Skywatcher f4 Carbon Fibre OTA

[DJ N]

Just wondering if anyone has purchased one of these yet for imaging. There seems to be some favourable reports and images on some of the UK sites. Seems a Baader MPCC or similar is a given for this focal ratio.

I was doing a quick comparison, and in terms of my ED120 which is f7.5, would be 3.5x quicker exposure.........for a very similar focal length 800mm versus 900mm. Downside is a lot more fiddling. With the ED120 or ED80, it is just plug and play, whereas at F4, I imagine collimation would be a bit finicky.

Very tempting..... might do a bit more research!!;)


Cheers,

Daniel

[CoolhandJo]

Do you have a link?

[DavidU]

http://www.firstlightoptics.com/reflectors/skywatcher-quattro-f4-imaging-newtonian.html

[DJ N]

That's the one ;)

[Marke]

I wouldnt mind the 300mm version if the price was right.

[LightningNZ]

Andrews Communications is selling these. http://www.andrewscom.com.au/site-section-10.htm

I fully intend to buy one when I have enough money saved. That said, I'm a bit concerned over how much weight the focuser can hold, and where is the 2nd thumbscrew for tensioning? My GSO focuser for my refractor has the two thumbscrews in a row. I really hope the newt version has it on the opposite side to the locking screw.

Cheers,
Cam

[Tandum]

The GSO CF newts are half the price of the SW ones and the metal ones are half that again. I known CF tubes don't really cost that much extra so don't be taken for a ride.

[netwolf]

I am guessing Skywatcher and Celestron share the same distributor. I would get the GSO Newt, would be as good if not better.

[DJ N]

Might do some further investigation in order to "quicken" up my current set up. I see that William Optics have recently updated their flattener III, specifically for f7 to f7.5 systems.........

http://www.williamoptics.com/accessories/flattener3_features.php

I ordered one on Saturday.... already in transit. I will try on both the ED120 and the ED80. Hopefully will work well with at least one of them and will reduce the f7.5 to f6.

Still a bit nervous about going the Newtonian route with all the fiddling.

Then again.......... could always go a FSQ ;)

Anyhow, will keep everyone posted once the new reducer arrives.

cheers,

Daniel

[RobF]

There's a huge thread on these at the Stargazers lounge:
http://stargazerslounge.com/sponsor-announcements-offers/145677-skywatcher-quattro-f4-imaging-newtonian-telescopes.html


I haven't seen or used one, but have done a lot of imaging with an older F5 SW600 8" Newt. My first thoughts after reading the above thread:

Pros:
- they're F4 (faster and better FOV)
- CF is lighter and should be less flex
- Focuser a bit better
- Baffles
- Bigger secondary (vignetting should be lot easier to control/correct)

Cons: (speculative...)
- Rings much the same as ever
- F4 will be a lot tougher to get right and keep collimated
- Focuser - is it really up to holding precisely and reliably for a decent size and weight imaging train?
- conflicting info that MPCC may not be up to task of coma correction and RCC 90mm backfocus unit may or may not be better (image train will stick out further on that budget focuser though)
- lack of info on how an OAG might be used

I can't shake the feeling serious imagers will still need to tweak or modify these somewhat? (rings, flocking paint possibly, focuser, coma corrector/OAG rig)

On the other hand, you can do a lot of imaging damage sticking a CCD on a carefully set-up fast Newt - at an unbeatable performance/price ratio for those that can't afford an FSQ or CDK setup.

[DJ N]

Yeah, I have been following that thread closely. I think you have summarised things quite well. I agree that the OTA's would require a bit of tweaking, but once they are "settled", especially in a permanent setup in the home obervatory, they would make for capturing a lot of data very, very quickly.

Cheers,

Daniel

[Peter.M]

I have found that with my F4 newt collimation wasnt too much of a problem, get a good set of tools and you are set. The main thing that I would be thinking about is guiding/vignetting. With my rolled steel tube I found that guiding had alot of flexture involved, the futher your focuser is away from the guidescope the greater the problem as the steel tube flexes signifigantly. I decided on going for an OAG because it seemed to be the best option completely negating diff flex. This caused different problems, I decided to go with a large format OAG because the 9mm varients I had seen cast a shadow on the chip, which was not something that I wanted. I then did not have signifigant backfocus to use the larger OAG. The other problem I encountered is the more you have hanging off the tube the larger the secondary you theoretically need. This is less of a problem with slower scopes because the light cone is less sharp, what I mean here is the parralel light rays that enter the scope are bent in towards the focal plane at a greater angle the faster the scope. So the more of the cone you have in the focuser the wider the secondary and everything after it needs to be.

I have now moved the mirror up the tube to increase backfocus and I can get the camera and guider to focus. I am yet to produce an image as the weather has been ****house but I will post what It looks like as soon as i give it a crack.

