21 replies to this topic

[John Miele]

I just bought the subject scope and had first light a few nights ago. I was going to post a min-review but after seeing the first image, I have a  problem. This is a stack of 24 x 60 sec subs using my ASI2600MC and the new FF107 @ f7. No filter. This looks like a pretty bad case of pinched optics.  I'm in the 30 day window and well within the 1 yr warranty period. I'm going to open a dialog with the vendor tomorrow. 

 

Reading other posts about this issue, I understand it may very well be fixable using heater strips around the objective and the corrector element. The ambient temp when I took this image was about 34 deg. F and I had no heater strips on the scope at all.  So I can see how the OTA may have contracted in the cold weather and put some pressure on the lenses. That said, this looks pretty bad to me.

 

My proposed plan of action...

 

1. Notify ZWO and the vendor tomorrow of this issue. Send image and details. Ask vendor to allow me extra time if needed beyond 30 days to try and fix the problem. I have 15 days left. My next clear night is at east 3 or 4 days away.

 

2. Repeat the image with heater  strips installed (they arrive tomorrow) and see if that fixes the issue.

 

3. If not, return scope for another example. I want the scope. I just need a good working copy.

 

4. If given clear instructions, I am willing to try loosening lens shipping screws as a 2nd try at a fix. But am not willing to do anything more than that.

 

Any advice or other ideas?

 

Thanks!

 

cs...John

 

 

 

 

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[John Miele]

star crop...

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[Poynting]

I'd definitely return. Looks like something is definitely wrong with the optics.

[John Miele]

ZWO asked me to loosen the tube rings. I did and l also installed my two new dew heater strips at each of the lens group locations and set them both to 100%. The night was colder last night than first night...26 deg. F vs 34 deg. F. This made no difference. Star shapes are the same. Here is another star crop from the 2nd test. Both nights I waited until M42 was near the meridian. This weird diffracted star shape thing affects every star in the image  and is oriented exactly the same all over the image. I'm going to contact ZWO again and see if there is anything else I can try before I send it back.

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[John Miele]

Looking into the front of the scope, I can see two notches or gaps in the retainer ring on the objective and the retainer ring in front of the correcting lens further back. The orientation of these notches roughly matches the darkest diffraction spikes in my star images. It appears similar to this...

 

https://www.cloudyni...w-esprit-100ed/

 

https://interferomet...e-esprit80.html

 

I think I have the same issue but no way am I going to do what this person did to fix it...

[bokemon]

Sharp spikes are, as you noted, are due to the sharp things poking into the light path.  Can you make an aperture mask that's barely smaller than the aperture? Edit: Or just slip in an o-ring.

Edited by bokemon, 10 January 2025 - 03:14 AM.

[John Miele]

ZWO tech support recommended that I just return the scope to the vendor. They do not have a procedure to fix this issue other than what I already tried. I requested a return authorization today. Hopefully this will go smooth...

[Spikey131]

When you read about pinched optics in Suiter’s book, the recommended solution is “redesign the lens cell”.

 

Sometimes there is no end-user solution to this problem.

[John Miele]

There is nothing in the light path that I can see. No lens spacers or other protrusions. The only thing I see are the two notches or gaps in the retainer rings on each lens cell. If these rings are too tight, maybe the unsymmetrical compression caused by these notches can stress the lens glass and cause artifacts. It's possible a thin mask could fix this but I do not want to mask off a defect and reduce aperture. and I don't want to disassemble  a brand new scope to get to these rings. 

[bokemon]

The aperture masking ideas only cost a few dollars to try, so I suggest that as a diagnostic.  It will tell you the difference between pinched optics vs light path protrusions.  The latter is a problem that cannot be solved even if you get another copy of the same scope.

[John Miele]

I tried an aperture mask already before your post but I made it much smaller than you suggested. I reduced the aperture from 107mm to 90mm. Maybe I should have only reduced it to 103mm instead. Not sure why I went so small. I think I wanted to see if there would be any difference and then make another one if there was. But after I decided to return, I did not make the other one.

 

That said, here is the same image with the 90mm mask. I cut the mask using a somewhat dull bladed exacto knife (all I had) out of foam board and the edges were a bit ragged. I think that is why there are so many spikes. But the big shadows are gone and overall the stars look better. Does this image indicate anything else that would be useful in deciding what to do?

 

Thanks

 

John

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[bokemon]

The purpose of a thin, barely skimming the edge, aperture mask is to remove the edge protrusions while still allowing the stress from pinching to show thru. And of course the mask has to be smooth.

[John Miele]

OK...that makes sense.

 

The way I am viewing this is that edge protrusions would be more of a physical design flaw affecting all scopes whereas pinched optics is an assembly error (something is too tight) that can be corrected. I searched astrobin for more examples from this scope, and the two I found quickly had perfect round stars. If it were a design flaw affecting all scopes, then there should be no good examples. But since there are, I lean to this being an assembly error on my particular scope so an exchange would be appropriate. I am waiting for the return/exchange to be approved right now.

 

John

[RichA]

ZWO asked me to loosen the tube rings. I did and l also installed my two new dew heater strips at each of the lens group locations and set them both to 100%. The night was colder last night than first night...26 deg. F vs 34 deg. F. This made no difference. Star shapes are the same. Here is another star crop from the 2nd test. Both nights I waited until M42 was near the meridian. This weird diffracted star shape thing affects every star in the image  and is oriented exactly the same all over the image. I'm going to contact ZWO again and see if there is anything else I can try before I send it back.

I'd make sure nothing was in the optical train other  than the camera (no filters) and take the star images.  Then I'd mount the camera on another scope and make sure  the problem isn't with it.

