New GSO 10 inch RC - Page 6

gregbradley · #**101** 11-12-2009, 07:30 AM

Quote:

Originally Posted by AlexN

Greg, Yeah I mentioned fast refractors earlier in the thread.. My TMB 80mm F/6 seems stable at prime, however insert the reducer and run it at F/4.8 and all of a sudden I get shift... I run a JMI motorfocus through a FCUSB controller for auto focus, and while its not temp compensating, I can script in focus confirmation through CCDAP.. There is no way I'd sit there watching a thermometer all night refocusing manually every hour or two...

The reason the faster scopes are more sensitive to thermal expansion is that the faster the optics, the slimmer the Critical Focus Zone.. at F/6 mine is 79 microns where as at F/4.8 its 50.6 microns... I'd hate to be trying to manually focus an F/2 camera lens with a CFZ of just 8 microns...

Interesting. So that's why.

CCDAP which program is that? I have to get my temp compensating robofocus callibrated. You have a routine to go through to set it up.

Greg.

rat156 · #**102** 11-12-2009, 08:09 AM

C'mon Doug, I hardly think it shifting 185 microns is going to amount to a lot of wear and tear!

CF is the way to go for these tubes. It's light but strong. I'm sure someone can engineer the mounts for the dovetails so that one has slip in one direction but it's firmly held perpendicular to that direction.

I understand that it will cost more, everywhere else in the world Aluminium is cheap, not in Aus though, so if you price Al tube locally it would be much of a muchness. This probably shows that the Chinese CF industry is not up the the standard of the developed world. I have Kevlar parts made for cars, hand made by a guy here, who charges less than $500 each for them.

If you can get me the dimensions of the tube I can ask him to make some if anyone is interested.

Cheers
Stuart

Kal (Andrew) · #**103** 11-12-2009, 09:00 AM

I'd have to agree with Stuart. If there was wear and tear people would be noticing it on the 8" RC's, and I haven't heard of any issues with it.

Hagar (Doug) · #**104** 11-12-2009, 09:31 AM

Quote:

Originally Posted by rat156

C'mon Doug, I hardly think it shifting 185 microns is going to amount to a lot of wear and tear!

CF is the way to go for these tubes. It's light but strong. I'm sure someone can engineer the mounts for the dovetails so that one has slip in one direction but it's firmly held perpendicular to that direction.

I understand that it will cost more, everywhere else in the world Aluminium is cheap, not in Aus though, so if you price Al tube locally it would be much of a muchness. This probably shows that the Chinese CF industry is not up the the standard of the developed world. I have Kevlar parts made for cars, hand made by a guy here, who charges less than $500 each for them.

If you can get me the dimensions of the tube I can ask him to make some if anyone is interested.

Cheers
Stuart

Quote:

Originally Posted by Kal

I'd have to agree with Stuart. If there was wear and tear people would be noticing it on the 8" RC's, and I haven't heard of any issues with it.

I understand 185 microns isn't a lot of movement but it still is a movement which isn't required. It is a bit like a corrugated iron roof. Screwed down to a hardwood frame the iron creaks and groans with temprature change. It is infact enlarging the holes the screws go through. I know this analogy is a lot more violent than the 185um talked about here but rgardless there will be some movement in areas the CF is used to prevent such movement.

It is possible to engineer a mount base which has no connection between the front and back of the scope, in fact RCOS provide this.

I actually own an 8"RC GSO and will watch for damage caused by expansion but doubt I will see much over this short length. It is getting plenty of time to stretch and shrink while waiting for the clouds to clear anyway. I have just fitted a robofocus motor to it and will be interested to see what if any movement there is with temprature shift.

The comments I made were purely based on engineering principles and I still stand by them as true. In the real world the mirrors and focuser etc will probably be totally stuffed by the time this wear and tear is evident anyway. It was purely an educated, informed statement of fact. My degrees allow me to make them.

Bassnut (Fred) · #**105** 11-12-2009, 11:08 AM

Quote:

Originally Posted by AlexN

Its funny that you have TCF-S on your SCT, and TCC on your RCOS, yet in both cases have not calibrated either for temp compensation

Well, the proceedure is not that clear and quite convoluted for the TCS-F, I think calibration requires constant refocusing during a sizable temp drop time period of maybe an hr or 2, and then all over again if anything is changed in the imaging chain. I always thought stuff it, ive wasted 2 hrs if it doesnt work, and multiple tries before I understand the instructions, id rather image now thank you, maybe tomorrow

.

netwolf · #**106** 11-12-2009, 06:27 PM

An interesting add here on amart, a US company custom making a CF tube for a C14 for ~500USD

http://www.astromart.com/classifieds...fied_id=660192

A bit more digging and found this site for selling the above and other CF OTA tubes. Looks like its a work in progress ad links dont work.
http://carbonscopetubes.com/

This is the companies normal website for hobby rocket frames
http://publicmissiles.com/

AlexN · #**107** 11-12-2009, 06:32 PM

Fahim, There are a few companies in the USA making CF tubes for the Celestron SCT's.. I was looking into getting one for my C11 back in the day.. It was $380USD or there abouts, plus about $130USD shipping...

netwolf · #**108** 11-12-2009, 08:45 PM

Alex one would think the C11 OTA might be in the same range as the GSO 10" RC so 1000$ seems quiet unresonably high.

