Recat 51 or Vixen FL55ss? (late runner GT71 wins by a head ;) )

[900SL]

I'm a novice to imaging and I use a Fornax LT2 with a D5600. I'm looking for a wide field refractor and  I don't want to go above 60mm due to weight, difficulties in accuracy of framing and tracking.

I've pretty much narrowed my choice down to either a Redcat 51 or Vixen 55

The Vixen is my preference but after a couple of man-days googling I'm unsure as to how good the coma is on this scope. I've seen some great images and also some with significant peripheral aberrations.

I don't know if these are a result of incorrect backfocus, tilt, or intrinsic to either the 300mm flattened image or the 240mm flattener/reducer. I've seen some excellent examples on astrobin which indictate that the aberrations can be dialed out but I'm not sure if these were simply cropped.

There are spot charts for the Vixen which show un-flattened, flattened and flattened/reduced results. I'd welcome the opinion of the more experienced members (or any Vixen FL55 users):

 

     

Edited October 16, 2021 by 900SL

[900SL]

Maybe this should be in the refractors thread?

[Stu]

I’ve moved this to the Imaging - Discussion forum where it will hopefully get some good input.

[Concordia000]

I don’t own the FL55 but I’ve done some research. It seems the FL55 suffers from coma compared to the RedCat without a flattener.
The FL55 is more flexible because you can use it for visual more easily, while the RedCat is a dedicated astrograph — almost. You can remove the tilt corrector to install the diagonal, but I can’t recommend this as it caused me a ton of troubles. FL55 also comes with a better focuser (imo) and can be used in two focal lengths. It is however much more expensive.

The RedCat has better image quality out of the box and it’s not even close. It’s a Petzval design that has a very flat field and very well corrected for CA and coma. The downside is that it is very sensitive to tilt, and despite the marketing it doesn’t quite support a full frame chip: the edges can have deformed stars. Collimation is a nightmare, I’ve attempted but I am probably going to send my scope back to FLO for help. The helical focuser is very good during daytime but not as precise at night.

On a side note, I own the RedCat + Lightrack combination myself. Your wedge is very important in this setup, since it affects your polar alignment. I don’t recommend using a ball head for the RedCat either: while it will work for <=2min exposures given very good PA, it will introduce a large moment on the mount and might cause it to turn if not sufficiently tightened. Even if your ball head is good enough, it will over-tighten your ball head and make a pain to take off.

[Adam J]

I think the Vixen for me if you want to pay the additional, just because I have a preference for the traditional focuser. 

 

[900SL]

17 hours ago, Concordia000 said:

I don’t own the FL55 but I’ve done some research. It seems the FL55 suffers from coma compared to the RedCat without a flattener.
The FL55 is more flexible because you can use it for visual more easily, while the RedCat is a dedicated astrograph — almost. You can remove the tilt corrector to install the diagonal, but I can’t recommend this as it caused me a ton of troubles. FL55 also comes with a better focuser (imo) and can be used in two focal lengths. It is however much more expensive.

The RedCat has better image quality out of the box and it’s not even close. It’s a Petzval design that has a very flat field and very well corrected for CA and coma. The downside is that it is very sensitive to tilt, and despite the marketing it doesn’t quite support a full frame chip: the edges can have deformed stars. Collimation is a nightmare, I’ve attempted but I am probably going to send my scope back to FLO for help. The helical focuser is very good during daytime but not as precise at night.

On a side note, I own the RedCat + Lightrack combination myself. Your wedge is very important in this setup, since it affects your polar alignment. I don’t recommend using a ball head for the RedCat either: while it will work for <=2min exposures given very good PA, it will introduce a large moment on the mount and might cause it to turn if not sufficiently tightened. Even if your ball head is good enough, it will over-tighten your ball head and

make a pain to take off.

Thank you for the reply Concordia. I'm 100% astrophotography (at present)

If I buy the FL55 it will be with the flattener and I'll use it as a 300mm f5.7 scope. I'll skip the 240mm reducer. I think on a cropped sensor this will hopefully deal with the coma? Would the image then be comparable to the Redcat in your opinion albeit slightly longer and slower?  My main concern would be the f5.7 aperture for exposure and any edge artifacts. I'm bortle 2 or 3 here in a short drive. 

With regard to the price, I've learned the hard way to go with Companies that have a good QA/QC system and from what I have read on the Redcat, it seems that these are a bit of a lottery with regard to collimation and flatness. Get a good one and its great, get a bad un and it's trouble. 

For set up, I have the fornax wedge and a DIY counterbalance so my set up is pretty good for tracking, typically ~ 1 arcsec.  Ive since modified this set up, removed the pan base and have a pretty solid set up now. I can get RA and Dec balance pretty much spot on with this 

 

 

 

 

Edited October 12, 2021 by 900SL

[900SL]

15 hours ago, Adam J said:

I think the Vixen for me if you want to pay the additional, just because I have a preference for the traditional focuser. 

 

Thanks Adam, always welcome your view. I may go for the TS 70mm F5 quadruplet flatfield APO as plan B. It's a bit longer than I was planning to use, but looks to be well made with a decent focuser and the few reviews I can find regard it quite highly

[kirkster501]

I've been waiting for the Redcat to come back in stock for over a year.  Maybe they have been available in very small batches at FLO but as soon as they arrive they sell out and I miss them.

[900SL]

8 minutes ago, kirkster501 said:

I've been waiting for the Redcat to come back in stock for over a year.  Maybe they have been available in very small batches at FLO but as soon as they arrive they sell out and I miss them.

