164 replies to this topic

[rgsalinger]

I used HocusFocus in NINA to focus the system. I think it's obvious to me now that the scope requires very precise back focus. 

 

I could argue that the "manual" wasn't perfectly clear in its explanation of how the scope worked. In the end, I should have been more attentive to the details. So there's that. I don't know why they won't take it back as frankly, whether it works or not.  I would never order a scope with a "built in flattener" under any circumstances. I just prefer to more pictures rather than try to adjust focus by tenths of a millimeter.

 

We now have 14 days of cloudy weather ahead of us here in Southern California so I have no way to test the scope. I've always been able to return things that I can't use or just don't want. 

 

Rgrds-Ross

Edited by rgsalinger, 27 December 2023 - 05:39 PM.

[Beaverpond Astro]

I have the GT81 WIFD...I know this is a different optical design that the new 68 WIFD, but thought I would share my experience and results with a full frame camera.

One of the reasons I bought the 81 WIFD (I previously had a GT81 IV) was that it was apparently capable of full frame imaging with the WO 68III flattener (which I already had on hand).  The 81IV was not 'capable' of FF...and the 68III flat would not fit (M98 thread).  With the larger tube size of the 81 WIFD, it did have M98 mating threads.

 

First, I had to ask WO tech support (Paul...very helpful guy) what was the back spacing was for the 68III flat, as it is not published on the website.  Once I had that set, I took some test images with a 6200MM (luminance filter) to see if I could get decent stars in the corners.  The images below are lightly processed...just a STF stretch, nothing else (other than ABE to fix a pretty bad gradient due to a 1/2 moon night).

 

Stars are not too horrible in the corners.  Definitely some aberration especially in the left top & bottom corners.  I didn't get around to tweaking the back spacing to see if I could improve the stars, or play with the sensor tilt.  That might have helped a bit.  

But with the new BXT release, not really an issue.

 

 

So again, obviously different optics than the 68 WIFD with its internal lens system for flattening, but perhaps similar in that the 68III flat is also a 3 lens APO design.

Quite pleased with the GT81 WIFD, especially now when using BXT2    (see next post). 

Edited by Beaverpond Astro, 27 December 2023 - 05:44 PM.

[Beaverpond Astro]

Same image as above with BXT2, AI4 processing:

 

 

Cleans up the stars quite nicely.

[rgsalinger]

Yes it does! I played around with that and found that it didn't seem to work on some problem images I had.

 

I'll go back now and test some more.

 

It would be terrific to not have to spend hours in the cold trying to add in .1mm spacers to my system just to use a telescope with a camera.

 

Rgrds-Ross

[zackyd]

Ross, can you confirm (and sorry if I missed this) if both the front element and rear element move with focuser adjustment?

my read on this product is you just need to make sure you allow some +- travel on either side of the focal plane / sensor. As long as you can drop the sensor plane at 55mm’ish from the flange, you should be good to achieve focus. Use the Bahtinov to have an objective confirmation that you are in focus, and then confirm that you have buffer on both sides of focus.
It touts 48mm corrected image circle and I would push for it if it’s clear this sample is not meeting expectations.
It is a new product so I appreciate you sticking your money on the line - lemons commonly can happen at this stage and I would try to quickly figure out if this is one of them with succinct documentation and fight for the situation to be corrected if it is indeed defective.


also I appreciate and utilize BXT, but having it invoked in this thread is not really helpful. If some company/s are going to design and advertise for optical specifications and they do not meet these with the proper operation, with a - “well just use BXT to achieve good stars”..

Hopefully you do not have the sensor at the focal plane and after getting that figured out you can achieve the potential of the optical system or its defective and try to fight to get it corrected by Agena or WO and keep up to date on how it all shakes out.

Edited by zackyd, 27 December 2023 - 09:59 PM.

[charles.tremblay.darveau]

Same image as above with BXT2, AI4 processing:

 

aberation inspect_withBXT.jpg

 

Cleans up the stars quite nicely.

I went back to my 'horror gallery' from when I started astrophotography, mostly cases with the hyperstar. The AI4 from BlurX really takes it to another level. 

