quasar117

On 20/05/2024 at 09:17, crush said:

Hello @quasar117

Out of interest what was the outcome of the test at FLO?

They couldn't see any astigmatism or chromatic aberration with their tests.  Artificial star test appeared pretty good.

However, after much thought I decided to swap it for a Stellamira 80mm F/10 ED.

On 23/04/2024 at 08:23, apaulo said:

Something quite simple, have you let another another astronomer look through the starfield. Or someone with decent to good eyesight. If they see what your seeing, get it back to the seller.  If not, get new eyeballs. lol. No need for rocket science.

Had my wife look through it who admittedly is not and astronomer, but has good eyesight. She saw the same artifact as me on the stars and Jupiter.

The Starfield is currently away for testing at FLO. Will be interested to see what the outcome is.

40 minutes ago, IB20 said:

Are you experiencing similar to this? https://www.cloudynights.com/topic/870714-interpreting-refractor-star-tests/

From reading what you’re seeing it doesn’t sound quite right and I wonder if you should contact your supplier to see if you could get it looked at or maybe even a replacement. 

Yes,  I'd say that is similar to what I am experiencing. Possible under correction.

I've contacted FLO and they have agreed to test it on their optical test bench. 

5 hours ago, IB20 said:

What bright stars are you trying to see as pin point? Some of the brightest, simply wont appear like that. Also, have you managed to see airy disks and diffraction rings when you’ve cranked up the magnification?

Mainly, Polaris, Capella, Castor and Dubhe. The latter of which seems quite good to star test as it is quite close to zenith when I go out to observe.

The only time I don't see the diffraction ring is in extra-focus. Intra-focus shows the rings and in focus when the seeing has been good I can see the airy disk.

Also when I have observed Jupiter, albeit very low, it was showing this flaring affect aswell.

Borrowed my brother's spotting scope and couldn't see it evident when looking through that.

6 hours ago, mikeDnight said:

Which eyepiece are you using? Is it one particular eyepiece or do different eyepieces show the same effect?Sometimes oily residue from eyelashes, oran accidental touch of the eye lens on the eyepiece can create a bluring effect on the image. Perhaps try cleaning the eyelens with a lens tissue or cloth.

I can see it in all my EPs: 24mm ES 68°, 12.5mm Ortho, each focal length of the 3-8mm SVbony zoom. I mainly use the SVbony at 4mm to do the star test.

Can I use eyeglasses cleaner on the lens with a tissue/ cotton bud?

18 hours ago, Louis D said:

How long did you allow for acclimation?  I see spiking with my 90mm triplet APO that looks like pinched optics for up to about 30 minutes.  It eventually disappears after acclimation.  Give your scope an hour to acclimate and check again.

I gave it 45 mins to acclimatize with dust caps off.

On 18/04/2024 at 08:24, Nik271 said:

There is an easy way to test for spherical aberration using a 30% central obtruction mask (cut out a 30mm paper disc and attach it to the front of the dew shield with some thin strip of cellotape for example).

 

Aim at Polaris with a medium power EP, focus. Now defocus equal amounts of about 3mm either side and compare the doughnuts. Does the central hole look similar in the doughnut? If not - you have a spherical aberration.

 

Another way is with a Ronchi eyepice, which costs about £40 from FLO.

Seeing for me wasn't bad tonight. Managed to compare views with and without a diagonal. Boths instances shared the same issue as before. So I'm confident it is not due to the diagonal.

Tomorrow I may try your obstruction mask idea to check for spherical aberration.

5 hours ago, Mr Spock said:

Which diagonal are you using?

Brand new William Optics carbon dura bright 2" dielectric.

5 hours ago, Elp said:

Have you tried another refractor during the same night for comparison?

The only other equipment I now have is very s very cheap 60mm refractor from the 80's. Star test was so bad it showed two airy disks.  Yet no sign of flaring. But as another member pointed out, it could be due to exit pupil.

I also have a pair Zeiss Victory 10x42 bins that show pinpoint stars.

