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William Optics GT71 vs William Optics RedCat 71

Refractor Astrophotography Equipment
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#1 Sep_f

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Posted 27 November 2021 - 08:30 AM

Hello, there everyone I have been looking for a new telescope and I'm choosing between two refactor telescope the William Optics GT71 or the William Optics RedCat 71 can someone help me and find out witch one is better or deep sky astrophotography and also find out the differences between the both. Thank you vary much



#2 900SL

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Posted 27 November 2021 - 08:51 AM

I have the GT71 with the 0.8 flattener. It's excellent.
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#3 Jaimo!

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Posted 27 November 2021 - 09:21 AM

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#4 bobzeq25

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Posted 27 November 2021 - 09:31 AM

Hello, there everyone I have been looking for a new telescope and I'm choosing between two refactor telescope the William Optics GT71 or the William Optics RedCat 71 can someone help me and find out witch one is better or deep sky astrophotography and also find out the differences between the both. Thank you vary much

Something to consider.

 

Learning DSO AP is a difficult task.  An easier setup to use is very useful for the purpose.  That's the Redcat.  The GT will need a field flattener, and some work to space it properly.  That's more significant than you may think right now.

 

To paraphrase a classic saying (and it's the truth).  I've had triplets and I've had quadruplets.  Quadruplets are easier.


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#5 Topographic

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Posted 27 November 2021 - 09:32 AM

I have a redcat 51, it has been excellent, choosing between the two at 71mm I would look at a few  things, both triplets, both FPL triplet glass. Price, Redcat much more expensive, less so if you add flattener and rotator to the basic GT setup. Very similar speed (with reducer). So how do you choose. Do you like the focusing mechanism of the Redcat or prefer the more traditional GT focuser, do you want to bother with a flattener, does backfocus fill you with trepidation on the GT.

 

I don't think performance is likely to be much different.

 

So personal preference, toss of a coin, which is actually in stock



#6 Rasfahan

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Posted 27 November 2021 - 09:54 AM

Since I have yet to see an example of a good RedCat 71 I recommend to buy with a generous return policy. I don‘t think fitting a flattener correctly is much of an added problem. The price of the RC is very high for what it is (and far too high for the performance I’ve seen so far). But so is the other WO scope when you add necessary accessories such as a flattener. It‘s difficult to buy quality for AP. I know everyone recommends a small refractor to start out, but if you ask for great quality < 4“, the same everyones become very quiet, very fast. My recommendation would be an Esprit 80ED if your mount can handle it. In any case, maybe you can get your vendor to test and collimate the scope before delivery.



#7 Topographic

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Posted 27 November 2021 - 10:30 AM

Since I have yet to see an example of a good RedCat 71 I recommend to buy with a generous return policy. I don‘t think fitting a flattener correctly is much of an added problem. The price of the RC is very high for what it is (and far too high for the performance I’ve seen so far). But so is the other WO scope when you add necessary accessories such as a flattener. It‘s difficult to buy quality for AP. I know everyone recommends a small refractor to start out, but if you ask for great quality < 4“, the same everyones become very quiet, very fast. My recommendation would be an Esprit 80ED if your mount can handle it. In any case, maybe you can get your vendor to test and collimate the scope before delivery.

Given that the Redcat 71 has only been around for a matter of a couple of weeks or so I think that is a little harsh. Wouldn't argue with the Esprit, they tend to have a good reputation. Tested and checked at First Light Optics in the UK.



#8 m2434

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Posted 27 November 2021 - 11:39 AM

Just went through this. Went with the gt. Prefer the focuser, color correction and f-ratio with the reducer. Have limited sky in my yard and need to spend less time on targets. I doubt there is any practical/noticeable image quality difference for processed images. The red cat is really cool, and my heart wanted one more. However, for me, not really any justification for the extra $600 from a practical view, other than to say I have a cool, red petzval (I’m not dismissing that as a valid justification 😀). Have had other WO scopes and their reducers work pretty good, with any ccd I can afford, once adjusted, so the “flat field” wasn’t enough of a driver either.

#9 gzljh96

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Posted 28 November 2021 - 08:03 AM

Keep in mind it’s basically not possible to use the RedCat visually. If the RC71 has the same mechanism as the smaller one, then you need to remove the tilt adjuster to install the diagonal and that process will probably introduce tilt once you fit it back on.

Askar’s FRA400 and in Europe Teleskop Service’s TS71 (SkyRover 70SA/Meade Quad) have very similar designs with no need for backspacing. Both of those are cheaper than the RedCat and might be something you want to consider.

#10 unimatrix0

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Posted 28 November 2021 - 09:59 AM

Since I have yet to see an example of a good RedCat 71 I recommend to buy with a generous return policy. I don‘t think fitting a flattener correctly is much of an added problem. The price of the RC is very high for what it is (and far too high for the performance I’ve seen so far). But so is the other WO scope when you add necessary accessories such as a flattener. It‘s difficult to buy quality for AP. I know everyone recommends a small refractor to start out, but if you ask for great quality < 4“, the same everyones become very quiet, very fast. My recommendation would be an Esprit 80ED if your mount can handle it. In any case, maybe you can get your vendor to test and collimate the scope before delivery.

