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


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George,

I assume these are from your Redcat. The two images are showing different results, neither of which are particularly good. I've found that CCDI tends to ignore coma if it's small as the star centre itself is still defined enough to get a reasonable FWHM figure. With your coma being so bad, it is affecting the results as your FWHM figures are also large. To be honest I don't think you can get any meaningful results from CCDI until the coma issue is resolved. 😔

Alan

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Posted (edited)
5 hours ago, symmetal said:

George,

I assume these are from your Redcat. The two images are showing different results, neither of which are particularly good. I've found that CCDI tends to ignore coma if it's small as the star centre itself is still defined enough to get a reasonable FWHM figure. With your coma being so bad, it is affecting the results as your FWHM figures are also large. To be honest I don't think you can get any meaningful results from CCDI until the coma issue is resolved. 😔

Alan

Thanks @symmetal,

To be honest, probably i want to believe that the issue is with tilt rather than anything else.

By the way - i see that you have a ZS61. Are you happy with it and are you using it as a travel scope? How does it compare with the Redcat51?

 

Best

George

Edited by George Sinanis
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Your coma stars all go to a sharp point which implies the focus is actually pretty good all over. If one side was out of focus due to tilt, that side would normally show less pronounced coma as well, as the de-focused point is spread out and dimmer. However, even your faint stars in the centre still show significant coma. Even with bad tilt though, one area of the image at least would be in focus with good stars. With yours, none of them are good, so tilt itself is not a significant concern at the moment.

I have 2 ZS61s on a dual rig setup on an HEQ5 though I haven't used it for a while and they both give sharp stars over an ASP-C sized sensor. I haven't tried them with a larger sensor. As others have said they work well straight out the box. I don't have a travel scope as such as I'm lucky enough to have dark skies here, though not often clear. 😦 I preferred it to the Redcat as it was easier to adapt for auto-focus, though there are kits available for redcat auto-focus now. The ZS61 has a narrower field of view and is a bit slower though, compared to the Redcat.

Alan

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I hope you didn't buy it off somebody on here...

The least the seller should be doing is taking it back and returning it for a warranty repair on your behalf.

If he/she/non are unwilling to help at all then you don't have much to lose by trying to fix it yourself. At the moment the scope is worthless. I doubt it left the factory like that ( at least I would like to believe that) so likely the shipping process has thrown it out. It may be that something has come loose. Worth investigating yourself. 

This was my first image with my Redcat and full frame Canon 6D. They can perform well so don't give up on it yet.

 

 

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10 hours ago, symmetal said:

The ZS61 has a narrower field of view and is a bit slower though, compared to the Redcat.

You can get a Starizona Apex S for the Z61 which gives Red/Spacecat like fov and makes it f3.8. From rough testing it does create coma at the edges but if you're going to crop it shouldn't be an issue.

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Posted (edited)

Unfortunately the seller is not willing to help or of course take any responsibility. It seems that someone tried to tinker with the alignment screws at the front lenses as a couple of them are wear off. Since he is also avoiding to provide me with the receipt it makes me believe that he knew about it. And no he is not from there forums - I bought it from ABS. 
 

It is an expensive mistake but, I have started looking into it on my own. The lenses are perfect but, removing the screws I found out 2 things:

1. WO are using very cheap plasticky-feel screws that can be very easily broken! Why WO?

2. If someone has the knowledge, they could make good of it. 
 

I have made the decision to offer for sale the OTA + Redcat ring + dovetail for around £150 in case some one is willing to try and fix it. And I will go for a new scope.

Edited by George Sinanis
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3 hours ago, George Sinanis said:

1. WO are using very cheap plasticky-feel screws that can be very easily broken! Why WO?

I suspect that the screw material needs to be softer than the glass they're pushing against to avoid getting 'pinched' optics. They are probably made of nylon. It's likely that whoever tried to adjust them used metric allen keys when they are possibly imperial sized grub screws. You can sometimes get away with it with metal grub screws but nylon ones are likely to burr over.

