Maybe I'm asking too much from this telescope (AT72EDII) [Deep Sky] Acquisition techniques · frankszabo75 · ... · 19 · 1415 · 3

Rajat Kumar:

I've recently acquired this telescope, but I still haven't made much of imaging with the AT72EDII.  I hoped for a short refractor for larger DSO's, but it seems like this telescope produces very large stars, compared to what I'm used to. I even searched astrobin to look at what others got using this telescope and surprisingly I see the same theme.  Mid-size and large stars look very big in it.  Maybe I'm used to the Newtonian, but then I also imaged with my Svbony 80ED and the stars don't look that big. 

When I asked someone, he said "It's a short/cheap refractor, what do you want? " I had the W.O. Z61 about 2yrs ago, and I don't remember having the stars this big either. 

I checked the spacing of the flattener several times and I tried different cameras (I have 4), but the results are the same. Even a very short exposure (5-10 seconds) produces stars that just look too big.  
I tried a different flattener (W.O. Flat 73A, since it's nearly for the same scope under W.O. brand ), but things didn't improve either. I was hoping that things could improve since it's a X1.0 with no reduction, but things look the same anyway, the stars seem to be bloating.  

I thought I've been spoiled by the Newtonian and the RC scope and they only look big for me, but still, if I attach the Svbony scope which is similarly priced 80mm;  and supposed to be "worse" glass (FPL 53 lanthanum vs FPL51) , the stars aren't bloating as much. 
Anyone has any ideas what's going on?

Hey, can you post few tests images from the scope? Recently even I purchased a doublet (WO Z73) and have issues with star shapes. I had emailed WO and they have given some suggestions which I'll do once the weather clears. Image samples may be helpful to diagnose the problem.

Karl Theberge:

Rajat Kumar:

I've recently acquired this telescope, but I still haven't made much of imaging with the AT72EDII.  I hoped for a short refractor for larger DSO's, but it seems like this telescope produces very large stars, compared to what I'm used to. I even searched astrobin to look at what others got using this telescope and surprisingly I see the same theme.  Mid-size and large stars look very big in it.  Maybe I'm used to the Newtonian, but then I also imaged with my Svbony 80ED and the stars don't look that big. 

When I asked someone, he said "It's a short/cheap refractor, what do you want? " I had the W.O. Z61 about 2yrs ago, and I don't remember having the stars this big either. 

I checked the spacing of the flattener several times and I tried different cameras (I have 4), but the results are the same. Even a very short exposure (5-10 seconds) produces stars that just look too big.  
I tried a different flattener (W.O. Flat 73A, since it's nearly for the same scope under W.O. brand ), but things didn't improve either. I was hoping that things could improve since it's a X1.0 with no reduction, but things look the same anyway, the stars seem to be bloating.  

I thought I've been spoiled by the Newtonian and the RC scope and they only look big for me, but still, if I attach the Svbony scope which is similarly priced 80mm;  and supposed to be "worse" glass (FPL 53 lanthanum vs FPL51) , the stars aren't bloating as much. 
Anyone has any ideas what's going on?

Hey, can you post few tests images from the scope? Recently even I purchased a doublet (WO Z73) and have issues with star shapes. I had emailed WO and they have given some suggestions which I'll do once the weather clears. Image samples may be helpful to diagnose the problem.

*** what did good ole WO suggested ? Did they acknowledged all their ZS73 have pinch optics?  Or that their reducer for it is pure garbage ?

I also have a Zs73, I also have bloated huge stars and I had pinch optic too.

***

Rajat Kumar:

Karl Theberge:

Rajat Kumar:

I've recently acquired this telescope, but I still haven't made much of imaging with the AT72EDII.  I hoped for a short refractor for larger DSO's, but it seems like this telescope produces very large stars, compared to what I'm used to. I even searched astrobin to look at what others got using this telescope and surprisingly I see the same theme.  Mid-size and large stars look very big in it.  Maybe I'm used to the Newtonian, but then I also imaged with my Svbony 80ED and the stars don't look that big. 

When I asked someone, he said "It's a short/cheap refractor, what do you want? " I had the W.O. Z61 about 2yrs ago, and I don't remember having the stars this big either. 

I checked the spacing of the flattener several times and I tried different cameras (I have 4), but the results are the same. Even a very short exposure (5-10 seconds) produces stars that just look too big.  
I tried a different flattener (W.O. Flat 73A, since it's nearly for the same scope under W.O. brand ), but things didn't improve either. I was hoping that things could improve since it's a X1.0 with no reduction, but things look the same anyway, the stars seem to be bloating.  

I thought I've been spoiled by the Newtonian and the RC scope and they only look big for me, but still, if I attach the Svbony scope which is similarly priced 80mm;  and supposed to be "worse" glass (FPL 53 lanthanum vs FPL51) , the stars aren't bloating as much. 
Anyone has any ideas what's going on?

