156 replies to this topic

[Tom62e]

 

What sensor size is being used for your pics Tom?

 



It's the ASI2600MC Pro (IMX571) APS-C size sensor.

I'm using the 585 sensor, which is significantly smaller on my current project. I'll post that this weekend.

[Tom62e]

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.

There may be a little tilt as the top-left corner looks slightly worse than the bottom-right corner (but not by much at all).

 

Does a Petzval design have a back-focus requirement?  I assumed as long as it comes into focus, it's good.  I certainly never bothered with the RedCat and those images were superb!

 

I'm looking at the Specs now; no mention of a back-focus requirement.  That said, these images were taking with a typical 55mm backfocus rig (just because it was already assembled that way from my last project).  By that I mean I had the 21mm filter drawer and 16.5mm spacer attached for the ZWO ASI2600MC Pro.

[Tom62e]

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

 

WILLIAM OPTICS Minicat Manual.jpg

 

Andy

That makes absolutely no sense.  How can a thin gasket "adjust backfocus" when we may be several inches off depending on the rig we are using.  In other words, you cannot make fine adjustments to a system that allegedly doesn't require raw (gross) adjustments. This is illogical.

[Drothgeb]

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

I agree, that looks terrible. 
 

I’m on the waiting list, and I’m supposed to get mine in November. But I intended to use it with a FF camera, and I don’t use PI or BlurX. Those stars aren’t even close to acceptable to me. I’m probably going to just cancel my order. 

[Tom62e]

I agree, that looks terrible. 
 

I’m on the waiting list, and I’m supposed to get mine in November. But I intended to use it with a FF camera, and I don’t use PI or BlurX. Those stars aren’t even close to acceptable to me. I’m probably going to just cancel my order. 

Absolutely cancel if your plan was to use a FF camera.  You have to crop so much you might as well have used a 8” SCT!  Slight exaggeration for dramatic affect, but you get my point.  

[Foobaria]

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

 

WILLIAM OPTICS Minicat Manual.jpg

 

Andy

Its possible but it should not be necessary with a Petzval scope like this one.   Just focusing should be enough. 

[Foobaria]

There may be a little tilt as the top-left corner looks slightly worse than the bottom-right corner (but not by much at all).

 

Does a Petzval design have a back-focus requirement?  I assumed as long as it comes into focus, it's good.  I certainly never bothered with the RedCat and those images were superb!

 

I'm looking at the Specs now; no mention of a back-focus requirement.  That said, these images were taking with a typical 55mm backfocus rig (just because it was already assembled that way from my last project).  By that I mean I had the 21mm filter drawer and 16.5mm spacer attached for the ZWO ASI2600MC Pro.

A real Petzval does not have a back focus requirement, its one of the "features" of a Petzval design, just focus it and you're at the right point to get a flat field picture.    The traditional Petzval design has 4 lenses.   I've owned the Redcat 61 and 71, and that is all that's necessary and its why its one of my favorite lens designs.  Once you go beyond the standard 4 lens design, all bets are off, as you know some have 5 or 6 lenses. 

Edited by Foobaria, 23 October 2024 - 10:08 PM.

[Drothgeb]

Absolutely cancel if your plan was to use a FF camera.  You have to crop so much you might as well have used a 8” SCT!  Slight exaggeration for dramatic affect, but you get my point.  

I’ve been using a FMA180 up til now. It’s pretty sharp, but only up to APS, and it does have a slight bit of CA. I was hoping that the MiniCat would be a faster/sharper/CA free scope that could handle FF. Apparently not.

 

I was just looking at one of my FMA180 images as a comparison, I think I’ll stick with it. This is un-cropped with a 2600MC. For the cost, the MiniCat should be at least this good.

 

It’s funny that the spots published for the Askar 180 are larger than the MiniCat’s. But it appears that it performs much better.

 

Edited by Drothgeb, 23 October 2024 - 10:18 PM.

[fmendes]

That makes absolutely no sense.  How can a thin gasket "adjust backfocus" when we may be several inches off depending on the rig we are using.  In other words, you cannot make fine adjustments to a system that allegedly doesn't require raw (gross) adjustments. This is illogical.

 

Only possible adjustment I can think of is to make the infinity mark on infinite. Irrelevant but makes focusing faster.

