302 replies to this topic

[rogeriomagellan]

Hi, folks!

 

I've just stumbled upon a new Bresser refractor. The description says that it has ED glass. Click on the link below for further information:

 

https://www.bresser....tical-Tube.html

 

 

[Sky Muse]

Hmm, that's getting pretty close to that 8" f/2 refractor that I've always wanted. 

 

But the specs do not reveal the nature of said "ED glass".  Still, it looks promising, for visual at least.  

 

I want one, too.

[Joe1950]

There is a similar thread about a Bressler 103, F/13 Ach, that is active. Consensus is that the shipping would be, well, astronomical.

 

Might want to check it out.

[Phillip Creed]

I'm skeptical.  A 4" f/4.5 ED refractor for ~$300 U.S.?

Yes, it'd be nice if they've come up with a Poor Man's Genesis for that price, but I find that hard to believe.  And wouldn't a 4" f/4.5 ED doublet have substantial spherochromatism?

 

Clear Skies,

Phil

[havasman]

Anybody know what HEXAFOC is?

 

They list it as a lunar instrument - dubious unless you like your moon with lots of colors.

Edited by havasman, 07 April 2017 - 11:16 AM.

[rogeriomagellan]

Anybody know what HEXAFOC is?

 

They list it as a lunar instrument - dubious unless you like your moon with lots of colors.

The Bresser Messier AR-102 f/4.5 comes with a 2.5" Hexafoc focuser which can be upgraded to dual speed version. The Hexafoc is known in the U.S. as Hexagonal. The same type of focuser can found in the ES FCD series. If you click on the link provided, you'll see smaller pictures beside the larger one. If you want to have a clearer view of what it is like, click on the small pictures of the focuser.

[rogeriomagellan]

I'm skeptical.  A 4" f/4.5 ED refractor for ~$300 U.S.?

Yes, it'd be nice if they've come up with a Poor Man's Genesis for that price, but I find that hard to believe.  And wouldn't a 4" f/4.5 ED doublet have substantial spherochromatism?

 

Clear Skies,

Phil

Hi, Phillip. 

 

I don't know how to answer your question. 

[rogeriomagellan]

Hmm, that's getting pretty close to that 8" f/2 refractor that I've always wanted. 

 

But the specs do not reveal the nature of said "ED glass".  Still, it looks promising, for visual at least.  

 

I want one, too.

Hi, Alan.

 

True. There is not much information about the nature of the ED glass. On the other hand, it is interesting to note that they don't call it an apo refractor. 

 

Althought it comes neither with a 50mm finder scope nor with a 2" dielectric diagonal mirror, it comes with a good focuser, which is something really impressive. Don't you think so?

 

Unless I am mistaken here, it was clearly designed for wide/rich field work. And in that sense I suppose that it may offer good results. But would you mind speculating a little here? From your past experience, how good could it be used for planetary viewing? Would it be of help if someone added a Baader Semi-Apo filter?

[Mitrovarr]

I'm skeptical.  A 4" f/4.5 ED refractor for ~$300 U.S.?

Yes, it'd be nice if they've come up with a Poor Man's Genesis for that price, but I find that hard to believe.  And wouldn't a 4" f/4.5 ED doublet have substantial spherochromatism?

 

Clear Skies,

Phil

Yeah, that's what I was just thinking. A 4" with ED glass for ~$300? No way.

[G.Richard]

Anybody know what HEXAFOC is?

 

They list it as a lunar instrument - dubious unless you like your moon with lots of colors.

I have it on my ES ed102 and the draw tube is hexagonal with a round center.  It's a very nice focuser Dick.

 

Gary

[G.Richard]

I just entered the US in there shipping rate calculator and it came back "There is currently no available shipping method for this country." so it doesn't look like they would send one here.  ES doesn't show it on there website even though they are owned by Bresser.

 

Gary

[rogeriomagellan]

Yeah, like their new 102mm f/13.2 achromat, it is still not available in the U.S. for sale. When it is available on the APM or Teleskop-Service websites, I guess that it will be possible to order it online. 

 

B&H in NY used to sell some Bresser stuff. But I have no idea if and when this particular model will be available for puchase there. If you visit their website, you'll learn that the Bresser Messier 4" f/5.9 is no longer available. In fact, if anyone attempts to buy any of the Bresser achromats with the 2.5" Hexagonal focuser in the U.S., he/she will fail to accomplish that mission. 

[Mitrovarr]

Someone in Europe should try to order one. If the scope is as described and the optical quality is decent, it's a crazy deal.

[jring]

Hi,

 

well I hope to get a look on and hopefully through one of these on some telescope meet in May.

