William Optics RedCat 51 APO

[Astroscot2]

Hello John, in your opinion can you confirm what type of optical aberration we are seeing in the centre crop if not a processing artifact?   I can see slight coma on the corner crops posted earlier but other than that I see in the centre crop slightly out of focus stars mis-shapen by image compression. I can also see dark rings around the stars indicating some sharperning of the image?

 

As Alan mentioned we would need to see an image where we know the RC scope and imaging train is securely fixed,  well guided, well focused, no processing and the image presented uncompressed to evaluate.

Mark

[Jkulin]

Hi Mark,

I am not optically qualified to comment as to the cause of the odd shapes, all that I can say is if I bought an OTA brand new that produced stars like that then I would not accept it.

It is fairly obvious that there is an issue along the line that is much more noticeable at the edges and on that basis I would not accept it, doesn't mean I know how to fix it or what is causing it.

In my own images I know when I have a guiding problem or tilt and try to work a way around it, not always successfully.

I really was seriously interested in the RedCat and nearly hit the button when I first saw it to buy from FLO, but it has since it's launch been plagued with reports of poor star shapes and even the highly respected Mr ES Reid has had a unit back for a second time to try and fix.

If the problems are resolved then I am truly happy for everyone concerned, but it does need fixing.

3 hours ago, Astroscot2 said:

As Alan mentioned we would need to see an image where we know the RC scope and imaging train is securely fixed,  well guided, well focused, no processing and the image presented uncompressed to evaluate.

Indeed I totally agree.

Looking at the quality of your images on Flickr you are far more likely to identify a resolution to the odd shapes than me.

BTW some lovely images on there and perfect star shapes 🙂

Edited June 14, 2019 by Jkulin
typos

[FLO]

 

5 hours ago, Jkulin said:

 since it's launch been plagued with reports of poor star shapes 

That is not true. The majority of RedCats sold at FLO are performing well and their owners are pleased. I have also spoken with two other WO dealers who say the same. If this situation changes you will know because we would then make RedCats available only with an Es’ Reid test. 

5 hours ago, Jkulin said:

 even the highly respected Mr ES Reid has had a unit back for a second time to try and fix.

That ‘is’ true but only because we didn’t do what we should have done - send him one from our stock so he could quietly take his time getting to know the optical design. Instead, because they were in such short supply, we released every one we had to customers. 

[FLO]

On 13/06/2019 at 00:07, Davey-T said:

Mine's disappeared into Es black hole but it's raining anyway 

I have a confession to make. We forgot to relay your scope to Es’ when we collected it and didn’t notice until you posted your comment. Entirely our fault. We dropped the ball. Not Es. Sorry 😟

It is now with Es’ and I will monitor its progress from here onwards. Promise. 

Steve 

[Davey-T]

2 hours ago, FLO said:

I have a confession to make. We forgot to relay your scope to Es’ when we collected it and didn’t notice until you posted your comment. Entirely our fault. We dropped the ball. Not Es. Sorry 😟

It is now with Es’ and I will monitor its progress from here onwards. Promise. 

Steve 

No worries 

Dave

[melsky]

On 13/06/2019 at 12:40, Jkulin said:

Problem is that I would have bought the Redcat to use full frame with my Sony, but with stars like that I won't go near it.

I think the Redcat is performing very satisfactorily, whilst it’s not up to the quality of my FSQ85 it only cost a fifth of the price. This was a single fifteen second exposure on a not very transparent night so I think some of the random shapes are down to the atmosphere as much as jpeg artefacts also it was shot at 3200iso, I do realise the left hand edge is inferior but this will not be a problem when used with my CCD and CMOS cameras. When I get the time I'll convert the raw file or maybe the one I shot at 1600iso, I posted the brighter shot to show how good the vignetting was for this lens, it’s better than my Takahashi in that regard. A daylight comparison with my Canon 300mm F4 L lens showed it matched that for performance, maybe I’ll do a star test of them both together.

[Jkulin]

6 hours ago, FLO said:

That ‘is’ true but only because we didn’t do what we should have done - send him one from our stock so he could quietly take his time getting to know the optical design. Instead, because they were in such short supply, we released every one we had to customers

With respect Steve, I have heard from a number of sources that they are not too pleased with the star shapes, I can’t substantiate it so regard it as hearsay.

Indeed, FLO acted correctly with the Esprit issues on first launch, and now they are cracking scopes.

So maybe you will need to offer an ES Reid service for the Redcat until quality levels are guaranteed, but then will it price it out of it’s competitive pricing?

I’d like to see a few other owners results with the RedCat before committing to buying one.

[FLO]

12 hours ago, Jkulin said:

With respect Steve, I have heard from a number of sources that they are not too pleased with the star shapes

Our sources are our customers. To date we have experienced only three RedCats that required attention (one of them is in progress). That is too small a number to justify us adding £75 for an Es Reid bench test. 

12 hours ago, Jkulin said:

Indeed, FLO acted correctly with the Esprit issues on first launch, and now they are cracking scopes.

I don't recall any optical issues with Esprit telescopes when launched?