I suspect you will need to place an order in advance, KS. 

[kirkster501]

16 minutes ago, 900SL said:

I suspect you will need to place an order in advance, KS. 

A member on here has very kindly lent me their Redcat (for over a year now with their agreement).  Due to terrible imaging conditions this last 12 months allied with other equipment problems I have only used the Redcat with a DSLR.  I really want to test it with my QHY268C and this is the very next thing I will do when I get a clear night.  My FSQ85 with the 0.73 reducer and QHY268C already gets down to 368mm FL so I want to see the difference the Redcat makes in practise with the same camera to see if the Redcat at 250mm FL is worthy additional FL combination in my kit bag.  I think it will be.  The Askar 200mm also looks very interesting too.

I can testify to the quality of the Redcat.  It is beautifully made and machined with a very high build quality.

[Adam J]

2 hours ago, 900SL said:

Thanks Adam, always welcome your view. I may go for the TS 70mm F5 quadruplet flatfield APO as plan B. It's a bit longer than I was planning to use, but looks to be well made with a decent focuser and the few reviews I can find regard it quite highly

My personal opinion is that flat field APOs are more trouble than they are worth, you have more handles on a triplet + corrector, it allows to adjust when things are not quite rite, when scopes have an in built corrector then there is not much the user can do to fix them beyond sensor tilt. Sure they are great when they do work though. 

Another reason why the vixen would be my choice. I take it that this is a replacement for the ASKAR 180 then?

Adam

[900SL]

@Adam JThat makes sense Adam. Unfortunately TS are out of stock either on scopes or associated reducer/flatteners (i.e. you can get a scope but not reducer/flattener or visa versa, on the scopes that fitted the bill)

I'll keep the Askar as it is a very convenient size wise, but would like a longer focal length around 300mm  to pair with the D5600 or a future dedicated camera. Also something better corrected for CA as my copy of the Askar does seem to suffer with this even with the L3 filter unless defocused slightly

The Vixen with a flattener would be the other option, giving around 300mm focal length. I should get a nice FOV and not too undersampled with the cropped sensor Nikon. 

 

  

Edited October 12, 2021 by 900SL

[Adam J]

27 minutes ago, 900SL said:

@Adam JThat makes sense Adam. Unfortunately TS are out of stock either on scopes or associated reducer/flatteners (i.e. you can get a scope but not reducer/flattener or visa versa, on the scopes that fitted the bill)

I'll keep the Askar as it is a very convenient size wise, but would like a longer focal length around 300mm  to pair with the D5600 or a future dedicated camera. Also something better corrected for CA as my copy of the Askar does seem to suffer with this even with the L3 filter unless defocused slightly

The Vixen with a flattener would be the other option, giving around 300mm focal length. I should get a nice FOV and not too undersampled with the cropped sensor Nikon. 

 

  

For me the ASKAR is just a bit of fun for mobile imaging, don't expect to win any awards with it or anything but, it performs sufficiently for what I am using it for I think. It does have a tiny but of CA after using the L3 but is really is slight for me. Its easier to cope with when using a mono camera. But if you look in that thread @PadrePeace virgo galaxy group then he is not getting the same amount of CA as you on his ASI294mc pro. So I still suspect a issue with colour balance and or focus. 

[Concordia000]

5 hours ago, 900SL said:

Thank you for the reply Concordia. I'm 100% astrophotography (at present)

If I buy the FL55 it will be with the flattener and I'll use it as a 300mm f5.7 scope. I'll skip the 240mm reducer. I think on a cropped sensor this will hopefully deal with the coma? Would the image then be comparable to the Redcat in your opinion albeit slightly longer and slower?  My main concern would be the f5.7 aperture for exposure and any edge artifacts. I'm bortle 2 or 3 here in a short drive. 

With regard to the price, I've learned the hard way to go with Companies that have a good QA/QC system and from what I have read on the Redcat, it seems that these are a bit of a lottery with regard to collimation and flatness. Get a good one and its great, get a bad un and it's trouble. 

For set up, I have the fornax wedge and a DIY counterbalance so my set up is pretty good for tracking, typically ~ 1 arcsec.  Ive since modified this set up, removed the pan base and have a pretty solid set up now. I can get RA and Dec balance pretty much spot on with this 

 

 

 

 

I think for a crop size sensor, neither scope will suffer from coma. Even my miscollimated RedCat performs decently when I cropped it down to APS-C size.

I do love my RedCat and my gripes with it is more about it’s not performing “as good as it could be”. Part of that was down to some user error too; my collimation efforts were not the most gentle. Hopefully FLO can fix it.

But I do wonder, from time to time, whether I would have been more happy with a FS-60CB with flattener-reducer or the FL55. I particularly love the looks of the FL55 and would love to own one. But given the price (2x as expensive when all accessories are included) I simply can’t say it’s a better choice than the RedCat.

K-Astec has a comparison of the three scopes. FL55 is using the flattener reducer here:

http://k-astec.cocolog-nifty.com/main/2018/11/post-3.html

[900SL]

OK, so I've done a complete about face and ordered a WO GT71 and reducer from FLO, one of the 2019 checked and tested ones. Hopefully arrives in KSA in good order and true to promise.

 

I'm probably pushing it on the Fornax with this scope but I should be able to balance the GT71 and guide no problem. Let's see how it goes

 

I'll use it for 'easy' targets for the autumn / winter season (Orion, Pleiedes, Rosette etc)