 

But I would not expect anything besides the rich field achromat they advertised, maybe they used some cheap chinese ED element to get their crazy fast f4.5 doublet to perform like the usual f6 achro, but I'm quite sure that we can't expect anything close to a semi apo here.

 

Field curvature will be an interesting topic besides CA - some of the larger Messier achros have a 4 element design, but I've got doubts here - we'll see.

 

Also the focal ratio is a bit fast for use with Uncle Al's Grenade or cheap chinese clones with a 6.8mm exit pupil but nice 5.5 deg tfov. A 21 Ethos or knockoff would give 4.6mm exitt pupil and 4.6 deg - quite nice. Not sure what else will work at that focal ratio...

 

Joachim

[Mitrovarr]

If they were able to get the color correction to equal a f/6-7 achromat this thing could be a great successor to the ST80/120 line. Faster, better build quality, less CA and not much more expensive.

Of course I don't think that price is correct and expect it to really cost something like $600-800.

[marcus_z]

The scope is an achromat and has the same limitations as all other achromats. Bresser has announced it to appear at the beginning of 2017. So finally it is on the market ;-)
I have been tempted by it quite for a while. It just sounds insane to use a 700€ N31T5 with a scope for 259€. If I buy it I will let you know how it performs...

[rogeriomagellan]

The scope is an achromat and has the same limitations as all other achromats. Bresser has announced it to appear at the beginning of 2017. So finally it is on the market ;-)
I have been tempted by it quite for a while. It just sounds insane to use a 700€ N31T5 with a scope for 259€. If I buy it I will let you know how it performs...

Hi, Marcus.

 

I'm not sure if you'll agree with me but it wouldn't be madness if the person already owned that Nagler. The point here seems to be weight and balance. But even if someone claims that a Nagler 31T5 can be too much weight for that OTA, there are still other eyepieces that may offer pleasing views of the night sky. 

 

Now, since you own a TAK-FC and that you're aware that it is obviously not in the same league, would you say that it is one level above the other Bresser model (AR-102 f/5.9) in terms of image quality?

 

By the way, you have a great set of eyepieces. 

[Riccardo_italy]

So, if you pass the mouse button over the pictures, you see the magnified detail.

 

Use the first picture, the one with the entire OTA, and magnify the gray label below the finder. You can read

 

AR102xs

Achromatic refractor telescope 102/460 f4.5

 

Moreover f4.5 I think (but I'm not sure) is the focal lenght of many 100mm straight through binoculars. I don't know if this is a coincidence...

[rogeriomagellan]

So, if you pass the mouse button over the pictures, you see the magnified detail.

 

Use the first picture, the one with the entire OTA, and magnify the gray label below the finder. You can read

 

AR102xs

Achromatic refractor telescope 102/460 f4.5

 

Moreover f4.5 I think (but I'm not sure) is the focal lenght of many 100mm straight through binoculars. I don't know if this is a coincidence...

Yeah, that is another possiblity to see the focuser in detail.

[Mitrovarr]

It being an achromat doesn't necessarily mean it doesn't contain ED glass. An ED doublet at F/4.5 is going to be an achromat. But, it'll have a lot less CA than a regular crown/flint achromat would at that focal ratio.

 

Still, not containing ED glass would be entirely in keeping with that price. I peeked into the manual and didn't see anything about ED glass there, either.

[Sky Muse]

 

Hmm, that's getting pretty close to that 8" f/2 refractor that I've always wanted. 

 

But the specs do not reveal the nature of said "ED glass".  Still, it looks promising, for visual at least.  

 

I want one, too.

Hi, Alan.

 

True. There is not much information about the nature of the ED glass. On the other hand, it is interesting to note that they don't call it an apo refractor. 

 

Althought it comes neither with a 50mm finder scope nor with a 2" dielectric diagonal mirror, it comes with a good focuser, which is something really impressive. Don't you think so?

 

Unless I am mistaken here, it was clearly designed for wide/rich field work. And in that sense I suppose that it may offer good results. But would you mind speculating a little here? From your past experience, how good could it be used for planetary viewing? Would it be of help if someone added a Baader Semi-Apo filter?

 

You can certainly push it up to 150x, 200x, and for planetary observations on most nights; especially on the Moon, perhaps even higher.  Hmm, let's see what would be required for 200x...

 

460mm ÷ 200x =  

 

...a 2.3mm eyepiece!  But I would 2x-barlow a wider-field 5mm for that, or 3x-barlow a 7mm.  Pick your poison.

 

Any filter will not correct the damage done to the image by chromatic aberration, but will only mask it.

 

There's Baader's fringe-killer, too.