Hope you will be happy with whatever new scope you get George. 😊 I bet it's put you off buying second hand in future though.

Alan

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Posted (edited)
51 minutes ago, symmetal said:

I suspect that the screw material needs to be softer than the glass they're pushing against to avoid getting 'pinched' optics. They are probably made of nylon. It's likely that whoever tried to adjust them used metric allen keys when they are possibly imperial sized grub screws. You can sometimes get away with it with metal grub screws but nylon ones are likely to burr over.

Hope you will be happy with whatever new scope you get George. 😊 I bet it's put you off buying second hand in future though.

Alan

I cannot agree more with you, re buying 2nd hand - especially without inspecting it first. 
 

I think I know where the come came from. 2 of the screws were extremely tight that could have easily pushed the lense even a bit. Those 2 screws seem to have been tinkered by someone. It did not look like a factory issue. 
 

Even the corrector lense at the back has 3 springs ( I assume for easier adjustment) but all 3 screws were again very tight. 
 

As I said the lenses are almost perfect and it could be a nice opportunity for someone to try and fix it. 
 


 

 

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Edited by George Sinanis
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Ah, right, slotted grub screws rather than allen key types. Someones made a right mess of those. 😠 For anybody who has the right optical bench setup to align the lenses it would be a bargain.

Alan

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Hi George, just a note - I use a 2nd hand (arg you say - maybe never again?) Canon 300mm F4 L lens with my asi533 and asi1600 (and canon 6d). Just needs the ZWO adapter.

Mine at least is pin sharp edge to edge even with the full frame 6d. I'm not the only one using this lens:

https://astrobackyard.com/canon-300mm-f4-astrophotography/

I got a great deal on ebay from a Japan dealer - the only benefit I've found from Brexit is no import duty from japan now. If you want to gamble again.. - it came in about 3 days for about 350 quid.

though there is a UK one auction finishing it a day or so at 181 quid just now:

https://www.ebay.co.uk/itm/185412590268?epid=100017066&hash=item2b2b739abc:g:OxgAAOSwQGJiciEb

Its a solid all metal lens that photographers swear by. Obviously as it's electronic you are shooting wide open at F4 with the asi camera, but at least with mine, that works lovely.

But you may have had enough of 2nd hand.

stu

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From what can can gather the Redcat can be knocked out of collimation in transit, due to the design. I think it's usually the rear elements. 

TS Express have a useful PDF download that walks you through collimation adjustment for a traditional Scope/flattener, if you need a guide. 

If you don't feel like having a go yourself, I'd look at getting it recollimated as it can be a very nice little petzval to have.

It's a crap shoot buying used, and shipping of delicate scopes is always a risk. I have an Askar 180 (not an APO, blue bloat), a Samyang 135 (couple of dodgy corners otherwise excellent), a GT71 (issues with tilt due to adjustable flattener design otherwise good), and a TS 72 ED f6 photoline doublet (good value, a little 'flat' on contrast)

 

 

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Hi all, I purchased George's Redcat from him to  have a go at fixing it.

So far, I stripped the back down, took off the rear corrector, went into the middle lense and found 6 screws, 3 lock tighted, and 3 not, so I just took the tension off those 3 so just finger tight in case pinched optics.

I fitted the rear corrector (the one with springs) fully tight for now.

I couldn't get front off so far, but have removed all 6 screws in case pinched optics - being careful how  I move it now of course - nylon replacement screws ordered.

I took some subs last night - about 10 at 12800, 1/5th second  and stacked, and 3 at 3200/30 seconds and stacked. Here are the mosaics.

It doesn't look too bad to me now ? one corner is off, but this seems to not be unusual with red cats ? I've posted full res fits too. what do you think ? ignore the blobs - didn't do flats so just dust bunnies.

George - I hope you won't mind me posting - you wanted it to be fixed too, you just had had enough of faffing with it.

