My best suturn with 6'' reflector 150F9

[wenjha]

I think it's my best suturn with 150F9

taken in 30th may

150F9 + 3X + 900nc

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150F9 + 3X + 2X + 900nc

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this is the star test of my 150F9

Not perfect, but Airy disk is clear

[greenkat]

great images

[steve_bham]

nice looking images

[johnh]

Hello Jha, very clear images for 6inches, looks like tube currents in your star test - do you have a fan as it is good to keep it running during captures. Star tests are not always the best way to test optics, my scope has strehl 99% and does not give perfect star test but this is normal and it performs brilliantly.

Star tests are always interesting to do but they are not definitive. Your results look very promising indeed. John.

[legion48]

If you're shooting Saturn as low as it is in the UK, then well done you. Great shots. :-)

[Kokatha man]

Those are absolutely "crackerjack" images of Saturn there brother.....for the 6" newt they are absolutely top-of-the-line!

Congratulations, beautifully defined banding and colour in those crisp images (if only my achromat could produce such nice colour-rendering....!):hello2:

[Kokatha man]

.....ps: why don't you try using extension tubes with just the one barlow to get greater image scale/magnification.....much better in my humble opinion than double stacking barlows with their subsequent light loss and slight image diffusing....?:)

[Lester]

Nice images for a 6", the limiting factor with Saturn is its lack of brightness, especially now with the rings edge on. So well done.

[wenjha]

thanks you guys

actually, it's a sphere mirror, but its performance really satisfy me

[wenjha]

Hello Jha, very clear images for 6inches, looks like tube currents in your star test - do you have a fan as it is good to keep it running during captures. Star tests are not always the best way to test optics, my scope has strehl 99% and does not give perfect star test but this is normal and it performs brilliantly.

Star tests are always interesting to do but they are not definitive. Your results look very promising indeed. John.

Hi, John

I am surprised to hear that: a mirror has strehl 99% can't give perfect star test

I can't belive this, Is your mirror a refractor?

if star test is not definitive, so what way can amateur to do to test optics?

ps:I don't have a fan, I will try to get one

[wenjha]

.....ps: why don't you try using extension tubes with just the one barlow to get greater image scale/magnification.....much better in my humble opinion than double stacking barlows with their subsequent light loss and slight image diffusing....?:)

thanks

I will try extension tubes next time:D

[johnh]

Hello Jha, my 99% strehl parabolic mirror give a good star test but not 'Suiter Star Test' perfect, there are some slight differences between intra/extra focus so it is not perfect but seeing can account for some differences, star tests should be undertaken when seeing is 9/10 or better.

With no interferometer test (definitive test) a star test is the only way to give a guide to quality but it is only a guide. Central parts of mirror have the most errors (but don't contribute to focus as much) and dominate any star test but the outer parts give all the image focus quality but don't contribute to star test as much - that is why star tests are not the best way to test definitively.

You got a nice diffraction ring Airy disc and if star rings/secondary dark centre size is same exactly either side of focus this looks very good indeed.

Your right hand star test shows oval shape with flaring - a fan would make it more circular. I would like to see your moon images and Jupiter when it rises too. Your scope performs very well indeed but Jupiter will show the most detail at end of July/August.

JohnH.

[wenjha]

thanks John

you teach me a lot

my tar test was taken under bad seeing, maybe 6/10 or 5/10

I don't think very good seeing like 9/10 exist in BeiJing;)

what does it mean 'Suiter Star Test' ?

so, star test is not suitable for reflector mirrors because of the central mirror error. Is it suitable for refractor mirror like APO under good seeing?

here is the moon, I took 1 month before. waiting jupiter...

[johnh]

Hello Jha, your moon image is of Copernicus crater and shows central complex quite well for that focal length - Jupiter will be good too soon.

'Suiter Star Test' is the name given describing Mr. [removed word] Suiter's star test in a book he published.

An APO refractor will give a more accurate star test but seeing 6/10 is not good enough you should wait till it is much better - your scope shows great quality considering seeing conditions. JohnH.

[wenjha]

Hi, JohnH, Is your mirror tested by interferometer?

can you take some images of your mirror's star test?

so I can compare with my results

you said that star test can only do in good seeing,

but I think I can use registax to stack many images to against bad seeing,right?

and the in and out of focus images are very big like the first and last one in my picture. I think they are not effected by seeing

here is the video I capture airy disk, you can see the bad seeing

but after stack, Airy disk is very clear

So why need very good seeing? I think 6/10 or 5/10 is enough

especially for in and out of focus test

airy disk.zip

[johnh]

Hello Jha, I did some star tests a while ago but seeing was so bad I did not keep them but did get different results on different nights. Stacking lots of short exposure images will help to some degree but seeing needs to be well above average as seeing can introduce abberations that are not from the mirror also tube currents can cause abberations. You should do star tests over many nights and compare them and you will see slight differences caused by seeing/tube currents. JohnH.

[wenjha]

Oh, I see JohnH

thanks, I will try another day

hope you can save your different test images next time

so I can compare with them

I have just installed a fan on my tube, so new star test will come soon