoff)]

So you loosened the lock screw as I suggested and you still have a drawtube travel issue?

[davidpretorius]

Matt,

just a thought, have you cadjusted your secondary. I fiddled with my secondary early on in the piece and found that i could no longer focus with my toucam. I had lost nearly 1 1/2 revolutions. If you haven't got it, buy this months AS&T it has a great article on collimation!!

Get your secondary spot on and see if that makes a difference???

[matt]

Starkler. It's not a focus lock issue. I figured out how that works pretty early in the piece.

The overall height of the unit is a full inch shorter than the Skywatcher stock standard R&P focuser. So there's your focus problem

DP ... the seccondary's pretty much where it was prior to the mod, when it was well-collimated. I've hardly touched it, save for a very minor tweek because of the new focuser's installation.

I've got the current issue of AS&T ... but I'm pretty much OK with collimation these days.

I fear it's just one of those things. You win some ... you lose some

I'll return it and keep on the hunt for a goodun

[anthony2302749]

Hi Matt

I may have an idea (it is only an idea) to fix your problem with "draw tube travel" you need to move the main mirror towards the front of the scope by about an 1" to 1 1/2" so that you can use the focuser with out the extention.

If I remember correctly the primary mirror cell is a push/pull type configuration for collimation purpose. Replace the original bolts with bolts that are about 1 1/2" this should move the main mirror forward by about an 1"+, this will fix the focuser travel problem. This mod should cause no problem with the performance of the scope.

Anthony

P.S. Forgot about the springs they will need to be replaced. Problem can find better ones then whats in the scope now. Also should have thought about this, "Balance", by moving the mirror forward the balance of the scope in the cradle will change.

Anyway it was just an idea.

Originally Posted by matt

The overall height of the unit is a full inch shorter than the Skywatcher stock standard R&P focuser. So there's your focus problem

[matt]

Hey Anthony

Thanks for the suggestion but I think I'd rather not reduce the focal length of what is already a fast scope (f5 - 1000mm), even by such a small amount.

I think a speedy refund will be the best solution and I'll be a little wiser for the experience

[janoskiss (Steve H)]

Matt, you cannot reduce the focal length without regrinding the mirror, but yes go the refund.

[anthony2302749]

Hi Matt

You are not reducing the focal length. Remember that in the manufactoring process the mirror was ground and figured to have a focal lenght of 1000mm (f5). It does not matter were in the tube the mirrors is placed the focal lenght will always be an 1000mm (f5)

By moving the mirror foward you a shifting the focal plane.

Anthony

Originally Posted by matt

Hey Anthony


Thanks for the suggestion but I think I'd rather not reduce the focal length of what is already a fast scope (f5 - 1000mm), even by such a small amount.

I think a speedy refund will be the best solution and I'll be a little wiser for the experience

[RAJAH235]

Matt, send it back & save the hassle. mho. L.
FWIW. I definitely wouldn't like my heavy mirror floating around on extra long screws. I fully compress the springs then back off 1 1/2 ~ 2 turns & do coll. from there. More tension = less chance of going out of collimation. L.

[matt]

Of course

Anyway, still don't fancy that sort of carry-on for a dud focuser.

My mind's made up. It's onwards and upwards. The question is: can anyone recommend a really good Crayford other than a Moonlite or Starlight????