Hey, can you post few tests images from the scope? Recently even I purchased a doublet (WO Z73) and have issues with star shapes. I had emailed WO and they have given some suggestions which I'll do once the weather clears. Image samples may be helpful to diagnose the problem.

*** what did good ole WO suggested ? Did they acknowledged all their ZS73 have pinch optics?  Or that their reducer for it is pure garbage ?

I also have a Zs73, I also have bloated huge stars and I had pinch optic too.

***

So after exchanging few emails they suggested to loosen up set of front screws holding the lens. One other suggestion which they have asked me to do is to try imaging with an unmodified DSLR. I am not sure it will help.. but lets see. Also, my issue is not just with the bloat but with the weird star shapes.  From the internet forums, my understanding is that pinched optics produce diffraction spikes around the stars. I think my problem is somewhat different - my stars are not round.  An eg. of it is here https://www.astrobin.com/b1llpp/C/#r0

Interesting that you mention the reducer. I am not using the reducer but their 73A flattener. I am just experimenting now and checking if by adjusting the back focus I can obviate some of these issues. But honestly, I am at my wits end. Did you have any difficulty in adjusting the back focus or the recommended values from WO worked for you?

Also, do you think a mono camera would help to overcome these issues? Sooner or later I would be shopping for a dedicated camera. Initially I was convinced to get an OSC camera but now with this scope I am now thinking of getting a mono camera. I have noticed that even you are are using mono version of ASI533. 

Any lead would be very helpful. Thanks

andrea tasselli:

Ok, so after going back to my post, since I'm the original poster of this thread, I tried another flattener with it (FLAT 73A from W.O.) and I'm seeing the same thing. Even though the scope is Astrotech brand.  The stars are too big. It could be just my perception though, I'm not sure. 

I have one more flattener I will try and see what happens. I'm waiting for a clear night. 

Here is the Pinwheel Galaxy, all I did was just a basic stretch in Pixinsight (EZ-Soft stretch)

I think these stars just looks to big? 

Someone tell me this scope is capable better than this.

https://www.astrobin.com/hpc2zj/

Two things to notice:

1. As others said, your objective cell is too tight and that gives the weird shape you're observing. To be honest this would be for me a red flag and I'd send the telescope back pronto (if bought new).

2. Your secondary spectrum is probably too wide and that gives raise to the apparent star bloating. If anything I'd try a filter such as the Baader Semi-APO which has been shown to contain secondary spectrum. No guarantees here as you didn't produce emough info to draw a conclusion on where the culprit lies.

I also suspect you are mixing me up with someone else posting into my thread his own problems.

Should I just loosen the cells? I mean, this is a replacement scope already to a first one with worse problems, I don't know if asking for another makes any sense, it seems like they 're all like this?

I couldn't help but to look. I've done this already and have the tools (lens caliper).  Well, the 4 x2 plastic screws around were completely loose, which is ok as far as the lens shouldn't be too tight, but the lens still didn't move. There should be a small movement by shaking it, at least feel a tiny movement.   
As it turns out, those screws won't make a difference whether they are loose or not, if the large retaining ring behind the second objective lens is ultra-tight via a retaining ring, squeezing the 2 lens together. 

That's where the caliper came handy and I slightly loosened it, as it was extremely tight. Immediately I felt  the pressure on the lens were gone, I'm talking about a small fraction of a turn on the retaining ring. 
Then, I tightened the small plastic screws, to a point where they just barely making contact with the primary lens, so the lens have that fraction millimeter of space if they need to expand a bit.  
The plastic screws are actually a good idea instead of metal, since it allows pressure without cracking the lens. 

A few more things though.  Looking the lens under light, I noticed smudges in the inside lens near the retaining ring, it looked like either glue or some sort of grease, I don't know. It might be the compound goop they use in the factory, to secure the retaining ring, preventing to get too loose.   It's similar to Locktite you can buy in a hardware store. 

I ended up using my sensor cleaner kit, and the swipes to get off the goop, carefully wiping with one that is soaked with sensor solvent and then wiping it dry with a dry swab.  It has to be done carefully, not to damage or scratch the coating on the glass.   It looks perfect now. 

Now, I want to test it on a star, so hopefully tonight there will be some break among the clouds and see if my tweaks done any good (or bad). 

I know my keyboard looks dusty, but it's a super bright light, I use it to inspect optical parts of my gear.  It will reveal any dirt or dust, I use it to check my camera sensors too, when I notice too many dust motes in my images. 

That's the retaining ring I'm talking about and if you notice that goop applied in the threads, that might have contaminated the lens on the edges inside that I managed to clean off.