Barlow between telescope and camera? - Forums

Topic starter

Jul 8, 2020

I've seen some people using a barlow to amplify the magnification of their telescope; placed between their telescope and camera.

Has anyone else done this? I am curious if/how this works.

Thanks!

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astropical

Jul 10, 2020

Yes, I have but only when imaging the moon and planets. Never for DSOs because a barlow doubles or triples exposure times, and, the less glass in the optical path the better, in that I prefer the native focal length also considering issues when using a flattener or coma corrector.
Cheers
Robert

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schmaks

Topic starter

Jul 10, 2020

Thanks, Robert!

I may try to find a good one for my ZenithStar 73 for solar system objects. Open to suggestions!

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matthew.maclean

Jul 10, 2020

It’s tough to beat large aperture for planets but I was surprised what my GT81 could do with Jupiter and Saturn last summer. My avatar icon of Jupiter is one I took with my GT81 and a 2.5X powermate. And I have tremendously bad seeing here in WNY, so you should be able to do at least as well.

Televue Powermates are a good option. They are good quality and have an optional Tring adapter that fits them to attach a camera. My understanding is that it is ideal to have a focal ratio around f/20 for planets; since your APO (and mine) is natively around f/6 without the flattener, you will likely want something between 3X-4X.

You also need a Camera that can take video. A DSLR is possible, but not ideal, because of the large pixel size. A camera with small pixels is better (178c and 290c are some good models to look at).

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schmaks

Topic starter

Jul 11, 2020

That's helpful to know! I'll look into that! Thanks!

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schmaks

Topic starter

Jul 11, 2020

You also need a Camera that can take video. A DSLR is possible, but not ideal, because of the large pixel size. A camera with small pixels is better (178c and 290c are some good models to look at).

Is the best route to video the planet then take stills after?

matthew.maclean

Jul 11, 2020

Yes, the usual method is to take a video for a few minutes and do "lucky imaging". The Powermate/Barlow will dim the image some, but I was using something like 0.1-second per frame integration. After a few minutes, you will have a few thousand frames. The two common lucky image stacking programs are Registax and Autostakkert (I like Registax the best). These will sort out a percentage of the best quality frames, then align and stack them for you. As with a DSO image, the stack after post-processing should look significantly better than any one single frame.

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schmaks

Topic starter

Jul 11, 2020

Good to know! I will try it out one day!

schmaks

Topic starter

Jul 11, 2020

With that method, do you have to boost the ISO a bunch to make up for short exposures? I have a C200, tempted to try it out with 12 bit raw footage.

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matthew.maclean

Jul 11, 2020

Jupiter especially is incredibly bright, so it doesn’t take much exposure time. The nice thing about planet imaging is that all you need is a couple minutes of video, so ,when you first do this, you can try out some different ISO/exposure combinations and see what works best for you. Likely an 8-bit video is fine too, but again you can try both. What you will get depends on seeing condition more than anything else. I have the best luck right after sunset in the twilight before the sky is completely dark.

One other little suggestion since your images will be fairly low resolution is try an evaluation trial of Topaz Labs Gigapixel AI. It increases image resolution by non-linear interpolating. It won’t be as good as if you had a higher resolution camera or bigger telescope, but I found it did a pretty nice job on the planets increasing the image resolution and eliminating some of the pixelization.

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schmaks

Topic starter

Jul 11, 2020

Thanks!

Marc V

Dec 27, 2020

I may try to find a good one for my ZenithStar 73 for solar system objects. Open to suggestions!

Hi All!
@schmaks I would be interested to be informed on your experience with the use of a barlow with your ZS73. I have the same lens, and I am also considering the barlow option to planets and the Sun.

Clearskies, Marc

Jérémie

Dec 27, 2020 · Edited: Dec 27, 2020

Hi @schmaks ,
I use from time to time a x2 Walimex teleconverter. It was made for catadioptric lenses but has a M42 thread that makes it convenient to use on standard optic trains.
It is very cheap : https://www.conrad.fr/p/teleconvertisseur-walimex-2x-konverter-t2-1052807
For the quality, well, it produces a strange vignetting, which requires long post processing.
I am not an expert to judge on quality, but here are some examples of what I got both on planetary and DSO, by plugging it on my quadruplet 71/347 from TS Optics :
DSO : https://astrob.in/u8xmhp/0/
Moon : https://astrob.in/k6fmvc/0/
Sun : https://astrob.in/jriomq/0/
Hope this helps you judging if that’s worthy for imaging.

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Marc V

Dec 27, 2020

@Jérémie very impressive images! Bravo.
A teleconverter is an option I haven't thought but I will definately consider.
Clearskies! Merci
Marc

Jérémie

Dec 27, 2020

Thanks Mark.
Well, if you look closely at my Bubble nebula, you will see very elongated stars on the corners, due to the coma introduce by my cheap teleconverter.
My point was more that you can get acceptable results with very cheap piece of equipment, but at the price of a much longer post processing and if you are not very strict with the optical quality of your train :-)
Using Barlow or not, and cheap or high quality grade Barlow, will depend on your standards of imaging. I don’t encourage people to buy this walimex teleconverter if they wants to achieve great images : I have stopped using it since my Bubble, too much work to get something clean :-)

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