Tonight was clear and steady to my eye. The star I selected was Dubhe; due it being high in the sky and relatively bright.

Intra focus revealed a nice diffraction pattern of concentric rings. In extra focus I could just about see some contrast between rings but the whole thing appears very milky and misty.

In focus I could see the airy disk which was quite steady- so can assume seeing was good. However, it was accompanied by flaring around the edge shooting off at symmetrical angles. I believe this is either astigmatism or spherical aberration? This feature could also be seen in intra and extra focus. Those airy disks did not appear oval but round. I believe astigmatism would have shown these to be oval. So am slightly confused at this.

Briefly observed Jupiter before it set. Some banding was just about discernible. Jupiter also showed this symmetrical flaring.

I wanted to test without the diagonal but I discovered I need a 2" extension to achieve focus with an EPs in that configuration.

So my next step is to buy one and test without the diagonal.

I was really hoping I would have been happy with what I would see tonight but alas it didn't come true.

I'll keep trying though.

20 hours ago, Louis D said:

IIRC, rings on one side of focus and smoother on the other side indicates spherical aberration of the objective.  Refer to telescopeѲptics.net Refracting Lens Objective page for more information.  I've grabbed a snippet of the spherical aberration explanation below:

So if I'm seeing rings on intra focus but misty rings in extra focus the scope could be under corrected for spherical aberration?

With good seeing I should see the focused star appear as an airy disk that is pin sharp?

Could an artificial star test (torch with pinhole in the centre of covered lens) achieve the same results or is that a waste of time?

Sorry for the slow reply. I've come down with the flu the past couple of days. Which is typically, as I bet there will be good seeing tonight 🙃

The closest example to what I'm seeing when in focus on a star is as per this image although the black spikes are more severe in this image than what I'm seeing. 

16 minutes ago, dweller25 said:

Are you seeing any of these ?

The image I was seeing on Polaris in intra focus was as per the top left example.  The bigger I made the image the more rings appeared.

16 minutes ago, John said:

If the seeing is not too good, the pattern of diffraction rings around the airy disk will not be well defined on one side of sharp focus as it is on the other. 

This test needs to be done at quite high magnification - around 200x for a 4 inch scope is good.

This is what a decent 4 inch refractor star test should look like under very good seeing conditions:

Under less than good seeing conditions, the image on one side of focus may well look "mushy" rather than showing well defined diffraction rings. You might still get a nice in focus image though.

Polaris is a good test star. 

So last night on Polaris I could get good diffraction rings in intra focus but no notable ring separation in extra focus.

The intra focus image was stable. 

20 minutes ago, Tiny Clanger said:

OK, so cross that possibility off the list.

You tried various eyepieces, and it showed in all of them. Could you try removing the diagonal and seeing if a straight through view still shows the problem ?

The only other kit related (rather than seeing related) possibility I can think of is something inside the 'scope protruding into the optical path and causing diffraction (similar to the spikes caused by the  secondary supports in a Newtonian)

 

Yes I'm going try directly mounting the EPs to eliminate the diagonal from the equation.

The sky isn't looking great here at the moment, looks like a good chance of rain soon. 

Should I see an airy disk both inside and outside of focus? As yesterday I could only see it when racking the focuser in.

Apparently my eyesight has improved since my last check in 2021! Also minimal  signs of astigmatism - so I can probably rule out my vision affecting it.

Hoping it's a clear night tonight.

1 hour ago, Tiny Clanger said:

I wonder if what you are seeing is astigmatism in your eye showing up in the Starfield, but not in your 'toy' refractor ?

As I understand it (i.e. not very much) any astigmatism your eye may have will show more with a setup's greater exit pupil. If  the old 'toy' 'scope has a higher f number vs the Starfield, perhaps the smaller exit pupil it gives allowed you to see pinpoint stars ... it could also be the reason you never saw the problem in a mak.

 

That's definitely a plausible answer. The old refractor is a 60mm Simmons generic department store telescope. Can't remember  the focal length/ratio  but guessing its around F/9.

