WO GT81 stars with many peaks, help...

[gazul]

Hello, this is my first question.

I recently bought a triplet APO William Optics GT-81 80/478 and my first photo shows the bright stars with many peaks, it this normal?

In "astrobin" I dont see stars with peaks in other photos taken with similar refractors triplets. I show you what I've taken;

http://www.astrobin.com/133909/

http://www.astrobin.com/133906/

http://www.astrobin.com/134881/

I tried to make the "star test" (I unfocused a star to 150x) and non concentric circles appear, I see concentric polygons !!!,  as I show in this picture

http://www.astrobin.com/134880/

I think, this is not normal, that you think might be going, my camera is the Canon EOS 450D.

I would appreciate help.

Greetings.

[Stargazer33]

The 'spikes' are caused by the aperture blades in your camera lens. If you stop down the lens you will get these spikes. They are similar to the defraciton spikes on a newt. This is normal.

[ronin]

The 'spikes' are caused by the aperture blades in your camera lens. If you stop down the lens you will get these spikes. They are similar to the defraciton spikes on a newt. This is normal.

Looks like that but why is the lens on the camera?

I would have assumed prime focus on to the DSLR sensor and so no camera lens and no aperture blades.

Would not expect someone to get a GT81 then have a camera lens in the system. :confused:

Gazul needs to supply more information on the specific setup and arrangement.

Doesn't seem to be caused by pinched lens or the distance seperators in the lens cell - too many spikes for that

[lensman57]

Hello, this is my first question.

I recently bought a triplet APO William Optics GT-81 80/478 and my first photo shows the bright stars with many peaks, it this normal?

In "astrobin" I dont see stars with peaks in other photos taken with similar refractors triplets. I show you what I've taken;

http://www.astrobin.com/133909/

http://www.astrobin.com/133906/

http://www.astrobin.com/134881/

I tried to make the "star test" (I unfocused a star to 150x) and non concentric circles appear, I see concentric polygons !!!,  as I show in this picture

http://www.astrobin.com/134880/

I think, this is not normal, that you think might be going, my camera is the Canon EOS 450D.

I would appreciate help.

Greetings.

These are diffraction spikes and are caused by the clip spacers  between the lens elements. Why it should happen at all is anyones guess . I have a WO Star 71 that exhibits similar diffraction pattern. The problem is that the manufacturer does not recognise this as a fault. In my case  I am still waiting to hear anything from WO. This is not just a WO problem and almost all other multi element air spcaced refractors show this to some degree or the other but usually it is not so evident so one gets the impression of having round stars. I have been told that oil spaced apos do not show this but then we are talking megabox prices. Have a word with whomever you bought it from first. TBH I am quite annoyed about mine as I have to stick to the two element Megrez 72 when the target has bright stars.

A.G

[lensman57]

I have done simulation  of the diffraction effect in StarTools for a GT 81 assuming 3 clips and a focuser extension of 15mm. The effect is smilar to what you are seeing on the bright stars, ignore the left side as this is for a Newtonian. The 2nd simulation is for  a clip size of 3mm making the effect more pronounced.

A.G

[gazul]

Thanks for your answers, I do not use the camera lens, the light goes straight to the 450d sensor.

On Monday asked the seller,  I just do not know if I'm doing something wrong.

I've seen some pictures of other refractors, show some diffraction, but mine shows very large peaks.

[gazul]

But what I really do not understand is why the "star test" shows concentric polygons !!

The airy disk must be concentric circles, because my airy disk are polygons?

[Thalestris24]

Hi

I'd say A.G.'s (Lensman57) simulation is very similar to your problem so I think the clips are likely to be the root cause, unless you have any other obstructions to the light path - I can't imagine you do have any.

Louise

[lensman57]

But what I really do not understand is why the "star test" shows concentric polygons !!

The airy disk must be concentric circles, because my airy disk are polygons?

Look at the 2nd simulation the star is no longer round but a polygon.

A.G

[gazul]

Hmmm, very interesting.

But refractors have clip ?. I knew bringing collimation screws, could be causing this?

[lensman57]

Hmmm, very interesting.

But refractors have clip ?. I knew bringing collimation screws, could be causing this?

They have spacers, clips to ahieve the correct spacing between the elements. The more the elements the more pronouced the spikes.

A.G

[gazul]

They have spacers, clips to ahieve the correct spacing between the elements. The more the elements the more pronouced the spikes.

A.G

ok lensman57, I've learned a lot this evening, thank you all.

[ollypenrice]

If there were a world championship for telescope makers in which the winner would be the one to make the prettiest instruments with the worst performance I wonder who would win it?

Olly

[steppenwolf]

Errrrr, ummm, Takahashi perhaps? Just kidding ....

Sent from my iPhone from somewhere dark .....

[gazul]

If there were a world championship for telescope makers in which the winner would be the one to make the prettiest instruments with the worst performance I wonder who would win it?

Olly

I'm beginning to suspect who ...

[lensman57]

I'm beginning to suspect who ...

This could happen to any scope even a Tak, the problem is that recently it has been happening a lot to WO scopes. Here is a link to one from a Tak 106, to be fair it doesn't look as bad but it is still there even on a scope costing nearly seven times  a GT81 .http://www.madmanrc.com/images/Tadpole_Tak106P_H18_SiiHaOiii_51h_DSS_ps1_New.jpg

A.G

[Owmuchonomy]

Hello, this is my first question.