[John Miele]

I did. Nothing in the optical train except the scope itself and the camera No filters. No reducers. No OAG. Nothing.

 

The camera takes perfect round and clean star images on my FRA500. No problem with camera itself.

[John Miele]

I have an update that may be helpful to share.

 

BLUF: This was my first dealing with ZWO tech support and their return process. I found them to be reasonable and responsive. They stood behind the product and did the right thing. A replacement scope will be on the way soon.

 

Background: Being that ZWO is not really known for refractors, I had received some feedback that customer/product support might not be all that great compared to other companies. This was a bit worrisome but as we all know, I went ahead and ordered the scope anyway and encountered the issue I documented in this thread.

 

After I first reported this issue to my dealer and  ZWO tech support and tried a few more troubleshooting ideas, I created an account on the ZWO support website and was asked to upload pictures showing the images I was getting. I was next asked to upload pictures of the OTA as I had it set up for use and showing where the dew heaters were installed and the scope S/N. I was asked about the camera I was using and if there were any other optics in play (filters, reducers, etc).  After a few days reviewing all this data, ZWO responded and said they agreed there was a problem and to send the scope back and they would ship a replacement direct to me. They sent me a prepaid shipping label the same day as the return decision was made (today). All my exchanges with their tech support persons were friendly and their requests for information as we worked through this issue were reasonable. This is just one data point, but I can only say positive things about their support. The entire time from first reporting the problem to the replacement decision was a little over 1 week.

 

cs...John

[johrich]

Sorry you are unable to resolve your issue with your FF107.  I bought an FF107 about a year and a half ago. During the Fall the images were fine, but then in December when we were getting nights in the 30s and 40s, my stars looked like yours. I also contacted ZWO support, but their first response was they thought it might be tilt.  I often measure my tilt with with ASTAP and it is always below 10%, and I wrote back insisting that I thought it was pinched optics.  At that time, the response was to turn the problem over to ZWO engineering.  I did some further research, and loosened my tube rings, (which were very tight) and also put dew heater straps around the lens cells.  In my case, that worked, my stars became round without the strange spikes.  I notified ZWO support that I had solved the problem and what my solutions were.  As a side note, a few weeks ago when I was imaging in 30 degree temperatures, I forgot to turn on the dew straps and the auto setting on the Pegasus Power Box didn't turn them on because the humidity was very low.  Sure enough, the resulting stars looked a bit spikey, but not as bad as a year earlier.  Ever since, I always make sure I manually turn on the dew straps.  Other than that issue, I have been very happy with my FF107.

 

Good luck with your replacement scope.

 

John

[John Miele]

Update: My replacement FF107 arrived today and of course it also brought along clouds and rain. Hope to try it soon and see if the optical  issue is resolved.

 

At least the unboxing went well. Fit and finish are very nice. No marks or paint defects anywhere. Dew shield has a nice snug fit and slides smoothly. Lens coatings look very clean and uniform. Nothing protruding into the optical path that I can see as I look down the tube. Focuser feel is very smooth. No discernable wobble or backlash. So the initial checkout scores a 100.  Now to get it under the stars!

[John Miele]

So the forecast tonight was all clouds. I went to see family. I drive back home, exit the car, look up and by Golly its clear! Make a mad dash inside and grab the new scope, put the asiair on it search desperately for the asiair power cable, find it, grab a diagonal, head out back to mount the scope and its wall to wall clouds...from clear sky to solid clouds in less than 10 minutes...good grief! The cloud Gods got me tonight...fingers crossed for tomorrow.

[John Miele]

Success!!!!

 

Tonight it cleared up and I was able to run the replacement scope through all the paces. I started with a quick visual test. First target was Rigel. Rigel presented a nice tiny airy disc with a faint 1st ring. The little companion stood easily off to the side. Very crisp view. I next went right to Jupiter. At150X, it had a sharp snappy focus with lots of contrast on the belts and zones. A pleasing image of Jupiter tells me about all I need to know on a scope. This one definitely passed.

 

Then removed the diagonal  and in went the camera. Back to M42. Moment of truth. Took ten 30 second subs and and all the strange diffraction spikes were completely gone! The stars were smooth and round. Big relief. The scope works as it should.  You can see the stars here in this completely uncalibrated image. In case you are wondering, the dust donuts are on my camera front window and not any of the scope optics. I confirmed this with the astronomy tools dust spot calculator. They are about 10mm from the sensor. I must have collected some new dust particles storing my camera over the  past few weeks and I need to blow them off. 

 

Anyway, glad I can stop testing and now go back to having some fun!

 

cs...John

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[mblack]

 

…Rigel presented a nice tiny airy disc with a faint 1st ring. The little companion stood easily off to the side. Very crisp view. I next went right to Jupiter. At150X, it had a sharp snappy focus with lots of contrast on the belts and zones. A pleasing image of Jupiter tells me about all I need to know on a scope. This one definitely passed.

 

Anyway, glad I can stop testing and now go back to having some fun!

 

cs...John

from the stars in the latest image, and the snippet from your report, I would agree the second scope is quite good. Very happy for you, great nights ahead :-)

[John Miele]

Thanks David. It's been a bit of a long road with this one. I think it's performing right where one would expect it to in this class of scope. I did not mention it, but the star shapes also looked good even in the corners of my APS-C sized sensor. Not fully sure yet how well the CA control will be controlled in images, but visually I did not notice anything excessive on Rigel or Jupiter. I'll just say it seems like it should be a fairly solid performer at this point. I also got a free matching reducer when I bought it so I think it was a fair deal on the OTA.

 

cs...John