RF 70-200mm F2.8 L IS USM Flare patterns in astrophotography

[migEOSRP]

EOS RP with RF 70-200mm F2.8 L IS USM for astro

I am evaluating the RF 70-200mm F2.8 lens for astro. So far I am reasonably impressed with some preliminary results (comparing to a 135 mm Rokinon prime lens). I have a question about a bright star flare pattern. The attached photo is a 15 sec alt-az tracked photo ISO-1000 at full 2.8 aperture and 200mm fully manual mode on a very slightly hazy but otherwise clear sky. Focus is as sharp as possible and the manual focusing is very smooth and works extremely well. The region is the constellation of Lyra with Vega the bright star at top of image. What are the 2 dark radial bands in the flare pattern due to? I get exactly the same flare pattern with the Rokinon 135 mm prime lens. Obviously the star is very overexposed.

[ebiggs1]

Being an old, very old, astrophotographer I would first try stopping your lens down to f4. I also think the Rok would be your better choice it's a fantastic lens and super sharp.

[migEOSRP]

some results for basic star shots with this Canon 70-200mm lens:

Canon RF 70-200mm F2.8 L IS USM & Canon EOS RP

[Hazel_T]

Hi migEOSRP,

Looking at the example photo it is difficult to say for sure what may be causing the darker bars. Especially since it is happening with multiple lenses from different manufacturers.

Aperture blades can cause similar things. Typically that would be when the lens is stopped down further and it would usually look different when using the two different lenses. It's unlikely it is a sensor issue with the camera since it is only happening in one portion of the photo. Usually if the sensor is malfunctioning we would expect the issue to happen across the entire photo.

There are a couple of things to double check. One is this only showing when you view the photo on your computer or is it also visible in the photo saved to the memory card on the camera? The other thing is since it was happening with multiple lenses, was there an event happening at the time that may have altered the light from that portion of the sky?

[migEOSRP]

thank you. Yes the Rokinon 135mm prime is fantastic. I bought one a few weeks ago. I needed one very high quality general use zoom lens for my Canon EOS RP for both typical photo usage as well as nearer nature photos in the 70 - 200 mm range and reasonably good performance for astro usage is also important for my interests. Based on my tests (I posted a link to my more detailed results but I think it was removed) I'm quite impressed with this lens.

[ebiggs1]

"Looking at the example photo it is difficult to say for sure what may be causing the darker bars."

That was my reason for not offering any further solutions besides trying a stop it down to f4.

" I'm quite impressed with this lens."

So am I and I have long considered the EF and now the RF versions to be the best 70-200mm zoom lenses made by anybody.  However, I still don't think I would use a zoom for astro work. Not as a first choice anyway. For one thing zooms tend to be heavier than primes.

Good luck and keep looking up!

[migEOSRP]

I stopped down the lens from f/2.8 to f/3.5 and that cleans up the dark-band flares. Two attached ~1900x1600 crops from original L jpg 4160x6240 of Vega region shows the expected reasonably symmetric star ray pattern for the aperture blades. Both at f=200mm, June 29th shot 15sec ISO-1000 f2.8 July 3 shot 20sec ISO-1000 f3.5

[ebiggs1]

Nice.

[migEOSRP]

thank you for your valuable comments here and in my other posted topics here. I appreciate guidance by experienced folks such as yourself (I'm somewhat of an old timer and have taken up low-level astro within the last 3 years).