I do remember some initial confusion over the Esprit 80's spacing requirements (a US retailer quoted wrong stats) but that was soon overcome. 

Unless you are referring to the 5-element model that was launched (years ago) then withdrawn almost immediately because it struggled to hold its optical alignment? But FLO never stocked or sold that one and as far as I know it was never rereleased. 

12 hours ago, Jkulin said:

So maybe you will need to offer an ES Reid service for the Redcat until quality levels are guaranteed, but then will it price it out of it’s competitive pricing?

If over time it proves necessary then we will but it would be a shame to increase its purchase price without good reason. 

12 hours ago, Jkulin said:

I can’t substantiate it so regard it as hearsay.

When hearsay is mistaken for fact, it muddies the water. 

Steve 

[melsky]

OK as requested here is a TIFF version from the raw file of a full frame shot through my Redcat 51, taken with a SonyA7s @1600iso 15 seconds exposure. Yes its not perfect but I think its more than acceptable for the price of the lens, I've overlaid crops for smaller camera's, the red line is APS-C, the yellow line Micro 4/3 and the green line for my Atik One 6.0 which is what the lens will primarily be used for.

Redcat Tiff.tif

[symmetal]

Thank you for the tiff with the overlays melsky. Yes, I would certainly be happy with that. For APS-C and smaller there is no problem with the stars, at least not to me. 

Alan

Edited June 16, 2019 by symmetal

[R3tr0]

Hi 

An update on my situation the Redcat has been tested and replaced by a tested version from Rother Vally Optics (thanks for there help, very good lads) I got out last night and did a few test shots. No editing except to save out as tff and crop out the cls filter on the "Med Exp" (this was taken in full frame mode, others were in APSC mode).

Test Recat 01 (Short Exp).tif Test Recat 03 (Med Exp).tif Test Recat 02 (Long Exp).tif

[symmetal]

Hi R3tr0,

Your replacement is certainly an improvement. There is still slight coma in the corners but whether that would bother you in real images where stacking would likely make it less noticeable only you can say.

Alan

[R3tr0]

On 17/06/2019 at 14:02, symmetal said:

Hi R3tr0,

Your replacement is certainly an improvement. There is still slight coma in the corners but whether that would bother you in real images where stacking would likely make it less noticeable only you can say.

Alan

Yeah it produces better images from my original, I'm ok with this version, I will post some images weather dependent.

[Adam J]

On 13/06/2019 at 12:02, Jkulin said:

Sorry but at 100% the stars are truly awful

Got to agree with others, those look fine for a full frame sensor. I would be less pleased if it was a APS-C but I would find the performance acceptable for full frame. 

Its certainly worlds better than many of the examples images I have seen from the red cat. But the thing to remember with that is the large number sold over a short period and the bias involved, people don't post test images to forums when its working correctly only when there is an issue. That makes it really difficult to determine how wide spread any problems are or are not as the case may be. 

Best thing to do is look on astrobin and see how its performing over a wide range of images as opposed to a thread like this one.  

Adam

Edited June 21, 2019 by Adam J

[Davey-T]

28 minutes ago, Adam J said:

Best thing to do is look on astrobin and see how its performing over a wide range of images as opposed to a thread like this one.  

Plenty of images taken with the RC online, many with dodgy stars in the corners but only shows if you zoom in.

Mine is winging its way back from FLO after being hit with Es's big hammer so will post some before and after images.

Dave

[JimmyDigital]

Here is a single shot I took this past weekend with my brand new Redcat. Thoughts?

The camera used was a 294mc-pro.

Edited July 3, 2019 by JimmyDigital

[symmetal]

Hi JimmyDigital,

That image looks very good and no obvious coma visible. It looks like the bottom of the image is a bit out of focus compared to the top so there is a bit of sensor tilt in the imaging train but the RedCat itself looks a good one. It's a 4/3 size sensor so there may be some coma with a larger sensor but you should be happy with what you have. 

Here's the CCD Inspector result showing the bottom just a little out of focus.

Alan

Edited July 4, 2019 by symmetal
Added CCDI Image

[JimmyDigital]

7 hours ago, symmetal said:

Hi JimmyDigital,

That image looks very good and no obvious coma visible. It looks like the bottom of the image is a bit out of focus compared to the top so there is a bit of sensor tilt in the imaging train but the RedCat itself looks a good one. It's a 4/3 size sensor so there may be some coma with a larger sensor but you should be happy with what you have. 

Here's the CCD Inspector result showing the bottom just a little out of focus.

Alan

Thank you very much.  I am new to this art and didn’t even know that existed.  So I guess something is just a little tilted that needs to be tightened up?

[symmetal]

3 minutes ago, JimmyDigital said:

Thank you very much.  I am new to this art and didn’t even know that existed.  So I guess something is just a little tilted that needs to be tightened up?

Hopefully that's just the case. The stars at the bottom of the image are slightly larger than the stars on the rest of the image as they are a little out of focus. It's only very slight so not worth worrying about it too much.  This is because the sensor isn't perfectly perpendicular to the telescope's optical axis. Working out what part of the optical train is the cause of the tilt can be time consuming, and you can waste a lot of imaging time trying to get it perfect.

