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Friday, September 11, 2009

Active otics and Meade LX200 GPS 12"

I have made some experiments wirh SXV-AO and QHY9.
Since QHY9 has a very small pixels, 5,4microns, there will be serious over sampling with LX200.
I do have a f6.3 reducer/flattener but even eith f6.3 image scale is oversampled.
I tested to increase the distance between QHY9 and a reducer, it seems that I'm able to
go up to f4.65 focal lenght by this method!
There is some wignetting, but not very serious. Some distortion with stars can be seen in outer corners, but I'm able to live with that.
I didn't think it's possible to turn f10 telescope toreltively fast f4.65 scope.
QHY9 has a lightly smaller chip than APS-size in QHY8, that heps a litle.

Images, taken with this imaging configuration, can be seen here:
Click "Older Posts" at the end of the page to see more.


srchadwi said...

Hi there

Just wondered how you've made the extension tube for the lodestar? I actually got one from SX but it's not really long enough.

Also, what is the silver tape for around the end of the Lodestar?

Are you using two inch filters? At the moment I'm using 1.25" with my QHY9 and I'm not really getting much vignetting.



J-P Metsavainio said...

I'm using an extesion tube from SX
at top of the original tube with OAG.

Heh, the Silver tape is just for ensure the cable to a guideport.
The blug is really tiny and the cable went loose few times.
Ugly thing though...

I have 2" filters since I bought them for QHY8.


srchadwi said...


Thanks for that.

I've just noticed that you are using the lead from the lodestar to the mount rather than the one on the AO unit. Is there any reason for this?

Have you found the 'aggressiveness' variable really makes any difference?

Thanks for all the help.


J-P Metsavainio said...

Connecting LS to a mount was what I did first. It works fine, so I never tryed anything else.

There might be some minor effects with aggression setting, I usually have it around eight. If too strong, there might be some oscilation, I havent seen that though.

Unknown said...

Hi J-P

I see you've managed to force the scope to f4.5 by increasing the distance between the camera and the reducer. How are you managing to get enough back focus. Is the LX200 particularly good in that respect?



J-P Metsavainio said...

Yes, SCT's generally have a long backfocus.
And even though the whole imaging system looks so long and narrow, it doesn't bend. I have tested that by using CCDInspector software.

Anonymous said...

I man very impressed by your homemade equipment/adaptation big work! I wonder about backfocus between the focal reducer and the camera , I remember the recommanded backfocus is 110mm, but withextentiontube+SXV-OAG+filter drawer+camera itself, I think you have more than 200mm! is there an astute?
regards, thank you and congrtulations again!

J-P Metsavainio said...

Thanks Laurent!

You are right, 110mm is a recomanded distance.
I have tested this "wrong" assembly to see if it's usable.
You can judge it youself by looking my latest images with this combo.
There is some coma and curvature, but nothing fatal.
Wignetting is not as bad as I was waiting, very easy to deal with good flats.

Anonymous said...

I am very surprised by the length your configuration, I was told the best distance between the FR and CCD was around 100mm I think you have quite more than this!

J-P Metsavainio said...

Yes, the recomnted distance is 110mm, as mentioned in ealier comments here.
This is kind of experimental test. There is some coma though.

Robin Lee said...

Hey J-P,

Have you considering converting your LX200 into "hyperstar"? May I know why you said your setup was oversampling? Was the resolution (measured in arcsec/pixel) way smaller than what your sky allowed?


J-P Metsavainio said...

Hi Robin,

The answer for both is yes.

The system is little oversampled versus my sky quality and , yes, I have considered the hyperstar too.

They don't have a hyperstar conversion kit for the 12" Meade and I can live with a small over sample, in face, it's good for deconvolution.

Anonymous said...

Please can you tell me what the distance is between your focal reducer and the CCD?


J-P Metsavainio said...

Hi Lee,

The recommended distance is 110mm but I have set it large by a trial and error method. The maximum usable distance is depending your optics and the size of the CCD-shell. In my case, there is some coma visible but I can live with that.

I don't recall the accurate distance but it's around 180mm or so.


Hi j-p

what do you think about the qhy9m???, did you any issue with it !!!!, will you Recommends the qhy9m or i go to the SBIG STF-8300M


J-P Metsavainio said...

Hi Sam,

QHY9 is a great value for the money! I have been very happy with it. The first production model did had a problem with frost. New models are equipped with a CCD Chamber heater and there have been no problems since. (BTW SBIG had a same problem at first.)

QHY9 has a much better cooling, than SBIG.