AAF3 with heavy load (G4-16000)

[-Amenophis-]

Hello,

I would like to acquire a MORAVIAN G4-16000 camera with external filter wheel and ASA3 "corrector for my Newton ASA telescope.

My focuser is an AAF3.
I would like to know if a person has this camera and this eyepiece holder in order to know if it is well supported.

I previously had a lighter camera, the G2-4000, and had a lot of tilt that was difficult to correct.

Before buying the G4, I would prefer to inquire.

Thank you very much for your help.

[MarkS]

I have not used my G4 with my ASA10N/ASA3" Wynne/AAF3, but I use a G3EC with external filter wheel with absolutely no problem. This camera weighs 2.9kg, whereas the G4EC plus L FW weighs 3 kg. So you shouldn't have any trouble.

However, the ASA 10 alignment and collimation will be critical to minimising tilt. The dof for a f/3.6 scope is only ~+/-17micron. Therefore focal plane curvature plus tilt plus focus inaccuracy must be within a 35 micron band across the sensor dimensions. The axial position of the OTA secondary mirror must be spot on to take tilt out of the equation - it isn't good enough to just have axial collimation!

The G4 Mkll of course has a tilt corrector, but it still pays to ensure the OTA alignment is as good as possible.

Hope this helps.

Mark

[-Amenophis-]

Hello, Mark.

Thanks a lot for your answer. 😉

These are the old G4 cameras so no built-in tilt adjustment. I use the optical divider from SKYMECA which manufactures this very simple and formidable system.

For OTA alignment and collimation, I use the CATSEYE system which works very well and gives me satisfaction. Hope this can correct / minimize all these issues.

Anyway, if the focuser didn't give me satisfaction, I changed everything for the OPTEC Leo system.

I hope that with the CATSEYE everything will go well and that I will not go into interminable adjustments ..... That's what scares me.

[MarkS]

The Cats Eye will give excellent on-axis collimation, even if the secondary mirror is not at the correct distance from the primary. So there may still be tilt. Only adjust  two secondary screws at  a time, and don't touch the centre screw. This will ensure that the secondary is only being tilted, and stay in the correct axial position.

If the secondary has never been moved along the optical axis of the OTA, you should not have tilt problems (Unless the camera itself needs correcting. This can happen!)  If the secondary needs re-positioning, there is an ASA document on how to get it right.

Mark

[-Amenophis-]

Thank you Mark 

[-Amenophis-]

Last question Mark, 

Do you take 57.29mm as a backfocus for the Wynne corrector?

By analyzing my images, I get 24% curvature on my images.
It seems strange to me since I calculated everything to the nearest millimeter.

BF Canon Ra = 20mm

BF Adaptator = 29mm

BF T-RING = 8,3mm 

TOTAL = 57,3mm

[MarkS]

I assume you are using CCDInspector to analyse for curvature. This may seem heretical, but I do not take a lot of notice of CCDInspector. I find it can give highly variable results - even within a single run.

Having said that, there is always going to be some field curvature, and the FWHM of stars will deteriorate as you move out from the centre of the image. The deterioration may or may not have a curvature component. I find the most reliable - if very tedious - way to assess the image is by eye! (I produce my images primarily for printed display, so it's very important that the stars in the corners can stand up to very close inspection.)

The sort of typical figures that CCDI gives for curvature of subframes from my ASA10/G3-16200 system are between 16 and 25 degrees, and these numbers bear little relationship to the visual result in the corners of the finished image.

Even my Custom Officina Stellare RiDK/G4-9000 set-up yields 10-15 degree measurements in CCDI when all corner stars are spectacularly tight.

So I assess collimation and alignment using Pixinsight Script>Image Analysis>Aberration Inspector and FWHM Eccentricity. These give good visual and numerical indications of image quality. As I say, it's tedious, but I find it worthwhile.

Hope this helps.

Mark

[-Amenophis-]

Thank you very much for your response