William Optics RedCat Erecting Prism Diagonal and CatEye 10mm Eyepiece

[Buzzard75]

I now have both in hand. I was on the WO page last week and just happened to be looking at the erecting prism diagonal when I realized it said it was in stock. I immediately purchased one along with the CatEye 10mm eyepiece. A day or two later I got an email from WO telling me that the only diagonals they had available were in silver. While I certainly would have preferred the red, I accepted the silver as I knew the red would be the most desirable and it could be some time before I would get one. I just received them today so I haven't had much opportunity to try them out other than a little terrestrial viewing from my front porch and out my back window. I'm not at all qualified to give a thorough optical test and review of these items. I will say that the eye relief and field of view of the CatEye coupled with the RedCat is excellent in my opinion. The image is even clearer and sharper than my Leupold spotting scope that I paid almost twice as much for to use with target shooting. As for the diagonal, it's what you would expect from WO in terms of quality. It's a solid little piece. My only complaint is that you have to remove the adapter on the RedCat to install the diagonal as the diagonal has male M56 threads that screw into the body of the scope. I would have rather seen it just screw onto the M48 threads of the adapter that you attach your camera to. Removing the adapter from the scope requires you to loosen three small set screws. The adapter is where you would also install any 2" filters, as the inside has M48 threads. Swapping from diagonal/eyepiece to camera or the other way around in the field is going to be a bit fiddly and not something you're going to want to do often. I'm sure there is an adapter out there somewhere to go from M56 to M48 threads and I may look for one. The opening on the diagonal is still considerably smaller than the backend of the scope. I don't know why they would have made that design choice. Overall though, I'm happy with them both. Can't wait for some clear skies to try it out though. Friday and Saturday night both look really good so I may try some planetary imaging with my dob one night and some widefield with the RedCat the other.

[Louis D]

Are both the diagonal AND the eyepiece erecting?  Seems weird to use them together.

I have a feeling the RedCat won't reach focus with the M48 thread (less than 60mm of backfocus at that position) and diagonal (generally around 64mm of optical path for a prism), thus the M56 thread (78mm of backfocus).

M48 step rings are plentiful, but M56 step rings are very uncommon.  Adding those extra step rings will almost certainly prevent you from reaching focus.

[Buzzard75]

6 minutes ago, Louis D said:

Are both the diagonal AND the eyepiece erecting?  Seems weird to use them together.

I have a feeling the RedCat won't reach focus with the M48 thread (less than 60mm of backfocus at that position) and diagonal (generally around 64mm of optical path for a prism), thus the M56 thread (78mm of backfocus).

M48 step rings are plentiful, but M56 step rings are very uncommon.  Adding those extra step rings will almost certainly prevent you from reaching focus.

No, both are not erecting, just the prism diagonal. It provides a corrected image and everything is up/down/left/right as if you were looking at it without a telescope. The eyepiece is just a normal 10mm eyepiece. There aren't a lot of details on its construction other than it's a 10mm eyepiece with an AFOV of 60 degrees. I have no idea how many lenses or groups are in it.

It's possible it won't reach focus, but I had to rack the focuser pretty far to get focus on an object in the distance. Granted the object in the distance wasn't dozens of light-years away and essentially at infinity. I'll try it out when we get some clear skies and check the focuser measurement. I'll hold the diagonal with the eyepiece in it up to the adapter and see if I can reach focus.

 

[Louis D]

I found my misreading of WO's description.  I glossed over the word optional for the RedCat erecting prism:

CatEye 10mm

Be the first to review this product

In stock

SKU E-CE10

$99.00

Optional

1.25 inch RedCat erecting prism (For RedCat 51 only) + $99.00

[Buzzard75]

You were correct. Focus was just out of reach with both the adapter and the diagonal. Needed just a bit more inward focus.

That being said, it turns out it's a fantastic little scope for observing. Views of the moon with the diagonal and CatEye were extremely crisp and sharp. The view is flat and in focus all the way to the field stops. When viewing Jupiter, I could also see a hint of the major bands. It's a nice, compact scope and all you need is a standard tripod and ball mount once you flip the foot over.

[Louis D]

10 minutes ago, Buzzard75 said:

You were correct. Focus was just out of reach with both the adapter and the diagonal. Needed just a bit more inward focus.

That being said, it turns out it's a fantastic little scope for observing. Views of the moon with the diagonal and CatEye were extremely crisp and sharp. The view is flat and in focus all the way to the field stops. When viewing Jupiter, I could also see a hint of the major bands. It's a nice, compact scope and all you need is a standard tripod and ball mount once you flip the foot over.

So, a super expensive, but super good, 51mm spotting scope? 🤔

[Buzzard75]

46 minutes ago, Louis D said:

So, a super expensive, but super good, 51mm spotting scope? 🤔

Yes and no. I can't take pictures with my spotting scope (because it has a specialized eyepiece that screws in) which suffers from chromatic aberration and cost me twice as much. The only thing my other spotting scope has going for it is the larger aperture. High quality spotting scopes are not cheap either. I would say it's a fair price for what you get. You may be just as well served getting a high quality 60-70mm refractor, but you're probably going to pay just as much, if not more. I'll post an image I took with my DSLR when I get home.

[Buzzard75]

For what it's worth, the CR2 file is the RAW file straight from the camera, a Canon 750D (t6i). The jpg is a simple edit. All I did was crop it, mask the moon and do levels adjustments. No sharpening, no RAW camera filters, no curves, nothing. I was actually surprised I nailed that focus as close as I did just using live view. Settings were 1/250s and ISO-200.

IMG_4127.CR2