[jml79]

We need a comprehensive, nebula photos (Nico Carver) style battle of the super wide field refractors. Starting with the RedCat 51 and anything wider that is at least a triplet. These are the options I know of;

 

RedCat 51 WIFD - 250mm f/l, f/4.9, FF

SharpStar 50 (with reducer) - 231mm f/l, f/4.6, APS-C

Askar FMA230 - 230mm f/l, f/4.6, APS-C? Possibly being replaced by the SharpStar 50

Askar ACL200 - 200mm f/l, f/4, FF, out of production but there is still old stock available.

Askar FMA180 Pro - 180mm f/l, f/4.5, APS-C

RedCat MiniCat 51 - 178mm f/l, f/3.6, APS-C (FF theoretically possible)

 

There are a few honourable mentions the reduce down close to 300mm and some of those are FF and fast but that isn't what most of use are shopping for. I didn't cover the few options at 135mm f/l.

Edited by jml79, 25 October 2024 - 07:27 AM.

[Foobaria]

That makes absolutely no sense. How can a thin gasket "adjust backfocus" when we may be several inches off depending on the rig we are using. In other words, you cannot make fine adjustments to a system that allegedly doesn't require raw (gross) adjustments. This is illogical.

[Foobaria]

Well, their ideas that you would focus it first and then you would add very thin sub-mm gaskets after that focusing to get to the exact point where you want to be. But this is very different from the standard focus and go approach of the original Petzval design.

Edited by Foobaria, 25 October 2024 - 08:39 PM.

[Cinnamon]

I'm glad I read this post. I was set to order this lens, but no way I'm paying that much for poor performance. I have a 135mm Rokinon, 200f2.8 Canon lens that I can use BXT on, rather than spending a lot of money for something not much better.

[Drothgeb]

We need a comprehensive, nebula photos (Nico Carver) style battle of the super wide field refractors. Starting with the RedCat 51 and anything wider that is at least a triplet. These are the options I know of;

 

RedCat 51 WIFD - 250mm f/l, f/4.9, FF

SharpStar 50 (with reducer) - 231mm f/l, f/4.6, APS-C

Askar FMA230 - 230mm f/l, f/4.6, APS-C? Possibly being replaced by the SharpStar 50

Askar ACL200 - 200mm f/l, f/4, FF, out of production but there is still old stock available.

Askar FMA180 Pro - 180mm f/l, f/4.5, APS-C

RedCat MiniCat 51 - 178mm f/l, f/3.6, APS-C (FF theoretically possible)

 

There are a few honourable mentions the reduce down close to 300mm and some of those are FF and fast but that isn't what most of use are shopping for. I didn't cover the few options at 135mm f/l.

I’m pretty happy with how the FMA180 does with APS-C. My pic above is pretty indicative of how it performs. Just need some other comparative images.

 

I would also put the Evoguide 50ED on the list. It’s only a doublet (true petzvals are doublets), but it performs as well as some of the others. 

[Tom62e]

I’ve been using a FMA180 up til now. It’s pretty sharp, but only up to APS, and it does have a slight bit of CA. I was hoping that the MiniCat would be a faster/sharper/CA free scope that could handle FF. Apparently not.

 

I was just looking at one of my FMA180 images as a comparison, I think I’ll stick with it. This is un-cropped with a 2600MC. For the cost, the MiniCat should be at least this good.

 

It’s funny that the spots published for the Askar 180 are larger than the MiniCat’s. But it appears that it performs much better.

 

 

Very nice image sir!  Very nice indeed!

 

Tommy

[Tom62e]

Well, their ideas that you would focus it first and then you would add very thin sub-mm gaskets after that focusing to get to the exact point where you want to be. But this is very different from the standard focus and go approach of the original Petzval design.

Yeah, I don't get it. 

 

William Optics really did us an injustice with this system.  I pre-ordered as soon as I saw the Minicat because I was in the market for that exact FL scope, and I 100% trusted it would be a great scope based on my prior experience with the Redcat (and based on the price tag!). 

 

I regret selling my Redact soooo much!

[Tom62e]

We need a comprehensive, nebula photos (Nico Carver) style battle of the super wide field refractors. Starting with the RedCat 51 and anything wider that is at least a triplet. These are the options I know of;

 

RedCat 51 WIFD - 250mm f/l, f/4.9, FF

SharpStar 50 (with reducer) - 231mm f/l, f/4.6, APS-C

Askar FMA230 - 230mm f/l, f/4.6, APS-C? Possibly being replaced by the SharpStar 50

Askar ACL200 - 200mm f/l, f/4, FF, out of production but there is still old stock available.