As it happens I'm going for a eye test this afternoon so will ask the question about astigmatism.

Managed to get out for a couple of hours last night. There was a thin cloud but with some breaks.

The young moon looked stunning. Crater rims along the terminator were very sharp. No complaints there.

Using the ZVbony zoom and 12.5mm Ortho - I observed Capella and Polaris. Again as before the Star appeared to be 'hairy' around the circumference and not pinpoint like the stars in the background starfield. Also if my eye was not perfectly centered the star would distort and create a spike.

In-focus revealed concentric rings. However, out-focus I could not discern any rings it just appeared as a solid white circle. Is this normal?

For comparison I dusted off my old department store "toy' refractor. I was surprised that when focused on a star, the star appeared more pinpoint than viewing through the Starfield 102. Very strange.

Whilst I'm happy with the lunar views, I still felt something is not quite right when viewing stars. Could it be just the seeing again?

To put me at ease somewhat, I have carried out an observation of a far away conifer tree branch from the kitchen - with patio doors open as it was drizzling outside a bit.

At 238x magnification the small leaves and branches were sharp - however, appeared  to oscillate in and out of focus to my eye. 

I assume the oscillation of focus was due to warm air currents inside the kitchen being drawn outside to the patio causing disturbance. Either that or my eye was having trouble keeping focus.

In summary though, I'm more confident that last night's observation, or lack of.... was due to the poor seeing conditions and not the optics, which is a relief.

Eager for another clear night now though!

On another note - I'm loving the Baader SF III. It really makes target acquisition a breeze. The Vixen GP is also really a joy to operate, slo mos are definitely for me.

6 minutes ago, Alan White said:

I expect your issue was that last night the Jet Stream would have been playing havoc with the seeing.

To check the jet stream try using the following site: https://www.meteoblue.com/en/weather

You need to click on Outdoor Sports and select Astronomy to get to this data.

Hope that helps.

Thanks Alan, will definitely check that out!

12 minutes ago, RobertI said:

I think it must have been something like that; if you saw no belts on Jupiter, something was seriously amiss! 

Hopefully I get a chance for another session this week - as it's playing on my mind a lot now haha.

5 hours ago, Elp said:

Could also be low altitude thin cloud. Even in a cheap acromat stars are usually pin sharp, I've also looked at Saturn very low in altitude in my Z61 and could still see some slight banding of surface detail. The SF 102 provides even better views. Also always check the objective isn't dewing even if it doesn't feel damp out, though the SF has quite a long dew shield so should be okay.

I did have a look for dewing but didn't notice any.

I remember my first views through a "department store" acromat and even they would have blown these views away. 

Perhaps there could have been a thin cloud as others have suggested.

5 hours ago, RobertI said:

Could you see the two equatorial bands on Jupiter? 

Surprisingly no, I couldn't see any banding. It just appeared as a bright star. No amount of altering the focus changed that.

Next time I go out I will compare the views with my binoculars. 

Hi all, after owning the Starfield for about a month now I've finally had a clear night to observe. 

I'm not sure if it was down possible poor seeing conditions, my eyes, or the scope but I was very underwhelmed by my first observation. I was hoping to see pinpoint stars but on bright stars they just appeared to flare and were not pin sharp at all.

I allowed the scope to cool for half a hour before observing.  The three eyepiece I used all showed the same issue - ES 24mm 68°, 12.5 circle T Ortho, 3-8mm SVbony zoom. Diagonal is William Optics 2" durabright.

Jupiter appeared just as a bright blob with no detail visible. However, it was very low on the horizon, certainly less than 30 degrees. 

I carried our a star test on Polaris with the 3-8mm SVbony zoom. I could see clear evenly spaced concentric rings. The outermost bright ring appeared soft, not sure if that means anything.

Whilst I could see the companion star, Polaris itself was not pin sharp. I'm unsure if what I was seeing was astigmatism. 

In my previous scope (mak 127) I never experienced this issue.

I highly doubt the scope is at fault but I wasn't expecting such a poor observation session from it.

Will have to wait for another clear night to test again.