AlexN · #**109** 11-12-2009, 09:28 PM

I'd agree Fahim.. I wouldn't pay $1000 extra for the CF tube on the GSO 10" RC. I'd pay ~$700 for robofocus.... Temp compensation, automated focus routine, and $300 cheaper.. you end up with 0 focus shift (better than the CF tube, as the Aluminium parts will still shift. Temp Compensating focusers negate any and all focus drift due to temperature...

I think if anyone was considering the 10" RC, get the Al tube model... I would love one.. I don't have the mount for it though..

marki · #**110** 11-12-2009, 09:56 PM

Alex you probably need to factor in the time it will take you to get the temp compensation working properly (right pain) and also that any changes to the imaging line will require you to do it all over again. What is your hourly rate coz you need to factor that in as well

. I have a temp compensation system on my LX200 and everytime I get close to getting it right I go and buy something else to stuff it up.

Mark

AlexN · #**111** 11-12-2009, 10:20 PM

Yeah this is true.. but even if you get the CF tube model, the mirror cells are aluminium, and will expand and contract. the focuser and extension tubes are aluminium, and will expand... So pay $1000 and still have to fix the focus when the focuser and extensions expand, or spend 700 and a night calibrating a temp compensated focuser....

Oh, better yet, dont calibrate the temp compensating focuser, Just automate your imaging run using CCD Commander / CCD Auto Pilot etc and have it check focus periodically during the imaging run, and adjust if required... There you go, 0 time spent calibrating it, reliable good focus, and $1000 cheaper on the OTA.

This could be done using something a lot less sophisticated than Robofocus. I have a JMI Motor focuser on my TMB using a shoestring FCUSB controller... we're talking $300 all up, and I do not touch the focuser at all... despite it adjusting and compensating for temperature changes during the imaging run..

Hagar (Doug) · #**112** 11-12-2009, 11:17 PM

I have temp compensation on both scopes fitted with robo focus and it is a real pain to get the focus slope set correctly and the temp sensor is not on the focuser but mounted in the bottom of the control box. It is a lot easier to run focus max at the start of your imaging, get a couple of good V curves and use it during your session. It seems a lot more accurate and an auto focus takes about 28 seconds using Maxim and focus max with robofocus. I think I would also stick with the Al tube as the CF in this case is expensive and somewhat of a gimmick. Looks good but serves no real purpose.
Please don't argue about this statement, just my thoughts and what I would do. By the way Robofocus is only $500 at the moment and a second motor is about $132.

AlexN · #**113** 12-12-2009, 12:13 AM

Robofocus is only $500!!

!! Bargain..

I agree completely Doug, if robofocus is that cheap, FocusMAX is free, there is the simplest solution to beating any focus drift.... You most definitely understand the need too.. From what I've read, the FSQ106 with the reducer is a focus shift nightmare... I'm kind of happy I went for the TMB 80/480 in that respect... Sure the field is not flat like an FSQ, but its minus that major pain in the backside...

Hagar (Doug) · #**114** 12-12-2009, 08:10 AM

Quote:

Originally Posted by AlexN

Robofocus is only $500!!

!! Bargain..

I agree completely Doug, if robofocus is that cheap, FocusMAX is free, there is the simplest solution to beating any focus drift.... You most definitely understand the need too.. From what I've read, the FSQ106 with the reducer is a focus shift nightmare... I'm kind of happy I went for the TMB 80/480 in that respect... Sure the field is not flat like an FSQ, but its minus that major pain in the backside...

It does appear a pain but with focusmax and robofocus the job is a real easy task. Pause image collection push one button an hey presto perfect focus. Resume imaging. Temp changes mor than 1 degree benifit from a focus reset.

The FSQ does drift quite abit with focus but to be honest the scope really performs at it's best at F5, 530mm witha huge image circle, no vignetting and a flat at field. I love it.

Mighty_oz (Marcus) · #**115** 12-12-2009, 02:36 PM

Q for u all how do u think this RC will compare to say a C11 optic wise for imaging with current knowledge ?

AlexN · #**116** 12-12-2009, 02:53 PM

Going purely on the quality of the optics in the 8" RC, I would say that the RC was better for deep sky imaging than the C11.. The RC is also faster at F/8, this is a plus and a minus really... it shortens your focal length a bit, but the advantage is that you're sucking photons in at F/8 rather than F/10.. The C11 is fairly heavy, I would not be surprised if the 10" RC comes in a little lighter. If buying new for new, the C11 OTA will cost you more too...

In either case, I would say minimum spend on a mount for either of these scopes with deep sky imaging on the agenda would be around the $3500 mark.. I would't mount either scope on less than a Losmandy G11 with the intention of deep sky imaging... An EQ6 Pro will hold both, but the whether or not you get the results you're hoping for will depend greatly on too many things... The EQ6 would be fine if you had adaptive optics for instance...

Optically, If I was buying a new scope tomorrow, the 10" RC would be chosen over a C11..

el_draco (Rom) · #**117** 06-06-2010, 04:09 PM

Read lots about these scopes and am now contemplating a new OTA. Has anyone now got/used an RC-10 for a sufficiently long period to give a simple opinion of:

a/ Photographic performance
b/ Visual performance

For simplicity sake,

, lets say compared to a C11