Alan

[MartinB]

14 hours ago, symmetal said:

Working out what part of the optical train is the cause of the tilt can be time consuming, and you can waste a lot of imaging time trying to get it perfect.

Very true!

[CCD Imager]

Been a busy last few months, but I have recently been able to assess my Redcat more. I did post a mini review a few months ago and there were some comatic stars in a corner due to mis-collimation (as it transpires). If you unthread the dew shield exposing the lens, you can see 4 sets of 2 collimation screws, each pair seperated by 90 degrees. I really dont know what they are doing, is there a set screw and adjustment screw per pair or perhaps they sit either side of the lens cell. Any way, by experimenting, I managed to improve the collimation by going back and forth between opposite pairs in the direction of the coma. If any one actually know what the pairs of screws do, I would love to know.

My second observation is that the Redcat is not a typical Petzval design. Usually there are 2 doublets at a fixed distance apart in the OTA and focus is achieved by moving the telescope focus to achieve the correct distance from sensor to rear doublet optics. However, the redcat is focused by moving the front two elements and hence the distance from the rear 2 elements from the sensor is crucial and fixed. Therefore, please insert the correct adapters to achieve the required distance of 77.7mm. This may explain the comatic stars in some peoples images?

My collimation is nearly there and I am much happier than before. Of course you can return the scope to the supplier, or if you are confident, adjust the collimation yourself.

Adrian

[Buzzard75]

10 minutes ago, CCD Imager said:

My second observation is that the Redcat is not a typical Petzval design. Usually there are 2 doublets at a fixed distance apart in the OTA and focus is achieved by moving the telescope focus to achieve the correct distance from sensor to rear doublet optics. However, the redcat is focused by moving the front two elements and hence the distance from the rear 2 elements from the sensor is crucial and fixed. Therefore, please insert the correct adapters to achieve the required distance of 77.7mm. This may explain the comatic stars in some peoples images?

I found with my specific camera I needed at least 8mm of spacer (not counting the M48 to M42 adapter) to get focus at one extreme and about 40mm to maintain focus at the other. I didn't do any tests to determine if there was a difference in coma at one end or the other of focus. Might prove to be interesting though.

[FLO]

6 hours ago, CCD Imager said:

If you unthread the dew shield exposing the lens, you can see 4 sets of 2 collimation screws, each pair seperated by 90 degrees. I really dont know what they are doing, is there a set screw and adjustment screw per pair or perhaps they sit either side of the lens cell. Any way, by experimenting, I managed to improve the collimation by going back and forth between opposite pairs in the direction of the coma. If any one actually know what the pairs of screws do, I would love to know.

My collimation is nearly there and I am much happier than before. Of course you can return the scope to the supplier, or if you are confident, adjust the collimation yourself.

Adrian

Eek!

I am sure Adrian meant well when he posted his advice but my advice to anyone reading this is please do not attempt to adjust your RedCat’s optics at home. Four element designs are not easy to collimate. If your RedCat requires realignment then we recommend you contact your supplier (I don’t think Adrian purchased his from FLO). 

HTH, 

Steve

[CCD Imager]

1 hour ago, FLO said:

Eek!

I am sure Adrian meant well when he posted his advice but my advice to anyone reading this is please do not attempt to adjust your RedCat’s optics at home. Four element designs are not easy to collimate. If your RedCat requires realignment then we recommend you contact your supplier (I don’t think Adrian purchased his from FLO). 

HTH, 

Steve

Hi Steve

I would agree, if you are inexperienced with refractor collimation, then don't start. I've done a few in my time, previously using the Tak collimating scope to good effect, but I dont have that any more. A petzval design is two doublets, one at the front of the scope and one at the rear. In the Redcat, the one at the rear is fixed and cannot be altered. The front two elements have 2 sets of screws at the 12, 3, 6 and 9 position. It's honestly as easy as collimation a Newtonian, if the coma becomes worse, just reverse the change you made.

Can you do harm? Over tightening can cause pinched optics and worse, damage the cell, I tighten the collimation screws until I feel resistance, no more. 

My only issue is that I dont know how the collimation screws work as mentioned above, but Im finding out by trial and error

Steve, I didn't buy from FLO and this is my second Redcat. I returned the first because of mis collimation, but as it was also present in the second and I really wanted to keep the scope, I just had to collimate myself. Once collimated, it is a very nice little widefield imaging platform. I did also note that the collimation screws were a little loose when I first got the scope, I checked this after I found collimation changed when pointing the scope 120 degrees to a different part of the sky.

Adrian

[FLO]

It is good to hear you saw an improvement but I promise you there is more to collimating a 4-element refractor than simply tweaking a few screws. It is not like collimating a Newtonian. Your supplier should do or arrange the collimation for you.

I don’t want to sound melodramatic but, seriously, if you encourage people to collimate their RedCats it will almost certainly end in tears. Please don’t. 

Steve