RedCat 51 first image - Oh No!

[barkis]

Who manufactures the RC's   WO, or some other outfit?   Just curious. I'd have put WO's Quality Control at a high level.
Of course  perhaps the problem if one exists, could be confined to a particular batch.

Ron.

[FLO]

11 minutes ago, barkis said:

Of course  perhaps the problem if one exists, could be confined to a particular batch.

From what I have seen and heard so far I don't think there is a problem. I will know more after Es' has checked it on the bench. 

Steve

[barkis]

I'm sure everyone is hoping for good outcome on this.  My interest stems from a personal interest in owning one too.

Ron.

[symmetal]

Here's the results from last night white RedCat tests. They are 15 sec L exposures on an ASI1600 given a levels stretch to make it clearer. I've shown the CCD Inspector 3D plot and a crop of the worst area and centre of each image (at full size). View images at full size for best comparison. The main problem is the camera rotator causes varying tilt depending on its angle. The previous Redcat had a more constant tilt while rotated. The first 4 images are with the rotator arrow at 0, 90, 180, 270 degrees with the last image being the best at around 300 degrees. As you can see the out of focus stars exhibit 'coma' like trails rather than just being a bit 'soft', even on the final image which doesn't look too bad in CCD Inspector. If the tilt can be eliminated it would be better and resampling to 50% or so which the images shown elsewhere seem to be, would give good results.

Some might say I'm being too fussy  I suppose.

The red RedCat is with Es' Reid now. Hopefully he can fix the problem if it is just caused by tilt somewhere.

Using a tilt corrector would improve matters, though it would mean leaving the rotator in one place and having to rotate the whole scope in its clamp which is fairly easy to do. I'll buy an M48 fitting tilt corrector from FLO and try it on the white RedCat. The M48 one just allows enough space to adjust it with the ASI1600 and filter wheel in place. The T2 tilt adjuster after an M48 to T2 adaptor doesn't allow room.

Alan

[Nubian]

Compared to other scopes, how bad are the results? Would i notice the problem on a crop camera?

The sharpest 250, but not the flattest?

When I look at this one here:

https://www.astrobin.com/full/391674/0/?real=&mod=

the stars on the right are everything but round. ;(

 

[symmetal]

Hi Nubian,

I suppose you can only compare it with 250mm camera lenses so in that respect if you get one without tilt it would be significantly better. The image you indicated does show the tilt problem with the 'coma' like stars on the right.

For the tests above I focused using the 'thirds' rule and with the last most flat image the stars in the centre still rate as the sharpest so it might be better to focus even closer to the edge than the thirds rule. I used the same focus point for each image so for those showing tilt, focusing closer to the area where the stars are at their worst would most likely give an improvement. 

The ASI1600 is a 4/3 size sensor (2x crop mode) compared to an APS-C sensor ( 1.6x crop mode) so the APS-C would show larger corner defects, though the colour sensor and pixel size may mitigate the effects to a degree. When the M48 to Canon adaptor arrives I can try it with my 700D camera.

Alan

[Alien 13]

I expect its early days for this scope but it was announced as the sharpest 250 mm lens but that doesn't mean it can get anyway near the Sammy 135mm or even the Canon 300mm.

Alan

[Davey-T]

24 minutes ago, Alien 13 said:

I expect its early days for this scope but it was announced as the sharpest 250 mm lens but that doesn't mean it can get anyway near the Sammy 135mm or even the Canon 300mm.

Alan

I'll let you know when mine shows up 

Dave

[souls33k3r]

Well I had the similar story with the WO Star 71 MKii but that was a quad. I'm sure ES will be able to make it all better but if I'm being honest I don't fall in to all the hype the paid contributors create all over the Internet, real tests are performed by people like yourself and many others here. I think one should get the hint when you hear things like WO are unable to keep up with the demand then of course someone is bound to cut corners and unfortunately QC is always the first to take the hit. 

I just hope this is not wider issue and was only with the two scopes you had. 

[symmetal]

10 hours ago, souls33k3r said:

Well I had the similar story with the WO Star 71 MKii but that was a quad. I'm sure ES will be able to make it all better but if I'm being honest I don't fall in to all the hype the paid contributors create all over the Internet, real tests are performed by people like yourself and many others here. I think one should get the hint when you hear things like WO are unable to keep up with the demand then of course someone is bound to cut corners and unfortunately QC is always the first to take the hit. 

I just hope this is not wider issue and was only with the two scopes you had. 

Reading up on Petzval designs it says that the front doublet is designed to introduce coma to effectively cancel out the coma of the rear doublet. So that it seems is not happening on the two Redcats I've tried. I don't think that focus itself is the main problem, as even on the corners showing severe coma the stars themselves (ignoring the coma) are reasonably small.

I took some blue images last night which showed significant coma on all four corners, with no appreciable tilt but severe curvature shown in CCDI (focusing using the thirds rule). Just as a test I took another image focusing right in the corner and the result was no different. The bahtinov pattern shows the same in focus display all over the frame. So my assumption in a previous post that getting a tilt free image and focusing nearer to the edge would improve matters,  doesn't.  If you have an image displaying tilt you can get coma free stars in two corners (and worse in the others) even if the tilt seems to be caused by the rotator after the rear elements. So I'm a bit confused. By its very design If the petzval elements aren't properly aligned you will get coma, but tilt and not focus can somehow change the coma effects. 

Eagerly waiting to see Es' Reid's analysis and whether he can achieve a fix. 

Alan

Edited March 29, 2019 by symmetal

[FLO]

On 27/03/2019 at 10:45, FLO said:

It won't a problem either way. It has at least given us an opportunity to send one to Es' for assessment. If we had withheld one for any other reason I think we'd have been lynched! ? 