 

That being said, if I'm paying a premium for a premium design refractor then I truly expect the manufacturer to meet their claims without having to rely on aberration correction. Otherwise, there are cheaper options that can do equally well (like my Askar FRA400 and my 107PHQ). 

[rgsalinger]

Well I'm assessing what to do as I know that I have some degree of culpability in this matter in the first place. I know from long experience when buying Asian products (and working in Asia) that any written documentation emanating from there needs very careful attention. I was so excited by the specs, that I failed to do that.

 

Since the scope is now all repacked for shipment, I can't confirm that the back element moves. If it did, though, I would have noticed it when I was moving the focuser back and forth while installing the EAF on it. 

 

It's still hard to imagine those results caused by nothing other than bad back focus but one must liven and learn. It seems as if there is no way to get all my money back, though. So it might be worth my while to take a chance and see if it's not that hard to adjust it and get acceptable results. If we only could get a clear enough night to actually test it before return time runs out.

 

Personally, I likes the BI4 post because everyone should be aware of that tool and I'm not sure how many folks are. I have not found it to be very useful but I've been careful not to need it. All of my scopes have almost zero tilt and the two that have flatteners/reducers have been carefully adjusted until the stars are just nice and round in the corners. 

 

Rgrds-Ross

[Kevin_A]

Well I'm assessing what to do as I know that I have some degree of culpability in this matter in the first place. I know from long experience when buying Asian products (and working in Asia) that any written documentation emanating from there needs very careful attention. I was so excited by the specs, that I failed to do that.

 

Since the scope is now all repacked for shipment, I can't confirm that the back element moves. If it did, though, I would have noticed it when I was moving the focuser back and forth while installing the EAF on it. 

 

It's still hard to imagine those results caused by nothing other than bad back focus but one must liven and learn. It seems as if there is no way to get all my money back, though. So it might be worth my while to take a chance and see if it's not that hard to adjust it and get acceptable results. If we only could get a clear enough night to actually test it before return time runs out.

 

Personally, I likes the BI4 post because everyone should be aware of that tool and I'm not sure how many folks are. I have not found it to be very useful but I've been careful not to need it. All of my scopes have almost zero tilt and the two that have flatteners/reducers have been carefully adjusted until the stars are just nice and round in the corners. 

 

Rgrds-Ross

Ross, FYI…. I have been working on a fast f2.8 system recently and it has a backfocus of 47.12 (46.5+0.62mm) as it is a Nikon lens plus filter. This lens had zero coma on a fullframe camera. It now resides on a much smaller sensor asi183mc pro camera. While I was testing backfocus effect on how to get my infinity focus point adjusted to my infinity mark on the lens to where it always was on my fullframe camera, I added 0.5mm to the backfocus distance to achieve that and that did the trick… I thought. With the smaller sensor infinity was previously at the 3ft mark. With that issue corrected I did test shots.  

 

The results I got was that with fast glass and just slightly wrong backfocus distance, all my stars even near the centre had lots and lots of really bad coma. I reset my backfocus back to 46.5 plus 0.62 for my 1.85mm thick uvir cut filter and the coma is now gone again. With my f5.6 scopes I never had this issue as all it does is make my stars in the corners elongated. 

To sum up, backfocus matters a lot more the faster the optics are!

Edited by Kevin_A, 28 December 2023 - 03:23 PM.

[jmX]

I appreciate rgsalinger accepting that this is somewhat on him or her, we all make mistakes.    Agena is tough on returns because no scope is perfect and I think we've all gotten picky.  I myself would return my FSQ106 based on the quality of images, but it turns out thats just how they all are with the $2000 reducer.  $$$ != perfect stars apparently.  

Anyway, to get this thread back on track and show how good the P68 scope is, I'd like to share my corners on a FULL FRAME camera.   I posted my "first light" on astrobin about a week ago and have been impressed with the scope, but I did measure my spacers out to get the correct backfocus before even taking my first photo.   The corner image is here:
 

Attached Thumbnails

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[rgsalinger]

I'd be curious to know how close to the 55mm back focus you ended up with and whether you were using and IR/UV filter. The last time I tried to put a reducer on a fast scope, I just could not get it to work and gave up. That's why I'm "gun shy" about trying to get this one to work.