[Sarkikos]

I don't understand why any observer would bother viewing the Moon and planets through a 102mm f/4.5 achro.  Or even bother thinking about it.  That's like using a screwdriver to hammer a nail.  What you need is a hammer.  

 

The telescope would have a CA ratio of 1.13.  The Sidgwick Standard is 3 or greater.

 

This scope should be used for low-power wide-field deep sky.   That's exactly how I would use it.

 

Mike

Edited by Sarkikos, 07 April 2017 - 10:38 PM.

[Mitrovarr]

I don't understand why any observer would bother viewing the Moon and planets through a 102mm f/4.5 achro.  Or even bother thinking about it.  That's like using a screwdriver to hammer a nail.  What you need is a hammer.  

 

The telescope would have a CA ratio of 1.13.  The Sidgwick Standard is 3 or greater.

 

This scope should be used for low-power wide-field deep sky.   That's exactly how I would use it.

 

Mike

I dunno. I look at the moon and the planets with my ST80/ST120 all the time when I have them out. They're not ideal for that use, but they're not nearly as bad as people's comments would suggest.

[jring]

I'm not sure if you'll agree with me but it wouldn't be madness if the person already owned that Nagler. The point here seems to be weight and balance.

Hi,

 

I'm confident the focuser on this will hold the grenade or other EPs in the heavyweight class just fine. Balance could indeed be tricky with the fixed and not too long dovetail. The question remains if another one can be fitted (possibly sacrificing the focus lock screw underway).

 

Joachim

[marcus_z]

 

The scope is an achromat and has the same limitations as all other achromats. Bresser has announced it to appear at the beginning of 2017. So finally it is on the market ;-)
I have been tempted by it quite for a while. It just sounds insane to use a 700€ N31T5 with a scope for 259€. If I buy it I will let you know how it performs...

Hi, Marcus.

 

I'm not sure if you'll agree with me but it wouldn't be madness if the person already owned that Nagler. The point here seems to be weight and balance. But even if someone claims that a Nagler 31T5 can be too much weight for that OTA, there are still other eyepieces that may offer pleasing views of the night sky. 

 

Now, since you own a TAK-FC and that you're aware that it is obviously not in the same league, would you say that it is one level above the other Bresser model (AR-102 f/5.9) in terms of image quality?

 

By the way, you have a great set of eyepieces. 

 

Hi Rogerio,

 

Those two achromats don't differ too much in my opinion, but they have cenrtain advantages and disadvantages. You will see CA below at a certain exit pupil in both. Lichtenknecker has defined the RC Value as: RC=D² x 0.508 / f, with D=aperture diameter in mm and f=focal length in mm. An achromat is considered to have acceptable correction at RC=4.2. Now this value is based on an exit pupil of 1mm. At a higher exit pupil you look at the RC_eff=RC / EP with EP=exit pupil in mm.

 

Bresser has different AR102 models:

AR102xs/480:

RC=102² x 0.508 / 460 = 11.5

with an exit pupil of 2.7mm your effective RC value is RC_eff=11.5 / 2.7 = 4.2

only complex eyepieces will be acceptable for this aperture ratio. Consider Nagler, Ethos, Panoptics...

 

AR102s/600:

RC=102² x 0.508 / 600 = 8.8

with an exit pupil of 2.1mm your effective RC value is RC_eff=8.8 / 2.1 = 4.2

not every eyepiece can be used. I don't accept Plössls at this aperture ratio.

 

AR102/1000:

RC=102² x 0.508 / 1000 = 5.3

with an exit pupil of 1.3mm your effective RC value is RC_eff=5.3 / 1.3 = 4.2

all different kinds of eyepieces can be used.

 

AR102L/1350:

RC=102² x 0.508 / 1350 = 3.9

with an exit pupil of 0.9mm your effective RC value is RC_eff=3.9 / 0.9 = 4.2

all different kinds of eyepieces can be used. Consider an 12.5mm Abbe ortho for max magnification (~10mm eye reilef :-)

 

I don't have experience with achromats, but I expect that every observer will differ in his opinion on which RC value is acceptable. People with better than average "visual acuity" will probably require lower RC values than 4.2 to accept the CA. Now this theoretical POV is just based on the CA...

 

I think balancing the AR102xs/460 with a N31T5 is possible. I had a 80/480 triplet mounted on this bimbal head: http://fotopro.com/product/wh-30/ The center of gravity of scope, diagonal, and eyepiece could be tuned to be right on the elevation axis. That was a fine combination, especially at the low magnifications of the N31T5.

 

clear skies,

Marcus

 

PS: Thank you four your compliment on my eyepiece collection. I want to get a custom case inlay for my 2" Televue eyepieces. Whenever that's ready I will post a picture at CN.