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Backfocus and Moravian G3 cameras


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#1 lukepower

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Posted 28 June 2016 - 08:27 AM

Hi guys,

soon I am going to get a second system running - a 12" Astrograph from ASA on a DDM60 mount - and I am struggling to get my imaging train fit into the backfocus. I'd like to go for a Moravian G3-16200 camera, but I also want an OAG. And here the mess begins:

According to Moravian, their normal setup would require 62.5mm of backfocus, but the Wynne corrector only allows for 58.25mm.

 

Alright, now there would be a particular OAG for theor G4 cameras which is made explicitely to attach the setup directly to ASA's Wynne corrector - but this only works on G4 cameras and no others  <_<

 

I also considered other OAG's, like some of Teleskop Express, but they all require more or less adapters which, in turn, eat up the backfocus. I was wondering if somebody here is using Moravian CCD's with an OAG and how they solved this situation.

 

Thanks


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#2 pauloastro

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Posted 23 July 2016 - 02:52 AM

Hi Luke,

 

The ASA wynne corrector really have a small back focus distance. This would be a nice think for ASA to change on a near future. But in your case I would study the possibility of using a non ASA corrector. Teleskop Service have a 2,5'' Wynne corrector that could be used with the G3-16200 with a backfocus position of 70mm, or even a the TS Wynne corrector by Massimo Riccardi  with 65mm of backfocus. Orion Optics could also be an option with their 3'' Wynne corrector with 70mm of backfocus.

 

Best Regards,

Paulo.             


Paulo Nunes.

 

AstroSite: https://sites.google...trobicesse/home

 


#3 lukepower

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Posted 23 July 2016 - 07:29 AM

Hi Paolo,

 

thanks for your thoughs. The point is that the ASA Wynne has a better overall performance compared to the TS one, especially with the field of view I require.

Anyway, together with ASA, we seemingly found a solution: ASA will build a custom adapter with an integrated OAG, which (narrowly) fits the count.

But I agree, if there would be a way to get a longer usable backfocus without compromising performance it'd be great


Lukas Demetz
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www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#4 MarkS

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Posted 09 August 2016 - 03:28 AM

Hi Lukas,

 

I can't help with the backfocus, but I thought you might be interested in the enclosed image. I got a G3-16200 more than two months ago, but the weather here has been horrible! So last night I got it under the stars for the first time.

 

Unfortunately I was in suburban Melbourne, and there was 25% Moon, so the SQL was 18.3. Narrow band was in order.

 

In the event I got only one 10 minute sub in Ha that was not ruined by cloud....

 

So here it is: it has been very mimimally processed - just calibrated and given a very little clean-up with MLT, then stretched, in Pixinsight. The frame was prepared for the web in CS5, with a very low dose of sharpening to compensate for the file size reduction.

 

I've shown the full frame so you can see how the ASA10N and Wynne Corrector handle the corners.

 

ASA10N at f/3.6; DDM60; G3-16200; Astrodon 5nm Ha filter; 10minute exposure.

 

Mark 

Attached Files



#5 lukepower

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Posted 09 August 2016 - 07:09 AM

Hi Mark,

thanks for your effort, and congratulation for that setup and the image. As far as I can tell, it looks awesome!  :) 
Can't wait to get the new setup running


Lukas Demetz
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www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#6 ChristerS

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Posted 09 August 2016 - 10:00 AM

Hi Mark,

 

I'm about to order a G3-16200 with external FW, and Moravian told me they will produce an adapter for the G3 camera to attach a Wynne corrector to get right BF (with no OAG), how did you resolve the BF distance on your Wynne and G3?

 

//Christer


Cheers,
//Christer

www.astropix.se


#7 lukepower

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Posted 09 August 2016 - 12:02 PM

Hi Christer,

 

they told you so? I was told that they have an adapter for the G4 series of cameras, but not the G3 as there was some space constraint...


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#8 MarkS

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Posted 09 August 2016 - 01:35 PM

Hi Christer,

 

With no guiding, there is no problem.

 

I used the Moravian M48 nosepiece, and designed an adapter to fit between the ASA Wynne and the nosepiece. The front of the nose piece to sensor distance is 41mm. With 3mm filter thickness the adapter needs to be 17.6mm thick - or 17.3mm if there is no glass cover on the sensor. The final result is similar to the ASA style adapters.

 

You need different thickness adapters for the reducer and barlow.

 

If I was getting a second set made, I would possibly design for a larger aperture than M48 for the Wynne as there is a little vignetting in the corners. However, as you can see from the image, calibration deals with the vignetting well. For the reducer and barlow I wouldn't bother, because they both have image circles that do not cover the 16200 sensor  - necessitating a crop to manage coma.

 

Mark



#9 ChristerS

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Posted 09 August 2016 - 02:29 PM

Hi Lukas,

 

They told me they had only an adapter for the G4 series of cameras but decided to build a G3 adapter, as I suggested ;)  with no OAG support due to short BF distance of the Wynne, se reply below. This adapter and camera should be of interest for all ASA OTA users, the camera have a good price compared to FLI. This adapter is with the G3 + EFW-3S-7 external filter wheel attached, there internal FW have only 5 spots. 

 

"We decided to build the G3 to Wynne adapter and offer it as regular item. However, the whole process of introduction of a new item takes a time as our manufacturing is oriented to mass production and prototype manufacturing has to be “inserted” into regular stream of batches.