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redcat_test2_eq6_12800_RGB_session_1_crop_lpc_cbg_mosaic.png

redcat.test2.eq6.3200-RGB-session_1-lpc-cbg.stretched.fits redcat.test2.eq6.12800-RGB-session_1-crop-lpc-cbg.stretched.fits

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I'm using a canon 6d. And this is a FF DSLR I used for the test, to get the 'worst case'.. usually I'd be using with an asi533 or asi1600 so only using the middle bit of the lens.

I've read of others seeing square stars when the sampling is wrong for the lens. maybe this is cause here ? I was testing through an L-extreme also - since again, that would be what I'd normally use. So that's why the bright star is oii bloated.

 

 

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yeh, I've just ran it through Siril PSF, which is showing me loads of stars are below 2 pixels FWHM, so I think that means - square stars ?

It also means its focused well, and performing pretty well too I think ?

 

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On 02/05/2022 at 08:35, david_taurus83 said:

I hope you didn't buy it off somebody on here...

The least the seller should be doing is taking it back and returning it for a warranty repair on your behalf

 

Exactly this, they should take it back and return it to be fixed, terrible behaviour. 

 

Adam

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On 02/05/2022 at 13:33, George Sinanis said:

 I bought it from ABS. 

You really must report him to ABS they look very dimly on this type of behaviour and will ban him. 

Adam 

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Some folk are just nastly Adam. I bought and EQ6 from someone (not here)... the had an observatory, fancy expensive kit. etc. Nothing to not trust... but on getting home I found the screws all stripped, the ALT actually bolted solid, the '5 year old EQ6' turned out to be one of the first made (version of circuit board), and I'm still struggling to get it guiding nice... seller wanted nothing to do with it. Just makes me sad. Unfortunately ABS doesn't have a rating system.

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4 minutes ago, powerlord said:

 Just makes me sad. Unfortunately ABS doesn't have a rating system.

No but they do ban people for selling broken kit. :) 

Adam

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15 minutes ago, Adam J said:

No but they do ban people for selling broken kit. :) 

Adam

No use to the folk with the broken kit though and if you're prepared to sell shoddy kit it'll do absolutely nothing to stop them doing it again I'm afraid....

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3 minutes ago, scotty38 said:

No use to the folk with the broken kit though and if you're prepared to sell shoddy kit it'll do absolutely nothing to stop them doing it again I'm afraid....

Do you think a small claims court would be able to help?🤔

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31 minutes ago, powerlord said:

Some folk are just nasty Adam. I bought and EQ6 from someone (not here)... the had an observatory, fancy expensive kit. etc. Nothing to not trust... but on getting home I found the screws all stripped, the ALT actually bolted solid, the '5 year old EQ6' turned out to be one of the first made (version of circuit board), and I'm still struggling to get it guiding nice... seller wanted nothing to do with it. Just makes me sad. Unfortunately ABS doesn't have a rating system.

Unfortunately you are right and some people do not see to have a conscience at all.
Over the years I have become quite distrusting of people I do not know and wary wary of buying 2nd hand, although to be honest the much maligned Ebay is actually very good at getting your money back in cases like this, but still not bought any astro gear off them as generally just too expensive anyway.
That just seems to be how the world has gone over the past years, too may people just willing to con others for monetary gain.
I think what makes buying 2nd had astro stuff open to abuse is that pretty much all genuine Astronomers (whether visual or AP) are very trustworthy (well seems to me so far) and all genuine Astronomers seem to look after their gear extremely well and in cases something is wrong or even suspected wrong with the gear they are selling are very honest.
So as a result I tend to trust them more than I probably should, fortunately buying mostly of SGL and on add item off ABS have been well pleased with my purchases.
So when this sort of thing happens and the seller just turns their back on any issues it is quite shocking.

I think I will continue to stick to 2nd hand from SGL mainly.

Steve

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I think the forum community helps. A seller knows that if he is dishonest on here, folk will hear about it. And on ebay, you get hit with bad ratings, etc. On ABS, you get banned. so what, you use another email address.

I'll certainly be much much more careful in the future buying from ABS.

stu

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