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CCD Imager

William Optics Redcat 51 Short review for imaging

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For the last few years, I have been looking for a good refractor telescope with a focal length around 250mm. I have the Tak FSQ, but even with the reducer can only get down to around 390mm FL. Those wide field vistas of the North American and Pelican nebulae come to mind. Camera lenses can be good, but they are a pain to focus and give odd shapes to brighter stars due to the aperture blades. The best I have used in the past was a Canon 200mm lens

Picked up the WO Redcat 51 last weekend and so far have managed a one short sessions imaging with it. I used the Redcat 51 with an ASI 183 camera on top of a rather overkill 10 micron GM2000HPS, but as this week has been very windy, probably a good choice of mount!

The little scope comes in a soft case with plenty of space for accessories if needed. It looks very well made, robust with an excellent finish, not so sure about the cat with whiskers logo though! There is a rear M48 male thread with dustcap and a front dew shield with cap that includes a Bartinov mask which is opaque, so renders brighter star images than previous metal versions. I bought an £8 M48 to T adapter to allow a threaded connection to my camera. The dew shield needs to be unscrewed, reversed and re-threaded ready for action. This also reveals the helical black focusing ring that is easy to operate. I found the focuser to be very smooth with just the right amount of tension and using the Bartinov mask was straightforward, achieving focus within a minute at most.

Being a petzval design means no additional field flattener is required, an often forgotten and costly addition to other refractors in this range and also no need to get the perfect distance from reducer to CCD/CMOS sensor, the Redcat 51 is literally plug and play, a big advantage of a Petzval design.

How is the optical quality? To some extent and because of over-sampling with CCD/CMOS/DSLR’s, the optical resolution is not so critical, nevertheless I used the ASI183 with 2.4 micron pixels to give sampling at 2 arc sec/pixel. After taking a test image, I examined the corners where the stars appeared round with no obvious aberrations, next  I checked focus for each RGB filter and stars appeared to maintain the same focus position, indicating no or minimal chromatic aberration and no blue bloat that can often be seen with less quality optics, particularly doublets.

So far, so good, but I have found an issue with slight out of focus stars to the right of the frame and this could be due to a number of factors which I need to debug with a second imaging session. Its minor, but I want to get to the bottom of it.

My experience so far has been pleasurable, it's easy to setup, achieve focus and as its such a small package it will be great for taking on holiday. I've just purchased a modified Fuji X A2 for less than £200, so coupled with this gives me a system free from laptops and electricity cables.

Two pictures shown, one of the setup and one first ‘light’ – 800 secs each RGB of M37, so only 40 minutes total

IMG_1014.JPG

M37-RGB-image-St.jpg

Edited by CCD Imager
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Looking good then, eagerly awaiting Redcat delivery from FLO when WO decide to part with some :rolleyes:

Don't think I'll be putting it on the 10Micron though more like the Star Adventurer.

Dave

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Yes, the Star Adventure is the exact mount I will take on holidays with me

Adrian

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Nice review! :)
 

Looks like the right side has a slight coma....

But looking at the setup image, - it is probably related to camera tilt - not optics :)
I want it more now!!!!

Bad boy!

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22 minutes ago, Tubby Bear said:

Can you clarify the rear thread size : i thought it was a M48 size, not M42 ??

I'm sorry,, a typo, yes its M48

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20 minutes ago, RolandKol said:

Nice review! :)
 

Looks like the right side has a slight coma....

But looking at the setup image, - it is probably related to camera tilt - not optics :)
I want it more now!!!!

Bad boy!

I agree with you and I will be able to determine this the next clear night and hopefully the cause

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Trying to wrap my head around exactly what I would need to adapt both a Canon DSLR and and ZWO ASI178MC. The DSLR is easy as there are EOS T-mounts with M48 threads that give you the exact spacing required. What I can't quite suss out is the ZWO camera. The T2 ring on the ASI178MC, and the ASI178MC itself, has M42 threads. Would I just then need an M48 to M42 adapter? Would I need any spacers since I'm not using a filter wheel? Do I need to remove the T2 ring and attach the camera directly using a female-female adapter? No one has posted any close up pictures of the connections between the scope and such a camera yet or detailed exactly what they used.

It's hard for me to visualize without one in my hand and know exactly what I need to get the correct spacing and I don't want to buy a bunch of extra parts that I don't need and I certainly don't want to wait until I get the scope only to find out I don't have everything and have to wait even longer. Doing the math in my head, with the T2 ring, the camera sensor is 12.5mm back from the face of the T2 ring, the WO M48 to M42 adapter is 7.2mm (Not sure this is correct as it just says this is the thickness, not the spacing). The mechanical drawing says the focal plane is 59.7mm behind the M48 threads. I would still need an additional 40mm (59.7-12.5-7.2=40) of spacing is that correct?

 

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Because its a quadruplet design, you dont need worry about spacing. The spacing is the focal point behind the rear 2 elements and there is plenty of focus travel to achieve this with a DSLR or CCD/CMOS camera. Altair Astro or Ian King Imaging both sell M48 to T2 adapters that will connect the ZWO camera to the scope.

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