8 replies to this topic

[Ghost332]

Hey guys,

Recently I made a post about which achro would be the best from 2 choices. Due to my circumstances I nailed it down to the Skywatcher Evostar 120/1000 Achro.
Since the curfew here (can only legally leave the flat between 5am till 8pm due to covid situation)  wouldn't allow me to use it at the moment, and there are stock issues as well, I haven't yet bought it. However, what I did not realise is I haven't even considered the Bresser Lineup on achromats. 

I came across the Refractor in the title, and I would like to know the exact dimensions of the Bresser 127L to see if I could fit it in the truck of the car. Also, is the Dew shield removeable? ( that would save some inches for sure in terms of length). Since it is possible to fit a 2" diagonal, what would be the lowest power 2" eyepiece I could use without any serious vignetting and aberration? 


Right now I am seriously considering this over the evostar 120, since its longer focal length would allow to have less CA (it would be nice to know just how bad/good the CA on this particular model from people how have actually used it ), so technically better view on planets, its a tiny bit bigger in terms of aperture ( around 10-15% more light gathering than the 120 ), but since low power widefield is important, I'd like to know how it performs in this area as well. 

The mount I will be using is the Skywatcher EQ5.

Many thanks for all answers in advance!

Edited by Ghost332, 01 March 2021 - 08:03 AM.

[LU1AR]

Your telescope is F/9,4. According to Sidgwick (Astronomers Handbook); will be "Usable with filters, for visual observations" (Focal ratio 1.3 times the objective diameter in inches is 'acceptable').
According to Alexander Conrady ("Applied Optics and Optical Design"), for visual colorlessness (With Filters), the F/Ratio should be "At least" 3 times the aperture in inches. More than 5 is optimum.
You can reach the Conrady index masking your objetive to 4" (F/12) and using a Fringe Killer filter.
A 4" mask, will avoid the external part of the lenses, where the worst defects are concentrated and detract from the rest of a good optics.
The improvement in optical quality, definition, clear focus and resolution of details, far exceeds the reduction of the capture area. And you can always remove the mask. and restore the original lens diameter.
Regards.
Edgardo

Edited by LU1AR, 01 March 2021 - 09:37 AM.

[donadani]

I think this scope is one of the best in price/perfomance you can buy - bought mine used in very good condition.

 

Therefore I got:

 

- nicely made tube with three baffles and good blackening

- nicely focuser (Hexafoc) that allows heavier weight too without twisting or wobbling - but it has some play when changing direction what is acceptable when you learned how to use it and it has only 45mm of travel

- very good optics (in mine) in a metal cell - fully collimatable (lens to tube as well as lenses against each other)

- mine had the micropinion option installed (75,- EUR when bought new) - a bit pasty but it works nice too

- nicely finderholder and 8x50 finder

- nicely rings with handle

 

I was very impressed by what you get for a very low price with a perfectly centered optics and a relativ low color error.

 

Downs in my view are:

 

- big and heavy 

- adapter between tube and lenscell is made of plastic (but a very stiff kind)

- frontring of the lenscell is from plastic too and seems to be clued in a careless way (lots of clue!)

- nine colimation screws for lenses - three for each lens and three for the frontring it seems?!?!? - ha! 

 

Would I buy it new - yes! great value and very nice optics for sure!

 

But the best thing is - that if you ever come over an unused LZOS 130/9 lens you can plug it in by only loosening the three screws that hold the lenscell to the adapter and use the same ones to fix the LZOS lens. Ready is your new super apo!

 

Honestly that was the only reason I bought it - but wasn´t aware that the original lens is very nice too and that the swap is so easy to do. Of course the achomat shows some color - but not as much as I thought and it´s very well figured too.

 

Pics of the final swap:

 

 

 

 

 

Btw. the dewcap is only stucked to the adapter and can easily be removed - length with it is about 123cm without around 110cm. Weight with LZOS lens rings, handle and rail is 10.2kg - with the original lens about 5kg less

Edited by donadani, 01 March 2021 - 02:23 PM.

