Weird stars with the WO Z73 with the 73A Flattener

[spooked velociraptor]

Hey,

I recently bought a z73 second hand on astroukbuysell. I'm really happy with it, but I'm getting a few issues with stars that I'm trying to figure out, and wanted some advice on. I've heard that there can be some issues with the screws appearing in the field of view, but before I start messing around with it I thought I'd post here to get some external advice.

A picture of the stars (with the flattener 73a flattener attached) is below. The image take was perfectly focussed (I used a bahtinov mask to perform the focus). The flattener is set to 11.4mm which from what I've heard is the distance required for a DSLR, which is what I'm using for my camera. 

Thanks in advance :)

[newbie alert]

Don't look like a spacing issue...

[spooked velociraptor]

Yeah that's what  I was thinking looking at other posts here. Any idea whether it's screws in the OTA or the flatteners?

[callisto]

2 hours ago, spooked velociraptor said:

Hey,

I recently bought a z73 second hand on astroukbuysell. I'm really happy with it, but I'm getting a few issues with stars that I'm trying to figure out, and wanted some advice on. I've heard that there can be some issues with the screws appearing in the field of view, but before I start messing around with it I thought I'd post here to get some external advice.

A picture of the stars (with the flattener 73a flattener attached) is below. The image take was perfectly focussed (I used a bahtinov mask to perform the focus). The flattener is set to 11.4mm which from what I've heard is the distance required for a DSLR, which is what I'm using for my camera. 

Thanks in advance

Looks like you might have pinched optics  🤔

Edited August 29, 2022 by callisto
Change wording

[spooked velociraptor]

4 hours ago, callisto said:

Looks like you might have pinched optics  🤔

Hey, thanks! Is there any way of fixing this myself or can it only really be fixed by WO themselves?

[Steve Ward]

Spikes caused by the spacers between the front elements ... 😉

 

 

Edited August 30, 2022 by Steve Ward

[newbie alert]

10 hours ago, spooked velociraptor said:

Yeah that's what  I was thinking looking at other posts here. Any idea whether it's screws in the OTA or the flatteners?

Take a few images without the flattener and compare 

I nearly said it looks like pinched optics but it looks kind of different , so it maybe the screws... Maybe a job for ES Reid or I think RVO also do a optical repair service  ..

[inFINNity Deck]

You can test whether it is caused by pinched optics or by screws or spacers in the light path by applying an aperture mask. A reduction in aperture of about 4mm should suffice. Try to make the opening as smooth as possible as any deviation from a perfect circle will add new spikes. If the pattern is caused by pinched optics, the make-shift aperture mask will only add more spikes, but not remove the ones you already have. If caused by screws or spacers in the light path, the three large dark spikes should be gone (and replaced by irregular spaced new ones from the mask).

I had similar issues with an Esprit 80ED, which I solved using a 79mm aluminium aperture mask, see this Dutch thread (opening in Chrome should translate it): https://www.starry-night.nl/het-verwijderen-van-artefacten-bij-een-refractor-met-een-brilletje/

Nicolàs

[Martthebass]

I think this is not an uncommon issue on WO scopes.  I had it on my old GT81 but to a much lesser extent on my old GT71.  If you're brave it can be removed by loosening off the collimation screws (do a search for which ones), I wasn't brave but found that the spikes could be just about eliminated by putting a couple of dew strips on (it was worse on winter nights).  I did inform the supplier (not FLO) of the issue but didn't get anywhere; when I got my last APO I made sure it was one that was checked/tested by the supplier (in this case FLO).