I would be interested in seeing what one of these running a guidescope could do If all of the flexture problems were dealt with. If you were thinking of using an OAG with the system I would wonder if the extra price for the carbon fiber would be worth it, I would much rather deal with steel for modifications and with an OAG the expanding and contracting of the tube should not cause too many problems.

[DJ N]

Thanks for the reply Peter. You have made some very interesting points. Initially I was expecting to use a separate guide scope (ED80) with the though of going down the path of an OAG. However, this does seem a bit of a hit and miss affair. And as you pointed out, once you have a coma corrector, OAG, guide camera plus CCD hanging off "non-centrally", this opens up a new can of worms.

[RobF]

You'd expect the carbon fibre should control steel tube flex far better, so perhaps a guidescope rig is ok. Mike Sidonio is using a guidescope with his super AG12 rig with great success.

It's great to see the chinese manufacturers tweaking their gear towards the ever growing imaging market. The baffling, larger secondary, and presumably better backfocus and ease of using 2" cameras etc have to be aplauded.

Be nice if they provided some better OAG options in future - fingers crossed.

[netwolf]

How about the ONAG as mentioned in another thread here. There is a review on CN http://www.cloudynights.com/item.php?item_id=2706

[Tandum]

I believe you'll find the tube is distorting around the focuser. Moon (James) found the same issue on the 8" and 12" steel tubes so I imagine the 10" will be the same, see here. (http://deepspaceplace.com/at12in.php) You have to solve this problem or your collimation will be unstable and shift with altitude. I believe you are mistaking this for flex, no brand of OAG will fix this issue. I recently had a similar issue with a prostar tube and found putting a separate ring around the tube next to the focuser appeared to fix it but the scope went back to it's owner before I'd finished testing. If you dig up some pics of Mikes 12" newt you'll see an extra pair of rings, one each side of the focuser assembly.

Here's a pic of Mike focuser. (http://www.pbase.com/strongmanmike2002/image/133046308)

[strongmanmike]

Yes, as Robin points out fast Newts need good stiffness around the focuser and this requirement goes up exponentially in proportion to the camera weight attached and increase in photographic speed.

If you are using a small web cam I imagine the stock focuser and tube might be fine but most wanting a wide field fast scope are usually interested in using something bigger and usually including filter wheels, electric focusers and off axis guiders etc all of which add significant weight at 90deg to the tube and impart all sorts of torsional and twisting forces. As you step up in camera size and add on accessories the need for extra stiffening really goes up particularly as chip size increases - the larger the chip the more obvious any problems become.

My scope has attempted to address much of the potential problems with a fast Newtonian and you could look to modify a new cheaper OTA in similar ways if you like:

Tube rings to support the focuser base (http://www.pbase.com/strongmanmike2002/image/132998041/original)

Strong rear tube stiffening (http://www.pbase.com/strongmanmike2002/image/133046313/original)

Solid internal tube stiffening around the focuser and thick one piece spider (http://www.pbase.com/strongmanmike2002/image/132998031/original)

Direct threaded adapters where possible and a robust electronic focuser (http://www.pbase.com/strongmanmike2002/image/133257301/original)

Having good solid well spaced tube rings held together top and bottom (as in the first link above) is a very good idea too and even more seperated than I have would be better.

A carbon fibre tube is stiff but also has lower expansion qualities that will reduce the need for refocusing during the night, at F3.8 I have had no issues with refocusing over several hours.

Ensuring that the main mirror is held properly with in the main cell is very important here too, all the retaining devices ie side supports and retaining clips, must be physically touching the mirror so it can not move at all but not applying any net force on the mirror (or else astigmatism is possible).

In a nut shell, anything that improves the ability of the OTA to resist bending, flexing and twisting forces and careful attention to stabilising the main and secondary mirrors will be needed.

Then if you are going to use piggyback guiding the guide scope and camera need to be held hard and fast to the OTA or mount (this is one area I need to improve actually).

If all this is done then you can really take advantage of the extra aperture and speed a scope like this will provide over the more popular and trouble free but smaller and usually slower APO alternatives or the field and speed restricting RC and similar scopes.

Hope that helps :)

Mike

[Peter.M]

Since moving to an OAG with my system I think flexture was most of the problem on my system, I am now able to get acceptable stars in 15 minute exposures. I think i will look into stiffening the area around my new moonlite focuser. The problem I was having was I was previously guiding using a finderscope, the finder bracket was attached to a standard finder dovetail. Thermal expantion of the newt tube, and the tube flexibility in general cause difference in position from the finder to the main camera. This is why I suggested mounting the guidescope as close to the focuser as possible to eliminate the amount of steel that can move between them.

If I was to use a guidescope now I would probally look into a longer focal legnth scope, and far better mounting for it. With my heq5 I didnt want to add more weight to the system so the OAG was my solution. After using one for the first time a few nights back I dont think I will go back to a guidescope with my newt.

