15 replies to this topic

[rodsager]

I made an image of M42 with a cheap Orion 80mm f/5 achromat using an APSc camera with a 0.71x Metabones focal reducer. I was really surprised at how well it came out considering all the chromatic aberration and the simple achromat doublet optics. It worked perfectly on my little SkyTracker Pro. This got me thinking how nice it would be to have a proper imaging refractor. I really want to be able to use it on that little SkyTracker and an optical tube assembly around 3 to 3.5 lbs works with my camera and focal reducer.

 

I have been thinking about purchasing a used Redcat 51 for wide field imaging. I have seen images made with these small light weight refractors that are amazing and I am intrigued. I can run that on my lightweight SkyTracker. Having a lightweight setup will help encourage me to go out in the backcountry away from my Bortle 7 skies and get better images. Then I stumbled onto a sale right now at Astronomics on the Astro-Tech 60 ED which is a doublet with one FPL 53 element and one Lanthanum element. I really like imaging at around FL 300mm. The Redcat is 250mm f/4.9 the AT 60 is 360mm f/6. Of course I'll need a flattener and AT makes a .80x flattener that is reasonably priced. At .80x I end up with f/4.8 so exposure time is about the same as the Redcat. I like the extra focal length even with the flattener it's still 288mm and having a bit more aperture is usually nice. The AT will also make a nice grab and go telescope for visual, the Redcat not so much.

 

So I am torn on which is the better path. Theoretical resolution is higher on the larger 60mm scope but whether that will materialize on a camera is another thing altogether. The primary use will be imaging but the notion of having the ability to use it visually with good results is nice. 

 

I am trying to stay at around $500ish budget, that's why the Redcat is used and the AT 60ED is new. Is the Redcat's premium Petzval optical train that much better than a quality ED doublet with a flattener? Which would you choose and why? 

 

 

[Andros246]

I would take the sharper optics being the redcat.

Even with fpl-53 I’m done with doublets.

You’ll still get some CA my fpl-53 doublet has bloat.

You’ll be able to resolve finer details with the redcat just because the optics are sharper even though the AT has more aperture.

Edited by Andros246, 16 February 2025 - 10:33 PM.

[DeepSky Di]

Which RedCat? There are 3 generations. The v3 has a WIFD focuser; the V1 and V2 have a helical focuser that needs a belt drive addition to fit an EAF. I find my V2 less convenient for travel because this additional bracket to hold the belt and EAF works great but is not designed for easy fitting and removal.

[daveco2]

I have an AT60ED.  The narrow section at the bottom of the attachment foot acts like a spring when you put a camera at the rear of the scope.  I added an extra saddle to mine.

I also added the AT 1X flattener and found its true back focus position to be about 15 mm from advertised, but I got it to work.  Otherwise, the scope is fine.

[John Berger]

+1 for Redcat

[The0s]

As a biased Redcat user, I'd say Redcat 51 all the way. The AT60ED is by no means a bad scope (plenty of people on this forum have had a lot of success with it), but I've always found the images from doublets (even higher end apochromatic ones) to be less sharp and to have more bloat in the blue channel (there's a good post somewhere on this site with sample images showing this) compared to Petzvals. Plus, with the Redcat you won't have to deal with back focus issues and since it's already used, it'll have better resale value if you ever decide to upgrade.

 

Edit: Found the CN post I mentioned above

Edited by The0s, 17 February 2025 - 12:31 AM.

[rodsager]

Which RedCat? There are 3 generations. The v3 has a WIFD focuser; the V1 and V2 have a helical focuser that needs a belt drive addition to fit an EAF. I find my V2 less convenient for travel because this additional bracket to hold the belt and EAF works great but is not designed for easy fitting and removal.

There are plenty out there the Version one is often under $500

[rodsager]

I have an AT60ED.  The narrow section at the bottom of the attachment foot acts like a spring when you put a camera at the rear of the scope.  I added an extra saddle to mine.

I also added the AT 1X flattener and found its true back focus position to be about 15 mm from advertised, but I got it to work.  Otherwise, the scope is fine.

I would put an Arca Swiss plate on it for the little Sky Tracker and a small vixen dovetail for any of my other mounts. 

Edited by rodsager, 17 February 2025 - 01:25 AM.

[rodsager]

As a biased Redcat user, I'd say Redcat 51 all the way. The AT60ED is by no means a bad scope (plenty of people on this forum have had a lot of success with it), but I've always found the images from doublets (even higher end apochromatic ones) to be less sharp and to have more bloat in the blue channel (there's a good post somewhere on this site with sample images showing this) compared to Petzvals. Plus, with the Redcat you won't have to deal with back focus issues and since it's already used, it'll have better resale value if you ever decide to upgrade.

