156 replies to this topic

[licho52]

Wow, IMO it's quite shameless for a manufacturer to tell customers: "Oh well, stars are not too good at the corners, but hey, you can use BXT". Come on, is it well corrected for an APSC format or not? Unbelievable!

It's a very relevant information, if BX is able to fix the issue then it's not such a big issue. The star shapes in corners obsession will at some point become a thing of a past, as it should.

[Voyager_sr2]

Well, it is a matter of principle mostly, either "it is corrected" or "you have to correct it yourself".

I did not cancel my order because I can correct it, but I see issues with off-axis guiding and autofocusing (in NINA you can chose to use inner part of image, but not with ASI Air).

And also with mosaics, despite it should be a rare case for such a wild field of view, I am going to do some and will have to do some processing before stitching panels together.

Edited by Voyager_sr2, 16 October 2024 - 10:16 PM.

[licho52]

Well, it is a matter of principle mostly, either "it is corrected" or "you have to correct it yourself".

I did not cancel my order because I can correct it, but I see issues with off-axis guiding and autofocusing (in NINA you can chose to use inner part of image, but not with ASI Air).

And also with mosaics, despite it should be a rare case for such a wild field of view, I am going to do some and will have to do some processing before stitching panels together.

The "corrected" stuff was never anything to go by, it's meaningless.  Askars are "corrected" through spherical aberration and the masses gobble it up.

[Sergio_2014]

The "corrected" stuff was never anything to go by, it's meaningless.  Askars are "corrected" through spherical aberration and the masses gobble it up.

Would be interesting if you could please elaborate on this. I've heard that Askar refractors are "corrected" to the edge of FOV at the expense of less sharpness in the center... Don't know if that makes sense.

[RetiredDave]

 Here is an image of M31 (stack of ~70 60 second images with a 2600MCP) I took on 13 Oct with the Minicat 51 I received earlier this week. On the left is the uncorrected image, and on the right is after BlurXterminator correct only. I Included the FWHM/Eccentricity and Abberation Inspector images. Other than some left right tilt, what do you make of these images before and after (other than BlurX is indistinguishable from magic). Thanks,

 

Dave

I hate to quote my own post, but the corner stars in my uncorrected image look much worse than in other images posted here. Some of that is due to tilt and the fact that my sensor size is APS-C. Also, both the ASIAir and Pixinsight report my focal length as 174mm rather than the advertised (and input by me) 178mm. Could this be one of the reasons for my poor corner stars? If so, is there a way to increase the system focal length? I already added an additional 5mm (still able to focus) to the back spacing with no change to the FL reported by the ASIAir (still 174mm). Will adding or removing spacers improve the corner stars, as long as I can come to focus? If not, this little scope may have to go back to the retailer. Thanks.

 

Dave

Edited by RetiredDave, 21 October 2024 - 08:05 PM.

[Tom62e]

Here is my first stacked image without any processing—and no calibration frames.  I am very disappointed to say the least.  The stars are wonky in all four corners.  All streaking away from center.  Hope you can see it in this poor image file.

 

 

 

[Tom62e]

Here is a zoom crop of one of the corners . . . 

 

[Tom62e]

Here is the adjacent corner . . . 

 

[Foobaria]

Here is a zoom crop of one of the corners . . . 

 

MiniCat_Test2.jpg

I can see a little comet effect here. 

[Tom62e]

I can see a little comet effect here. 

Yeah, it’s pretty ugly.  I don’t think this is acceptable performance for a new scope.

[BlakPhoenix]

Yeah, it’s pretty ugly.  I don’t think this is acceptable performance for a new scope.

What sensor size is being used for your pics Tom?

[dobrychemik]

Yeah, it’s pretty ugly.  I don’t think this is acceptable performance for a new scope.

Have you optimized backfocus and tilt? f/3.5 is extremely sensitive to getting both parameters right. In particular, remember that backfocus doesn't necessarily have to be 55mm.

[rapture91]

I just sent the Minicat back to the retailer since the corner stars on my relatively small 1“ sensor (ASI533) were heavily affected by coma. My scope also had a tilt problem, but fixing that would very likely not changed image quality.

Since this is a Petzval design, you do NOT have to adjust backfocus. As long as you reach focus, that‘s fine. So there‘s no possibility to play with that.

It‘s really shame that William Optics just updated their disclaimer on the home page, saying that they recommend using BlurXT since the corners are poorly corrected…

Also, in a mail conversation WO recommended to focus on a star in the corner to mask those noticeable aberrations… I wonder what would have happened to stars and most importantly the object in the middle of the sensor?

I really liked that small scope with respect to handling, portability, looks etc.

But I will opt for another small refractor now…

Cheers,
Johannes

[Foobaria]

I just sent the Minicat back to the retailer since the corner stars on my relatively small 1“ sensor (ASI533) were heavily affected by coma. My scope also had a tilt problem, but fixing that would very likely not changed image quality.

Since this is a Petzval design, you do NOT have to adjust backfocus. As long as you reach focus, that‘s fine. So there‘s no possibility to play with that.

It‘s really shame that William Optics just updated their disclaimer on the home page, saying that they recommend using BlurXT since the corners are poorly corrected…

Also, in a mail conversation WO recommended to focus on a star in the corner to mask those noticeable aberrations… I wonder what would have happened to stars and most importantly the object in the middle of the sensor?

I really liked that small scope with respect to handling, portability, looks etc.

But I will opt for another small refractor now…

Cheers,
Johannes

Oh no, so sorry to hear this!  I don't feel they should be releasing products that cause inaccurate results. 

[PeteConrad]

I just sent the Minicat back to the retailer since the corner stars on my relatively small 1“ sensor (ASI533) were heavily affected by coma. My scope also had a tilt problem, but fixing that would very likely not changed image quality.

