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Redcat 51 - focusing issue. What am I doing wrong?


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Last night everything worked perfectly for me bar the focus part for the Redcat 51.

gave up after 3 hours.

 

Here is a 3mins sub of the heart nebula. With the Bahtinov mask it seemed focused pretty well….but, something is wrong here.

setup:

Redcat51

ZWO filter drawer with L-Extreme

ASI533mc

spacers as per the guides

 

including a screenshot as fyi in case it helps

 

 

C60CB0A0-D59D-49AA-ADB3-9D11B788A2BF.png

B1D5E49F-DFB8-43ED-A267-EF0218239A7E.jpeg

B0A917E6-CF8A-431F-B2D4-2E5CDBDFF1B7.jpeg

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Hi George,

Is this a new scope you're trying for the first time?

What your seeing is severe coma over the whole image. Early releases of the Redcat were prone to these problems due to the internal lenses not being properly aligned. I bought one of the first releases and had to return it as they had issues like this. The replacement was worse and FLO sent one off to Es Reid to be aligned. The one I kept in the end has slight coma in one corner but was acceptable.

The spacing itself isn't critical as it's a Petzval design and the specified spacing merely makes focusing at infinity line up with the infinity mark on the tube.

I'm afraid your only recourse is to return it or get its lenses professionally aligned. 🙁

Alan

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12 minutes ago, symmetal said:

Hi George,

Is this a new scope you're trying for the first time?

What your seeing is severe coma over the whole image. Early releases of the Redcat were prone to these problems due to the internal lenses not being properly aligned. I bought one of the first releases and had to return it as they had issues like this. The replacement was worse and FLO sent one off to Es Reid to be aligned. The one I kept in the end has slight coma in one corner but was acceptable.

The spacing itself isn't critical as it's a Petzval design and the specified spacing merely makes focusing at infinity line up with the infinity mark on the tube.

I'm afraid your only recourse is to return it or get its lenses professionally aligned. 🙁

Alan

Thanks Alan,

I thought so…..no this is a 2nd hand RC51 bought allegedly from RVO and it was immaculate. It might be a case that it was mistreated during shipping (al though it was in its case and very well packed).

 

Would FLO/RVO help with this if of course I pay for the service?

Best

George

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4 minutes ago, George Sinanis said:

Would FLO/RVO help with this if of course I pay for the service?

It's worth asking. I'm assuming it's not that you've bought from RVO second hand, but from someone else who had bought it from RVO. Guarantees are not normally transferable, one of the risks of second hand purchases. I'm hoping it's not that the person you bought it from found out how bad it was, and passed it on without telling you.

Normally coma only exists away from the centre optical axis, getting worse the further from the centre, and it also points towards the centre. Yours is all pointing in the same direction just like one of the examples I had initially, so it looks like the correcting lenses at the rear of the scope which are there to correct the coma and field curvature of the front petzval lens pair have shifted quite a lot. I don't know how the lens adjustment screws are kept in place, so bouncing during transport may well cause them to loosen.

There were some postings of people who have made their own adjustments to the rear lenses and had some success, but a proper optical alignment rig is needed really.

Good luck,

Alan

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Morning - I just checked also WO’s inspection checklist and it seems that this one left the factory on 14/8/2021 so I would assume that are not from the first releases. I will speak with the seller and RVO today and see what can be done.

 

 

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Posted (edited)

Unfortunately, not much help from the seller or RVO on this matter. My only alternative now is to go to William Optics and try to see if they can help or what they advice.

Is there a way to test this by myself and try to fix it? Any step-by-step guide on how to investigate this matter on my own, will be highly appreciated. Otherwise i just threw £500+ in the bin. I would assume you buy cheap --> you buy twice.

 

Edited by George Sinanis
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1 hour ago, tompato said:

Don't RVO do servicing and test reports on refractors and stuff now?

They could still do so but, for this type of OTA it needs to go to WO, if a repair/ service is required.

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Posted (edited)
11 minutes ago, Elp said:

Just a thought, did you try taking a preview image without the filter in it? It may however be as @symmetal has described above.

I did try it indeed without the filter but, not without the filter drawer. The results btw were the same. But, i do not understand how could that impact the image to get such a coma.

 

 

Edited by George Sinanis
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There's a lengthy discussion here on CN forum about RC51 alignment though it doesn't seem to describe how to make any actual lens adjustments and seems to focus more on the tilt plate.

If you unscrew the dew shield you can see the adjustment screws for the front lens pair. It's worth checking that none are loose, along with the screws around the rear pair of lenses.

An artificial star is best for making any checks as you can do it indoors at any time if you want to try it yourself. You really couldn't make it much worse than it is at the moment.

Have you tried asking FLO as to whether they would be willing to send it to Es Reid for adjustment, if you cover all the costs involved. It would be easier than sending it back to WO.

Alan 

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44 minutes ago, George Sinanis said:

I did try it indeed without the filter but, not without the filter drawer. The results btw were the same. But, i do not understand how could that impact the image to get such a coma.

 

 

Just a process of elimination, it sounds as @symmetal has described then.

Edited by Elp
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48 minutes ago, George Sinanis said:

I did try it indeed without the filter but, not without the filter drawer. The results btw were the same. But, i do not understand how could that impact the image to get such a coma.

 

 

Looks very similar to mine when it was new from FLO, they sent it to Es and got it fixed.

Dave

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16 hours ago, George Sinanis said:

Last night everything worked perfectly for me bar the focus part for the Redcat 51.

gave up after 3 hours.