[DJ N]

Great food for thought Mike. Very valuble insight, especially for people like myself who have not really had the opportunity to play around with imaging scopes apart from refractors.

Cheers,

Daniel

[DJ N]

Well, finally did a bunch of testing last night. Initially set up the 56mm spacing between the flattener and QHY8L as specified per the William Optics website, and I could not bring either the ED80 or ED120 to focus. Not enough "in focus". I then proceeded to play around with reducing the spacing between the flattener and CCD. To make a long story short..... with a 20mm spacer in place, I am getting round stars in the corners of the frame with both the ED120 and the ED80. Very strange result considering the WO spec, however, very pleased with the final result. I will post the images later, but I think for now I will stick with the 2 refractors especially now that I have them "singing" at both f6 (with the WO reducer/flattener) and at f7.5 with the hotech flattener. Cannot really asks for more than that!!:thumbsup: Might leave the f4 reflectors to another time. But I do thank everyone for their input!!

Cheers,

Daniel

[Logieberra]

Quatro 10" review on YouTube, provide by Astronomy Shed:

http://www.youtube.com/watch?v=wcvHOHwg1j4&feature=youtube_gdata_player

[AstronomyShed]

That would be me :D Bit of an update after reading the various questions in this thread.

Is it a pain to collimate?

No, you will get a decent collimation using nothing more than a cheshire collimater, however I would suggest star testing the primary at the start of every session, I'm now working on an advanced colli with mine where I star test and adjust primary, then use cheshire to adjust secondary and then star test primary and adjust again, in other words, not using the cheshire collimater to adjust the primary at all. There is obviously a relationship between the two mirrors (thats how newts work) meaning star testing adjusting primary knocks out secondary a tiny bit, each iteration of the above needs a smaller/finer adjustment until both are spot on. This is a one off, very fine collimation of secondary really and the secondary does hold colli pretty darn well, but still, always a star test on primary at each use.

is the focuser adequate?

Yes and no, if you're considering a scope like this, you should be experienced enough to tweak this area, it has focuser locks each side of the focuser, as pointed out on the video linked above, however, I don't like them, and no matter how I used these two locks, they created image shift when moving focus in and out (obviously not fully tightened but used as tensioners) which in effect also shifts collimation a fair amount in an F4, so I no longer use them. HOWEVER, this is not like the bog standard skywatcher focusers, it's much beefed up, has twice the number of bearings that the tube runs in, and the actual crayfor 'rack' is what looks like a stainless steel screwed on track that actually also runs in bearings, so, each side of the focuser lock on the knobs side of the focuser there are also two tensioning grub screws, taking a little time in adjusting these means focus remains smooth, but stiff enough to easily support my QHY8L and extensions & filter and a baader MPCC with no slippage whatsoever.

Hows the Coma?

Well, with the baader MPCC it's tolerable, just, the plain fact is that at F4 the MPCC is at the very edge of it's tolerance, if you want better, pay a lot more, maybe such as a parracor or one of the 700 uk pounds ASA correctors.

Does it perform?

Ohhhh yes!!!! The beast does take a little taming but to be honest, if you want the results, you have to put the work in, would I buy it again? Now that I feel I've put the time into it, then definitely yes as it's now starting to perform for me.


Finally, the proof is in the pudding, this is 11 frames only, unfortunately we only get about 3 decent hours of imaging time in my part of the UK at this time of year, guided with a piggybacked ST80 and QHY5 using PHD, processed in nebulosity and photoshop. 11 frames, 50 flats, 55 darks, half moon was up and obviously it needs more data, but.... :-

[RobF]

Welcome "Down Under" Dion and thanks for your comprehensive comments :welcome:

(err, G'Day Mate! :D)

[AstronomyShed]

Thanks, just as long as I don't have to wear one of those corky hats and sing Rolf Harris songs! :D

I've actually been reading 'Ice' for a long time, just never subscribed, then I came across this thread re my Quattro vid and thought I'd input the aftermath.

You have some really good hardware guys here and that's why I read here a fair amount.

[wasyoungonce]

Every time I see that scope...I get excited...as only a man could!:eyepop:

[DJ N]

Hi Dion,

Really appreciate the reply. Looks like you are getting great results!! I too have the QHY8L, and I like it quite a lot. They are not too bad a camera for the money.

At this stage, I have not progressed my thinking any further with regards to the Quattros. For now, I am pretty happy with the simplicity of the ED80 and ED120.

Anyhow, looking forward to some more of your images.

All the best.

Daniel

[AstronomyShed]

I love the very wide field that the ED80 gives with the QHY8L, if you get a lot of data to keep the noise at bay and use the field flattener it can give some really nice results, this was ED80 and QHY8L :-

http://i1032.photobucket.com/albums/a407/astronomyshed/Deep%20Sky/lookingood22.png