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Old 04-05-2024, 03:45 PM
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AstroViking (Steve)
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Join Date: Mar 2022
Location: Melbourne
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First light for the Megalens

Hi all,

Remember that 1000mm camera lens that I bought about a year ago? (Probably not, but that's OK. )

I put together a suitable mounting plate that allowed me to put it on the HEQ5, with an EAF because I can't focus anything these days, and a second dovetail mount for my guide scope. It's compact and surprisingly heavy.

We had a clear night a few days back and I was able to get everything setup and running to capture it's first light after getting the EAF dialled in and a 'near-enough' position found.

I eventually narrowed it down to step 3650 gave me the best focus. I really do need to get this tuned correctly - there are a million options in Ekos to work with. Some of them are designed specifically for lenses like this, with a large central obstruction.

I initially chose the star Hadar as my first target because it's bright and clear (and I knew where in the sky it was). As the image below shows, I had the focus pretty well sorted out. Then I saw the huge reflection / halo extending down and right from Hadar. I don't know if this is caused by the UV-IR cut filter (I kind of doubt it, as nothing like this has ever appeared before) or some strange internal reflection within the lens. Given that the lens appears to have been dropped somewhere in it's life, I'm guessing that something is a little bit out of alignment.

For now, I'll just avoid the really big, really bright stars.

The second and third images below show the 'Keyhole Nebula'. It's big, it's bright, and we all know what it looks like. So it makes a very cliched sense to image it as your first target.

Initially the Keyhole wasn't in the centre of the frame, so I recentred the frame on it and kicked off a sequence of 30 second exposures. What I forgot to do was restart the guiding. I'm still kicking myself here for forgetting this very important step - especially at longer focal lengths.

I am impressed with how well my mount tracked, though. 30 seconds at 1000mm would leave massive star trails on a badly performing mount.

As good as it was, Siril still kicked up a stink and rejected about 2/3 of my images when I came to stack them. So these images are the result of about 20 minutes of data. Yes, they are slightly out of focus and the stars are a little stretched. They're faults I can work and improve.

One thing I did not find was the 'V' shaped stars in the image corners. It looks like my hypothesis of having a small camera sensor (only 13.2 x 8.8mm) paid off and the distorted stars are outside the sensor area. Yay! Or the 'V' stars in my previous test images were a result of the DSLR's shutter moving...

I only had the 'Dark' configuration frames to work with. So when I get a way to create the 'Flat' frames I'll be able to properly process the images from the lens. At this stage, I'm happy that I've got something recognisable out of it.

Cheers,
V.

Yes, I know it's an ancient lens of unknown origin with optics that are likely to be highly dubious in quality and alignment. I had fun(?) putting it together, and I'm getting images of things I can't see in my usual scope. That's all that matters to me.
Attached Thumbnails
Click for full-size image (Mega-lens-1.jpeg)
61.9 KB26 views
Click for full-size image (Mega-lens-4.jpg)
207.5 KB28 views
Click for full-size image (Hadar.jpg)
116.3 KB34 views
Click for full-size image (AF_Recomposition.jpg)
199.8 KB35 views
Click for full-size image (Siril_Recomposition.jpg)
188.6 KB35 views
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