 

Here is a 3mins sub of the heart nebula. With the Bahtinov mask it seemed focused pretty well….but, something is wrong here.

setup:

Redcat51

ZWO filter drawer with L-Extreme

ASI533mc

spacers as per the guides

 

including a screenshot as fyi in case it helps

 

 

C60CB0A0-D59D-49AA-ADB3-9D11B788A2BF.png

B1D5E49F-DFB8-43ED-A267-EF0218239A7E.jpeg

B0A917E6-CF8A-431F-B2D4-2E5CDBDFF1B7.jpeg

Honestly i would be trying to get your money back from the seller as this scope has obvious coma across the entire image. 

ES reed may be able to help, if you cant get your cash back. Not sure if the redcat has user accessible collimation screws on the front element? Is so then you might be able to fix it yourself using a Cheshire collimator. 

Adam 

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4 hours ago, George Sinanis said:

Unfortunately, not much help from the seller or RVO on this matter. My only alternative now is to go to William Optics and try to see if they can help or what they advice.

Is there a way to test this by myself and try to fix it? Any step-by-step guide on how to investigate this matter on my own, will be highly appreciated. Otherwise i just threw £500+ in the bin. I would assume you buy cheap --> you buy twice.

 

Not sure its user adjustable (push pull screws on the front lens cell) but you should check that the front cell is not loose as a first step. 

Adam 

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@Adam J thanks for your post - it seems the seller has made his position clear and not much to wait from that side.

The telescope has a tilt adjuster that i was advised by RVO to use but, i am not sure if the tilt adjust can make any difference in such a severe coma situation. I have emailed WO awaiting their input and i have also asked FLO for any possible advice, although they have no responsibility whatsoever to answer/ help me.

 

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Just now, George Sinanis said:

@Adam J thanks for your post - it seems the seller has made his position clear and not much to wait from that side.

The telescope has a tilt adjuster that i was advised by RVO to use but, i am not sure if the tilt adjust can make any difference in such a severe coma situation. I have emailed WO awaiting their input and i have also asked FLO for any possible advice, although they have no responsibility whatsoever to answer/ help me.

 

@Adam J Also i was trying to get more info regarding ES Reed...do you happen to have any link? Many thanks in advance.

 

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Posted (edited)

OK - i am still trying to figure out how to proceed with this but, i need to comment that @FLO has been great with their willingness to help, even if they do not have to. A genuinely great company to deal with - hats off.

So, i need a wide field, light and with great optics travel scope, to work very well with my ASI533MC. My options are:

  • New Redcat51
  • ASKAR230
  • Sharpstar 61EDPH II (do i need a reducer for flat field)?

 

If i did not have 2nd thoughts, i would have gone for a new Redcat51 but, may i please check (if you know) how susceptible are they to lose lenses alignment or to other issues?

Edited by George Sinanis
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Ask @Andeif they've still got the Z61 for sale, it's what I use and an awesome scope. They've also got a flattener for it listed. They are widely available otherwise.

Edited by Elp
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9 minutes ago, Elp said:

Ask @Andeif they've still got the Z61 for sale, it's what I use and an awesome scope. They've also got a flattener for it listed. They are widely available otherwise.

Thanks for the nod 😃

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1 hour ago, George Sinanis said:

OK - i am still trying to figure out how to proceed with this but, i need to comment that @FLO has been great with their willingness to help, even if they do not have to. A genuinely great company to deal with - hats off.

So, i need a wide field, light and with great optics travel scope, to work very well with my ASI533MC. My options are:

  • New Redcat51
  • ASKAR230
  • Sharpstar 61EDPH II (do i need a reducer for flat field)?

 

If i did not have 2nd thoughts, i would have gone for a new Redcat51 but, may i please check (if you know) how susceptible are they to lose lenses alignment or to other issues?

Hello George.

 

I use a ZWO 2600MC with my Spacecat51 which is identical to the red cat,  the stars are pretty good across the FOV even with this larger CMOS chip with only very slight tilt in one corner which does not bother me.  My only issue with the space cat is the focuser, I changed out the bat mask and replaced with the finer grate version that Lucomatico was selling which helped, Ideally I want to autofocus it going forward.

 

Mark

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8 minutes ago, Ande said:

Thanks for the nod 😃

No probs, was thinking about it myself for dual setup but I should be reducing my stuff not adding to it!

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2 hours ago, George Sinanis said:

OK - i am still trying to figure out how to proceed with this but, i need to comment that @FLO has been great with their willingness to help, even if they do not have to. A genuinely great company to deal with - hats off.

So, i need a wide field, light and with great optics travel scope, to work very well with my ASI533MC. My options are:

  • New Redcat51
  • ASKAR230
  • Sharpstar 61EDPH II (do i need a reducer for flat field)?

 

If i did not have 2nd thoughts, i would have gone for a new Redcat51 but, may i please check (if you know) how susceptible are they to lose lenses alignment or to other issues?

If you want the highest probability of trouble free imaging then I will second the choice of a ZS61 an F6 doublet is a really safe bet. 

On the other hand its not fast either. 

The I love my ASKAR 180 and the ASKAR230 seems to be of similar optical quality at F4.5 ish, hence not quite fully APO unless you use a L3 filter with it or a L-Pro filter. But then its much cheaper than a redcat isnt it. For that reason I could live with it but could you?

Then you have the redcat, a more complex optical design than the above and so still has some sample to sample variation, you pay for it but if new you can send it back cant your. 

I would have thought that the original could be colimated though I assume from this line of questioning that was not possible?

Adam

 

 

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