QHY8 Pro with canon lens

[orionoffelt]

I have been imaging for a few years now mainly with telelscopes But I bought a canon 200mm F 2.8 lens a while back and have managed to try it last night for a spell just before the clouds rolled in I coupled it up to my old OSC  a QHY8 Pro and find looking at this image of 2 x 60 frames that the brighter stars have flares has anyone come across this before and I wonder what is causing it and is there a solution ?

 

Bob

[dobblob]

Looks like coma /spherical aberration inherent to the lens. No surprise really, most long camera lenses will show some aberration but this does look quite extreme.

Is this a cropped image off center ? I ask because the comas point to a "center" somewhat left and upper in the frame.

Not sure there is a solution unless if the lens is new it can be proved to be defective and can be returned under warranty. Unlikely. Maybe other users of this lens can chime in on it's quality.

One could try stopping the lens down to say f 8 to see if the aberration reduces.

There aren't many camera lenses truly suitable for astrophotography. I think the SamYang 135 mm (not sure of model #) is said to be pretty good. 

I certainly see similar effects and chromatic aberration with my Canon EF 75-300 mm zoom which is definitely known to be poor but not as bad as yours.

[orionoffelt]

Thanks for the reply I thought it looked like coma spherical abbreviation myself this was the full frame I did manage one more frame a 300 second one but half of it was through cloud and the bright stars looked the same. 

I have a Canon DSLR I may try the lens on it and see what the stars look like as the ccd may have a different result but they are still OSC cameras. With the lens attached to the DSLR during the day the view looks perfect which I would have expected as day time imaging is more forgiving.

[Craney]

Hi there,   I too have a QHY8pro.    

Never really used it to its full potential as I also have a mono Atik 414  which is just amazingly sensitive and always gets first dibs on a clear night.

Ever since the 414 started to produce bands (unexplained as yet )  I have gone back to the QHY8 to try to get it singing.... but lack of continuous clear nights has really made it a stop-start procedure. ... a bit like learning AP all over again.

Anyway....  Looking at your image,  apart from the optics of the lens mentioned above......

my immediate  question would be, how are you attaching the lens to the camera?    Is there any  'skew'  ??   

Also, are you using any filters as such ??  ... and are they possibly slightly mis-aligned or the source of a off-centre reflection ??....   Just guessing but might be something to look for.

Not related, but what values for GAIN and OFFset do you use ??

Cheers,
Sean

[Seelive]

I have a Canon 200mm F2.8 USM MkII and use it wide open with my Canon 200D (APS-C sensor) with what appears to be less abberations.  This example is a full frame image at F2.8, ISO1600, 60 x 60s exposures centred on the Virgo cluster (apologies for the poor post processing).

Edited February 12, 2021 by Seelive
Typo

[orionoffelt]

Hi Sean

Thanks for the comments. I have had the QHY8 Pro since 2010 when I moved from a DSLR to a ccd I have found it a great camera I use it at -18 C and use the QHY driver at 1 - 140 hope that’s useful info.

I used no filters and the adaptor is a one supplied by Modern astronomy which gives a good level fit between camera and lens.

Hi Typo

Thanks for the feed back. Your image shows a lot less aberrations with me just trying the lens out to get focus I had to turn the setting from infinity to further down F settings on the lens I wonder if another spacer ring were to be added it would then enable me to get closer to the infinity mark on the lens when achieving focus and this may give me less aberrations ?

Bob

 

[orionoffelt]

I was out imaging tonight and tried out the lens again I noticed before hand that the lens had a HOYA HMC UV  filter on the front of the lens which i removed and the frames from tonight were perfect so that has been my problem i bought the lens second hand and did not notice the UV filter. Thanks for the help .

Bob