Redcat 51 L-RC51II vs new L-RC51II-U model. What is the différence ?

According to the picture on WO website. A small change in appearance, hidden tilt adapter, everything is same. The fourth to last picture.

https://williamoptics.com/redcat-51-ii-u

The picture also states, "Please note that, unlike previous versions of the Redcat telescope, this latest II-U version CANNOT be used visually."

Quinn Groessl:
According to the picture on WO website. A small change in appearance, hidden tilt adapter, everything is same. The fourth to last picture.

https://williamoptics.com/redcat-51-ii-u

Wow, I don't know how I missed that.

I have the original RedCat 51 and since the new version has a tilt adaptor, this must be an issue with many users. I wonder then how you would correct tilt (if you had an issue) while on the original model? Any ideas?

Gerry:
Eric,

I have used the RedCat 51 years ago and found it to be an excellent telescope, but there new RedCat 71 is a good upgrade.  I purchased the 71 months ago and it is quite a better telescope.  Much like the 51 in features,  just better optics and able to get ore detail on deep sky objects.  Of course it's more expensive, so that most like would be something to consider. before you make a purchase.  i would recommend that you contact High Point Scientific, they are a good vendors that offer excellent customer service and willing to help you make the correct decision on your purchase.  I included a like to there web site with the RedCat scopes for your information.  Best of luck in your purchase.

Gerry D.

https://www.highpointscientific.com/shop?q=cat+red

Unfortunately here in Canada it's more than just more expensive,  it's twice the price.

If I go with the 71 I will have to stick to my modified 600d which I was going to change for a zwo ASI<some model>MC Pro to go with the 51.

Eric Gagne:
Unfortunately here in Canada it's more than just more expensive,  it's twice the price.

If I go with the 71 I will have to stick to my modified 600d which I was going to change for a zwo ASI<some model>MC Pro to go with the 51.

I gave a look at your current setup (from your posts) and if you are not planning on changing mount (Star Adventurer GTI), I would not consider the 71 if I was in your shoes. You would be pushing it to the very limit, especially if you decide to add a Guidescope + Camera.

The RedCat 51 v2 (or 2.5 if you only care about astrophotography) is a perfectly fine telescope, that pairs very well with the IMX533 (e.g. ASI533) or IMX571 (e.g. ASI 2600) sensors, and is a good match for you mount.
I have a very similar setup and even though I only posted one picture here on AstroBin, I have plenty more shots that turned out pretty good.

Some may say "wait, you are way undersampled!". To whom I answer: "dither+drizzle".

Eric Gagne:

Claudio Parisi:

Eric Gagne:
Unfortunately here in Canada it's more than just more expensive,  it's twice the price.

If I go with the 71 I will have to stick to my modified 600d which I was going to change for a zwo ASI<some model>MC Pro to go with the 51.

I gave a look at your current setup (from your posts) and if you are not planning on changing mount (Star Adventurer GTI), I would not consider the 71 if I was in your shoes. You would be pushing it to the very limit, especially if you decide to add a Guidescope + Camera.

The RedCat 51 v2 (or 2.5 if you only care about astrophotography) is a perfectly fine telescope, that pairs very well with the IMX533 (e.g. ASI533) or IMX571 (e.g. ASI 2600) sensors, and is a good match for you mount.
I have a very similar setup and even though I only posted one picture here on AstroBin, I have plenty more shots that turned out pretty good.

Some may say "wait, you are way undersampled!". To whom I answer: "dither+drizzle".

Yes I know the gti weight limit is quite low, no more than a 2i and not much more than my SAM but I wanted an affordable goto mount until I have the money for an AM5. 

For the moment I want 2 things.  First, more focal length than the Samyang 135, it is a great length but I want a little more.  I know the R51 is still wide field but some targets won't be so small anymore.

The 2nd thing is a cooled camera.  I really like the dslr but a cbuted camera will allow me to take darks at anytime leaving me more time for taking lights when I get a clear sky.

It feels like reading myself a few years ago

The GTI is enough for the RedCat51 (I have it on a 2i with it's superflimsy tripod). It becomes a bit challenging on a windy day but using some weights at the base of the tripod helps quite a bit.

The cooled camera is gonna be a game changer, for the reason you mention and many, many others.

Don't forget to dither and drizzle x2, and you'll end up with a lot of detail, even at the 250mm focal length of the RedCat.
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IMHO, you're on a good path!

On a GTI definitely nothing more than 2Kg of OTA.
Under what sky are you imaging? Bortle?
I don't think you'll need 10-15min of exposure to overcome the read noise of a cooled chip.

Probably not even of a 600D if it's cold enough outside. I used a 600D as well for a while and if I'm not mistaken I never needed more than 5min under dark sky.

Eric Gagne:
I'm under bortle 6 according to lightpollution.org but I think it's closer to 7.

OTA ?

Optical Tube Assembly... basically it means "telescope only", without brackets, filters, etc.
So 2Kg of telescope + whatever else you attach to it, and you get to the weight limit of the GTI. the RedCat51 by itself is 1.8Kg, so you are good to go.

In a roughly Bortle 6.8 you are getting ~7 e/px/s (electron per pixel per second) from the sky background, without any filter.
I don't recall the read noise of the 600D (it also varies with ISO) but, in general, there are diminishing returns after Read Noise < 10% of Sky Background.
At a given point is better to shorten the exposures to avoid satellites, wind vibrations, guiding errors, etc.
Losing a 10 or 15 minutes sub is way worse than losing a 2 or 3 minutes one for the reasons above.