Best Regards

Pavel Cagas, Moravian Instruments"

 

By the way I read somewhere ASA may release in the future (whatever that means) a Wynne with longer BF distance witch should be of interest to you, check with ASA. 

 

//Christer


Cheers,
//Christer

www.astropix.se


#10 ChristerS

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Posted 09 August 2016 - 02:35 PM

Hi Mark,

 

Thanks for the info! I was thinking of 3D plotting an adapter from a local 3D plotter company. I currently have a SX filter wheel 36mm a bit tight for the 16200 chip but was thinking a way to fit it to the G3 and see what the vignetting effect is, buying new Astrodon 50 mm filters is more expensive than the G3 camera ;)

 

//Christer


Cheers,
//Christer

www.astropix.se


#11 lukepower

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Posted 09 August 2016 - 05:13 PM

Interesting...

Well, I found a solution together with ASA so am fine now, however I am thinking about exchanging the 8300 FLI camera I am operating in Spain with an 16200 from Moravian, that could come handy there, too...

Let's wait and see  :)


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#12 MarkS

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Posted 09 August 2016 - 11:17 PM

Hi Christer,

 

Good luck with that!

I 'bit the bullet' and bought a set of 50mm filters. As you say, more expensive than the camera!

Moravian were not enthusiastic about the use of 36mm, but with a good set of flats you might get away with it.

Incidentally, I bought the EC (extended cooling) version, due to our summer night time temperatures. But I guess you don't have that problem.

 

Mark



#13 lukepower

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Posted 10 August 2016 - 10:51 AM

Mark,

 

as you mention the extended cooling option, how far from ambient are you able to cool?
I still wonder how there could be such a big difference between FLI and SBIG, for instance. With the FLI in Spain I easily go down to -30°C  (so about -55 from ambient), while the SBIG manages barely to get to -25 from ambient...


Lukas Demetz
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www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#14 MarkS

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Posted 10 August 2016 - 01:39 PM

I haven't found the limit yet, as it's winter here, but at 43C below ambient it is running at less than 70% power.

 

Mark



#15 ChristerS

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Posted 10 August 2016 - 03:10 PM

Hi Mark,

Don't think I need the extended cooling option it gets down to -25 here up north ;)

Did you go for the grade 1 or 2 chip? I think 15 columns defects or so can be handled by the FF.

Nice image by the way!

 

/Christer


Cheers,
//Christer

www.astropix.se


#16 MarkS

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Posted 11 August 2016 - 12:01 AM

Hi Christer,

 

I went for the Class2. My sensor has one noticeable column defect at room temperature, which is almost invisible at -25C. As you say, this easily accounted for by calibration. I understand that the Onsemi processing is producing a high proportion of Class1 sensors, but they are still asking a high premium!

 

Mark



#17 Benoit Gagnon

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Posted 28 September 2016 - 02:46 AM

hi guys, I was thinking  about upgrading my QSI683WSG-8 to a G3-16200 from Moravian but the difference in performance was not really that big, so  I decided to go for more money but not that much to a G4-16000EC and I got my OFF-Axis from Sky Meca in France ( the slim model with a tilt corrector inside and only 15mm ) . I am planning on getting either the 10N or the 12N . Here is a picture of the Off-Axis (that will work with the back focus of the ASA Wynne corrector) installed on my FQS.

Attached Files


Edited by Benoit Gagnon, 28 September 2016 - 02:49 AM.


#18 MarkS

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Posted 29 September 2016 - 05:31 AM

Hi Benoit,

 

One of the most important differences between the 16200 and the16803 is the pixel size. One aspect of this is plate scale. The 16200 on the ASA10/Wynne gives 1.37"/px, whereas the 16803 gives 2.05"/px. The ASA12/Wynne with its 20% longer focal length will be better suited to the 16803 than the ASA10, as it gives, theoretically at least, a more favourable plate scale of 1.7"/px. Of course, the importance of this consideration depends on the seeing conditions you experience.

 

(Just my 2cents worth :))

 

Mark



#19 Benoit Gagnon

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Posted 29 September 2016 - 06:43 PM

hi MarkS,

 

Over the years I came to realize that the perfect sampling is not the ultimate consideration when matching a telescope to a camera. The signal strength and the signal to noise ratio are the key elements, I would rather work with pixel of 9um than 6um (16200) or 5.4um (KAF8300) anytime, also to give an extreme example, have you ever seen a picture taken with an FSQ106 (530mm) and a 16803 that didn't look amazing even if it was highly undersampled ? Being undersampled is way more preferable than being oversampled wich can destroy your end result (very weak signal) , also when undersampled the Drizzle X 2 works like magic under Pixinsight. This is the main reason why I did not consider the 16200 for my upgrade from a KAF8300, might as well do it right and go all the way to the king of sensors , the 16803. 

 

Now my only decision left, do I buy a 10N or 12N , many factors to consider here , portability, does anyone here find the 12N a bit big for field operations ? , cost in not a factor for me, the weight of the scope is not critical for the mount ( I have a Paramount MX+) only to carry the scope itself is, if I go with the 12N I will be tempted to say at the 2 available focal lengths,  if I go with the 10N the temptation will be strong to also get a 14.5" Dall-Kirkham in the future ( and that is a good thing). At the end, it all come down to decisions, decisions...



#20 MarkS

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Posted 30 September 2016 - 12:15 AM

Hi Benoit,

 

I understand your reasoning here. FOV and how big the prints are to be (if any) also enter the consideration....Hava fun with the decision!

 

Mark






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