Since this is a Petzval design, you do NOT have to adjust backfocus. As long as you reach focus, that‘s fine. So there‘s no possibility to play with that.

It‘s really shame that William Optics just updated their disclaimer on the home page, saying that they recommend using BlurXT since the corners are poorly corrected…

Also, in a mail conversation WO recommended to focus on a star in the corner to mask those noticeable aberrations… I wonder what would have happened to stars and most importantly the object in the middle of the sensor?

I really liked that small scope with respect to handling, portability, looks etc.

But I will opt for another small refractor now…

Cheers,
Johannes

that's really unfortunate to hear! I really hope it was just a bad copy; I should be getting mine sometime middle of November. I've talked with a few guys that received theirs and they aren't too thrilled about the corners using a 533 either, but they did confirm that Blurx does fix the star shapes. 

 

 

If I get mine and am happy enough to keep, I'll be selling my FMA180 Pro if ur interested. 

[rapture91]

I‘m located in Germany and already own the Askar FMA180 Pro, which btw doesn‘t show any aberrations in the sensor corners. However, it‘s not f/3.5 but f/4.5 of course.

I will probably opt for the Sharpstar 61EDPH III and sell the Askar FMA180 Pro.
The former’s 270 mm focal length will allow me to fit most extended objects in the FOV…

[fmendes]

I joked about the Rokinon 135mm, but checked back on my latest image using it with an APS-C sensor, 3.76μ pitch. In f/2.8, that's what it looks like. Yes, corners are not perfect, but not poor either. But the big "problems" with this lens are: 1. Back focus is difficult to achieve. 0.3mm away from optimeal is very visible.  2. Cannot use with OAG, tricky to use with a rotator.

 

Edited by fmendes, 22 October 2024 - 02:51 PM.

[RetiredDave]

I compared FOVs on the astronomy tools FOV calculator. The FOV with a 533/Minicat 51 is about the same size as a 2600/Redcat 51 (same height - the 2600 is a little wider since it is a rectangle). As far as I know, the Redcat 51 is flat across an APS-C sensor, so what is the point of the Minicat if the image is only usable (not great) with a 533 sensor? I'm thinking WO rushed this one out of R+D and into production too quickly.
In any case, I am returning my copy for an exchange. I'm hoping I received a particularly bad copy. The retailer said if I was not satisfied with the replacement that I can return it for a refund no problem.

Edited by RetiredDave, 22 October 2024 - 03:38 PM.

[rapture91]

Hey Dave,

I really don‘t think that exchanging your copy by one from another batch etc. will improve those bad corner stars.

But you can give it a try of course^^

CS
Johannes

[dobrychemik]

Since this is a Petzval design, you do NOT have to adjust backfocus. As long as you reach focus, that‘s fine. So there‘s no possibility to play with that.
 

It's not so obvious. MiniCat has six lenses, so it's a Petzval with a built-in reducer. I don't know how it's built inside. Is the reducer fixed or connected to a movable WIFD? Only in the latter case you don't have to worry about backfocus.

[Robservatory]

I am disheartened that William Optics didn't provide this information until well after my Minicat had arrived and I placed an order for a 6200MC Pro. At the end of the day I will probably be happy with the results of the insanely wide FOV, but this was bad business etiquette on their part. I'm going to test is on the next clear night with a mirrorless camera and see how bad the stars are. If they are horrendous, this cat is going back the very next day.

[fmendes]

It's not so obvious. MiniCat has six lenses, so it's a Petzval with a built-in reducer. I don't know how it's built inside. Is the reducer fixed or connected to a movable WIFD? Only in the latter case you don't have to worry about backfocus.

 

Technically, you are correct, and we don't have data to absolutely confirm that all elements move together (although all Petzval designs will have that characteristic). An owner (or former owner) can confirm if all elements move together.

 

However the manual does not say anything about back focus. The vendor says the telescope performs poorly in the edges. I'd say these evidences suggest that backfocus is any.

[RetiredDave]

Hey Dave,

I really don‘t think that exchanging your copy by one from another batch etc. will improve those bad corner stars.

But you can give it a try of course^^

CS
Johannes

    I really don't think so either, but my stars look much worse than stars from other copies of the same scope. I know at least some of those examples were from smaller sensors than my 2600, so I guess I'll have to wait and see if the other scope is any better.

    I was really hoping to take advantage of the wide FOV this scope offers. The increased speed is a secondary benefit (but also a double-edged sword due to sensitivity to tilt, etc.). However, if only 50% of that FOV is usable, then there is not much point to blowing close to $1000 on a Minicat 51 when it seems the Redcat 51 will produce better results with my sensor. I already have a Rectcat 61, so the increase in FOV of a Redcat 51 is minimal.

    I will note that contrary to William Optics advertising, at least with the Minicat 51 I received, the distorted stars in the corners, and even on the edges of images taken with my APS-C sensor were not completely corrected by BlurXterminator.

 

Dave

[rapture91]

It's not so obvious. MiniCat has six lenses, so it's a Petzval with a built-in reducer. I don't know how it's built inside. Is the reducer fixed or connected to a movable WIFD? Only in the latter case you don't have to worry about backfocus.

I was in contact with William Optics support. This was their response:

 

“Yes, I noticed a little bit of tilt, but I think you should not adjust the tilt now.

Since this is a petzval design the backfocus is Adjusting with the focusing mechanism. This is why when you focus on a orner star you will adjust the telescope focus and at the same time it will adjust the backfocus.
Regards,
Tim“

[Andy Lucy]

The manual for the Minicat implies that backfocus fine tuning is indeed possible.  Here is a screen shot from the online manual:

 

 

Andy