I recently bought a triplet APO William Optics GT-81 80/478 and my first photo shows the bright stars with many peaks, it this normal?

In "astrobin" I dont see stars with peaks in other photos taken with similar refractors triplets. I show you what I've taken;

http://www.astrobin.com/133909/

http://www.astrobin.com/133906/

http://www.astrobin.com/134881/

I tried to make the "star test" (I unfocused a star to 150x) and non concentric circles appear, I see concentric polygons !!!,  as I show in this picture

http://www.astrobin.com/134880/

I think, this is not normal, that you think might be going, my camera is the Canon EOS 450D.

I would appreciate help.

Greetings.

Very similar scenario to my AA 102 triplet. It doesn't bother me and stacking/processing seems to reduce the effect somewhat. To be honest, I prefer it to the huge starburst from a reflector.

[gazul]

This could happen to any scope even a Tak, the problem is that recently it has been happening a lot to WO scopes. Here is a link to one from a Tak 106, to be fair it doesn't look as bad but it is still there even on a scope costing nearly seven times  a GT81 .http://www.madmanrc.com/images/Tadpole_Tak106P_H18_SiiHaOiii_51h_DSS_ps1_New.jpg

A.G

Thanks lensman57 , comforts me a little.

regards

[gazul]

Very similar scenario to my AA 102 triplet. It doesn't bother me and stacking/processing seems to reduce the effect somewhat. To be honest, I prefer it to the huge starburst from a reflector.

Very similar scenario to my AA 102 triplet. It doesn't bother me and stacking/processing seems to reduce the effect somewhat. To be honest, I prefer it to the huge starburst from a reflector.

Thanks Owmuchonomy, encourages me your opinion, I do not dislike too see stars as protagonists. only fear that something this bad.

regards

[gdallmann]

Well I guess misery loves company...

I'm having the same problem as you Gazul but mine seems a little worse.  All my stars look like Maltese crosses and it's consumed way too much of my time trying to figure out what I was doing wrong.  At first I thought that I was getting the spacing wrong between the Field flattener and the CCD, but I'm at most 0.5 mm off and the tolerance just can't be that tight.  Any nebulosity I try to capture is just washed out by this weird effect. 

I tried to enclose a crop of an image of the Bubble Nebula from last night that shows how bad it is.  M52 was just a smear with all of the spikes

Did you find a solution to this problem or is my only recourse to return the thing?  I'd say this is pretty much useless for the wide field imaging I bought it for.

Thanks,

Garry

[lensman57]

Well I guess misery loves company...

I'm having the same problem as you Gazul but mine seems a little worse.  All my stars look like Maltese crosses and it's consumed way too much of my time trying to figure out what I was doing wrong.  At first I thought that I was getting the spacing wrong between the Field flattener and the CCD, but I'm at most 0.5 mm off and the tolerance just can't be that tight.  Any nebulosity I try to capture is just washed out by this weird effect. 

I tried to enclose a crop of an image of the Bubble Nebula from last night that shows how bad it is.  M52 was just a smear with all of the spikes

Did you find a solution to this problem or is my only recourse to return the thing?  I'd say this is pretty much useless for the wide field imaging I bought it for.

Thanks,

GarryBubble Nebula crop WO GT81 w FFFR.jpg

This one is not good. I get a very mild diffraction pattern with my WO star71 but the core of the star is still round. Yours seems to be squashed. Check the focuser to make sure it is concentric to the optical path and contact the vendor regarding the problem.

A.G

[gazul]

Well I guess misery loves company...

I'm having the same problem as you Gazul but mine seems a little worse.  All my stars look like Maltese crosses and it's consumed way too much of my time trying to figure out what I was doing wrong.  At first I thought that I was getting the spacing wrong between the Field flattener and the CCD, but I'm at most 0.5 mm off and the tolerance just can't be that tight.  Any nebulosity I try to capture is just washed out by this weird effect. 

I tried to enclose a crop of an image of the Bubble Nebula from last night that shows how bad it is.  M52 was just a smear with all of the spikes

Did you find a solution to this problem or is my only recourse to return the thing?  I'd say this is pretty much useless for the wide field imaging I bought it for.

Thanks,

GarryBubble Nebula crop WO GT81 w FFFR.jpg

Sorry "gdallmann" for taking in reply, I sent him the telescope the supplier, turn to William Optics manufactures, they are looking at the solution, I have no news. When you have some important news will tell you. A greeting ...

[Sp@ce_d]

Hmmm only just noticed this thread. Seems this is a more widespread problem than I realised last October when I had to return my GT81 too.

Sent from my iPhone using Tapatalk

[gazul]

Hmmm only just noticed this thread. Seems this is a more widespread problem than I realised last October when I had to return my GT81 too.

Sent from my iPhone using Tapatalk

Hi, I solved the problem ?, they did?

A greeting ...

[Sp@ce_d]

Hi, I solved the problem ?, they did?

A greeting ...

Hi

Yes I decided to get an Esprit 80 instead. Although the first one had to go back too as it had odd star shapes. Different to the GT81 problem though. So it was 3rd time lucky

This is where buying from a good dealer is so important. I had no issues getting them refunded/replaced.

I was well looked after by FLO.

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