NGC6188 Redcat 51 first light

[gregbradley]

I recently got a William Optics Redcat 51 petsval lens/scope.

Its a beautifully made instrument and looks fantastic with its red anodising. It matches the annodising on a PME mount.

I was concerned about what its optical performance would be after reading some threads where there were some problems and others where it was good.

I imaged with it using both a Canon EOS R full frame mirrorless and a Sony A7Riii full frame mirrorless.

The usual suspects - Eta Carina, Rho Ophiuchi, NGC6726, Running Chicken, LMC.

It has a very narrow critical focus zone so its fairly easy to tell if its focused or not. Turning the focus ring it clearly goes in and out of focus rapidly.

I am using it manually focused. It comes with a Bahtinov mask but I haven't used that yet.

Stars seem quite good in the corners, perhaps some not perfect but overall quite good. I am also currently using it with a FLI Microline 16. Some images of Vela look fabulous.

I have been using a Pentax 645 F4 EDIF lens and the Redcat 51 is similar but overall better. The Pentax is no slouch so that is statement in itself.

Here is one image from the first set of deep sky images I intend to bore you with!

Mounted piggyback on an AP1600 at my dark site under good seeing and clear skies. NGC6188 was quite high in the sky as well. It was autoguided.
I used an external intervalometer.


https://pbase.com/image/169325482/large

https://pbase.com/image/169325482/original

Greg.244977

[RobF]

Very nice widefield Greg.
Was wondering when someone would put one of these through its paces.

[Peter Ward]

Remarkably wide field, and great to see the lens performs as advertised.
Nice one :thumbsup:

[gregbradley]

Thanks Rob,

I've had it for a little while and only gotten around to processing some of the images I have taken with it.



Thanks Peter.

The very corner stars are a little off in some corners - nothing to worry about but in the pursuit of perfection I have gotten a tilt/tip adapter from Teleskop Services (M48 version) that should enable me to fine tune it.
I am using it with my Microline 16 and I packed it out on one corner so all 4 corners are pefect with that so I know its merely a minor tilt adjustment needed.
Its a beautifully made little unit and the focus ring is nice to work with and it holds focus well. All manual of course.

A micro FSQ. I am surprised there aren't more scopes out there using the Petsval design.

Greg.

[Paul Haese]

Expansive View Greg, nice colour by the looks, but maybe just a little saturation pushed. The high res shows some saturation artifacts. Can I also see some tilt in the top let and top corners too? Overall a promising scope though.

[gregbradley]

Me oversaturate an image?? hehehe

OK I toned it down a tad and its more natural. Thanks someone has to keep me inline hehe.

Yes there is some minor corner issues. I have the tilt /tip adapter now to correct this. I got it pretty spot on using my Microline 16 and some packers so it shouldn't be too much of a problem.

Greg.

[willik]

Hell of a wide field Greg with that refractor looks good
Martin

[gregbradley]

Thanks Martin.

Yes its very widefield. I could afford to crop out bad corners if it comes to that.

Greg.

[RobF]

Would be interested to hear a bit more on your thoughts for this versus high quality lens for widefields Greg. Believe you had fair bit of experience with Pentax medium/large format lenses, which presumably take a bit of work to mount, attach cameras, sort out adaptors, focus.

Even though the Redcat is about $1000 aud, cost of sorting the issues above is probably significant too. Must be advantages in convenience, use of standard astro threads/mountings for dovetails and cameras etc?

[multiweb]

Looks great Greg. :thumbsup: I always wondered about the field color difference in my shots between left and right of the claws but now seen in the wider context realise it's real and not a gradient.

[strongmanmike]

Nice sharp FOV that Greg, any minor imperfections in the edge star images are largely inconsequential to me :thumbsup:

Mike

[codemonkey]

Nice one Greg. I saw the Redcat in passing but hadn't really taken it seriously before now. I have been wanting something short to pair with the QHY178m, looks like this might do the trick...

[gregbradley]

The Redcat is very well made and beautiful to look at. The focuser on mine is slightly stiff but this a good thing as I did read an early model had some shift at different angles and the solution was to tighten the focus lock ring.
I think it will loosen over time and I can still focus it precisely manually.

Stars are quite good to the corners with some images showing some weaker stars in the corners. I am also currently using it at home mounted on a FLI Microline 16 and I had to pack out one corner to get all 4 corners with round stars which I am getting.

I also got a Teleskop Services tilt/tip adapter M48 size that should simply screw onto the end of the Redcat and I can adjust it one night for my full frame cameras to get them as perfect as I can. Probably take me an hour. This adapter I think cost around AUD$80 perhaps less.

The cameras are mounted on T rings and the Sony adapter is a larger one and also very well made. William Optics are now offering a copper T ring adapter for Canon and I'll probably get that to see if that corrects the tilt or not. T rings were about $15 each but the Sony one was more like $40.

I have been using a Pentax 300mm 645 F4 EDIF at about F5.2 with a step down ring. It gives good results, also had to be packed out to get round stars to the corners. Almost the same as the Redcat.

The Redcat though is noticeably sharper and stars are tighter. The Pentax is no slouch though and cost me around AUD$650 or less.

The Redcat also offers a custom diagonal for visual. I would think 51mm is a tad small for visual but maybe its not.

Overall I prefer the Redcat's 250mm focal length as its long enough for many wide objects on a full frame camera but shorter than 300mm. Not a big deal though.

I really did like some downloads I got on Vela using the Redcat. I'll have to process that little mosaic.

The cost of the Redcat is more like $1200 and with the exchange rate falling more like $1300 so you'd have to want to do widefield for that.

Keep in mind its much the same optical design as a Tak FSQ - Petsval.
Not a lot of those around besides the FSQ and the TV NP scopes.

Greg.

[gregbradley]

Widefields are good for that sort of thing. Also seeing how objects fit in to the surrounding environment.



Cheers Mike. Yes in a widefield like this you are only going to see a few wonky stars by pixel peeping but we all like our stars to be round in the corners. A bit of cropping or a bit of time sorting out some tilt will handle it. On my ML16 I have it sorted and am getting nice sand like specks of stars and round to the corners. Not sure if the Proline 16803 will make it round to the corners - I doubt it and its not specified to be able to either.

I agree we can obsess sometimes about star roundness and take it too far.

Greg.



Smaller sensors will have an easy time of it. This image was with a full frame sensored camera 36x 24mm I think it is.

Correcting for a bit of tilt has become standard practice for me anyway.

Greg.

[Ryderscope]

A lovely wide field view Greg. Looks like a good combination of gear.

[gregbradley]

Thanks Rodney.

I am also still learning the best approach to processing these DSLR type images. This one used Adobe Lightroom and Photoshop.

Greg.

[Retrograde]

Congrats on a very nice first light. The Redcat sure looks like a great little instrument. :thumbsup:

[RobF]

Thanks for the extra detail Greg
Looking forward to any future images

[gregbradley]

Thanks for that Pete.



I have a few already and more to come. Probably already have about 6.

Greg.

[topheart]

Awesome Greg.
Sounds and looks like a great bit of glass you have there!
I look forward to more of this.
Cheers,
Tim

[gregbradley]

Thanks Tim. I am quite happy with it. Its somewhere between a camera lens and a telescope.

Greg.