Very bad Jupiter image, barlow recommendation?

[MKR]

Hi,

I've been trying to image Jupiter with my setup: SW 200P, ASI224MC. I have two barlows (2x): Astro Essentials and the one included with the SW scope. I tried two approaches:

1) One barlow (astro essentials, as I think it "should be" better. The image is tiny, but I think considering the size, it's not too bad. I don't like it though, it's just too small and can't seem much detail. 2x barlow and 1000mm f/5 gives me f10, 2000mm

2) Two barlows, connected to each other. That's 4000mm f/20. Jupiter has a decent size, but... the quality isn't great (see the attached, stacked maybe 25% of 3 minutes ~120fps)

Now, what is the reason of my image being so poor? Is it rubbish quality of 2x2x barlows? Or maybe I should never use two barlows at the same time? I think the focus was more or less correct, but it's hard to get it right with such a bad image quality (I'm yet to get a bahtinov mask - using live view atm).

Can you recommend any decent barlow which will cost less than TV and will give me good magnification for my scope, please? I'm parcicularly interested in your opinions of: https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html (5x Explore Scientific) or perhaps getting two https://www.firstlightoptics.com/barlows/skywatcher-ed-deluxe-2x-two-inch-barlow-lens.html  and combining them together?

PS Please don't bother the spot on my image in the middle of Jupiter - I think it's not GRS but rather a dust particle on my camera 😛

Many thanks.

[ONIKKINEN]

I dont think your Jupiter is bad at all. Considering the equipment used its pretty good to my eyes. I also shot Jupiter earlier this year with similar equipment and a similar result.

I used this: https://www.teleskop-express.de/shop/product_info.php/info/p55_TS-Optics-Optics-TSB251-2-5x-Barlow-Lens--1-25-inch---apochromatic-triplet-design.html

and a Celestron t-adapter 2x barlow which is probably very similar to the astro essentials 2x.

The TS2.5x barlow is very good for the money. Visually it is noticeably better than the cheap Celestron. 

Jupiter is getting pretty low in the sky right now which will rapidly reduce image quality the lower it gets. How high was it? I doubt it was much higher than 20 degrees if you shot from the UK. Could also be you had poor seeing that night? Collimation should also be as perfect as possible with planetary. I dont think a bahtinov mask will help with planetary captures, its probably better to just visually focus with live view. Its difficult but looking at the edge of the planetary disk is a good method. When the edge is well defined and sharp you are in good focus. Jupiters atmospheric bands might also be a good visual focus target.

 

3 minutes is perhaps a bit too much for a single capture as Jupiter rotates very quickly. Try shooting a bunch of 60-120s captures and hope one of them hits good focus and good seeing? You could also try to stack with stricter settings, maybe a 10% stack or similar. With 120fps you have lots of frames to spare.

 

This is what my try in July looks like, a mostly blurry disk. This is 15minutes of rotation which is shockingly short for such an obvious movement and the reason 3min might be too much. I took 90s recordings and stacked best 35% but only because my framerate was only 38fps.

[MKR]

Thanks! Wow, I hadn't realised how fast it rotates! I thought 3 minutes is still ok. I like the moon transit and GSR on yours.

I think 3x barlow/equivalent might be safer than going for 5x - it seems like pushing it - F25.

[Laurieast]

6 minutes ago, MKR said:

I think 3x barlow/equivalent might be safer than going for 5x - it seems like pushing it - F25.

I had good results with this :

https://www.amazon.co.uk/Svbony-Advanced-Chromatic-Telescope-Eyepieces/dp/B07RQLQ9WN/ref=sr_1_2?dchild=1&keywords=svbony+3x+barlow&qid=1634916138&sr=8-2

On my Explorer 150p and Asi 224mc. I had good results the first time and then very dissapointing the second time, and it was the seeing, it was boiling. 

I would say 5x is too much. 

 

[ONIKKINEN]

3 minutes ago, MKR said:

Thanks! Wow, I hadn't realised how fast it rotates! I thought 3 minutes is still ok. I like the moon transit and GSR on yours.