 

However, since there's no such thing as a free replacement and I can't get a full refund, I'll just have to wait for a clear night and test it properly, I guess. The last time I returned a scope I got full credit (less my 30 dollar shipping cost) and that was that. Times change.

 

Rgrds-Ross

[Apennine]

I'm surprised you are having issues with Agena. I received a "defective" Askar 65PHQ earlier this year, and Agena was helpful in communicating with Askar. Once we determined it was an issue, they exchanged for a good scope at no additional cost. I would expect the same for you once you take some test images at 55mm?

 

Good luck!

 

-Chris

[HubSky]

I'd be curious to know how close to the 55mm back focus you ended up with and whether you were using and IR/UV filter. The last time I tried to put a reducer on a fast scope, I just could not get it to work and gave up. That's why I'm "gun shy" about trying to get this one to work.

 

However, since there's no such thing as a free replacement and I can't get a full refund, I'll just have to wait for a clear night and test it properly, I guess. The last time I returned a scope I got full credit (less my 30 dollar shipping cost) and that was that. Times change.

 

Rgrds-Ross

 

I know on post 19 you said you weren't going to comment on the vendor anymore, but since then you've posted twice about the refund which wants me to know more since probably everyone on this thread are Agena customers. 

 

Looking at Agena's return policy. As an aside, they refer to it as "liberal", but to me it's one of the most restrictive, rules based, if, and, or but policies I've come across.  But anyways it would seem the worst case scenario would be returning an item that doesn't meet your needs. 

 

So, it seems for a return of an item that doesn't meet your needs, it would entail.

 

1) Paying for shipping costs to you and shipping costs to return. 

2) Paying for any credit card/Paypal fees that are not reimbursed to them for purchases over $500.  (I've been caught with that one myself).  Unless you return for store credit, then that is waived. 

3) A restocking fee of 10% if the item is not in new/unused resealable condition.  

 

If exchanging for a non-defective item, then 1 and 3 would apply. 

 

For this to be considered a defective item, in my experience, you have to prove it.  In their policy it says it has to be "definitively determined to be defective" and further down "Also, please note that the word "Defective" does not include optical aberrations or other performance shortcomings you may observe, especially in eyepieces."  I had to put together a dossier of images and screen captures from ASTAP to prove an FRA400 was performing lousy.  

 

So, after all that, my only question is if they are telling you something or treating you outside of their stated liberal (that just makes me chuckle) return/exchange policy?

 

Thanks

[hyiger]

I know on post 19 you said you weren't going to comment on the vendor anymore, but since then you've posted twice about the refund which wants me to know more since probably everyone on this thread are Agena customers. 

 

Looking at Agena's return policy. As an aside, they refer to it as "liberal", but to me it's one of the most restrictive, rules based, if, and, or but policies I've come across.  But anyways it would seem the worst case scenario would be returning an item that doesn't meet your needs. 

 

So, it seems for a return of an item that doesn't meet your needs, it would entail.

 

1) Paying for shipping costs to you and shipping costs to return. 

2) Paying for any credit card/Paypal fees that are not reimbursed to them for purchases over $500.  (I've been caught with that one myself).  Unless you return for store credit, then that is waived. 

3) A restocking fee of 10% if the item is not in new/unused resealable condition.  

 

If exchanging for a non-defective item, then 1 and 3 would apply. 

 

For this to be considered a defective item, in my experience, you have to prove it.  In their policy it says it has to be "definitively determined to be defective" and further down "Also, please note that the word "Defective" does not include optical aberrations or other performance shortcomings you may observe, especially in eyepieces."  I had to put together a dossier of images and screen captures from ASTAP to prove an FRA400 was performing lousy.  

 

So, after all that, my only question is if they are telling you something or treating you outside of their stated liberal (that just makes me chuckle) return/exchange policy?

 

Thanks

I love these "restocking fees" which is really the differential they resell it for as an "open box item" (assuming it's not defective of course). 

[whwang]

Anyway, to get this thread back on track and show how good the P68 scope is, I'd like to share my corners on a FULL FRAME camera.   I posted my "first light" on astrobin about a week ago and have been impressed with the scope, but I did measure my spacers out to get the correct backfocus before even taking my first photo.   The corner image is here:

Hi Jon,

 

Looks like the lower-right corner is a bit soft.  Are all your other images like this?  My first light with the original RedCat was perfect, then it started to show noticeably softer stars in certain corners.  Later I figured out if I use the build-in camera rotator, the collimation may become off.  So I ended up with finding the best rotator angle and then rotate the whole OTA for framing.