[Bomber Bob]

But the best thing is - that if you ever come over an unused LZOS 130/9 lens you can plug it in by only loosening the three screws that hold the lenscell to the adapter and use the same ones to fix the LZOS lens. Ready is your new super apo!

 

Wow!  I'd call that a great Bonus Feature!

 

I reviewed a brand new Bresser AR-102L F13.5 achromatic almost 2 yrs ago, and though I didn't care for all the plastic, I found the optics very good.

Edited by Bomber Bob, 01 March 2021 - 12:38 PM.

[BarrySimon615]

Ghost 332,

 

Several things to consider in your telescope choice.

 

1) While the Skywatcher EQ5 would be adequate for a 120 mm f/8.3, a 127 mm f/9.4 would be too much telescope for that mount as the recommended top weight capacity is just about 20 lbs.  (It would be severely undermounted due to the combination of increased weight and moment arm.)

 

2) Reduction of chromatic aberration would not be achieved with the 127 mm as compared to the 120 mm.  Chromatic aberration is a function of not only f/ratio but also aperture.  Check out the table attached.  The chromatic aberration of both scopes would be essentially the same.  Not horrible, but not super well controlled either.

 

3)Length, I have an Antares 127 mm f/9.4 with a 1200 mm focal length.  With the dewshield attached and with a 2" diagonal attached the total length of the telescope with the diagonal fully racked in is 52 inches.  (Take the dewshield off and removed the diagonal and you can reduce the length to about 42 inches.)

 

For your mount, and the other considerations I would get the 120 mm scope.  If you had an Atlas or a CGEM I would get the 127 mm.

 

Barry Simon

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Edited by BarrySimon615, 01 March 2021 - 03:49 PM.

[AndresEsteban]

Ghost 332, 

 

I'd stay with the Bresser 127L/1200 Messier Hexafoc OTA! although it weights about 7 kg  your Skywatcher EQ5 can handle 9.1 kg, so for visual observation is OK!

Consider also de extra 200 mm in focal length over the Skywatcher 120/ FL=1000 mm, this will como handy if you decide to mask down your objective. The hexafocus feature with 2 inches focuser also!

I know  a 127 mm FL 1200 f/9,45 achro has a CA index = 1.89 (ouch!), which is not particularly good (I'm a Conrady criteria guy, so for me anything less than CA>5 makes me very unconfortable...) but for DSO and low power observation in low light pollution areas is an excellent aperture!

Now, if you mask the objective to 4 inches (102 mm) you'll have a f/11,76 scope with a CA index of 2,93, almost verifying Sidgwick criteria as referred above by other colleagues, this is a nice improvement.

But hen, you may mask it down to 3 inches thus making it a 76 mm FL=1200 mm f/15.8 with a CA index of 5.27. And believe me, this is really other league compared to above examples! I have a 3 in f/16.4 Fl= 1250 mm vintage achro (+50 years) with a CA = 5.46 and lunar, planetary, double star images at 210x are really amazing. Contrast is amazing. Lunar details, breathtaking!

You may cut two masks, one of 4 inches (102 mm) and another for  3 inches (76 mm). Play with them! You'll have a nice refractor between 5 to 3 inches objective! If you feel that image with full aperture and high power is a little "mushy" due to chromatic aberration, you mayput a mask on it, lower a bit magnification and enjoy a better and crisper view!

200 mm increase in focal length may seem small but it really changes the game! I

The Bresser 127L/1200 OTA weights 7.9 kg and your Skywatcher EQ5 handles 9,1 kg, so it's ok for visual observation!

Just my two cents! I'd go for the Bresser 127L/1200 without any doubt!

Clear skies for us all!
Andy

 

[LU1AR]

Ghost 332, 

 

I'd stay with the Bresser 127L/1200 Messier Hexafoc OTA! although it weights about 7 kg  your Skywatcher EQ5 can handle 9.1 kg, so for visual observation is OK!