The redcat 71 is a 4-lens Petzval design and doesn't need a flattener.   

 

Beside that , I still think it's too expensive, considering that the WO GT71+flattener is around $1200    while the Redcat 71 is $1700  and the Wo GT71 is a crayford focuser, while the redcat71 helical focuser.  if someone considering motorizing the focuser, the GT71 has plenty of choices for autofocuser, the redcat71 maybe only 1 as I have heard, the same one who made it for the redcat 51



#11 Rasfahan

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Posted 28 November 2021 - 11:00 AM

I was referring to fitting a Flattener with correct distance to a scope like the GT71.

#12 OldManSky

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Posted 29 November 2021 - 09:09 AM

...and the Wo GT71 is a crayford focuser, while the redcat71 helical focuser.  if someone considering motorizing the focuser, the GT71 has plenty of choices for autofocuser, the redcat71 maybe only 1 as I have heard, the same one who made it for the redcat 51

Actually the GT71 is a rack and pinion focuser, not a Crayford.

Your comment about motorizing is certainly correct, though -- fitting a ZWO EAF or a Pegasus Cube is a less than 10-minute operation on the GT71.  It requires adapters and belts and mounts and other accessories for the Redcat.

 

I love my GT71.  It's extremely sharp, well-corrected, well-built.  With the Flat6AIII and a tiny bit of tweaking, stars are wonderful all the way to the edges of an APS-C field.  

I also have an Askar FRA500 (90mm 5-element Petzval).  It's really nice to not have to worry about spacing (same as on the RC71).  But the focus setup on the RC71 -- I just don't get why WO would make these Petzvals designed for imaging and then put on such a pain-in-the-butt focuser. :(


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#13 davidparks

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Posted 29 November 2021 - 03:39 PM

Some differences to consider:

 

GT71 is designed for both visual and imaging.

Redcat 71 is designed for imaging  (I can't even confirm that the Redcat 51 diagonal will work with the 71, but regardless, it's made for imaging)

 

GT71, you may want the Camera Rotator, at an additional cost.

Redcat has camera rotator built in.

 

GT71 is a triple, so it has color correction 'built in'.  You would need the Flat6AIII for a flat field, at an additional cost.

Redcat is a quad, so it has both color correction and flat field 'built in'.

 

GT71 uses a rack & pinion focuser, which moves a rear drawtube.  You will need to mind and manage backfocus for any and all accessories, including the Flat6AII, OAG, Filter Wheels, Camera Body, etc.

Redcat is a Petzval design with helical focuser which moves the inner and object lens front side.  You won't really need to worry about backfocus, as long as your image train comes to focus.

 

GT71, you  may want/need a tilt adjuster, some CMOS cameras have this built in... so this may be camera dependent. I don't think DSLR's have built in tilt adjustment.

Redcat has tilt adjuster built in, regardless of what camera you use.

 

Speaking of 'tilt' also puts me in mind of 'sag', and focus creep.  Sag can occur if the weight of your image train flexes the focus draw tube.  Creep can occur, particularly at high angles near the zenith by the action of gravity on the weight of your image train.  There are simples ways to respond to creep, such as focus locks.  I'm not sure how you would respond to Sag.  The Redcat won't experience Sag (no draw tube), and I've never seen or heard of a helical focuser ever creeping, however, the Redcat has a focus lock built in.  I believe the GT also has a built in focus lock via a thumbscrew.  The GT under 'usual' circumstances also should not experience Sag, but R&P focusers have weight limits, so be mindful.

 

Speaking of focuser preference... Po-TAY-to, Po-TAH-to...  some people prefer rack-pinion, it's more "telescope-ish", others prefer helical, it's more "dslr lens-ish".

Motorizing either is about the same to me, same effort, same pieces, parts.... pulley vs coupler, bracket, mount.. whatever, once it's done, it's done and works well for both... It may not be a deciding factor, but might be worth considering.  Also may not be a deciding factor, but an "in-line" helical focuser is easier to case, with or without a focus motor, particularly if you hard-case it (instead of using the soft case that comes with)

A perpendicular focuser, particularly with motor attached, is much more challenging to case, even requiring you to remove the focus motor.   Also, it can throw off the balance of the mount (which may or may not matter)

 

GT71 focal length is 419mm

RC71 focal length is 348mm

Comparing results, assuming you are using the Flat6AIII with the GT, are about the same, as expected with their glass and differentiated by their focal length. Not a strong difference for or against either way.

 

Price difference:  You know how to shop, so I'll let you do the math...  What's In Your Wallet?

 

Ease of Use:  The Redcat, because it's both a Quad and a Petzval, is easier to use.  Not that the GT71 (or other triplets, flatteners, rack & pinion) are that difficult, they are pretty easy too.  But on a 5 point scale where a Redcat is a 5, the GT71 would be a 4.  Possibly not enough to be a deciding factor, but a notable observation either way.

 

So there are some of the difference between the two...

Which one is best for deep sky astrophotography, or which is best for you?  You tell us lol.gif


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#14 TareqPhoto

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Posted 30 November 2021 - 03:52 AM

Good that i bought FRA400 before WO decided to release RC71, and even if i have to buy 70mm aperture scope between those two WO scopes i will go with GT71 anyway.




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