[jmX]

Hi Jon,

 

Looks like the lower-right corner is a bit soft.  Are all your other images like this?  My first light with the original RedCat was perfect, then it started to show noticeably softer stars in certain corners.  Later I figured out if I use the build-in camera rotator, the collimation may become off.  So I ended up with finding the best rotator angle and then rotate the whole OTA for framing.

This is just how it was right out of the box.  If you click on the astrobin thread linked earlier I also post the tilt graph from the abberation inspector in NINA.  Truly "first light".

[rgsalinger]

I spent 2 hours tonight using the WO68 with an ASI2600MC. I started at a measured 54mm of back focus and HocusFocus said that the I was within critical focus zone, but I didn't like the stars in the corners. So I added another mm and that made the stars a bit better, but introduced some "moderate" tilt to the system 

 

The moon came up and it was getting a bit hazy so I have to abandon further testing. My judgement is that the optics are mediocre, but I think that I can make nice pictures with it. Also, it may well be that tweaking the back focus will give me even better results.

 

For those who don't know CCDI, any aspect ratio over 20 percent is worthless but I usually like to see the results under 15 percent. The corners just did not measure very well at all. The FWHM in CCD Inspector was in the 4.4 arc second range - much poorer than what I get with my FRA400 but again, this scope needs a better night and perhaps some small additional adjustments to get the best out of it.The long exposures were unguided using a Paramount MYT and Protrack.

 

 

I confirmed that the rear element doesn't move and I have to say that the manual (now that I understand the verbiage) had an excellent diagram showing how to measure the back focus distance. So, case closed for now. I can't really recommend it at this point but I have to admit that getting the BF close eliminated almost all of the apparent collimation error. What was very odd, though was that out of focus stars in the corners still looked like comets. I think that because they were just 1.6 pixels in HFR when in focus it would be hard to see the distortion.

 

Rgrds-Ross

Edited by rgsalinger, 29 December 2023 - 02:03 AM.

[dan_hm]

Ross, can't you just use the tilt plate on the scope to adjust backfocus?  You should be able to make small, equal adjustments to the tilt plate until stars in all four corners look acceptable, and then adjust unevenness from there.  This should be a heck of a lot easier and quicker than adding shims.  Certainly the WO tilt plate is not as precise as an Octopi or Photon Cage, but it should be good enough to start with.

[rgsalinger]

Well, to get rid of the tilt my first port of call is to play around with the spacers (3 of them) that I'm using. There was no tilt when the back focus was off and I was just using 1 spacer at the time. Now I have one adapter - M42 to M48 and two spacers. They seem likely to be the source of the "moderate" tilt.

 

I got rid completely of the tilt in my ASKAR 107PHQ by playing around with the spacers and adapters until I got a good set.

 

Spacers are not machined as precisely as one might like. After that experience, I've bee wondering about whether this is more common than people think.

 

No clear skies for the next week so it will be a while before I can do some more testing. At least I got to the point where the scope is useable. I'm also baffled by how badly the subs measure using CCD Inspector and MaximDL but look good when simply eyeballed.

 

Rgrds-Ross

Edited by rgsalinger, 29 December 2023 - 11:43 AM.

[whwang]

Tilt can occur anywhere. Sometimes the spacer. Sometimes the camera adapter. Sometimes inside the camera. It's really hard to tell.  If your camera consistently shows good corner image quality over different sets of spacers and fast lenses, then at least you can rule out the camera being the source of tilt.

 

When there are no stars for testing, I attach several horizontal and vertical paper rulers on a wall and point my scope at them from a distance. By aligning the scope with the center of the set of rulers (using tiles on the floor and matching the vertical heights of the scope and the ruler center point), I can ensure that the wall is nearly perpendicular to the pointing direction (optical axis) of the scope. Then I examine the image of the rulers in the four corners, and adjust the tilt until the four corners have comparable sharpness. If I feel the ruler images are about equally sharp, then I usually also get equally good stellar images later when I use the scope for stars. This only helps to adjust the tilt though. This doesn't help to find the best back focus, since the wall is not at infinity.