I think 3x barlow/equivalent might be safer than going for 5x - it seems like pushing it - F25.

Yes, but i had 4.3 micron pixels and a base focal ratio of 4.5 so for me it was pretty decent at F22. Something i see quoted in many places is that for planetary captures the focal ratio should be 5 times pixel size in microns. Dont know where this comes from but i think it has something to do with sampling rate. More than this is not useful and less can be undersampled.

 

For the 3.76 micron pixels of your 224mc it gives an f ratio of 18.8. Using this method a single 4x barlow or a 3x barlow with extra spacing would be ideal. Barlows vary in magnification based on how far the lens is from the sensor, so either the 3x with extra spacing or a 4x with less would work.

[MKR]

5 minutes ago, ONIKKINEN said:

Using this method a single 4x barlow or a 3x barlow with extra spacing would be ideal

Can you please explain what do you mean by extra spacing? (Sorry, noob). Do I just insert an empty tube between the camera and a barlow (or barlow and the focuser)? Does it increase the magnication? What's the math here, how do I calculate this? Thanks.

[ONIKKINEN]

Just now, MKR said:

Can you please explain what do you mean by extra spacing? (Sorry, noob). Do I just insert an empty tube between the camera and a barlow (or barlow and the focuser)? Does it increase the magnication? What's the math here, how do I calculate this? Thanks.

I am not math oriented so cant help you there..

Perhaps this thread in CN helps? https://www.cloudynights.com/topic/643961-actual-barlow-magnification/

But yes, adding more room between the lens and the camera  with 1.25 inch extenders (sold in all astro vendors)will increase magnification and having less than what it came with will decrease. Barlow lenses are typically threaded with a normal 1.25 inch filter thread, so you can change the "tube" it is threaded to for a longer or shorter one to change the effect. Adding something between the barlow and focuser is not helpful since it wouldnt affect the spacing.

[johninderby]

Should be noted that with the focal / tele extenders magnification doesn’t change with the distance between camera and tele extender unlike with barlows.

Edited October 22, 2021 by johninderby

[Laurieast]

2 hours ago, MKR said:

or perhaps getting two https://www.firstlightoptics.com/barlows/skywatcher-ed-deluxe-2x-two-inch-barlow-lens.html  and combining them together?

I don't think this will be a very good idea, the 2" barlow is huge and weighs 310g !  The scope will fall over 😁

 

[symmetal]

59 minutes ago, ONIKKINEN said:

Yes, but i had 4.3 micron pixels and a base focal ratio of 4.5 so for me it was pretty decent at F22. Something i see quoted in many places is that for planetary captures the focal ratio should be 5 times pixel size in microns. Dont know where this comes from but i think it has something to do with sampling rate. More than this is not useful and less can be undersampled.

Here's a very good and easy to understand explanation for the reasoning. It's written by a member on this forum and is is Dutch, but selecting 'translate to English' in google works perfectly. His conclusion for the optimal focal ratio is

f#  = 3 x pixel size in microns for a mono camera

f#  = 6 x pixel size in microns for a colour camera

Alan

Edited October 22, 2021 by symmetal

[MKR]

3 hours ago, johninderby said:

Should be noted that with the focal / tele extenders magnification doesn’t change with the distance between camera and tele extender unlike with barlows.

Thanks, I wouldn't have known this.

Thank you all. Very useful. I think I'll settle either on TV barlow 3x with some extension tube, or on ES 3x focal extender (ideally would be 4x..) It will be used for visual too, so hopefully worth the investment.

[johninderby]

The Altair tele extender is a bit cheaper than the ES version but is the same inside.

https://www.harrisontelescopes.co.uk/acatalog/altair-lightwave-3x.html#SID=564

Wish they would stop calling them Tele Extrnder Barlows because they aren’t barlows at all but I suppose some don’t realise that a Tele Extender can be used instead of a barlow.

Edited October 22, 2021 by johninderby