Askar FMA180 Pro - 180mm f/l, f/4.5, APS-C

RedCat MiniCat 51 - 178mm f/l, f/3.6, APS-C (FF theoretically possible)

 

There are a few honourable mentions the reduce down close to 300mm and some of those are FF and fast but that isn't what most of use are shopping for. I didn't cover the few options at 135mm f/l.

That's a great idea.  I bet if you ask Rico or Cuiv nicely, one of them would do it.  Collectively, they probably already own all those options 

[jlinsobe]

This is a 6 element petzval design.
The regular redcats designs are 4 element petzval. 

 

svbony has a new astrograph lense .  That says “More clear image; APO astro camera lens consists of a 3-group 5-piece petzval objective lens structure; which includes a set of triplet lens; bringing you a clearer image;”

Honestly, I’m confused, not even sure what petzval new definition is.

[andysea]

I’m pretty sure that a pezval design has four elements in two groups. I need to check in the Smith, Berry, Ceragioli book and confirm.

[BlakPhoenix]

I’m pretty sure that a pezval design has four elements in two groups. I need to check in the Smith, Berry, Ceragioli book and confirm.

A classic Petzval does does. The problem with the Petzval design is that field curvature and coma/spherical aberration are in a constant fight which becomes more difficult to contain as the focal length shrinks. Improving one, worsens the other. The Mini Cat has a very different setup though with 6 elements. Only the front 2 are shared between the regular Cat and this Mini Cat. Seems that they struggled to keep the aberrations in check, even with the extra glass, due to the much shorter focal length in inherent extra field curvature that creates.

[Voyager_sr2]

Looks like the second batch has arrived to dealers, got email from Agena that mine will be shipped soon.

[Foobaria]

Nice, let see how this batch works out. 

 

Looks like the second batch has arrived to dealers, got email from Agena that mine will be shipped soon.

[Drothgeb]

Looks like the second batch has arrived to dealers, got email from Agena that mine will be shipped soon.

I got my email too. Just trying to decide if I still want it.

[Astro-Goat]

There is now some interesting information on the WO website for the Minicat 51.

 

It says “Due to the nature of MiniCat’s fast aperture optical design, edge stars may not be as round as with other RedCats. However, our tests show it still outperforms conventional lenses. With aberration correction software like BXT, peripheral distortions can be perfectly corrected on APS-C sensors, while Full Frame may need some fine-tuning for even better results.”

https://williamoptic...re_after_NfE4EE

 

One of the images shown, an aberration inspector taken from an image of M24 using a APS-C sensor, shows pretty poor star shapes in the edges and corners.  Possibly this is why they recommend using BXT software.

 

Although the Minicat is called a Petzval design, the manual has a short section called “Ultra Flat Back Focus Adjustment” and shows the insertion of a pvc gasket into the optical train as a means of adjusting backfocus, along with a picture of what happens with the wrong backfocus.  

https://support.will...ocus-adjustment

The aberration inspector image of M24 actually looks to me as if the back focus distance was incorrect (camera sensor too close).

 

Andy

Yup. That's a hard pass for me.

With a Roki 135mm, at F2.8, I can get sharp stars throughout AND at half the cost.  William Optics selling the RC Mini at close to $1k is almost highway robbery.

[Astro-Goat]

 

Soo I finally have two pictures to share with you. 

After closer inspection of the sensor corners, stars don't look as good as I had imagined for a ~1000 € telescope. After checking back with WO support, they told me that there was some minor tilt and stars were slightly out of focus. I will of course pay attention to perfectly nail focus the next time I get the chance.

 

 

 

Fortunately, after applying BlurXT in PixInsight amongst others, this is what the final result looked like with the uncooled ZWO ASI533 MC (around 4.2 hours integration time):

 

 

The little cat is indeed an imaging machine and I'm happy with the end result. However, I don't like the fact that my copy did not work as intended "out of the box" and there's some tweaking to do ...

 

Looks like Dan had more luck? Or is it maybe the smaller chip of the 585?

CS
Johannes

 

TBH tho, one should have to be dependent on BTX to get a good image, out of box, for 1k.  What if someone doesn't have BTX? Sure there are other software options but at 1k, that's a hard pass for me.