Just a quick update to say Es did find "a little coma" in @symmetal's RedCat. Fortunately he was able to adjust it out so all is good. 

We are going to use this opportunity to play with assess it our ourselves with a camera under the night sky. 

HTH, 

Steve 

[Dinglem]

44 minutes ago, FLO said:

We are going to use this opportunity to play with assess it our ourselves with a camera under the night sky. 

Can you judge coma looking at clouds ☁️

[FLO]

Just now, Dinglem said:

Can you judge coma looking at clouds ☁️

We have the Zarkov Cloud Gun ? 

[Dinglem]

1 minute ago, FLO said:

We have the Zarkov Cloud Gun ?

Today would have been a good day for a marketing push on these ?

[symmetal]

59 minutes ago, FLO said:

Just a quick update to say Es did find "a little coma" in @symmetal's RedCat. Fortunately he was able to adjust it out so all is good. 

We are going to use this opportunity to play with assess it our ourselves with a camera under the night sky. 

HTH, 

Steve 

That's good news that Es adjusted it out Steve.  I suppose the definition of 'a little' is in the eye of the beholder.  A full frame sensor would show it worse than the 1600 I'd have thought. Hope your assessment goes well. If it does there's a WhiteCat here that I think would enjoy a visit to Es.  

Alan

Edited April 1, 2019 by symmetal

[Tim]

On 28/03/2019 at 01:39, symmetal said:

Here's the results from last night white RedCat tests. They are 15 sec L exposures on an ASI1600

1

Following this thread with interest

At least from the White Redcat you have equal effects of coma, and it is not too awful. It's a shame there isn't a way to get software adjustment suitable for each telescope and camera, the same way you can get software adjustments for Canon lenses for example.

Out of interest, is the coma worse if you focus and image via a blue filter? Use a central bright star to focus and then nudge the same star to the edge of the field and try again. This will also demonstrate the extent of any focal shift. If you have parfocal filters it will demonstrate how "apo" the scope is too. Luminance filters are a compromise in refractors, there is nearly always a bit of deviation in one of the colours, usually blue, even with fluorite lenses. 

Cheers

Tim

[symmetal]

2 hours ago, Tim said:

Following this thread with interest

At least from the White Redcat you have equal effects of coma, and it is not too awful. It's a shame there isn't a way to get software adjustment suitable for each telescope and camera, the same way you can get software adjustments for Canon lenses for example.

Out of interest, is the coma worse if you focus and image via a blue filter? Use a central bright star to focus and then nudge the same star to the edge of the field and try again. This will also demonstrate the extent of any focal shift. If you have parfocal filters it will demonstrate how "apo" the scope is too. Luminance filters are a compromise in refractors, there is nearly always a bit of deviation in one of the colours, usually blue, even with fluorite lenses. 

Cheers

Tim

Hi Tim,

About 5 posts after the one you quoted I did do a test with a blue filter and focus. I found the focus was more critical using the bahtinov mask in the corner rather than a 'third' but having achieved the central spike in the corner, I checked over the whole image moving the bright star around and focus was still very good with the mask over the whole image. The CCDI analysis of my first test focusing on a third, and the second test focusing in the corner were almost identical so I think the image field with the Redcat is actually pretty flat. Coma is therefore the main problem, and it would seem that the bahtinov spikes are not affected by coma, and the coma isn't really changed by focus. Here's a longer exposure of 120s using the blue filter with the imaging train orientation like the last one of my L images above, which gave the best 'flat' analysis for L. As you can see the blue result is worse than L which is to be expected. View the image at full size to see it more clearly. Three of the corners showed significant coma with the fourth corner slight coma.

Alan

 

[ippiu]

I look forward to receiving the little red baby...I ordered one from italian reseller....

I had a big and great expactations on it, so reading this topic made me angry and sad...

Hope this bad story is caused by just one isolated single badly assembled piece...and not by a common problem affecting all redcat family...

Follow with anxiety this topic 

[Adam J]

Not sure about a little coma, in all the images here even the white cat shown later, if I had that much coma on my ASI1600mm pro / 130PDS I would be reaching for the laser collimator.

Edited April 6, 2019 by Adam J

[symmetal]

On 01/04/2019 at 16:25, FLO said:

Just a quick update to say Es did find "a little coma" in @symmetal's RedCat. Fortunately he was able to adjust it out so all is good. 

We are going to use this opportunity to play with assess it our ourselves with a camera under the night sky. 

HTH, 

Steve 

Have you had a chance to try it out yet Steve? It looked clear over Exeter yesterday. 

Alan

[FLO]

26 minutes ago, symmetal said:

Have you had a chance to try it out yet Steve? It looked clear over Exeter yesterday. 

My colleague tried it and found Es' has adjusted most of the aberration out but a little remained so Es asked us to send it to him again. I think he is enjoying finding his way around this new telescope. As are we ? 

Will let you know when it is available. Promise. 

Steve 

[symmetal]

Thanks for the update Steve. 

Alan

[Nubian]

If "our" Redcats show the same coma, shall we send it to Es or will FLO take care of the adjustment? If not, how much does Ed take?

[FLO]

20 minutes ago, Nubian said:

If "our" Redcats show the same coma, shall we send it to Es or will FLO take care of the adjustment? If not, how much does Ed take?

If it has a fault you should contact your supplier for service. If you purchased it from FLO then you contact FLO ? 

Does your RedCat have a problem? 

HTH, 

Steve 

[Nubian]

I purchased from FLO but Im still waiting for delivery. I was just curious how possible issues will be handled