[rgsalinger]

There were several odd things in my testing last night that I wonder about. The first was that tilt went from 3 percent to around 10 percent when I got the back focus adjusted by adding two spacers. The second oddity was that the stars in the corners, when slightly out of focus, were NOT round at all. They looked like comets. I'll look around and see if I saved one of those. The final oddity was that HocusFocus told me my back focus with within the CFZ, IIRC 2 microns, when I was at 54mm. When I added a 1mm spacer the corner stars looked better.

 

I suspect that the complex optics - 6 lenses - may make this scope a little different from my other refractors. I've never seen comet like stars when adjusting back focus. Given the image scale, stacking and processing, I figure to just keep the scope and see if I can dial it in a bit better next time I go out to the observatory. 

 

Rgrds-Ross

[hyiger]

 

I suspect that the complex optics - 6 lenses - may make this scope a little different from my other refractors. I've never seen comet like stars when adjusting back focus. Given the image scale, stacking and processing, I figure to just keep the scope and see if I can dial it in a bit better next time I go out to the observatory. 

 

Rgrds-Ross

That's really no different than sticking a 3 or 4 element reducer/flattener to the back end of a triplet. The only difference in my case (except for my RedCat) is the flattener travels outside the tube and is a fixed distance from the camera. 

[rgsalinger]

I decided to keep the WO68 and just dial in the back focus. Seemed as if people thought that comet shaped stars could be just a back focus issue. 

 

So, I used the ZWO large OAG which, with it's adapter to fit a ZWO2600 camera, results in precisely (and I measured it) 55mm of back focus. I decided not to put in a filter as I didn't want any complications. The results are definitely uninspiring. Here's a link to 55mm back focus images.

 

What I found is that the backfocus is easy to adjust on this scope as there's a ring that you can move in/out. So what I did was get it to 55mm with the ZWO stuff and then add a 1mm spacer inside the ring and then tightened it. Here's a link to 56mm back focus images. As you can see the stars are still comets at 56mm and not getting any better. Curvature was worse as well I recall at 56mm.

 

As far as I can tell this means that the scope is not collimated. I'm curious now to get any additional input from folks who know more about optics than I do. Maybe I'm still missing something. 

 

Rgrds-Ross

 

 

 

Rgrds-Ross

Edited by rgsalinger, 17 January 2024 - 01:44 PM.

[whwang]

Hi Ross,

 

In your first folder, some images look better than others.  I wonder if there is any difference you made between the images, or it's just that some of them have shorter exposures so the faint "comet tails" are less visible.

 

Anyway, in the two 120s images in the first folder, some corners are worse than others.  This means there is definitely collimation error or focal plane tilt involved.  One thing you can try is to use the scope's camera rotator to rotate the camera.  Take exposures at different rotation angles from 0 to 360 degree, and see if images taken at certain rotation angle are better than others.  If all of them are equally bad, then I think it's time to contact WO.

 

I suggested the above because all three RedCats I had from WO had very good stars to begin with.  As soon as I rotated the camera through their camera rotators, I started to see poor corners.  So I ended up with rotating the camera to try to find the best rotation angle, lock it once I find it, and never touch the rotator again.  If I need to rotate for framing, I rotate the whole scope.  This works on RedCat, but not quite so on your 68 as the focuser knob will prevent free/full rotation.  But the rotation test I suggested has the potential of telling you what's wrong.

[rgsalinger]

That's an excellent suggestion. When I added the extra mm of back focus I necessarily rotated the system. So there really were two variables involved and I didn't think of that. I don't think that guiding enters into it though. Oddly enough the guiding was under .3 arc seconds on the MYT which is quite rare - it usually settles down to right around .4. I've sent them in to WO but that means a long involved wait as I don't think that they service anywhere in North America. Collimating something like this needs the right tools, I bet.

 

Rgrds-Ross

[whwang]

If it's simple misalignment between the optical axis and the rotational axis of the camera rotator (or camera adapter), the solution can be simple.  If it's really the collimation of the lenses in the OTA, I honestly don't know how to deal with it other than send it back to the manufacture.