 

Edit: Found the CN post I mentioned above

Thanks for fishing out the article.

[matt_astro_tx]

I use the AT60ED with the 0.8x reducer on a star tracker.  Over time I've added auto guiding, an EAF, and the ASIAir.  It is a mighty combination and, in fact, it's outside imaging the southern pinwheel galaxy right now.

 

 

I really like the AT60.  Yes it does exhibit some CA but with todays tools, namely starnet++, as long as you don't saturate the stars I find the CA is easily managed by not stretching the stars too hard during recombination.

 

The telescope weighs in the 3.5lb range, and with all of my accessories and cabling included my total weight is 7.7lbs.  That's easily manageable for the star tracker's 11lb capacity.

 

All of that being said, I think the Redcat 51 wins this fight. Sharper optics, little to no CA, and no fighting with back focus.

 

But if the AT60ED is closer to your budget, and if the smaller field of view is what you're after, then by all means go for it!

 

Edited to add:

 

Here are a few recent images taken with my AT60 and ASI183MC Pro.  

 

Note that you can see the CA I mentioned on the brighter blue stars in this first image of Messier 22 and the Sag. Star Cloud.  That's because in this "star only" image I couldn't do any star separation.  So my only CA controls were 1. stretching and 2. saturation.  I balanced them as well as I could and even with the CA I'm pleased with it.

 

 

 

Edited by matt_astro_tx, 17 February 2025 - 04:37 AM.

[rodsager]

I would take the sharper optics being the redcat.

Even with fpl-53 I’m done with doublets.

You’ll still get some CA my fpl-53 doublet has bloat.

You’ll be able to resolve finer details with the redcat just because the optics are sharper even though the AT has more aperture.

I bought a Redcat, but after looking at its design it is basically an ED doublet with a field flattener. One of these days I will get a quintuplet  

[rodsager]

 

I use the AT60ED with the 0.8x reducer on a star tracker.  Over time I've added auto guiding, an EAF, and the ASIAir.  It is a mighty combination and, in fact, it's outside imaging the southern pinwheel galaxy right now.

 

 

 

I really like the AT60.  Yes it does exhibit some CA but with todays tools, namely starnet++, as long as you don't saturate the stars I find the CA is easily managed by not stretching the stars too hard during recombination.

 

The telescope weighs in the 3.5lb range, and with all of my accessories and cabling included my total weight is 7.7lbs.  That's easily manageable for the star tracker's 11lb capacity.

 

All of that being said, I think the Redcat 51 wins this fight. Sharper optics, little to no CA, and no fighting with back focus.

 

But if the AT60ED is closer to your budget, and if the smaller field of view is what you're after, then by all means go for it!

 

Edited to add:

 

Here are a few recent images taken with my AT60 and ASI183MC Pro.  

 

Note that you can see the CA I mentioned on the brighter blue stars in this first image of Messier 22 and the Sag. Star Cloud.  That's because in this "star only" image I couldn't do any star separation.  So my only CA controls were 1. stretching and 2. saturation.  I balanced them as well as I could and even with the CA I'm pleased with it.

 

 

 

 

Those are great images

[rodsager]

Thanks for fishing out the article.

I bought the Redcat but technically it is an ED Doublet with a field flattener built in. I am going to use the heck out of this Redcat but like I mentioned to another poster, I want a quintuplet

[soojooko]

I bought the Redcat but technically it is an ED Doublet with a field flattener built in.

Not quite. A doublet + flattener will not colour correct as well as a RedCat. Plus, unlike a doublet+flattener, there's no accurate backspacing to worry about with the RC.

[Andros246]

I bought a Redcat, but after looking at its design it is basically an ED doublet with a field flattener. One of these days I will get a quintuplet

You think that until you look at side by comparisons of them and or the spot graphs, don’t worry there’s a big difference.

Edited by Andros246, 26 February 2025 - 08:34 AM.

[dx_ron]

I bought the Redcat but technically it is an ED Doublet with a field flattener built in. I am going to use the heck out of this Redcat but like I mentioned to another poster, I want a quintuplet

I expect the Redcat will make you happy and keep you happy for some time. If you really have the urge to try a triplet objective, you could watch for an AT65EDQ to come up in the classifieds. No longer made, but a really nice little scope - and they should sell for not much more than a new AT60ED.