Consider also de extra 200 mm in focal length over the Skywatcher 120/ FL=1000 mm, this will como handy if you decide to mask down your objective. The hexafocus feature with 2 inches focuser also!

I know  a 127 mm FL 1200 f/9,45 achro has a CA index = 1.89 (ouch!), which is not particularly good (I'm a Conrady criteria guy, so for me anything less than CA>5 makes me very unconfortable...) but for DSO and low power observation in low light pollution areas is an excellent aperture!

Now, if you mask the objective to 4 inches (102 mm) you'll have a f/11,76 scope with a CA index of 2,93, almost verifying Sidgwick criteria as referred above by other colleagues, this is a nice improvement.

But hen, you may mask it down to 3 inches thus making it a 76 mm FL=1200 mm f/15.8 with a CA index of 5.27. And believe me, this is really other league compared to above examples! I have a 3 in f/16.4 Fl= 1250 mm vintage achro (+50 years) with a CA = 5.46 and lunar, planetary, double star images at 210x are really amazing. Contrast is amazing. Lunar details, breathtaking!

You may cut two masks, one of 4 inches (102 mm) and another for  3 inches (76 mm). Play with them! You'll have a nice refractor between 5 to 3 inches objective! If you feel that image with full aperture and high power is a little "mushy" due to chromatic aberration, you mayput a mask on it, lower a bit magnification and enjoy a better and crisper view!

200 mm increase in focal length may seem small but it really changes the game! I

The Bresser 127L/1200 OTA weights 7.9 kg and your Skywatcher EQ5 handles 9,1 kg, so it's ok for visual observation!

Just my two cents! I'd go for the Bresser 127L/1200 without any doubt!

Clear skies for us all!
Andy

 

It is an experience that must be lived personally. By putting on a mask that takes Conrad's Rating to 5, the focus becomes very sharp and the planetarium or lunar details appear out of nowhere, as by magic.
I had friends look at my cheap refractor (90/900 masked to 70/900) and everyone was amazed at the improved image and details.
Regards.
Edgardo

[John Huntley]

I've owned a Bresser 127 / 1200 achromat and used it successfully on an EQ5 class mount, the Celestron CG4, but that was mounted on a 2 inch steel tubed tripod. The mount coped quite well with the long tube - well enough for visual astronomy anyway. The 2 inch steel tube tripod is a good idea for a scope of this spec - it is taller as well as stable, which helps keep the eyepiece at a comfortable level. If your EQ5 is on the aluminum tripod, at least try and upgrade that to the 1.75 inch steel tubed tripod.

 

I didn't find the CA objectionable with the F/9.4 so I would not bother to mask it down to a smaller aperture (and I have tried it !) with the reduction in resolution and light grasp that would entail. Used at full aperture, a 127mm F/9.4 achromat should resolve closer separation double stars, show more lunar and planetary detail and show deep sky targets better than a 76mm aperture F/15.8 aperture achromat will, unless there is another underlying issue with the 127mm aperture.

Edited by John Huntley, 01 March 2021 - 08:20 PM.

[BarrySimon615]

I know others have said that they feel that a 127/1200 can be used successfully on an EQ5/CG4 class mount and maybe you can for "emergency" visual only type use but I will strongly suggest again that such a set up will be marginal at best.  I feel I can say this because I have used my Antares 127 mm by 1200 mm focal length refractor on an AVX mount and while it is ok for visual use it is not optimal.  Additionally the AVX has a recommended payload capacity of 9 to 10 lbs. more than an EQ5/CG4 type mount.  I have had a CG4 and I can verify that the payload ratings are a pretty fair accessment of the mount's capabilities.

 

I have pictured below images of my Antares 127 on the AVX mount.  With that mount it does work but a beefier mount would be better.  The smaller 120 mm f/8.3 scope would be a much better match for EQ/CG4 class of mounts.  (When a telescope is much larger than this or the mount much smaller, a vision of John Wayne riding a Shetland pony comes to mind).

 

Barry Simon

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Edited by BarrySimon615, 03 March 2021 - 08:33 AM.